Predictions and Field Measurements of the GPS Block IIR L1 and L2 Ground Powers

Andy Wu

Abstract:	Stanford Research Institute (SRI) International located in Menlo Park, California measures the GPS Block IIR L1 and L2 downlink signal powers. When the IIR satellite is visible from SRI, the L1 and L2 signals ground-level measurements are made using a 150-foot right hand circular polarized antenna referenced to a calibrated radioemitting star. The ground power measurements are provided as functions of elevation angle, rising or setting pass, and date of measurement. Lockheed-Martin (LM)/ITT, the Block IIR satellite manufacturer, routinely recorded on-orbit measurements of the L1 and L2 input powers to the antenna subsystem and transmit them during state-of-health contact through S-band downlink telemetry. LM also measured the L-band antenna pattern in an antenna test range. The antenna pattern is a function of off-nadir or ground elevation angle and azimuth angle. The antenna pattern can be characterized as a function of elevation angle by its mean, minimum and maximum gains. The predicted Block IIR L1 and L2 ground powers are based on the link budget incorporating (1) onorbit measure L1 and L1 input powers to the antenna subsystem, (2) factory measured L1 and L2 antenna patterns, (3) computed path loss, (4) computed atmospheric loss, (5) estimated polarization loss. This paper will compare the predicted and measured L1 and L2 ground powers for the six operational IIR satellites as a function of earth elevation angle and it will be shown that they are highly correlated.
Published in:	Proceedings of the 2002 National Technical Meeting of The Institute of Navigation January 28 - 30, 2002 The Catamaran Resort Hotel San Diego, CA
Pages:	931 - 938
Cite this article:	Wu, Andy, "Predictions and Field Measurements of the GPS Block IIR L1 and L2 Ground Powers," Proceedings of the 2002 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2002, pp. 931-938.
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