Reverberation Chambers

This book covers important and timely issues in Reverberation Chambers (RCs) and their applications to EMC and Antenna measurements. Developed specifically for university students, researchers, practicing industrial engineers and designers who work with antennas in radio frequency (RF) engineering, EMC, radar, and radio communications. This book will provide the reader with a firm theoretical and practical understanding of the RCs operation, allowing them to undertake practical antenna and EMC measurement work with confidence and accuracy. The book is built on many years of research by the authors that encompass many of the new advances in antenna design.

Auteur

Dr Stephen J. Boyes, Defence Science and Technology Laboratories, UK
Stephen Boyes is a Principal RF Engineer at security services department at the Defence Science and Technology Laboratories.

Dr Yi Huang, University of Liverpool, UK
Yi Huang received the BSc in Physics from Wuhan University and a MSc in RF/Microwave engineering from Nanjing, China in 1984 and 1987 respectively, and a DPhil in Communications and Electromagnetics from the University of Oxford in 1993. He joined the University of Liverpool in 1995.

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1
Introduction

1.1 Background

The concept of the Reverberation Chamber (RC) was first proposed by H. A. Mendes in 1968 as a novel means for electromagnetic field strength measurements [1]. The RC can be characterised as an electrically large shielded metallic enclosure with a metallic stirrer to change the field inside the chamber that is designed to work in an 'over-mode' condition (i.e. many modes). It has taken some time for the facility to gain universal acceptance, but by the 1990s, their use for performing Electromagnetic Compatibility (EMC) and Electromagnetic Interference (EMI) measurements was well established and various aspects were studied [2-11]. An international standard on using the RC for conducting EMC testing and measurements was published in 2003 [12]. The RC is now used for radiated emission measurements and radiated immunity tests, as well as for shielding effectiveness measurements. It was in this role that the facility was known for a long time and in part still continues to be [13, 14]. More recently the RC has been employed for antenna measurements due to the rapid development of wireless communications.

It is clear that the role and function of wireless technology in everyday life have reached unprecedented levels as compared to 20-30_years ago. For this change to take place, it has meant that antenna designs and their characterisation have had to evolve also. A question exists as to how the RC has risen to prominence to be proposed and also to be used for antenna measurements, which represents a brand new capability for the chamber that diverges from its initial intended use. To answer this question, we must partly examine the nature of antenna designs and their operational use.

Traditionally, antennas have always been orientated, and their communication channels configured in a Line of Sight (LoS) manner. For example, we have terrestrial antennas mounted on roof tops, and other directive types of antenna that are employed in satellite communications. The characterisation of these types of antenna for use in LoS communications are widely defined by the application of an equivalent free space reflection-free environment, which is typified by the Anechoic Chamber (AC). In a real application environment, reflection, scattering and diffraction effects may still exist to a certain extent, which brings about the creation of additional wave paths within the communication channel. However, the AC is still the preferred environment to characterise these types of antennas as their radiation patterns (and other subsequent parameters of interest) are of prime importance to the LoS scenario.

When we consider the modern mobile terminals (such as the mobile/cell phone), they do not operate under the premise of an LoS scenario. The antennas inside mobile phones might seldom 'see' the base station and they are expected to work perfectly in Non-Line of Sight (NLoS) environments. This type of environment will readily give rise to signals that will be exposed to reflections caused by large smooth objects, diffraction effects caused by the edges of sharp objects and scattering effects caused by small or irregular objects. When these effects occur, they will cause the creation of additional wave paths which will eventually add at the receiving side. These wave contributions have independent complex amplitudes (i.e. magnitude and phase information), such that at recombination, they may add constructively or destructively or anything in between these extremes. The wave paths and their complex amplitudes are also subject to rapid changes with time, with the terminal moving or parts of the environment (communication channel) changing. This brings about variations in the signal at the receiver and is commonly referred to as fading. The largest variations occur when there is a complete block on the LoS, which is more accurately referred to as

Contenu

About the Authors viii

Acknowledgements x

1 Introduction 1

1.1 Background 1

1.2 This Book 3

References 5

2 Reverberation Chamber Cavity Theory 7

2.1 Introduction 7

2.2 Cavity Modes and Electromagnetic Fields 8

2.3 Mode Stirring Techniques 17

2.4 Plane Wave Angle of Arrival 21

2.5 Average Mode Bandwidths 24

2.6 Chamber Quality (Q) Factor 26

2.7 Statistical Forms 30

2.8 Line of Sight Elements 44

2.9 Reverberation Chamber as a Radio Propagation Channel 52

References 56

3 Mechanical Stirrer Designs and Chamber Performance Evaluation 58

3.1 Introduction 58

3.2 Paddle Design Methodology 61

3.3 Numerical Analysis 63

3.4 Comments on Practical Validation 78

3.5 Measurement Parameters for Validation 80

3.6 Measurement Results 81

3.7 Summary 92

References 92

4 EMC Measurements inside Reverberation Chambers 94

4.1 Introduction to EMC 95

4.2 EMC Standards 98

4.3 EMC Measurements and Tests 101

4.4 EMC Measurements Inside Reverberation Chambers 103

4.5 Comparison of Reverberation Chamber and Other

Measurement Facilities for EMC Measurements 123

4.6 Conclusions 127

Acknowledgements 127

References 127

5 Single Port Antenna Measurements 129

5.1 Introduction 130

5.2 Definitions and Proof: Antenna Efficiency 131

5.3 Definitions: Textile Antennas 134

5.4 Measurement Procedures 134

5.5 Free Space Measurement Investigation 138

5.6 OnBody Antenna Measurements 145

5.7 Theoretical and Simulated Evidence 161

5.8 Measurement Uncertainty 163

5.9 Summary 166

References 167

6 Multiport and Array Antennas 169

6.1 Introduction 169

6.2 Multiport Antennas for MIMO Applications 171

6.3 Measurement Parameters 174

6.4 Diversity Gain from Cumulative Distribution Functions (CDF) 175

6.5 Diversity from Correlation 180

6.6 Channel Capacity 185

6.7 Embedded Element Efficiency 186

6.8 Definitions: Conventional Array Antenna Measurements 191

6.9 Measurement Parameters 192

6.10 Deduction of Characterisation Equation 194

6.11 Measurement Results 196

6.12 Measurement Uncertainty 200

6.13 Summary 200

References 201

7 Further Applications and Developments 203

7.1 Shielding Effectiveness Measurements 203

7.2 Antenna Radiation Efficiency Measurements without a Reference Antenna 209

7.3 Antenna Diversity Gain Measurements without a Reference Antenna 213

7.4 Wireless Device and System Evaluation 214

7.5 Other Reverberation Chambers and the Future 216

7.6 Summary 218

References 218

Appendix A: Deduction of Independent Samples 220

Appendix B: Multivariate Normality Test for SIMO Channels 225

Appendix C: Surface Current Nature 230

Appendix D: BS …