Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems (Signals and Communication Technology) 9789811965364, 9789811965371, 9811965366

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Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems (Signals and Communication Technology)
 9789811965364, 9789811965371, 9811965366

Table of contents :
Preface
Contents
About the Authors
Abbreviations
1 Introduction and Overview
1.1 Introduction
1.2 Reconfigurable Planar Antennas
1.2.1 Feeding Techniques
1.2.2 Passive Antennas
1.2.3 Active Antennas
1.3 Advantages of Planar Antennas
1.4 Disadvantages of Planar Antennas
1.5 RF Switches and Their Performance
1.5.1 Types of RF Switches
1.6 Switch Modeling Techniques
1.6.1 Ideal Approach
1.6.2 Non-Ideal Approach
1.7 Organization of the Book
References
2 Principle and Types of Reconfigurability
2.1 Introduction
2.2 Principle of Reconfigurability
2.3 Reconfiguration Techniques
2.3.1 Electronic Reconfiguration Techniques
2.3.2 Mechanical Reconfiguration Techniques
2.3.3 Optical Reconfiguration Techniques
2.3.4 Material Reconfiguration Techniques
2.4 Advantages and Disadvantages of Different Reconfiguration Techniques
2.5 Different Types of Reconfigurable Antennas
2.5.1 Frequency Reconfigurable Antennas
2.5.2 Polarization Reconfigurable Antennas
2.5.3 Radiation Pattern Reconfigurable Antennas
2.5.4 Compound Reconfigurable Antennas
2.6 Summary
References
3 Active Integrated Antennas and Their Classification
3.1 Introduction
3.2 Classification of Active Integrated Antennas (AIAs)
3.2.1 Amplifier Type
3.2.2 Oscillator Type
3.2.3 Frequency Conversion Type
3.3 Oscillator-Type Active Integrated Antennas
3.3.1 Negative Resistance Oscillator-Type Active Integrated Antennas
3.3.2 Feedback Loop Oscillator-Type Active Integrated Antennas
3.4 Design Procedure of Negative Resistance Oscillator-Type Active Integrated Antennas
3.5 Design Procedure of Feedback Loop Oscillator-Type Active Integrated Antennas
3.5.1 Two-Port Radiator Design
3.5.2 Amplifier Design
3.5.3 Active Integrated Antenna Design
3.5.4 Oscillation Test
3.5.5 Harmonic Balance Test
3.5.6 Active Integrated Antenna Design
3.5.7 Measurements
3.6 Summary
References
4 Frequency Reconfigurable Passive and Active Planar Antennas
4.1 Introduction
4.2 Classification of Frequency Reconfigurable Antennas
4.2.1 Discrete Frequency Reconfigurable Antennas
4.2.2 Continuous Frequency Reconfigurable Antennas
4.3 Frequency Reconfigurable Passive Planar Antenna Using Different Approaches
4.3.1 Frequency Reconfiguration Using an Additional Patch or Stub
4.3.2 Frequency Reconfiguration Using Reconfigurable Matching Network
4.3.3 Frequency Reconfiguration Using Shorting Posts or Reactive Loading of the Radiating Element
4.3.4 Frequency Reconfiguration by Varying the Slot Length
4.3.5 Frequency Reconfiguration Using Metasurfaces
4.4 Frequency Reconfigurable Active Planar Antennas Realized Using Different Approaches
4.5 Summary
References
5 Polarization Reconfigurable Passive and Active Planar Antennas
5.1 Introduction
5.2 Basis of Polarization
5.3 Obtaining Circular Polarization from Microstrip Patch Antennas
5.4 Reconfigurable Microstrip Patch Antenna with Switchable Polarization
5.4.1 Reconfigurable Stub Loaded Microstrip Patch Planar Antenna with Switchable Polarization
5.4.2 Reconfigurable Corner Truncated Microstrip Patch Planar Antenna with Switchable Polarization
5.5 Polarization Reconfigurable Slot Antennas
5.6 Polarization Reconfigurable Compact Slot Antennas
5.6.1 Reconfigurable Compact Rectangular Slot Antenna with Switchable Polarization
5.7 Polarization Reconfigurable Active Planar Antennas
5.7.1 Polarization Reconfigurable Active Antenna with a Symmetrically Coupled Passive Radiator
5.7.2 Polarization Reconfigurable Active Antenna with an Asymmetrically Coupled Passive Radiator
5.8 Summary
References
6 Radiation Pattern Reconfigurable Passive and Active Planar Antennas
6.1 Introduction
6.2 Concept of Radiation Pattern Reconfigurability in Antennas
6.3 Beam Steering/Switching in Passive Planar Antennas
6.4 Beam Steering/Switching in Active Planar Antennas
6.5 Summary
References
7 Null Broadening and Steering in Passive Planar Antennas
7.1 Introduction
7.2 Null Steering Antennas
7.3 Null Broadening Techniques
7.4 Four-Element Slot Array Antenna with DT Distribution
7.4.1 Array Design
7.4.2 Results
7.5 Four-Element Slot Array Antenna with Binomial Distribution
7.5.1 Array Design
7.5.2 Results
7.6 Null Steering
7.7 Summary
References
8 Compound Reconfigurable Planar Antennas
8.1 Introduction
8.2 Compound Reconfigurable Antennas
8.3 Reconfigurable Microstrip Patch Antenna with Polarization Agility in Two Switchable Frequency Bands
8.4 Reconfigurable Microstrip Patch Antenna with Polarization Agility in Three Switchable Frequency Bands
8.5 Summary
References
9 Applications of Reconfigurable Planar Antennas in Wireless Communication Systems
9.1 Introduction
9.2 Applications of Frequency Reconfigurable Antennas
9.3 Applications of Polarization Reconfigurable Antennas
9.4 Applications of Pattern Reconfigurable Antennas
9.5 Applications of Compound Reconfigurable Antennas
9.6 Future Directions
9.7 Scope of Reconfigurable Passive Planar Antennas for Future Wireless Applications
9.8 Scope of Active Integrated Planar Antennas in Power Combining
9.9 Non-linearity of Switches at High RF Power
References
Index

Citation preview

Signals and Communication Technology

Shiban Kishen Koul Rajesh K. Singh

Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems

Signals and Communication Technology Series Editors Emre Celebi, Department of Computer Science, University of Central Arkansas, Conway, AR, USA Jingdong Chen, Northwestern Polytechnical University, Xi’an, China E. S. Gopi, Department of Electronics and Communication Engineering, National Institute of Technology, Tiruchirappalli, Tamil Nadu, India Amy Neustein, Linguistic Technology Systems, Fort Lee, NJ, USA H. Vincent Poor, Department of Electrical Engineering, Princeton University, Princeton, NJ, USA Antonio Liotta, University of Bolzano, Bolzano, Italy Mario Di Mauro, University of Salerno, Salerno, Italy

This series is devoted to fundamentals and applications of modern methods of signal processing and cutting-edge communication technologies. The main topics are information and signal theory, acoustical signal processing, image processing and multimedia systems, mobile and wireless communications, and computer and communication networks. Volumes in the series address researchers in academia and industrial R&D departments. The series is application-oriented. The level of presentation of each individual volume, however, depends on the subject and can range from practical to scientific. Indexing: All books in “Signals and Communication Technology” are indexed by Scopus and zbMATH For general information about this book series, comments or suggestions, please contact Mary James at [email protected] or Ramesh Nath Premnath at [email protected].

Shiban Kishen Koul · Rajesh K. Singh

Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems

Shiban Kishen Koul Centre for Applied Research in Electronics Indian Institute of Technology Delhi New Delhi, India

Rajesh K. Singh Department of Electronics Engineering Defence Institute of Advanced Technology (DIAT) Pune, India

ISSN 1860-4862 ISSN 1860-4870 (electronic) Signals and Communication Technology ISBN 978-981-19-6536-4 ISBN 978-981-19-6537-1 (eBook) https://doi.org/10.1007/978-981-19-6537-1 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Singapore Pte Ltd. The registered company address is: 152 Beach Road, #21-01/04 Gateway East, Singapore 189721, Singapore

We would like to dedicate our efforts to our wonderful families who inspired and supported us through everything.

Preface

To meet the current and future requirements of a portable and multifunction wireless system, researchers are paying attention to realize active and passive printed antennas. Many related compacts and planar geometries with frequency, polarization, radiation pattern, and compound reconfigurable operation have been reported. Many significant advances in achieving polarization/pattern reconfigurability in various switchable frequency bands have been published in the scientific literature. By using/combining available switching techniques, one can easily achieve polarization/frequency/radiation pattern reconfigurability in antennas. The purpose of writing this book is to organize planar designs of reconfigurable active and passive antennas reported recently. A more detailed description of active antenna realization is provided; it can be used as a design guide by active antenna designers. The planar designs covered in this book are divided into two groups: reconfigurable passive planar antennas and reconfigurable active planar antennas. The book is organized into nine chapters. Chapter 1 presents an overview of the reconfigurable active and passive planar antennas. The ideal and non-ideal modelling of RF switches used in performing numerical analysis and the practical realization of reconfigurable antennas are discussed and elaborated. The performance of a switch considering ideal and non-ideal modelling is explained in terms of S-parameters. Various types of RF switches and their advantages and disadvantages are also discussed. Chapter 2 discusses the basic theory of reconfigurability and various types of reconfiguration techniques existing in antenna systems. The advantages and disadvantages of different reconfiguration techniques are also presented. Based on these reconfiguration techniques, four different types of reconfigurable antennas are explained. Chapter 3 presents a discussion on active integrated antennas (AIAs) and their classification. It starts with a typical active antenna consisting of one active device such as a two-terminal device (Diode) or three-terminal device (Transistor) integrated with a passive planar radiating element such as a microstrip patch of various shapes, printed dipole, monopole, or slot and discusses the design steps of negative resistance and feedback loop oscillator-type AIAs. It also discusses the benefits and limitations of different configurations of oscillator-type AIAs. Various

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configurations of the AIA to fulfil the requirements for multiple communication and sensor applications are discussed in detail. Chapter 4 discusses various frequency reconfigurable antennas that are extensively used in modern wireless communication systems. The demand and benefit of frequency reconfigurability for wireless systems are next discussed. Various types of frequency reconfigurable antennas such as narrowband-to-narrowband, narrowbandto-wideband or notch band-to-wideband, wideband-to-wideband, multiband-tonarrowband, and multiband-to-multiband reconfigurable antennas are then described. Frequency reconfiguration techniques that are used in realizing reconfigurable AIAs are presented next. The focus of the chapter is on the development of oscillator-type frequency reconfigurable active antennas. Chapter 5 presents the circularly polarized antennas and polarization reconfigurability in planar antennas. Polarization reconfigurable antennas are the key elements for current and future wireless communication systems. The wide use and advantages of CP antennas for various wireless systems including satellite communications, mobile communications, wireless local area networks (WLAN), radio frequency identification (RFID), wireless power transfer (WPT), global navigation satellite system (GNSS), and global positioning system (GPS) are presented in detail. The design, simulation, and measurement of recently published polarization reconfigurable planar antennas switchable between linear polarization (LP) and circular polarization (CP) with both senses, i.e. left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP) are then discussed in detail. The benefits of compact and wideband polarization reconfigurable antennas for portable wireless devices are discussed. Polarization reconfigurability in planar AIAs that is advantageous for advanced wireless systems is presented. Chapter 6 discusses the radiation pattern reconfigurable antennas that are extensively used in a wide variety of applications, such as in mobile devices, directionfinding systems, satellite communication, remote sensing, and different types of radars. Various techniques to achieve pattern reconfigurable active and passive planar antennas are presented in this chapter. The focus of the chapter is to discuss the specific radiation beam switchable active and passive planar antennas switchable among conical or broadside achieving sum or difference pattern. Various planar designs and new techniques of pattern reconfigurable antennas are reported in the chapter. Chapter 7 discusses the null steering-based radiation pattern reconfigurable planar antennas that are widely used in radars. Null steering, a special case of reconfigurability in radiation pattern has received great attention in the polluted electromagnetic scattering environment. Null steering is an efficient technique to suppress spurious signals coming from unwanted sources. A deep null can be placed in that undesired direction to enhance the signal-to-interference (S/I) ratio. If the incident interference signal changes its direction with time, a broad range of null is required. Various planar designs especially on null steering and null broadening are discussed in this chapter. With the rapid growth of wireless technology, the demand for multifunction antennas has increased. To support a wide range of services, multifunction antennas

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offer a better choice. A multifunction antenna can be a compound reconfigurable antenna by which one can dynamically reconfigure more than one radiation characteristic, e.g. both frequency and polarization, frequency and radiation pattern, polarization and radiation pattern, or a combination of all three in a single antenna. Modern wireless communication systems require multifunction antennas to fulfil new wireless requirements. Chapter 8 discusses the compound reconfigurable planar antennas based on frequency and polarization reconfiguration and their benefit in current and future wireless applications. Chapter 9 discusses the application of frequency, polarization, radiation pattern, and compound reconfigurable antennas. Initially, the application of reconfigurable antennas is discussed by modifying only one of its characteristics among frequency, polarization, and radiation pattern. Next, combinations of any two or all three characteristics are discussed. This chapter also discusses the scope of reconfigurable passive planar antennas for future wireless applications, AIAs in spatial power combining, and the nonlinearity issue of RF switches at high RF power. New Delhi, India Pune, India

Shiban Kishen Koul Rajesh K. Singh

Contents

1 Introduction and Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Reconfigurable Planar Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.1 Feeding Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.2 Passive Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2.3 Active Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Advantages of Planar Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Disadvantages of Planar Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 RF Switches and Their Performance . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.1 Types of RF Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 Switch Modeling Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.1 Ideal Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.2 Non-Ideal Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 Organization of the Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 2 2 5 6 6 7 7 7 8 9 9 11 13

2 Principle and Types of Reconfigurability . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Principle of Reconfigurability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Reconfiguration Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Electronic Reconfiguration Techniques . . . . . . . . . . . . . . . . . . 2.3.2 Mechanical Reconfiguration Techniques . . . . . . . . . . . . . . . . . 2.3.3 Optical Reconfiguration Techniques . . . . . . . . . . . . . . . . . . . . 2.3.4 Material Reconfiguration Techniques . . . . . . . . . . . . . . . . . . . 2.4 Advantages and Disadvantages of Different Reconfiguration Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Different Types of Reconfigurable Antennas . . . . . . . . . . . . . . . . . . . . 2.5.1 Frequency Reconfigurable Antennas . . . . . . . . . . . . . . . . . . . . 2.5.2 Polarization Reconfigurable Antennas . . . . . . . . . . . . . . . . . . . 2.5.3 Radiation Pattern Reconfigurable Antennas . . . . . . . . . . . . . . 2.5.4 Compound Reconfigurable Antennas . . . . . . . . . . . . . . . . . . .

15 15 15 15 16 17 20 20 20 22 23 23 24 25

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2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3 Active Integrated Antennas and Their Classification . . . . . . . . . . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Classification of Active Integrated Antennas (AIAs) . . . . . . . . . . . . . 3.2.1 Amplifier Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Oscillator Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Frequency Conversion Type . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Oscillator-Type Active Integrated Antennas . . . . . . . . . . . . . . . . . . . . 3.3.1 Negative Resistance Oscillator-Type Active Integrated Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Feedback Loop Oscillator-Type Active Integrated Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Design Procedure of Negative Resistance Oscillator-Type Active Integrated Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Design Procedure of Feedback Loop Oscillator-Type Active Integrated Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.1 Two-Port Radiator Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2 Amplifier Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.3 Active Integrated Antenna Design . . . . . . . . . . . . . . . . . . . . . . 3.5.4 Oscillation Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.5 Harmonic Balance Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.6 Active Integrated Antenna Design . . . . . . . . . . . . . . . . . . . . . . 3.5.7 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4 Frequency Reconfigurable Passive and Active Planar Antennas . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Classification of Frequency Reconfigurable Antennas . . . . . . . . . . . . 4.2.1 Discrete Frequency Reconfigurable Antennas . . . . . . . . . . . . 4.2.2 Continuous Frequency Reconfigurable Antennas . . . . . . . . . 4.3 Frequency Reconfigurable Passive Planar Antenna Using Different Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 Frequency Reconfiguration Using an Additional Patch or Stub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2 Frequency Reconfiguration Using Reconfigurable Matching Network . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.3 Frequency Reconfiguration Using Shorting Posts or Reactive Loading of the Radiating Element . . . . . . . . . . . . 4.3.4 Frequency Reconfiguration by Varying the Slot Length . . . . 4.3.5 Frequency Reconfiguration Using Metasurfaces . . . . . . . . . .

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32 34 35 37 37 38 39 39 40 40 42 43 44

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4.4 Frequency Reconfigurable Active Planar Antennas Realized Using Different Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Polarization Reconfigurable Passive and Active Planar Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Basis of Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Obtaining Circular Polarization from Microstrip Patch Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Reconfigurable Microstrip Patch Antenna with Switchable Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Reconfigurable Stub Loaded Microstrip Patch Planar Antenna with Switchable Polarization . . . . . . . . . . . . . . . . . . . 5.4.2 Reconfigurable Corner Truncated Microstrip Patch Planar Antenna with Switchable Polarization . . . . . . . . . . . . . 5.5 Polarization Reconfigurable Slot Antennas . . . . . . . . . . . . . . . . . . . . . 5.6 Polarization Reconfigurable Compact Slot Antennas . . . . . . . . . . . . . 5.6.1 Reconfigurable Compact Rectangular Slot Antenna with Switchable Polarization . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7 Polarization Reconfigurable Active Planar Antennas . . . . . . . . . . . . . 5.7.1 Polarization Reconfigurable Active Antenna with a Symmetrically Coupled Passive Radiator . . . . . . . . . . 5.7.2 Polarization Reconfigurable Active Antenna with an Asymmetrically Coupled Passive Radiator . . . . . . . . 5.8 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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57 61 62 65 65 66 66 68 69 72 75 80 81 86 87 93 98 98

6 Radiation Pattern Reconfigurable Passive and Active Planar Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Concept of Radiation Pattern Reconfigurability in Antennas . . . . . . 6.3 Beam Steering/Switching in Passive Planar Antennas . . . . . . . . . . . . 6.4 Beam Steering/Switching in Active Planar Antennas . . . . . . . . . . . . . 6.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

103 103 103 104 105 131 134

7 Null Broadening and Steering in Passive Planar Antennas . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Null Steering Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Null Broadening Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Four-Element Slot Array Antenna with DT Distribution . . . . . . . . . . 7.4.1 Array Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Contents

7.5 Four-Element Slot Array Antenna with Binomial Distribution . . . . . 7.5.1 Array Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 Null Steering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

144 144 145 145 149 151

8 Compound Reconfigurable Planar Antennas . . . . . . . . . . . . . . . . . . . . . . 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Compound Reconfigurable Antennas . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Reconfigurable Microstrip Patch Antenna with Polarization Agility in Two Switchable Frequency Bands . . . . . . . . . . . . . . . . . . . . 8.4 Reconfigurable Microstrip Patch Antenna with Polarization Agility in Three Switchable Frequency Bands . . . . . . . . . . . . . . . . . . 8.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

153 153 153

9 Applications of Reconfigurable Planar Antennas in Wireless Communication Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Applications of Frequency Reconfigurable Antennas . . . . . . . . . . . . 9.3 Applications of Polarization Reconfigurable Antennas . . . . . . . . . . . 9.4 Applications of Pattern Reconfigurable Antennas . . . . . . . . . . . . . . . 9.5 Applications of Compound Reconfigurable Antennas . . . . . . . . . . . . 9.6 Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7 Scope of Reconfigurable Passive Planar Antennas for Future Wireless Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.8 Scope of Active Integrated Planar Antennas in Power Combining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.9 Non-linearity of Switches at High RF Power . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

155 163 171 180 183 183 183 184 186 187 189 189 189 190 190

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197

About the Authors

Shiban Kishen Koul received the B.E. degree in electrical engineering from Regional Engineering College, Srinagar, India, in 1977, and the M.Tech. and Ph.D. degrees in microwave engineering from the Indian Institute of Technology Delhi, New Delhi, India, in 1979 and 1983, respectively. He has been an Emeritus Professor with the Indian Institute of Technology, Delhi, since 2019. He served as Deputy Director (Strategy and Planning) with IIT Delhi from 2012–2016 and Mentor Deputy Director (Strategy and Planning, International affairs) with IIT Jammu, J&K, India, from 2018–2021. He also served as the Chairman of Astra Microwave Products Limited, Hyderabad, from 2009–2019, and Dr. R. P. Shenoy Astra Microwave Chair Professor at IIT Delhi from 2014–2019. His research interests include RF MEMS, high-frequency wireless communication, microwave engineering, microwave passive and active circuits, device modelling, millimetre and submillimetre wave IC design, body area networks, flexible and wearable electronics, medical applications of subterahertz waves and reconfigurable microwave circuits, including miniaturized antennas. He has successfully completed 38 major sponsored projects, 52 consultancy projects, and 61 technology development projects. He has authored/co-authored 576 research papers, 20 stateof-the-art books, 4 book chapters, and 2 e-books. He holds 26 patents, 6 copyrights, and one trademark. He has guided 30 Ph.D. theses and more than 120 master’s theses. He is a Life Fellow of IEEE and Fellow of INAE and IETE. He is the Chief Editor of the IETE xv

xvi

About the Authors

Journal of Research, Associate Editor of the International Journal of Microwave and Wireless Technologies, Cambridge University Press. He served as a Distinguished Microwave Lecturer of IEEE MTT-S for the period 2012–2014. Prior to this, he served as a Speaker Bureau Lecturer of IEEE MTT-S. He also served as an AdCom member of the IEEE MTT-S from 2010– 2018 and is presently a member of the Awards, Nomination and Appointments, MGA, M&S, and Education Committees of the IEEE MTT-S. He is recipient of numerous awards, including IEEE MTT Society Distinguished Educator Award (2014); Teaching Excellence Award (2012) from IIT Delhi; Indian National Science Academy (INSA) Young Scientist Award (1986); Top Invention Award (1991) of the National Research Development Council for his contributions to the indigenous development of ferrite phase shifter technology; VASVIK Award (1994) for the development of Ka-band components and phase shifters; Ram Lal Wadhwa Gold Medal (1995) from the Institution of Electronics and Communication Engineers (IETE); Academic Excellence Award (1998) from Indian Government for his pioneering contributions to phase control modules for Rajendra Radar, Shri Om Prakash Bhasin Award (2009) in the field of Electronics and Information Technology, VASVIK Award (2012) for the contributions made to the area of Information, Communication Technology (ICT) and M N Saha Memorial Award (2013) from IETE. Rajesh K. Singh received the B.Tech. degree in electronics and communication engineering from Gautam Buddh Technical University, Lucknow, India, in 2010 and M.Tech. degree in microwave electronics from Delhi University South Campus, Delhi, India, in 2013. He received his Ph.D. degree in microwave engineering from the Indian Institute of Technology, Delhi, India, in 2018. He is an Assistant Professor at the Department of Electronics Engineering, Defence Institute of Advanced Technology (DIAT), Pune. He has worked as an RF consultant (October 2018–December 2018) at Eron Energy Pvt. Ltd., New Delhi, India. He was a Postdoctoral Researcher (February 2019–December 2021) at Microwave and Radiation Laboratory, Department of Information Engineering, University of Pisa,

About the Authors

xvii

Pisa, Italy. His research interests include Active Integrated Antennas (AIAs), RFID, EMI/EMC, Wireless Power Transfer, Reconfigurable 2D and 3D antennas for current and future wireless systems, Smart Gloves for near-/far-field UHF-RFID, SSPP, and Antenna Modules for Automotive. He has authored/co-authored more than 40 international journal articles and conference contributions. He is an active reviewer of various reputed journals Including IEEE TAP and AWPL. He served as Chairman for the period 2016–2018 and Treasurer for the period 2014–2016 of the IEEE MTT-S Student Branch Chapter at the Indian Institute of Technology Delhi, India. He is a recipient of the Young Scientist Award from the International Union of Radio Science (URSI) General Assembly and Scientific Symposium (GASS) 2020 and the Distinguished Service Award for RFID-TA 2019.

Abbreviations

2D 3D 4G 5G AA ADS AIA ARBW BARITT BJT BLC BSF BW BWCS CA CP CPW CST CW DC DT EIRP EM FET GHz GNSS GPS HBT HEMT IMBW IMPATT

Two-Dimensional Three-Dimensional Fourth Generation Fifth Generation Active Antenna Advanced Design System Active Integrated Antenna Axial Ratio Bandwidth Barrier Injection Transit-Time Bipolar Junction Transistor Branch Line Coupler Band Stop Filter Bandwidth Body-centric Wireless Communication System Carrier Aggregation Circular Polarization Co-Planar Waveguide Computer Simulation Technology Continuous Wave Direct Current Dolph Tchebyscheff Effective Isotropic Radiated Power Electromagnetic Field Effect Transistor Gigahertz Global Navigation Satellite System Global Positioning System Heterojunction Bipolar Transistor High Electron Mobility Transistor Impedance Bandwidth Impact Ionization Avalanche Transit-Time xix

xx

IoT KHz LHCP LP LTE MIMO mmW MOSFET MW PET PSK RBW RF RHCP S/I S-Matrix S11 S21 SA SDR SNR TL TM UWB V2V VNA Wi-Fi WiMAX WLAN WPD WPT

Abbreviations

Internet of Things Kilohertz Left-Hand Circular Polarization Linear Polarization Long-Term Evolution Multiple Input Multiple Output Millimetre Wave Metal–Oxide–Semiconductor Field Effect Transistor Microwave Piezoelectric Transducer Phase Shift Keying Resolution Bandwidth Radio Frequency Right-Hand Circular Polarization Signal-to-Interference Ratio Scattering Matrix Reflection Coefficient Transmission Coefficient Spectrum Analyzer Software-Defined Radio Signal-to-Noise Ratio Transmission Line Transverse Magnetic Ultra-Wideband Vehicle-to-Vehicle Vector Network Analyzer Wireless Fidelity Worldwide Interoperability for Microwave Access Wireless Local Area Network Wilkinson Power Divider Wireless Power Transfer

Chapter 1

Introduction and Overview

1.1 Introduction An antenna is the necessary component of any wireless communication system. Over the years, the development of reconfigurable antennas has been receiving great attention to fulfil the requirement of different wireless applications such as Bluetooth, Global Positioning System (GPS), satellite, Wi-Fi, Wireless Local Area Network (WLAN), and Worldwide interoperability for Microwave Access (WiMAX) by using a single terminal [1–5]. Although fixed antennas can be used in different wireless systems, for different services different antennas are needed to fulfil the requirements. A reconfigurable antenna regarded as a single element meets this demand and accommodates multiple services. Reconfigurable antennas are popular and extensively used in modern wireless communication systems due to their low profile, low cost, light weight, ease of integration, and ability to accommodate various wireless services [6–14]. Considerable progress has been made in the development of reconfigurable antennas in the past two decades from both academia and industry. Reconfigurable antennas have the capability to dynamically change their characteristics such as frequency, polarization, and radiation pattern. Reconfigurable antennas provide more functionality and flexibility. The multifunctional capabilities of such planar antennas make them attractive for current and next-generation wireless applications. In modern wireless systems, it is required to integrate various functions into a single component or antenna to achieve new requirements that are increasing day by day [15–23]. Apart from the reconfigurable function, a compact antenna can reduce the size of the device and provide more area to incorporate other system-level components on the board. Portable devices are very sensitive to the orientation of the transmitter and receiver; circularly polarized compact antennas can be advantageous over linearly polarized antennas for portable devices [24–26]. This chapter gives an overview of the reconfigurable active and passive planar antennas. Reconfigurable antennas use RF switches to dynamically change their characteristics [27, 28]. The modeling of RF switches used in performing numerical analysis © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1_1

1

2

1 Introduction and Overview

and the practical realization of reconfigurable antennas are discussed and elaborated in this chapter.

1.2 Reconfigurable Planar Antennas Antennas consisting of planar or curved surface radiating elements or their variations and at least one RF feed are called planar antennas. A planar antenna has its geometry etched on one plane, making it two-dimensional (2D). Planar antennas are low profile and low-cost when produced utilizing printed circuit board technology. Planar antennas can be easily integrated into a limited volume. Such advantages of planar antennas make them ideal for wireless applications. Planar antennas developed with printed circuit board technology can be easily integrated with other electronic components. Although planar antennas suffer from low radiation efficiency, narrow bandwidth, and low gain, there are existing techniques that can enhance the radiation efficiency, gain and bandwidth of these antennas.

1.2.1 Feeding Techniques Planar antennas can be realized by using planar geometry such as patch, slot, etc. Microstrip patch antenna has a simple geometry, and it could be of any shape such as rectangular, circular, triangular, etc. as shown in Fig. 1.1. There are various feeding mechanisms for exciting microstrip patch antennas. The most used techniques are microstrip line feed, coaxial probe feed, proximity coupled feed, and aperture coupled feed. In the microstrip line feed, a conducting strip is directly connected to one edge of the microstrip patch as shown in Fig. 1.2a. The conducting strip (microstrip line) is narrower in width compared to the patch width. The advantage of this technique

(a)

(b)

(c)

Fig. 1.1 Different shapes of patch, a rectangular or square, b triangular and c circular

1.2 Reconfigurable Planar Antennas

3

is that the feed and the patch can be etched on the same layer of the substrate for realizing a planar antenna structure. Apart from it, to match the input impedance of the microstrip patch to the impedance of the feed port (50 Ω), an inset cut in the patch is needed as shown in Fig. 1.2b. Another way of matching the impedance is to use a quarter-wave transformer in-between the microstrip patch and the conducting strip (50 Ω feed line) as shown in Fig. 1.2c. Coaxial feed is one of the most common feed techniques used to excite microstrip patch antennas. To feed a conventional rectangular microstrip patch antenna, a metallic pin or wire can be soldered at the location on the microstrip patch, where the input impedance of the patch is 50 Ω as shown in Fig. 1.3a. A coaxial connector is used to feed a microstrip patch as shown in Fig. 1.3b. The centre pin of the coaxial

(a)

(b)

(c)

Fig. 1.2 Microstrip line feed exciting a microstrip patch antenna, a microstrip line is etched on the same layer of the substrate as patch, impedance matching can be obtained by using b inset feed and c quarter-wave transformer

4

1 Introduction and Overview

connector is soldered to the microstrip patch while the outer part is soldered to the ground plane. This technique is also called the probe feed technique. Coaxial probe feed has low spurious radiation. Depending on the requirement and constraints, both feed techniques are used in practice. Normally, microstrip feed is preferred in the case of single layer printed antennas where there is no space for attaching a connector on the backside. Both feed techniques give almost similar performance in terms of impedance bandwidth, gain, radiation pattern, efficiency, etc. Both feed techniques inherently offer narrow bandwidth. Probe or microstrip feed generates higher-order modes which result in cross-pol radiation, and it happens due to the presence of inherent asymmetries in both feed techniques. To get wide bandwidth, aperture coupled, and proximity coupled feeds are used. Figure 1.4 shows the geometry of an aperture coupled feed. In an aperture coupled feeding technique, two substrate layers are used. The microstrip patch is etched on one substrate (substrate 2 shown in Fig. 1.4) while the feed line is on the other substrate (substrate 1). The ground plane is sandwiched in between the substrates; a small aperture is cut in the ground plane of substrate 1 to feed the microstrip patch. It is also called a noncontact or indirect feeding technique. The energy of a microstrip feed line etched at the bottom of substrate 1 is coupled to the microstrip patch through a slot etched in the ground plane. There is considerable freedom in this feed technique; one can independently optimize the performance of the feed and patch element. Typically, a thin substrate with a high dielectric constant is used to realize the feed while a thick substrate with a low dielectric constant is used to realize the radiator (microstrip patch). In this technique, feed is isolated from the radiating patch, and it is due to the presence of a ground plane in between the feed and patch. One can achieve an excellent polarization purity using this feed technique. Figure 1.5 shows the geometry of a proximity coupled feed. In this technique, two dielectric substrates are used. Proximity coupled feeding gives larger bandwidth compared to other techniques. The microstrip patch antenna is excited through proximity coupled feed in which the feed line is sandwiched between the

(a) Fig. 1.3 Coaxial probe feed technique, a top view, b side view

(b)

1.2 Reconfigurable Planar Antennas

5

Fig. 1.4 Aperture coupled feed technique

Fig. 1.5 Proximity coupled feed technique

ground and radiating element. The coupling nature of the proximity coupled feed is capacitive whereas, in the direct contact methods, the coupling is inductive. The difference in the coupling affects the impedance bandwidth. The inductive coupling of the edge and probe-fed patches limits the thickness of the material. Thus, the bandwidth of a proximity coupled patch antenna is inherently larger than the direct contact fed patches. The reader may get more details about these feeding techniques from the scientific literature.

1.2.2 Passive Antennas A passive antenna contains only the passive components such as resistors, inductors, capacitors, and metal posts. It doesn’t have any electronic amplification components such as transistors. In reconfigurable passive antennas, radio frequency (RF) switches are used to reconfigure their characteristics. Although the RF switches are active components, such a category of antennas comes under passive antennas.

6

1 Introduction and Overview

1.2.3 Active Antennas An antenna is called an active antenna only when it is integrated with an amplification unit or component such as a transistor. Active devices are integrated with the passive antenna structure to enhance the performance of the overall antenna [29, 30]. In the conventional approach, the passive radiator, and active device such as amplifier and oscillator are two separate components connected by a transmission line, and the performance of both components can be enhanced independently. In the active antenna approach, both components form the complete circuit, and the components are dependent on each other [31]. The passive element in active integrated antennas acts as a radiator and it also serves other functions like duplexing, filtering, resonating, etc. An active antenna can generate, amplify, and process the signal. The term ‘active integrated antenna’ comes when the active circuitry and passive radiating elements are integrated on the same substrate. The development of active integrated antennas offers several advantages, for example, enhancing the bandwidth, reducing the mutual coupling between multiple input multiple output (MIMO) elements, improving the noise figure, etc. Active integrated antennas are classified based on the basic function of an active circuit, namely, the amplifier type, the oscillator type, and the frequency conversion type. Two terminal semiconductor devices such as Gunn diode, Impact ionization Avalanche Transit-Time (IMPATT) diode, barrier injection transit-time (BARITT) diode, and three-terminal devices such as bipolar junction transistor (BJT), field-effect transistor (FET), heterojunction bipolar transistor (HBT) and high-electron-mobility transistor (HEMT) can be used as active devices for realizing active antennas.

1.3 Advantages of Planar Antennas Numerous advantages of planar antennas are listed below. . . . . . . .

Low cost Light weight Low profile Ease of fabrication Simple structure High polarization purity Compact size

1.5 RF Switches and Their Performance

7

1.4 Disadvantages of Planar Antennas Although, planar antennas offer numerous advantages listed above, there are some disadvantages while using planar antennas. Planar antennas have low radiation efficiency and hence low gain compared to three-dimensional (3D) antennas. However, techniques exist to enhance the radiation efficiency and the gain of planar antennas.

1.5 RF Switches and Their Performance RF switches play a key role in reconfigurable antennas. Switches are placed on the aperture to change the radiator shape by which, the radiation from the patch is controlled and hence the reconfigurability is achieved. The wide spectrum used for wireless applications involves different switch technologies for different applications. Proper selection of the most suited RF switch can make difference in achieving the best performance from the antenna structure or system. RF switch could be optimized to achieve desired performance for different applications.

1.5.1 Types of RF Switches RF switches can be classified into two main categories, i.e., solid state electronic RF switches and electromechanical switches. This classification of switches is based on their principle of operation. Capability of RF switches can be seen by comparing the performance parameters such as frequency range, insertion loss, return loss, isolation, switching speed, repeatability, power handling, etc.

1.5.1.1

Solid State Electronic RF Switches

Solid state RF switches are based on semiconductor technology, i.e., PIN diode, FET, MOSFET, etc. In general, solid-state switches offer faster switching speed and excellent repeatability but these switches operate from few KHz frequency range. Among these, PIN diode is faster and offers good isolation.

1.5.1.2

Electromechanical Switches

In such switches, switching is done electromechanically through a make or break in the transmission path by applying a control signal. RF Microelectromechanical Systems (RF MEMS) switches are popular and offer low insertion loss and moderate

8 Table 1.1 Comparison of the performance of RF switches

1 Introduction and Overview Features

Switch type Electromechanical FET

Frequency range From DC

PIN

From DC From KHz

Insertion loss

Low

High

Medium

Return loss

Good

Good

Good

Isolation

Excellent

Good

Good

Switching speed

Slow

Fast

Faster

Power handling

Moderate

Low

Low

Operating life

Medium

High

High

Repeatability

Good

Excellent

Excellent

power handling. Operating frequency of RF MEMS starts from DC. Comparison of the performance of RF switches is given in Table 1.1.

1.6 Switch Modeling Techniques As seen from the above Table, PIN diodes are more popular due to their faster switching speed, relatively high current handling capacity and small physical size. This section explains how PIN diode is modeled using full-wave electromagnetic software. PIN diode circuit in series configuration is shown in Fig. 1.6. It consists of single PIN diode, RF choke inductors to protect DC power supply from RF and DC blocking capacitors to protect RF measuring instruments. The electrical reconfiguration techniques use RF switches to control the radiation by turning the switches ON/OFF. Proper modeling of the RF switch can be done after including the effects of physical switches. In a simulation tool, switch can be Fig. 1.6 PIN diode circuit (series configuration)

1.6 Switch Modeling Techniques

(a)

9

(b)

Fig. 1.7 Ideal switch model a ON-state b OFF-state

modeled using an ideal or non-ideal approach. In the following sections, PIN diode modeling is briefly discussed.

1.6.1 Ideal Approach In this approach, PIN diode is modeled as an ideal switch. A metallic strip of width (0.2 mm) and length (0.4 mm) is connected between the two transmission lines as shown in Fig. 1.7a. When the metallic strip is connected, it represents the ON-state of the switch. Removing the strip represents the OFF-state as shown in Fig. 1.7b. The ideal model does not consider the capacitance effect of the physical diode in the OFF-state and series resistance in the ON-state. Here MA4SPS402 pin diode is considered as an example. Performance of the switch in terms of S-parameters is obtained through ideal switch modeling. A 50 Ω microstrip line is used to evaluate the performance of the switch.

1.6.2 Non-Ideal Approach 1.6.2.1

Lumped Element Approach

In this approach, switch is treated as non-ideal component. The equivalent circuit can be obtained from the datasheet of the diode. The lumped elements can be considered in the simulations to represent the diode in the ON- and OFF-states. Here, the equivalent circuit of a PIN diode is shown in Fig. 1.9. PIN diode can be modeled as a series resistor (Rs) in the ON-state and as a parallel combination of capacitor (Cp) and resistor (Rp) in the OFF-state. The inductance (Lp) is the parasitic inductance, and it can be ignored in the simulations due to its low value. The value of series resistance normally varies between 0.1 and 5 Ω, depending on the type of switch used in the circuit. The OFF-state capacitance is normally small in the range from 0.02 to 2 pF. Once again, we consider the same MA4SPS402 pin diode. Performance of the switch in terms of S-parameters is obtained through non-ideal switch modeling approach. A 50 Ω microstrip line is considered to see the performance of the switch. Results are plotted in Fig. 1.10. In the ON-state, the transmission coefficient is not

10

1 Introduction and Overview

(a)

(b) Fig. 1.8 Simulated S-parameters of MA4SPS402 PIN diode using ideal model, a OFF-state and b ON-state

1.7 Organization of the Book

11

Fig. 1.9 Equivalent circuit of a PIN diode in the OFFand ON-states

0 dB, it offers losses which are due to the non-ideal modeling of the switch. A series resistance of 5 Ω in ON-state is taken from diode datasheet. In the OFF-state, a parallel combination of resistance (40 kΩ) and capacitance (0.035 pF) is taken. The OFF-state of the diode is not very clear from Fig. 1.10. It can be observed that the resonance frequency shifts after adding capacitance in the OFF-state. Here a 50 Ω microstrip line is considered this is the reason why frequency shift is not observed.

1.6.2.2

Discrete or Internal Port Approach

The lumped element approach becomes complex when more switches are present in the circuit; the discrete port approach is best suited in such cases. Internal or discrete ports can be connected in place of the diodes. One discrete port is used to represent one physical diode in the circuit. Performance in terms of S-parameters can be obtained from any EM simulator. These S-parameters have all information of the signal at each port. The S-parameter data is then imported in a circuit simulator such as Advanced Design System (ADS) and added with the data obtained from the datasheet of the diode.

1.7 Organization of the Book Chapter 1 deals with the introduction of reconfigurable active and passive planar antennas and their benefits in modern and future wireless systems. It also discusses the modeling of RF switches that are used in numerical analysis. Chapter 2 discusses the principle of reconfigurability, and it also lists different reconfiguration states that exist in the realization of reconfigurable antennas. Chapter 3 deals with the active integrated antennas and their modeling. It also discusses the oscillation conditions, and advantages and disadvantages of different approaches used in developing active integrated antennas. Chapter 4 focuses on frequency reconfigurability in active and passive planar antennas. Chapter 5 deals with the polarization reconfigurable active and passive planar antennas switchable among linear polarization (LP) or circular polarization (CP), or among left-hand circular polarization (LHCP) or

12

1 Introduction and Overview

(a)

(b) Fig. 1.10 Simulated S-parameters of the MA4SPS402 PIN diode considering non-ideal modeling approach, a OFF-state and b ON -state

References

13

right-hand circular polarization (RHCP). Radiation pattern reconfigurable antennas are discussed in Chapter 6. Beam steering is discussed in both active and passive planar antennas in Chapter 7. Chapter 8 deals with compound reconfigurable planar antennas. Chapter 9 describes the applications of reconfigurable antennas in modern and future wireless communication systems. This Chapter also includes the future scope of compact and multifunction active and passive planar antennas.

References 1. Christodoulou, C.G., Tawk, Y., Lane, S.A., Erwin, S.R.: Reconfigurable antennas for wireless and space applications. Proc. IEEE 100(7), 2250–2261 (2012) 2. Mansoul, A.: Reconfigurable multiband bowtie antenna for WiFi, WiMax, and WLAN applications. In: 2017 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, pp. 1147–1148. San Diego, CA (2017) 3. Bernhard, J.T.: Reconfigurable antennas. Synthesis Lectures Antennas 2(1), 1–66 (2007) 4. Jiajie, Z., Anguo, W., Peng, W.: A survey on reconfigurable antennas. In: 2008 International Conference on Microwave and Millimeter Wave Technology, pp. 1156–1159. Nanjing (2008) 5. Parihar, M.S., Basu, A., Koul, S.K., Reconfigurable printed antennas. IETE J. Res. 59(4), 383–391 6. Haider, N., Caratelli, D., Yarovoy, A.G.: Recent developments in reconfigurable and multiband antenna technology. Int. J. Antennas Propag. 2013, 1–14 (2013) 7. Nella, A., Gandhi, A.S.: A survey on microstrip antennas for portable wireless communication system applications. In: 2017 International Conference on Advances in Computing, Communications and Informatics (ICACCI), pp. 2156–2165 (2017) 8. Sravani, B., Krishna, D.R., Singh, R.K., Koul, S.K.: Reconfigurable antenna with frequency switching capability for C-band application. In: 2017 IEEE International Conference on Antenna Innovations & Modern Technologies for Ground, Aircraft and Satellite Applications (iAIM), pp. 1–4 (2017) 9. Paliwal, R., Singh, R.K., Koul, S.K.: Reconfigurable UWB monopole antenna with switchable frequency notched bands. IEEE Applied Electromagnetics Conference (AEMC) 2017, 1–2 (2017) 10. Yadav, S., Singh, R.K., Abegaonkar, M.P., Sharma, M.M.: Stub loaded reconfigurable microstrip patch antenna with frequency agility. IEEE Indian Conference on Antennas and Propogation (InCAP) 2018, 1–4 (2018) 11. Leingthone, M.M., Hakem, N.: Implementation of a pattern-reconfigurable antenna for modern wireless sensor network applications. IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting 2019, 683–684 (2019) 12. Kim, J., Nam, S.: A compact multiband reconfigurable quasi-isotropic antenna with planar structure. In: 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC), pp. 1–1 (2019) 13. Awan, W.A., Hussain, N., Naqvi, S.A., Striker, A.I.R., Mitra, D., Braaten, B.D.: A miniaturized wideband and multi-band on-demand reconfigurable antenna for compact and portable devices. AEU-Int. J. Electron. C. 122, 153266 (2020) 14. Shahmirzadi, N.V., Oraizi, H.: Design of reconfigurable coplanar waveguide-fed planar antenna for multiband multi-input–multi-output applications. IET Microw. Antennas Propag. 14(13), 1493–1503 (2020) 15. Shah, S.A.A., Khan, M.F., Ullah, S., Flint, J.A.: Design of a multi-band frequency reconfigurable planar monopole antenna using truncated ground plane for Wi-Fi, WLAN and WiMAX applications. International Conference on Open Source Systems and Technologies 2014, 151–155 (2014)

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1 Introduction and Overview

16. Mabrouki, M., Gharsallah, A.: Multi-band frequency reconfigurable planar bow-tie antenna. In: 2020 5th International Conference on Advanced Technologies for Signal and Image Processing (ATSIP), pp. 1–6 (2020) 17. Singh, R.K., Basu, A., Koul, S.K.: A novel reconfigurable microstrip patch antenna with polarization agility in two switchable frequency bands. IEEE Trans. Antennas Propag. 66(10), 5608–5613 (2018) 18. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable microstrip patch antenna with polarization switching in three switchable frequency bands. IEEE Access 8, 119376–119386 (2020) 19. Bhattacharjee, A., Dwari, S.: Wideband monopole antenna with circular polarization reconfigurability and pattern diversity. IEEE Indian Conference on Antennas and Propagation (InCAP) 2021, 957–960 (2021) 20. Tiwari, A., Sinha, S., Vignesh, S.J., Yadav, D.: A ring shaped frequency reconfigurable microstrip planar antenna with suspended ground for multi-band wireless application. In: 2021 5th International Conference on Electronics, Materials Engineering & Nano-Technology (IEMENTech), pp. 1–6 (2021) 21. Gan, T.H., Tan, P.K., Liu, A., Lu, J., Sow, S.M.: A planar wide-angle scanning array using pattern-reconfigurable antenna. In: 2021 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting (APS/URSI), pp. 557–558 (2021) 22. Wang, Z., Liu, S., Dong, Y.: Compact wideband pattern reconfigurable antennas inspired by end-fire structure for 5G Vehicular communication. IEEE Trans. Vehicular Tech. 71(5), 4655– 4664 (2022) 23. Jin, X., Liu, S., Yang, Y., Zhou, Y.: A frequency-reconfigurable planar slot antenna using S-PIN diode. IEEE Antennas Wirel. Propag. Lett. 21(5), 1007–1011 (2022) 24. Singh, R.K., Basu, A., Koul, S.K.: Asymmetric coupled polarization switchable oscillating active integrated antenna. Asia-Pacific Microwave Conference (APMC) 2016, 1–4 (2016) 25. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable microstrip patch antenna with switchable polarization. IETE J. Res. 66(5), 1–10 (2018) 26. Singh, R.K., Basu, A., Koul, S.K.: Novel high gain polarization switchable rectangular slot antenna for L-band applications. In: 2017 11th European Conference on Antennas and Propagation (EUCAP), pp. 3820–3824 (2017) 27. Singh, R.K., Basu, A., Koul, S.K.: A novel pattern-reconfigurable oscillating active integrated antenna. IEEE Antennas Wirel. Propag. Lett. 16, 3220–3223 (2017) 28. Singh, R.K., Basu, A., Koul, S.K.: Efficient null broadening and steering using slot antenna array for radar applications. Asia-Pacific Microwave Conference (APMC) 2016, 1–4 (2016) 29. Lin, J., Itoh, T.: Active integrated antennas. IEEE Trans. Microw. Theory Tech. 42(12), 2186– 2194 (1994). https://doi.org/10.1109/22.339741 30. Chang, K., York, R.A., Hall, P.S., Itoh, T.: Active integrated antennas. IEEE Trans. Microw. Theory Tech. 50(3), 937–944 (2002). https://doi.org/10.1109/22.989976 31. Singh, R.K., Basu, A., Koul, S.K.: Two-port reconfigurable passive radiator with switchable pattern for active antenna application. IEEE MTT-S International Microwave and RF Conference (IMaRC) 2017, 1–5 (2017)

Chapter 2

Principle and Types of Reconfigurability

2.1 Introduction This chapter discusses the principle of reconfigurability and different types of reconfiguration techniques in the antenna technologies. The advantages and disadvantages of different reconfiguration techniques are discussed. Reconfigurable antennas can be categorized based on the antenna’s characteristics typically the frequency, radiation pattern, and polarization. This chapter discusses various techniques that are used to reconfigure the antenna characteristics for various applications. The need of each category of reconfigurable antennas is discussed.

2.2 Principle of Reconfigurability Reconfigurability of an antenna refers to the capacity to adjust a radiator’s characteristics in terms of polarization, resonant frequency, and radiation pattern. Antenna parameters such as frequency, polarization, and radiation pattern could be dynamically changed by employing a switching technique through controlled electronic, mechanical, optical switches or the use of smart materials.

2.3 Reconfiguration Techniques Various reconfiguration techniques reported in the literature are used for many applications of current and modern wireless systems [1]; four major types of reconfiguration techniques are explained below:

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1_2

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. . . .

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Electronic reconfigurations Mechanical reconfigurations Optical reconfigurations Material reconfigurations

2.3.1 Electronic Reconfiguration Techniques The electronic reconfiguration technique is the most common, and it is based on the use of electronic switches. Switches are used to connect or disconnect the geometries or parts involved in the radiation and modify the surface current distribution. In reconfigurable antennas, resonance occurs based on the effective electrical length of the modified surface current. Switching components such as radio frequency (RF) Microelectromechanical systems (MEMS), PIN diodes, varactor diodes, and FETs are used in developing electronically reconfigurable antennas [2–7]. PIN diode switches are more popular in reconfigurable antennas due to their fast switching and ease of integration with microwave circuits. Electronic reconfiguration employs two types of switching, i.e., discrete switching [2–5] and continuous switching [6, 7]. Discrete switching can be obtained by using PIN diodes, FETs, and RF MEMS while continuous switching can be achieved by using varactor diodes. For example, a discrete frequency reconfigurable antenna is illustrated in Fig. 2.1a. The PIN diode is used to achieve the switching behavior of the antenna. Two different resonances are obtained by turning the PIN diode ON or OFF as shown in Fig. 2.1b. The effective electrical length of surface currents is modified (increased in this case) after connecting a small stub hence resonance is shifted downwards. The performance of the PIN diode must be tested separately to get the insertion loss in the ON-state and isolation in the OFFstate. Biasing circuits in electronically reconfigurable antennas are designed in such a way that the interference must be minimum because metal wires may distort the radiation pattern of the antenna. A PIN diode (model: MA4SPS402) is separately tested on a printed circuit board where a microstrip line is etched on one side of a substrate and the ground plane is on the other side (Fig. 2.2a). A biasing circuit is designed to give DC supply to the PIN diode. Lumped capacitors of 100 pF are used on both sides of the PIN diode to block DC flowing into measuring instruments and lumped inductors of 100 nH are used to block RF flowing into the DC power supply. Performance in terms of S-parameters is measured and shown in Fig. 2.2b. It can be seen from Fig. 2.2 that the insertion loss increases with the frequency and isolation reduces with the frequency. The large value of insertion loss degrades the efficiency hence the gain of a reconfigurable antenna. Insertion loss/isolation can have different values for different diodes. The efficiency of reconfigurable antennas can be enhanced by using high-quality switches. A continuous frequency reconfigurable antenna using a varactor diode is shown in Fig. 2.3a. A varactor diode presents different capacitances while varying the bias across it hence continuous switching can be obtained by employing it in the circuit. Reflection coefficients are plotted in Fig. 2.3b by varying bias voltage across the varactor diode.

2.3 Reconfiguration Techniques

17

Fig. 2.1 Discrete frequency reconfigurable microstrip patch antenna using PIN diode, a geometry, b reflection coefficient plots in the OFF-and ON-states

(a)

(b)

2.3.2 Mechanical Reconfiguration Techniques Mechanical reconfiguration can be obtained by mechanically adjusting the radiator. Mechanical reconfigurable antennas are free from any active switching element hence biasing circuits are not needed. The flexibility of such antennas is limited; it is difficult to achieve multifunction characteristics from such antennas. A frequency reconfigurable rotatable microstrip antenna is reported in [8]. The shape of the radiator can be modified by using the rotation technique as shown in Fig. 2.4. A circular rotating part is embedded in the antenna structure to change its shape. Several mechanically reconfigurable antennas are reported in the literature [9–12].

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2 Principle and Types of Reconfigurability

Fig. 2.2 PIN diode, a photograph of a diode integrated onto a microstrip line with biasing mechanism, b reflection coefficient in the OFF-state c reflection coefficient in the ON-state

(a)

(b)

(c)

2.3 Reconfiguration Techniques

19

Fig. 2.3 Continuous frequency reconfigurable microstrip patch antenna using varactor diode, a geometry and b reflection coefficient plots with different bias across the varactor diode

(a)

(b) Fig. 2.4 Photograph of a mechanically reconfigurable antenna. Reproduced with permission from IEEE [8]

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2.3.3 Optical Reconfiguration Techniques Optical reconfiguration techniques are based on the use of photoconductive switches. These switches are made of semiconductor materials such as silicon and germanium. Photoconductive switches do not require biasing circuits and metal wires and less interference occurs in the circuit with the use of photoconductive switches. Apart from this, photoconductive switches exhibit fast switching speeds. In [13], various techniques for optical control of reconfigurable antennas using commercially available devices have been discussed. An optically controlled frequency switchable patch antenna using a silicon-based switch is reported in [14]. Geometry and photograph are shown in Figs. 2.5a and b, respectively. The frequency response with different operating states of the antenna is shown in Fig. 2.5c. Various optically reconfigurable antennas with frequency, polarization, and beam switching capability have been reported in the scientific literature [15–18].

2.3.4 Material Reconfiguration Techniques Smart material-based reconfigurable antennas change their characteristics by changing the material property in terms of relative dielectric constant and permeability [19]. There are challenges in realizing such smart material-based reconfigurable antennas; an investigation for getting better reliability and efficiency of smart material-based antennas is still ongoing. A frequency-reconfigurable patch antenna using low-loss transformer oil is investigated in [20]. In this antenna, a twolayer substrate is introduced between the patch and the ground plane. The upper layer is made of homogeneous polytetrafluoroethylene substrate, while the lower layer consists of a transparent container, including air and transformer oil layers. The volume ratio of air to liquid is changed by varying the height of the transformer oil layer; the effective permittivity of the entire substrate can be tuned to realize a frequency reconfiguration. The geometry is shown in Fig. 2.6. A broadband polarization-reconfigurable water spiral antenna of low profile [21], a liquid–metal polarization-pattern-reconfigurable dipole antenna [22], etc., have been reported earlier.

2.4 Advantages and Disadvantages of Different Reconfiguration Techniques The advantages and disadvantages of different reconfiguration techniques are given below:

2.4 Advantages and Disadvantages of Different Reconfiguration …

(a)

21

(b)

(c) Fig. 2.5 Optically shorted stub-loaded frequency-switching patch antenna, a geometry, b photograph and c frequency response of the antenna for eight states of operation. Reproduced with permission from IEEE [14]

Reconfiguration technique

Advantages

Disadvantages

Electronic reconfiguration

• Low-cost • Ease of realization

• Complex structure due to biasing circuits

Mechanical reconfiguration • Doesn’t require active elements and biasing circuits

• It needs power source • It exhibits a slow response

Optical reconfiguration

• Doesn’t require bias lines • There is no intermodulation distortion

• Lossy • Activation mechanism is complex

Material reconfiguration

• Low-profile • Light weight

• Low efficiency • Limited application

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2 Principle and Types of Reconfigurability

(a)

(b) Fig. 2.6 A frequency reconfigurable patch antenna using low-loss transformer oil, a geometry, bphotograph and c frequency response of the antenna with different value of h3 . Reproduced with permission from IEEE [20]

2.5 Different Types of Reconfigurable Antennas Reconfigurable antennas are basically divided into four categories: . Frequency reconfigurable antennas . Polarization reconfigurable antennas

2.5 Different Types of Reconfigurable Antennas

23

Fig. 2.6 (continued)

(c)

. Radiation pattern reconfigurable antennas and . Compound reconfigurable antennas

2.5.1 Frequency Reconfigurable Antennas In frequency reconfigurable antennas, the frequency of the antenna can be varied by means of RF switches based on the requirements of the system. A single frequency reconfigurable antenna is preferred instead of using more fixed band antennas [23, 24] operating at different frequency bands. Frequency reconfigurable antennas can efficiently utilize the available space with acceptable performance as modern systems are becoming compact day by day [25–27]. Newly added wireless standards such as 4G and 5G are introduced in the spectrum; new wireless services lying in the wide frequency band are introduced. Frequency reconfigurable antennas can support more than one wireless standard and provide similar performance as that of multiple fixed frequency band antennas. There are various categories of frequency reconfigurable antennas i.e., narrowband-to-narrowband [28, 29], narrowband-to-wideband [30, 31], wideband-to-notch band [32–34], wideband-to-wideband, and multibandto-multiband [35] reconfigurable antennas. Frequency reconfigurable antennas can be tunable or switchable. Switchable antennas are developed by mounting PIN diodes while tunable antennas are developed by employing varactor diodes.

2.5.2 Polarization Reconfigurable Antennas The surface current distribution on the radiating structure determines the polarization of the antenna. The direction of current flow at different time instants translates directly into the polarization of the electric field. The current movement (clockwise

24

2 Principle and Types of Reconfigurability

or anticlockwise) on the surface of an antenna represents the sense of polarization (either LHCP or RHCP). Different polarization states can be obtained by altering the flow of surface current. Ideally, the impedance and frequency characteristics must be the same in different polarization states, but practically it differs due to slight change in the physical structure of the antenna in different polarization modes. The design challenge is to obtain similar characteristics in different polarization states. An antenna with switchable polarization capability may double the system capacity by using the frequency reuse concept. Circular polarized antennas are largely used in current wireless communication systems such as WLAN, RFID, and GPS. Circularly polarized antennas suppress multipath fading and enhance the signal power. Polarization diversity in an antenna system has gained attention in modern wireless systems. Dual polarized/circularly polarized antennas have been realized earlier but these antennas have fixed polarization. Polarization switchable antennas between Linear Polarization (LP) and Circular Polarization (CP) (including both Left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP)) have been discussed in the literature [36–39]. There are various existing techniques to achieve CP from an antenna. Techniques to get CP are discussed in Chapter 5. Compact polarization switchable antennas are in great demand for various modern and future wireless applications.

2.5.3 Radiation Pattern Reconfigurable Antennas Radiation pattern reconfigurable antennas are divided into two categories i.e., beam reconfigurable (beam steering) and null reconfigurable (null steering). The radiation pattern can be steered in both horizontal and elevation planes. Normally, beamsteered antennas are used to cover the entire space. Pattern reconfigurable antennas have received significant attention due to their ability to enhance the performance of wireless systems. Conical and broadside pattern switchable antennas are used to save energy by better directing the signal toward intended users and to provide better coverage by redirecting the main radiation beam. Null steering has gained much attention due to increasing pollution in the electromagnetic environment. Steering of null is more advantageous in radar systems where the desired signal is weak compared to that coming from various sources in directions other than the one of interest. Null can be placed in an undesired direction to enhance the signal to interference ratio. Various reconfigurable antennas with beam and null steering have been reported in the literature [40–48].

References

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2.5.4 Compound Reconfigurable Antennas Compound reconfigurable antennas are the combination of the above three types (frequency, polarization, and radiation pattern). These antennas might have reconfigurable features between frequency and radiation pattern, frequency and polarization, polarization and radiation pattern, and a combination of all three characteristics (frequency, polarization, and pattern). Modern wireless communication systems require multifunction antennas to fulfill the new requirements [49]. The combination of frequency and polarization [7, 50], radiation pattern and polarization [51, 52], frequency and radiation pattern [53], and a combination of all three [54] have been reported in the literature. Compact compound reconfigurable antenna could be a better candidate for future wireless communication systems.

2.6 Summary In this chapter, various kinds of reconfigurable antennas are discussed. Four major types of reconfiguration techniques and their advantages and disadvantages are reviewed. Also, this chapter introduces four different categories of reconfigurable antennas such as frequency, polarization, radiation pattern, and compound reconfigurable antennas.

References 1. Zhang, S., Zeng, Q., Shang, Y., Wu, Y.: An overview of antenna reconfiguration technologies: overview of reconfigurable antenna. Int. Conf. Inf. Technol. Comput. Appl. (ITCA) 2019, 25–28 (2019) 2. Panaia, P., et al.: MEMS-based reconfigurable antennas. In: 2004 IEEE International Symposium on Industrial Electronics, pp. 175–179. Ajaccio, France (2004) 3. Yang, X., Lin, J., Chen, G., Kong, F.: Frequency reconfigurable antenna for wireless communications using GaAs FET switch. IEEE Antennas Wirel. Propag. Lett. 14, 807–810 (2015) 4. Singh, R.K., Basu, A., Koul, S.K.: A Novel Reconfigurable Microstrip Patch Antenna with Polarization Agility in Two Switchable Frequency Bands. IEEE Trans. Antennas Propag. 66(10), 5608–5613 (2018) 5. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable microstrip patch antenna with polarization switching in three switchable frequency bands. IEEE Access 8, 119376–119386 (2020) 6. Behdad, N., Sarabandi, K.: A varactor-tuned dual-band slot antenna. IEEE Trans. Antennas Propag. 54(2), 401–408 (2006) 7. Row, J., Shih, C.: Polarization-diversity ring slot antenna with frequency agility. IEEE Trans. Antennas Propag. 60(8), 3953–3957 (2012) 8. Tawk, Y., Costantine, J., Christodoulou, C.G.: A frequency reconfigurable rotatable microstrip antenna design. In: 2010 IEEE Antennas and Propagation Society International Symposium, pp. 1–4.Toronto, ON, Canada (2010) 9. Tawk, Y., Christodoulou, C.G.: A new reconfigurable antenna design for cognitive radio. IEEE Antennas Wirel. Propag. Lett. 8, 1378–1381 (2009)

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10. Jang, T., Zhang, C., Youn, H., Zhou, J., Guo, L.J.: Semitransparent and flexible mechanically reconfigurable electrically small antennas based on tortuous metallic micromesh. IEEE Trans. Antennas Propag. 65(1), 150–158 (2017) 11. Washington, G., Yoon, H.S., Angelino, M., Theunissen, W.H.: Design, modeling, and optimization of mechanically reconfigurable aperture antennas. IEEE Trans. Antennas Propag. 50(5), 628–637 (2002) 12. Ma, W., Wang, G., Zong, B.F., Zhuang, Y., Zhang, X.: Mechanically reconfigurable antenna based on novel metasurface for frequency tuning-range improvement. In: 2016 IEEE International Conference on Microwave and Millimeter Wave Technology (ICMMT), pp. 629–631. Beijing, China (2016) 13. Patron, D., Daryoush, A.S., Dandekar, K.R.: Optical control of reconfigurable antennas and application to a novel pattern-reconfigurable planar design. J. Lightwave Techn. 32(20), 3394– 3402 (2014) 14. Pendharker, S., Shevgaonkar, R.K., Chandorkar, A.N.: Optically controlled frequencyreconfigurable microstrip antenna with low photoconductivity. IEEE Antennas Wirel. Propag. Lett. 13, 99–102 (2014) 15. Panagamuwa, C.J., Chauraya, A., Vardaxoglou, J.C.: Frequency and beam reconfigurable antenna using photoconducting switches. IEEE Trans. Antennas Propag. 54(2), 449–454 (2006) 16. Sivakumar, E., Ramachandran, B., Indhu bala, B.: Optically controlled reconfigurable antenna array. In: 2015 International Conference on Communications and Signal Processing (ICCSP), pp. 1839–1843. Melmaruvathur, India (2015) 17. Su, H., Shoaib, I., Chen, X., Kreouzis, T.: Optically tuned polarisation reconfigurable antenna. In: 2012 IEEE Asia-Pacific Conference on Antennas and Propagation, pp. 265–266. Singapore (2012) 18. Jin, G., Li, L., Wang, W.: A wideband polarization reconfigurable antenna based on optical switches and C-shaped radiator. In: 2019 International Conference on Microwave and Millimeter Wave Technology (ICMMT), pp. 1–3. Guangzhou, China (2019) 19. Aljonubi, K., AlAmoudi, A.O., Langley, R.J., Reaney, I.: Reconfigurable antenna using smart material. In: 2013 7th European Conference on Antennas and Propagation (EuCAP), pp. 917– 918. Gothenburg, Sweden (2013) 20. Wang, S., Zhu, L., Wu, W.: A novel frequency-reconfigurable patch antenna using low-loss transformer oil. IEEE Trans. Antennas Propag. 65(12), 7316–7321 (2017) 21. Hu, Z., Wang, S., Shen, Z., Wu, W.: Broadband polarization-reconfigurable water spiral antenna of low profile. IEEE Antennas Wirel. Propag. Lett. 16, 1377–1380 (2017) 22. Zhang, G.B., Gough, R.C., Moorefield, M.R., Cho, K.J., Ohta, A.T., Shiroma, W.A.: A liquidmetal polarization-pattern-reconfigurable dipole antenna. IEEE Antennas Wirel. Propag. Lett. 17(1), 50–53 (2018) 23. Naser-Moghadasi, M., Sadeghzadeh, R.A., Fakheri, M., Aribi, T., Virdee, B.S.: Miniature hook-shaped multiband antenna for mobile applications. IEEE Antennas Wirel. Propag. Lett. 11, 1096–1099 (2012) 24. Li, Y., Zhang, Z., Feng, Z., Iskander, M.F.: Design of penta-band omnidirectional slot antenna with slender columnar structure. IEEE Trans. Antennas Propag. 62(2), 594–601 (2014) 25. Cleetus, R.M.C., Bala, G.J.: Frequency reconfigurable antennas: a review. In: 2017 International Conference on Signal Processing and Communication (ICSPC), pp. 160–164. Coimbatore, India (2017) 26. Jenath, M., Nagarajan, V.: Review on frequency reconfigurable antenna for wireless applications. In: 2017 International Conference on Communication and Signal Processing (ICCSP), pp. 2240–2245. Chennai, India (2017) 27. Nguyen-Trong, N., Piotrowski, A., Fumeaux, C.: A frequency-reconfigurable dual-band lowprofile monopolar antenna. IEEE Trans. Antennas Propag. 65(7), 3336–3343 (2017) 28. Majid, H.A., Rahim, M.K.A., Hamid, M.R., Ismail, M.F.: A compact frequency-reconfigurable narrowband microstrip slot antenna. IEEE Antennas Wirel. Propag. Lett. 11, 616–619 (2012) 29. Rahim, M.K.A., Hamid, M.R., Samsuri, N.A., Murad, N.A., Yusoff, M.F.M., Majid, H.A.: Frequency reconfigurable antenna for future wireless communication system. In: 2016 46th European Microwave Conference (EuMC), pp. 965–970. London (2016)

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30. Ghanem, F., Hall, P.S., Kelly, J.R.: Two port frequency reconfigurable antenna for cognitive radios. Electron. Lett. 45, 534–535 (2009) 31. Yang, S., Zhang, C., Pan, H.K., Fathy, A.E., Nair, V.K.: Frequency-reconfigurable antennas for multi-radio wireless platforms. IEEE Microw. Magaz. 10(1), 66–83 (2009) 32. Ghanem, F., Bitchikh, M.: An UWB to seven sub-bands frequency reconfigurable antipodal vivaldi antenna. In: 2013 IEEE Antennas and Propagation Society International Symposium (APSURSI), pp. 672-673. Orlando, FL (2013) 33. Yadav, D., Abegaonkar, M.P., Koul, S.K., Tiwari, V., Bhatnagar, D.: Frequency reconfigurable monopole antenna with switchable band characteristics from UWB to band-notched UWB to dual-band radiator. In: 2016 Asia-Pacific Microwave Conference (APMC), pp. 1–4. New Delhi (2016) 34. Bitchikh, M., Ghanem, F.: UWB to 30 narrow sub-bands frequency reconfigurable antipodal Vivaldi antenna. Electron. Lett. 52(19), 1580–1582 (2016) 35. Saghati, P., Azarmanesh, M., Zaker, R.: A novel switchable single- and multifrequency tripleslot antenna for 2.4-GHz Bluetooth, 3.5-GHz WiMax, and 5.8-GHz WLAN. IEEE Antennas Wirel. Propag. Lett. 9, 534–537 (2010) 36. Singh, R.K., Basu, A., Koul, S.K.: Asymmetric coupled polarization switchable oscillating active integrated antenna. In: 2016 Asia-Pacific Microwave Conference (APMC), pp. 1–4. New Delhi (2016) 37. Wong, H., Lin, W., Wang, X., Lu, M.: LP and CP polarization reconfigurable antennas for modern wireless applications. In: 2017 International Symposium on Antennas and Propagation (ISAP), pp. 1–2. Phuket (2017) 38. Chen, S.L., Wei, F., Qin, P.Y., Guo, Y.J., Chen, X.: A multi-linear polarization reconfigurable unidirectional patch antenna. IEEE Trans. Antennas Propag. 65(8), 4299–4304 (2017) 39. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable microstrip patch antenna with switchable polarization. IETE J. Res. 66, 590–599 (2018) 40. Dong, J., Li, Y., Zhang, B.: A survey on radiation pattern reconfigurable antennas. In: 2011 7th International Conference on Wireless Communications, Networking and Mobile Computing, pp. 1–4. Wuhan (2011) 41. Yong, S., Bernhard, J.T.: Reconfigurable null scanning antenna with three dimensional null steer. IEEE Trans. Antennas Propag. 61(3), 1063–1070 (2013) 42. Deng, C., Li, Y., Zhang, Z., Feng, Z.: A hemispherical 3-D null steering antenna for circular polarization. IEEE Antennas Wirel. Propag. Lett. 14, 803–806 (2015) 43. Sabapathy, T., Jusoh, M., Soh, P.J., Ahmad, R.B., Kamarudin, M.R.: Radiation pattern reconfigurable antenna: the design challenges at GHz frequencies. In: 2016 IEEE Asia-Pacific Conference on Applied Electromagnetics (APACE), pp. 301–304. Langkawi (2016) 44. Dicandia, F.A., Genovesi, S., Monorchio, A.: Null-steering antenna design using phase-shifted characteristic modes. IEEE Trans. Antennas Propag. 64(7), 2698–2706 (2016) 45. Singh, R.K., Basu, A., Koul, S.K.: Efficient null broadening and steering using slot antenna array for radar applications. In: 2016 Asia-Pacific Microwave Conference (APMC), pp. 1–4. New Delhi (2016) 46. Singh, R.K., Basu, A., Koul, S.K.: Two-port reconfigurable passive radiator with switchable pattern for active antenna application. In: 2017 IEEE MTT-S International Microwave and RF Conference (IMaRC), pp. 1–5. Ahmedabad, India (2017) 47. Babakhani, B., Sharma, S.K.: Dual null steering and limited beam peak steering using triplemode circular microstrip patch antenna. IEEE Trans. Antennas Propag. 65(8), 3838–3848 (2017) 48. Singh, R.K., Basu, A., Koul, S.K.: A novel pattern-reconfigurable oscillating active integrated antenna. IEEE Antennas Wirel. Propag. Lett. 16, 3220–3223 (2017) 49. Bernhard, J.T.: Reconfigurable multifunction antennas: Next steps for the future, pp. 16– 17. International Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications Symp, Aug (2007) 50. Liang, B., Sanz-Izquierdo, B., Parker, E.A., Batchelor, J.C.: A frequency and polarization reconfigurable circularly polarized antenna using active EBG structure for satellite navigation. IEEE Trans. Antennas Propag. 63(1), 33–40 (2015)

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51. Cao, W., Zhang, B., Liu, A., Yu, T., Guo, D., Pan, K.: A reconfigurable microstrip antenna with radiation pattern selectivity and polarization diversity. IEEE Antennas Wirel. Propag. Lett. 11, 453–456 (2012) 52. Row, J.S., Tsai, C.W.: Pattern reconfigurable antenna array with circular polarization. IEEE Trans. Antennas Propag. 64(4), 1525–1530 (2016) 53. Rodrigo, D., Jofre, L.: Frequency and radiation pattern reconfigurability of a multi-size pixel antenna. IEEE Trans. Antennas Propag. 60(5), 2219–2225 (2012) 54. Rodrigo, D., Cetiner, B.A., Jofre, L.: Frequency, radiation pattern and polarization reconfigurable antenna using a parasitic pixel layer. IEEE Trans. Antennas Propag. 62(6), 3422–3427 (2014)

Chapter 3

Active Integrated Antennas and Their Classification

3.1 Introduction This chapter discusses active integrated antennas (AIAs) and their classification. A typical active antenna consists of one active device such as two-terminal device or three-terminal device integrated with a passive planar radiating element such as microstrip patch of various shapes [1–4], printed dipole [5], monopole [6] or slot [7, 8]. Integration of an active device with radiating passive element has numerous advantages, e.g., an active antenna eliminates the feed network (which is lossy at mmW frequencies) used in combining power from more than one active unit, it effectively decreases the overall size of the antenna system, and it also provides the active impedance matching. There are various existing configurations of AIA to fulfil the requirements for multiple communication and sensor applications. The benefits and limitations of different configurations are discussed here. The design steps of negative resistance and feedback loop oscillating active integrated antennas are also discussed in this chapter.

3.2 Classification of Active Integrated Antennas (AIAs) The active integrated antennas can be classified by their applications [9]. Transmitting and receiving type active antennas are the two basic categories of active integrated antennas. Transceivers, repeaters, transponders, etc. are the other types of active integrated antennas with functions of both transmission and reception of the signal. An active device may be integrated with a passive radiator at its input or output port to realize a transmitter or receiver, respectively. Repeater could be realized by integrating passive antenna elements at both ports of the amplifier. All these combinations have a common feature: the integration of an amplifier (designed by using an active device) and the passive antenna (radiator). Active integrated antennas © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1_3

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(a)

(b)

Fig. 3.1 Amplifier type active integrated antennas, a transmitting antenna and b receiving antenna

can be classified based on the different functions of the active devices. In general, the active device or circuit is one that can be used for amplification, rectification, or changing energy from one form to another. Based on these aforesaid functions, amplifiers, mixers, multipliers, and oscillators are the basic types of active circuits. The basic functions of these circuits are to generate the RF signal, amplify the signal, or convert the signal of one frequency to other frequencies. Therefore, the active integrated antennas can be classified into three groups, namely, oscillator type [10–12], amplifier type [13–15], and frequency conversion type [16–20]. These three types of active integrated antennas may be combined further to have complex functions in a single module, e.g., the transceiver module [21–23]. These three types of AIAs are explained in the next section.

3.2.1 Amplifier Type The amplifier type AIA integrates a two-port active device and passive radiator at its input or output port. When a passive radiator is attached at the output port, it acts as a transmitter while a passive radiator is attached at the input port, it works as a receiver. If the antenna is integrated at both input and output ports, it becomes a quasi-optical amplifier. Amplifier-type active integrated antennas are illustrated in Fig. 3.1.

3.2.2 Oscillator Type Oscillator-type active integrated antennas are also called quasi-optical oscillators as the produced RF power radiates into free space. Figure 3.2a shows a general integrated antenna oscillator circuit [24]. Two- and three-terminal devices are used to develop an active antenna oscillator. Two-terminal devices such as Gunn and IMPATT diodes are well suited for high power applications at millimeter-wave frequencies, but active circuits with such devices have the disadvantage of low DC-to-RF efficiency. On the contrary, three-terminal devices such as BJT and FET have high DC-to-RF efficiency, but the performance degrades at the lower cut-off frequencies while HEMT and HBT show the advantages of high DC-to-RF efficiency, low noise factor, and high gain at millimeter-wave frequencies. In terms of integration with planar circuits,

3.2 Classification of Active Integrated Antennas (AIAs)

(a)

31

(b)

Fig. 3.2 Feedback loop oscillator type active integrated antenna (AIA), a general block diagram and b with two-port patch radiator as a feedback element

three-terminal devices are preferred due to their advantage of easy integration either in a hybrid or monolithic approach. Radiating elements such as patches and slots are usually used in oscillator-type active integrated antennas. Figure 3.2b shows a feedback loop oscillator-type active integrated antenna (AIA), a patch radiator integrated into the feedback loop of the oscillator circuit. Here, FET is used as an active device, and the patch element acts as a radiator and feedback element as well. The ways in which the oscillating AIA can be realized are injection locking [25, 26], cavity backed [27, 28], phase-locked loop [29], and feedback loop approach [30, 31]. The feedback loop approach provides a compact design with good phase noise performance and hence is popular [32].

3.2.3 Frequency Conversion Type A quasi-optical mixer is an example of a frequency conversion type active integrated antenna. In a quasi-optical mixer, the receiving antenna and mixer are integrated together, and it functions as the front end of an RF receiver. In a self-oscillating mixer, the non-linear property of the oscillating device is utilized to perform the frequency conversion [33]. The function is not limited to the above-mentioned three basic types of active integrated antenna. Some of the oscillator-type active integrated antennas can be modified slightly to be used as transceiver circuits. The reconfigurable active antenna can be a good candidate at mmW in quasi-optical power combining [34, 35], wireless charging [36], broadcasting, secure communications, etc. [37].

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3 Active Integrated Antennas and Their Classification

Oscillator-type active integrated antennas have received great attention recently because of the huge demand for compact and high-power sources at mmW frequencies. A compact passive radiating element integrated with the active device for power generation finds applications in communication and radar systems due to its small size, fabrication simplicity, light weight, and low cost. Free space power combining without using the feed network, and beam scanning without phase shifters are the advantages that could be achieved by integrating two or more oscillating active antennas in realizing arrays. When the output power from multiple radiating structures is combined in free space, the losses are avoided. All elements of an array must be mutually injection-locked to achieve combined power. Injection locking can be achieved through mutual coupling between the array elements.

3.3 Oscillator-Type Active Integrated Antennas There are two basic types of oscillator-type active integrated antennas. These are (a) negative resistance oscillator-type active integrated antennas and (b) feedback loop oscillator-type active integrated antennas. In the traditional approach, the passive antenna and active circuit are two separate elements interconnected by a transmission line. In this approach, there is freedom to optimize the performance of a passive radiator and active circuit independently because there is an obvious distinction between the active circuit and the radiating element. On the other hand, in the AIA approach, there is no obvious distinction between the active circuit and radiating element. Here, the passive element acts as a radiator and a load for the active device. The active integrated oscillator is advantageous compared to the conventional approach. It is compact in size, low-cost and has lower loss compared to the conventional approach.

3.3.1 Negative Resistance Oscillator-Type Active Integrated Antennas The general integrated antenna oscillator circuit and its equivalent circuit are shown in Fig. 3.3. Here, Zd is the input impedance of an active device looking into the transistor while Za is the input impedance of an antenna (passive radiator). Z d = Rd + j X d

(3.1)

Rd is the resistance and Xd is the reactance. Zd , Rd and Xd are the functions of frequency, DC bias current, temperature, and RF current, i.e., [Zd (f, Io , T, IRF )]

3.3 Oscillator-Type Active Integrated Antennas

(a)

33

(b)

Fig. 3.3 Negative resistance oscillator-type active integrated antenna (AIA), a general block diagram and b equivalent circuit

Z a = Ra + j X a

(3.2)

Load impedance is a function of frequency, i.e., [Za (f)]. The oscillation occurs when the following two conditions are satisfied. X a ( f 0 ) + X d ( f 0 , I0 , T , I R F ) = 0

(3.3)

Ra ( f 0 ) + Rd ( f 0 , I 0 , T , I R F ) = 0

(3.4)

In terms of reflection coefficients, the oscillation condition can be expressed as Γd Γa = 1

(3.5)

where fo is the oscillation frequency. The first condition requires the circuit at resonance (fo ) determined by the circuit resonant frequency given by (3.3) by considering the imaginary part of the active device and passive load. The second condition requires the negative resistance of the active device to be greater than or equal to the load resistance. The negative resistance of the device slowly decreases with the increasing amplitude of the oscillating signal such that it satisfies conditions (3.3) and (3.4) simultaneously at the desired frequency. Therefore, we need to design a terminating network and choose a suitable series feedback inductor or capacitor such that Zd becomes negative and satisfies the above conditions. If Ra ( f 0 ) ≤ |Rd ( f 0 , I O , T, I R F )|

(3.6)

then the circuit is unstable and the amplitude of the oscillating signal grows until the condition (3.4) is satisfied. The location of the active device in a passive radiator needs to be selected correctly to satisfy the above conditions.

34

3 Active Integrated Antennas and Their Classification

3.3.2 Feedback Loop Oscillator-Type Active Integrated Antennas In the classical feedback approach, the output port of the amplifier is fed to one port of the feedback network and the other port of the feedback network is fed back to the input of the amplifier in-phase. The general block diagram and its equivalent circuit are shown in Fig. 3.4. The loading effect of the feedback network on the amplifier and the loading effect of the amplifier on the feedback network are neglected. Closed-loop transfer function can be written as A( j ω) Vout ( jω) = Vin ( j ω) 1 − A( j ω)F( j ω)

(3.7)

Loop gain of the system is T( j ω) = A( j ω)F( j ω). From (3.7), if 1 − A( j ω)F( jω) = 0, then we get nonzero output even with Vin = 0. Therefore, the system oscillates. The oscillation occurs in a feedback loop oscillator-type active integrated antenna if the following conditions are satisfied. A( jω)F( j ω) = 1

(3.8)

where A(jω) is the amplifier gain and F(jω) is the frequency dependence of the feedback loop. 1. Loop gain must be unity i.e., A( j ω)F( j ω) = 1 2. The total phase shift around the loop must be zero or an integer multiple of 2π, i.e., ∠A( jω)F( j ω) = 2π n; {n = 0, 1, 2, . . .) The above two conditions in a combined manner are called Barkhausen’s criterion.

(a)

(b)

Fig. 3.4 Feedback loop oscillator-type active integrated antenna (AIA), a general block diagram and b equivalent circuit

3.4 Design Procedure of Negative Resistance Oscillator-Type Active Integrated Antennas

• For oscillation to startup : |A( j ω)F( jω)| > 1 and arg[A( j ω)F( j ω)] = 0 • For sustained oscillations : 1 − A( j ω)F( jω) = 0

35

(3.9) (3.10)

Oscillators are non-linear circuits; therefore, the condition (3.9) will exist initially upon power-up. The amplifier begins to saturate with the increasing current and voltage magnitude resulting in gain reduction until A( j ω)F( j ω) is less than unity. Therefore, a steady-state condition is reached when A( j ω)F( j ω) = 1. Barkhausen’s criteria (3.10) must be satisfied at one single frequency to avoid multiple simultaneous oscillations. Usually, the frequency selection is done by feedback network F( j ω). Barkhausen’s criterion is a necessary condition for oscillation but not a sufficient condition. Circuit satisfying the criterion doesn’t guarantee that it will oscillate. Some limitations of the feedback loop approach are: • Amplifier’s input impedance, i.e., Zd which is a function of frequency and current amplitude and decreases with an increase in frequency and current amplitude. Therefore, at high frequencies, the feedback network loads the amplifier and the amplifier loads the feedback network and it makes the earlier assumption invalid at high frequencies. The loop gain is not simply A( j ω)F( j ω) at higher frequencies and hence (3.9) does not hold good. • At high frequencies, various feedback paths exist due to the significant amplifier’s parasitic inductance and capacitance thus the calculation of loop gain is difficult. Feedback loop oscillators are difficult to realize at high frequencies.

3.4 Design Procedure of Negative Resistance Oscillator-Type Active Integrated Antennas An oscillator is a non-linear circuit that converts DC power into RF power. In this design, a three-terminal device is used which provides two-port oscillators and is operated in an unstable region. Modern RF oscillators are mostly based on a transistor which is characterized as a two-port active device. The one-port negative resistance design concept can be extended to transistor oscillator design by applying the oscillation conditions at each port. The one-port oscillation conditions as given in (3.3) and (3.4) are really a special case of a more general oscillation condition for networks with an arbitrary number of ports. A block diagram of a two-port negative resistance oscillator is shown in Fig. 3.5. The design steps for a microwave oscillator are like that of the amplifier. The difference between the two designs is that the amplifier needs an RF signal as an input, but an oscillator does not need any RF input signal. To design an oscillator circuit, first, we choose the transistor, whose S-parameters satisfy the condition for oscillation. Since power is generated in an oscillator, the reflection coefficients are greater than unity. The resonator input network in the design gives the oscillation frequency, whereas the terminating network gives the proper loading function.

36

3 Active Integrated Antennas and Their Classification

Fig. 3.5 Block diagram of a two-port oscillator

Transistor selection The transistor must be chosen in such a way that its S-parameters should satisfy the oscillation conditions. There are three conditions required to be satisfied at “steadystate” for oscillations to occur. These conditions are as follows: Condition 1: It should be an unstable device (K < 1). It indicates that the negative resistance device itself is in the oscillation mode. Condition 2: Oscillating input port (Γ I N Γ R = 1). Condition 3: Oscillating output port (Γ OU T ΓT = 1). Here, ZR ΓR ZT ΓT ZIN Γ IN ZOUT Γ OUT [S]

Impedance of the resonating input network Reflection coefficient of the resonating input network Impedance of the terminating output network Reflection coefficient of the terminating output network Input impedance of the Transistor Input reflection coefficient of the transistor Output impedance of the Transistor Output reflection coefficient of the transistor Scattering-matrix of the transistor

Select the transistor that is potentially unstable at the desired frequency of the oscillation. Further, the transistor is terminated using an appropriate load value in the unstable region, such that it gives the largest possible negative resistance at the input of the transistor. Finally, the resonator input network can be selected so that it should satisfy the oscillation start-up condition. Since the resonator input network and terminating network are passive, |Γ R | < 1 and |Γ T | < 1 Thus, to satisfy condition 2 and condition 3, we need to have, |Γ in | > 1 and |Γ out | > 1. Check the stability condition of the given transistor (find the value of K). If the transistor is potentially unstable, plot the output stability circle using a smith chart and design the resonator and load network of the transistor.

3.5 Design Procedure of Feedback Loop Oscillator-Type …

37

3.5 Design Procedure of Feedback Loop Oscillator-Type Active Integrated Antennas Here, the design of a feedback loop oscillator-type active integrated antenna is discussed. The feedback loop approach consists of an amplifier and a frequency selective network (passive radiating element), the output of the frequency selective network is applied to the amplifier input with the same phase of the input signal.

3.5.1 Two-Port Radiator Design Here, a microstrip patch is used as a radiating element (feedback element) for the AIA circuit. The antenna has two ports to be connected to two terminals of a transistor. The two-port radiator is electromagnetically coupled on both sides to isolate the gate and drain bias. Normally, this electromagnetically coupled microstrip patch radiator is a narrowband antenna. In the narrowband, the half signal will come out to the second port and half will be radiated out from the patch (if it is designed for a 50–50% ratio), and outside the narrowband, the complete signal will be reflected. The geometry of the proposed two-port radiator is shown in Fig. 3.6a. The two-port radiator is electromagnetically coupled through a T-shaped microstrip feed. Here, the feedback element is a linearly polarized antenna. An antenna is designed and simulated with full-wave electromagnetic software (CST microwave studio). The proposed two-port radiator is fabricated on a 30-mil thick N9000 Neltec substrate. The relative permittivity of the substrate is 2.2 and the loss tangent is 0.002. The photograph of the fabricated antenna is shown in Fig. 3.6b. Measured and simulated reflection coefficients are plotted in Fig. 3.7. As observed, the designed antenna resonates at 5 GHz.

(a) Fig. 3.6 Two-port passive radiator, a geometry and b photograph

(b)

38

3 Active Integrated Antennas and Their Classification

Fig. 3.7 Simulated and measured reflection coefficient plots of a two-port passive radiator

3.5.2 Amplifier Design An n-channel FET (NE3210S01) is used to design the amplifier circuit. The device is operated in depletion mode. The operating point of the device is VDS = 2 V and ID = 20 mA. The device is calibrated and measured separately. The measured gain is plotted in Fig. 3.8. The S21 parameter represents the gain of the active device. The measured gain of the device is 11.85 dB at 5 GHz.

(a)

(b)

Fig. 3.8 An n-channel FET NE3210S01device, a biasing circuit and b S-parameters

3.5 Design Procedure of Feedback Loop Oscillator-Type …

39

Fig. 3.9 Schematic of the oscillator-type AIA

3.5.3 Active Integrated Antenna Design Oscillating AIA is designed by integrating a two-port radiator with the amplifier circuit in a feedback loop as shown in Fig. 3.9. The extra 50-Ω lines are connected on both sides of the radiator to adjust the overall loop phase. Two-port measured S-parameter data of the feedback element is imported as a data file in the Agilent ADS software and standard S-parameter analysis is then performed.

3.5.4 Oscillation Test The oscillation test predicts the frequency of oscillations. Oscillations begin when the magnitude of the loop gain becomes slightly greater than 1 and the closed-loop phase becomes zero. To check the oscillations, an oscillation test probe is connected between the amplifier and the S-parameters data of a feedback element as a data item. The circuit diagram of a simulation scheme in ADS is shown in Fig. 3.10. Polar plots are illustrated in Fig. 3.11a. The loop gain is 1.03 and the loop phase is 0° at 5 GHz. Fig. 3.10 Simulation scheme in ADS

40

3 Active Integrated Antennas and Their Classification

(a)

(b)

Fig. 3.11 Simulated results of AIA, a loop gain and b oscillation power

3.5.5 Harmonic Balance Test The harmonic balance test is performed to get the oscillating power of the AIA and to have an idea of the output power at the harmonics. Harmonic balance analysis is performed by replacing a test probe with the oscillator port. Output oscillation power at fundamental frequency and harmonics is plotted in Fig. 3.11b. The output power at the second harmonic is 19.2 dB less than that at the fundamental frequency. The designed prototype has stable oscillation at a frequency that is very close to the design frequency. A maximum of 0.99% deviation is observed between the design and measured frequency.

3.5.6 Active Integrated Antenna Design The final layout of an oscillator-type active integrated antenna is shown in Fig. 3.12. An amplifier circuit is integrated with the feedback element to realize an AIA circuit. Band stop filters are introduced in the final layout. There may be a chance of oscillations at the lower frequencies because of the high gain of the active device at low frequencies; band stop filters (BSFs) are connected in shunt to the circuit to remove other resonance modes or unwanted signals. From Fig. 3.7, there is an extra resonance around 2.8 GHz. There may be a chance of oscillation at 2.8 GHz. To prevent this oscillation or other spurious bands, band stop filters (BSF) can be used to filter out these unwanted resonances from the circuit. Schematic and simulated S-parameters of a BSF are shown in Fig. 3.13. A 50 Ω resistor is used at the end of the band stop filter to dissipate the power at 2.8 GHz and other spurious frequencies. The 50 Ω resistor doesn’t play any role in

3.5 Design Procedure of Feedback Loop Oscillator-Type …

(a)

41

(b)

Fig. 3.12 a Final layout of active integrated oscillator, b photograph

Port 1

W = 2.4 mm L = 5 mm

W = 2.4 mm L = 5 mm

Z = 50Ω

Z = 50 Ω

Port 2

Z = 50 Ω

W = 2.4 mm L = 5 mm

Z = 50 Ω

W = 2.4 mm L = 3 mm

ZOC =177.7Ω W = 0.13 mm L = 11.6 mm

50Ω 0.8 pF

(a)

(b)

Fig. 3.13 Band Stop Filter, a schematic b simulated S-parameters, Reproduced with permission from IEEE [37]

the phase noise because the BSF isolates the resistors from the circuit at the design frequency. The final layout of the AIA is fabricated, and its photograph is shown in Fig. 3.12b.

42

3 Active Integrated Antennas and Their Classification

3.5.7 Measurements The radiation pattern of the fabricated AIA is measured in an anechoic chamber. AIA used as a transmitter is mounted on a turntable that rotates horizontally, and a standard wideband horn is used as a receiver at a distance to satisfy the far-field condition as shown in Fig. 3.14. Power is received by means of a spectrum analyser (SA). The measured output is recorded at the spectrum analyser as shown in Fig. 3.15. An active antenna does not require any RF source as it generates RF signal on its own and radiates as well through a passive radiator. The measured result shows that the active antenna oscillates at 5.04 GHz whereas it was designed at 5 GHz. A minute shift is observed between the designed and measured oscillation frequency. It is observed when the bias voltage of the oscillator circuit changes, the oscillation frequency as well as its amplitude changes. The measured radiation pattern of the AIA is plotted in Fig. 3.16 and compared with the results of a separately designed two-port feedback network. Measurement of the two-port feedback network is performed by connecting 50 Ω termination at one of its ports. The effective isotropic radiated power (EIRP) is calculated by using the Friis formula, ( ) Pr 4πr 2 E I R P = Pt G t = G r l c λo

(3.11)

In (3.11), Pr is the received power, Gr is the gain of the horn antenna, r is the distance between the transmitter and receiver (r = 200 cm), λo is the free space wavelength at measured oscillation frequency, and lc is the transmission loss of the cable. The calculated received power is −34.02 dBm. The calculated value of EIRP is 12.956 dBm. Complex voltages at the source and drain terminals are noted and inserted into CST as the excitations at the feed ports, this is the well-known technique to calculate the gain of the transmitting antenna in AIA circuits. The radiated power

Fig. 3.14 Experimental setup for measuring radiation pattern of the AIA

3.6 Summary

43

Fig. 3.15 Measured output power at the spectrum analyser

Fig. 3.16 Measured radiation pattern of the AIA and compared to that of two-port passive feedback radiator. Reproduced with permission from IEEE [37]

(Pt ) is calculated as 11.456 dBm. The DC power consumption of the circuit is 40 mW (2 V × 20 mA). The DC-to-RF conversion efficiency is calculated as 34.95%. The phase noise is measured by setting a resolution bandwidth (RBW) of 100 kHz at the spectrum analyser. The measured phase noise at 1 MHz offset from the carrier is − 104.1 dBc/Hz as shown in Fig. 3.17.

3.6 Summary In this chapter, the classification of the active integrated antenna is discussed. Design steps of the two most used oscillator circuits are discussed in detail. The negative resistance method can start-up an oscillation easily without dealing with the complex

44

3 Active Integrated Antennas and Their Classification

Fig. 3.17 Measured phase noise of the AIA circuit

parasitic inside the blocks but concerning the loaded Q and power, the negative resistance method is inadequate compared to the feedback loop method. The design steps of both methods are discussed in detail.

References 1. Ip, K.H.Y., Kan, T.M.Y., Eleftheriades, G.V.: A single-layer CPW-fed active patch antenna. IEEE Microw. Guided Wave Lett. 10(2), 64–66 (2000) 2. Mueller, C.H., et al.: Small-size X-band active integrated antenna with feedback loop. IEEE Trans. Antennas Propag. 56(5), 1236–1241 (2008) 3. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable oscillating active integrated antenna using two-element patch array for beam switching applications. Eng. Rep. 1–10 (2019). Doi: https:// doi.org/10.1002/eng2.12071 4. Singh, R.K., Basu, A., Koul, S.K.: Two-port reconfigurable passive radiator with switchable pattern for active antenna application. IEEE MTT-S Int. Microw. RF Conf. (IMaRC) 2017, 1–5 (2017) 5. Bubnov, I.N., Falcovich, I.S., Gridin, A.A., Stanislavsky, A.A., Reznik, A.P.: Diamond dipole active antenna. Int. Conf. Antenna Theory Tech. (ICATT) 2015, 1–3 (2015) 6. Ragheb, H.A., Yamani, A.: FET resonant active monopole antenna. In: Symposium on Antenna Technology and Applied Electromagnetics [ANTEM 1994] (1994) 7. Choi, D.-H., Park, S.-O.: Active integrated antenna using T-shaped microstrip-line-fed slot antenna. IEEE Antennas Propag. Soc. Int. Symp. 2005, 213–216 (2005) 8. Choi, D.-H., Park, S.-O.: A varactor-tuned active-integrated antenna using slot antenna. IEEE Antennas Wirel. Propag. Lett. 4, 191–193 (2005) 9. Lin, J., Itoh, T.: Active integrated antennas. IEEE Trans. Microw. Theory Tech. 42(12), 2186– 2194 (1994) 10. Camilleri, N., Bayraktaroglu, B.: Monolithic millimeter-wave IMPATT oscillator and active antenna. IEEE Trans. Microw. Theory Tech. MTT-36, 1670–1676 (1988) 11. Birkeland, J., Itoh, T.: Two-port FET oscillators with applications to active arrays. IEEE Microw. Guided Wave Lett. 1, 112–1 13 (1991) 12. Chou, G.J., Tzuang, C.C.: Oscillator-type active-integrated antenna: the leaky-mode approach. IEEE Trans. Microw. Theory Tech. 44(12), 2265–2272 (1996)

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13. An, H., Nauwelaers, B.K.J.C., Van de Capelle, A.R.: Broadband active microstrip antenna design with the simplified real frequency technique. IEEE Trans. Antennas Propag 42(12), 1612–1619 (1994) 14. Chung, Y., et al.: AlGaN/GaN HFET power amplifier integrated with microstrip antenna for RF front-end applications. IEEE Trans. Microw. Theory Tech. 51(2), 653–659 (2003) 15. Kumari, R., Basu, A., Koul, S.K.: Development of GaN HEMT based high power active integrated antenna. IEEE MTT-S Int. Microw. RF Conf. (IMaRC) 2018, 1–4 (2018) 16. Stephen, K.D., Camilleri, N., Itoh, T.: A quasi-optical polarization duplexed balanced mixer for millimeter-wave applications. IEEE Trans. Microw. Theory Tech. MTT-31, 164–170 (1983) 17. Stephen, K.D., Itoh, T.: A planar quasi-optical sub-harmonically pumped mixer characterized by isotropic conversion loss. IEEE Trans. Microw. Theory Tech. 32, 97–102 (1984) 18. Hwang, V.D., Itoh, T.: Quasi-optical HEMT and MESFET self-oscillating mixers. IEEE Trans. Microw. Theon1 Tech. MTT-36, 1701–1705 (1988) 19. Zmuidzinas, J., LeDuc, H.G.: Quasi-optical slot antenna SIS mixers. IEEE Trans. Microw. Theory Tech. 40, 1797–1804 (1992) 20. Zhang, J., Wang, Y., Chen, Z.: Integration of a self-oscillating mixer and an active antenna. IEEE Microw. Guided Wave Lett. 9(3), 117–119 (1999) 21. Birkeland, J., Itoh, T.: A microstrip based active antenna doppler transceiver module. In: 1989 19th European Microwave Conference, pp. 172–175 (1989) 22. Birkeland, J., Itoh, T.: FET-based planar circuits for quasi-optical sources and transceivers. IEEE Trans. Microw. Theory Tech. 37(9), 1452–1459 (1989) 23. Flynt, R., Fan, L., Navarro, J., Chang, K.: Low cost and compact active integrated antenna transceiver for system applications. In: IEEE NTC, Conference Proceedings Microwave Systems Conference, pp. 89–92 (1995) 24. Chang, K., York, R.A., Hall, P.S., Itoh, T.: Active integrated antennas. IEEE Trans. Microw. Theory Tech. 50(3), 937–944 (2002) 25. Hayata, K., Kawasaki, S.: Beam steering due to injection locking operation of active integrated antenna with parallel feedback loop. In: Proceedings IEEE 28th European Microwave Conference, pp. 172–177. Amsterdam, The Netherlands (1998) 26. Upadhayay, M.D., Basu, A., Abegaonkar, M.P., Koul, S.K.: Active integrated antenna using BJT with floating base. IEEE Microw. Wirel. Compon. Lett. 23(4), 202–204 (2013) 27. Adhikary, M., Sahoo, S.K., Sarkar, A., Sharma, A., Biswas, A., Jaleel Akhtar, M.: Active integrated empty SIW cavity backed slot antenna for increased EIRP. In: 2018 IEEE Indian Conference on Antennas and Propogation (InCAP), pp. 1–3 (2018) 28. Zheng, M., Hall, P.S., Chen, Q., Fusco, V.F.: Cavity-backed active slot loop antenna. In: IEEE Antennas and Propagation Society International Symposium. 1998 Digest. Antennas: Gateways to the Global Network. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.98CH36), vol. 3, pp. 1620–1623 (1998) 29. Andrews, J.W., Hall, P.S.: Phase-locked-loop control of active microstrip patch antennas. IEEE Trans. Microw. Theory Tech. 50(1), 201–206 (2002) 30. Singh, R.K., Basu, A., Koul, S.K.: Asymmetric coupled polarization switchable oscillating active integrated antenna. In: Asia-Pacific Microwave Conference (APMC), pp. 1–4. New Delhi (2016) 31. Choi, D.H., Park, S.O.: Active integrated antenna using a T-shaped microstrip coupled patch antenna. Microw. Opt. Technol. Lett. 44(5), 434–436 (2005) 32. Chang, K., Hummer, K.A., Gopalakrishnan, G.K.: Active radiating element using FET source integrated with microstrip patch antenna. Electron. Lett. 24(21), 1347–1348 (1988) 33. Cha, K., Kawasaki, S., Itoh, T.: Transponder using self-oscillating mixer and active antenna. In: IEEE MTT-S International Microwave Symposium, pp. 23–27. San Diego, CA (1994) 34. York, R.A., Compton, R.C.: Quasi-optical power combining using mutually synchronized oscillator arrays. IEEE Trans. Microw. Theory Techn. 39(6), 1000–1009 (1991)

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35. Mink, J.W.: Quasi-optical power combining of solid-state millimeter-wave sources. IEEE Trans. Microw. Theory Tech. 34(2), 273–279 (1986) 36. Wu, C., Chen, H.H., Ma, T.: On the wireless charging using active integrated antenna. In: 2015 IEEE 4th Asia-Pacific Conference on Antennas and Propagation (APCAP), pp. 419–420 (2015) 37. Singh, R.K., Basu, A., Koul, S.K.: A novel pattern-reconfigurable oscillating active integrated antenna. IEEE Antennas Wirel. Propag. Lett. 16, 3220–3223 (2017)

Chapter 4

Frequency Reconfigurable Passive and Active Planar Antennas

4.1 Introduction Frequency reconfigurable antennas are extensively used in modern wireless communication systems. Although the fixed multiband [1–3] and broadband antennas [4–6] can be used to cover various applications such as Wi-Fi, Bluetooth, WLAN, etc., these antennas lack the flexibility to accommodate new services compared to the antennas that have reconfigurable feature. Also, different wireless standards need different frequency bands. To fulfill the increasing demand and requirements, frequency reconfigurable antennas are needed [7–9]. Frequency reconfigurable antennas can be divided into different categories based on the frequency of operation i.e., narrowbandto-narrowband [10, 11], narrowband-to-wideband or notch band-to-wideband [12– 16], wideband-to-wideband [17], multiband-to-narrowband [18, 19] and multibandto-multiband [20, 21]. This chapter discusses various frequency reconfiguration techniques used to realize frequency reconfigurable passive antennas. Later in this chapter, frequency reconfiguration techniques used in developing reconfigurable active antennas are discussed. The focus of the chapter is on the development of oscillator-type frequency reconfigurable active antennas. Oscillator-type frequency reconfigurable active antennas have found many applications such as in wireless charging, power transmission systems, etc. Frequency reconfigurable active and passive antennas discussed in this chapter are planar in geometry.

4.2 Classification of Frequency Reconfigurable Antennas Frequency reconfigurable antennas can be classified into two main types: discrete frequency reconfigurable antennas and continuous frequency reconfigurable antennas.

© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1_4

47

48 Fig. 4.1 Discrete frequency reconfigurable antenna, a geometry b measured reflection coefficients when PIN diode is ON or OFF

4 Frequency Reconfigurable Passive and Active Planar Antennas

(a)

(b)

4.2.1 Discrete Frequency Reconfigurable Antennas Discrete frequency reconfigurable antennas are developed by mounting PIN diodes or RF MEMS switches while continuous frequency reconfigurable antennas are realized by incorporating varactor diodes. The discussion is given here keeping in mind the electronic reconfiguration only. Figure 4.1a shows the geometry of a discrete frequency reconfigurable antenna using a PIN diode. The operating frequency of the antenna can be switched by connecting or disconnecting the additional patch with the help of a switching diode. Reflection coefficients are plotted in Fig. 4.1b. When the PIN diode is OFF, the antenna operates at 5.2 GHz and when it is ON, the antenna resonates at 5.7 GHz.

4.2.2 Continuous Frequency Reconfigurable Antennas Continuous frequency reconfigurable antennas are realized by means of a varactor diode. A continuous frequency reconfigurable antenna is shown in Fig. 4.2a. A varactor diode is mounted in between the main and additional patch to tune the

4.3 Frequency Reconfigurable Passive Planar Antenna Using Different … Fig. 4.2 Continuous frequency reconfigurable antenna, a photograph b measured reflection coefficients for different bias voltages, ©IETE Journal of Research. Reproduced by permission of IETE [22]

49

(a)

(b)

frequencies. The measured reflection coefficients of the reported antenna are plotted in Fig. 4.2b [22]. By varying the bias across the varactor diode, the resonance frequency can be varied.

4.3 Frequency Reconfigurable Passive Planar Antenna Using Different Approaches The frequency reconfigurable antenna can control and improve the overall performance of the system by selecting different operating frequencies to minimize interference from other wireless systems and thereby increase the throughput. The resonance frequency of an antenna is decided by the effective length of the radiator. The radiator may be a dipole, monopole, loop, slot, microstrip antenna, etc. The effective length is determined by the path length of surface current flow so by controlling the effective path length, the frequency can be configured. There are several switching techniques by which frequency reconfigurability can be achieved in passive antenna systems. Few techniques such as the use of an additional patch or stub; the use of a reconfigurable matching network; the use of shorting posts or reactive loading of the radiating element; changing the current flow; and mechanically configuring

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using Metasurfaces are the available switching techniques by which one can realize frequency reconfigurable antenna. These switching techniques are explained in the following subsections.

4.3.1 Frequency Reconfiguration Using an Additional Patch or Stub Frequency reconfiguration can be achieved by connecting or disconnecting an additional patch or stub. By connecting this additional patch, the frequency can be increased or decreased from the reference frequency. This frequency shift depends on various parameters such as the length and width of the stub, the gap between the main patch and stub, and the position of the switch placed between them. Parametric analysis is done by varying these parameters and its effect is observed on the resonance frequency. The geometry of the antenna is shown in Fig. 4.3. First, the length of the stub is varied, while other parameters remain fixed. Initially, the gap (g) between the main and additional patch is fixed at 0.3 mm, while the width of the additional patch (Wadda ) is kept at 18.8 mm. The simulations are done for various values of length, out of which, reflection coefficients are shown here for only five different values. From Fig. 4.4, it is observed that the reflection coefficient, which is a function of frequency, does not show significant changes in its value and resonance peak with variation in the length. The frequency is slightly shifted because the effective length of surface currents on the additional patch is not changing significantly. The noticeable change in the frequency is observed by varying the width of the stub. Figure 4.5 shows the surface current distribution for various values of Wadda . At Wadda (width of the additional patch) = 3 mm, the surface current on the additional patch flows in the same direction as on the main patch (see Fig. 4.5a), the effective length of the surface current is increased, and the frequency reduced. At Wadda = 20 or 25 mm, the surface current on the additional patch flows along the width and Fig. 4.3 Discrete frequency reconfigurable antenna using an additional patch or stub; Dimensions: g = 0.3, Lg = 65, Lp = 18.65, Lt = 11.9, Ladda = 4.0, Wp = 18.80, Wf = 2.4, Wt = 0.58, Wadda = 18.80, Wg = 60, all units are in mm

4.3 Frequency Reconfigurable Passive Planar Antenna Using Different …

51

Fig. 4.4 Simulated reflection coefficients showing the effect of variation of the length of the additional patch

goes inside the main patch in the opposite direction as shown in Fig. 4.5e and f; this opposite directed surface current makes the effective electrical length of the surface current flowing in the main patch reduced and hence the antenna resonates at a higher frequency above the reference one. Figure 4.6 shows the simulated reflection coefficients as a function of different ‘Wadda ’. The gap between the main and the additional patch is varied next. The gap is varied from 0.25 mm to 13.5 mm, while other parameters remain fixed. From Fig. 4.7, when the gap (g) = 0.3 mm, the resonance frequency is greater than the reference frequency. At g = 8.5 mm, frequency becomes equal to the reference frequency, because the surface current on the additional patch does not have any impact on the overall effective length of the antenna. With a further increase in the gap to 13.5 mm, the frequency decreases and now it is below the reference frequency. Initially, surface current decreases with an increase in the gap width, further increment in the length, surface current changes its direction and adds in-phase with the reference current as on the main patch, as a result, effective surface current increases and hence the resonance frequency decreases. In all the above parametric variations, position of the switch was fixed, and it was at the center of the radiating edge of the microstrip patch. Now, at different positions of the switch, reflection coefficients are plotted as shown in Fig. 4.8. The y = 0 mm represents the center of the radiating edge. In this variation, a significant change is obtained in the resonance frequency. Parametric variation with the position of the switch is more useful to get dual-band or tri-band operation. The above study is useful in achieving lower or higher resonance from the reference frequency of the main radiator and getting dual- or tri-band behavior.

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(a) Wadda = 3 mm

(c) Wadda = 12 mm

(e) Wadda = 20 mm

(b) Wadda = 6 mm

(d) Wadda = 16 mm

(f) Wadda = 25 mm

Fig. 4.5 Surface current distributions for different values of Wadda Fig. 4.6 Simulated reflection coefficients showing the effect of varying the width of the additional patch

4.3 Frequency Reconfigurable Passive Planar Antenna Using Different …

53

Fig. 4.7 Simulated reflection coefficients for different gaps between the main and additional patch

Fig. 4.8 Simulated reflection coefficients for different positions of the switch

4.3.2 Frequency Reconfiguration Using Reconfigurable Matching Network With the help of a tunable matching network, a simple antenna can be reconfigured and operated in different frequency bands over a wide range of frequencies [23]. This reconfiguration technique is independent of the geometries and the dimensions of the antennas. A topology to achieve a wideband frequency reconfigurable antenna using a wide frequency tuning matching network is illustrated in Fig. 4.9a. In this technique, a wideband antenna is required, and then different frequency bands can be switched by means of a tunable matching network. A simple LC tunable matching network is shown in Fig. 4.9b. The tunable network can be realized using lumped components, varactor diodes, etc. By applying a different bias across the varactor diode, different capacitance values can be obtained. By varying the capacitance, different resonance frequencies can be obtained.

54 Fig. 4.9 Wideband frequency reconfigurable antenna with wide frequency tuning matching network, a topology b tunable matching network to obtain different resonances by selecting different capacitance values

4 Frequency Reconfigurable Passive and Active Planar Antennas

(a)

(b)

4.3.3 Frequency Reconfiguration Using Shorting Posts or Reactive Loading of the Radiating Element Fundamentally, a microstrip patch antenna is a resonating element. Therefore, reactive loading of the microstrip patch will change its resonant frequency. Normally capacitors and inductors are used to load the circuit [24–26]; resistors can be ignored because they are lossy components. The geometry of a frequency switchable antenna with two lumped capacitances loading the antenna is illustrated in Fig. 4.10a. Capacitances are placed at two opposite corners of the patch antenna. The antenna behavior was studied by varying both lumped capacitance values C1 and C2 . Reflection coefficients are plotted as a function of frequency in Fig. 4.10b. Varactor diodes can be used in place of capacitors to electronically tune the resonance frequency of the antenna. Reactive loading has been achieved electronically by using varactor diodes [27, 28] or switching diodes [29–31]. Also, the resonance frequency of the antenna can be varied by inserting shorting posts at appropriate locations. In [32], a compact tunable rectangular microstrip patch antenna with slots etched in the patch to reduce its size and increase the tuning range is presented as shown in Fig. 4.11a. Thin posts are placed at selected positions near the patch edge, and each can be short-circuited to the ground plane through a PIN diode, and tunability is achieved by appropriate selection of the posts to be shorted. A photograph of the fabricated structure is shown in Fig. 4.11b. Reflection coefficients for four resonant frequencies corresponding to the four different states of the diode are plotted in Fig. 4.11c.

4.3 Frequency Reconfigurable Passive Planar Antenna Using Different …

55

Fig. 4.10 Frequency reconfigurable antenna with loading using two lumped capacitances, a geometry b simulated reflection coefficients for different values of capacitors. Reproduced with permission from IEEE [24]

(a)

(b)

4.3.4 Frequency Reconfiguration by Varying the Slot Length Using proper configuration of the RF switches alters the flow of surface current and changes the resonances [33–37]. The geometry of a semicircular slot antenna is shown in Fig. 4.12a. The effective length of current distribution on the semicircular slot decides the resonant frequency. The increase in the length of the slot causes an increase in the effective length of the current flow, thus making the structure resonate at a lower frequency. Similarly, the decrease in the length of the slot causes an increase in the frequency. Measured reflection coefficients for various states of the PIN diodes are plotted in Fig. 4.12b.

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(a)

(b)

(c) Fig. 4.11 Widely tunable compact patch antenna, a geometry b photograph c reflection coefficient for four resonant frequencies corresponds to the four different states of the diode. Reproduced with permission from IEEE [32]

4.3.5 Frequency Reconfiguration Using Metasurfaces Another technique to reconfigure the operating frequency of the antenna is the use of Metasurfaces instead of embedding RF switches [38–41]. The geometries of the slot, metasurface, unit cell, and the complete antenna are shown in Fig. 4.13a, b, c, and d. It consists of a simple slot and a metasurface is fixed on the top of the slot antenna. The slot antenna and metasurface are placed together in direct contact, therefore the proposed antenna is very compact and low profile. The rotation angle θ of the metasurface is measured from the x-axis as shown in Fig. 4.13b. Figure 4.13e plots the simulated reflection coefficient with different rotation angles θ of the metasurface. It can be observed that the resonant frequency shifts down continuously from 4.0 to 2.58 GHz with the rotation angle increasing continuously from 0° to 45° by rotating the metasurface.

4.4 Frequency Reconfigurable Active Planar Antennas Realized …

57

(a)

(b) Fig. 4.12 Frequency agile semicircular slot antenna, a geometry b measured reflection coefficients for various states of the PIN diodes. Reproduced with permission from [34]

4.4 Frequency Reconfigurable Active Planar Antennas Realized Using Different Approaches Frequency reconfigurable passive antennas realized by using various techniques are discussed in the above section. The techniques used in the realization of frequency reconfigurable active antennas are quite different from that of passive antenna realization. Although, in amplifier-type active antennas, where a passive radiator integrates with the two-port active device at its input or output port, the realization of frequency reconfigurable passive radiator is quite easy and it is similar to that used to realize reconfigurable passive antennas but in the case of oscillator-type active integrated antennas where the passive radiator is a part of an oscillator circuit, the realization

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(a)

(b)

(d)

(c)

(e)

Fig. 4.13 Geometries of a slot, b metasurface c unit cell d proposed antenna and e simulated reflection coefficient for different rotation angles θ. Reproduced with permission from IEEE [41]

of frequency reconfigurable active antennas is a bit complex task. Oscillator-type frequency reconfigurable active antennas can be realized using approaches such as feedback loop and negative resistance. The idea of frequency reconfiguration in feedback loop oscillator-type active antennas is explained in this section. Here, we are considering a two-port frequency reconfigurable passive radiator integrated with the feedback loop of an oscillator circuit as shown in Fig. 4.14. Let us assume that the passive radiator resonates at frequencies f1, f2, f3, and so on. The oscillator circuit must oscillate at all these resonance frequencies, which is possible only if it satisfies the oscillation criteria at all these frequencies. To set up the oscillation, the loop gain must be unity and the total phase shift around the loop must be zero or an integer multiple of 2π, which is not simple to achieve especially for all frequencies. Feedback loop oscillator-type frequency reconfigurable antennas have already been reported in the scientific literature [42–50]. A dual-frequency active antenna is reported in [43] as shown in Fig. 4.15; the feedback element (radiator) is a dual-band antenna hence only line lengths of the feedback loop will have an impact on the oscillations. An open-circuited stub is attached through PIN diode D3 to suppress unwanted frequency bands. Feedback path lengths are adjusted by two RF switches (D1 and D2). The feedback passive radiator must resonate at the chosen operating frequency and at the same time feedback path must provide a total loop phase shift of

4.4 Frequency Reconfigurable Active Planar Antennas Realized …

59

Fig. 4.14 Schematic of a frequency reconfigurable feedback loop oscillator-type AIA

0° or an integer multiple of 2π then only the circuit will oscillate. Further, feedback loop oscillator-type antennas could be made compact by embedding an active device onto the radiator itself [44–50]. The geometry of a compact oscillating frequency reconfigurable active antenna is shown in Fig. 4.16a. The passive radiator consists of two semi-circular rings. The outer semi-circular ring serves as the main radiator as well as the feedback path of the oscillating circuit, while the inner one functions as a pair of loaded stubs or an auxiliary radiator by turning diodes ON or OFF. Received power at two different oscillation frequencies is shown in Fig. 4.16b. Frequency reconfigurable active antennas can also be realized by a negative resistance approach. A topology of negative resistance-based frequency reconfigurable AIA is illustrated in Fig. 4.17. By using tunable or multiple matching networks,

(a)

(b)

Fig. 4.15 Dual frequency active antenna, a schematic b response. Reproduced with permission from IEEE [43]

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(a)

(b)

Fig. 4.16 Frequency reconfigurable feedback loop oscillator-type AIA, a geometry b received power at two different oscillation frequencies. Reproduced with permission from IEEE [45]

different resonances can be obtained. Here, the frequency reconfigurability is not incorporated in the passive radiator but in the active circuit, where reconfigurability is achieved by switching different paths between the amplifier and passive radiator. A prototype using the negative resistance approach is shown in Fig. 4.18a [51]. Two different matching networks are designed to oscillate the antenna at 2.4 and 5.2 GHz as shown in Fig. 4.18b.

Fig. 4.17 Topology of negative resistance based frequency reconfigurable AIA

4.5 Summary

61

(a)

(b)

Fig. 4.18 Frequency reconfigurable AIA using negative resistance approach, a photograph b received power at 2.4 and 5.2 GHz. Reproduced with permission from IEEE [51]

4.5 Summary In this chapter, frequency reconfigurable passive and active antennas are discussed. There are various techniques to realize frequency reconfigurable passive antennas, but it is limited for realizing frequency reconfigurable AIA due to their topology and operating principle. Frequency reconfigurable AIA must satisfy the oscillation criteria for all operating frequencies. Frequency reconfigurability by connecting or disconnecting an additional patch in passive antennas is a quite useful technique to achieve lower or higher resonance as compared to the reference frequency (original resonance obtained when an additional patch is disconnected). The reconfigurable matching network technique is advantageous when we need to choose a specific frequency band and reject signals coming from unwanted sources. Frequency can be reconfigured by increasing or decreasing the path length of the surface current. By changing the slot length, the resonance frequency of the antenna can be varied. Frequency reconfiguration is also possible using Metasurfaces; RF switches are not needed in such designs. Frequency reconfigurable oscillator-type AIAs can be realized by using two approaches namely the negative resistance approach and the feedback loop approach. The negative resistance approach is less attractive compared to the feedback loop approach. Compact oscillator-type AIA designs with low phase noise can be realized using a feedback loop approach. Oscillator-type active antennas have found applications in wireless charging and power transmission systems. In passive radio frequency identification (RFID) tags, the readable range of tags can be enhanced by giving excess RF power from an oscillator circuit. In this context, the performance of an RFID system can be improved by installing a greater number of unmodulated continuous wave (CW) sources around the passive tags. It would be advantageous to have an unmodulated CW source with a frequency reconfiguration function so that frequency can be varied according to the requirements as different frequency bands are used in different countries. This makes a single unique and suitable design globally.

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References 1. Naser-Moghadasi, M., Sadeghzadeh, R.A., Fakheri, M., Aribi, T., Virdee, B.S.: Miniature hookshaped multiband antenna for mobile applications. IEEE Antennas Wireless Propag. Lett. 11, 1096–1099 (2012) 2. Joseph, S., Paul, B., Mridula, S., Mohanan, P.: A novel planar fractal antenna with CPW-feed for multiband applications. Radioengineering 22(4), 1262–1266 (2013) 3. Li, Y., Zhang, Z., Feng, Z., Iskander, M.F.: Design of penta-band omnidirectional slot antenna with slender columnar structure. IEEE Trans. Antennas Propag. 62(2), 594–601 (2014) 4. Kumar, G., Ray, K.P.: Broadband Microstrip Antennas. Artech House, USA (2003) 5. Veeresh, G.K., Vinoy, K.J.: A wideband microstrip antenna with symmetric radiation patterns. Microw. Optical Tech. Lett. 50, 1991–1995 (2008) 6. Behera, A.R., Harish, A.R.: A novel printed wideband dipole antenna. IEEE Trans. Antennas Propag. 60(9), 4418–4422 (2012) 7. Cleetus, R.M.C., Bala, G.J.: Frequency reconfigurable antennas: a review. In: 2017 International Conference on Signal Processing and Communication (ICSPC), pp. 160–164 (2017) 8. Jenath, M., Nagarajan, V.: Review on frequency reconfigurable antenna for wireless applications. In: 2017 International Conference on Communication and Signal Processing (ICCSP), pp. 2240–2245 (2017) 9. Nguyen-Trong, N., Piotrowski, A., Fumeaux, C.: A frequency-reconfigurable dual-band lowprofile monopolar antenna. IEEE Trans. Antennas Propag. 65(7), 3336–3343 (2017) 10. Hamzah, S.A., Esa, M., Malik, N.N.N.A., Ismail, M.K.H.: Narrowband-to-narrowband frequency reconfiguration with harmonic suppression using fractal dipole antenna. Int. J. Antennas Propag. 2013, 1–9 (2013) 11. Rahim, M.K.A., Hamid, M.R., Samsuri, N.A., Murad, N.A., Yusoff, M.F.M., Majid, H.A.: Frequency reconfigurable antenna for future wireless communication system. In: 2016 46th European Microwave Conference (EuMC), pp. 965–970 (2016) 12. Ghanem, F., Bitchikh, M.: An UWB to seven sub-bands frequency reconfigurable antipodal Vivaldi antenna. In: 2013 IEEE Antennas and Propagation Society International Symposium (APSURSI), pp. 672–673. Orlando, FL (2013) 13. Yadav, D., Abegaonkar, M.P., Koul, S.K., Tiwari, V., Bhatnagar, D.: Frequency reconfigurable monopole antenna with switchable band characteristics from UWB to band-notched UWB to dual-band radiator. In: 2016 Asia-Pacific Microwave Conference (APMC), pp. 1–4. New Delhi (2016) 14. Bitchikh, M., Ghanem, F.: UWB to 30 narrow sub-bands frequency reconfigurable antipodal Vivaldi antenna. Electron. Lett. 52(19), 1580–1582 (2016) 15. Deng, J., Hou, S., Zhao, L., Guo, L.: Wideband-to-narrowband tunable monopole antenna with integrated bandpass filters for UWB/WLAN applications. IEEE Antennas Wireless Propag. Lett. 16, 2734–2737 (2017) 16. Xiao, J., Kong, F., Yang, X.: Frequency reconfigurable antenna for band-notched UWB and C-band communications. In: 2019 IEEE International Conference on Computational Electromagnetics (ICCEM), pp. 1–3 (2019) 17. Rhee, C.Y., Kim, J.H., Jung, W.J., Park, T., Lee, B., Jung, C.W.: Frequency-reconfigurable antenna for broadband airborne applications. IEEE Antennas Wireless Propag. Lett. 13, 189– 192 (2014) 18. Mun, B., Jung, C., Park, M., Lee, B.: A compact frequency-reconfigurable multiband LTE MIMO antenna for laptop applications. IEEE Antennas Wireless Propag. Lett. 13, 1389–1392 (2014) 19. Sun, M., Zhang, Z., Zhang, F., Chen, A.: L/S multiband frequency-reconfigurable antenna for satellite applications. IEEE Antennas Wireless Propag. Lett. 18(12), 2617–2621 (2019) 20. Behdad, N., Sarabandi, K.: A Varactor-tuned dual-band slot antenna. IEEE Trans. Antennas Propag. 54(2), 401–408 (2006)

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Chapter 5

Polarization Reconfigurable Passive and Active Planar Antennas

5.1 Introduction Circularly polarized antennas are the key components for modern and future wireless communication systems. Circularly polarized (CP) antennas are advantageous over linear polarized antennas. With CP antennas, there is no need to align the transmitting and receiving antennas in the same direction. These antennas suppress multipath interferences or fading and enhance the signal strength. CP antennas are widely used for various wireless systems including satellite communications, mobile communications, wireless local area networks (WLAN), radio frequency identification (RFID), wireless power transfer (WPT), global navigation satellite system (GNSS), and global positioning system (GPS). Polarization diversity in an antenna system has recently gained attention in modern wireless systems. Dual polarized and circularly polarized antennas have been reported in the literature [1–12], but these antennas have fixed polarization. An antenna with switchable polarization capability doubles the system’s capacity in satellite communication systems by using the frequency reuse concept [13–21]. Polarization switchable antennas among linear polarization (LP) or circular polarization (CP), and left-hand circular polarization (LHCP) or righthand circular polarization (RHCP) have been extensively discussed in the literature [15, 16, 18–21]. To accommodate more channels, wideband polarization reconfigurable antennas are the key for future wireless systems [22–27]. For portable devices, polarization reconfigurable compact antennas are needed to be fixed in a limited volume [28, 29]. Polarization reconfigurable active antennas are popular and beneficial for advanced wireless systems. Oscillator-type polarization reconfigurable active antennas are advantageous in applications such as IoT, etc. [30–32]. Such applications require advanced circuits, antennas, and other low-cost hardware to configure wireless modules. Additionally, wireless technologies are used not only for communication or broadcasting but also in other areas such as wireless power transfer and radars [33]. Various polarization reconfigurable active and passive planar antennas are reported in this chapter. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1_5

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5 Polarization Reconfigurable Passive and Active Planar Antennas

5.2 Basis of Polarization The surface current distribution on the radiating structure determines the type of polarization of that structure. The direction of current flow at different time instants translates directly into the polarization of the electric field. The current movement (clockwise or anticlockwise) on the surface of the antenna represents the sense of polarization (either LHCP or RHCP). Different polarization states can be obtained by altering the surface current. It can be obtained by changing the material properties, feed configuration, antenna structure, etc. Ideally, the impedance and frequency characteristics must be the same in different polarization states, but practically it varies because the physical structure of the antenna changes in different polarization modes. Obtaining similar characteristics in different polarization states is the design challenge that is addressed in this chapter.

5.3 Obtaining Circular Polarization from Microstrip Patch Antennas Normally, a conventional rectangular microstrip patch antenna radiates linearly polarized waves. Circular Polarization (CP) can be obtained from a microstrip patch by perturbing the original shape of the radiator by inserting some slots or slits of various shapes or truncating the corners. To generate CP, two orthogonal modes must be excited with equal amplitude and quadrature-phase between these two modes. Two orthogonal modes (TM01 and TM10 ) can be obtained using a single feed or dual feed mechanism. Several techniques for generating circular polarization modes are available in the scientific literature. Techniques of achieving circular polarization may be classified as single- feed and dual-feed. Circularly polarized antennas are discussed in detail in [34]. Circularly polarized microstrip patch antennas are popular due to their advantages of planar structure, low cost, less weight, ease of fabrication, and conformability to curved surfaces. Circular polarization can be obtained from a microstrip patch antenna by means of a single or dual feed technique. A simple CP microstrip patch antenna using a dual-feed technique is shown in Fig. 5.1. A square microstrip patch antenna is fed by two microstrip feeds that excite two orthogonal modes so that the antenna generates both horizontal and vertical polarized waves simultaneously. A microstrip 90° hybrid is incorporated to produce a phase difference of 90° between these waves. The disadvantage of using the hybrid is its large size. Although the hybrid is easy to realize using the conventional photolithography process, it occupies a large space. Circularly polarized microstrip patch antennas can also be fed by other techniques such as coaxial feed, aperture coupled feed, proximity coupled feed, etc. Also, the radiating element may be of different shapes like rectangular, triangular, circular, annular ring, and so on.

5.3 Obtaining Circular Polarization from Microstrip Patch Antennas

67

Fig. 5.1 A microstrip patch antenna fed through a 90° hybrid

It is also possible to generate circular polarization using more than two feeds. The multi-feed techniques (e.g., sequential rotation feeding technique) can reduce higher-order modes and provide high polarization purity and wide bandwidth. The drawback of this feeding technique is the large size and complexity of the feed network. To simplify the feed network of such antennas, a single-feed technique has been developed. Five different designs of circularly polarized microstrip patch antennas based on a single feed are shown in Fig. 5.2. Figure 5.2c shows a square patch with two corners truncated. By truncating corners, two orthogonal modes can be excited. By creating notches, circular polarization can also be achieved as shown in Fig. 5.2d. The perturbation can also take the form of a narrow rectangular-shaped slot cut in the center of the square patch as shown in Fig. 5.2e. CP generated from other shapes of the patch have also been reported in the literature [35]. The single-feed technique for generating circularly polarized waves is having a simple geometry but the disadvantage of this technique is the narrow axial ratio bandwidth. CP can also be generated from other antenna structures such as crossed dipole, helix, Quadrifilar Helix, spiral, slot, and so on. Among all, microstrip patch and slot are simple in geometry, light-weight, and low profile. In this chapter, Microstrip patch and slot-based polarization reconfigurable antennas are discussed in detail.

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5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.2 Single feed circularly polarized microstrip patch antennas, a elliptical patch b nearly square patch c square patch with corner truncation d circular patch with perturbations e square patch with inserted slot [34]

5.4 Reconfigurable Microstrip Patch Antenna with Switchable Polarization Microstrip patch-based polarization reconfigurable passive planar antennas are discussed in this section. In a conventional microstrip patch, two orthogonal modes can be excited by truncating two diagonal corners of the radiator [37, 38] or inserting small slits [39] or slots [40] into the microstrip patch. By using these techniques, both senses of circular polarization i.e., RHCP and LHCP can be obtained by symmetrically perturbing the patch with respect to the feed while LP is the original polarization of the microstrip patch antenna. Antenna performance in all polarization states in terms of impedance matching, radiation patterns, radiation efficiency, and gain can

5.4 Reconfigurable Microstrip Patch Antenna with Switchable …

69

be analysed, and based on it one can say that the antenna resonates at almost similar resonance frequencies in all polarization states. In practice, it is difficult to achieve good impedance matching at almost similar frequencies among different polarization states because the physical dimensions of the radiator are changed. Polarization switching between LP and CP has been achieved by using two switches in [36, 41]. Polarization switching among LHCP or RHCP has been achieved by truncating two corners of the patch and using a piezoelectric transducer (PET) [42]. A simple method to excite CP is obtained by loading a stub at one of the patch corners. By doing this, the change in the physical size of the patch for different polarization states is minute hence frequency shift in all three polarization states is insignificant. Additionally, in this scheme, two switching diodes are required to get polarization reconfigurability among LP, LHCP, or RHCP.

5.4.1 Reconfigurable Stub Loaded Microstrip Patch Planar Antenna with Switchable Polarization A reconfigurable stub-loaded microstrip patch antenna with polarization switching between LHCP, RHCP, and LP is presented in this section. The geometry of the proposed antenna is shown in Fig. 5.3a. The antenna consists of a square patch; two stubs are connected at the corners with two PIN diodes. PIN diodes (MA4SPS402 from MA-Com) denoted as D1 and D2 are employed in the circuit. Two rectangular stubs are connected at two corners of the microstrip patch antenna using two PIN diodes to get both senses of polarization. The length and width of the microstrip patch antenna are calculated from the standard equations [43]. The equivalent circuit of a PIN diode in the ON-and OFF-states is discussed in Sect. 1.6.2 of Chap. 1. From the datasheet [44], the equivalent circuit of the PIN diode is represented by a series resistor (Rs) of 5 Ω in the ON-state and a parallel combination of a 40 KΩ resistor (OFF-state resistance, Rp) and a 0.03 pF capacitor (Cp) in the OFF-state. The series parasitic inductance (Lp) of a PIN diode is 0.45 nH. The antenna is fed by a quarterwave transformer. The dimensions of the antenna are listed in Fig. 5.3. Here, two orthogonal modes are excited by loading a stub at one of the patch corners close to the feed. The amplitudes and phases of these modes can be adjusted by choosing the proper dimensions of the stub. The antenna is designed on a 31-mil thick RT/Duroid 5880 substrate. The dielectric constant of the substrate is 2.2 and the loss tangent is 0.0009. Antenna is simulated with the full-wave electromagnetic simulator (CST Microwave Studio). When forward bias (+Vdc) is applied to the circuit, diode D1 is ON and diode D2 is OFF, consequently, the antenna radiates LHCP. In the second case, if reverse bias (−Vdc) is applied, diode D1 is reverse biased and D2 is forward biased, the right-hand circularly polarized wave is generated. In the third case, if both diodes D1 and D2 are OFF, antenna radiates a linearly polarized wave.

70

5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.3 Polarization reconfigurable stub-loaded microstrip patch antenna [21] a geometry b photograph; Lg = 56, Lh = 11.3, Lp = 18.5, Lt = 2.1, Ltr = 11.4, Wf = 2.4, Wg = 56, Wh = 0.2, Wp = 18.3, Wtr = 0.6, W1 = 0.7, W2 = 2, all units are in mm

The surface current is plotted at different time instants (ωt = 0°, 45°, 90°, 135°, and 180°) for LHCP and LP modes. The surface current with reference to the feed is rotating in the left direction with ωt values, and the antenna exhibits LHCP as shown in Fig. 5.4. For LP mode, the current direction is always linear as shown in Fig. 5.5, and the antenna is linearly polarized. The antenna is fabricated using a conventional photolithography process. A photograph of the fabricated prototype is shown in Fig. 5.3b. The reflection coefficients of the antenna are measured using an Agilent vector network analyser (VNA). The measured and simulated reflection coefficients are plotted for all three polarization states as shown in Fig. 5.6. The measured impedance bandwidths (IMBWs) for LHCP, LP and RHCP are 70 MHz (5151–5221 MHz), 72 MHz (5159–5231 MHz), and 74 MHz (5158–5232 MHz), respectively while simulated values are 122 MHz (5154–5276 MHz), 60 MHz (5178–5238 MHz), and 124 MHz (5156–5280 MHz), respectively. The radiation pattern of the proposed antenna is measured in an anechoic chamber with an Agilent signal analyzer (Model MG3694B) and Anritsu MG3694B microwave signal generator. The proposed reconfigurable antenna is used as a receiving antenna kept on a turntable that rotates horizontally (0°–360°). A wideband double-ridged linearly polarized horn antenna is used as a transmitter. The distance between the horn and the proposed antenna is 200 cm (satisfying the far-field condition). The normalized radiation patterns are plotted in the y–z plane (H-plane) as shown in Fig. 5.7. The cross-polarization level is better than 21 dB in LP mode. The gain of the antenna is plotted for all three polarization modes as shown in Fig. 5.7d. The gain is calculated with respect to the isotropic radiator hence the gain is in dBi. The variation in the measured gain across the band is not more than 0.62 dB. The axial ratio beamwidth for LHCP and RHCP mode are plotted in Fig. 5.8. The measured 3-dB axial ratio beamwidth for LHCP mode is from −105° to 42° while

5.4 Reconfigurable Microstrip Patch Antenna with Switchable …

71

Fig. 5.4 Surface currents for LHCP mode at different phase ωt, a 0° b 90° c 180° d 270° [21]

simulated value is from −65° to +105°. The measured and simulated 3-dB axial ratio beamwidths for RHCP mode are from −72° to +87° and from −66° to +105°, respectively. The axial ratio bandwidths (ARBWs) are plotted for LHCP and RHCP in Fig. 5.9. The measured ARBW for LHCP is 64 MHz (5144–5208 MHz) while the simulated is 36 MHz (5173–5209 MHz). The measured ARBW for RHCP is 60 MHz (5145– 5205 MHz) while the simulated is 33 MHz (5176–5209 MHz). A summary of the results is given in Table 5.1.

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5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.5 Surface currents for LP mode at different phase ωt, a 0° b 90° c 180° d 270° [21]

5.4.2 Reconfigurable Corner Truncated Microstrip Patch Planar Antenna with Switchable Polarization A corner-truncated square microstrip patch has a length and width of 45.3 mm designed on a substrate with a relative dielectric constant of 4.4 and thickness of 1.6 mm as shown in Fig. 5.10a. The antenna resonates at 1.59 GHz. Two pairs of opposite corners having an equal side length of 4.6 mm are cut to provide perturbation to obtain two orthogonal modes for CP. The gap between the patch and triangular conductors is 1.4 mm. The side length of parasitic triangular-shaped conductors is 2.3 mm. Four PIN diodes are used to switch the polarization among LHCP, LP, or RHCP. Reflection coefficients are plotted in Fig. 5.10b. A shift in resonance frequencies is observed while switching between LP and LHCP/RHCP modes; it is due to a change in the physical size of the patch while switching the modes. Radiation patterns for LP and LHCP modes are plotted in Fig. 5.10c and d, respectively.

5.4 Reconfigurable Microstrip Patch Antenna with Switchable …

73

Fig. 5.6 Measured and simulated reflection coefficients of the stub-loaded microstrip patch antenna for a LHCP mode b RHCP mode c LP mode [21]

A reconfigurable rotated V-shaped corner truncated microstrip patch antenna with polarization switching among LHCP, LP or RHCP is shown in Fig. 5.11a. The antenna consists of a nearly square microstrip patch truncated at two of its corners close to the feed and two small parasitic patches are connected using two RF switches. One corner of the antenna is cut off from the main patch through a narrow-rotated Vshaped cut to get CP and by doing this a slight change in the physical dimension of the patch occurs while getting CP or LP and due to this, the shift in the resonance frequency is insignificant. The antenna is designed on RT/Duroid 5880 substrate with a relative permittivity (εr ) of 2.2, thickness (h) of 0.762 mm, and loss tangent (tanδ) of 0.0006. The photograph of the fabricated antenna is shown in Fig. 5.11b. Two PIN diodes denoted as D1 and D2 are incorporated into the structure. The simple bias circuitry is designed to control the switching among different polarization states. The biasing circuit consists of DC pads, RF chokes made from high impedance quarterwave lines, DC block capacitors (100 pF), and a DC power supply. When no bias is applied, diodes D1 and D2 are in the OFF-state, small parasitic conductors will get disconnected from the main patch, the antenna generates a linearly polarized wave. When 0.8 V is applied to the circuit, diode D1 turns ON and D2 turns OFF, antenna radiates LHCP and when −0.8 V is given, diode D2 turns ON, and D1 turns OFF,

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5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.7 Normalized radiation patterns of the stub-loaded microstrip patch antenna in y–z plane for a LHCP mode b RHCP mode c LP mode d peak gain of the antenna [21]

Fig. 5.8 Axial ratio beamwidth of the stub-loaded microstrip patch antenna for a LHCP mode b RHCP mode [21]

5.5 Polarization Reconfigurable Slot Antennas

75

Fig. 5.9 Axial ratio bandwidth of the stub-loaded microstrip patch antenna for a LHCP mode b RHCP mode [21]

Table 5.1 Summary of the results of stub-loaded microstrip patch antenna [21] Polarization state

−10 dB IMBW (MHz)

3 dB ARBW (MHz) Gain (dBi)@5.2 GHz

Simu

Simu

Meas

Meas

Simu

Meas

LHCP

122

70

36

64

7.99

6.19

LP

60

72





7.66

5.97

RHCP

124

74

33

60

7.99

6.13

the antenna generates RHCP. The measured and simulated reflection coefficients are plotted in Fig. 5.12. The measured impedance bandwidth (IMBW) is 203 MHz for LHCP mode and 211 MHz for RHCP mode. The measured IMBW for LP mode is 82 MHz. A minute shift in the resonance frequency in LP mode is observed and it is due to the disconnection of small patches from the corners in LP mode. The normalized radiation patterns are plotted in the y–z plane (H-plane) as shown in Fig. 5.13. The measured axial ratio beamwidth (AR < 3 dB) for LHCP and RHCP modes are from −35° to 45° and −38° to 44°. The ARBW for LHCP and RHCP mode are plotted in Fig. 5.14. The measured ARBWs are 108 MHz for LHCP mode and 111 MHz for RHCP mode (Table 5.2).

5.5 Polarization Reconfigurable Slot Antennas Polarization reconfigurability can be achieved from a microstrip patch antenna by inserting slots of different shapes and sizes [45–54] in its geometry. Polarization reconfigurable U-slot patch antenna is shown in Fig. 5.15 [14]. The dimensions of the antenna are listed in Table 5.3. A U-slot is inserted into a rectangular microstrip

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5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.10 a Configuration of the corner-truncated square microstrip patch antenna with switchable polarization b reflection coefficients c simulated H-plane radiation pattern for LP mode d measured radiation pattern for LHCP mode. Reproduced with permission from IEEE [36]

Fig. 5.11 Polarization reconfigurable rotated V-shaped corner truncated microstrip patch antenna, a geometry b photograph; a = 2.28, g = 0.3, Lg = 48, Lp = 18.95, Lt = 2.1, Ltr = 11.4, Wf = 2.4, Wg = 50, Wh = 0.2, Wp = 18.8, Wtr = 0.6, all dimensions are in mm, ©IETE Journal of Research. Reproduced by permission of IETE [20]

5.5 Polarization Reconfigurable Slot Antennas

77

Fig. 5.12 Simulated and measured reflection coefficients of rotated V-shaped corner truncated microstrip patch antenna for a LHCP mode b LP mode c RHCP mode, ©IETE Journal of Research. Reproduced by permission of IETE [20]

patch printed on a dielectric substrate (dielectric constant = 2.2). Two PIN diodes are used to switch the polarization among LP, LHCP, or RHCP. By adjusting the location of the PIN diodes, two degenerate modes with the same magnitude and a phase difference of 90° at a given frequency are generated thus enabling the antenna to generate CP radiation. The antenna radiates LHCP when the left arm of the U-slot is longer than the right arm. RHCP can be achieved if the right arm is longer than the left arm. When both diodes are either ON or OFF, the U-slot becomes symmetrical which enables the antenna to generate LP. Different polarization states of the antenna are listed in Table 5.4. Reflection coefficients for LHCP and LP modes are plotted in Fig. 5.16a while the axial ratio for LHCP mode is plotted in Fig. 5.16b. A single feed rectangular microstrip antenna with reconfigurable polarization capability is reported in [46]. A cross patch is obtained by removing the four-square regions from the corners of a rectangular patch and then an X-shaped slot is inserted at the center of a rectangular cross-shaped patch. The X-shape is chosen to induce symmetric current distributions to achieve two orthogonal modes as well as to achieve compactness. The polarization can be switched between CP and LP by changing the

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5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.13 Measured and simulated normalized radiation patterns of rotated V-shaped corner truncated microstrip patch antenna in y–z plane for a LHCP mode b LP mode c RHCP mode, ©IETE Journal of Research. Reproduced by permission of IETE [20]

Fig. 5.14 Simulated and measured axial ratio bandwidths of rotated V-shaped corner truncated microstrip patch antenna for a LHCP mode b RHCP mode, ©IETE Journal of Research. Reproduced by permission of IETE [20]

5.5 Polarization Reconfigurable Slot Antennas

79

Table 5.2 Summary of the results of rotated V-shaped corner truncated antenna Polarization state

−10 dB IMBW (MHz)

3 dB ARBW (MHz) Gain (dBi)@5.2 GHz

Simu

Simu

Meas

Meas

Simu

Meas

LHCP

135

203

68

108

6.35

5.72

LP

63

82





6.27

5.54

RHCP

136

211

67

111

6.37

5.68

©IETE Journal of Research. Reproduced by permission of IETE [20]

Fig. 5.15 Schematic of the reconfigurable U-slot antenna, a top view and b side view. Reproduced with permission from IEEE [14] Table 5.3 Dimensions of the U-slot antenna Parameters

W1

W2

W3

W4

W5

Value (mm)

0.5

0.65

5.3

13.8

40

Parameters

L1

L2

L3

L4

L5

Value (mm)

5.95

9.3

2.9

14.2

5.1

Reproduced with permission from IEEE [14] Table 5.4 Polarization states of the U-slot antenna

Diode (left)

Diode (right)

Polarization

State 1

OFF

OFF

LP

State 2

ON

ON

LP

State 3

ON

OFF

RHCP

State 4

OFF

ON

LHCP

Reproduced with permission from IEEE [14]

80

5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.16 Simulated and measured results of the U-slot antenna a reflection coefficient for the LP and LHCP modes and b axial ratio for LHCP mode. Reproduced with permission from IEEE [14]

shape of the slot by turning the diodes ON or OFF. Several broadband polarization reconfigurable slot-based antennas have been reported in the scientific literature [28, 55–58].

5.6 Polarization Reconfigurable Compact Slot Antennas Compact antennas are of great interest in the field of cellular telephony and wireless communication systems. Many applications of the Internet of Things (IoT) require wireless systems that can offer a wide frequency range with high data rate capability. These systems must be compact and cost-effective. Many wireless systems require different frequency bands for various applications. For these systems, multiple antennas are required to fulfill the requirement. The size of an antenna for portable devices is one of the major benchmarks to consider. It is difficult to find enough space in portable devices to accommodate multiple antennas. The antenna needs to be designed in such a way that the antenna must fit in these portable devices. There is a great need for compact and wideband antennas that can operate over many wireless communication systems. Polarization reconfigurable wideband antennas have gained a lot of attention in modern communication systems. Instead of having multiple antennas, a single broadband polarization reconfigurable antenna can cover the entire frequency range of different wireless communication systems and reduce the system complexity.

5.6 Polarization Reconfigurable Compact Slot Antennas

81

5.6.1 Reconfigurable Compact Rectangular Slot Antenna with Switchable Polarization There are various compact antennas reported in the literature in the past [28, 56–58]. A reconfigurable compact rectangular slot antenna with switchable polarization is shown in Fig. 5.17. The antenna consists of a rectangular slot etched in a metallic ground plane, while the feed mechanism is on the other side of the substrate. Five PIN diodes are employed in the circuit to switch the polarization between three polarization states i.e., LHCP, LP, and RHCP. Three different geometries are obtained by turning diodes ON or OFF to achieve three different polarization states as shown in Fig. 5.18. The width of the microstrip feed line is 2.4 mm. A compact meander Wilkinson power divider (WPD) is designed to get the LP. WPD consists of two quarter-wavelength meander microstrip lines (length = 49.25 mm, width = 1.36 mm). The geometry of WPD is shown in Fig. 5.19. A chip resistor of 100 Ω is connected between two output arms of WPD to provide isolation between ports 2 and 3. The power is equally distributed in both the arms (ports 2 and 3). Slot as such has a bi-direction pattern and to make the radiation pattern unidirectional and enhance the gain of the antenna, a metal sheet (as a reflector) is positioned parallel to the slot surface at 23 mm from the slot. Antenna is designed and fabricated on a RT/Duroid 5880 substrate (εr = 2.2, h = 0.787 mm and tanδ =

Fig. 5.17 Geometry of a wideband reconfigurable slot antenna; Dimensions: d1 = 22.8, d2 = 22.75, L = 87, Lm = 115, Ls1 = 41.4, Ls2 = 37.85, W = 84, Wm = 115, Ws = 0.65; all dimensions are in mm. Reproduced with permission from IEEE [16]

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5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.18 Three different geometries of the antenna for, a LHCP mode b LP mode and c RHCP mode. Reproduced with permission from IEEE [16]

0.0004). The size of the circuit is 115 × 115 mm2 . The photograph of the fabricated antenna is shown in Fig. 5.20. Five PIN diodes (MA4SPS402) are incorporated into the circuit to get three polarization states. In the first case, when diode D2 is forward biased while other diodes are reverse biased, the antenna radiates left hand circularly polarized waves (as shown in Fig. 5.18a). In the second case, diode D1 is ON while other diodes are OFF, the antenna generates RHCP. In the third case, diodes D3, D4, and D5 are ON while D1 and D2 are OFF, the antenna radiates LP. The different polarization states of the antenna with diodes ON/OFF conditions are given in Table 5.5. The biasing circuit consists of a DC blocking capacitor (100 pF), an RF choke inductor (100 nH), bias pads and a DC power supply.

Fig. 5.19 Layout of the compact Wilkinson power divider. Reproduced with permission from IEEE [16]

5.6 Polarization Reconfigurable Compact Slot Antennas

83

Fig. 5.20 Photograph of a wideband reconfigurable slot antenna a front view b back view. Reproduced with permission from IEEE [16]

Table 5.5 Polarization states of the wideband reconfigurable slot antenna States

D1

D2

D3

D4

D5

LHCP

OFF

ON

OFF

OFF

OFF

LP

OFF

OFF

ON

ON

ON

RHCP

ON

OFF

OFF

OFF

OFF

Reproduced with permission from IEEE [16]

Parametric analysis Parametric analysis is shown here to understand the effects of varying the parameters on the performance of the antenna. The impact of reflector size and spacing between the reflector and the slot surface is studied because the impact of these two parameters is more on axial ratio and gain. Effect of Variation of Spacing between the Reflector and Slot Surface The spacing between the reflector and slot surface is varied while other parameters are fixed. The axial ratio beamwidths are plotted for different values of d3 as shown in Fig. 5.21a. Here we are showing only five different values of ‘d3 ’. The gains are plotted in Fig. 5.21b. The simulated results are plotted for LHCP mode. Effect of Variation of the Size of the Reflector In this analysis, the size of the reflector is varied while other parameters are kept fixed. The simulated axial ratio beamwidth and gain are plotted with different sizes of the reflector as shown in Fig. 5.22. Significant changes are observed in the axial ratio beamwidth and gain by varying the size of the reflector. The optimized value of the reflector considered is 115 × 115 mm2 .

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5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.21 Simulated results showing the effect of variations of ‘d3 ’ on a axial ratio beamwidth b realized gain. Reproduced with permission from IEEE [16]

Fig. 5.22 Simulated results showing the effect of variations of the reflector size (Wm, Lm) on a axial ratio beamwidth b realized gain. Reproduced with permission from IEEE [16]

Surface Currents Polarization can be interpreted by seeing the surface current distributions on the antenna. The simulated surface current distributions are plotted at different time instants (ωt = 45°, 135°, 225°, and 315°) for RHCP and LP modes. The surface current rotates anticlockwise with time and follows the right-hand rule as shown in Fig. 5.23, and consequently the antenna radiates the right hand circularly polarized waves. In the LP mode, the current is flowing in the same direction and following the linear behaviour as shown in Fig. 5.24, the antenna radiates linearly polarized waves.

5.6 Polarization Reconfigurable Compact Slot Antennas

(a) ωt = 450

(c) ωt = 2250

85

(b) ωt = 1350

(d) ωt = 3150

Fig. 5.23 Surface current distribution for RHCP mode. Reproduced with permission from IEEE [16]

Reflection Coefficients The simulated and measured reflection coefficients for all the three polarization states are depicted in Fig. 5.25. The reflection coefficients are below −10 dB across the band. Radiation Patterns The simulated and measured normalized radiation patterns are plotted in the x–z plane as shown in Fig. 5.26. As observed, the maxima are formed at θ = 180° (negative z-axis) for all the three polarization states. For the LP mode, the cross-pol level is below 20 dB from the co-pol. Axial Ratios and Gain The axial ratio beamwidth is depicted in the broadside direction for all three states as shown in Fig. 5.27. The simulated and measured axial ratio bandwidth for LHCP and RHCP mode are depicted in Fig. 5.28. The axial ratio bandwidth in both CP modes is more than 10% with respect to the center frequency (1.2 GHz). The simulated and

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5 Polarization Reconfigurable Passive and Active Planar Antennas

(a) ωt = 450

(c) ωt = 2250

(b) ωt = 1350

(d) ωt = 3150

Fig. 5.24 Surface current distribution for LP mode. Reproduced with permission from IEEE [16]

measured gain is plotted for LP mode as shown in Fig. 5.29. The comparison of the simulated and measured reflection coefficients, axial ratios, and gains for all three polarization states are listed in Table 5.6.

5.7 Polarization Reconfigurable Active Planar Antennas Here, we are discussing only the polarization reconfigurable oscillator-type active antennas. Polarization agile self-oscillating AIAs have been demonstrated earlier [59–63]. Polarization reconfigurable ring-slot active antenna employing Gunn oscillators is studied in [30]. A polarization reconfigurable antenna for spatial modulation applications has been reported in [59]. This oscillator-type active antenna mainly consists of 12 microstrip patch radiators, a four-port Gunn oscillator, and PSK modulators. A simple polarization switchable active antenna reported in [60] consists of an annular slot etched in the ground plane and fed by a microstrip line. It can be switched between LP, LHCP, and RHCP.

5.7 Polarization Reconfigurable Active Planar Antennas

87

Fig. 5.25 Simulated and measured reflection coefficients of a wideband reconfigurable slot antenna for a LHCP mode b RHCP mode c LP mode. Reproduced with permission from IEEE [16]

Simple geometries of polarization reconfigurable active antenna using feedback loop approach are considered and discussed in the next subsection.

5.7.1 Polarization Reconfigurable Active Antenna with a Symmetrically Coupled Passive Radiator A polarization switchable active antenna with a symmetrically coupled passive radiator is illustrated in Fig. 5.30. Antenna consists of a passive feedback radiator and active circuit. To understand the operation of the antenna, a passive feedback network is realized separately on a substrate. Two-Port Radiator Design A two-port polarization reconfigurable microstrip patch antenna is designed first. The geometry of a two-port feedback radiator is shown in Fig. 5.31a. This passive radiator can be switched in three polarization states namely LHCP, LP, and RHCP.

88

5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.26 Simulated and measured normalized radiation patterns of a wideband reconfigurable slot antenna in x–z plane for a LHCP mode b RHCP mode c LP mode. Reproduced with permission from IEEE [16]

To obtain CP, two diagonal corners are cut-off from the microstrip patch through a narrow L-shaped cut. The two-port radiator is electromagnetically coupled through a T-shaped microstrip feed. Here, the coupling is symmetric on both sides of the microstrip patch. The dimensions of the antennas are listed in Table 5.7. The proposed two-port radiator is designed on a 30-mil thick N9000 Neltec substrate. The relative permittivity of the substrate is 2.2 and the loss tangent is 0.002. The photograph of the fabricated antenna is shown in Fig. 5.31b. A microstrip patch is designed using the standard equations but fed through a T-shaped microstrip line. For proper designing of a T-shaped microstrip line; the length of the T-shaped line is taken the same as the width of the microstrip patch while width, and gap of the T-shaped line are properly optimized to get narrow impedance bandwidth at the design frequency. Operating Principle Four PIN diodes are connected at each corner of the patch radiator. In the first state, when diodes D1, D2, D3 and D4 turn ON, all four small conductors are connected to the radiator, and the antenna generates linearly polarized waves. In the second

5.7 Polarization Reconfigurable Active Planar Antennas

89

Fig. 5.27 Simulated and measured axial ratio beamwidth of a wideband reconfigurable slot antenna for a LHCP mode b RHCP mode c LP mode. Reproduced with permission from IEEE [16]

Fig. 5.28 Simulated and measured axial ratio bandwidth of a wideband reconfigurable slot antenna for a LHCP mode b RHCP mode. Reproduced with permission from IEEE [16]

90

5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.29 Simulated and measured gain of a wideband reconfigurable slot antenna for LP mode. Reproduced with permission from IEEE [16]

Table 5.6 Results summary of a wideband reconfigurable slot antenna Polarization state

S11 (dB) Simu

Meas

Simu

Meas

Simu

Meas

Simu

Meas

LHCP

−12.40

−16.10

1.19

1.17

105

125

8.0

6.99

Frequency (GHz)

3 dB AR BW (MHz)

Gain (dBi)

LP

−12.50

−25.55

1.20

1.24





8.1

7.18

RHCP

−12.45

−16.20

1.19

1.17

105

120

8.0

6.97

Reproduced with permission from IEEE [16]

state, diodes D1 and D4 turn ON while D2 and D3 turn OFF, the antenna generates RHCP. In the third state, diodes D1 and D4 turn OFF while D2 and D3 turn ON, the antenna radiates LHCP. The biasing circuit consists of RF choke inductors (made from high impedance microstrip line), DC block capacitors (100 pF), bias pads and a DC power supply. The reflection and transmission coefficients are plotted in Fig. 5.32. The radiation pattern of the two-port radiator is measured by terminating one of its ports to 50 Ω. The simulated and measured normalized radiation patterns are plotted in the y–z plane (H-plane) as shown in Fig. 5.33. Active Antenna Design After verifying the performance of a passive radiator, an AIA is designed by integrating this two-port radiator in the feedback loop. The extra 50 Ω lines are connected on both sides of the radiator to adjust the loop phase. The band stop filters are designed at the operating frequency and integrated in shunt with the circuit to remove oscillations at lower resonating modes because there may be a chance of oscillations (gain of the device is high at low frequencies). The design of the band stop filter is shown in Fig. 3.13 of Chap. 3. An FET (NE3512S02) is integrated in the feedback loop with its drain connected at port 1 while the gate is connected at port 2. The geometry

5.7 Polarization Reconfigurable Active Planar Antennas

91

Fig. 5.30 Geometry of a polarization switchable active antenna with symmetrically coupled passive radiator: Dimension: Lt1 = 55.40 mm, Lt2 = 47.80 mm. Reproduced with permission from IEEE [33]

Fig. 5.31 Two-port symmetrically coupled polarization reconfigurable passive radiator, a geometry b photograph

92 Table 5.7 Dimensions of a symmetrically coupled polarization reconfigurable two-port passive radiator

5 Polarization Reconfigurable Passive and Active Planar Antennas Parameters

Values (mm)

Parameters

Values (mm)

g1

00.15

t

00.25

Lp

18.40

Wp

18.80

Lb

09.10

Wb

00.10

Lc

01.55

Wt

02.40

Lg

00.30

Fig. 5.32 Simulated and measured S-parameters of a symmetrically coupled two-port radiator for a LHCP mode b RHCP mode c LP mode

of the proposed AIA is shown in Fig. 5.30. The photograph of the fabricated AIA is shown in Fig. 5.34. Results and Discussion The simulation of oscillating AIA is completed by importing S-parameters of the two-port radiator into Agilent Advanced Design System (ADS) as shown in Fig. 3.10 of Chap. 3. An oscillation test probe is connected to the feedback loop to check the oscillations in the circuit. A wideband double-ridged horn antenna of gain 11 dBi

5.7 Polarization Reconfigurable Active Planar Antennas

93

Fig. 5.33 Simulated and measured normalized radiation patterns of a symmetrically coupled twoport radiator in y–z plane for a LHCP mode b RHCP mode c LP mode

at 5.2 GHz is used to capture the power from the active antenna. The measurement setup is shown in Fig. 3.14. The received power is −44.85 dBm for LHCP mode. EIRP can be calculated by the Friis Eq. (3.11). The EIRP is calculated as 10.25 dBm for LHCP mode.

5.7.2 Polarization Reconfigurable Active Antenna with an Asymmetrically Coupled Passive Radiator In this case, the coupling mechanism is changed on both sides of the microstrip patch radiator. The microstrip patch is tightly coupled at the drain side and loosely coupled at the gate side. In this coupling mechanism, feedback power is low compared to that achieved in a symmetrically coupled patch; to fulfill the oscillation criteria (loop gain must be unity) the active element is driven hard (biased with high drain voltage and low gate voltage) to get extra power. This power is coupled to the microstrip patch

94

5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.34 Photograph of the fabricated prototype

and enhances the EIRP of the circuit. The proposed geometry is shown in Fig. 5.35. The photograph of the fabricated circuit is shown in Fig. 5.36. Simulated and Measured Results Again, a two-port feedback radiator is separately designed. The magnitude of S11 and S12 are measured and compared with the simulated results as shown in Fig. 5.37. The simulated and measured ARBWs for RHCP and LHCP are depicted in Fig. 5.38. The summary of the results is given in Table 5.8. After analyzing the performance of the two-port radiator, an active antenna is realized. The simulated and measured radiation patterns of the active antenna are plotted in Fig. 5.39. The cross-polarization level is below −12.1 dB for LP mode. The proposed asymmetric coupled active antenna is compared with the symmetric coupled active antenna. The received powers at the horn in asymmetrical coupled AIA for all polarization modes are at least 4.35 dB higher compared to that of symmetrically coupled. The comparison of received power is given in Table 5.9.

5.7 Polarization Reconfigurable Active Planar Antennas

95

Fig. 5.35 Geometry of a polarization switchable active antenna with an asymmetrically coupled passive radiator; dimension: Lt1 = 55.40 mm, Lt2 = 47.80 mm. Reproduced with permission from IEEE [33]

Fig. 5.36 Photograph of fabricated structures a complete AIA circuit b two-port asymmetrically coupled feedback radiator. Reproduced with permission from IEEE [33]

96

5 Polarization Reconfigurable Passive and Active Planar Antennas

Fig. 5.37 Simulated and measured S11 and S12 magnitude responses of a two-port asymmetrically coupled feedback radiator for a LHCP mode b RHCP mode c LP mode. Reproduced with permission from IEEE [33]

Fig. 5.38 Simulated and measured ARBW of a two-port asymmetrically coupled feedback radiator for a LHCP mode b RHCP mode. Reproduced with permission from IEEE [33]

5.7 Polarization Reconfigurable Active Planar Antennas

97

Table 5.8 Summary of a two-port asymmetrically coupled feedback radiator Polarization state

S11 (dB) Simu

S12 (dB) Meas

Simu

Meas

Frequency (GHz)

3 dB ARBW (MHz)

Simu

Simu

Meas

Meas

LHCP

−15.20

−15.55

−6.05

−7.15

5.20

5.18

41

51

LP

−12.50

−12.12

−6.15

−6.80

5.18

5.16





RHCP

−15.15

−14.85

−6.05

−7.12

5.20

5.18

43

53

Reproduced with permission from IEEE [33]

Fig. 5.39 Simulated and measured radiation patterns of AIA with an asymmetrically coupled passive radiator for a LHCP mode b RHCP mode c LP mode. Reproduced with permission from IEEE [33] Table 5.9 Comparison of the AIAs with symmetrically and asymmetrically coupled passive radiators for LHCP mode

Bias condition of the active device

Received powers (DBm)

Symmetrically coupled

Vds = 1.5 V, Vgs = 0.63 V, Id = 10 mA

−44.85

Asymmetrically coupled

Vds = 1.8 V, Vgs = 0.54 V, Id = 20 mA

−40.38

Reproduced with permission from IEEE [33]

98

5 Polarization Reconfigurable Passive and Active Planar Antennas

5.8 Summary In this chapter, polarization reconfigurable passive and active antennas are discussed. There are various techniques to realize polarization reconfigurable antennas; a few of them were discussed here. The major focus of the chapter was on the microstrip patch and slot antennas due to their planar geometry, low cost, ease of realization, and easy placement on curved surfaces. Polarization reconfigurability by using single or multiple feeds was discussed in detail. Different single feed antennas generating CP were presented. Techniques to achieve CP from a single feed patch antenna e.g., elliptical patch, nearly square patch with feed at its diagonal, square patch with corner truncation, circular patch with perturbations and square patch with an inserted slot were discussed. Later, the performance in terms of reflection coefficients, radiation patterns, axial ratio, and gain of the polarization switchable antennas i.e., rotated V-shaped corner truncated antenna and loading stubs based was presented. Compact antennas are of great interest in the field of cellular telephony and modern wireless communication systems. Continuous efforts in realizing compact and wideband polarization reconfigurable antennas are necessary to get a significant outcome and fulfill various novel wireless services. Polarization reconfigurable oscillating type active antennas find applications in RFID and power transmission systems. A readable range of tags can be enhanced by giving higher RF power from an oscillator circuit. The performance of an RFID system can be improved by using polarization switchable sources around the passive tags. There is no need to align the tag with the source in case of CP enabled source.

References 1. Karmakar, N.C., Bialkowski, M.E.: Circularly polarized aperture-coupled circular microstrip patch antennas for L-band applications. IEEE Trans. Antennas Propag. 47(5), 933–940 (1999) 2. Padhi, S.K., Karmakar, N.C., Law, C.L., Aditya, S.: A dual polarized aperture coupled circular patch antenna using a C-shaped coupling slot. IEEE Trans. Antennas Propag. 51(12), 3295– 3298 (2003) 3. Chu, L.C.Y., Guha, D., Antar, Y.M.M.: Comb-shaped circularly polarised dielectric resonator antenna. Electron. Lett. 42(14), 785–787 (2006) 4. Alizadeh, F., Ghobadi, C., Nourinia, J., Mohammadi, B.: A novel triple-broadband dualpolarized antenna. In: 2017 IEEE 4th International Conference on Knowledge-Based Engineering and Innovation (KBEI), pp. 0194–0196. Tehran, Iran (2017) 5. Kumar, A., Sharma, N., Yadav, M., Sankhla, V.: Compact offset CPW-fed inverted Lshaped dual-band dual-polarized reconfigurable printed antenna. In: 2017 IEEE Applied Electromagnetics Conference (AEMC), pp. 1–2. Aurangabad, India (2017) 6. Liu, Y., Li, X., Yang, L., Liu, Y.: A dual-polarized dual-band antenna with Omni-directional radiation patterns. IEEE Trans. Antennas Propag. 65(8), 4259–4262 (2017) 7. Li, H., Kang, L., Wei, F., Cai, Y., Yin, Y.: A low-profile dual-polarized microstrip antenna array for dual-mode OAM applications. IEEE Antennas Wireless Propag. Lett. 16, 3022–3025 (2017) 8. Zhou, C., Wong, H., Yeung, L.K.: A wideband dual-polarized inductor-end slot antenna with stable beamwidth. IEEE Antennas Wireless Propag. Lett. 17(4), 608–612 (2018)

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9. Sun, K., Yang, D., Chen, Y., Liu, S.: A broadband commonly fed dual-polarized antenna. IEEE Antennas Wireless Propag. Lett. 17(5), 747–750 (2018) 10. Zhao, Y., Wang, E., He, D., Zhang, T., Yang, J.: Design of wideband dual-circularly polarized endfire antenna array on gap waveguide. In: 2019 13th European Conference on Antennas and Propagation (EuCAP), pp. 1–3 (2019) 11. Zhao, Z., Liu, F., Ren, J., Liu, Y., Yin, Y.: Dual-sense circularly polarized antenna with a dual-coupled line. IEEE Antennas Wireless Propag. Lett. 19(8), 1415–1419 (2020) 12. Pan, Y., Cheng, Y., Dong, Y.: Dual-polarized directive ultrawideband antenna integrated with horn and Vivaldi array. IEEE Antennas Wireless Propag. Lett. 20(1), 48–52 (2021) 13. Wu, Y., Wu, C., Lai, D., Chen, F.: A reconfigurable quadri-polarization diversity aperturecoupled patch antenna. IEEE Trans. Antennas Propag. 55(3), 1009–1012 (2007) 14. Qin, P., Weily, A.R., Guo, Y.J., Liang, C.: Polarization reconfigurable U-slot patch antenna. IEEE Trans. Antennas Propag. 58(10), 3383–3388 (2010) 15. Row, J., Liu, W., Chen, T.: Circular polarization and polarization reconfigurable designs for annular slot antennas. IEEE Trans. Antennas Propag. 60(12), 5998–6002 (2012) 16. Singh, R.K., Basu, A., Koul, S.K.: Novel high gain polarization switchable rectangular slot antenna for L-band applications. In: 2017 11th European Conference on Antennas and Propagation (EUCAP), pp. 3820–3824. Paris (2017) 17. Li, W., et al.: Polarization-reconfigurable circularly polarized planar antenna using switchable polarizer. IEEE Trans. Antennas Propag. 65(9), 4470–4477 (2017) 18. Lian, R., Tang, Z., Yin, Y.: Design of a broadband polarization-reconfigurable Fabry-Perot resonator antenna. IEEE Antennas Wireless Propag. Lett. 17(1), 122–125 (2018) 19. Singh, R.K., Basu, A., Koul, S.K.: A novel reconfigurable microstrip patch antenna with polarization agility in two switchable frequency bands. IEEE Trans. Antennas Propag. 66(10), 5608–5613 (2018) 20. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable microstrip patch antenna with switchable polarization. IETE J. Res. 66(5), 1–10 (2018) 21. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable microstrip patch antenna with polarization switching in three switchable frequency bands. IEEE Access 8, 119376–119386 (2020) 22. Lin, W., Wong, H.: Wideband circular-polarization reconfigurable antenna with L-shaped feeding probes. IEEE Antennas Wireless Propag. Lett. 16, 2114–2117 (2017) 23. Tran, H.H., Nguyen-Trong, N., Le, T.T., Park, H.C.: Wideband and multipolarization reconfigurable crossed bowtie dipole antenna. IEEE Trans. Antennas Propag. 65(12), 6968–6975 (2017) 24. Pan, P., Guan, B.: A wideband polarization reconfigurable antenna with six polarization states. In: 2018 12th International Symposium on Antennas, Propagation and EM Theory (ISAPE), pp. 1–4 (2018) 25. Wu, F., Luk, K.M.: A wideband high-efficiency polarization reconfigurable antenna for wireless communication. In: 2017 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, pp. 1371–1372 (2017) 26. Row, J., Wei, Y.: Wideband reconfigurable crossed-dipole antenna with quad-polarization diversity. IEEE Trans. Antennas Propag. 66(4), 2090–2094 (2018) 27. Zhang, Z., Sun, M., Fu, X., An, K., Chen, A.: A wideband quad-polarization-agile antenna with 1-bit phase reconfigurable Baluns. IEEE Antennas Wireless Propag. Lett. 20(9), 1671–1675 (2021) 28. Cai, Y., Gao, S., Yin, Y., Li, W., Luo, Q.: Compact-size low-profile wideband circularly polarized omnidirectional patch antenna with reconfigurable polarizations. IEEE Trans. Antennas Propag. 64(5), 2016–2021 (2016) 29. Li, M., Zhang, Z., Tang, M.-C.: A compact, low-profile, wideband, electrically controlled, tri-polarization-reconfigurable antenna with quadruple gap-coupled patches. IEEE Trans. Antennas Propag. 68(8), 6395–6400 (2020) 30. Toyoda, I., Furukawa, Y., Nishiyama, E., Tanaka, T., Aikawa, M.: Polarization agile selfoscillating active integrated antenna for spatial modulation wireless communications. IEEJ Trans. Electron. Inf. Syst. 138(6), 678–684 (2018)

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31. Hasan, M., Nishiyama, E., Toyoda, I.: A polarization switchable active integrated array antenna with a single-lambda slot-ring Gunn oscillator and PSK modulator. IEICE Commun. Express 8(12), 560–565 (2019) 32. Hasan, M., Nishiyama, E., Toyoda, I.: A microstrip-line Gunn oscillator loaded active integrated array antenna using inclined patches for polarization switching function. In: 2020 International Symposium on Antennas and Propagation (ISAP), pp. 797–798 (2021) 33. Singh, R.K., Basu, A., Koul, S.K.: Asymmetric coupled polarization switchable oscillating active integrated antenna. In: Asia-Pacific Microwave Conference (APMC), pp. 1–4. New Delhi (2016) 34. Gao, S.S., Luo, Q., Zhu, F.: Introduction to circularly polarized antennas. In: Circularly Polarized Antennas, pp. 1–28. IEEE (2014) 35. James, J.R., Hall, P.S.: Handbook of Microstrip Antennas, IEE Electromagnetic Waves Series, vol. 1 (1989) 36. Sung, Y.J., Jang, T.U., Kim, Y.-S.: A reconfigurable antenna for switchable polarization. IEEE Microw. Wireless Compon. Lett. 14(11), 534–536 (2004) 37. Parihar, M.S., Basu, A., Koul, S.K.: Polarization reconfigurable microstrip antenna. In: Asia Pac. Microwave Conference (APMC), pp. 1918–1921. Singapore (2009) 38. Chung, K., Nam, Y., Yun, T., Choi, J.: Reconfigurable microstrip patch antenna with switchable polarization. ETRI J. 28(3), 379–382 (2006) 39. Sung, Y.J.: Reconfigurable patch antenna for polarization diversity. IEEE Trans. Antennas Propag. 56(9), 3053–3054 (2008) 40. Kim, B., Pan, B., Nikolaou, S., Kim, Y.S., Papapolymerou, J., Tentzeris, M.M.: A novel single-feed circular microstrip antenna with reconfigurable polarization capability. IEEE Trans. Antennas Propag. 56(3), 630–638 (2008) 41. Yang, X., Shao, B., Yang, F., Elsherbeni, A.Z., Gong, B.: A polarization reconfigurable patch antenna with loop slots on the ground plane. IEEE Antennas Wireless Propag. Lett. 11, 69–72 (2012) 42. Hsu, S., Chang, K.: A novel reconfigurable microstrip antenna with switchable circular polarization. IEEE Antennas Wireless Propag. Lett. 6, 160–162 (2007) 43. Balanis, C.A.: Antenna Theory Analysis and Design, 2nd edn, Ch. 6, pp. 249–305. Wiley, New York 44. Data Sheet of MA4SPS402 PIN diodes, MA-Com, Application Note 45. Yoon, W.-S., Han, S.-M., Pyo, S., Baik, J., Kim, Y.: A polarization switchable microstrip patch antenna with a circular slot. In: 2008 Asia-Pacific Microwave Conference, pp. 1–4 (2008) 46. Nishamol, M.S., Sarin, V.P., Tony, D., Aanandan, C.K., Mohanan, P., Vasudevan, K.: An electronically reconfigurable microstrip antenna with switchable slots for polarization diversity. IEEE Trans. Antennas Propag. 59(9), 3424–3427 (2011) 47. Osman, M.N., Rahim, M.K.A., Yussof, M.F.M., Hamid, M.R., Majid, H.A.: Polarization reconfigurable cross-slots circular patch antenna. In: 2013 Proceedings of the International Symposium on Antennas & Propagation, pp. 1252–1255 (2013) 48. Dorsey, W.M., Zaghloul, A.I., Parent, M.G.: Perturbed square-ring slot antenna with reconfigurable polarization. IEEE Antennas Wireless Propag. Lett. 8, 603–606 (2009) 49. Mak, K.M., Lai, H.W.: Polarization reconfigurable slotted circular patch antenna. In: 2016 10th European Conference on Antennas and Propagation (EuCAP), pp. 1–4 (2016) 50. Wong, H., Lin, W., Wang, X., Lu, M.: LP and CP polarization reconfigurable antennas for modern wireless applications. In: 2017 International Symposium on Antennas and Propagation (ISAP), pp. 1–2 (2017) 51. Qin, J., Kong, X., Liu, S.: A wideband polarization reconfigurable antenna using quasicross-shaped coupling slot. In: 2018 IEEE International Conference on Computational Electromagnetics (ICCEM), pp. 1–3 (2018) 52. Yang, S., Chiu, S., Lai, C., Chen, S.: Polarization-reconfigurable slot loop antenna based on a novel varactor-loaded feeding network. In: 2016 IEEE International Symposium on RadioFrequency Integration Technology (RFIT), pp. 1–3 (2016)

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53. Sim, C., Liao, Y., Lin, H.: Polarization reconfigurable eccentric annular ring slot antenna design. IEEE Trans. Antennas Propag. 63(9), 4152–4155 (2015) 54. Moroishi, R., Nishiyama, E., Toyoda, I.: A quad-polarization agile microstrip antenna with diode loaded cross slot and microstrip line. In: 2020 International Symposium on Antennas and Propagation (ISAP), pp. 493–494 (2021) 55. Yang, Z., Yang, H., Hong, J., Li, Y.: Bandwidth enhancement of a polarization-reconfigurable patch antenna with stair-slots on the ground. IEEE Antennas Wireless Propag. Lett. 13, 579–582 (2014) 56. Zhe, Z.X., Cao, Y.F., Cheung, S.W., Yuk, T.I.: Wideband circular polarization reconfigurable slot antenna with compact size for GNSS. In: 2016 10th European Conference on Antennas and Propagation (EuCAP), pp. 1–4 (2016) 57. Huang, J., Shirazi, M., Gong, X.: A wide-band dual-polarized reconfigurable slot-ring antenna/array with a compact CPW feeding structure. In: 2017 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, pp. 1329–1330 (2017) 58. Zhu, N., Yang, X., Lou, T., Cao, Q., Gao, S.: Broadband polarization-reconfigurable slot antenna and array with compact feed network. IEEE Antennas Wireless Propag. Lett. 18(6), 1293–1297 (2019) 59. Hasan, M., Ushiroda, H., Nishiyama, E., Toyoda, I.: A polarization switchable active array antenna integrating a multiport oscillator and PSK modulators. In: Proceedings 2018 AsiaPacific Microwave Conference (APMC2018), pp. 1253–1255. Kyoto, Japan (2018) 60. Kumar, P., Abegaonkar, M.P., Koul, S.K., Basu, A.: Polarization reconfigurable active antenna. In: International Symposium on Antennas and Propagation (ISAP), pp. 1–5 (2010) 61. Singh, R.K., Basu, A., Koul, S.K.: A novel pattern-reconfigurable oscillating active integrated antenna. IEEE Antennas Wirel. Propag. Lett. 16, 3220–3223 (2017) 62. Singh, R.K., Basu, A., Koul, S.K.: Two-port reconfigurable passive radiator with switchable pattern for active antenna application. In: 2017 IEEE MTT-S International Microwave and RF Conference (IMaRC), pp. 1–5 (2017) 63. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable oscillating active integrated antenna using two-element patch array for beam switching applications. Eng. Rep. 1–10 (2019)

Chapter 6

Radiation Pattern Reconfigurable Passive and Active Planar Antennas

6.1 Introduction Radiation pattern reconfigurable antennas are used extensively in a wide variety of applications, such as mobile devices, direction finding systems, satellite communication, remote sensing, radar, etc. [1–11]. An antenna with the capability of switching its radiation pattern in different directions can save power by redirecting the radiated beam toward the designated receiver. There are several techniques to achieve radiation pattern reconfigurable active and passive antennas. According to its capabilities and functioning, radiation pattern reconfigurable antennas have continuously been investigated through numerous techniques to provide acceptable performance. There are numerous designs available in the scientific literature which focus on the pattern reconfigurability in antennas using different techniques. Here, our focus is to discuss the reconfigurable radiation beam active and passive planar antennas switchable among conical or broadside, and sum or difference patterns. Various planar designs are incorporated into the discussion.

6.2 Concept of Radiation Pattern Reconfigurability in Antennas Radiation pattern reconfiguration is based on the intentional adjustment of the spherical distribution of radiation patterns in different directions. By controlling the current distribution which is directly related to the radiation characteristic of the antenna, the radiation beam can be reconfigured. Getting good impedance matching while switching the radiation patterns (changing the current distribution) in different directions is a challenging task in realizing radiation pattern reconfigurable antennas. Reconfiguration in radiation pattern can be obtained by various techniques such as reactively loaded parasitic elements, switching with various parasitic elements © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1_6

103

104

6 Radiation Pattern Reconfigurable Passive and Active Planar …

or structures, and switching among two different modes. By using these techniques, radiation pattern can be switched between broadside and end-fire, conical and broadside, and wide beamwidth and narrow beamwidth. The radiation patterns can also be switched among broadside or conical patterns. In the phased array antennas, signal is fed to the individual antenna elements with different phases, in this way the radiation beam can be controlled. The aim of the chapter is to discuss pattern reconfigurable antennas of simple and planar geometry.

6.3 Beam Steering/Switching in Passive Planar Antennas Radiation pattern reconfigurable antennas discussed in this section are passive. This section starts with the discussion of beam steering and then discusses various designs of beam switchable antennas. Beam steering can be achieved by using a phasecontrolled array, parasitic patch or stub, mechanically moving parts or components, multilayer structures, frequency selective surfaces, phase-shifting surfaces, etc. A bent H-sectoral horn antenna with two movable metallic flaps has been reported to mechanically vary the aperture length in the H-plane direction to get beam reconfiguration [12]. A beam-reconfigurable aperture antenna consisting of a mechanically tuned flexible periodic surface has been presented in [13]. Beam reconfiguration was achieved by stretching or reshaping a flexible substrate. A beam steering structure based on a parasitic layer has been reported in [14]. The parasitic layer has rectangular-shaped metallic pixels. The geometry of this parasitic pixel surface can be changed by turning the switches ON or OFF which changes the current distribution of the antenna, resulting in a different radiation pattern. Pattern reconfigurability has been achieved by placing parasitic elements in the antenna structure [15–19]. An antenna consisting of a driven patch element surrounded by four parasitic circularshaped elements which act either as reflector(s) or director(s) depending on diode states has been reported in [15]. This configuration can switch radiation patterns in different directions. The photograph of the antenna is shown in Fig. 6.1 while radiation patterns are plotted in Fig. 6.2. Radiation patterns by selecting few switching states are reported here. A compact pattern reconfigurable planar circular disk UWB monopole antenna, capable of switching its maximum radiation over a wideband using four PIN diodes placed on two parasitic microstrip stubs is shown in Fig. 6.3. Bias configuration to get different modes is given in Table 6.1. Simulated and measured H-plane radiation patterns for three different modes are shown in Fig. 6.4. Pattern reconfiguration is also possible in Yagi-like structures using RF switches [20–23]. An idea of reconfiguration in Yagi-like antennas is illustrated in Fig. 6.5. Three elements are considered, namely an active element (fed element in the center) and two parasitic elements on both sides of it. When diodes D1 and D2 turn ON while D3 and D4 turn OFF, the antenna radiates more along the positive x-axis. A parasitic element placed on the left works as a reflector while the right one is a director. The role of parasitic elements reverses when diodes D1 and D2 turn OFF

6.4 Beam Steering/Switching in Active Planar Antennas

105

Fig. 6.1 Photograph of a pattern reconfigurable antenna with driven patch element surrounded by four parasitic circular-shaped elements. Reproduced with permission from IEEE [15]

while D3 and D4 turn ON. Another possibility to reconfigure the radiation pattern in a Yagi-like structure is to apply different phases to the parasitic elements. A radiation pattern reconfigurable planar Yagi-Uda antenna is investigated in [21]. The electrical lengths of the director and reflector elements are modified through the presence of PIN diodes in the gap contained in these elements as shown in Fig. 6.6. When PIN diodes 1 and 2 are ON and diodes 3 and 4 are OFF, the beam directs toward −X direction and it is said that “side 1” is activated. When diodes 3 and 4 are ON and diodes 1 and 2 are OFF, the beam is focused onto +X direction, and consequently “side 2” is activated. 3D Radiation patterns are illustrated in Fig. 6.7. Pattern reconfiguration can be obtained between broadside and conical patterns. Several such pattern reconfigurable antennas have been reported earlier in the scientific literature [24–34]. A compact pattern reconfigurable antenna consists of a Uslot patch and eight shorting posts as reported in [25]. Each edge of the patch is connected to two shorting posts through PIN diodes as shown in Fig. 6.8. Antenna can be operated in either monopolar patch or normal patch mode (Fig. 6.9). An antenna capable of switching between the monopole-like pattern and the boresight pattern has been reported in [26]. The idea is to disturb the slot by turning PIN diodes ON or OFF, it provides either a monopole-like or broadside pattern. This monopole antenna is fed by a coplanar waveguide (CPW) line. When the slot of the initial CPW-fed monopole antenna is disturbed, the pattern is changed to a boresight pattern. To disturb the slot, PIN diodes are placed at the proper location (Figs. 6.10).

6.4 Beam Steering/Switching in Active Planar Antennas Radiation beam reconfigurable active antennas are popular and extensively used for various applications. Again, active antennas with pattern reconfiguration features can

106

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.2 Simulated and measured radiation patterns a all PIN diodes are ON b PIN diodes A and D are OFF c PIN diode C is OFF. Reproduced with permission from IEEE [15]

be realized to reconfigure their radiation pattern in various directions. It is possible to reconfigure the radiation beam continuously by using varactor diodes or appropriate phase shifters. The radiation beam can be switched between broadside and conical or between sum and difference patterns. Oscillator-type Active antennas are used as transmitters; these antennas can be used to broadcast information and can also be used in power combining. Beam switchable active antennas can be switched between conical and broadside to cover space efficiently. A continuous wave source with a capability of spatial reconfiguration could provide better coverage over the space. A radiation pattern reconfigurable oscillator-type active antenna has been reported in [35], it can switch among four different states with two omnidirectional and two end-fire patterns. The antenna consists of two monopoles and a semi-ring radiator

6.4 Beam Steering/Switching in Active Planar Antennas

107

Fig. 6.3 Geometry of a pattern reconfigurable ultra-wideband antenna using parasitic elements; dimension: W = 38, W1 = 1.5, W0 = 2.9, W2 = 7, W3 = 14, L = 42, L0 = 14, L1 = 20, L2 = 4.5, L3 = 2.5, L4 = 2.5, L5 = 8, r = 10, h = 0.4, all dimensions are in mm. Reproduced with permission from IEEE [16]

Table 6.1 Bias configuration of the antenna Operating mode

V1 (V)

V2 (V)

V3 (V)

V4 (V)

V5 (V)

Mode-0

10

0

10

0

10

Mode-1

0

−10

0

3

0

Mode-2

0

3

0

−10

0

Reproduced with permission from IEEE [16]

as illustrated in Fig. 6.12. Radiation pattern states were switched by using a varactor and two PIN diodes. Three-dimensional field patterns are shown in Fig. 6.13. Radiation pattern reconfigurable quasi-Yagi active antenna has been reported in [36]. It consists of a square patch (in the center) and four small patches placed around it. The center patch is connected to the small patch by using two RF switches, A Gunn diode is employed at the center of the patch. Different radiation pattern states have been achieved by connecting one of the four small patches to the center patch. A new topology has been proposed to reconfigure the radiation pattern in oscillator-type active antennas [37]. The topology is shown in Fig. 6.14. The proposed topology consists of an active circuit and a passive feedback network. The active circuit is composed of FET, biasing circuits, and a DC power supply. The feedback network consists of Wilkinson power dividers, delay-line phase shifters, and radiating elements. Wilkinson power divider acts as a divider at the drain side (port 1) to divide the power equally and couple to both radiating elements, and as a combiner at the gate side (port 2) to combine the power equally coupled from the radiating elements. Wilkinson equal power divider is designed at 5.05 GHz using standard equations. Microstrip-based switched-line phase shifters are designed and connected at the drain

108

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.4 Simulated (black curves) and measured (grey curves) normalized radiation patterns in the H-plane in a Mode–0, b Mode–1, and c Mode–2; solid lines represent co-polar while dashed lines represent the cross-polar component. Reproduced with permission from IEEE [16]

side to provide phase shift to the radiating elements and compensate the phase (add extra phase) at the source side to maintain the overall phase shift of the feedback loop same in each switching state. To validate the concept, a pattern reconfigurable active integrated antenna is realized. For better understanding, the antenna design can be divided into two sections, namely the active section and the passive section. The passive section of the design is discussed first. Two-Port Passive Network To realize a pattern reconfigurable oscillating AIA, a two-port passive feedback network is designed first, and later it is integrated into the feedback path of the

6.4 Beam Steering/Switching in Active Planar Antennas

109

Fig. 6.5 An approach of pattern reconfiguration in Yagi-Uda antennas; L ≈ λ/2 (at design frequency), L1 < λ/2 (for a director), L2 > λ/2 (for a reflector)

Fig. 6.6 Planar Yagi-Uda antenna geometry and the design parameters. Dimensions: L0 = 14.5, L1 = 89.17, L2 = 81, L3 = 50.97, L4 = 48.44, a = 30.7, b = 15.2 and W = 4.51, all dimensions are in mm. Reproduced with permission from IEEE [21]

oscillator circuit. The geometry of the two-port feedback network is shown in Fig. 6.15. An array of patches (Lp = 19.2 mm and Wp = 24.0 mm) are designed by using standard formulas reported in the literature. The microstrip patches are electromagnetically fed through T-shaped microstrip lines on both sides. The optimized value of the gap (g) between the patch and T-shaped microstrip junction is 0.1 mm. Wilkinson

110

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.7 3D radiation patterns at 1.5 GHz when side 1 and side 2 are excited at a time. Reproduced with permission from IEEE [21]

Fig. 6.8 Radiation pattern reconfigurable U-slot antenna switchable between broadside and conical patterns by selecting different states of PIN diodes a geometry b photograph. Reproduced with permission from IEEE [25]

6.4 Beam Steering/Switching in Active Planar Antennas

111

Fig. 6.9 Simulated and measured normalized radiation patterns in y–z plane a state 1: diodes group A and B are OFF b state 2: diodes group A OFF while diodes group B ON. Reproduced with permission from IEEE [25]

Fig. 6.10 Radiation pattern reconfigurable CPW fed slot antenna switchable between broadside and conical patterns a geometry b photograph. Reproduced with permission from IEEE [26]

equal power divider of length 13.2 mm and width 1.4 mm is designed. The thickness (t) of the T-shaped junction is 0.25 mm. The length of the delay lines on the right side (dl1 or dl2) are 17.9 mm and on the left side (dl3 or dl4) are 45.1 mm. The two-port feedback network is fabricated on a 31-mil thick RT/Duroid 5880 substrate with a relative dielectric constant of 2.2 and loss tangent of 0.0009. The photograph of the fabricated structure is shown in Fig. 6.16. Operation Three different radiation pattern states are achieved from this structure. To achieve different states, RF switches (PIN diodes) are used. There are total of 8 MA4SPS402

112

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.11 Simulated 3-D radiation patterns a monopole-like radiation pattern in the OFF-state b boresight radiation pattern in the ON-state. Reproduced with permission from IEEE [26]

Fig. 6.12 Radiation pattern reconfigurable self-oscillating AIA. Reproduced with permission from IEEE [35]

PIN diodes denoted as D1, D2, D3, D4, D5, D6, D7, and D8. These are employed in the circuit to get three different states of the radiation pattern. When diodes D1, D4, D5, and D8 are ON and D2, D3, D6, and D7 are OFF, the antenna radiates in the broadside direction (main beam at θ = 0°), in this case, all delay lines are disconnected from the circuit. In the second state, if diodes D2, D4, D6, and D8 are ON and D1, D3, D5, and D7 are OFF, delay lines dl1 and dl3 are connected while delay lines dl2 and dl4 are disconnected, the antenna steers its main beam at θ = +30°. In the third state, when diodes D1, D3, D5, and D7 are ON and diodes D2, D4, D6, and D8 are OFF, delay lines dl2 and dl4 are connected and dl1 and dl3 are disconnected, consequently antenna steers its main beam at θ = −30°. Although, the delay lines

6.4 Beam Steering/Switching in Active Planar Antennas

113

Fig. 6.13 3D field patterns of the proposed AIA in four different states at 4.6 GHz. Reproduced with permission from IEEE [35]

Fig. 6.14 Topology of the pattern reconfigurable active antenna. Reproduced with permission from IEEE [37]

are disconnected from the circuit, they present undesired shunt impedance because these lines are open-ended. To overcome the effect of shunt impedances, circuit dimensions are optimized. Biasing circuit is realized to bias the PIN diodes; the bias circuit consists of RF chokes (100 nH), small conductive pads for soldering the wires, dc wires, and DC power supply.

114

6 Radiation Pattern Reconfigurable Passive and Active Planar … L Bias pad Z

Patch

Node D Gap (g)

X

t

Wp

D5

Wilkinson power divider

D1

dl3 Lw

D6

dl1

Node A

D2

W50

Y

100Ω resistor

W dl2

Ww

Node E

D3

D7

Node B

D4 dl4

D8

RFC

Lp

Fig. 6.15 Geometry of a two-port feedback network

Fig. 6.16 Photograph of the two-port feedback network Reference plane for port 1 Port 1

Port 2

Simulation of the passive feedback network after considering an equivalent model of the PIN diode is carried out with the full-wave EM simulator. To validate the performance, the two-port feedback network is fabricated separately and experimentally characterized. S-parameters are measured by means of a vector network analyser. Simulated and measured S-parameters are plotted in Fig. 6.17. The measured reflection coefficient for all three states is below −10 dB at the operating frequency. The measured and simulated phase of S21 is shown in Fig. 6.18. The measured S21 values at the design frequency for states 1, 2, and 3 are −4.73, −5.17, and −5.42 dB, while simulated ones are −3.73, −4.44, and −4.43 dB, respectively. The variation in the measured phase of S21 (coupling phase) among all three states is not more

6.4 Beam Steering/Switching in Active Planar Antennas

115

than 0.8° at the operating frequency. The coupling phase of the feedback network is approximately the same in all the operating states. Fig. 6.17 Simulated and measured S-parameters for a state 1 b state 2 c state 3. Reproduced with permission from IEEE [37]

116 Fig. 6.18 Simulated and measured coupling phases for a state 1 b state 2 c state 3. Reproduced with permission from IEEE [37]

6 Radiation Pattern Reconfigurable Passive and Active Planar …

6.4 Beam Steering/Switching in Active Planar Antennas

117

The reference plane is taken at the ends of the WPDs for measuring its Sparameters as shown in Fig. 6.16. The radiation patterns of the two-port network are measured by terminating one of its ports to 50 Ω. The simulated and measured normalized radiation patterns are plotted in Fig. 6.19. After verifying the switching operation of the feedback network, an active antenna is developed by integrating the two-port passive radiator in the feedback path of the oscillator circuit. The geometry and photograph of the proposed oscillating active antenna are shown in Fig. 6.20. Port 1 (drain side) is the input port and port 2 (gate side) is the coupled port. The bias voltages for the oscillator circuit are Vg = −0.5 V, Vd = 1.9 V, and drain current (Id ) = 15 mA. Two band stop filters (BSFs) are integrated in shunt to the circuit to remove other unwanted resonance modes as discussed previously. The working of BSF is already discussed in Chap. 3 (Fig. 3.13). The complete circuit is analyzed in ADS. The imported data of S-parameters of the two-port passive radiator is inserted into ADS and simulations are performed. The simulation scheme is explained in Chap. 3 (Fig. 3.10). The polar plots are plotted for all three switching states as shown in Fig. 6.21. The loop gains are 1.03∠0.04°, 1.04∠0.07°, and 1.04∠0.07° for states 1, 2, and 3, respectively. The output oscillations powers are depicted in Fig. 6.22. The proposed circuit shows stable oscillations in all three switching states. The oscillation frequencies in three different states are close to the design frequency. The radiation patterns are measured in an anechoic chamber; the same setup is used as discussed in Chap. 3. The measured radiation patterns of the pattern reconfigurable AIA in H-plane are plotted in the Fig. 6.23. The EIRP is calculated by using Friis formula, The received powers for state 1, 2 and 3 are −34.02 dBm with the main beam at θ = 0°, −37.67 dBm at θ = 30° and −37.84 dBm at θ = −30°, respectively. EIRPs are calculated and their values are 12.956, 9.306 and 9.137 dBm, for state 1, 2 and 3, respectively. The radiated powers (Pt ) are calculated as 11.456 dBm, 9.326 dBm and 9.187 dBm for states 1, 2 and 3, respectively. DC power consumptions are 40 mW (2 V × 20 mA), 36 mW (2 V × 18 mA), and 36 mW (2 V × 18 mA) for states 1, 2 and 3, respectively. The DC-to-RF conversion efficiencies for states 1, 2 and 3 are calculated as 34.95%, 23.78%, and 23.02%, respectively. The measured phase noises at 1 MHz offset from the carrier are −104.1 dBc/Hz, −103.1 dBc/Hz, and −103.6 dBc/Hz for states 1, 2 and 3, respectively as shown in Fig. 6.24. Another configuration of pattern reconfigurable active integrated antenna is realized using a similar topology. The above design was realized by keeping in mind the beam reconfigurability in the broadside direction. Another design capable of switching its beam in sum and difference pattern is realized in [38]. The two-port radiator (two-elements patch array) is designed to switch the radiation beam either in sum or in difference pattern. An array of microstrip patches is considered. The distance between the patch elements is d. Again, the two-port network is electromagnetically coupled through T-shaped microstrip lines. The geometry and photograph of the reconfigurable two-port passive radiator are shown in Fig. 6.25. Four PIN diodes namely D1, D2, D3, and D4 are integrated to switch the beam between sum and difference pattern. By connecting or disconnecting the delay lines, the radiation

118 Fig. 6.19 Simulated and measured normalized radiation patterns for H-plane cut a state 1 b state 2 c state 3. Reproduced with permission from IEEE [37]

6 Radiation Pattern Reconfigurable Passive and Active Planar …

6.4 Beam Steering/Switching in Active Planar Antennas Fig. 6.20 Pattern reconfigurable oscillator-type AIA a geometry and b photograph. (Lt1 = 83.3 mm, Lt2 = 80.4 mm). Reproduced with permission from IEEE [37]

119

120

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.21 Loop gain of the pattern reconfigurable AIA a state 1 b state 2 c state 3. Reproduced with permission from IEEE [37]

Fig. 6.22 Oscillation powers of the pattern reconfigurable AIA a state 1 b state 2 c state 3. Reproduced with permission from IEEE [37]

6.4 Beam Steering/Switching in Active Planar Antennas

121

Fig. 6.23 Normalized radiation patterns of the pattern reconfigurable AIA in y–z plane a state 1 b state 2 c state 3. Reproduced with permission from IEEE [37]

patterns can be switched among sum or difference patterns. The two-port passive radiator is designed and fabricated on a 31-mil thick RT/Duroid 5880 substrates. The bias circuit consists of RF chokes, DC block capacitors (100 pF), DC bias pads, DC wires, and a DC power supply. To achieve a sum pattern, diodes D1 and D3 must be in the forward bias while diodes D2 and D4 are in the reverse bias; in this scenario the delay lines dl1 and dl2 are disconnected from the circuit and the antenna generates a sum pattern in the broadside direction. To obtain a difference pattern, diodes D2 and D4 must be in the forward bias and diodes D1 and D3 must be in the reverse bias, delay lines dl1 and dl2 are connected to the radiator, and hence a phase difference of 180° is introduced between the patch elements, radiator generates null (difference pattern) in the broadside direction. Again, the disconnected open-ended lines provide the shunt impedance, the effect of undesired impedances is considered and accordingly dimensions are optimized. S-parameters of the two-port passive radiator are measured by using Agilent E8364C vector network analyzer (VNA). The reflection (S11 ) and coupling (S21 ) coefficients in the case of sum and difference patterns are plotted in Fig. 6.26. The

122

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.24 Measured phase noise of the pattern reconfigurable AIA at 1 MHz offset. Reproduced with permission from IEEE [37]

measured values of the reflection coefficients (S11 ) at the design frequency for the sum and difference pattern are −11.14 dB and −12.32 dB, respectively. The measured values of transmission coefficient (S21 ) for the sum and difference pattern are − 4.36 dB and −4.08 dB, respectively. The measured coupling phases at the ends of the WPD (reference plane is chosen as discussed in the previous design) are 164.58° and 165.77° for the sum and difference pattern, respectively as shown in Fig. 6.27. The measured coupling phase in both pattern cases is approximately the same at the design frequency. The normalized H-plane radiation patterns for sum and difference patterns are illustrated in Fig. 6.28. A pattern reconfigurable oscillator-type active antenna is designed by integrating the two-port passive radiator in the feedback path of the oscillator circuit. The schematic of the oscillating AIA circuit is shown in Fig. 6.29. The microstrip lines (TL1 = 78.5 mm and TL2 = 80.5 mm) are connected to the feedback passive radiator to make the overall phase in multiples of 2π and hence the oscillation condition will be fulfilled. An active device used in the circuit is (HJFET) NE3512S02. Two capacitors (10 nF each) are integrated to separate the biasing of the passive network and active circuit. The loop gains for both patterns are plotted as shown in Fig. 6.30. The values of loop gains for the sum and difference pattern are 1.03∠0° and 1.05∠0°, respectively. Figure 6.31 shows the oscillation powers of the antenna. The oscillation frequency and power for the sum pattern are 5.194 GHz and 11.016 dBm, respectively. The oscillation frequency and power for the difference pattern are 5.188 GHz and 11.993 dBm, respectively. The bias voltages and currents for the oscillator circuit are the gate voltage (Vg ) = −0.48 V, drain voltage (Vd ) = 1.8 V, and drain current (Id) = 15 mA.

6.4 Beam Steering/Switching in Active Planar Antennas

123

Fig. 6.25 Beam switchable two-port passive radiator a geometry b photograph: d = 9.50; g = 0.1; Ls = 74; dl1 = 19.7; t = 0.2; dl2 = 19.7; Lpd = 12.85; Lp = 18.52; Lind = 10.5; Wpd = 1.38; Ws = 76; Wp = 23.5; Wtl1 = 2.40; all dimensions are in mm. Reproduced with permission from IEEE [38]

124

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.26 Simulated and measured S-parameters of beam switchable two-port passive radiator a sum pattern b difference pattern. Reproduced with permission from IEEE [38]

6.4 Beam Steering/Switching in Active Planar Antennas

125

Fig. 6.27 Coupling phase of the beam switchable two-port passive radiator. Reproduced with permission from IEEE [38]

Fig. 6.28 Normalized H-plane patterns of the beam switchable two-port passive radiator. Reproduced with permission from IEEE [38]

The AIA circuit is fabricated on a 31-mil thick RT/Duroid 5880 substrate. The photograph of the complete oscillating AIA is shown in Fig. 6.32. The measured normalized H-plane radiation patterns of the antenna are plotted in Fig. 6.33. The null depth of −12.45 dB from the peak is achieved in the difference pattern of the

126

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.29 Schematic of the beam switchable oscillator-type active antenna: Lst1 = 16.5 mm, Lst2 = 28.9 mm, LSF1 = LSF2 = 11.6 mm. Reproduced with permission from IEEE [38]

Fig. 6.30 Loop gain of the beam switchable oscillator-type active antenna a sum pattern b difference pattern. Reproduced with permission from IEEE [38]

AIA circuit. The EIRPs are evaluated as 15.1712 dBm and 2.7212 dBm for the sum and difference pattern, respectively. The oscillation output powers are calculated as 11.05 dBm and 11.18 dBm for the sum and difference pattern, respectively. Summary of the results are given in Table 6.2.

6.4 Beam Steering/Switching in Active Planar Antennas

127

Fig. 6.31 Output power spectrums of the beam switchable oscillator-type active antenna a sum pattern b difference pattern. Reproduced with permission from IEEE [38]

128

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.32 Photograph of the beam switchable oscillator-type active antenna. Reproduced with permission from IEEE [38]

In the above design, although there exists a null in the difference pattern in the broadside direction, the depth of null is not sufficient from the application point of view. There is an essential requirement of high null depth in the difference pattern to use it practically. The null depth can be improved further by modifying the design of a two-port passive network [39]. The geometry and photograph of the modified circuit are shown in Fig. 6.34. The dimensions of the circuit are listed in Table 6.3. Eight PIN diodes are incorporated into the circuit to switch the radiation pattern among sum or difference patterns. To get the sum pattern, microstrip lines L1 and L4 are connected while L3 and L5 are disconnected from the circuit. Power is coupled to the patch elements in such a way that the powers are combined in the far-field, and the maximum is formed in the broadside direction (θ = 0°). In the second state, to get the difference pattern, microstrip lines L3 and L5 are connected while L1 and L4 are disconnected. Power is fed to the elements in such a way that the fields get canceled; consequently, the null is obtained in the broadside. The two-port passive radiator is separately designed and fabricated on a 31-mil thick RT/Duroid 5880 substrate.

6.4 Beam Steering/Switching in Active Planar Antennas

129

Fig. 6.33 Measured normalized H-plane radiation patterns of the beam switchable oscillator-type AIA. Reproduced with permission from IEEE [38]

Table 6.2 Summary of the results of the beam switchable oscillator-type active antenna Pattern state

EIRP (dBm)

Measured oscillation freq (GHz)

Pt (dBm)

ηdc-to-RF (%)

Phase noise (dBc/Hz) @ 1-MHz offset

Sum

15.17

5.176

11.05

35.87

−105.2

Difference

02.72

5.17

11.18

36.96

−105.6

Reproduced with permission from IEEE [38]

S-parameters of the two-port passive radiator are plotted in Fig. 6.35. The measured values of transmission coefficients for the sum and difference pattern are −5.19 dB and −5.08 dB respectively and these values are noted at the operating frequency (5.20 GHz). The measured coupling phases for the sum and difference patterns are obtained as −161.12° and −162.03°, respectively as shown in Fig. 6.36. The measured null depth from the peak is achieved as −24.7 dB as shown in Fig. 6.37. The simulated values of the loop gains for the sum and difference pattern are 1.03∠0° and 1.02∠0°, respectively. The simulated oscillation powers for the sum and difference pattern are 11.43 dBm and 9.83 dBm, respectively. A null depth of − 19.86 dB is achieved in the difference pattern from the modified reconfigurable beam switchable active antenna circuit as shown in Fig. 6.38. The EIRPs are evaluated as 14.86 dBm and −4.97 dBm for the sum and difference patterns, respectively. The oscillation output powers are calculated as 10.15 dBm and 10.70 dBm for the sum and difference patterns, respectively. The results summary of this antenna is given in Table 6.4.

130 Fig. 6.34 Modified beam switchable oscillator-type AIA [39] a geometry b photograph

6 Radiation Pattern Reconfigurable Passive and Active Planar …

6.5 Summary Table 6.3 Dimensions of the modified beam switchable oscillator-type AIA [39]

131 Parameters

Values (mm)

Parameters

Values (mm) (mm)

g

00.20

Lp

18.32

L1

28.52

Lt1

94.00

L2

16.30

Lt2

88.50

L3

16.30

t

00.30

L4

61.29

W

106.0

L5

28.52

Wp

18.32

L

90.00

6.5 Summary Reconfigurable active and passive planar antennas switchable between different radiation patterns (conical and broadside, sum and difference) were discussed in this chapter. There are various existing pattern reconfigurable antennas reported in the scientific literature, but our focus here was to discuss the beam reconfigurable and switchable planar antennas among sum or difference, and conical or broadside. Phase addition/compensation technique to achieve pattern reconfiguration in feedback loop oscillator-type active antennas have been discussed in detail. Three configurations of pattern reconfigurable oscillator-type active antenna have been elaborated in this chapter. In the first configuration, three reconfiguration states (main beam at θ = 0°, +30°, and −30°) of the radiation pattern have been achieved from the first configuration. The radiated powers were 11.456 dBm, 9.326 dBm, and 9.187 dBm for states 1, 2, and 3, respectively. The DC-to-RF conversion efficiencies for states 1, 2, and 3 were 34.95%, 23.78%, and 23.02%, respectively. The measured phase noise for all the three states was better than −103.1 dBc/Hz at 1 MHz offset from the carrier. This configuration is suitable for power combining and wireless charging. The second configuration showed that the radiation beam can be switched between sum and difference patterns by providing proper phase shift to the individual patch of a feedback radiator. A good impedance matching (|S11 | < −10 dB) was achieved for both sum and difference pattern states at the operating frequency. This configuration achieved a null depth of −12.45 dB. For various applications, a good null depth is required. Further improvement in the null depth (−19.86 dB) was obtained by modifying the feed to the patch elements of the passive radiator. The modified structure has measured oscillation power and frequency for the sum and difference pattern as 10.15 dBm, 5.214 GHz, and 10.70 dBm, 5.219 GHz, respectively. The measured phase noise of both structures was better than −105.1 dBc/Hz at a 1 MHz offset. The DC-to-RF efficiencies for both the structures were better than 34.05%. The radiation beam switchable oscillator-type active antenna configurations are suitable for security applications.

132

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.35 S-parameters of the two-port passive radiator [39] a sum pattern b difference pattern

6.5 Summary

Fig. 6.36 Measured coupling phase of the two-port passive radiator [39]

Fig. 6.37 Normalized H-plane radiation patterns of the two-port passive radiator [39]

133

134

6 Radiation Pattern Reconfigurable Passive and Active Planar …

Fig. 6.38 Measured normalized H-plane radiation pattern of the modified beam switchable oscillator-type active antenna [39]

Table 6.4 Summary of the results of the modified beam switchable oscillator-type active antenna [39] Pattern state

EIRP (dBm)

Measured oscillation freq (GHz)

Pt (dBm)

ηdc-to-RF (%)

Phase noise (dBc/Hz) @ 1-MHz offset

Sum

14.86

5.214

10.15

34.05

−105.2

Difference

−4.97

5.219

10.70

38.64

−105.1

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7. Mahlaoui, Z., Antonino-Daviu, E., Ferrando-Bataller, M.: Radiation pattern agile antenna using PIN diodes and SPDT switches. In: 2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting, pp. 1771–1772 (2020) 8. Hao, J., Ren, J., Du, X., Mikkelsen, J.H., Shen, M., Yin, Y.Z.: Pattern-reconfigurable Yagi-Uda antenna based on liquid metal. IEEE Antennas Wireless Propag. Lett. 20(4), 587–591 (2021) 9. Rahmani, F., Touhami, N.A., Taher, N., Kchairi, A.B.: Reconfigurable radiation pattern antenna with eight switchable beams in azimuth plane for WLAN wireless system. In: 2020 International Conference on Intelligent Systems and Computer Vision (ISCV), pp. 1–7 (2020) 10. Ghaffar, A., Li, X.J., Hussain, N., Awan, W.A.: Flexible frequency and radiation pattern reconfigurable antenna for multi-band applications. In: 2020 4th Australian Microwave Symposium (AMS), pp. 1–2 (2020) 11. Wang, Y., Zhao, J.P., Xu, J.: Design of 5G antenna with frequency and radiation pattern dual reconfigurable. In: 2020 International Conference on Microwave and Millimeter Wave Technology (ICMMT), pp. 1–3 (2020) 12. Jouade, A., Himdi, M., Chauloux, A., Colombel, F.: Mechanically pattern-reconfigurable bended horn antenna for high-power applications. IEEE Antennas Wireless Propag. Lett. 16, 457–460 (2017) 13. Moghadas, H., Zandvakili, M., Sameoto, D., Mousavi, P.: Beam-reconfigurable aperture antenna by stretching or reshaping of a flexible surface. IEEE Antennas Wireless Propag. Lett. 16, 1337–1340 (2017) 14. Li, Z., Mopidevi, H., Kaynar, O., Cetiner, B.A.: Beam-steering antenna based on parasitic layer. Electron. Lett. 48(2), 59–60 (2012) 15. Jusoh, M., Aboufoul, T., Sabapathy, T., Alomainy, A., Kamarudin, M.R.: Pattern-reconfigurable microstrip patch antenna with multidirectional beam for WiMAX application. IEEE Antennas Wireless Propag. Lett. 13, 860–863 (2014) 16. Aboufoul, T., Parini, C., Chen, X., Alomainy, A.: Pattern-reconfigurable planar circular ultrawideband monopole antenna. IEEE Trans. Antennas Propag. 61(10), 4973–4980 (2013) 17. Akhoondzadeh-Asl, L., Laurin, J.J., Mirkamali, A.: A novel low-profile monopole antenna with beam switching capabilities. IEEE Trans. Antennas Propag. 62(3), 1212–1220 (2014) 18. Rodriguez, J.A., Franceschetti, G., Ares, F.: Beam reconfiguration in antenna arrays by using parasitic elements. In: 2007 IEEE Antennas and Propagation Society International Symposium, pp. 3141–3144 (2007) 19. Tang, M., Zhou, B., Duan, Y., Chen, X., Ziolkowski, R.W.: Pattern-reconfigurable, flexible, wideband, directive, electrically small near-field resonant parasitic antenna. IEEE Trans. Antennas Propag. 66(5), 2271–2280 (2018) 20. Kittiyanpunya, C., Krairiksh, M.: A four-beam pattern reconfigurable Yagi-Uda antenna. IEEE Trans. Antennas Propag. 61(12), 6210–6214 (2013) 21. Sharma, S.K., Fideles, F., Kalikonda, A.: Radiation pattern reconfigurable planar YagiUda antenna. In: 2013 IEEE Antennas and Propagation Society International Symposium (APSURSI), pp. 190–191 (2013) 22. Kittiyanpunya, C., Krairiksh, M.: Pattern reconfigurable printed Yagi-Uda antenna. In: 2014 International Symposium on Antennas and Propagation Conference Proceedings, pp. 325–326 (2014) 23. Maruyama, T., Uesaka, T., Yamaguchi, S., Ohtsuka, M., Miyashita, H.: Four-element array antenna based on pattern reconfigurable Yagi-Uda antenna with complementary parasitic elements. In: 2015 IEEE 4th Asia–Pacific Conference on Antennas and Propagation (APCAP), pp. 183–184 (2015) 24. Chen, S.H., Row, J.S., Wong, K.L.: Reconfigurable square-ring patch antenna with pattern diversity. IEEE Trans. Antennas Propag. 55(2), 472–475 (2007) 25. Qin, P.-Y., Guo, Y.J., Weily, A.R., Liang, C.-H.: A pattern reconfigurable U-slot antenna and its applications in MIMO systems. IEEE Trans. Antennas Propag. 60(2), 516–528 (2012) 26. Lim, I., Lim, S.: Monopole-like and boresight pattern reconfigurable antenna. IEEE Trans. Antennas Propag. 61(12), 5854–5859 (2013)

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27. Jiang, X., Zhang, Z., Li, Y., Feng, Z.: A novel null scanning antenna using even and odd modes of a shorted patch. IEEE Trans. Antennas Propag. 62(4), 1903–1909 (2014) 28. Sun, L., Huang, W., Sun, B., Sun, Q., Fan, J.: Two-port pattern diversity antenna for 3G and 4G MIMO indoor applications. IEEE Antennas Wireless Propag. Lett. 13, 1573–1576 (2014) 29. Cui, L., Wu, W., Fang, D.-G.: Wideband circular patch antenna for pattern diversity application. IEEE Antennas Wireless Propag. Lett. 14, 1298–1301 (2015) 30. Sun, L., Zhang, G.-X., Sun, B.-H., Tang, W.-D., Yuan, J.-P.: A single patch antenna with broadside and conical radiation patterns for 3G/4G pattern diversity. IEEE Antennas Wireless Propag. Lett. 15, 433–436 (2016) 31. Yang, Y., Simorangkir, R.B.V.B., Zhu, X., Esselle, K., Xue, Q.: A novel boresight and conical pattern reconfigurable antenna with the diversity of 360° polarization scanning. IEEE Trans. Antennas Propag. 65(11), 5747–5756 (2017) 32. Lin, W., Wong, H., Ziolkowski, R.W.: Wideband pattern reconfigurable antenna with switchable broadside and conical beams. IEEE Antennas Wireless Propag. Lett. 16, 2638–2641 (2017) 33. Lin, W., Wong, H., Ziolkowski, R.W.: Circularly polarized antenna with reconfigurable broadside and conical beams facilitated by a mode switchable feed network. IEEE Trans. Antennas Propag. 66(2), 996–1001 (2018) 34. Pu, Z., Zhan, Z.: A compact and wideband microstrip antenna design with switchable pattern between conical and broadside beam. In: 2019 International Conference on Microwave and Millimeter Wave Technology (ICMMT), pp. 1–3. Guangzhou, China (2019) 35. Wu, C.-H., Ma, T.-G.: Pattern-reconfigurable self-oscillating active integrated antenna with frequency agility. IEEE Trans. Antennas Propag. 62(12), 5992–5999 (2014) 36. Xiao, S., Shao, Z., Fujise, M.: Pattern reconfigurable millimeter wave microstrip quasi-Yagi active antenna. In: 2005 Asia–Pacific Microwave Conference Proceedings, 3p (2005) 37. Singh, R.K., Basu, A., Koul, S.K.: A novel pattern-reconfigurable oscillating active integrated antenna. IEEE Antennas Wireless Propag. Lett. 16, 3220–3223 (2017) 38. Singh, R.K., Basu, A., Koul, S.K.: Two-port reconfigurable passive radiator with switchable pattern for active antenna application. In: 2017 IEEE MTT-S International Microwave and RF Conference (IMaRC), pp. 1–5 (2017) 39. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable oscillating active integrated antenna using two-element patch array for beam switching applications. Eng. Rep. 1, 1–10 (2019)

Chapter 7

Null Broadening and Steering in Passive Planar Antennas

7.1 Introduction Radiation pattern reconfigurable antennas are widely used for various wireless applications. Beam steering in the broadside or beam switching between conical and broadside or sum and difference are used to cover the space efficiently and tracking of the objects on radar. Null steering and null broadening are special cases of pattern reconfigurability. Null broadening and steering techniques have received much attention in the polluted electromagnetic scattering environment [1–11]. If an antenna can steer its null, it can be advantageous in applications where the desired signal has very low strength compared to the unwanted signal. Null steering is an efficient technique to suppress the spurious signal coming from unwanted sources. A deep null can be placed in the undesired direction to enhance the signal-to-noise ratio (SNR). A broad range of null is needed when the incident interference signal changes its direction with time. Various planar designs have been reported in the scientific literature especially on null steering and null broadening by using different radiating elements.

7.2 Null Steering Antennas There are special classes of pattern reconfigurable antennas that focus on steering a null in the radiation pattern. Due to the increasing pollution in the electromagnetic environment, synthesis methods, which allow placing one or more nulls in the radiation pattern in well-defined directions, are becoming important and are used for placing nulls in arbitrary directions to reduce interference. Null control in an antenna array can be achieved in various ways. Some common and popular configurations e.g., control of both amplitude and phase of each element of an array, control of phase-only, are available to get the control of null and beam so that the main beam remains pointing toward the wanted (desired) signal, while nulls are created in the © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1_7

137

138

7 Null Broadening and Steering in Passive Planar Antennas

Fig. 7.1 Slot antenna fed through a microstrip line

directions of undesired signal. The first technique is costly compared to the second one but there is extra freedom in the first technique to control the beam as well as the null. Another technique of getting nulls has been explained in [3], where the null steering is carried out by controlling the positions of the element. Beamforming [5] and direction-of-arrival [5, 8] considerations have already been explained previously in the literature. Wideband beam and null steering using a rectangular array of planar monopole antennas have been discussed in [9], and weights were realized by amplifiers or attenuators leading to a low-cost realization of a wideband antenna with beam and null steering capability. A comparative analysis of null steering has been done in [12]. Various null steering antennas have been realized in the scientific literature by using different techniques [13–31]. Also, various types of radiators used in the realization of such antennas are reported in the literature. Compared to other radiating elements, the slot antenna has higher immunity to the spurious signals received by the connectorized transitions and feed lines as shown in Fig. 7.1 [13]. The feed line and slot are on the opposite sides of the substrate. The signal coming towards the feed can be blocked by using a cavity on that side so that feed will not absorb or receive that unwanted signal. The next major issue arises when the incident interference signal changes its direction with time, in this situation, we must switch the null in that direction. It is challenging to direct the null in any arbitrary direction because it needs a continuous observation of interference signals. The efficient way of suppressing the interference signal in this dynamic situation is to create a broad null in the radiation pattern.

7.3 Null Broadening Techniques Null broadening is discussed in detail in this section. An approach by considering four radiating elements is discussed first. Two different configurations of four slot elements are explained in the next section.

7.3 Null Broadening Techniques

139

Fig. 7.2 Geometry of a conventional four-element slot antenna array

Four-Element Slot Antenna Array As per the above discussion, a slot radiator is used in the realization of an array antenna. The geometry of the four-element slot antenna array is shown in Fig. 7.2. Four identical slots are considered to realize an array. In general, the received signal (output) is dependent on excitation amplitudes of the elements, the separation between the elements, and phase differences. The A1, A2, A3, and A4 are the amplitude excitations of the slot element 1, 2, 3, and 4, respectively. The distance between the elements is d. The phase shifts between the elements are β2, β3, and β4 , with β1 = 0 (taken as a reference). The array factor can be written as AF =

N Σ

an e j (n−1)ψ

(7.1)

n=1

where Ψ = β + kd sin θ and k = 2π λ The array factor of four slot elements is given by AF = a1 + a2 e j (β2 +kd sin θ) + a3 e j (β3 +2kd sin θ) + a4 e j (β4 +3kd sin θ)

(7.2)

Assumption: F = 0° is the x-axis, y-axis corresponds to F = 90°. To get broad null at θ = θo , the following conditions are required Aout (θ0 ) = d Aout (θ0 )/dθ = d 2 Aout (θ0 )/dθ 2 = 0

(7.3)

140

7 Null Broadening and Steering in Passive Planar Antennas

Here, θo is the direction of null and Aout (θo ) is the normalized output voltage. For simplification, the distances between the elements are taken same (d1 = d2 = d3 = d). Six equations obtained from (7.2) and (7.3) are given below: a2 cos(β2 + kd sin θo ) + a3 cos(β3 + 2kd sin θo ) + a4 cos(β4 + 3kd sin θo ) = −1 (7.4) a2 sin(β2 + kd sin θo ) + a3 sin(β3 + 2kd sin θo ) + a4 sin(β4 + 3kd sin θo ) = 0 (7.5) a2 cos(β2 + kd sin θo ) + 2a3 cos(β3 + 2kd sin θo ) + 3a4 cos(β4 + 3kd sin θo ) = 0 (7.6) a2 sin(β2 + kd sin θo ) + 2a3 sin(β3 + 2kd sin θo ) + 3a4 sin(β4 + 3kd sin θo ) = 0 (7.7) a2 cos(β2 + kd sin θo ) + 4a3 cos(β3 + 2kd sin θo ) + 9a4 cos(β4 + 3kd sin θo ) = 0 (7.8) a2 sin(β2 + kd sin θo ) + 4a3 sin(β3 + 2kd sin θo ) + 9a4 sin(β4 + 3kd sin θo ) = 0 (7.9) For d = λ/2, and θ0 = 90°, −1 = −a2 cos β2 + a3 cos β3 − a4 cos β4

(7.10)

0 = −a2 sin β2 + a3 sin β3 − a4 sin β4

(7.11)

0 = −a2 cos β2 + 2a3 cos β3 − 3a4 cos β4

(7.12)

0 = −a2 sin β2 + 2a3 sin β3 − 3a4 sin β4

(7.13)

0 = −a2 cos β2 + 4a3 cos β3 − 9a4 cos β4

(7.14)

0 = −a2 sin β2 + 4a3 sin β3 − 9a4 sin β4

(7.15)

By using these equations, the four-element slot array is designed by considering non-uniform amplitudes to each slot element.

7.4 Four-Element Slot Array Antenna with DT Distribution

141

7.4 Four-Element Slot Array Antenna with DT Distribution 7.4.1 Array Design Four–element slot array with non-uniform amplitudes is designed and discussed in this section. The null of the antenna can be broadened by increasing the amplitude excitations of the centrally placed elements (Dolph-Tschebyscheff array concept). Initially, we have chosen the normalized amplitudes that are a1 = 1, a2 = 2.2, a3 = 2.2 and a4 = 1. Out of six Eqs. (7.4–7.9), four equations are satisfied by taking the distance between elements the same (d = λ/2) and phase differences as β2 = β3 = β4 = 0. To realize these non-uniform amplitude excitations, the combination of equal and unequal WPD is used as shown in Figs. 7.3 and 7.4, respectively. The geometry of the four-element slot array antenna is shown in Fig. 7.5. Four identical slots are etched in the ground plane, while the feed network is etched on the other side of the substrate. The dimensions of the circuit are listed in Table 7.1. The frequency of operation of the slot array antenna is 8 GHz. The slot array is fabricated on a 30-mil thick N9000 Neltec substrate. The relative permittivity of the substrate is 2.2. A photograph of the fabricated antenna is shown in Fig. 7.6.

Fig. 7.3 Wilkinson equal power divider. Reproduced with permission from IEEE [20]

Fig. 7.4 Wilkinson unequal power divider. Reproduced with permission from IEEE [20]

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7 Null Broadening and Steering in Passive Planar Antennas

Fig. 7.5 Geometry of the four-element slot array antenna with DT distribution. Reproduced with permission from IEEE [20]

Table 7.1 Dimensions of the four-element slot array antenna with DT distribution Parameters

Value (mm)

Parameters

Value (mm)

La

75.50

La10

07.05

La1

08.40

La11

05.35 74.00

La2

23.37

Wa

La3

07.17

Wa1

2.40

La4

07.35

Wa2

1.33

La5

35.75

Wa3

0.14

La6

07.20

Wa4

1.36

La7

07.40

Wa5

3.30

La8

35.80

Wa6

3.90

La9

11.80

Wa7

0.60

Reproduced with permission from IEEE [20]

7.4.2 Results The simulated and measured reflection coefficients are plotted in Fig. 7.7. The normalized H-plane radiation patterns of the four-element slot array antenna are

7.4 Four-Element Slot Array Antenna with DT Distribution

143

Fig. 7.6 Photograph of the four-element slot array antenna with DT distribution a front view b back view. Reproduced with permission from IEEE [20]

plotted in Fig. 7.8. The radiation pattern of the antenna has two nulls around θ = + 90° and − 90°. The summary of the measured and simulated results is given in Table 7.2.

Fig. 7.7 Normalized reflection coefficients of four-element slot array antenna with DT distribution. Reproduced with permission from IEEE [20]

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7 Null Broadening and Steering in Passive Planar Antennas

Fig. 7.8 Normalized H-plane radiation patterns of the four-element slot array antenna with DT distribution. Reproduced with permission from IEEE [20]

Table 7.2 Angular ranges of nulls with a null depth of ≤ − 20 dB from peak (DT distribution)

Simulated range

31° (87° to 118°)

30° (−80° to −110°)

Measured range

30° (90° to 120°)

30° (−60° to −90°)

Reproduced with permission from IEEE [20]

7.5 Four-Element Slot Array Antenna with Binomial Distribution 7.5.1 Array Design By increasing the excitation ratio of the center elements further, the null angular range can be enhanced. The analyses are done for various values of amplitudes. In this case, the normalized amplitude excitations for four-slots are taken as a1 = 1, a2 = 3, a3 = 3 and a4 = 1. It is difficult to realize this using WPD with a conventional photolithography process because the high impedance arm of a WPD results in a very thin line. The above-mentioned amplitudes are realized by using an unequal branch-line coupler (BLC). Again, we are using the same Eqs. [(7.1), (7.2)] to obtain the broad null, six equations result with d = λ/2 and β2 = β3 = β4 = 0. −1 = −3 cos β2 + 3 cos β3 − cos β4

(7.16)

0 = −3 sin β2 + 3 sin β3 − sin β4

(7.17)

7.6 Null Steering

145

0 = −3 cos β2 + 6 cos β3 − 3 cos β4

(7.18)

0 = −3 sin β2 + 6 sin β3 − 3 sin β4

(7.19)

0 = −3 cos β2 + 12 cos β3 − 9 cos β4

(7.20)

0 = −3 sin β2 + 12 sin β3 − 9 sin β4

(7.21)

These six equations are satisfied by taking amplitude excitations of A1 = 1, A2 = 3, A3 = 3, and A4 = 1. This non-uniform distribution is achieved by combining equal and unequal branch line couplers. The geometries of the equal and unequal branch-line couplers are shown in Fig. 7.9a and b, respectively. The complete circuit that achieves non-uniform amplitude distributions is shown in Fig. 7.10. In practice, the circuit achieves amplitude excitations of A1 = 1, A2 = 2.8, A3 = 2.8, and A4 = 1 due to the limitations of the fabrication process, an approximation is taken here. The geometry of the second design is shown in Fig. 7.11. In this case, null steering is also achieved along with the null broadening. Null steering is achieved by integrating RF switches. Delay lines are connected to the main lines by using RF switches (PIN diodes are employed). The disconnected open lines offer shunt impedances. The shunt impedance effects of the open-ended lines are simulated to optimize the dimensions of the complete circuit. The layout is fabricated on a 30-mil N9000 Neltec substrate. The photograph of the final antenna circuit is shown in Fig. 7.12. The size of the layout is 92 × 82 mm2 . The biasing circuit consists of RF choke inductors, bias pads, and a DC power supply Table 7.3.

7.5.2 Results The measured reflection coefficient agrees with the simulated one as shown in Fig. 7.13. When diodes D1 and D3 are ON while D2 and D4 are OFF, two symmetric nulls are obtained around θ = + 90° and + 90°. The simulated and measured normalized H-plane radiation patterns are shown in Fig. 7.14. The measured radiation pattern has broad nulls around θ = ± 90°. The summary of the results is given in Table 7.4.

7.6 Null Steering Null steering is achieved by connecting or disconnecting the delay lines from the circuit. To steer the null at 0°, both delay lines (length = λ/2) are connected to the circuit as shown in Fig. 7.11. A λ/2-line length corresponds to a phase shift of 180°.

146

7 Null Broadening and Steering in Passive Planar Antennas

Fig. 7.9 Branch line coupler a equal power divider b unequal power divider. Reproduced with permission from IEEE [20]

Now, the phase excitations to the elements are β1 = 0°, β2 = 180°, β3 = 0°, and β4 = 180°. In this case, all six equations are satisfied. −1 = 3 cos β2 + 3 cos β3 + cos β4

(7.22)

0 = 3 sin β2 + 3 sin β3 + sin β4

(7.23)

0 = 3 cos β2 + 6 cos β3 + 3 cos β4

(7.24)

0 = 3 sin β2 + 6 sin β3 + 3 sin β4

(7.25)

7.6 Null Steering

147

Fig. 7.10 Geometry to achieve non-uniform amplitudes (binomial distribution). Reproduced with permission from IEEE [20]

0 = 3 cos β2 + 12 cos β3 + 9 cos β4

(7.26)

0 = 3 sin β2 + 12 sin β3 + 9 sin β4

(7.27)

Results In the first case, when diodes D1 and D3 are ON while D2, and D4 are OFF, the antenna generates its nulls around θ = ± 90° as shown in Fig. 7.14. In the steering case, if diodes D1 and D3 are OFF while D2 and D4 are ON, the antenna steers its nulls towards θ = 0° and 180°. The simulated and measured results show shifting of nulls at θ = 0° and 180° as depicted in Fig. 7.15.

148

7 Null Broadening and Steering in Passive Planar Antennas

Fig. 7.11 Geometry of the four-element slot array antenna with binomial distribution. Reproduced with permission from IEEE [20]

Fig. 7.12 Photograph of the four-element slot array antenna with binomial distribution a front view b back view. Reproduced with permission from IEEE [20]

7.7 Summary

149

Table 7.3 Dimensions of the four-element slot array antenna with binomial distribution Parameters

Value (mm)

Parameters

Value (mm)

Lb

92.00

Lb11

05.45

Lb1

07.10

Wb

82.00

Lb2

07.15

Wb1

02.40

Lb3

38.73

Wb2

03.80

Lb4

06.16

Wb3

02.40

Lb5

05.80

Wb4

02.60

Lb6

33.30

Wb5

00.20

Lb7

11.90

Wb6

00.70

Lb8

16.80

Wb7

02.00

Lb9

30.61

Wb8

02.00

Lb10

14.22

Reproduced with permission from IEEE [20]

Fig. 7.13 Reflection coefficients of the four-element slot array antenna with binomial distribution. Reproduced with permission from IEEE [20]

7.7 Summary Null broadening and steering in passive planar antennas are discussed in this chapter. There are various techniques to steer the null, but here we discussed one technique in detail. Null broadening was achieved analytically and validated through measurements. Two configurations of the slot array antenna were designed and discussed.

150

7 Null Broadening and Steering in Passive Planar Antennas

Fig. 7.14 Normalized H-plane radiation patterns of the four-element slot array antenna with binomial distribution. Reproduced with permission from IEEE [20] Table 7.4 Angular ranges of nulls with a null depth of ≤ − 20 dB from peak (binomial distribution)

Simulated range

50° (60° to 110°)

41° (−77° to −118°)

Measured range

52° (70° to 122°)

45° (−80° to −125°)

Reproduced with permission from IEEE [20]

Fig. 7.15 Normalized H-plane radiation patterns showing null steering. Reproduced with permission from IEEE [20]

References

151

Slot antennas were considered due to their advantages over other radiating elements. Slot array antennas with non-uniform amplitude excitations are developed to broaden the angular ranges of nulls. Both array configurations consist of four identical slot elements with different amplitude excitations. The broad nulls (null depth ≤ −20 dB from peak) were achieved in the angular range of 30° from the first design (DT distribution). Further broadening of nulls has been achieved. The second design (Binomial distribution) achieved an angular range of 45°. Null steering has also been achieved in the second design. As observed from this study, when we increase the amplitude of the center elements of an array, it indirectly increases the amplitude ratio which is not simple to achieve practically. Issues arise when we increase the amplitude ratio; it is hard to realize such power divisions. There is a limit where we have to stop since we cannot increase the null broadening beyond a limit.

References 1. Shore, R.A.: Nulling at symmetric pattern location with phase-only weight control. IEEE Trans. Antennas Propag. AP-32, 530–533 (1984) 2. Steyskal, H., Shore, R.A., Haupt, R.L.: Methods for null control and their effects on the radiation pattern. IEEE Trans. Antennas Propag. AP-34(3) (1986) 3. Ismail, T.H., Dawoud, M.M.: Null steering in phased arrays by controlling the element positions. IEEE Trans. Antennas Propag. 39(11) (1991) 4. Gao, T., Guo, Y., Li, J.: Wide null and low sidelobe synthesis for phased array antennas. In: Proceedings of Asia Pacific Microwave Conference, vol. 1, pp. 42–45. Hsinchu, Taiwan (1993) 5. Godara, L.C.: Application of antenna arrays to mobile communications. II. Beam-forming and direction-of-arrival considerations. Proc. IEEE 85(8), 1195–1245 (1997) 6. Ohira, T., Gyoda, K.: Electronically steerable passive array radiator antennas for low-cost analog adaptive beamforming. In: Proceedings 2000 IEEE International Conference on Phased Array Systems and Technology (Cat. No. 00TH8510), pp. 101–104 (2000) 7. Heath, T.: Simultaneous beam steering and null formation with coupled, nonlinear oscillator arrays. IEEE Trans. Antennas Propag. 53(6), 2031–2035 (2005) 8. Taillefer, E., Hirata, A., Ohira, T.: Direction-of-arrival estimation using radiation power pattern with an ESPAR antenna. IEEE Trans. Antennas Propag. 53(2), 678–684 (2005) 9. Uthansakul, M., Bialkowski, M.E.: Wideband beam and null steering using a rectangular array of planar monopoles. IEEE Microw. Wireless Compon. Lett. 16(3), 116–118 (2006) 10. Goshi, D.S., Leong, K.M.K.H., Itoh, T.: Interleaved retrodirective sub-arrays for null-steering interference rejection. In: 2007 IEEE/MTT-S International Microwave Symposium, pp. 1719– 1722 (2007) 11. Albani, M., et al.: A 2-D electronic beam steering phased array for point-multipoint communication applications. In: 2007 European Microwave Conference, pp. 1629–1632 (2007) 12. Qamar, R.A., Khan, N.M.: Null steering, a comparative analysis. In: 2009 IEEE 13th International Multitopic Conference, pp. 1–5 (2009) 13. Parihar, M.S., Basu, A., Koul, S.K.: Efficient spurious rejection and null steering using slot antennas. IEEE Antennas Wireless Propag. Lett. 10, 207–210 (2011) 14. Yong, S., Bernhard, J.T.: A pattern reconfigurable null scanning antenna. IEEE Trans. Antennas Propag. 60(10), 4538–4544 (2012) 15. Yong, S., Bernhard, J.T.: Reconfigurable null scanning antenna with three dimensional null steer. IEEE Trans. Antennas Propag. 61(3), 1063–1070 (2013) 16. Jiang, X., Zhang, Z., Li, Y., Feng, Z.: A novel null scanning antenna using even and odd modes of a shorted patch. IEEE Trans. Antennas Propag. 62(4), 1903–1909 (2014)

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17. Li, Y., Zhang, Z., Deng, C., Feng, Z.: A simplified hemispherical 2-D angular space null steering approach for linearly polarization. IEEE Antennas Wireless Propag. Lett. 13, 1628–1631 (2014) 18. Chaipanya, P.: Null steering using low profile weights for base station antenna. In: 2015 IEEE 6th International Symposium on Microwave, Antenna, Propagation, and EMC Technologies (MAPE), pp. 179–183 (2015) 19. Deng, C., Li, Y., Zhang, Z., Feng, Z.: A hemispherical 3-D null steering antenna for circular polarization. IEEE Antennas Wireless Propag. Lett. 14, 803–806 (2015) 20. Singh, R.K., Basu, A., Koul, S.K.: Efficient null broadening and steering using slot antenna array for radar applications. In: 2016 Asia–Pacific Microwave Conference (APMC), pp. 1–4. New Delhi (2016) 21. Babakhani, B., Sharma, S.K.: Dual null steering and limited beam peak steering using a triple mode microstrip patch antenna. In: 2016 IEEE International Symposium on Antennas and Propagation (APSURSI), pp. 2141–2142 (2016) 22. Artiga, X.: Null-steering reflect arrays for 5G backhaul networks limited by interference. In: 2017 11th European Conference on Antennas and Propagation (EUCAP), pp. 439–442 (2017) 23. Chatterjee, S., Chatterjee, S., Majumdar, A.: Edge element controlled null steering in beamsteered planar array. IEEE Antennas Wireless Propag. Lett. 16, 2521–2524 (2017) 24. Noguchi, T., Takyu, O., Fujii, T., Ohtsuki, T., Sasamori, F., Handa, S.: Secure information sharing with mirroring null steering through untrusted relay with two antennas. In: 2018 IEEE Radio and Wireless Symposium (RWS), pp. 203–205 (2018) 25. Laohapensaeng, T.: Adaptive null steering circular parallel plate capacitor array antenna. In: 2018 15th International Conference on Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology (ECTI-CON), pp. 788–792 (2018) 26. Gao, C., Lu, Z.L., Liu, M.: Design of frequency and pattern reconfigurable wideband semicircular slot ring antenna. In: 2019 4th International Conference on Mechanical, Control and Computer Engineering (ICMCCE), pp. 13–134 (2019) 27. Potelon, T., Ettorre, M., Le Coq, L., Bateman, T., Francey, J., Sauleau, R.: Reconfigurable CTS antenna fully integrated in PCB technology for 5G backhaul applications. IEEE Trans. Antennas Propag. 67(6), 3609–3618 (2019) 28. Zhang, Z.-K., Sun, L.-J., Xu, L.: Multiple beamforming with null steering based on improved invasive weed optimization. In: 2020 12th International Conference on Knowledge and Smart Technology (KST), pp. 36–40 (2020) 29. Tamura, J., Arai, H.: Improvement of null steering antenna using two parasitic elements. In: 2020 IEEE Asia–Pacific Microwave Conference (APMC), pp. 950–952 (2020) 30. Tamura, J., Arai, H.: Compact null steering antenna with two parasitic elements for angle-ofarrival estimation. IEEE Antennas Wireless Propag. Lett. 19(7), 1123–1126 (2020) 31. Hamza, A., Attia, H.: Fast beam steering and null placement in an adaptive circular antenna array. IEEE Antennas Wireless Propag. Lett. 19(9), 1561–1565 (2020)

Chapter 8

Compound Reconfigurable Planar Antennas

8.1 Introduction The need for multifunction antennas for modern wireless systems is increasing day by day. The multifunction antennas offer a wide range of services. A multifunction antenna can be a compound reconfigurable antenna by which one can dynamically reconfigure more than one radiation characteristic e.g., frequency and polarization, frequency and pattern, polarization and pattern, or a combination of all three characteristics. Modern wireless communication systems require multifunction antennas to fulfil their new wireless requirements. For realizing multifunction antennas, microstrip planar antennas are popular among others. The advantages of microstrip patch antennas have already been discussed in the previous chapters. As mentioned earlier, a compound reconfigurable antenna can reconfigure any two or all three characteristics simultaneously, but the focus of this chapter is on the simultaneous reconfiguration of both frequency and polarization of the antenna. The benefits of compound reconfigurable antennas for current and future wireless systems are discussed.

8.2 Compound Reconfigurable Antennas Here we are discussing compound reconfigurable antennas altering frequency and polarization only. A combined frequency and polarization reconfigurable antenna can provide more flexibility than a single polarization or frequency reconfigurable antenna; it provides remarkable benefits for various wireless communication systems [1–13]. For example, software defined radios (SDRs), which may operate at different frequencies and/or polarizations. The use of carrier aggregation (CA) has been initiated in the current wireless systems such as LTE and 5G. In CA, a device can transmit or receive on several channels simultaneously with different polarizations © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1_8

153

154

8 Compound Reconfigurable Planar Antennas

for increased data rate. The combinations of frequency and polarization reconfigurable antennas have also been reported in the scientific literature. The design of a reconfigurable microstrip patch antenna with frequency and polarization diversity functions has been reported in [1]. A U-slot is inserted into the patch and an RF switch (Diode 1) is incorporated to achieve frequency agility. Polarization diversity between LP and RHCP is achieved from the structure by using two RF switches (Diodes 2 and 3). Here, LP is obtained at one frequency while RHCP at another frequency. Multifunction antennas and their uses have been discussed in detail in [2]. The configuration of an aperture-coupled microstrip antenna consisting of two stacked dielectric substrates has been presented in [4]. A 50 Ω feed line is printed on the bottom layer. Feed is connected to an open stub line through an impedance transformer and located at the end of this open stub line, a PIN diode (D1) connected with another stub line. The ground plane is located at the top layer of the lower substrate; a circular ring slot is embedded into the ground plane and a PIN diode (D2) is placed on the slot. A square radiating patch is printed on the top layer of the upper substrate. When diodes D1 and D2 turn ON, the antenna radiates horizontal polarization while diodes D1 and D2 are OFF, it radiates vertical polarization. In this structure, both horizontal and vertical polarization is achieved at different frequencies. More freedom can be introduced in the antenna structure to switch frequency and polarization independently e.g., antenna can generate different polarizations at more than one frequency band. Frequency and polarization reconfigurable stub-loaded microstrip patch antennas have been reported in [5, 8]. In [5], the reported antenna consists of a square microstrip patch with a single RF feed positioned along the diagonal line as shown in Fig. 8.1. The center of each radiating or non-radiating edge of the patch is connected to a shorting post via PIN diode for changing the polarization and two varactor diodes for tuning the frequency. Horizontal, vertical, or 45° linear polarizations have been achieved from this antenna structure. Each polarization of the antenna at different frequencies can be independently tuned by varying the bias across the varactor diodes. Reflection coefficients for state 1 and state 2 are plotted here in Figs. 8.2 and 8.3 respectively. Another frequency and polarization reconfigurable microstrip patch antenna is demonstrated in [8] as shown in Fig. 8.4. Reconfigurability has been achieved in a fractional bandwidth of around 40% using 12 varactor diodes while allowing selection between RHCP, LHCP, and LP. There is a freedom to switch three different polarizations at various frequencies independently. The reflection coefficient and axial ratio are plotted for RHCP in Fig. 8.5 for different combinations of bias voltages across the varactor diodes. The simulated and measured radiation patterns in the x–z plane are plotted in Fig. 8.6 while the simulated and measured gain is plotted in Fig. 8.7. Although the polarization switching has been achieved for a wide frequency range in a single operating band, it offers limited bandwidth. To accommodate more channels, more bandwidth is required in a single switchable band. A frequency and polarization reconfigurable antenna reported in [10] offers sufficient bandwidth to cover more channels. The design and operating principle of the antenna are discussed in detail.

8.3 Reconfigurable Microstrip Patch Antenna with Polarization …

155

Fig. 8.1 Continuous frequency switchable microstrip patch antenna with polarization diversity. Reproduced with permission from IEEE [5]

Fig. 8.2 Measured and simulated reflection coefficients for different bias voltages across varactor diodes for State 1. Reproduced with permission from IEEE [5]

8.3 Reconfigurable Microstrip Patch Antenna with Polarization Agility in Two Switchable Frequency Bands The geometry and photograph of a reconfigurable microstrip patch antenna with polarization agility in two switchable frequency bands are shown in Fig. 8.8 [10]. To design a reconfigurable microstrip patch antenna with polarization reconfigurability in two switchable bands, a standard patch antenna at the operating frequency of 5.2 GHz was designed first by using standard formulas. An additional small patch

156

8 Compound Reconfigurable Planar Antennas

Fig. 8.3 Measured and simulated reflection coefficients for different bias voltages across varactor diodes for State 2. Reproduced with permission from IEEE [5]

Fig. 8.4 Polarization and frequency reconfigurable stub-loaded microstrip patch antenna. Reproduced with permission from IEEE [8]

or stub is then connected to the main patch. By connecting the additional patch, the frequency can be increased or decreased from the reference (original resonance) frequency. The increase or decrease in the frequency depends on various design parameters such as the length and width of the stub, the gap between the main patch and stub, and the position of the RF switch placed between them. The concept of frequency shift while adding an additional patch or stub has been explained in Sect. 4.3.1 of chapter 4.

8.3 Reconfigurable Microstrip Patch Antenna with Polarization …

157

Fig. 8.5 a Reflection coefficient and b axial ratio (AR) for different combinations of bias voltages (V1 , V2 ) for RHCP operation. Reproduced with permission from IEEE [8]

Fig. 8.6 Normalized radiation patterns (xz-plane) for CP operating at 3.01 GHz. Reproduced with permission from IEEE [8]

158

8 Compound Reconfigurable Planar Antennas

Fig. 8.7 Simulated and measured gain of the fabricated antenna operating with CP. Reproduced with permission from IEEE [8]

An antenna is designed in such a way that polarization switching can be obtained in two switchable frequency bands. Polarization switching has been achieved between LHCP and RHCP. To achieve this, the switch is positioned in the center to maintain symmetry in the structure to get LHCP and RHCP with good axial ratio and impedance matching within the operating bands. The antenna is designed at two switchable bands (center frequencies are 5.2 and 5.7 GHz). The CP performance (good axial ratio) of the structure is mostly decided by two parameters, the side length of the L-shaped truncated corner and the gap between the small parasitic patch and the truncated corner. These parameters are also varied to get a good axial ratio and impedance matching in both bands. The antenna consists of the rectangular patch (main patch) truncated through an Lshaped cut at all its corners and a stub which is connected to the main patch through a PIN diode, truncated at two corners as shown in Fig. 8.8. Six small conductive patches of size 1.5 × 1.5 mm are connected through PIN diodes with the spacing of 0.3 mm from the truncated corners. The specialty of the structure is that three different polarization states can be achieved at two different frequency bands without using any extra matching network. A simple bias circuitry is etched to bias the RF switches. Seven PIN diodes (D1, D2, D3, D4, D5, D6, and D7) are employed in the circuit. To achieve one sense of CP at 5.2 GHz, the diagonally placed pair of small conductors are disconnected from the main patch, and to change the sense of polarization, other diagonal pairs can be disconnected. To achieve CP at 5.7 GHz, diode D5 must be turned ON so that additional patch would be connected to the main patch. Two small conductors at the diagonal ends are disconnected from the circuit (either D3, D6 are OFF or D1, D7 are OFF). By disconnecting these two diagonal pairs, two orthogonal modes can be generated at 5.7 GHz. All polarization states with diode ON/OFF conditions are given in Table 8.1. The reflection coefficients are measured by means of an Agilent E8364C vector network analyser (VNA). The simulated and measured reflection coefficients are plotted in Fig. 8.9. The frequency is shifted slightly in the LP mode, and it is due to an increment in the overall physical size (all four conductors are connected to the main patch) of the antenna compared to that with LHCP or RHCP mode. The small shift in the simulated and measured results is due to the fabrication imperfections.

8.3 Reconfigurable Microstrip Patch Antenna with Polarization …

159

Fig. 8.8 Reconfigurable microstrip patch antenna with switchable polarization at dual frequencies a geometry b photograph: g = 0.3 mm, ga = 0.3 mm, L = 65 mm, lpa = 18.65 mm, ladda = 4 mm, lt = 11.9 mm, Wf = 2.4 mm, W = 60 mm, Wadda = 18.8 mm, Wpa = 18.8, Wt = 0.58 mm, lsa = 1.5 mm. Reproduced with permission from IEEE [10]

The radiation patterns are measured in the anechoic chamber by using a wideband double-ridged horn as a transmitter and the designed antenna as a receiver. The simulated and measured normalized radiation patterns are plotted in Fig. 8.10. The summary of the results is given in Table 8.2. The axial ratio bandwidths are plotted in Fig. 8.11a, b. The measured realized gain for all three modes is plotted in Fig. 8.11c. As discussed in the previous section, the requirement for bandwidth is increasing day by day to accommodate more channels, the bandwidth is enhanced for the current

160

8 Compound Reconfigurable Planar Antennas

Table 8.1 Polarization states of the antenna Polarization

Freq. (GHz)

D1

D2

D3

D4

D5

D6

D7

LHCP

5.2

ON

OFF

OFF

ON

OFF

OFF

OFF

LP

5.2

ON

ON

ON

ON

OFF

OFF

OFF

RHCP

5.2

OFF

ON

ON

OFF

OFF

OFF

OFF

LHCP

5.7

ON

ON

OFF

ON

ON

OFF

ON

LP

5.7

ON

ON

ON

ON

ON

ON

ON

RHCP

5.7

OFF

ON

ON

ON

ON

ON

OFF

Reproduced with permission from IEEE [10]

geometry. The impedance and axial ratio bandwidths are enhanced by changing the feed of the antenna. Proximity coupled feed is used to excite the antenna. In proximity feeding, the feed line is sandwiched between the patch and the ground plane. The radiating patch is on the top of the substrate and ground plane is on the bottom. The power from the feed is coupled to the patch electromagnetically, as opposed to direct contact. Proximity coupling is capacitive in nature whereas direct contact is inductive. This difference in the coupling affects the matching (impedance bandwidth). The inductive coupling of the edge and probe-fed structures limits the thickness of the material. Thus, the bandwidth of a proximity coupled antenna is inherently wider compared to the direct contact fed antennas. Figure 8.12 shows the layout of proximity fed microstrip patch. The equivalent circuit of the proximity-fed patch is shown in Fig. 8.13. Coupling capacitor Cf is in series with the parallel R-L-C resonant circuit. The microstrip feed is open in the end. The bandwidth can also be enhanced by increasing the height of the substrate but there is a limitation for considering the thickness of the substrate; the generation of the surface waves limits the thickness of the substrate. The bandwidth increases with an increase in the thickness of the substrate. The antenna has multilayers in case of proximity coupled feed, it needs proper alignment for fixing all the layers and there should be no air gap between the layers because it may affect the matching. A proximity coupled antenna prototype has been designed on a Neltec N9000 substrate as shown in Fig. 8.14. Initially, both substrates have been taken with the same thickness (0.762 mm) and relative permittivity (2.2). The measured ARBWs were 2.16% and 1.05% across the lower and higher band, respectively. Later, the thickness (h1) of the bottom substrate was increased to 1.524 mm, ARBWs were further improved, and the values were 2.57% and 1.61% in the lower and higher band, respectively. This modified antenna has two switchable bands having center frequencies of 5.28 and 6.1 GHz. The operating principle of the antenna is the same as that of the antenna with microstrip feed. The simulated and measured reflection coefficients for two different polarization modes (LHCP and LP) across the lower and higher frequency band were measured. In addition, the normalized radiation patterns and the axial ratio were also measured. A small shift in the measured and simulated results were

8.3 Reconfigurable Microstrip Patch Antenna with Polarization …

161

(a)

(b)

(c)

(d)

(e)

(f)

Fig. 8.9 Simulated and measured reflection coefficients against frequency. a LHCP across the lower band. b LP across the lower band. c RHCP across the lower band. d LHCP across the higher band. e LP across the higher band. f RHCP across the higher band. Reproduced with permission from IEEE [10]

162

8 Compound Reconfigurable Planar Antennas

(a)

(b)

(c)

(d)

(e)

(f)

Fig. 8.10 Simulated and measured normalized radiation patterns a LHCP at 5.2 GHz b LP at 5.2 GHz c RHCP at 5.2 GHz d LHCP at 5.7 GHz e LP at 5.7 GHz f RHCP at 5.7 GHz. Reproduced with permission from IEEE [10]

8.4 Reconfigurable Microstrip Patch Antenna …

163

Table 8.2 Summary of the results of the microstrip-fed antenna Polarization state

Impedance BW (MHz)

3 dB ARBW (MHz)

Gain (dBi)

Simu.

Meas.

Simu.

Meas.

Simu.

Meas.

LHCP_lower band

5128–5263

5138–5330 (3.7%)

5172–5209

5148–5206 (1.11%)

7.81

6.49

LP_lower band

5086–5147

5106–5188 (1.57%)





7.20

6.41

RHCP_lower band

5126–5264

5126–5239 (2.17%)

5173–5212

5156–5220 (1.23%)

7.83

6.39

LHCP_higher band

5672–5711

5681–5770 (1.56%)

5686–5696

5670–5709 (0.68%)

6.88

6.37

LP_higher band 5654–5694

5692–5732 (0.71%)





6.71

6.20

RHCP_higher band

5650–5752 (1.78%)

5686–5696

5680–5712 (0.56%)

6.89

6.33

5673–5712

Reproduced with permission from IEEE [10]

observed which could be due to the air gap between the top and bottom substrates. The LHCP and RHCP pattern must have symmetry but, in the measurement, both patterns are not exactly similar, it could be due to the misalignment of the substrates. The results are summarized in Table 8.3.

8.4 Reconfigurable Microstrip Patch Antenna with Polarization Agility in Three Switchable Frequency Bands Another compound reconfigurable antenna switchable between frequency and polarization is discussed in detail in this section. Initially a polarization switchable reconfigurable microstrip patch antenna at a single frequency band is designed and then it is extended further to achieve polarization switching in three different switchable frequency bands by using corner connection/disconnection and additional patch connection/disconnection techniques. Three switchable operating bands are obtained with center frequencies of 5.1 GHz (first band), 5.45 GHz (second band), and 6.3 GHz (third band). The antenna can switch between left-hand circular polarization (LHCP), right-hand circular polarization (RHCP), and linear polarization (LP) at all three switchable frequency bands. The geometry of a polarization switchable reconfigurable microstrip patch antenna at a single frequency band is illustrated in Fig. 5.3.

164 Fig. 8.11 a Simulated and measured ARBW across the lower band, b measured and simulated and ARBW across the higher band and c measured realized gain. Reproduced with permission from IEEE [10]

8 Compound Reconfigurable Planar Antennas

8.4 Reconfigurable Microstrip Patch Antenna …

165

Fig. 8.12 Proximity fed microstrip patch antenna

Patch

feed h2

Fig. 8.13 Equivalent circuit of a proximity fed patch antenna

h1

Cf

L

C

R

After realizing a single band polarization reconfigurable antenna, polarization reconfigurability is achieved at two other frequencies by combining two techniques (corner truncation technique and stub connection/disconnection technique). Enhancement in the impedance and axial ratio bandwidth is also aimed in this design for use in modern wireless applications where more bandwidth is required. The microstrip antenna suffers from narrow impedance bandwidth. The impedance bandwidth of microstrip antennas can be enhanced by using various techniques explained in [14–17]. One of the simplest techniques for increasing bandwidth is to increase the thickness of the dielectric substrate but it limits it up to 4–5%. There are other techniques such as stacking the patches with slightly different dimensions to get two nearer resonances [14]. Impedance bandwidth can also be enhanced by using the proximity coupled feeding techniques [15]. In the proximity feeding technique, the feed line is sandwiched between the ground plane and the patch. The patch is etched on top of the substrate and the ground plane is on the bottom side of the substrate. Bandwidth can also be enhanced by modifying the shape of the feed line so that the coupling to the patch is modified. Impedance bandwidth can also be enhanced by using a tapered feed. Various taper feeds such as triangular, exponential, continuous and stepped have been explored earlier [14, 17]. In this design, a triangular tapering feed is used to couple signals to the patch which improves the matching in a broad frequency range. Now, this design is extended to switch between different polarization states at three different frequency bands. To achieve this, corner truncation techniques are applied to get LHCP or RHCP from a patch. The corner truncation technique is already explained in the above section. To

166

8 Compound Reconfigurable Planar Antennas

Fig. 8.14 Proximity coupled reconfigurable antenna a geometry b photograph. g = 0.3 mm, gb = 0.3 mm, lb = 65 mm, lpb = 17.8 mm, laddb = 4 mm, lf = 28 mm, Wb = 60 mm, Waddb = 18.15 mm, Wpb = 18.15, lsb = 2.2 mm. Reproduced with permission from IEEE [10]

get polarization switching between LHCP and RHCP, two RF switches are placed onto the truncated corners to connect/disconnect small conductors to/from the patch, respectively. By doing this, another resonance is achieved which is different from that obtained with loading small stubs. To get the third resonance from the circuit, a stub is connected to the main patch through an RF switch as shown in Fig. 8.15a. After optimizing the geometry, three different switchable resonances are achieved by turning RF switches ON or OFF. The effects of varying the dimensions of an additional patch (stub) are analyzed. A detailed analysis is carried out because there is a range of frequencies that we can obtain by varying the additional patch parameters. All four parameters (length of the stub, Lstub, width of the stub, Wstub, gap between the main patch and stub, g, and the position of switch placed between main patch

8.4 Reconfigurable Microstrip Patch Antenna …

167

Table 8.3 Results summary of the proximity coupled antenna Polarization state

Impedance BW (MHz)

3 dB ARBW (MHz)

Gain (dBi)

Simu.

Meas.

Simu.

Meas.

Simu.

Meas.

LHCP_lower band

5138–5521

5131–5544 (7.82%)

5220–5322

5182–5325 (2.70%)

6.76

5.96

LP_lower band

5126–5258

5075–5337 (4.96%)





6.56

5.81

RHCP_lower band

5131–5506

5141–5528 (7.32%)

5223–5326

5184–5320 (2.57%)

6.68

5.91

LHCP_higher band

5944–6228

5980–6241 (4.27%)

6086–6120

6050–6148 (1.61%)

5.85

5.54

LP _higher band

5948–6083

5942–6181 (3.91%)





5.77

5.40

RHCP_higher band

5939–6221

5993–6255 (4.29%)

6084–6118

6042–6147 (1.72%)

5.81

5.49

Reproduced with permission from IEEE [10]

and stub, P) are considered in this analysis which affects the resonance frequency of the whole antenna circuit as shown in Fig. 8.15a. The first parameter varied in this study is the length of the additional patch while keeping other parameters constant. Initially, the gap between the main and additional patch (g) is taken as 0.4 mm, and the width of the stub (Wstub) is taken as 16.7 mm (same as the width of the main patch). Simulation is carried out for various values of length, out of which, reflection coefficients are plotted at five different values. From Fig. 8.16, the reflection coefficient does not show significant changes in its value and resonance peak by changing the stub length. A slight shift in the resonance is noticed and it is due to the small change happening in the effective length of surface current on the additional patch. A significant change in resonance frequency happens when the width of the stub varies. When the width of the stub increases, the surface current increases. Also, the change in the direction of the surface current is observed by varying the width. Based on an effective length of the surface current flow, resonance occurs below or higher than the reference frequency. The reference frequency is the original frequency of the main patch without connecting a stub. This phenomenon is explained in [10]. Simulated reflection coefficients after varying the width of the stub are shown in Fig. 8.17. The third parameter which is varied in this analysis is the gap between the main patch and the stub. The gap is varied from 0.4 to 18 mm, while other parameters remain fixed. From Fig. 8.18, when g = 0.4 mm, the resonance is at high frequency compared to the reference frequency but at g = 14 mm, the resonance frequency becomes the same as the reference frequency, because the surface current which is flowing on the stub does not impact on the effective length of the antenna. Further with an increase in the gap width, resonance frequency starts decreasing and at g = 18 mm, the antenna is resonating at a frequency that is below the reference frequency. In

168

8 Compound Reconfigurable Planar Antennas

Fig. 8.15 Proximity coupled polarization reconfigurable antenna at three switchable frequency bands [12] a geometry b photograph

starting, surface current decreases with an increase in the gap width till g = 14 mm, but when we further increase the gap, surface current changes its direction and adds in-phase with the current which is flowing onto the surface of the main patch, as a result, the effective surface current starts increasing, and resonance frequency starts decreasing. In the above analysis, the position of the RF switch was kept fixed, and it was at the center of the radiating edge of the patch. The position of the switch is varied, and reflection coefficients are plotted at different positions of the switch as shown in Fig. 8.19. It is assumed that the switch is in the center at P = 0 mm. By varying the position of the switch, dual-band or tri-band behavior can be obtained and it is due to the creation of an asymmetry in the structure. When we place the switch in the centre then only, we can achieve the symmetric nature for LHCP and RHCP states.

8.4 Reconfigurable Microstrip Patch Antenna … Fig. 8.16 Simulated reflection coefficients for various lengths of the stub [12]

Fig. 8.17 Simulated reflection coefficients for various widths of the stub [12]

Fig. 8.18 Simulated reflection coefficients for different gaps between the main patch and the stub [12]

169

170

8 Compound Reconfigurable Planar Antennas

Antenna is optimized to get symmetric behavior in terms of axial ratio, impedance matching, radiation patterns, and gain for RHCP and LHCP modes. It is designed on the same substrate as used for the first structure. Two right-side corners of the stub are chamfered to get a good axial ratio. The photograph of the fabricated antenna is shown in Fig. 8.15b. Two dielectric substrates (0.787 mm thick each) are used to develop the antenna. Reconfigurable antenna structures with patches and biasing lines are etched on the top side of the upper substrate while whole copper is removed from the lower side of the upper substrate. A microstrip tapered feed is etched on the top side of the lower substrate and the ground plane is on the bottom of the lower substrate. A thin layer of silicone paste is applied to fix both the substrates. Additionally, four Teflon screws are attached at the corners of the antenna to properly fix the substrate layers to avoid the formation of air bubbles between the substrates. Teflon screws have been considered during the simulation; these screws are far away from the radiator, so they do not affect the performance of the antenna significantly. A slight deviation is observed in the simulated and measured results. It may be due to the misalignment of the feed with the radiator and the air gap between the two dielectric substrates near the coaxial connector. Dimensions of the final layout are given in Table 8.4. Fig. 8.19 Simulated reflection coefficients for various positions of the RF switch [12]

Table 8.4 Dimensions of the polarization reconfigurable antenna operating in three switchable frequency bands [12]

Parameters

Values (mm)

Parameters

Values (mm)

a

02.75

Lstub

03.12

b

00.75

W1

02.20

g

00.40

W2

07.00

L1

23.50

Wg

58.00

Lg

58.00

Wp

16.70

Lp

16.90

8.5 Summary

171

Table 8.5 Polarization states of the antenna at different frequency bands [12] Polarization States

Centre Freq. (GHz)

D1

D2

D3

D4

D5

LHCP

5.1

ON

OFF

ON

ON

OFF

LP

5.1

ON

ON

ON

ON

OFF

RHCP

5.1

OFF

ON

ON

ON

OFF

LHCP

5.45

OFF

OFF

OFF

ON

OFF

LP

5.45

OFF

OFF

ON

ON

OFF

RHCP

5.45

OFF

OFF

ON

OFF

OFF

LHCP

6.3

OFF

OFF

OFF

ON

ON

LP

6.3

OFF

OFF

ON

ON

ON

RHCP

6.3

OFF

OFF

ON

OFF

ON

Five MA4SPS552 PIN diodes are employed in the circuit to get polarization switching at three switchable frequency bands. Centre frequencies of these bands are around 5.1, 5.45, and 6.3 GHz. Polarization states at different frequency bands with diode conditions are explained in Table 8.5. Surface current distributions at 5.45 and 6.3 GHz are plotted at different time instants as shown in Figs. 8.20, 8.21, 8.22 and 8.23 for LHCP and RHCP mode, respectively. Reflection coefficients for each state are plotted in Fig. 8.24. Discrepancies in the simulated and measured results are observed. In most cases, resonance frequencies are shifted upwards; this is due to the formation of air bubbles in-between the substrates near the coaxial connector. The effective dielectric constant reduces due to the presence of an air bubble in between the substrates resulting in an upward shift in the resonance frequencies. Simulated and measured normalized radiation patterns at 5.15, 5.45, and 6.3 GHz are illustrated in Fig. 8.25. For LP, the cross-pol level is below 19.5 dB from the co-pol level in all the three switchable frequency bands. Simulated and measured axial ratios are plotted in Fig. 8.26a, b and c. Axial ratios are less than 3 dB across the band for all three bands. Realized gain is plotted in Fig. 8.26d. Gain is decreased at the high frequency band, and it is due to an increase in the radiation in the backward direction. The summary of the results is given in Table 8.6. Compound reconfigurable planar antennas switchable in frequency and polarization are discussed above. There are other types of compound antennas available in the literature [18–28] that are not discussed in this chapter.

8.5 Summary Frequency and polarization switchable compound reconfigurable antennas were discussed in this chapter. Various types of compound reconfigurable antennas realized using different techniques are available in the scientific literature. Here, our focus was to discuss the freedom of polarization switching at different frequencies, such

172

8 Compound Reconfigurable Planar Antennas

Fig. 8.20 Surface current distribution at 5.45 GHz for LHCP mode at different time instants (ωt) [12] a 0° b 90° c 180° d 270°

antennas are capable of independent switching among different polarization states at more than one frequency. New technologies such as 4G LTE and 5G require polarization switching at more than one frequency band, for that purpose we discussed this category of compound reconfigurable antennas in this chapter. Few antennas were realized to switch its polarization at various frequencies (continuous frequencies using varactor diodes or discrete frequencies using PIN diodes). Additionally, more bandwidth is needed for modern wireless standards in a single operating band; we need to have wideband polarization antennas for such applications. Reconfigurable microstrip patch antenna with polarization agility in two switchable frequency bands has been discussed here. An antenna has good bandwidth in a single operating band

8.5 Summary

173

Fig. 8.21 Surface current distribution at 5.45 GHz for RHCP mode at different time instants (ωt) [12] a 0° b 90° c 180° d 270°

which is enhanced by using a proximity coupled feed. There are challenges in developing a compound reconfigurable antenna that can simultaneously achieve wideimpedance bandwidth, large axial ratio bandwidth, polarization switching among LHCP or RHCP, good gain, and good efficiency. To achieve LHCP and RHCP both from the structure, we need to make the structure symmetric so that we can achieve similar performance for both polarization modes. Various bandwidth enhancement techniques (by varying feed types) have been discussed. Polarization reconfigurable antenna with good impedance and axial ratio bandwidth using one of the bandwidth enhancement techniques is discussed in detail in this chapter.

174

8 Compound Reconfigurable Planar Antennas

Fig. 8.22 Surface current distribution at 6.3 GHz for LHCP mode at different time instants (ωt) [12] a 0° b 90° c 180° d 270°

8.5 Summary

175

Fig. 8.23 Surface current distribution at 6.3 GHz for RHCP mode at different time instants (ωt) [12] a 0° b 90° c 180° d 270°

176 Fig. 8.24 Measured and simulated reflection coefficients [12] a first band b second band c third band

8 Compound Reconfigurable Planar Antennas

8.5 Summary

177

Fig. 8.25 Measured and simulated normalized radiation patterns [12] a LHCP at 5.15 GHz b LP at 5.15 GHz c RHCP at 5.15 GHz d LHCP at 5.45 GHz e LP at 5.45 GHz f RHCP at 5.45 GHz g LHCP at 6.3 GHz h LP at 6.3 GHz i RHCP at 6.3 GHz

178

Fig. 8.25 (continued)

8 Compound Reconfigurable Planar Antennas

8.5 Summary

179

Fig. 8.26 Measured and simulated a AR in first band b AR in second band c AR in third band d realized gain, [12] Table 8.6 Summary of the results of the polarization reconfigurable antenna in three switchable bands [12] Polarization state

−10 dB Impedance BW (MHz) Simu.

Meas.

Simu.

Meas.

Simu.

Meas.

LHCP@first band (centre is at 5.1 GHz)

4928–5281

5030–5410

5054–5168

5043–5171

7.35

6.5

LP@first band (centre is at 4.95 GHz)



4914–5070





6.3

6.5

RHCP@first band (centre is at 5.1 GHz)

4926–5280

5040–5469

5050–5159

5049–5182

7.35

6.65

LHCP@second band (centre is at 5.45 GHz)

5264–5592

5390–5591

5361–5483

5312–5514

7.9

7.5

LP@second band (centre is at 5.3 GHz)



5210–5341





6.55

6.0

3 dB ARBW (MHz)

Peak gain (dBi)

(continued)

180

8 Compound Reconfigurable Planar Antennas

Table 8.6 (continued) −10 dB Impedance BW (MHz)

3 dB ARBW (MHz)

Peak gain (dBi)

Simu.

Meas.

Simu.

Meas.

Simu.

Meas.

RHCP@second band (centre is at 5.45 GHz)

5256–5592

5391–5600

5368–5490

5328–5521

7.9

7.42

LHCP@third band (centre is at 6.3 GHz)

6129–6400

6138–6367

6311–6333

6292–6351

4.1

3.9

LP@third band (centre 6004–6178 is at 6.1 GHz)

6002–6210





4.6

4.5

LP@third band (centre – is at 6.5 GHz)

6402–6570





4.7

4.6

RHCP@third band (centre is at 6.3 GHz)

6136–6380

6308–6330

6277–6322

4.1

4.0

Polarization state

6136–6402

References 1. Chung, K., Nam, Y., Yun, T., Choi, J.: Reconfigurable microstrip-patch antenna with frequency and polarization-diversity functions. Microw. Opt. Technol. Lett. 47(6), 605–607 (2005) 2. Bernhard, J.T.: Reconfigurable multifunction antennas: next steps for the future. In: 2007 International Symposium on Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications, pp. 1–4 (2007) 3. Hu, C.H., Chen, T.R., Wu, J.F., Row, J.S.: Reconfigurable microstrip antenna with polarisation diversity and frequency agility. Electron. Lett. 43(24) (2007) 4. Wu, W., Row, J., Han, T., Sim, C.: An aperture-coupled microstrip antenna with frequency agility and polarization diversity. In: 2009 Asia Pacific Microwave Conference, pp. 763–765 (2009) 5. Qin, P.-Y., Guo, Y.J., Cai, Y., Dutkiewicz, E., Liang, C.-H.: A reconfigurable antenna with frequency and polarization agility. IEEE Antennas Wirel. Propag. Lett. 10, 1373–1376 (2011) 6. Row, J.S., Shih, C.J.: Polarization-diversity ring slot antenna with frequency agility. IEEE Trans. Antennas Propag. 60(8), 3953–3957 (2012) 7. Liang, B., Sanz-Izquierdo, B., Parker, E.A., Batchelor, J.C.: A frequency and polarization reconfigurable circularly polarized antenna using active EBG structure for satellite navigation. IEEE Trans. Antennas Propag. 63(1), 33–40 (2015) 8. Nguyen-Trong, N., Hall, L., Fumeaux, C.: A frequency- and polarization-reconfigurable stubloaded microstrip patch antenna. IEEE Trans. Antennas Propag. 63(11), 5235–5240 (2015) 9. Zhang, P., Liu, S., Chen, R., Huang, X.: A reconfigurable microstrip patch antenna with frequency and circular polarization diversities. Chinese J. Electron. 25(2), 379–383 3 (2016) 10. Singh, R.K., Basu, A., Koul, S.K.: A novel reconfigurable microstrip patch antenna with polarization agility in two switchable frequency bands. IEEE Trans. Antennas Propag. 66(10), 5608–5613 (2018) 11. Sim, C., Chen, B., Lin, C., Su, H., Han, T., Huang, G.: A simple aperture coupled circular patch antenna with CP radiation and frequency agility. In: 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, pp. 329–330 (2018) 12. Singh, R.K., Basu, A., Koul, S.K.: Reconfigurable microstrip patch antenna with polarization switching in three switchable frequency bands. IEEE Access 8, 119376–119386 (2020) 13. Waterhouse, R.B.: Microstrip Patch Antennas: A Designer’s Guide, ch. 2, pp. 817–821. Springer Science + Business Media, New York (2003)

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14. Klopfenstein, R.W.: A transmission line taper of improved design. Proc. IRE 44(1), 31–35 (1956) 15. Croq, F., Kossiavas, G., Papiernik, A.: Stacked resonators for bandwidth enhancement: a comparison of two feeding techniques. In: IEE Proceedings H-Microwaves, Antennas and Propagation, vol. 140, (no. 4), pp. 303–308 (1993) 16. Pozar, D.M.: Increasing the bandwidth of a microstrip antenna by proximity coupling. Electron. Lett. 8, 368–396 (1987) 17. Pues, H.F., Capelle, V.D.: An impedance matching technique for increasing the bandwidth of microstrip antennas. IEEE Trans. Antennas Propag. AP-37(11), 1345–1354 (1989) 18. Huff, G.H., Feng, J., Zhang, S., Bernhard, J.T.: A novel radiation pattern and frequency reconfigurable single turn square spiral microstrip antenna. IEEE Microw. Wirel. Compon. Lett. 13(2), 57–59 (2003) 19. Nikolaou, S., Bairavasubramanian, R., Lugo, C., Jr., Carrasquillo, I., Thompson, D.C., Ponchak, G.E., Papapolymerou, J., Tentzeris, M.M.: Pattern and frequency reconfigurable annular slot antenna using PIN diodes. IEEE Trans. Antennas Propag. 54, 439–448 (2006) 20. Yang, X.-S., Wang, B.-Z., Wu, W., Xiao, S.: Yagi patch antenna with dual-band and pattern reconfigurable characteristics. IEEE Antennas Wirel. Propag. Lett. 6, 168–171 (2007) 21. Rodrigo, D., Jofre, L.: Frequency and Radiation Pattern Reconfigurability of a Multi-Size Pixel Antenna. IEEE Trans. Antennas Propag. 60(5), 2219–2225 (2012) 22. Guo, T., Leng, W., Wang, A., Li, J., Zhang, Q.: A novel planar parasitic array antenna with frequency- and pattern-reconfigurable characteristics. IEEE Antennas Wirel. Propag. Lett. 13, 1569–1572 (2014) 23. Cao, W., Zhang, B., Liu, A., Yu, T., Guo, D., Pan, K.: A reconfigurable microstrip antenna with radiation pattern selectivity and polarization diversity. IEEE Antennas Wirel. Propag. Lett. 11, 453–456 (2012) 24. Row, J.S., Tsai, C.W.: Pattern reconfigurable antenna array with circular polarization. IEEE Trans. Antennas Propag. 64(4), 1525–1530 (2016) 25. Qin, P.Y., Chen, S. L., Guo, Y.J.: A compound reconfigurable microstrip antenna with agile polarizations and steerable beams. In: 2017 International Symposium on Antennas and Propagation (ISAP), pp. 1–2. Phuket (2017) 26. Aris, M.A., Ali, M.T., Abd Rahman, N.H., Pasya, I.: Compound reconfigurable microstrip patch antenna array using integrated controlled ground modified structure and sub delay line feeding network. In: 2017 IEEE Asia Pacific Microwave Conference (APMC), pp. 120–123 (2017) 27. Rodrigo, D., Cetiner, B.A., Jofre, L.: Frequency, radiation pattern and polarization reconfigurable antenna using a parasitic pixel layer. IEEE Trans. Antennas Propag. 62(6), 3422–3427 (2014) 28. Panneer Selvam, Y., et al.: A patch-slot antenna array with compound reconfiguration. IEEE Antennas Wirel. Propag. Lett. 17(3), 525–528 (2018)

Chapter 9

Applications of Reconfigurable Planar Antennas in Wireless Communication Systems

9.1 Introduction Rapid advancement in wireless communication systems demands smart antennas. Reconfigurable antennas are the key for new generation wireless systems. Wireless services are continuously increasing day by day. A reconfigurable antenna has proved to be a good candidate for covering various wireless services by providing good performance. Characteristics such as frequency, polarization, and radiation patterns can be altered by means of RF switches. Proper biasing of switches can dynamically change the antenna characteristics. A frequency reconfigurable antenna can alter its resonance frequency by keeping other characteristics unaltered. Similarly, if the antenna is designed to switch only one characteristic, then it will switch without significantly affecting the other characteristics. This specialty makes reconfigurable antennas a potential candidate for modern wireless communications. Reconfigurable antennas are continuously in demand. As wireless communication demands are increasing, reconfigurable antennas are becoming smart and multifunctional. Various wireless systems need planar antennas due to their size limitation. The available volume for the antenna inside the system is limited. In this book, we focused more on the planar antennas and discussed several planar reconfigurable antennas.

9.2 Applications of Frequency Reconfigurable Antennas In modern wireless systems, services are increasing day by day. The demand for multiple services using a single wireless device has increased significantly. To cover these services, the operating range of the antenna must be increased. Fortunately, many wireless systems require one frequency at a time for their operation, but these systems operate in a wide range of frequencies. In such systems, multiple antennas are required to fulfill the current requirements which takes more space in the system. A © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1_9

183

184

9 Applications of Reconfigurable Planar Antennas …

Fig. 9.1 Frequency reconfigurable antenna

frequency reconfigurable antenna would be an excellent choice to fulfill the requirement. It can cover a wide range of the spectrum by modifying its current distribution as shown in Fig. 9.1. It will save the space and cost of the system. Frequency reconfigurable passive planar antennas are extensively used in various applications such as cognitive radio, laptops, public safety, LTE/WWAN Tablet Computer, satellite, IOT, etc., [1–19]. New wireless standards such as 5G operating over a wide range of frequencies are expected to simultaneously support several connections. To enable 5G services, the main spectrum is divided into low bandwidth (600, 800, and 900 MHz), the medium band (2400, 3500, and 3700–4200 MHz), and the high-frequency band (28, 38, and 60 GHz). The medium band (sub-6 GHz) is used for long-range and considerably high data rate communications. It can send data at high rates over long distances; it is suitable to be used in both urban and rural areas. Sometimes there is huge interference at some frequencies, in this situation, specific frequency bands can be selected with negligible interference, the switching ability of any antenna between multiple frequency bands helps in making a noisefree communication. Advanced antenna designs such as reconfigurable antennas are mandatory to address such functionality requirements.

9.3 Applications of Polarization Reconfigurable Antennas Circularly polarized antennas have been popularly used in various contemporary wireless communications systems, such as Worldwide Interoperability for Microwave Access (WiMAX), Global Positioning System (GPS), satellite communication, Wireless Local Area Network (WLAN) and, Radio-frequency identification (RFID) reader and tag because of the adaptable orientation of the transmitter and receiver [20–38]. It is observed that transmitter and receiver systems utilizing CP antennas present better immunity to multipath propagation. In the case of RFID communication, readers need not be in the same polarization plane as RFID tags, unlike linearly polarized readers. The reader having a CP antenna does not require knowledge of tag orientation. Linear or circular polarization reconfigurable antennas have several advantages such as enhancement in signal-tonoise ratio, reduction of the multipath interference, etc. Normally, the polarization

9.3 Applications of Polarization Reconfigurable Antennas

185

Fig. 9.2 Polarization reconfigurable antenna

mismatch occurs at the transmitter side which can be compensated by using the polarization diversity concept in the receiver antenna, the signal transmission can be affected by the multipath distortion and polarization mismatch. Polarization diversity is used in the antennas to improve the quality of the wireless links. Polarization can be switched between LP, LHCP, and RHCP as shown in Fig. 9.2. One of the examples of polarization diversity is the body-centric wireless communication system (BWCS) as shown in Fig. 9.3. ON-body and OFF-body are two major links in the biological communication systems operated in linear mode. The orientation of these devices is arbitrary because of the free movement of the human body, which may cause polarization mismatch and multipath fading. To overcome polarization mismatch and multipath fading, receiver antennas require a polarization diversity feature. During the period before the 1990s, circularly polarized antennas were used only for satellite communication. CP antennas allowed satellites and ground station antennas to communicate without worrying about the horizontal/vertical alignment of conventional linearly polarized antennas. The satellite’s rotation is there and due to this angle of view changes. Another factor that can rotate microwaves is atmospheric disturbances. Keeping linearly polarized antennas in alignment will require constant rotation. However, the field of a circularly polarized antenna is always rotating. Also, it can rotate in two possible directions called the sense of rotation. Right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) senses allow a 2× multiplexing frequency reuse to the same satellite since an LHCP and RHCP antenna reject each other’s signals. Two simultaneous RF links may be used with RHCP and LHCP antennas for a single frequency allocation. It can be a huge benefit to mobile devices as well, where the vertical/horizontal orientation of their linear antennas is always changing with movement and reflections. It does not matter to the linear antenna whether the CP antenna has a left-hand or right-hand rotational sense. The GPS and other navigation satellites use RCHP downlink signals. A simple linear antenna can be used in GPS receivers. There is a loss of 3 dB in the signal strength while using a linearly polarized antenna because of its ability to receive only one component (like the vertical or horizontal polarization) of the GPS signal. Modern GPS receivers use an RHCP antenna for improving the performance of the system. Sensitivity improves by using an RHCP antenna since it receives 3 dB more

186

9 Applications of Reconfigurable Planar Antennas …

Fig. 9.3 Body centric communication showing OFF-body and ON-body link

than a linear polarized antenna-based GPS receiver. CP signals also reverse their rotation sense when reflected. An RHCP antenna can reject reflections (arrives as LHCP), often from large buildings in an urban environment.

9.4 Applications of Pattern Reconfigurable Antennas A pattern reconfigurable antenna offers diverse pattern configurations and beam steering/switching to cater to the polluted electromagnetic environment while maintaining the system performance, as well as enhancing the signal and data security [39–64]. In wireless applications such as sensor and ad hoc networks, an antenna with an omni-directional radiation pattern is preferred for receiving control packets or periodic updates from the nearby nodes. whereas directional radiation is preferred to send information to a selected node or a sink of known location. The radiation patterns can be switched between broadside and conical patterns as shown in Fig. 9.4 [64]. Broadside and conical patterns are used to efficiently cover the space. Vehicle-to-vehicle communication scenario is shown here. Pattern reconfigurable antennas with a broadside and conical patterns can control the main beam or null direction in a specific direction. Another major area of research is to switch the radiation beam among sum and difference pattern. Beam switching between sum and difference patterns is useful in communication and tracking objects. Radiation pattern steering and switching in active antennas

9.5 Applications of Compound Reconfigurable Antennas

187

Fig. 9.4 Vehicle-to-vehicle communication scenario [64]

could be useful in various applications. An oscillator (RF generating) type active antenna capable of switching the beam in broadside and conical directions is shown in Fig. 9.5. There is no need to connect an RF generator to such antennas, a DC power supply is sufficient to drive the circuit and DC supply can be provided by a battery or using an efficient energy harvesting circuit. It is also useful in broadcasting to the receivers that are not always in the broadside directions as shown in Fig. 9.5. The use of radiation pattern/polarization reconfigurable antennas in a MIMO environment enhances the channel capacity, the figure of merit, and reliability of a wireless link. Pattern Reconfigurable arrays are also an attractive solution for MIMO systems keeping good communication links. Pattern reconfigurable antennas are suitable to transmit/receive signals to/from various directions. A satellite communication scenario is explained in Fig. 9.6. Satellite is communicating with another satellite (inter-satellite link), vehicle (mobile link), and ground station. A pattern reconfigurable antenna can provide all these services.

9.5 Applications of Compound Reconfigurable Antennas A compound reconfigurable antenna can change multiple antennas’ characteristic. A single compound reconfigurable antenna can replace multiple antennas used for different applications. Moreover, a compound reconfigurable antenna includes all the individual advantages of frequency, polarization, and radiation pattern reconfigurable antennas together. If all the three characteristics (frequency, polarization, and radiation pattern) are reconfigured simultaneously, the spectrum can be used efficiently. Compound reconfigurable antennas with the ability to reconfigure both the frequency and radiation pattern, frequency and polarization, polarization, and pattern have been realized for various modern wireless applications [65–79].

188

9 Applications of Reconfigurable Planar Antennas …

Fig. 9.5 Application scenario where radiation pattern can be switched between broadside and conical patterns [55]

Fig. 9.6 Usefulness of pattern reconfigurable antenna in satellite communication

9.8 Scope of Active Integrated Planar Antennas in Power Combining

189

9.6 Future Directions This section summarizes the results presented in this book and provides some concluding observations as well as prospects for potential future applications. The book presents the latest ideas in realizing active and passive printed antennas for modern and future wireless communication systems. Book started with the introduction of reconfigurable active and passive planar antennas and their benefits in modern and future wireless systems. Electronically reconfigurable antennas need RF switches for achieving switchable characteristics hence modeling of RF switches is required for performing numerical analysis. Ideal and non-ideal modeling of RF switches has been presented. Principles of reconfigurability and different types of reconfiguration techniques are briefly presented. Book discussed not only the reconfigurable passive printed antenna; it also provided a detailed description about reconfigurable active printed antennas. It discussed various new approaches for realizing active integrated antennas for modern and future applications. The idea of radiation beam steering/switching is discussed for oscillator-type active antennas. Book also briefs the advantages and applications of active and passive printed antennas for modern and future wireless applications.

9.7 Scope of Reconfigurable Passive Planar Antennas for Future Wireless Applications Reconfigurable passive planar antennas play a key role in smart, adaptive, and compact systems. It offers several advantages such as multifunctional capabilities, to be fitted in a compact space, low-cost, low-profile, conformable and ease of fabrication; these advantages make antenna well suited to be used in wireless applications such as long-term evolution (LTE), fourth generation (4G) and fifth generation (5G) mobile terminals. With the use of RF switches such as varactor or PIN diodes, an antenna’s characteristics can be altered by altering the current flow on the antenna structure. Compound reconfigurable antennas have more functionality among others; these antennas will be well suited for automotive applications. The requirements of the automotive industry are changing day by day; their demands are expected to increase in adding functionalities in the radiating element.

9.8 Scope of Active Integrated Planar Antennas in Power Combining Active integrated antennas (AlAs) are an emerging technology in which antennas are integrated with the active circuits—such as amplifiers, oscillators, and mixers. An active antenna is obtained by mounting an active device such as BJT, FET, and Gunn

190

9 Applications of Reconfigurable Planar Antennas …

diode on or near a radiating element, and it operates as an oscillator or an amplifier, or a mixer. With the advancement in the technologies at mmW systems, demand for high output power antennas is increasing. The maximum output power of a single amplifier is limited, it no longer fulfills the requirements of high output power. Therefore, power combining is needed. The traditional method for power combining realized by parallelizing several amplifiers is not efficient at millimeter-wave frequencies. The losses in the power combining network are increased and the traditional systems occupy a large volume. The quasi-optical and spatial power-combining approaches had been extensively investigated recently. By realizing spatial power combining arrays, losses can be reduced. In spatial power-combining systems, the antenna array elements must be appropriately selected to achieve high power combining solid-state millimeter-wave sources. Active antenna arrays can be small-sized sources in the millimeter-wave region and power losses in traditional power combining networks can be avoided in spatial power combining techniques. Radiation from all unit cells (integration of the solid-state device with a radiating element as a single unit cell) combines coherently in free space. Spatial power combining can be done by using linearly or circularly polarized active antennas. A single unit cell with a reconfiguration (polarization and/or pattern) feature can provide more freedom to the power combining systems. Beam steering active antennas are well suited for wireless charging. Beam switchable active antennas can be used for security purposes in broadcasting the information to dedicated receivers.

9.9 Non-linearity of Switches at High RF Power The study of the non-linear behavior of RF switches in reconfigurable antennas is important if the antenna is used as a transmitting device. To transmit high RF power using reconfigurable antennas, the behavior and operating limits of RF switches must be known. Non-linearity is an issue in electronically reconfigurable antennas; it can be observed when the antenna is supplied with high RF power [29]. The linear range of the transmitting circuit can be increased by using high-power handling switches. The performance of the reconfigurable antennas can also be increased by using more advanced RF MEMS switches.

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Index

A Active antennas, 6 Active device, 29 Amplifier design, 38 Amplifier type AIA, 30 Antenna oscillator circuit, 30, 32

B Band stop filter, 41 Bandwidth axial ratio Bandwidth, 173 impedance Bandwidth, 70, 165 Barkhausen criteria, 35 Basis of polarization, 66 Beam steering, 104, 105 Beam switching, 137, 186 Bias circuit of PIN diode, 8, 9 Binomial distribution, 150 Body-centric wireless communication, 185 Branch line coupler, 146 Broadside Pattern, 186

C Circular polarization, 67 Compact antennas, 80, 81 Computer Simulation Technology, 37, 42, 69 Conical pattern, 186, 188

D Dolph Tchebyscheff distribution, 141–144, 151

E Effective Isotropic Radiated Power, 42

F Feedback loop approach, 31, 35 Feeding techniques, 2 Field Effect Transistor, 6 Frequency conversion type AIA, 31

H Harmonic balance test, 40

M Metasurface, 56, 58

N Negative resistance approach, 59 Nonlinearity, 190 Null broadening, 145 Null steering, 151

O Oscillation test, 39 Oscillator type AIA, 30, 31

© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2022 S. K. Koul and R. K. Singh, Reconfigurable Active and Passive Planar Antennas for Wireless Communication Systems, Signals and Communication Technology, https://doi.org/10.1007/978-981-19-6537-1

197

198 P Passive antennas, 5 Planar antennas, 1, 2 Polarization left hand circular polarization, 11, 65, 185 linear polarization, 65 right hand polarization, 84 Power combining, 190 Principles of reconfigurability, 15

R Reactive loading, 54 Reconfigurability compound, 25 frequency, 23 pattern, 24 polarization, 23 Reconfiguration Techniques electronic reconfiguration, 16 material reconfiguration, 20 mechanical reconfiguration, 17 optical reconfiguration, 20 RF switch

Index electromechanical switch, 7 solid state electronic RF switch, 7

S Scattering parameter reflection coefficient, 16 transmission coefficient, 9, 90 Simulation scheme of oscillation, 39 Slot antennas, 80 Switch modeling ideal modeling, 189 non-ideal modeling, 189

V Vehicle-to-Vehicle communication, 186, 187

W Wilkinson Power Divider equal power divider, 146 unequal power divider, 146 Wireless Power Transfer, 65