6. RADAR
6-32
Sidelobe echoes
Each time the radar transmits, some radiation leaves on each side of the beam. This
lost energy has the name "sidelobes" If a target is detected by both the sidelobes and
the mainlobe, the sidelobe echoes can appear at both sides of the true echo at the
same range. Sidelobes normally show only on short ranges and from strong targets.
You can reduce sidelobes if you reduce the gain, or correctly adjust the sea clutter.
6.27.2 Search and rescue transponder (SART)
A ship in distress uses a radar-SART to show a series of dots on the radar display of
nearby ships to indicate distress. A SART transmits when it receives a radar pulse
from any X-Band (3 cm) radar within a range of approximately 8 nm. When a SART
receives a radar pulse, the SART transmits a response across all the radar frequency
band.
How to detect the SART response
• Use the range scale of 6 or 12 NM.
• Turn off all the automatic clutter filters.
• Turn off the interference rejector.
Mainlobe (beam)
Sidelobe Sidelobe
Antenna
True target
False echoes by sidelobes
Radar antenna beamwidth
Screen A: When SART is distant
Screen B: When SART is close
Position of
SART
24 NM
1.5 NM
Own ship positionOwn ship position
Echo from SART
(Lines of 12 dots
are displayed in
concentric arcs.)
Own ship positionOwn ship position
Position of
SART
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