Unambiguous triplet array beamforming and calibration algorithms to facilitate an environmentally adaptive active sonar concept

Cardioid or triplet towed arrays are utilized in sonar applications to resolve left/right ambiguity by placing a null on the ambiguous direction. This leaves an uncalibrated residual signal on the opposite direction from which the desired signal is arriving. Here the mechanism of cardioid beamforming is presented and analytical expressions for the calibration of continuous wave (CW) and linear frequency-modulated (LFM) signals are derived. The validity of these expressions is verified using simulated and real data. The same data sets are also used for comparing the performance between the standard beamformer and a modified version designed to suppress endfire singularities. The effect of correlated vs. uncorrelated intra-triplet noise is assessed using a simulation scenario with a point target