ON THE USE OF ZERO TRACKING TO OVERCOME INCIDENTAL CANCELLATION PROBLEM IN ADAPTIVE ARRAY

Abstract

Incidental signal cancellation due to large look direction errors remains one of the principle obstacle prohibiting adapti.ve arrays from applications where a fast and robust response is required. This thesis examines the cause of the problem and suggests two new zero tracking algorithms to overcome this problem in fully and partially adaptive arrays. After reviewing the general theory of adaptive signal processing and some relevant research topics, a simple and fast zero tracking algorithm is presented to solve the problem of incidental cancellation in fully adaptive arrays. Basically, the algorithm is based on adjusting the complex zeros of a power inversion array in a time-multiplexed manner to track all the sources in the environment. To preserve the desired signal which is supposed to be closest to the look direction of 0°, the algorithm removes the zero with the shortest distance to ej0 so that the directional response consists of only nulls steered at the jammers. An algorithm for overcoming the problem of incidental cancellation and improving the convergence behaviour of partially adaptive arrays is then proposed. The algorithm is based on the employment of an auxiliary adaptive source tracker to separate individual sources in the environment before using the resulting outputs to cancel unwanted jamming picked up through the main beam of the system. By adding back the desired signal to the canceller output in the event that the former is cancelled in the adaptation process, the algorithm is able to solve the problem of incidental cancellation in the most natural manner.