Focusing filters for wide-band direction finding

A time-domain equivalent of the coherent signal-subspace transformations (CST) is established for wideband direction finding in a possible multipath environment using general arrays. Time-domain equivalents of focusing are derived based on the least squared error approach for general transformations, and the Taylor series expansion approach for closed-form transformations. The preprocessor is realized by a multichannel digital finite impulse response filter. For diagonal transformations, the problem reduces to implementing different delays at each sensor, which in turn leads to computational simplicity. Various tapped delay line filters for realizing an arbitrary delay are proposed and compared. Simulation results reveal that low-order filter structures in the time domain achieve similar performance to the frequency domain approach, even at detection and resolution thresholds