Phase synchronizing large antenna arrays using the spatial correlation properties of radar clutter

Interest has developed in using large, thinned, random or periodic antenna arrays in applications that require a very narrow beam such as high accuracy tracking, direction finding, target counting or high resolution radar imaging. Since large structures are very likely to flex with time, the need arises for techniques for the real time self calibration of the antenna system. A bistatic radar imaging system is described, where adaptive retrodirective beamforming techniques focus the array upon a point source, following which the focused beam is moved in range and angle to a target area and scanned across the target. The need for a point source (e.g., a corner reflector or a beacon) for system calibration limits its use especially in uncontrolled environments. Two techniques are presented for self calibrating such a system in the absence of a point source, capitalizing on the spatial correlation properties of radar clutter.