An improved null steering digital beamformer based on multi-group time delays for echo separation in HRWS SAR.

Digital beamforming with null steering in elevation can be used to separate echoes corresponding to different sub-pulses, but the pulse extension loss will decrease performance on echo separation. To resolve this problem, an improved null steering beamformer based on multi-group time delays is proposed. In the proposed beamformer, the phase weighting matrix is multiplied and the multi-group time delays are used to improve the coherence between echoes from different channels. Then, the modified phase weighing matrix for null steering is introduced to further improve the capacity of echo separation. Compared with the conventional null steering beamformer, the multi-group time delays can provide the more accurate time delay compensation for better echo separation. Simulation results on both point and distributed targets validate the proposed beamformer. [ABSTRACT FROM AUTHOR]