A broadband adaptive beamforming approach based on the concept of signal-subspace alignment is formulated and contrasted with the conventional approach. The proposed method involves a preprocessor that focuses the signal spaces at different frequencies to a common one and a narrowband beamformer following the preprocessor. The merits that result as a consequence are partial adaptivity due to single frequency weights and decorrelation of coherent signals thus combating signal cancellation. The latter effect is studied by deriving expressions for the desired-signal distortion in a minimum variance distortionless response (MVDR) beamformer and analyzing them. Implementation issues of the preprocessor are addressed. Simulation results confirm the utility of the focusing preprocessor.
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