Figure 144.
How a Paraboloid Works.
b. Dish reflectors are usually made of wire mesh or from solid
material, with small holes to make them lighter and to reduce the amount of
surface exposed to the wind. The holes have very little effect on reflector
operation as long as they are small compared to the wavelength of the RF.
Some radar sets use just a section of a dish as a reflector.
23. A section of a dish reflects energy in a fan-shaped pattern.
a. If you feed RF energy to just a section of a dish like the one in
Part A of Figure 145, you get a radiation pattern that looks like a fan.
The beam is still sharp horizontally, but it is broad vertically because
there is less reflector surface to concentrate the beam in that plane. This
type of reflector is used with search radar sets for two reasons:
(1) The
narrow
horizontal
beamwidth
gives
accurate
azimuth
information.
(2) The broad vertical beamwidth allows the set to pick up targets at
any altitude.
201
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