Page 327 - Fundamentals of Radar Signal Processing

CHAPTER 5

Doppler Processing

Doppler processing is the term applied to filtering or spectral analysis of the
signal received from a fixed range over a period of time corresponding to
several pulses. The purpose is generally to suppress clutter returns and to
enable the detection of targets in the presence of significant clutter.
Figure 5.1a shows a notional scenario where a down-looking stationary
radar observes four moving targets in a ground clutter background. The gray

dashed lines represent range bins. Receding targets are in bins 4, 11, and 18,
while an approaching target shares bin 11. Figure 5.1b is a stylized
representation of the range-Doppler power spectrum that might result from this
scenario. The light gray background represents the receiver noise floor, which
is spread uniformly throughout the range-Doppler map. The band of energy
extending through all of the range bins represents the ground clutter echo.

Because the radar is stationary, the clutter is centered at zero Doppler shift, and
its power fades with range in accordance with the range equation. The four
small ovals represent the returns from the moving targets. Their echo energy is
located in the appropriate range bins. Their Doppler coordinates depend on the
direction and speed of each target with respect to the radar.