Introduction to Antennas

140 Pages·1988·5.49 MB·English

by  Martin S. Smith MA

Introduction to Antennas
Macmillan New Electronics Series
Series Editor: Paul A. Lynn
Paul A. Lynn, Radar Systems
A. F. Murray and H. M. Reekie, Integrated Circuit Design
Martin S. Smith Introduction to Antennas
Introduction to
Antennas
Martin S. Smith
MA, PhD, CEng, MIEE
Senior Principal Research Engineer, S.T.L., Harlow
formerly
Lecturer in Electronic Engineering, University College London
Macmillan New Electronics
Introductions to Advanced Topics
M
MACMILLAN
EDUCATION
© Martin S. Smith 1988
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First published 1988
Published by
MACMILLAN EDUCATION LTD
Houndmills, Basingstoke, Hampshire RG21 2XS
and London
Companies and representatives
throughout the world
British Library Cataloguing in Publication Data
Smith, Martin S.
Introduction to antennas.-(Macmillan
new electronics).
1. Antennas (Electronics)
I. Title
621.38'028'3 TK7871.6
ISBN 978-0-333-44559-4 ISBN 978-1-349-19384-4 (eBook)
DOI 10.1007/978-1-349-19384-4
For my wife Sandy and
for my brother Steve
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Contents
Series Editor's Foreword ix
Preface X
List of Symbols xi
1 Basic Antenna Concepts 1
1.1 Introduction 1
1.2 From ELF to mm waves 1
1.3 Maxwell's equations and plane waves 5
1.4 Basic antenna properties 8
1.5 Reciprocity and receiving antennas 10
1.6 Choice of frequency 13
1. 7 Antenna analysis and design 15
Reference 16
2 Wire Antennas 17
2.1 Introduction 17
2.2 The Hertzian dipole 18
2.3 Dipoles and monopoles 21
2.4 Parasitic elements 23
2.5 Loops and slots 25
2.6 Printed antennas 27
2. 7 An introduction to moment methods 29
2.8 Case study: antennas on aircraft 31
References 32
3 Aperture Theory 33
3.1 Diffraction by apertures 33
3.2 Aperture theory in two dimensions 35
3.3 Applications of aperture theory 44
3.4 Aperture theory in three dimensions 48
3.5 Gain 55
3.6 Case study: airport radar antennas 56
4 Linear Arrays 59
4.1 Introduction 59
4.2 The radiation pattern of a linear array 59
4.3 Nulls 63
vii
viii Contents
4.4 Pattern multiplication 67
4.5 Beam steering 68
4.6 Woodward synthesis of antenna patterns 70
4. 7 Case study: the ILS array system 73
References 76
5 Antenna Measurements 77
5.1 Introduction 77
5.2 Input impedance 77
5.3 Radiation patterns 78
5.4 Gain measurements 82
5.5 Polarisation measurements 84
5.6 Case study: a vertical antenna range 85
References 88
6 Further Array Topics 89
6.1 Introduction 89
6.2 Scanning antennas 89
6.3 Orthogonal beams and multiple beam formers 92
6.4 Planar arrays 100
6.5 Mutual coupling in phased arrays 105
6.6 Circular arrays 106
6. 7 Case study: a Rotman lens multiple beam former 109
References 112
Appendix A: Vector Differential Operators 114
Appendix B: The Fields of a Hertzian Dipole 116
Appendix C: Derivation of Aperture Theory in Three
Dimensions 118
Exercises 121
Bibliography 123
Answers to Exercises 124
Index 125
Series Editor's Foreword
The rapid development of electronics and its engineering applications
ensures that new topics are always competing for a place in university and
polytechnic courses. But it is often difficult for lecturers to find suitable
books for recommendation to students, particularly when a topic is
covered by a short lecture module, or as an 'option'.
Macmillan New Electronics offers introductions to advanced topics. The
level is generally that of second and subsequent years of undergraduate
courses in electronic and electrical engineering, computer science and
physics. Some of the authors will paint with a broad brush; others will
concentrate on a narrower topic, and cover it in greater detail. But in all
cases the titles in the Series will provide a sound basis for further reading of
the specialist literature, and an up-to-date appreciation of practical
applications and likely trends.
The level, scope and approach of the Series should also appeal to
practising engineers and scientists encountering an area of electronics for
the first time, or needing a rapid and authoritative update.
ix
Preface
Antennas are a vital part of many communication and radar systems, as
they form and control the link between cable and radiative transmission of
signals. As such they are usually an important topic in final year under
graduate courses and M.Sc. courses in Electronic Engineering and related
disciplines. This book is intended to cover the theory and practice of
antennas at a level suitable for such courses; it should also be a useful
introduction to the subject for recently qualified engineers working in
industry.
The first five (of six) chapters treat the basic theoretical analysis and
experimental techniques. The main topics are wire antennas, aperture
antennas, linear arrays and antenna measurements. There is an extensive
literature covering more advanced and specialised antenna topics. The
final chapter of this book includes a small selection of these topics, mainly
associated with phased arrays. These have been chosen on the grounds that
they contain some important principles of which a future antenna, or
system, designer should be aware. Each chapter contains a case study of a
practical application to illustrate the work of the chapter.
Thanks are due to many colleagues who have passed on their own
experience to me. I am particularly indebted to the .following people.
Dr Kenneth Budden supervised my research in radio wave propagation.
Mr Norman Pavey first introduced me to antennas, particularly for aircraft
use. Professor 'Den' Davies led me into various microwave antenna
research topics, while Professor Alec Cullen introduced me to lecturing on
antennas. I would also like to thank Mrs Margaret Ringsell for her expert
typing of the manuscript.
MartinS. Smith
X