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178 MATLAB Simulations for Radar Systems Design
For this design select 5 waveforms, one for search and four for track. Typi-
cally search waveforms are longer than track waveforms; alternatively, track-
ing waveforms require wider bandwidths than search waveforms. However, in
the context of range, more energy is required at longer ranges (for both track
and search waveforms), since one would expect the SNR to get larger as range
becomes smaller. This was depicted in the example shown in Fig. 1.13 in
Chapter 1 .
Assume that during search and initial detection the single pulse peak power
is to be kept under 10 KW (i.e., ). Then by using the single pulse
energy calculated using Eq. (2.115) in Chapter 2, one can compute the mini-
mum required pulsewidth as
P t
20 KW
0.1147
20
--------------------
τ min
=
5.735µ s
(3.149)
10 3
×
Choose , with bandwidth and use LFM modulation.
Fig. 3.18 shows plots of the real part, imaginary part, and the spectrum of this
search waveform. This figure was produced using the GUI workspace
ÐLFM_gui.mÑ. As far as the track waveforms, choose four waveforms of the
same bandwidth (
τ search
=
20µ s
B
=
5 MHz
) and with the following pulsewidths.
B track
=
20 MHz
TABLE 3.1. ÐMyRadarÑ design case study track waveforms.
Pulsewidth
Range window
τ t 1
=
20µ s
R max
0.75 R max
τ t 2
=
17.5µ s
0.75 R max
0.5 R max
τ t 3
=
15µ s
0.5 R max
0.25 R max
τ t 4
=
12.5µ s
R
0.25 R max
Note that refers to the initial range at which track has been initiated. Fig.
3.19 is similar to Fig. 3.18 except it is for
R max
.
τ t 3
For the waveform set selected in this design option, the radar duty cycle var-
ies from 1.25% to 2.0%. Remember that the PRF was calculated in Chapter 1
as
; thus the PRI is
.
f r
=
1 KHz
T
=
1 ms
At this point of the design, one must verify that the selected waveforms pro-
vide the radar with the desired SNR that meets or exceeds what was calculated
in Chapter 2, and plotted in Fig. 2.21. In other words, one must now re-run
these calculations and verify that the SNR has not been degraded. This task
will be postponed until Chapter 5, where the radar equation with pulse com-
pression is developed.
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