Page 253 - Fundamentals of Radar Signal Processing

FIGURE 4.15 Pulse burst matched filtering when target is range ambiguous by
one PRI: (a) whole-waveform matched filter output. Compare to Fig. 4.13b. (b)

Slow-time data in pulse-by-pulse processing viewpoint. Compare to Fig. 4.14.

This behavior creates two problems. The reduced amplitude of the target

component of the matched filter output reduces the SNR and thus the probability
of detecting the target. Assuming the reduced-amplitude response does prove
large enough to be detected, the processor will assume the target is at delay t 0
when in fact it is at t + T. This phenomenon whereby there is more than one
0
possible range that can be associated with a detection is called a range
ambiguity. First discussed in Chap. 3, it is a characteristic of pulse burst
waveforms. It is not readily apparent if a peak at the matched filter output is due

to a target at the implied range or at that range plus a multiple of the
unambiguous range R = cT/2 meters.
ua
As will be seen in Chap. 5, it is common in some radars to operate at a
PRF for which the unambiguous range is less than the maximum detection range,
so methods are needed to counter these two problems. Range ambiguities can be
resolved using multiple pulse burst waveforms at different PRFs as discussed in

Chap. 5. The reduction in matched filter output amplitude and SNR for range-
ambiguous targets is countered by noting that it occurs because the pulse burst
echo is not fully overlapped with the matched filter reference pulse burst at the
output sampling time when the target time delay t > T. The solution to this
0
problem is to extend the transmitted waveform. Suppose the radar can be