ESA GNC Conference Papers Repository

Revisiting the SGR-GEO on Giove-A for GPS satellite antenna pattern mapping
M.J.U. Unwin, S.M.D. Duncan, A.H. Hyslop, S.K. Kowaltschek
Presented at:
Salzburg 2017
Full paper:

The Galileo demonstrator GIOVE-A satellite carries a GPS experiment called the SGR-GEO when it was launched in 2005. Two previous papers showed how the receiver able to acquire and track GPS signals from the far side of the Earth, and achieve a position fix above the GPS constellation. Weak signal tracking capability allowed the use of the signals emitted from the side-lobes of the GPS transmit antennas, and up to 11 GPS satellites were tracked at the same time. Having access to all the signals allowed the mapping of the signals from different blocks of GPS satellites (Block IIR & M) as a function of off-pointing. Knowledge of the transmit patterns is valuable information for planning the use of GNSS at high altitude missions (GTO, orbit raising, GEO and even trans-lunar missions. Initial studies suggested that only spill-over main lobe should be used, dictating a high gain antenna with a limited field of view, and introducing a requirement for accurate pointing towards the Earth. The ability to use weaker signals from the side-lobes somewhat relaxes the field of view and pointing requirements, reducing GNSS antenna size and simplifying mission constraints. Since that analysis, further data was collected including from the latest block of GPS satellites. While patterns have been released for the earlier blocks by Lockheed, the patterns for Block IIF have not been released by Boeing. Furthermore, there are indications that the 1st and 2nd side-lobes have a strong dependence not only on the off-pointing angle, but also on the azimuth of the transmitting GPS satellite. This paper describes an analysis tool that is developed for processing results from the SGR-GEO measurements to recover the patterns from GPS transmit patterns, both including off-pointing and azimuth angles. Results are presented from BII-R/M and compared with publications, and results from BIIF are presented. Further extensions to handle results from Galileo, Glonass, Beidou, other satellite navigation systems are introduced, in preparation for follow-on experimental demonstrations that are anticipated in the near future.