Antenna Nulling Technique for GPS Adaptive Antenna

Zhen-Biao Lin

Abstract:	GPS receivers may be threatened by intentional jammers or by increasing pollution of the electromagnetic environment. The challenge in design of an adaptive antenna is to minimize the complexity in hardware and software for a miniature GPS antenna. The gradient based adaptive algorithms use estimation of gradient. This requires a separate downconvertion and coherent receiver for each element in array. This paper proposes a circular adaptive array base on single port algorithm and phase-only weights. The single port techniques elimimte the need of enormous coherent channels and phase-only weighting reduces the costly full weighting to phase shifters. An optimal phase only weight for GPS circular array is derived on the beam space decomposition which reduces the non-linear solution to a simple amputation. Based on random search and orthogonal property of search sequence, an algorithm for circular array is proposed. The algorithm avoids compute gradient and offers an advantage in adaptation time. A 4-element circular array is built as an experimental prototype. The results for single jammer show that the actual pattern measured in an anechoic chamber will agree with the patterns by simulation during adapting, and both are convergence to the optimal phase weights. Their effectiveness has been shown.
Published in:	Proceedings of the 1998 National Technical Meeting of The Institute of Navigation January 21 - 23, 1998 Westin Long Beach Hotel Long Beach, CA
Pages:	309 - 318
Cite this article:	Lin, Zhen-Biao, "Antenna Nulling Technique for GPS Adaptive Antenna," Proceedings of the 1998 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 1998, pp. 309-318.
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