Adaptive arrays - An introduction

This paper provides a tutorial introduction to adaptive arrays from the viewpoint of antenna beam-forming and null steering. The particular vehicle chosen for discussion is the Howells-Applebaum analog servo-control-loop processor. This processor derives feedback control error signals from the correlations between element signals, i.e., on the basis of the covariance matrix of the set of system inputs. A simple two-element array with a single adaptive control loop is addressed first, in order to set the stage for analysis of a basic K-element linear array with K adaptive control loops. Performance characteristics have been calculated for different distributions of interference sources to demonstrate the effects of power level, source location with respect to the quiescent beam pattern, source spacing in terms of array resolution, source bandwidth, continuous source distributions, and the array 'degrees of freedom' captured.