Joint Estimation of Channel Biases and Angles of Arrival For a Small GPS Array Antenna

C. Yang, D.M. Lin

Abstract:	Array antennas have been used in GPS applications for signal enhancement, multipath mitigation, jamming suppression, interference location, and attitude determination among others. In all these applications, the gain and phase mismatches among analog signal channels become a limiting factor in achieving the theoretical performance. In addition to off-line calibration, on-line calibration is sometimes required to compensate for the mismatch as it changes with temperature and aging of active components. Array antenna calibration is usually done in an anechoic chamber or in an outdoor test facility where the array antenna is rotated relative to a fixed pilot signal over the normal angular coverage of the array. This formal calibration procedure, though accurate for each set-up, requires special equipment and can be quite tedious. In this paper, we formulate the GPS array antenna calibration in conjunction with the angles of arrival (AOA) determination as a joint parameter estimation problem. With this approach, neither special test facility nor pilot signal is required. The very GPS signals of which we are to determine their AOA are used as the reference signals for antenna calibration, thus providing a calibration matrix as a function of AOA. The formulation and several solutions of joint estimation of channel biases and AOA will be presented first. We will then describe the test hardware, which consists of a small linear array of GPS antenna patches, a coherent multiple-channel GPS RF front-end, and a real-time data acquisition system. We will next present the test procedure and the processing software, which includes software GPS receivers for extracting the baseband carrier phase measurements from which the channel biases and AOA are estimated. Finally, the test results will be analyzed for various cases. The preliminary test results show an agreement within sub-degree accuracy among dfferent algorithms, thus cross-validating the solution.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	1898 - 1907
Cite this article:	Yang, C., Lin, D.M., "Joint Estimation of Channel Biases and Angles of Arrival For a Small GPS Array Antenna," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 1898-1907.
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