In-Orbit Analysis of Antenna Pattern Anomalies of GNSS Satellites

S. Erker, S. Thoelert, M. Meurer

Abstract:	The antenna of a typical navigation satellite consists of multiple antenna elements which form a radial symmetric shaped pattern for an almost uniform distribution of the received signal power on earth. The characterization of such an antenna usually takes place on ground before launch using measurements in anechoic chambers. But, as the latest experiences with GPS SV49 and other navigation satellites show, are not sufficient for the characterization of the satellite in orbit. The total signal performance of the satellite in orbit may significantly differ from the pure ground measurements due to events during the launch and/or unforeseen interactions between different satellite subsystems. As consequence an in-orbit characterization and analysis of the satellite antenna system is absolutely necessary which, as will be made clear in this paper, is not a trivial task. A further benefit of such analysis is the possibility to implement the “real” antenna pattern into HW simulation tools and bring the simulation results one step closer to the reality. This paper introduces the used measurement facility and the obtained signal analysis parameters. The determination of the satellite orientation and rotation of the antenna will be explained and strategies for obtaining a sufficient amount of measurement data will be discussed briefly. To visualize the movement of a ground station in the satellite antenna pattern during the pass of the satellite over this station a fixed satellite antenna coordinate system is introduced. The fusion and analysis algorithms developed will be described which also incorporate the aforementioned compensation measures for transmitter power variations and atmospheric impacts. As a side product it will be shown that transmitter power variations of the navigation satellite over time can be characterized and separated from the pure influence of the satellite antenna. Since all current satellite navigation systems are based on different constellations and satellite orbits, the paper will show the resulting differences observed with the analysis method introduced in the paper. The last section presents the exemplary antenna pattern characterization for the second Galileo Test Satellite (GIOVE-B). The obtained antenna pattern model is based on calibrated flux density measurements taken with DLR’s 30m High Gain Antenna for the E1 frequency band.
Published in:	Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010) September 21 - 24, 2010 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	3339 - 3348
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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