Furuno WR110, Installation Manual

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5
Front-to-Back Ratio:
The front-to-back ratio of an antenna is the
proportion of energy radiated in the principal
direction of radiation to the energy radiated in
the opposite direction. A high front-to-back
ratio is desirable because this means that a
minimum amount of energy is radiated in the
undesired direction.
 Azimuth direction:
Antenna side lobes show both P0N
(unmodulated pulse emission for radars) and
Q0N (frequency modulation within each pulse)
covered area.
 Range direction:
Pulse compression (Range) side lobes show
Q0N only. It improves sensitivity of long pulse
but increase blind range. However this blind
area can recover using un- modulated pulse.
Pulse compression
：
Pulse compression is useful for weather radar to increase the average transmitted power by
transmitting a longer pulse but without reducing the range resolution of the radar.
Side lobe suppression is helping to eliminate the problem. For a radar pulse signal after compression,
the narrower pulse main lobe is always accompanied by higher side lobes. So, all pulse compression
radars suffer from range side lobes which cause energy from strong reflections to leak into adjacent
range cells. High suppression of side lobes is not required in some other non-meteorological radar, but
is important for meteorological radar because weather phenomena can have significant reflectivity
gradients, and ground clutter echo can be much larger than medium rain. Furthermore, the side lobes
of strong signal will falsely be recognized as an existence of small target. Therefore, range side lobes
must be suppressed by a large amount to prevent contamination in adjacent range cells.
Figure 1.6: High level echo with side lobes
Antenna
Side lobe
Range
Side lobe
Figure 1.5:
Antenna pattern in a polar-coordinate graph
Front to Back
Side lobe
Main lobe
Beam width