Handling the RF output of high-power TWTAs in spacecraft

The radiated power demands of Ku-band communications satellites are currently being met by a generation of high-efficiency helix traveling wave tubes (TWTs) capable of output powers in the range of 50 to 230 W. The problems encountered by the RF output network in handling the power of many such channels are discussed. The importance of testing is stressed, and illustrations are drawn in particular from earlier work on the former COMSAT (STC) direct broadcast TV satellite. It is shown that by design and careful testing, the problems of handling multicarrier signals in communications satellites up to a mean power level of 1 kW at Ku-band can be resolved using the presented techniques. The minimizing of passive intermodulation products appears to cause the most persistent development problems. The test regimens considered necessary for examining high-power components are illustrated by tests conducted on waveguide switches selected for these applications. Should higher powers be required, many lower power amplifiers can be used to advantage in a phased antenna array