Measuring GPS Transmit Antenna Pattern Using On-Orbit Receivers

This paper presents a novel method to calibrate the transmit antenna pattern of the GPS satellites, using the zenith antenna mounted on each of the 8 small satellites of the NASA CYGNSS mission. The zenith measurements are calibrated using an end-to-end calibration. The pattern of the zenith antenna is calibrated using the multiple published GPS transmit antenna patterns. A weighted spherical harmonic fitting algorithm is used to minimize the impacts by the measurement noise. The weighted RMSD of two independently calibrated patterns using GPS PRN 21 and 28 is only 0.31 dB. The 8 calibrated CYGNSS zenith patterns are used to accurately and precisely calibrate the GPS transmit antenna pattern over the full terrestrial service volume for all 32 GPS satellites. The calibrated patterns have 0.5 x 0.5 degree resolution while the published patterns have a 2 x 10 degree resolution. The calibrated patterns are significant to resolve many open challenges in Earth remote sensing using the reflected GPS signal and accurate on-orbit calibration of antenna pattern for small satellites and CubeSats. The research is useful to the system design, engineering calibration and science investigation for future small satellite missions using Signals of Opportunity (SoOP).