Factors in the design of adaptive antennas

A brief review of adaptive antenna technology is given, and two topic areas are addressed. The first is concerned with the general difficulties encountered in design, in particular the avoidance of nulling wanted signals, the provision of an adequate rate of convergence towards a desired characteristic, and the degradation of null depths caused by the proximity of the platform and by dispersion in the array and receiving channels. The second topic concerns specific design approaches. Closed loop processors, in which the array output is sensed in order to provide a drive to the weight networks, are exemplified by a feedback loop correlator design and a weight perturbation technique. An example of open-loop control of weight values is also included, and its lack of self-correction is shown to be disadvantageous compared to the closed loop approach. Advanced methods, associated with sample matrix inversion, are also summarized.