Figure 143.
How a Radar Reflector Works.
c. The antenna in Figure 143 uses a reflector having the geometric
shape of a paraboloid. Because a paraboloid looks something like a dish, it
is commonly called a dish reflector.
22. How a dish reflector works.
a. Figure 144 gives a cross-sectional view of a dish reflector. Notice
the point in front of the reflector called the focal point. The focal point
is important because any energy radiated from the focal point strikes the
reflector and bounces off in a straight line away from the reflector. So,
by locating the antenna at the focal point, we can feed RF energy at the
focal point and get a narrow cone-shaped beam. The beam, of course, is very
directional.
That's why an antenna using a dish reflector has a gain of
about 1,000 over a simple dipole antenna. Because of their directivity and
high gain, dish-type reflectors are used with radar sets that track targets.
200
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