Chapter 6 Principle of radar system
MDC-2200/2500 Series
0093125002-02
6-4
●
Duplicate target images
When there is a big reflective surface nearby and perpendicular at a close distance,( i.e. when your
ship is passed by a big ship, etc.), radio wave bounce between your ship and the other ship. Therefore,
2 to 4 images may appear at equal range in the direction of this target. The false image generated by
this multi-path reflection is referred to as “double targets”. In this case, the closest target is the real
one.
You will notice as the distance and bearing between own ship and the reflective target changes the
duplicate targets will disappear. Therefore, this false image can be easily distinguished.
The microwave beam radiated from the antenna has a side lobe in different direction than that of the
main beam. Since this side lobe level is lower than that of main beam, the effect is negligible for targets
at long range, but a close, strong reflecting target may cause false image appearing in a circular arc
shape.
CAUTION
Close to large targets such as land, a circular image may
appear.
3
1
H
U
Double image
Figure 7-6 False image caused by double image
Own ship
Large vessel
6-
3
1
HU
Side lobe
Main lobe
Antenna
Virtual image
by sidelobe
Real image
Figure 7-7 False image by sidelobe
6-
Real image
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