Page 340 - Fundamentals of Radar Signal Processing

FIGURE 5.9 Frequency response of basic MTI cancellers: (a) two-pulse
canceller, (b) three-pulse canceller.

The two-pulse canceller is a very simple filter. Its implementation requires
no multiplications and only one subtraction per output sample. As Fig. 5.9a
shows, however, it is a poor approximation to an ideal highpass filter for clutter
suppression. The next traditional step up in MTI filtering is the three-pulse
(second-order or double) canceller obtained by cascading two two-pulse

cancellers. The flowgraph and frequency response are shown in Figs. 5.8b and
5.9b. The three-pulse canceller clearly improves the null breadth in the vicinity
of zero Doppler, but it does not improve the consistency of response to moving
targets at various Doppler shifts away from zero Doppler. It requires only two
subtractions per output sample.
Despite their simplicity, the two-and three-pulse cancellers can be very
effective against clutter with moderate-to-high pulse-to-pulse correlation.

Figure 5.10 shows a simulated clutter sequence formed by passing a white noise
sequence through a filter with a Gaussian power spectrum having a standard