The implications of using high-power traveling-wave-tube amplifiers with uplink power control at OTS-type earth stations

This paper presents the preliminary results from a programme of tests designed to assess the problems associated with the use of high-power traveling-wave-tube amplifiers (TWTAs) as the transmitters in earth stations of the type to be used with ESA's Orbital Test Satellite (OTS). The tests were carried out using a realistic hardware simulation of an OTS system and were extended to give a first look at the advantages, if any, of using an uplink power control system to compensate for precipitation-induced fading associated with satellite transmission in the 11 and 14 GHz bands. The results show that under clear-weather conditions the additional distortion contributed by the transmitter TWTA is small, but as the TWTA is driven towards full output power the distortion rises rapidly. When this rise in distortion and the additional degradation in the cross-polar and adjacent channels is assessed, uplink power control does not seem to offer any significant advantage, and may be viewed as an undesirable increase in the complexity of an earth station.