b. Right about now you are probably wondering what all this has to do
with radar antennas. Well, all radar antennas need a beam that is narrow in
at least one direction. So, the type of beam we need determines the type of
antenna used.
16. Why radar needs a narrow beam.
a. A radar indicator gives you at least one of the following three
kinds of information:
(1) Range.
(2) Azimuth.
(3) Elevation.
b. The accuracy of the azimuth and elevation information depends upon
how narrow the beam is.
17. A narrow horizontal beam gives accurate azimuth information.
a. To provide accurate azimuth information, the radar set must send out
a narrow horizontal beam. You can see why by comparing the two radar search
sets in Figure 141. The set in Part A of Figure 141 has a broad horizontal
beam. Therefore, the set picks up echoes from an enemy jet bomber even when
the antenna is pointed in a direction 10 degrees away from the target. The
operator of the set knows only that the bomber is somewhere between 30 to 50
degrees east.
At a range of 100 miles, the distance between 30 and 50
degrees is about 35 miles. If fighters are sent out to intercept the jet,
they have to look for it in this 35-mile area. Considering the speed of a
jet, the enemy plane can cause considerable damage before the fighter planes
find it. Because the beam is so broad, the azimuth information is just not
accurate enough.
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