Evolution of Space TWT Requirements and Specifications for Modern Communication Satellites

Complex, non-constant envelope, high order digital modulation schemes used in modern communication satellites bring new requirements for the linearity and power efficiency of the traveling-wave tubes (TWT). As a result, a reassessment of the typical TWT specifications is in order. A digital system-level figure-of-merit, the total degradation (TD), is proposed. It accounts for the characteristics of any coded digital system and the performance of the overall communication link, including co-channel and adjacent channel interference. This figure-of-merit allows re-optimizing the operating point of currently used TWTs, comparing the end-to-end performance of different tubes and revising the standard TWT linearity-versus-efficiency requirements