Characteristic Modes: Theory and Applications in Antenna Engineering

By Yikai Chen and Chao-Fu Wang

Describes how to systematically implement various characteristic mode (CM) theories into designs of practical antenna systems

This book examines both theoretical developments of characteristic modes (CMs) and practical developments of CM-based methodologies for a variety of critical antenna designs. The book is divided into six chapters. Chapter 1 provides an introduction and discusses the recent advances of the CM theory and its applications in antenna engineering. Chapter 2 describes the formulation of the characteristic mode theory for perfectly electrically conducting (PEC) bodies and discusses its numerical implementations. Chapter 3 presents the CM theory for PEC structures embedded in multilayered medium and its applications. Chapter 4 covers recent advances in CM theory for dielectric bodies and also their applications. Chapter 5 discusses the CM theory for N-port networks and its applications to the design of antenna arrays. Finally, Chapter 6 discusses the design of platform-integrated antenna systems using characteristic modes.

This book features the following:

• Introduces characteristic mode theories for various electromagnetic structures including PEC bodies, structures in multilayered medium, dielectric bodies, and N-port networks
• Examines CM applications in electrically small antennas, microstrip patch antennas, dielectric resonator antennas, multiport antennas, antenna arrays, and platform mounted antenna systems
• Discusses numerical algorithms for the implementation of the characteristic mode theories in computer code

Characteristic Modes: Theory and Applications in Antenna Engineering will help antenna researchers, engineers, and students find new solutions for their antenna design challenges. 

• Language: English
• Publisher: Wiley
• Release date: May 19, 2015
• ISBN: 9781119038894

Book preview

PREFACE

Characteristic mode (CM) theory has received a great deal of attention in the field of antenna engineering in recent years. It is increasingly becoming a popular and general approach to characterize the modal resonant behavior of arbitrarily shaped objects such as antennas and scatterers. Its resultant characteristic currents form a weighted orthogonal set over the surface of the objects and their corresponding characteristic fields form an orthogonal set over the radiation sphere at infinity. These attractive features are useful in terms of the designs of reconfigurable antenna systems. Fully exploiting and making use of the characteristic modes of an antenna can significantly enhance its fundamental parameters, such as efficiency, gain, polarization purity, compactness, as well as much flexibility in the design of its excitation structures.

Quite a number of papers on the CM theory and its applications have been published by different research groups in many journals and conference proceedings. Although these papers are readily available to be read for understanding the CM theory through many electronic databases, some fundamental questions are still frequently raised by antenna engineers in many occasions, formal or informal. For instance, the top five questions raised are as follows:

What are the characteristic modes?

When do we need the CM theory for antenna designs?

What kind of antenna structures or materials can be analyzed using CM theory?

How to apply CM theory in practical antenna designs?

What are the merits of the characteristic modes in antenna designs?

Therefore, it is now the right time to write a book that can act as a one-stop reference to antenna scientists and engineers. We believe that this book will make CM theory become a standard approach for antenna analysis and design. We hope this book will stimulate more novel antenna designs based on the CM theory. We also hope this book can help eliminate some misconceptions on antenna design after the underlying physics of antenna structures are understood from the viewpoint of characteristic modes. For example, antenna design is often regarded as an easy task that can be completed effortlessly with the help of user-friendly electromagnetic simulators equipped with capable optimizers. With this misconception, it is claimed that any kind of antennas can be produced upon the request of sponsors despite the lack of practical design experience. However, this cognition is not true as the product of computer-aided design tools lacks physical meanings and can never replace the wisdom of human beings. Based on the authors’ personal experience in CM-based antenna developments, the antenna design in turn is a scientific, rigorous, and systematic process. It should start from certain required radiation performance and end with practical and beautiful antenna structure, which is physically determined by the required radiation performance and produces better or optimal radiation performance if possible.

Technically, this book aims to provide antenna scientists and engineers with up-to-date knowledge on the CM theories, numerical implementations, as well as novel antenna design concepts, methodologies, and typical antenna designs developed based on the CM theory. It gives a full picture of the CM theory family, ranging from the CM theory for perfect electric conductors, planar antennas in multilayered medium, dielectric material bodies, and multiport networks. This book is the first book that clearly describes how to implement the various CM theories into the designs of practical antenna systems in a systematic manner. It should be valuable for antenna engineers and designers to seek new solutions for the antenna design problems they face, which are too difficult to solve conventionally. It is also an ideal book for antenna scientists attempting to acquire in-depth physical insights in the radiation mechanisms of many conventional antennas.

Moreover, this book includes authors’ plentiful contributions featured on the study of the CM theory for solving practical problems. A wide range of applications including electrically small antennas, microstrip patch antennas, dielectric resonator antennas, multiport antenna systems, antenna arrays, and platform-integrated antenna systems are also covered. Through these illustrative design examples, readers will discover the great potential of the CM theory in many challenging antenna designs. The following topics will be covered in the six chapters of this book:

A detailed review of the CM theory and its applications in radiation and scattering problems;

Comprehensive descriptions for the CM theories of various electromagnetic structures;

Numerical algorithms of the CM theories and their implementations;

CM-based antenna design concepts and methodologies of various antenna system designs.

Reading of this book may require the basic knowledge of electromagnetic theory, computational electromagnetics, and antenna theory and technology. As a book for advanced topics in antenna engineering, we also assume the readers are familiar with various commonly used antennas in the industry, such as the microstrip patch antennas, dielectric resonator antennas, and other electrically small antennas in wireless communications.

Although we have prepared the manuscript of this book with great care, typos and errors will inevitably occur. We would greatly appreciate the notice of them via e-mail to Yikai Chen at [e-mail] and Chao-Fu Wang at [e-mail] or @ieee.org. Any comments, suggestions, and constructive criticisms will be also most welcome and may be forwarded to our e-mail addresses.

There are many people that we would like to thank who directly or indirectly contributed to the success of this book. We are indebted to many pioneering scholars and colleagues who have made great contributions to the study of the CM theory. Their great work has provided us a lot of fundamental materials making this book possible. We are happy to work with our colleagues in the Temasek Laboratories at National University of Singapore (TL@NUS), from whom we have received and learnt a lot. We would like to particularly thank Professor Hock Lim, Mr. Joseph Ting Sing Kwong, and Professor Boo Cheong Khoo for their great support and encouragement, Dr. Tan Huat Chio and Dr. Fu-Gang Hu for their very useful discussions, Mr. Peng Khiang Tan for his assistance in the fabrications and measurements of antennas described in this book.

Chao-Fu Wang would like to particularly thank Professor Jian-Ming Jin of University of Illinois at Urbana-Champaign, Professor Da-Gang Fang of Nanjing University of Science and Technology, and Professor Weng Cho Chew of University of Illinois at Urbana-Champaign, who have taught him a lot about electromagnetics and helped him a lot through many occasions. Thanks are expressed particularly to Professor Joshua Le-Wei Li of Monash University, Professor Qing Huo Liu of Duke University, Professor Yang Hao of Queen Mary University of London, Zhizhang (David) Chen of Dalhousie University, and Professor Ji Chen of University of Houston, for their great help and support during the writing of this book. Chao-Fu Wang would also like to thank Ms. Xin-Xin Wang for her help in wording some of the chapters of this book. Yikai Chen would also like to take this opportunity to thank Professor Shiwen Yang, Professor Zaiping Nie, and Professor Jun Hu of University of Electronic Science and Technology of China (UESTC), for their encouragement and patience when he pursued the Ph.D. degree in electromagnetics at the UESTC.

We are really grateful to the staff of John Wiley & Sons, Inc., especially Editor Brett Kurzman and Editorial Assistant Alex Castro of Global Research, Professional Practice and Learning, for their interest, support, and cooperation. Last but not least, we are grateful to our wives for their patience and loving support.

Yikai Chen and

Chao-Fu Wang

Temasek Laboratories

National University of Singapore

1

INTRODUCTION

1.1 BACKGROUNDS

Over the past few decades, the field of antenna engineering has undergone significant progress. Many new techniques and design concepts have been developed to overcome a myriad of challenges experienced in antenna engineering. Amongst the advancements, the increasing characteristic mode (CM) theory study, focusing on its extensive implementations in many critical antenna designs, is one of the exciting breakthroughs in antenna engineering. Its promising potentiality has been constantly attracting the attention of antenna engineers. The CM theory and its applications in antenna engineering are the topics of this book.

The booming of wireless communication is an important driving force for the advancement of antenna technology. Antennas are the sensors of wireless communication systems. They find wide range of applications from terminal devices (such as mobile phones) to advanced communication systems on aircrafts, ships, and so on. Antennas transfer microwave energy from transmission system to propagating waves in free-space and vice versa. Strong demands like small physical size, low weight, low cost, wideband/multiband bandwidth, reconfigurable capabilities, or even aesthetic consideration are increasingly specified as a must in modern antenna designs. The inherent challenges in these demands thus have further propelled the advance of antenna technology.

The rapid growth of numerical electromagnetic (EM) modeling techniques plays another vital role in antenna technology advancement. The numerical EM modeling techniques can provide an accurate way to validate antenna performance before carrying out expensive fabrications and measurements. Consequently, numerous in-house or commercial software packages based on the method of moments (MoM) [1] , the finite element method (FEM) [2, 3], and the finite difference time domain (FDTD) method [4–6] are extensively used in antenna designs. Given the antenna geometry and excitation structure, numerical techniques are able to simulate any antenna parameters.

However, from the practical point of view of antenna design problem, these numerical EM modeling techniques provide little information on the physical aspects of an antenna to be designed. The lack of physical insights brings difficulties in the further optimization of the antenna structure and feedings for achieving enhanced radiation performance. Therefore, antenna designs are heavily reliant on the designer’s experience and knowledge. In the worst cases, antenna designs become a trivial task where antenna engineers blindly modify the antenna and feeding structures and simulate the antenna performance via numerical EM modeling tools iteratively.

For the sake of convenience, numerical EM modeling techniques are extensively combined with modern evolution optimization algorithms such as the genetic algorithm (GA) [7] to help mitigate the heavy workload in antenna tunings. The assumption is that the optimization algorithm will eventually arrive at the expected antenna performance after the exhaustive search in their decision space. However, this is not always true in all antenna design problems. More often than not, the automatic optimization algorithm returns to a complicated antenna structure with the satisfactory level of performances. However, the complexity of the resultant antenna structure makes it too hard to understand the underlying radiation mechanism. In this case, the design will be generally regarded as a lack of scientific knowledge. Therefore, over-dependence on such brute force techniques is not a good way in antenna research. At least, it should not become antenna engineers’ primary choice.

It is evident that a successful antenna design is highly dependent on previous experiences and the physical understanding of antennas. To grasp such knowledge may require many years of practical exercise. The experience, however, is hard to be imparted from one to another, as such personal experience is usually formed based on one’s understanding of conventional antenna design concept introduced in textbooks. With such experience, solutions to some critical antenna design problems (e.g., the problems in Chapter 6) are usually not available.

Based on authors’ personal understanding, an ideal antenna design methodology should allow one to achieve optimal antenna performance in a systematic synthesis approach with very clear physical understandings. However, such antenna design methodology does not exist until the antenna community recognizes the great potential of the CM theory in antenna engineering. In the past decade, the extensive applications of the CM theory in antenna designs have witnessed the roadmap of the development of this ideal antenna design methodology.

In the new millennium, studies on the CM theory have revealed its promising potential in a variety of antenna designs. The CM theory makes antenna design much easier than ever as antenna engineers need not depend heavily on personal experiences or brute force optimization algorithms. Meanwhile, the CM theory provides an easy way to understand the physics behind many key performances such as the bandwidth, polarization, and main beam directions. These physical understandings provide a greater degree of freedom in terms of design. As compared to traditional antennas, the antennas designed with the CM theory have more attractive electrical performances and configurations. Based on the recent advances made by the authors from the Temasek Laboratories at National University of Singapore (TL@NUS), this book discusses the CM theory and the CM-based design methodologies for a wide range of antenna