Space-time adaptive processing with sparse antenna arrays

Sparse, or thinned arrays can provide the resolution and accuracy of a large aperture without the hardware expense of a fully populated array. This paper examines application of thinned arrays to an airborne radar that employs space-time adaptive processing (STAP) to reject ground clutter. It is shown that the rank of the clutter covariance matrix depends on the precise thinned configuration. Upper and lower bounds for the clutter covariance matrix are provided. An irregularly spaced thinned array can have the same rank as a filled array if all potential synthetic aperture positions get sampled at least once during the coherent processing interval. Beamspace STAP approaches with irregularly spaced arrays generally require more degrees of freedom (DOF) than that of a filled array because a thinned array beamspace transform cannot generally effect shifted subaperture beams. With additional DOF (and still much less than fully adaptive) a randomly spaced thinned array beamspace approach call still provide relatively low loss and avoid the additional angle-Doppler blind zones that result from regularly spaced thinned arrays.