Thinned array configurations for use with satellite-based adaptive antennas

The nulling resolution of an adaptive antenna determines that the spatial extent about an interference source over which the communication system's link margin is unacceptably low when the radiation pattern is shaped to place a null on interference sources present over the antenna field of view. This resolution is inversely related to
D/\lambda
, indicating that large apertures are required to achieve very narrow resolution. In order to achieve good resolution with few elements, highly thinned arrays are commonly employed. Thinned array configurations optimized in performance in accordance with specific criteria are developed. These criteria are used to optimize the element positions within the array considering both the close-in nulling resolution and the average coverage area over a fixed circular field of view for which it is desired that system users have a positive link margin to a satellite at a geosynchronous altitude. It is determined that the circular array configuration, with elements equispaced on the circle, generally produces the best close-in nulling resolution against arbitrary interference scenarios for large values of
D/\lambda
. However, the average coverage area of this array is compromised due to the high sidelobes and grating lobes generated by this configuration. Thus other array configurations are considered. It is shown that exponentially space tapering the elements on the circle improves the average coverage area with little loss in resolution but leads to element spacings which might be incompatible with finite element size constraints in a practical design. Consequently, a third array configuration, developed according to standard synthesis techniques for nonuniform arrays, is also considered and shown to lead to good performance.