An Adaptive Beamformer which Implements Constraints Using an Auxiliary Array Preprocessor

This paper presents a method of adaptive beamforming which makes use of a fixed, conventionally-weighted array and an auxiliary, adaptive array. The beamformed output is taken as the difference between the conventional and adaptive outputs. It is assumed that the sensor outputs, which are common to both arrays have been time-delay steered to the direction of interest. Similar structures have been described previously in which the auxiliary array is adapted using linearly-constrained adaptive algorithms. In the present work, it is shown that linear constraints can also be implemented by preceding the auxiliary adaptive array with a fixed preprocessor Ws. The adaptive algorithm then reduces to the simple; unconstrained LMS procedure. Thus, the proposed implementation separates out, in a natural manner, the three basic components of a linearly constrained adaptive beamformer: the conventional beamformer, the linear constraints, and the adaptive algorithm. This separation has significant advantages in practical implementations and suggests extensions to other beamformer structures.