3.6 Surface-Distributed Targets
51
Fig. 3.26 RCS of ground surface
Let us transfer to RCS finding of ground surface observed at some θ angle to
horizon by radar antenna with fan-shaped directional pattern of β width (Fig. 3.26).
Based on figure, it is easy to find that resolvable square S P can be calculated using
the following equation:
S p = BC · C D =
H δβ
sin α
δ D
cos α
=
2H δβδ D
sin 2α
,
(3.62)
where δ D is resolution capability in range, δ D = cτ/2.
Hence, RCS of ground surface can be found by formula:
A = γ (α)S p sin α.
(3.63)
For surfaces, close to diffused one, γ (α) = γ 0 and with regard to (3.62) equation,
we obtain:
A = γ 0
H δβδ D
cos α
= a
H δβδ D
cos 2 α
.
(3.64)
With a not so high range resolution capability, a square will limited by width of
antenna directional pattern ψ in a second plane as well, then the equation
A =
γ (ε)π H
2
δβδψ
4 sin α
is correct. As is obvious, RCS of extended (area extensive) target is proportional to
square range.
For surface-distributed targets, the value of specific RCS depends on wavelength
and type of surface. This is illustrated by data stated in Table 3.5.