Adaptive beamforming with augmentable arrays in non-stationary environments

This paper introduces a near-field reduced rank adaptive beamforming method for nulling more interferers than sensors using fully augmentable arrays in wide sense stationary interference. Augmentable arrays, such as minimally redundant or co-prime, can exploit additional degrees of freedom beyond the number of sensors in spatially stationary fields in order to increase array gain. However, near-field targets result in spatial non-stationarity due to range dependent wavefront curvature. Additionally, source or array motion limits the number of available snapshots. Adaptive near-field beamforming with far-field interference suppression is considered by nulling in the augmented, or co-array, dimensions but steering in the near-field with sensors in their physical locations. A reduced rank processing scheme is used that requires fewer snapshots than full rank methods. The proposed technique is shown to increase array gain when the number of interferers exceeds the number of sensors in both high and low snapshot support regions.