Self-cohering large antenna arrays using the spatial correlation properties of radar clutter

A technique for self-calibrating a large antenna array system in the absence of a beamforming point source is presented that uses the spatial correlation properties of radar clutter. The array could be real or synthetic. It is shown that if R(X), the spatial autocorrelation function of the field (as measured by adjacent element pairs), is ensured to be real and positive in the neighborhood of the origin, both periodic and aperiodic arrays can be synchronized, forming retrodirective beams pointing at the axis of symmetry of the radar transmitter, provided that the interelement spacing does not exceed some limit (the order of the size of the transmitting aperture). If the spatial autocorrelation function is complex but has a linear phase, it is shown that one can still synchronize both periodic and aperiodic arrays, while if the phase of R(X) is nonlinear, only periodic arrays can be synchronized. In both cases of complex R(X), a residual beam-pointing error occurs. Computer simulations and airborne sea clutter data are reported that verify the theory and practicality of the algorithm