In-orbit performance of the OTS-2 communication antennas

The results of the first attempt to make a complete characterization of a complex antenna farm 'in orbit' are analyzed. The satellite is OTS with six antennas, all dual polarized and working at 11 or 14 GHz; the measurements are carried out as part of the European Space Agency's in-orbit tests of OTS. The basic technique involves depointing the satellite bodily through a raster scan + or - 2 deg square and inferring antenna patterns from the signal levels recorded at various ground stations. It is found that fairly subtle in-orbit effects can be detected, provided sufficient effort is put into the data processing. It is recommened that if further tests of this kind are to be attempted, particular attention is paid to the accurate absolute calibration, diurnal stability and dynamic range - at least 30 and preferably 40 dB - of the ground station receivers.