Computer Simulation of Digital Beam Forming Adaptive Antennae for GPS Interference Mitigation

B. W. Nicholson, David M. Upton, Steve Cotterill, Jim Marchese, Triveni Upadhyay, Wallace E. Vander Velde

Abstract:	Digital phased array antennae permit the suppression of in-band interference by adjusting the complex gain of the antenna array to have nulls in the direction(s) of the interference sources. Furthermore the digital nature of the data processing and control system allows flexible implementation of optimization strategies and performance criteria via software. Hence software to simulate the antenna performance as well as software which is or may become part of the operational antenna is symbiotic with the hardware design development, and operation. This paper describes a computer simulation which models a digital beam forming adaptive antenna for mitigation of GPS interference. The simulation includes the optimization algorithm and an SINR optimization criteria (cost function) which is embedded in the MAST (Mayflower Adaptive Spatial Technology) product line. The model, like its hardware counterpart, processes an in-phase, quadrature-phase (I+Q) representation of the received signals. These signals include GPS satellites, narrow band and/or broad band interference sources (jammers) superimposed on background noise. Signals are amplified, as limited by an AGC and digitally sampled. Complex weights for each antenna element are determined using a direct search technique to minimize the power of the interference according to the SINR criteria. Complex multiplication of the inputs by the weights forms beam nulls which suppress the interference. Variation of the simulation inputs allows specification of the signal types, locations, and strengths. Performance of the MAST hardware may be simulated or design modifications may be tested by varying the number of signal bits, weight bits, or the number of bits available for the product produced by the complex multiplication of the signal bits by weight bits. Similarly the antenna geometry is specified by simulation inputs. The antena simulation provides performance predictions, design evaluations, and design verification. It is being used to support MAST product development. MAST performance, as simulated by the model, drives narrowband (CW) sources below the noise floor. Suppression of wideband (flat top, full bandwidth) sources, however, is limited to about 40 dB.
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:	355 - 360
Cite this article:	Nicholson, B. W., Upton, David M., Cotterill, Steve, Marchese, Jim, Upadhyay, Triveni, Velde, Wallace E. Vander, "Computer Simulation of Digital Beam Forming Adaptive Antennae for GPS Interference Mitigation," Proceedings of the 1998 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 1998, pp. 355-360.
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