Page 238 - Fundamentals of Radar Signal Processing

Defining Ω ≡ Ω – Ω i
D
diff

(4.29)

Equation (4.29) is plotted in Fig. 4.6. The first zero of this sinc function occurs
2
at F = 1/τ Hz. Relatively small Doppler mismatches (F 1/τ) will cause
diff
diff
only slight reductions in the matched filter output peak amplitude. Large
mismatches, however, can cause very substantial reductions.

FIGURE 4.6 Effect of Doppler mismatch on matched filter response at expected
peak time.

The effect of Doppler mismatch can be either good or bad. If targets are
moving and the velocities are unknown, mismatch will cause reductions in
observed peaks and, if severe enough, may prevent detection. The signal
processor must either estimate the target Doppler so that the matched filter can
be adjusted or construct matched filters for a number of different possible

Doppler frequencies and observe the output of each to search for targets. On the
other hand, if the goal is to be selective in responding only to targets of a
particular Doppler shift, it is desirable to have a matched filter that suppresses
targets at other Doppler shifts.
From Fig. 4.6, it is clear that the Rayleigh resolution of the Doppler
mismatch response is 1/τ Hz. The resolution in velocity is therefore λ/2τ meters