Graphics Programs Reference
In-Depth Information
The plots shown in Figs. 11.5 and 11.6 c an be reproduced using MATLAB
function Ðrcs_frequency.mÑ given in Listing 11.2 in Section 11.9. From those
two figures, RCS fluctuation as a function of frequency is evident. Little fre-
quency change can cause serious RCS fluctuation when the scatterer spacing is
large. Alternatively, when scattering centers are relatively close, it requires
more frequency variation to produce significant RCS fluctuation.
MATLAB Function Ðrcs_frequency.mÑ
The function Ðrcs_frequency.mÑ computes and plots the RCS dependency
on frequency. Its syntax is as follows:
[rcs] = rcs_frequency (scat_spacing, frequ, freql)
where
Symbol
Description
Units
Status
scat_spacing
scatterer spacing
meters
input
freql
start of frequency band
Hz
input
frequ
end of frequency band
Hz
input
rcs
array of RCS versus
aspect angle
dBsm
output
Referring to Fig. 11.2 , assume that the two scatterers complete a full revolu-
tion about the radar line of sight in . Furthermore, assume that an
X-band radar ( ) is used to detect (observe) those two scatterers
using a PRF for a period of 3 seconds. Finally, assume a NB
bandwidth and a WB bandwidth . It follows that
the radarÓs NB and WB range resolutions are respectively equal to
and
T rev
=
3sec
f 0
=
9 GHz
f r
=
300 Hz
B NB
=
1 MHz
B WB
=
2 GHz
R NB
=
150 m
R WB
=
7.5 cm
.
Fig. 11.7 shows a plot of the detected range history for the two scatterers
using NB detection. Clearly, the two scatterers are completely contained within
one range bin. Fig. 11.8 shows the same; however, in this case WB detection is
utilized. The two scatterers are now completely resolved as two distinct scat-
terers, except during the times where both point scatterers fall within the same
range bin.
11.4. RCS Dependency on Polarization
The material in this section covers two topics. First, a review of polarization
fundamentals is presented. Second, the concept of the target scattering matrix
is introduced.
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