Duration of Fades Associated with Radar Clutter

Consider a pulsed radar system "viewing" a range cell consisting of a stationary target along with many independent, randomly moving scatterers as shown in Fig. 1. Each received echo consists of the vector sum of all the elementary echoes originating from within the range cell. The contributions from the randomly moving scatterers arrive at the radar receiver with random phases. As a result, each received echo will consist of a steady signal, from the stationary target, plus a Gaussian perturbation. Accordingly, samples of the envelope of the pulse-to-pulse radar echoes can be considered as samples of an underlying Rayleigh process. Thus, the effect of the randomly moving scatterers is to cause the envelope of the pulse-to-pulse radar echoes to fluctuate or fade in an irregular manner. The envelope of the pulse-to-pulse radar echoes may fade below some critical threshold level for a duration such that the performance of the radar becomes unsatisfactory. 1285 1286 THE BELL SYSTEM TECHNICAL JOURNAL, OCTOBER 1966