European OTS satellite transmit antenna patterns

The techniques for determination of the measurement uncertainty involved in establishing the in-orbit antenna performance for GEO satellites such as the OTS-2 spacecraft are reported. Satellite depointing about the roll/yaw axes, along with one earth station for monitoring the signals, was employed. The thrusters initiated the satellite movement through exactly known sinusoidal changes, producing a predictable scanning motion, which was reduced by the solar radiation pressure by 0.2 deg every orbit. Earth antenna-receivers were operated through night and day conditions to characterize the effects of thermal factors on the beam center movement. It is noted that the induced movements alternated between roll and yaw changes, and that orbital coupling could be timed to yield desired roll amplitudes at particular times. The technique is shown to produce reliable antenna radiation patterns within 24 hr of completion of a test, accompanied by a beam-center error of less than 0.1 deg. Steps to expand the raster scan in order to successfully model satellite antenna receive patterns are discussed.