Antennas : from theory to practice

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ANTENNAS

FROM THEORY TO PRACTICE

Yi Huang

University of Liverpool, UK

Kevin Boyle

NXP Semiconductors, UK

A John Wiley and Sons, Ltd, Publication

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ANTENNAS

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ANTENNAS

FROM THEORY TO PRACTICE

Yi Huang

University of Liverpool, UK

Kevin Boyle

NXP Semiconductors, UK

A John Wiley and Sons, Ltd, Publication

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This edition first published 2008

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Library of Congress Cataloging-in-Publication Data

Huang, Yi.

Antennas : from theory to practice / Yi Huang, Kevin Boyle.

p. cm.

Includes bibliographical references and index.

ISBN 978-0-470-51028-5 (cloth)

1. Antennas (Electronics) I. Boyle, Kevin. II. Title.

TK7871.6.H79 2008

621.382

4—dc22 2008013164

A catalogue record for this book is available from the British Library.

ISBN 978-0-470-51028-5 (HB)

Typeset in 10/12pt Times by Aptara Inc., New Delhi, India.

Printed in Singapore by Markono Print Media Pte Ltd, Singapore.

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Contents

Preface xi

Acronyms and Constants xiii

1 Introduction 1

1.1 A Short History of Antennas 1

1.2 Radio Systems and Antennas 4

1.3 Necessary Mathematics 6

1.3.1 Complex Numbers 6

1.3.2 Vectors and Vector Operation 7

1.3.3 Coordinates 10

1.4 Basics of Electromagnetics 11

1.4.1 The Electric Field 12

1.4.2 The Magnetic Field 15

1.4.3 Maxwell’s Equations 16

1.4.4 Boundary Conditions 19

1.5 Summary 21

References 21

Problems 21

2 Circuit Concepts and Transmission Lines 23

2.1 Circuit Concepts 23

2.1.1 Lumped and Distributed Element Systems 25

2.2 Transmission Line Theory 25

2.2.1 Transmission Line Model 25

2.2.2 Solutions and Analysis 28

2.2.3 Terminated Transmission Line 32

2.3 The Smith Chart and Impedance Matching 41

2.3.1 The Smith Chart 41

2.3.2 Impedance Matching 44

2.3.3 The Quality Factor and Bandwidth 51

2.4 Various Transmission Lines 55

2.4.1 Two-wire Transmission Line 56

2.4.2 Coaxial Cable 57

2.4.3 Microstrip Line 60

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2.4.4 Stripline 63

2.4.5 Coplanar Waveguide (CPW) 66

2.4.6 Waveguide 68

2.5 Connectors 70

2.6 Summary 74

References 74

Problems 74

3 Field Concepts and Radio Waves 77

3.1 Wave Equation and Solutions 77

3.1.1 Discussion on Wave Solutions 79

3.2 The Plane Wave, Intrinsic Impedance and Polarization 80

3.2.1 The Plane Wave and Intrinsic Impedance 80

3.2.2 Polarization 82

3.3 Radio Wave Propagation Mechanisms 83

3.3.1 Reflection and Transmission 83

3.3.2 Diffraction and Huygens’s Principle 91

3.3.3 Scattering 92

3.4 Radio Wave Propagation Characteristics in Media 93

3.4.1 Media Classification and Attenuation 93

3.5 Radio Wave Propagation Models 97

3.5.1 Free Space Model 97

3.5.2 Two-ray Model/Plane Earth Model 98

3.5.3 Multipath Models 99

3.6 Comparison of Circuit Concepts and Field Concepts 101

3.6.1 Skin Depth 101

3.7 Summary 104

References 104

Problems 104

4 Antenna Basics 107

4.1 Antennas to Radio Waves 107

4.1.1 Near Field and Far Field 108

4.1.2 Antenna Parameters from the Field Point of View 112

4.2 Antennas to Transmission Lines 122

4.2.1 Antenna Parameters from the Circuit Point of View 122

4.3 Summary 125

References 126

Problems 126

5 Popular Antennas 129

5.1 Wire-Type Antennas 129

5.1.1 Dipoles 129

5.1.2 Monopoles and Image Theory 137

5.1.3 Loops and the Duality Principle 141

5.1.4 Helical Antennas 147

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5.1.5 Yagi–Uda Antennas 152

5.1.6 Log-Periodic Antennas and Frequency-Independent Antennas 157

5.2 Aperture-Type Antennas 163

5.2.1 Fourier Transforms and the Radiated Field 163

5.2.2 Horn Antennas 169

5.2.3 Reflector and Lens Antennas 175

5.2.4 Slot Antennas and Babinet’s Principle 180

5.2.5 Microstrip Antennas 184

5.3 Antenna Arrays 191

5.3.1 Basic Concept 192

5.3.2 Isotropic Linear Arrays 193

5.3.3 Pattern Multiplication Principle 199

5.3.4 Element Mutual Coupling 200

5.4 Some Practical Considerations 203

5.4.1 Transmitting and Receiving Antennas: Reciprocity 203

5.4.2 Baluns and Impedance Matching 205

5.4.3 Antenna Polarization 206

5.4.4 Radomes, Housings and Supporting Structures 208

5.5 Summary 211

References 211

Problems 212

6 Computer-Aided Antenna Design and Analysis 215

6.1 Introduction 215

6.2 Computational Electromagnetics for Antennas 217

6.2.1 Method of Moments (MoM) 218

6.2.2 Finite Element Method (FEM) 228

6.2.3 Finite-Difference Time Domain (FDTD) Method 229

6.2.4 Transmission Line Modeling (TLM) Method 230

6.2.5 Comparison of Numerical Methods 230

6.2.6 High-Frequency Methods 232

6.3 Examples of Computer-Aided Design and Analysis 233

6.3.1 Wire-type Antenna Design and Analysis 233

6.3.2 General Antenna Design and Analysis 243

6.4 Summary 251

References 251

Problems 252

7 Antenna Manufacturing and Measurements 253

7.1 Antenna Manufacturing 253

7.1.1 Conducting Materials 253

7.1.2 Dielectric Materials 255

7.1.3 New Materials for Antennas 255

7.2 Antenna Measurement Basics 256

7.2.1 Scattering Parameters 256

7.2.2 Network Analyzers 258

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7.3 Impedance, S11, VSWR and Return Loss Measurement 261

7.3.1 Can I Measure These Parameters in My Office? 261

7.3.2 Effects of a Small Section of a Transmission Line or a Connector 262

7.3.3 Effects of Packages on Antennas 262

7.4 Radiation Pattern Measurements 263

7.4.1 Far-Field Condition 264

7.4.2 Open-Area Test Sites (OATS) 265

7.4.3 Anechoic Chambers 267

7.4.4 Compact Antenna Test Ranges (CATR) 268

7.4.5 Planar and Cylindrical Near-Field Chambers 270

7.4.6 Spherical Near-Field Chambers 270

7.5 Gain Measurements 272

7.5.1 Comparison with a Standard-Gain Horn 272

7.5.2 Two-Antenna Measurement 272

7.5.3 Three-Antenna Measurement 273

7.6 Miscellaneous Topics 273

7.6.1 Efficiency Measurements 273

7.6.2 Reverberation Chambers 274

7.6.3 Impedance De-embedding Techniques 275

7.6.4 Probe Array in Near-Field Systems 276

7.7 Summary 281

References 281

Problems 282

8 Special Topics 283

8.1 Electrically Small Antennas 283

8.1.1 The Basics and Impedance Bandwidth 283

8.1.2 Antenna Size-Reduction Techniques 299

8.2 Mobile Antennas, Antenna Diversity and Human Body Effects 304

8.2.1 Introduction 304

8.2.2 Mobile Antennas 305

8.2.3 Antenna Diversity 318

8.2.4 User Interaction 325

8.3 Multiband and Ultra-Wideband Antennas 334

8.3.1 Introduction 334

8.3.2 Multiband Antennas 334

8.3.3 Wideband Antennas 337

8.4 RFID Antennas 340

8.4.1 Introduction 340

8.4.2 Near-Field Systems 343

8.4.3 Far-Field Systems 349

8.5 Reconfigurable Antennas 352

8.5.1 Introduction 352

8.5.2 Switching and Variable-Component Technologies 352

8.5.3 Resonant Mode Switching/Tuning 354

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8.5.4 Feed Network Switching/Tuning 355

8.5.5 Mechanical Reconfiguration 355

8.6 Summary 356

References 356

Index 357

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Preface

As an essential element of a radio system, the antenna has always been an interesting but

difficult subject for radio frequency (RF) engineering students and engineers. Many good

books on antennas have been published over the years and some of them were used as our

major references.

This book is different from other antenna books. It is especially designed for people who

know little about antennas but would like to learn this subject from the very basics to practical

antenna analysis, design and measurement within a relatively short period of time. In order

to gain a comprehensive understanding of antennas, one must know about transmission lines

and radio propagation. At the moment, people often have to read a number of different books,

which may not be well correlated. Thus, it is not the most efficient way to study the subject.

In this book we put all the necessary information about antennas into a single volume and

try to examine antennas from both the circuit point of view and the field point of view. The

book covers the basic transmission line and radio propagation theories, which are then used

to gain a good understanding of antenna basics and theory. Various antennas are examined

and design examples are presented. Particular attention is given to modern computer-aided

antenna design. Both basic and advanced computer software packages are used in examples to

illustrate how they can be used for antenna analysis and design. Antenna measurement theory

and techniques are also addressed. Some special topics on the latest antenna development are

covered in the final chapter.

The material covered in the book is mainly based on a successful short course on antennas

for practising professionals at the University of Oxford and the Antennas module for students

at the University of Liverpool. The book covers important and timely issues involving modern

practical antenna design and theory. Many examples and questions are given in each chapter. It

is an ideal textbook for university antenna courses, professional training courses and self-study.

It is also a valuable reference for engineers and designers who work with RF engineering, radar

and radio communications.

The book is organized as follows:

Chapter 1: Introduction. The objective of this chapter is to introduce the concept of antennas

and review essential mathematics and electromagnetics, especially Maxwell’s equations. Ma￾terial properties (permittivity, permeability and conductivity) are discussed and some common

ones are tabulated.

Chapter 2: Circuit Concepts and Transmission Lines. The concepts of lumped and dis￾tributed systems are established. The focus is placed on the fundamentals and characteristics

of transmission lines. A comparison of various transmission lines and connectors is presented.

The Smith Chart, impedance matching and bandwidth are also addressed in this chapter.

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xii Preface

Chapter 3: Field Concepts and Radio Waves. Field concepts, including the plane wave,

intrinsic impedance and polarization, are introduced and followed by a discussion on radio

propagation mechanisms and radio wave propagation characteristics in various media. Some

basic radio propagation models are introduced, and circuit concepts and field concepts are

compared at the end of this chapter.

Chapter 4: Antenna Basics. The essential and important parameters of an antenna (such

as the radiation pattern, gain and input impedance) are addressed from both the circuit point

of view and field point of view. Through this chapter, you will become familiar with antenna

language, understand how antennas work and know what design considerations are.

Chapter 5: Popular Antennas. In this long chapter, some of the most popular antennas (wire￾type, aperture-type and array antennas) are examined and analyzed using relevant antenna

theories. The aim is to see why they have become popular, what their major features and

properties are (including advantages and disadvantages) and how they should be designed.

Chapter 6: Computer-Aided Antenna Design and Analysis. The aim of this special and unique

chapter is to give a brief review of antenna-modeling methods and software development,

introduce the basic theory behind computer simulation tools and demonstrate how to use

industry standard software to analyze and design antennas. Two software packages (one is

simple and free) are presented with step-by-step illustrations.

Chapter 7: Antenna Manufacturing and Measurements. This is another practical chapter to

address two important issues: how to make an antenna and how to conduct antenna measure￾ment, with a focus placed on the measurement. It introduces S-parameters and equipment. A

good overview of the possible measurement systems is provided with an in-depth example.

Some measurement techniques and problems are also presented.

Chapter 8: Special Topics. This final chapter presents some of the latest important develop￾ments in antennas. It covers mobile antennas and antenna diversity, RFID antennas, multiband

and broadband antennas, reconfigurable antennas and electrically small antennas. Both the

theory and practical examples are given.

The authors are indebted to the many individuals who provided useful comments, suggestions

and assistance to make this book a reality. In particular, we would like to thank Shahzad

Maqbool, Barry Cheeseman and Yang Lu at the University of Liverpool for constructive

feedback and producing figures, Staff at Wiley for their help and critical review of the book,

Lars Foged at SATIMO and Mike Hillbun at Diamond Engineering for their contribution to

Chapter 7 and the individuals and organizations who have provided us with their figures or

allowed us to reproduce their figures.

Yi Huang and Kevin Boyle