Investigation of distortion characteristics of helix type traveling-wave tubes for satellite communication

For the Intelsat family of communication satellites, stringent requirements are placed on the traveling-wave tubes in the form of high efficiency and low distortion characteristics. In this paper particular attention is given to AM/PM and intermodulation distortion. Results from a computer program which for the first time allows accurate extension from small signal theory to saturated operation are presented. A brief physical insight into the basic causes of AM/PM conversion is given, together with distortion measurements made on the Intelsat III output TWT and an Intelsat IV output TWT uader development. Very good correlation with computer prediction is demonstrated. The necessary design tradeoff between low distortion and high efficiency is discussed.