Page 337 - Fundamentals of Radar Signal Processing

order to suppress the clutter component. Figure 5.6 illustrates the process. The

type of filtering needed can be understood by considering Fig. 5.7. In this figure,
it is again assumed that knowledge of the platform motion and scenario
geometry has been used to center the clutter spectrum at zero Doppler frequency.
Clearly, some form of highpass filter, as suggested by the notional frequency
response |H(F )| shown, is needed to attenuate the clutter without filtering out
D
moving targets in the clear portions of the Doppler spectrum.

FIGURE 5.7 The concept of moving target indication filtering: (a) Doppler
spectrum and MTI filter frequency response, (b) Doppler spectrum after
filtering.

The output of the highpass MTI filter will be a new slow-time signal
containing components due to noise and, possibly, one or more targets. This
signal is passed to a detector typically consisting of a matched filter followed
by a threshold test. If the peak matched filter output exceeds the threshold (i.e.,
its energy is too great to likely be the result of noise alone), a target will be

declared. Note that in MTI processing, the presence or absence of a moving
target in the range bin of interest is the only information obtained. The filtering
process of Fig. 5.6 does not provide any estimate of the Doppler frequency at
which the target energy causing the detection occurred, or even of its sign; thus,
it “indicates” the presence of a moving target but does not determine whether the