A Simple Polarization Diversity Technique for Radar Detection

There are many proposals for multi-channel radar, emanating from the conventional monostatic radar system where transmitter and receiver are collocated. Collocation makes it easy for transmitter and receiver to share a common stable clock (local oscillator), which is required for both range and Doppler measurements. Signal processing for multi-static radars (see [1]) with widely dispersed antenna elements is currently a very active research area, in part because of significant advances in hardware capabilities. Multi-static radar enables multiple views of the scene, and a (wide angle) tomographic approach to the recovery of the scene from the data. A major advantage of multi-static radar is substantial improvement in detection due to multiple views of the target being available. When system elements are widely dispersed, the coherent implementation of multi-static radar is rendered difficult by the problem of clock synchronization. An additional challenge is the degree of computation necessary to recover the scene, or detect a target, by integrating multiple views. It is natural to approach multi-channel radar in terms of spatial diversity concepts developed for multiple-input-multipleoutput (MIMO) communications ([3], [2]). Performance improvements in MIMO communications derive from spatial diversity, that is, the statistical independence of the different channels provided by the multiple antenna elements. Fishler et al.[3] correctly point out that sufficiently separated system elements do give rise to statistically independent views of the target. However, in their analysis of detection performance, they assume a target in the far-field by invoking a “narrow band” approximation which necessarily implies complete statistical dependence across the distributed antennas. Without the narrow band approximation, the analysis reduces to that of conventional multi-static radar systems. An important difference between wireless communication and radar sensing is that, in communication, timing information is shared between the base station and the mobile terminal. This is not the case in radar, where the primary objective