MODERN LENS ANTENNAS FOR COMMUNICATIONS ENGINEERING

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4 IEEE Press 445 Hoes Lane Piscataway, NJ IEEE Press Editorial Board 2013 John Anderson, Editor in Chief Linda Shafer Saeid Nahavandi George Zobrist George W. Arnold David Jacobson Tariq Samad Ekram Hossain Mary Lanzerotti Dmitry Goldgof Om P. Malik Kenneth Moore, Director of IEEE Book and Information Services (BIS)

5 MODERN LENS ANTENNAS FOR COMMUNICATIONS ENGINEERING John Thornton Kao-Cheng Huang IEEE PRESS

6 Cover Design: John Wiley & Sons, Inc. Cover Illustration: simon2579/istockphoto. Copyright 2013 by Institute of Electrical and Electronics Engineers. All rights reserved. Published by John Wiley & Sons, Inc., Hoboken, New Jersey. Published simultaneously in Canada. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning, or otherwise, except as permitted under Section 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, (978) , fax (978) , or on the web at Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) , fax (201) , or online at Limit of Liability/Disclaimer of Warranty: While the publisher and author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives or written sales materials. The advice and strategies contained herein may not be suitable for your situation. You should consult with a professional where appropriate. Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. For general information on our other products and services or for technical support, please contact our Customer Care Department within the United States at (800) , outside the United States at (317) or fax (317) Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic formats. For more information about Wiley products, visit our web site at Library of Congress Cataloging-in-Publication Data is available. ISBN: Printed in the United States of America

7 CONTENTS Preface Acknowledgments ix xi 1 INTRODUCTION 1 John Thornton and Kao-Cheng Huang 1.1 Lens Antennas: An Overview The Microwave Lens Advantages of Lens Antennas Materials for Lenses Synthesis Feeds for Lens Antennas Microstrip Feeds Horn Feeds Luneburg and Spherical Lenses Quasi Optics and Lens Antennas Lens Antenna Design Metamaterial Lens Planar Lens or Phase-Shifting Surface Reflect Array Planar Lens or Lens Array Applications Antenna Measurements Radiation Pattern Measurement Gain Measurement Polarization Measurement Anechoic Chambers and Ranges 38 v

8 vi CONTENTS 2 REVIEW OF ELECTROMAGNETIC WAVES 49 Kao-Cheng Huang 2.1 Maxwell s Equations Boundary Conditions Equivalence Theorem Antenna Parameters Beam Solid Angle and Antenna Temperature Directivity and Gain Antenna Beamwidth Aperture of a Lens Phase Center Polarization Wave Propagation in Metamaterials 71 3 POLYROD ANTENNAS 77 Kao-Cheng Huang 3.1 Polyrods as Resonators The Polyrod as a Radiator Tapered Polyrod Antenna Patch-Fed Circular Polyrod Array of Polyrods Multibeam Polyrod Array MILLIMETER WAVE LENS ANTENNAS 113 Kao-Cheng Huang 4.1 Millimeter Wave Characteristics Millimeter Wave Loss Factors Ray-Tracing Propagation Millimeter Wave Substrate Lens for Imaging Millimeter Wave and Submillimeter Wave Lens Extended Hemispherical Lens Off-Axis Extended Hemispherical Lens Submillimeter Wave Lens Antennas for Communications Analysis of Millimeter Wave Spherical Lens Waveguide-Fed Millimeter Wave Integrated Lens 141

9 CONTENTS vii 5 LENS ANTENNAS FOR COMMUNICATIONS FROM HIGH-ALTITUDE PLATFORMS 147 John Thornton 5.1 Introduction The High-Altitude Platform Concept Spectrum Reuse Using HAPs Example Results: Cell Power and Interference Advantages of Lenses over Reflector Antennas Reflectors Lenses Commercial Lens Antennas Development of a Shaped Beam Low-Sidelobe Lens Antenna with Asymmetric Pattern Primary Feed Symmetric 5 Beamwidth Antenna Asymmetric Beam Measurements Lens Antenna Payload Model Multifeed Lens Multiple Beam Spherical Lens Antennas for HAP Payload SPHERICAL LENS ANTENNAS 187 John Thornton 6.1 Introduction Spherical Lens Overview Analytical Methods Ray Tracing SWE Computational Method and Results Generic Feed Pattern Commercial Solvers Spherical Lens Materials and Fabrication Methods Machined Polymers Molding Polymer Foams PU Dielectric Loss Artificial Dielectrics 215

10 viii CONTENTS 6.5 Revisiting the Constant-Index Lens A Practical, Patch-Fed Hemispherical Constant-Index Lens Off-Axis Array-Fed Spherical Lens Cross-Polarization Properties of Spherical Lenses HEMISPHERICAL LENS-REFLECTOR SCANNING ANTENNAS 225 John Thornton 7.1 Introduction Candidate Scanning Antenna Technologies Spherical and Hemispherical Lens Antenna Hemispherical Lens Prototype Evolution of a Two-Layer Stepped-Index Polymer Lens A Hemispherical Lens-Reflector Antenna for Satellite Communications Requirements Lens Analysis Three-Layer Lens Geometry Lens Fabrication and Performance Mechanical Tracking System Ground Plane Effects Aperture Blockage in Scanning Lens Reflector A Low-Index Lens Reflector for Aircraft Communications (Contribution by D. Gray) 252 About the Authors 267 Index 268

11 PREFACE The aim of this book is to present the modern design principles and analyses of lens antennas. It gives graduates and RF/microwave professionals the design insights in order to make full use of lens antennas. The reader might ask: Why is such a book considered necessary and timely? The reply we would bring to such an inquiry is that the topic has not been thoroughly publicized recently and so its importance has become somewhat underestimated. Furthermore, the work has brought about an opportunity to gather together the authors contributions to several areas of research where lens antennas have been promoted. Foremost among these are communications applications, where of course antennas play a key role and where we will show why certain advantages accrue from the particular characteristics of lens antennas. The major advantages of lens antennas are narrow beamwidth, high gain, low sidelobes and low noise temperature. Their structures can be more compact and weigh less than horn antennas and parabolic reflector antennas. Lens antennas, with their quasi-optical characteristics, also have low loss, particularly at near millimeter and submillimeter wavelengths where they have particular advantages. Beam shaping can be achieved by controlling the phase distribution across the lens aperture in a manner that can be more accurate and less costly than would be the case for a reflector. Such a shaped dielectric lens can be more economical to produce in small- to medium-scale production runs than other antenna types where certain niche applications are considered. In addition, spherical lens antennas have the benefit of no scan loss and wide bandwidth, with the option for multiple beams from a common aperture. Modern Lens Antennas for Communications Engineering serves as an excellent tool for RF/microwave professionals (engineers, designers, and developers) and industries with microwave and millimeter wave research projects. For university students, this book requires a prerequisite course on antennas and electromagnetic waves, which covers propagation, reflection, and transmission of waves, waveguides, transmission lines, and some other antenna fundamental concepts. Such a course is usually followed by design projects. This book can be used as further study material in such design projects. Advanced students and researchers working in the field of modern communications will also find this book of interest. Included is a bibliography of current research literature and patents in this area. Based on these credentials, this book systematically conducts advanced and up-todate treatment of lens antennas. It does not purport to present a far-reaching treatise on every aspect of lens antennas, but rather, following the introductory chapters, the ix

12 x PREFACE emphasis of the work is taken from the authors own research of recent years. Example designs are presented and the analysis of their performance detailed. A summary of each chapter is as follows. Chapter 1 gives an overview of different types of lens antennas and their history. It discusses basic principles of delay lenses (in which the electrical path length is increased by the lens medium), fast lenses (in which the electrical path length is decreased by the lens medium), materials for lenses, and applications for lens antennas. It attempts a fairly broad review of some quite disparate antenna types that are nevertheless classed as lenses such as the planar or frequency selective surface type and also the Fresnel zone variants of dielectric lenses. Antenna measurement techniques are also summarized. Chapter 2 reviews important wave propagations and antenna parameters, for the purpose of consistency in notation and easy referencing. The material progresses from uniform plane waves in various media, such as lossless and lossy dielectrics, to all important antenna parameters. Chapter 3 focuses on low-cost yet high-directivity dielectric polyrod antennas. Different feeding methods, maximum gain, and beam tilting are discussed in detail. A multibeam polyrod array is presented where this increases radiation coverage, and phase compensation is introduced to adjust beam direction. Chapter 4 tackles millimeter wave issues such as high path loss and high power consumption. It then explores the variety of millimeter wave lens antennas and novel design methods. Quasi-optical characteristics of lens antennas are identified for aiding design at millimeter and submillimeter wavelengths. Chapter 5 discusses the properties of antennas which would be required for communications from high-altitude platforms. As such, it presents a case study where lens antennas were identified as being a potential solution for this niche area. Beginning with a system-level analysis of a cellular architecture employing spectrum reuse through multiple spot beams, the chapter goes on to show how a type of lens antenna, with shaped beam and low sidelobes, directly controls cochannel interference. A practical design and results are reported. Chapter 6 presents a summary of the properties of spherical lens antennas including the Luneburg lens and its relatives. Analytical techniques are discussed, beginning with ray tracing but then leading to the much more powerful spherical wave expansion technique. Lens construction problems are addressed, and then the properties of constant-index spherical lenses are summarized. Chapter 7 follows on from Chapter 6 and reports from several programs where hemispherical lens-reflector antennas were developed in practice. Here, a hemisphere with ground plane recovers the equivalent aperture of a spherical lens but in half the height a profound advantage where a low profile is required. A dual-beam lens antenna for satellite communications is reported, as is a constant-index lens reflector partially developed for aircraft-to-ground links. John Thornton Kao-Cheng Huang

13 ACKNOWLEDGMENTS The two authors contributed equally to this book. During the period of the manuscript s preparation, the authors have been obliged to many people. First of all, the authors wish to acknowledge the valuable comments from the reviewers. Also, the authors would like to acknowledge the copyright permission from IEEE. The authors also wish to thank Dr. Derek Gray for his contribution to Section 7.7. The authors are indebted to many researchers for their published works, which were rich sources of reference. Their sincere gratitude extends to IEEE editors for their support in writing the book. The help provided by Taisuke Soda, Mary Hatcher, and other members of the staff at John Wiley & Sons is most appreciated. In addition, Kao-Cheng Huang would like to thank Prof. David J. Edwards, University of Oxford (United Kingdom), Prof. Zhaocheng Wang, Tsinghua University (China), Prof. Mook-Seng Leong, National University of Singapore (Singapore), Prof. Zhichun Lei, University of Applied Sciences Ruhr West (Germany), Prof. Hsueh-Man Shen, New York University (United States), Prof. Jia-Sheng Hong, Heriot- Watt University (United Kingdom), and Miss Hsiang-Jung Huang, Illinois Institute of Technology (United States) for their many years of support. Dr. Huang would also like to acknowledge the copyright permission from John Wiley & Sons, Inc. (Chapters 5 and 6 of Millimetre Wave Antennas for Gigabit Wireless Communications: A Practical Guide to Design and Analysis in a System Context by Huang and Edwards, 2008), Springer (Chapter 17 in Antenna Handbook, Vol. 3: Antenna Applications by Lo and Lee, 1993), and Sophocles J. Orfanidis (Sections 1.5 and 2.12 in Electromagnetic Waves and Antennas by Sophocles J. Orfanidis, 2010), for extracts used in Chapters 2, 3, and 4. John Thornton thanks the following for supporting the work described in Chapters 5 7. At the University of York, Dr. David Grace (project manager, EU FP6 CAPANINA Project ) and Mr. Tim Tozer (leader of Communications Research Group). The middle part of Chapter 7 describes the European Space Agency-funded Multiscan project under Contract Number 20836/07/NL/CB during The Agency s support is gratefully acknowledged as is that of program manager Maarten van der Vorst. Thanks to Andy White and Andy Patterson for bringing that project to fruition, to Mark Hough for measurements and logistics support, and to Graham Long for mechanical design. Thanks to Philip Haines of Hollycroft Associates for contributing an industrial perspective. An article describing that project is also found in the August 2009 edition of Microwave Journal. xi

14 xii ACKNOWLEDGMENTS Dr. Thornton also thanks Derek Gray for coauthoring several papers on lens theory in the late 2000s and Stuart Gregson (Nearfield Systems Inc., Torrance, California) both for permission to use the scanner image in Chapter 1 and for moral support with authorship. J.T. K.-C.H.

15 1 INTRODUCTION John Thornton and Kao-Cheng Huang The topic of lens antennas was widely investigated during the early development of microwave antennas and was influenced by the extensive body of existing work from optics. Subsequently, interest declined somewhat as lens antennas were overtaken by reflectors for high efficiency, large aperture antennas; and by arrays for shaped-beam, multi-beam, and scanning antennas. Quite recently, as research interest has expanded into the use of millimeter wave and sub-millimeter wave frequency bands, lens antennas have again attracted developers attention. This chapter is organized as nine sections to introduce the basics of lens antennas. Section 1.1 gives an overview of lens antennas, including its advantages, disadvantages, and the materials encountered. This is followed by a discussion of antenna feeds at Section 1.2. Then Section 1.3 introduces the fundamentals of the Luneburg lens (a topic to which Chapters 6 and 7 are dedicated). Section 1.4 introduces quasi-optics and Section 1.5 treats design rules. A discussion of metamaterials for lens antennas makes up Section 1.6 and then the planar lens array, which is a relative of the reflect-array antenna, follows in Section 1.7. Applications are proposed in Section 1.8 and measurement techniques and anechoic chambers discussed in the final section. Modern Lens Antennas for Communications Engineering, First Edition. John Thornton and Kao-Cheng Huang Institute of Electrical and Electronics Engineers. Published 2013 by John Wiley & Sons, Inc. 1