SN04
SN04
SN04
Section IV Electromagnetics
The Electrical Engineering Handbook
Ed. Richard C. Dorf
Boca Raton: CRC Press LLC, 2000
High power gyrotron from CPI. The 110-GHz gyrotron is the current world record holder
for high frequency power generation. This gyrotron is used in electron cyclotron resonance heating (ECRH) by producing extremely high frequencies of microwaves which
heat a hydrogen gas plasma to very high levels in experimental fusion reactors.
In the photo, the lower section is the electron gun region that generates extremely
high-powered electron beam. Shown in the middle section of the gyrotron is an interactive
window. The produced microwave power is transformed into a microwave beam that
then passes through the high power interaction window. The large upper section is a fully
instrumented collector of the spent electron beam. (Photo courtesy of Communications
& Power Industries.)
2000 by CRC Press LLC
IV
Electromagnetics
35 Electromagnetic Fields
J.A. Kong
39 Microwave Devices
40 Compatibility
Banmali S. Rawat
University of Nevada, Reno
LECTRIC AND MAGNETIC FORCES are among the five original forces in the universe. These forces
are important as we are affected by them almost every instant. Electromagnetics is the combined effect
of electric and magnetic fields. Todays scientific development to a great extent is based on the electromagnetic fields, their propagation, and varying effects under different boundary conditions. Very few subjects
are understood as thoroughly as electromagnetics and have such wide applications. Electricity, telephones, radio,
television, datalinks, medical electronics, radar, remote sensing, etc.all have considerable impact on human
life. Now that impact is being carried out further with optical fiber technology, which is also based on the
concept of electromagnetic wave propagation. All of human society has been revolutionized by electromagnetics,
but still our understanding is not complete. As H.G. Wells once wrote, and this is still true, The past is but a
beginning of a beginning, and all that is and has been is but the twilight of the dawn.
2000 by CRC Press LLC
This section focuses on the basic electromagnetic field concepts, wave propagation, devices, circuits, and
other applications. The electric fields which are produced by stationary or moving charges are described in
Chapter 35. Maxwells equations and their solutions under different boundary conditions help in determining
the electric field components and resulting effects. The next chapter describes the magnetic fields and magnetic
effects due to moving charges or current. These magnetic fields are also governed by Maxwells equations and
their solutions are obtained for different boundary conditions. Particular magnetic materials with an assemblage
of ferromagnetic particles in a nonferromagnetic matrix are useful as audio or video tapes. This subject is
investigated in Chapter 36 to provide insight into the recording mechanism of the music we hear all the time.
The time-varying electromagnetic field propagation in space or in transmission lines provides the concept of
radio communication as discussed in Chapter 37. Another article in the chapter analyzes the transmission of
energy through waveguides and microstriplines. Microstriplines have become the basic building blocks for
microwave integrated circuits (MICS). For the propagation of electromagnetic fields in space, properly matched
antennas between generator and space are required, as described in Chapter 38. Wire and aperture antennas
are also described.
The high-frequency or microwave-frequency electromagnetic field concepts are helpful in studying the microwave devices as discussed in Chapter 39. The electromagnetic compatibility (EMC) study in the following chapter
is important for proper functioning of microwave devices and circuits. The important application of electromagnetic radiation in the form of radar, discussed in Chapter 41, is useful not only for defense but in remote
sensing and weather forecasting also. The next chapter explains the propagation of light through waveguides and
optical fibers/cables. Optical fiber technology is an emerging technology and is affecting every facet of human
life. Microwave circuits are the practical realization of electromagnetic field concepts and are discussed in
Chapter 42. With the arrival of sophisticated software packages and high-speed computers, now it is possible
and worthwhile to do 3-D analysis and computer modeling of electromagnetic fields in the circuits or devices,
as discussed in the last two chapters of this section. This is helpful in the accurate design of microwave components
and circuits. All the topics mentioned in this introduction are discussed in detail in their respective chapters.
Nomenclature
Symbol
Ae
Quantity
a
b
B
b
c
D
D
D
d
E
e
e0
fD
F
gm
G
electric displacement
divergent factor
directivity of antenna
penetrating depth
electric field intensity
permittivity
8.854 1012
Doppler frequency
receiver noise figure
transconductance
gain of antenna
Aem
Unit
Symbol
m2
g
G
H
h
J
J
k
k
L
l
m
m0
P
PT
Y
q
R
rs
S(q)
U
m2
neper/m
Hz
Wb/m2
rad/m
2.998
108 m/s
C/m2
dB
m
V/m
F/m
F/m
Hz
dB
S
dB
Quantity
propagation constant
Fresnel reflection coefficient
magnetic field intensity
intrinsic impedance
electric current density
electric charge density
wavenumber
radiation efficiency factor
antenna loss
wavelength
permeability
4p 107
Poynting vector
average power
grazing angle
electronic charge
detection range of target
roughness coefficient
shadowing function
unilateral power gain
Unit
m1
A/m
W
A/m2
C/m2
dB
m
H/m
H/m
W/m2
W
degree
1.6 1019 C
m
dB