TABLE OF CONTENTS The signal processor is the stage that filters the wanted echoes from other echoes that clutter the display. Generally, useful filtering involves a loss in signal-to-noise ratio, which must be accounted for in maximum range and accuracy calculations.
Losses depend on the type of signal processing used. The most simple is the display of the video signal on a cathode ray tube without any intervening processing. During a radar look, the echoes from a number of pulses reinforce each other (or are integrated) on the cathode ray tube phosphor. The signal-to-noise ratio for a particular probability of detection and false alarm rate is given for the Marcum and Swerling cases (with and without echo signal fluctuation) in Chapter 12.
Moving target indicator (MTI) processing involves removing the clutter signals by subtraction and, as a sideeffect, the wanted echo signals if their Doppler frequencies represent the blind speeds. The subtraction process increases the correlation of the noise and reduces the number of effective hits (see Figure 11.43) to be used for the signal-to-noise ratio for detection. The difference in the signal-to-noise ratios with and without moving target indicator processing represents a loss.
Coherent integration involves the adding of the wanted signals so that, ideally, the unwanted signals add vectorially to zero. Conceptually, all the signals and noise from the N pulses are combined into one. In order to reduce the responses to signals at nearby frequencies (compare with antenna sidelobes in Chapter...
