Spatial array processing methods for radio astronomical RFI mitigation

Over more than a decade there have been a variety of array signal processing methods proposed for interference canceling in radio astronomical observation. Approaches include adaptive filtering, statistically optimal null-steering beamformers, robust adaptive beamforming, vector subspace partitioning, interference tracking algorithms, and use of auxiliary reference antennas. Conventional imaging arrays are obvious candidates where the spatial signature across all antennas may be used to remove interference directly from the visibility/correlation terms. The new wave of phased array feeds under development (e.g. ASKAP, APERTIF, DRAO, BYU/NRAO, Arecibo) also opens up, to both single dish instruments and synthesis arrays, new possibilities for actively nulling interferers independently at each dish. Low frequency aperture arrays (e.g. LOFAR, MWA, LWA, PAPER) have such wide fields of view and operate in such crowded bands that spatial canceling is almost mandatory.