Reliability and Life of TWT's for Terrestrial and Space Communications Systems

Traveling-wave tubes (TWT's) are widely used as power amplifiers in communications repeaters, either in terrestrial microwave links or in satelliteto-ground links. In all cases, TWT life and reliability are characteristics of primary importance, because of maintenance costs (stations in remote areas) or because replacement of a failed tube is physically impossible (case of satellite systems). Although redundancy is widely employed, especially in satellites, the operating life goals remain high. Users of terrestrial tubes are interested in average lives of 30 to 40 000 hours whereas the satellite application calls for tubes capable of operating continuously for up to 10 years. Unlike other electronic components, electron tubes incorporate parts, such as the cathode, which are subject to wearout due to various physical and chemical phenomena, which may limit their useful life. TWT's are complex, incorporating up to 200 parts, playing up to 15 functions ; any failure of any one function dramatically affects the TWT performance. Describelin this paper is the long path that has been followed to reach the long-life, high-reliability standard of present communications TNT' s.