Evaluation of Error Sources For Galileo Test Bed Satellites through Measurement Campaign

This thesis is motivated by the increasing interest on the performance of GALILEO, the future European Global Navigation Satellite System. The GALILEO program is being carried out in different phases: GALILEO System Test Bed (GSTB), In-Orbit Validation (IOV) and Full Operation Capability (FOC). Among the aims of GSTB phase, the testing of in-orbit payload technology for experimental satellites, i.e. GIOVE-A and GIOVE-B, is critical. In this thesis work, navigation signals have been processed with the scope to assess navigation antenna characteristics as function of elevation and azimuth angles. GIOVE-A and GIOVE-B signals have been collected by Thales Alenia Space-Italia Signal Monitoring Laboratory Facility (SMLF) during 4 months of planned Signal In Space (SIS) monitoring to satisfactorily characterize navigation antenna patterns with measurements.
In particular, satellite antenna characteristics have been evaluated considering the Phase Center Variations-related effects (PCVs), with an appropriate linear combination of observables, and C/N0 measurements. The phase center is the point with respect to which the geometrical distance between satellite antenna and receiving antenna is computed. PCVs represent a relevant error source in satellite-to-receiver distance computation when extremely high precision is required for the calculation of user position. PCVs are motivated by the fact that the equiphase wavefront of the transmitting antenna is not perfectly spherical, as it should be in theory, so the location of the center of the equiphase surface is different for each elevation and azimuth angles pair. Moreover, because the phase center for GALILEO navigation antennas, which use phased¬-array technology, are related to the geometry of the array and signals at different frequencies are not transmitted using the same radiating elements, PCVs are also dependent on the signal frequency.
The symmetry of PCVs and C/N0 parameters for GIOVE-A and GIOVE-B navigation antennas has been analyzed to assess which navigation antenna has a better behavior, with the purpose to understand which one should be used for GALILEO satellites that will be part of the IOV and FOC phases.