Recent approaches to transducer array beamforming

The development of underwater acoustic array‐processing and beamforming methods over the past decade is reviewed briefly. The trend in this period is away from fixed designs typified by shaded‐aperture time‐delay beamforming toward stored‐coefficient and adaptive systems made possible in part by advances in digital hardware. Linear programming techniques have been used to generate prescribed directional response for arrays with fixed geometry, while nonlinear programming has allowed the inclusion of specified power response and element position as variables in the optimization process. More recently the emphasis has shifted to adaptively optimized systems, where the beam pattern adjusts to changing noise and interference fields. An example is given in which the beam pattern of an active Doppler‐processing sonar is adapted to the directional properties of the reverberation noise field. Limitations imposed by nonideal transducer response on the optimization are illustrated through the use of coherent calibration data obtained with the transducer array.