3-9
Figure 3-8.—Corner reflector.
Q-7. What type of reflector is most often used in directive antennas?
Q-8. Microwaves can be focused and reflected in the same way as what other type of waves?
Q-9. How many major lobes are radiated by a parabolic reflector?
Q-10. A horizontally truncated paraboloid antenna is used for what purpose?
Q-11. The beam from a horizontally positioned cylindrical paraboloid is narrow in what plane?
HORN RADIATORS
Like parabolic reflectors, you can use HORN RADIATORS to obtain directive radiation at
microwave frequencies. Because they do not use resonant elements, horns have the advantage of being
useful over a wide frequency band.
The operation of a horn as an rf radiating device is similar to that of an automobile horn radiating
sound waves. However, the throat of an automobile horn usually is sized much smaller than the sound
wavelengths for which it is used. The throat of the rf radiating horn is sized to be comparable to the
wavelength being used.
Horn radiators are used with waveguides because they serve both as an impedance-matching device
and as a directional radiator. Horn radiators may be fed by coaxial and other types of lines.
Horn radiators are constructed in a variety of shapes, as illustrated in figure 3-9. The shape of the
horn determines the shape of the field pattern. The ratio of the horn length to the size of its mouth
determines the beam angle and directivity. In general, the larger the mouth of the horn, the more directive
is the field pattern.
Figure 3-9.—Horn radiators.
