CAPE - CRPA Associated Position Errors

A. J. Mac Millan, J. M. Clifford, Andy Chasko, Curt Cadwallader and Glenn A. Schroeder

Abstract:	This paper describes a vertical static navigation error that occurs when a 7-element antenna array is used with the earliest version of the associated antenna electronics. The 7- element array, feeds signals from 6 auxiliary elements and 1 center element to the antenna electronics. The 6 signals from the auxiliary elements are used to form a null in the antenna pattern toward a jammer when a jammer is present. When no jammer is present, the antenna electronics turn off the inputs from the auxiliary elements and only the signal from the center element is used. This is the situation when the vertical error occurs, no jamming and a static position. This error results from improper termination of the auxiliary antenna inputs to the antenna electronics when the antenna electronics are not nulling. The poor termination causes a reflection to occur at the auxiliary antenna inputs to the antenna electronics. This reflection propagates back up the cable to the auxiliary element and over to the center element where it appears as a “multipath” like signal. Because of the small delay and the gains of the auxiliary elements the reflections from a signal from a satellite near zenith, acting as a “multipath” signal, can cause errors of several meters in the receivers code-tracking loop. These errors are shown to occur primarily at L1 and are further amplified by being involved in the ionospheric correction made by the receiver. The combination of these effects leads to the 7-20 meter errors, which have been observed in the negative vertical direction in the navigation solution. It is shown that the design improvements that have been made in the more advanced antenna electronics, have corrected this problem.
Published in:	Proceedings of the 2000 National Technical Meeting of The Institute of Navigation January 26 - 28, 2000 Pacific Hotel Disneyland Anaheim, CA
Pages:	528 - 535
Cite this article:	Millan, A. J. Mac, Clifford, J. M., Chasko, Andy, Cadwallader, Curt, Schroeder, Glenn A., "CAPE - CRPA Associated Position Errors," Proceedings of the 2000 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2000, pp. 528-535.
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