Furuno FAR-2107 Series Service Manual page 502

4) Bearing resolution
It refers to the limit of the bearing angle in which approaching targets at the
same range can be separately displayed on the screen. This is dependent on the
directivity of the antenna (beam width). The beam width of the antenna
(XN-24AF) is 0.95 degrees.
The relation between the antenna effective length D (m) and beam width
(deg.) is expressed in the following equation:
θ
(deg.) = 70 x
5) Propagation distance (Radar horizon)
The range to the horizon for radar waves is about 10% longer than the range to
the optical horizon and expressed in the following equation.
D (NM) = 2.23
D (NM) = 2.23 (
Radar antenna height: h1
Assuming that the radar antenna height is 30 m, and target height is 5 m,
D (NM) = 2.23 ( 30 +
D = 17.2 NM
6) Equation of wave propagation
The equation of the radar wave propagation in the free space is expressed as
follows:
×
P G
S１＝
π
× ×
4
Generally speaking,
there is a relation shown by this equation: A = G ×
× ×
2
P G
S１＝
π
×
3
4 ( )
However, since there is a need to take composite waves created by direct waves
and sea-reflected waves into consideration in the equation of the radar wave
propagation over the sea, the actual value differs from the value obtained in the
equation above. The transmission output and antenna
area determines the detection range. For instance, when
TX output is doubled, the detection range is increased
by 1.19 times and the antenna area is doubled, the
detection range is doubled. As is apparent from the
description above, to extend the detection range, it is
more effective to increase the antenna area than
increasing TX output. The graph on the right shows the
relation among the detection range, TX output and
antenna area when their magnification is changed.
λ
(m)/D (m)
h h: Radar antenna height
1 h + 2 h )
Target height: h2
5 )
A
σ
× ×
π
× ×
2
R 4 R
λ σ
×
2
×
4
R
8-21
S1 = Received power
P = Sending power
2
λ
2
/(4 ×
Range
G = Antenna gain
R = Distance
π
)
3
2
1
2
1
Power / Antenna
Q & A
θ
ANT
Power
3