Adaptive beamforming with a multiple beam antenna

Adaptive array processing is seen as one possible solution to the severe bandwidth and power restrictions in a communications system between a geostationary satellite and a mobile terminal. This paper considers the use of an offset parabolic reflector with an array feed, referred to as a multiple beam antenna (MBA), as a way of combining the high gain of the reflector with the spatial filtering ability of the antenna array. A signal model is developed in which the key quantity is the steering vector which represents the response of the antenna array to a plane wave arriving from a given angle. The steering vector for the MBA is found numerically by finding the secondary field of each of the antenna elements, and then using the principle of reciprocity to relate this held to the received amplitude. Statistically optimum beamforming on the MBA is demonstrated followed by a simulation of the Direct Matrix Inversion (DMI) algorithm.