Figure 3-19.—Two-wire transmission line.
Figure 3-20.—Quarter-wave section of transmission
line shorted at one end.
Note that quarter-wave sections are insulators at only
one frequency. This severely limits the bandwidth,
efficiency, and application of this type of two-wire
line.
Figure 3-21 shows several metallic insulators on
each side of a two-wire transmission line. As more
insulators are added, each section makes contact with
the next, and a rectangular waveguide is formed. The
lines become part of the walls of the waveguide, as
illustrated in figure 3-22.
The energy is then
conducted within the hollow waveguide instead of
along the two-wire transmission line.
The comparison of the way electromagnetic fields
work on a transmission line and in a waveguide is
not exact. During the change from a two-wire line
to a waveguide, the electromagnetic field configurations
also undergo
changes, the
many changes.
As a result of these
waveguide does not actually operate
Figure 3-21.—Metallic insulator on each side
two-wire line.
Figure 3-22.—Forming a waveguide by adding
quarter-wave sections.
like a two-wire line that is completely shunted
quarter-wave sections. If it did, the use of a wave-
guide would be limited to a single-frequency wave
length that was four times the length of the quarter-
wave sections. In fact, waves of this length cannot
pass efficiently through waveguides. Only a small
range of frequencies of somewhat shorter wavelength
(higher frequency) can pass efficiently.
of a
by
3-11
