(2) Guiding energy to test equipment.
(3) Guiding energy to a dummy load.
b. Waveguide is used extensively to guide RF energy to an antenna.
Figure 115 shows a waveguide feeding a reflector.
A reflector is an
important part of many antennas because it is used to direct the RF energy
into space.
Figure 115 shows how energy is coupled from the waveguide,
through the air, to the reflector using a "horn."
Figure 115. Waveguide Coupled to a Reflector.
17. Horn coupling.
a. Notice in the figure that the waveguide is flared at the end and
resembles a horn.
A horn is a common method of coupling energy from a
waveguide to a reflector.
b. You might think it would be easier if we just had the waveguide
opening pointed at the reflector. Well, it would be, so why bother with a
horn? Here's the reason: Remember, we said a waveguide should be terminated
in its characteristic impedance.
That's the purpose of the horn; it's an
impedance-matching device.
As the sides of the waveguide get wider, its
impedance increases.
c. A horn then, matches the comparatively
low
impedance
of
the
waveguide to the higher impedance of the air.
170
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