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Series Books Published 
Collin, R. E., Field  Theory of Guided Waves, 2d. rev. ed., 1991 
Tai, C. T.,  Generalized kctor and Dyadic Analysis: 
Applied Mathematics in FieM  Theory, 1991 
Dyadic Green Functions 
in Electromagnetic Theory 
Second Edition 
Chen-To Tai 
Professor Emeritus 
Radiation Laboratory 
Department of Electrical Engineering 
and Computer Science 
University of Michigan 
IEEE PRESS Series on 
Electromagnetic Waves 
G. Dudley, Series Editor 
Elliott, R. S., Electromagnetics: History, Theory, and Applications, 1993 
Harrington, R. F., Field  Computation by Moment Methoh, 1993 
Tai, C. T, Dyadic Green Functions in Electromagnetic Theory, 2nd ed., 1993 
Future Series Title 
Dudley, D. G., Mathematical Foundations of Electromagnetic Theory 
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Dyadic green functions in electromagnetic theory 
Tai Chen-To  (date) 
by Chen-to Tai.-2nd 
cm. 
p. 
ed. 
Sponsors : IEEE Antennas and Propagation Society and IEEE Microwave 
The0  and Techniques Society. 
~ n c l u z s  Biblio  aphical references and index. 
ISBN 0-7803-&-7 
1.  Electroma  etic theory-Mathematics. 
2.  Green's  functions. 
I. IEEE Antennas and Propagation 
3.  Boundary v a E  problems. 
Society.  11.  IEEE Microwave Theory and Techniques Society. 
Ill. Title 
93-24201 
CIP 
Contents 
PREFACE 
ACKNOWLEDGMENTS 
1  GENERAL THEOREMS AND FORMULAS 
1-1 Vector Notations and the Coordinate Systems 
1-2  Vector Analysis 
1-3  Dyadic Analysis 
1-4  Fourier Transform and Hankel Transform 
1-5  Saddle-Point Method of Integration and Semi-infinite 
4 
6 
12 
1 
Integrals of the Product of Bessel Functions 
16 
2  SCALAR GREEN FUNCTIONS 
2-1  Scalar Green Functions of a One-Dimensional Wave 
Equation-Theory  of Transmission Lines 
21 
2-2  Derivation of go(x, x')  by the Conventional Method 
and the Ohm-Rayleigh Method 
25 
2-3  Symmetrical Properties of Green Functions 
2-4  Free-Space Green Function of the Three-Dimensional 
33 
Scalar Wave Equation 
35 
3  ELECTROMAGNETIC THEORY 
3-1  The Independent and Dependent Equations 
and the Indefinite and Definite Forms 
of  Maxwell's Equations 
38 
3-2  Integral Forms of Maxwell's Equations 
3-3  Boundary Conditions 
3-4  Monochromatically Oscillating Fields 
42 
in Free Space 
47 
3-5  Method of Potentials 
49 
41 
xi 
xiii 
1 
38 
vii 
viii 
4  DYADIC GREEN FUNCTIONS 
4-1  Maxwell's Equations in Dyadic Form and Dyadic 
Green Functions of the Electric and Magnetic Trpe 
4-2  Free-Space Dyadic Green Functions 
4-3  Classification of Dyadic Green Functions 
4-4  Symmetrical Properties of Dyadic Green Functions 
4-5  Reciprocity Theorems 
4-6  Transmission Line Model of the Complementary 
62 
85 
59 
Reciprocity Theorems 
90 
4-7  Dyadic Green Functions for a Half Space Bounded 
by a Plane Conducting Surface 
92 
5  RECTANGULAR WAVEGUIDES 
5-1  Rectangular Vector Wave Functions 
5-2  The Method of Em 
5-3  The Method of ??, 
5-4  The Method of EA 
5-5  Parallel Plate Waveguide 
5-6  Rectangular Waveguide Filled 
103 
110 
114 
115 
with Two Dielectrics 
5-7  Rectangular Cavity 
5-8  The Origin of the Isolated Singular Term in F, 
118 
124 
128 
6  CYLINDRICAL WAVEGUIDES 
6-1  Cylindrical Wave Functions with Discrete 
Eigenvalues 
133 
6-2  Cylindrical Waveguide 
6-3  Cylindrical Cavity 
6-4  Coaxial Line 
143 
142 
140 
7  CIRCULAR CYLINDER IN FREE SPACE 
7-1  Cylindrical Vector Wave Functions with Continuous 
Eigenvalues 
149 
7-2  Eigenfunction Expansion of the Free-Space Dyadic 
Green Functions 
152 
7-3  Conducting Cylinder, Dielectric Cylinder, and Coated 
Cylinder 
154 
7-4  Asymptotic Expression 
159 
8  PERFECTLY CONDUCTING ELLIPTICAL CYLINDER 
8-1  Vector Wave Functions in an Elliptical Cylinder 
Coordinate System 
161 
8-2  The Electric Dyadic Green Function of the First 
Kind 
166 
9  PERFECTLY CONDUCTING WEDGE AND THE HALF SHEET 
9-1  Dyadic Green Functions for a Perfectly 
Conducting Wedge 
169 
9-2  The Half Sheet 
173 
Contents 
Contents 
55 
55 
74 
9-3  Radiation from Electric Dipoles in the Presence 
174 
of a Half Sheet 
9-3.1  Longitudinal Electrical Dipole 
9-3.2  Horizontal Electrical Dipole 
9-3.3  Vertical ~lectric Dopole 
178 
174 
176 
9-4  Radiation from Magnetic Dipoles in the Presence 
of a Half Sheet 
179 
9-5  Slots Cut in a Half Sheet 
9-5.1  Longititudinal Slot 
9-5.2  Horizontal Slot 
184 
182 
183 
96 
9-6  Diffraction of a Plane Wave by a Half Sheet 
9-7  Circular Cylinder and Half Sheet 
196 
187 
10  SPHERES AND PERFECTLY CONDUCTING CONES 
10-1 Eigenfunction Expansion of Free-Space Dyadic 
10-2  An Algebraic Method of Finding E,,  without the 
Green Functions 
198 
Singular Term 
204 
10-3  Perfectly Conducting and Dielectric Spheres 
10-4  Spherical Cavity 
10-5  Perfectly Conducting Conical Structures 
10-6  Cone with a Spherical Sector 
218 
223 
220 
210 
1 1  PLANAR STRATIFIED MEDIA 
11-1 Flat Earth 
11-2  Radition from Electric Dipoles in the Presence 
225 
of a Flat Earth and Sommerfeld's Theory 
228 
11-3  Dielectric Layer on a Conducting Plane 
11-4  Reciprocity Theorems for Stratified Media 
11-5  Eigenfunction Expansions 
11-6  A Dielectric Slab in Air 
11-7  Two-Dimensional Fourier Transform of the Dyadic 
244 
249 
233 
237 
Green Functions 
251 
12 
169 
INHOMOGENEOUS MEDIA AND MOVING MEDIUM 
12-1  Vector Wave Functions for Plane 
255 
12-2  Vector Wave Functions for Spherically 
Stratified Media 
Stratified Media 
255 
259 
12-3  Inhomogeneous Spherical Lenses 
12-4  Monochromatically Oscillating Fields in a Moving 
260 
Isotropic Medium 
270 
12-5  Time-Dependent Field in a Moving Medium 
12-6  Rectangular Waveguide with a Moving Medium 
12-7  Cylindrical Waveguide with a Moving Medium 
12-8  Infinite Conducting Cylinder 
293 
in a Moving Medium 
277 
286 
291 
APPENDIX A  MATHEMATICAL  FORMULAS 
A-1  Gradient, Divergence, and Curl 
296 
in Orthogonal Systems 
A-2  Vector Identities 
A-3  Dyadic Identities 
A-4  Integral Theorems 
APPENDIX B  VECTOR WAVE FUNCTIONS 
298 
298 
299 
A N D  THEIR MUTUAL RELATIONS 
B-1  Rectangular Vector Wave Functions 
B-2  Cylindrical Vector Wave Functions with Discrete 
302 
Eigenvalues 
304 
B-3  Spherical Vector Wave Functions 
B-4  Conical Vector Wave Functions 
APPENDIX C  EXERCISES 
305 
306 
REFERENCES 
NAME INDEX 
SUBJECT INDEX 
Contents 
296 
Preface 
The first edition of this book, bearing the same title, was published by Intext Edu- 
cation Publishers in 1971. Since then, several topics in the book have been found 
to have been improperly treated; in particular, a singular term in the eigenfunc- 
tion expansion of the electrical dyadic Green function was inadvertently omitted, 
an oversight that was later amended [Tai, 19731. 
In  the  present  edition,  some  major  revisions  have  been  made.  First, 
Maxwell's equations have been cast in a dyadic form to facilitate the introduction 
of the electric and the magnetic dyadic Green functions. The magnetic dyadic 
Green function was not introduced in the first edition, but it was found to be 
a very important entity in the entire theory of dyadic Green functions. Being a 
solenoidal function, its eigenfunction expansion does not require the use of non- 
solenoidal vector wave functions or Hansen's L-functions [Stratton, 19411. With 
the aid of Maxwell-Ampkre equation in dyadic form, one can find the eigenfunc- 
tion expansion of the electrical dyadic Green function, including the previously 
missing singular term. This method is used extensively in the present edition. 
Several other new features are found in this edition. For example, the inte- 
gral solutions of Maxwell's equations are now derived with the aid of the vector- 
dyadic Green's theorem instead of by the vector Green's theorem as in the old 
treatment.  By doing so, many intermediate steps can be omitted.  In reviewing 
Maxwell's theory we have emphasized the necessity of adopting one of two alter- 
native postulates in stating the boundary conditions. The implication is that the 
boundary conditions cannot be derived from Maxwell's differential equations 
without a postulate.  Reciprocity theorems in electromagnetic theory are dis- 
cussed in detail.  In addition to the classical theorems due to Rayleigh, Carson, 
and Helmholtz, two complementary reciprocity theorems have been formulated 
xii 
Preface 
to uncover the symmetrical relations of the magnetic dyadic Green functions not 
derivable from the Rayleigh-Carson theorem. 
Various dyadic Green functions for problems involving plain layered media 
have been derived, including a two-dimensional Fourier-integral representation 
of these functions. In the area of moving media, the problem of transient radi- 
ation is formulated with the aid of an affine transformation which enables us to 
solve the Maxwell-Minkowski equation in a relatively simple manner. 
Many new exercises have been added to this edition to help the reader bet- 
ter understand the materials covered in the book.  Answers for some exercises 
are given, and sufficient hints are provided for many others so that the book 
may be used not only as a reference but also as a text for a graduate course in 
electromagnetic theory. 
Acknowledgments 
I am very grateful to Professor Per-Olof  Brundell of  the University of  Lund, 
Sweden, who, in  1972, called my  attention to the incompleteness of the eigen- 
function expansion of the electric dyadic Green function in the original edition 
of this book.  My  discussion with Dr. Olov Einarsson, then a faculty member 
of the same institution, on the dependence of the integral of the electric dyadic 
Green function on the shape of the cell in the source region was very valuable, 
particularly, on the aspect ratio of  a cylindrical cell. The works of Prof. Robert 
E. Collin consolidate our understanding of the singularity behavior of the dyadic 
Green functions. His many communications with me on this subject were very 
valuable prior to the publication of  a book in this field by  Prof. J. Van  Blade1 
[1991].  I am also very grateful to Prof.  Donald G. Dudley and Dr.  William A. 
Johnson for their very careful review of my original manuscript. Section 5-8 of 
Chapter 5 was written as a result of their thoughtful comments. 
During the preparation of this manuscript I received the most valuable help 
from Ms. Bonnie Kidd. Her expertise in typing this manuscript was invaluable. 
The assistance of Dr. Leland Pierce and Ms. Patricia Wolfe are also very much 
appreciated. 
I would  also like to express my  sincere thanks to Prof. Fawwaz T.  Ulaby, 
Director of the Radiation Laboratory at the University of Michigan, for his con- 
stant encouragement by  providing me with the technical support necessary to 
complete this manuscript.  Mr. Dudley Kay, Director of  Book Publishing, and 
Ms.  Karen Miller, Production Editor of IEEE Press, have proved to be most 
efficient and helpful during all stages of the production of this book. 
Chen-To Tai 
Ann Arbor, Michigan 
xiii 
Dyadic Green Functions 
in Electromagnetic Theory 
General Theorems 
and Formulas 
In  this  chapter  we  review  some  of  the  important  theorems  and  formulas 
needed  in the subsequent chapters.  It is assumed that the reader has had  an 
adequate course in advanced calculus, including vector analysis, Fourier series 
and integrals, and the theory of complex variables. Our review will contain suf- 
ficient material so that references to other books will be kept to a minimum. We 
sacrifice to some extent the mathematic rigor that may be required in a more 
thorough treatment.  For example, we use quite freely the integral representa- 
tion of the delta function, assuming that an exponential function with imaginary 
argument is Fourier transformable. Whenever necessary, adequate references1 
will  be  given  to  strengthen  any  plausible  statement  or  to  remove  possible 
ambiguity. 
1-1  VECTOR  NOTATIONS AND THE COORDINATE 
SYSTEMS 
A vector quantity or a vector function will be denoted by F. A letter with a hat, 
such as P, is used to denote a unit vector in the direction of the covered letter. 
In most cases, these letters correspond to the variables 
- -  in a coordinate system. 
The -  scalar product of two vectors is denoted by A .  B and the vector product by 
A x B. The three commonly used systems in this book are 
1.  Rectangular, or Cartesian, x, y, z 
2.  Circular cylindrical or simply cylindrical, r, 4, z 
3.  Spherical, R, 0, 4 
'1n  the citations in the text, the author's name is used as the identification.  If  it is a book, 
either the section number or the pages will be cited, if necessary.