15.1 WAVES, TRANSMISSION LINES, WAVEGUIDES, AND ANTENNA FUNDAMENTALS 671
used to connect some television antennas. The coaxial cable of Figure 15.1.1(b) is the most widely
used of the many possible cable-type transmission lines. For printed-circuit and integrated-circuit
applications, transmission lines sketched in Figures 15.1.1(c) through (f) are commonly employed.
At higher frequencies, when power levels are large and attenuation in transmission lines is
significant, connections between system components are often made throughwaveguides, which
are usually hollow, closed, rigid conductor configurations (much like water pipes) through which
waves propagate. The most common waveguides are eitherrectangularorcircularin cross
section, as depicted in Figure 15.1.2, but other shapes and flexible varieties are also possible.
Coaxial transmission lines commonly operate in what is called thetransverse electric
magnetic(TEM)mode, in which both the electric and the magnetic fields are perpendicular
Conductor
Conducting strip
Conductors
d
h
d
Dielectric εr
Dielectric εr
Dielectric εr Dielectric εr
Dielectric
εr
(a)
(c)
(b)
W
W
h
2 h
Hot lead
(e)
W
Conducting strip
Dielectric εr h
Free space ε 0
(d)
W
h
(f)
S W
Ground Hot lead Ground
S
D
Figure 15.1.1Transmission lines (cross sections of some common types).(a)Two-wire line.(b)Coaxial
line (cable).(c)Parallel strip line.(d)Microstrip line.(e)Strip line.(f)Coplanar waveguide.
b
a
(a)
a
(b)
Figure 15.1.2Waveguides.(a)Rectangular.(b)Circular.