Furuno FAR-2107 Series Service Manual page 440

72. Give basic information on radars.
1) Comparison between S-band and X-band
In relation to electric
wave transmission
(Related to
meteorological
phenomena)
In relation to antenna
Others
2) Range resolution:
The distance R is determined by the pulse length: ( τ ).
R (m)=150 x τ
For instance, if the pulse length is 0.07 µ s for S1 pulse
R = 150 x 0.07
R = 10.5 m
3) Minimum range:
The pulse length ( τ ) determines the minimum range R.
R (m)=150 x τ
In the actual situation, the relation between the antenna height and vertical beam
width produce a shadow sector (target is not located within the vertical beam
width). This makes it impossible to detect targets at a close range. If the antenna
height is lowered to make the minimum detection range shorter, this makes the
maximum detection range shorter.
The minimum detection range can be calculated in the following equation:
Rmin = H / tan ( θ v/2)
where Antenna height (m) and vertical beam width ( θ v deg.).
Assuming that the antenna height is 30 m and the vertical beam width is 20
degrees (in case of the antenna XN-24AF)
Rmin = 30 / tan (20/2)
Rmin = 170.1 m
Characteristics
Loss due to raindrops
Sea returns
Size at the same gain and
the same horizontal directivity
Loss in waveguide tube
Size of waveguide tube
Detection range
Bearing and range resolution
Noise index of receiver
8-20
X-band S-Band
Large Small
4 mm/h: 4 mm/h:
0.064 dB/km 0.017 dB/km
Large Small
Large Small
Large Small
Small Large
Small Large
Large Small
Large Small
Q & A