Koden MDC-5004, Operation Manuals

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Chapter 8 Principal of radar system MDC-5000 Series
0093153004-00 8-4
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Duplicate target images
When there is a big reflective surface nearby and it is perpendicular at a close distance (i.e. when your
ship is passed by a big ship, etc.), the radio wave bounces between own ship and the other ship.
Therefore, two to four images may appear at equal range in the direction of this target. The false
images generated by this multi-path reflection are referred to as “double targets”. In this case, the
closest target is the real image.
If the distance and bearing between own ship and the reflective target changes, then the duplicate
targets will disappear. Therefore, this false image can be easily distinguished.
Double image
Real image
False image caused by double image
Own ship
Large vessel
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Side lobe images
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
When own ship is close to large targets such as land, a
circular image may appear.
Side lobe
Main lobe
Antenna
False image
by sidelobe
Real image
False image caused by sidelobe