Optimum clutter suppression in airborne phased array radars

The platform motion of an airborne radar system causes clutter returus to be doppler shifted. The doppler shift is proportional to the directional cosine between the velocity vector and the individual clutter element. Such clutter echoes are characterized by a two-dimensional velocity-azimuth spectrum. Therefore, suppression of clutter echoes requires two-dimensional sampling and filtering. The results presented are obtained from a theoretical study by applying optimum detection theory to a statistical clutter model. Optimum filtering as given by the LR-test may be difficult to implement, but gives some impression of how much gain in signal-to-clutter-ratio can be obtained. It turns out that the gain is limited by the receiver noise rather than by the clutter. In other words, two-dimensional spectra treated by two dimensional filters behave similar to the one-dimensional case. It is also shown that the number of spatial samples should be roughly equal to the number of time samples. Furthermore, the results promise that the optimum gain can be approached by much simpler suboptimum methods.