2. RADAR OBSERVATION
2-2
2.1.3 X-band and S-band
In fair weather, the equation on the previous page does not give a significant differ-
ence between X- and S-band radars. However, in heavy precipitation condition, an S-
band radar would have better detection than an X-band radar.
2.1.4 Radar resolution
There are two important factors in radar resolution (discrimination): bearing resolution
and range resolution.
• Bearing resolution is the ability of the radar to display as separate pips the echoes
received from two targets that are at the same range and close together. It is pro-
portional to the antenna length and reciprocally proportional to the wavelength. The
length of the antenna radiator should be selected for a bearing resolution better than
2.5° (IMO Resolution). This condition is normally satisfied with a radiator of 1.2 m
(4 ft) or longer in the X-band. The S-band radar requires a radiator of about 12 feet
(3.6 m) or longer.
• Range resolution is the ability to display as separate pips the echoes received from
two targets that are on the same bearing and close to each other. This is determined
by pulselength only. Practically, a 0.08 microsecond pulse offers the discrimination
better than 40 m as do so with all FURUNO radars.
Test targets for determining the range and bearing resolution are radar reflectors
having an echoing area of 10 m
2
.
Targets
Horizontal beam width
Separate target echoes
Ovelapped target echoes
Horizontal beam width
Targets
Transmission
pulse
Targets
TargetsTransmission
pulse
Separate target echoes
Ovelapped target echoes
Ovelapping
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