Coherence effects on the detection performance of quadratic array processors, with applications to large-array matched-field beamforming

The effect of coherence is examined using an exponential-power-law model for the signal wavefront correlation. Detection performance is quantified by the small-signal deflection criterion, which is first reviewed in the general setting of quadratic detectors and then applied to matched-field and optimal quadratic beamformers. It is shown that the detection performance of matched-field beamforming is substantially degraded for large arrays and typical coherence lengths. The optimal quadratic processor reduces this coherence loss, but at a cost of greatly increased processor complexity. Several suboptimal beamformers with reduced computational load are also developed, and their detection performance is compared to that of the matched-field and optimal beamformers. One suboptimal processor, the subarray beamformer, has proved outstanding for this application in three respects: it can realize within 1 dB of optimal performance; it is robust over a class of correlation functions; and it entails a computational burden no greater than that of full-array matched-field beamforming