Space-time signal processing of radar returns

Radar returns from complex targets that are large compared to the wavelength of the radar signal are composed of reflections from a number of scattering points on the surface of the target. Although the target may contain a large number of scattering points, experience indicates that at any particular instant of time the major portion of the returned signal energy comes from only a few such points. These predominant reflections combine at the receiving point with phases that are random because the range differences between reflecting points are random and critically dependent upon the aspect angle of the target. As a consequence of the random phase differences, the total signal power observed by the receiver is also random and fluctuates drastically around some average value as a result of changes in target attitude. The average value of power is simply the sum of the powers from the individual reflecting points, and this situation is referred to here as noncoherent signal summation. If the return signal from each of the predominant reflecting points had the same phase as all the other signals, then the voltages in the receiver would add rather than the powers. The resulting received signal power is then proportional to the square of the sum of the voltages and will always be larger than the average power obtained by noncoherent signal summation.