Chapter 3: Standard Radar Operations 3-5
Identifying False Echo
Returns
Identifying False Echo Returns
Not all echoes are directreturns to the radar antenna. Occasionallysignals
appearat positions where there is no actualtarget.These are called false
echoes, and may be caused by side lobes, ghost images, indirect echoes or
multiple echoes.
Thissection brieflydescribesthe echo patterns that can be produced by false
echoesandthelikelycause.It should be notedthatthe radaroperator, through
observation,practice,and experience,can generally detect theseconditions
veryquickly. These effects can usuallybe minimizedusing theradar controls.
Side Lobes
A small part of the RF energy from each transmittedpulse is radiated outside
thesingle narrowbeam. This producesside lobe patterns, shown in
Figure 3-3.
Side lobes have no effect on distant or small surface objects. However, the
echofroma largeobject at shortrangemay producean arc on the radar screen
similar to a range ring or a seriesof echoes forming a broken arc. Side-lobe
echoesnormally occur at ranges below 3nm, and can be reducedby adjusting
the SEA control.
Figure 3-3: Side Lobes
True echo Side echoes
Main lobe
Antenna
Arc
Side lobe Side lobe
D1638-2
81186_3.book Page 5 Thursday, August 22, 2002 8:23 AM
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