Page 369 - Fundamentals of Radar Signal Processing

FIGURE 5.16 The computed pulse Doppler spectrum is a frequency-sampled
version of an underlying discrete-time Fourier transform.

The advantages of pulse Doppler processing are that it provides at least a
coarse estimate of the radial velocity component of a moving target and that it
provides a way to detect multiple targets, provided they are separated enough in
Doppler to be resolved. The chief disadvantages are greater computational
complexity of pulse Doppler processing as compared to MTI filtering and

longer required dwell times due to the use of more pulses for the Doppler
measurements. Thorough discussions of pulse Doppler processing are contained
in Morris and Harkness (1996) and Stimson (1998). An excellent new addition
to the literature is Alabaster (2012).

5.3.1 The Discrete-Time Fourier Transform of a Moving Target
To understand the issues in pulse Doppler processing it is useful to understand
the appearance of noise, clutter, and target signals in the range-Doppler map.
Begin by again considering the Fourier spectrum of an ideal constant radial

velocity moving point target and the effects of a sampled Doppler spectrum. The
issues are the same as those considered when discussing the sampling of the
Doppler spectrum in Chap. 3. Consider a radar illuminating a moving target
over a CPI of M pulses, and suppose a moving target is present in a particular
range bin. If the target’s velocity is such that the Doppler shift is F Hz, the
D
slow-time received signal after quadrature demodulation is

(5.73)

where T is the radar’s pulse repetition interval and is the effective sampling
interval in slow time. The signal of Eq. (5.73) is the same signal considered in
Chap. 3 [Eq. (3.19)], except for the change from normalized frequency ω in
D
radians to analog frequency F in hertz; they are related according to ω =
D
D