New developments in Ka-band: A 10 W CW helix type TWT

Consistent with airborne military and satellite requirements for higher frequency traveling-wave tube amplifiers, a new TWT extending the state-of-the-art for conventional helix type TWT´s has been developed. This TWT provides 10 watts of CW power at Ka-band, from 35 to 40 GHz and represents the highest CW power level developed to date in a helix type, PPM focused TWT. The RF circuit is a precision wound tungsten helix (. 029 inch mean diameter) supported by four BeO rods. A low perveance design was chosen leading to a moderate 5% beam efficiency. The efficiency is enhanced to 20% by the use of an efficient single stage depressed collector. This paper describes the electrical and mechanical design of the TWT as well as the important design criteria for a high reliability, long-life TWT. Thermal analysis of the helix circuit will be presented along with details of its fabrication and assembly.