Polarization in Antennas and Radar

314 Pages·1986·32.81 MB·English

by  Harold Mott

POLARIZATION
IN ANTENNAS
AND RADAR
HAROLD MOTT
Department of Electrical Engineering
University of Alabama
A Wiley-Interscience Publication
JOHN WILEY & SONS
New York Chichester Brisbane Toronto Singapore
Copyright © 1986 by John Wiley & Sons, Inc.
All rights reserved. Published simultaneously in Canada.
Reproduction or translation of any part of this work
beyond that permitted by Section 107 or 108 of the
1976 United States Copyright Act without the permission
of the copyright owner is unlawful. Requests for
permission or further information should be addressed to
the Permissions Department, John Wiley & Sons, Inc.
Library of Congress Catalogin8 in Publication Data:
Mott, Harold.
Polarization in antennas and radar.
"A Wiley-Interscience publication."
Bibliography: p.
Includes Index.
1. Radar. 2. Antennas (Electronics)
3. Electromagnetic waves--Polarization. 1. Title.
TK6580.M68 1986 621.38'028'3 86-1349
ISBN 0-471-01167-3
Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
To my mother,
my wife Betty,
and my son John

PREFACE
It is my belief that the concepts of wave polarization, even though they are
not difficult to understand, are not known as widely as they should be.
Introductory electromagnetics texts normally restrict discussions of wave
propagation to linearly polarized waves, and the more advanced texts that
are widely used in this country devote only little attention to elliptical
waves. Antenna textbooks, with that of Kraus a notable exception, either
ignore the questions of polarization and polarization match or treat them
too lightly. Principles of Optics by Born and Wolf has a good discussion of
wave polarization, and Clarke and Grainger (Polarized Light and Optical
Measurement) treat polarized light extensively. Beckman (The Depolariz
ation of Electromagnetic Waves and The Scattering of Electromagnetic Waves
from Rough Surfaces, the latter book written with A. Spizzichino) discusses
polarization changes caused by scattering. None of these books is readily
usable by many who must deal with polarization problems, particularly
those associated with radar and antennas, and they must gather their
information from several sources, with incomplete coverage and inconsistent
notation.
Polarization effects can provide significant identification information
about radar targets, and the use of an optimum polarization can increase
target cross sections, decrease rain and ground clutter, and ameliorate the
effects of jamming on radar and communication systems. Adaptive arrays
can be used for polarization adaptivity as well as for beam forming and null
steering, and an example of such use is given in this book. Other examples
can be cited for microwave and millimeter-wave radar and communications,
and for optics. There is a clear need for a wider dissemination of the
methods of treating polarization problems, and I hope to answer that need
with this book.
The text is intended for use at the graduate or advanced undergraduate
level for engineering and physics students and as a reference for radar and
vii
viii PREFACE
communications engineers. It is expected to be useful also for those working
with coherent light sources. It has been used for a one-semester course for
graduate students and seniors, with good results. The necessary background
is a good understanding of calculus and vector analysis, some knowledge of
matrices, and a knowledge of electromagnetics equivalent to that acquired
by completing the study of a good undergraduate text. The chapter on
antennas will provide a satisfactory base for those without such a back
ground. The chapter necessarily omits a discussion of many types of
antennas and of many of the methods for determining radiation patterns and
impedances. It does, however, include definitions of the more important
antenna parameters (from the 1983 IEEE Standard) and developments of
the equations for using them in a communications or radar system. In fact,
Chapters 1 through 4 can be used for a one-semester course in antennas for
students interested in the use of antennas rather than in their design, if it is
supplemented by material on arrays. Chapter 3 discusses polarization match
ing for antennas in more detail than any of the standard antennas texts, and
it analyzes transmission between antennas that are not pointing at each
other and are not polarization matched. Euler angle transformations be
tween coordinate systems are given for use in the analysis. Such a complete
discussion is not commonly included in antennas texts, many of which are
oriented toward design rather than use of antennas. The analysis will also be
useful for optical and infrared systems. Chapter 4 describes polarization
properties of several antennas and appropriate test antennas for use with
them, to determine the degree to which they meet design criteria. Chapter 5
describes methods for generating waves with any desired polarization and
analyzes a system that is polarization adaptable. .
Chapter 6 is a discussion of polarization changes by reflection and
transmission. It introduces the scattering matrix and includes scattering
matrices for some common reflecting objects. Also presented is the de
polarization by reflections from an arbitrarily oriented plane. Chapter 7
develops the theory of partially polarized waves, which is useful in radio
astronomy and has applications to jamming in radar. Finally, in Chapter 8,
standard techniques (and one nonstandard) for measuring wave polarization
are presented.
In the text the polarization ratio P (or its modified form jP) and the
circular polarization ratio q are the primary descriptors of a wave or an
antenna. The Poincare sphere is an elegant device for presenting polar
ization information, and it is useful in developing certain theorems, for
example, the theorem that three polarization match factors (amplitudes)
between an unknown antenna and three antennas of known polarization
suffice to determine the polarization of the unknown antenna. Many of the
text developments, therefore, utilize the Poincare sphere, and since P is a
projection, onto a plane, of the polarization point on the sphere, any text
equation using P can be easily converted to coordinates on the Poincare
sphere. Description of wave polarization by axial ratio, tilt angle, and
PREFACE ix
rotation sense of the polarization ellipse is useful for visualization but
awkward mathematically. This description is therefore not extensively used
in the book.
Some of the material presented here is original, but much of it comes
from developments or presentations by others, most notably on the subject
of antennas by Kraus, Collin and Zucker, and Balanis, and on the subject of
polarization by Rumsey, Sinclair, Deschamps, Born and Wolf, and Beck
mann. I wish to acknowledge a great debt to them.
HAROLD MOTI
University, Alabama
May 1986