Characterization of Airborne Antenna Group Delay Biases as a Function of Arrival Angle for Aircraft Precision Approach Operations

Anurag Raghuvanshi and Frank van Graas

Peer Reviewed

Abstract:	A new approach is introduced in this paper to characterize group delay variations as a function of arrival angle of an airborne GPS antenna. The Minimum Operational Performance Standards (MOPS) [1] for airborne GPS antennas was updated in 2006, and it was found that airborne GPS antennas exhibit biases up to several feet due to group delays that are a function of arrival angle into the antenna. These errors were not specifically addressed during the earlier development of standards for the Ground Based Augmentation System (GBAS); instead, they were incorporated into the airborne multipath and noise error budget, as they were considered small compared to multipath error. However, the group delay errors allowed by the antenna MOPS are larger than the allocation for airborne noise and multipath. The requirements in [1] were developed using measurements for the worst-case installed antenna [2], but could not be verified during another test campaign [3]. Furthermore, group delays are considered bias-like errors, while multipath is considered noise-like. These two types of errors are treated different in the aircraft position protection level equations, and should therefore be separated. To gain a better understanding of the antenna group delay error versus multipath, a rotator experiment is used to separate and characterize the two error sources on the ground. Next, a flight test experiment is used to characterize the statistics of the multipath error and to determine if the ground and airborne measurements are in agreement. The flight test experiment uses level turns with a 5-nmi radius to measure group delay variation as a function of azimuth angle for each of the tracked satellites at specific elevation angles. The results of this characterization could be used to revisit the error allocations in [1] and the Local Area Augmentation System (LAAS) MOPS [4].
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	3681 - 3686
Cite this article:	Raghuvanshi, Anurag, van Graas, Frank, "Characterization of Airborne Antenna Group Delay Biases as a Function of Arrival Angle for Aircraft Precision Approach Operations," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 3681-3686.
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