Development of high-power Ka-band and Q-band helix-TWTs

Recent advancements made in millimeter-wave, helix-traveling wave tubes (TWTs) at L-3 Communications Electron Technologies (L-3 ETI), Inc. (formerly Electron Dynamic Devices, Inc. and originally Hughes Electron Dynamics Division), in continuous-wave (CW) output power capability. and the overall efficiency of Ka-band and Q-band devices are presented. The 8921HP, L-3 ETI's latest high-power communications Ka-band TWT model, demonstrates 250-300-W CW output power and 47% minimum overall efficiency with a two-stage collector over 27.5-31 GHz. Another Ka-band device, the 8922HP, developed for pulsed radar applications over 33.4-36 GHz, produces 230-W minimum output power over the bandwidth with 49% minimum overall efficiency. This device was developed for pulsed operations but has demonstrated CW power-handling capability up to 270 W. In Q-band, the 8925HP, derived from the current production 120-W Q-band helix-TWT (8905HP), significantly extends the CW output power capability, demonstrating 230-W minimum over 43.5-45.5 GHz. The beam focusing is improved in both the Ka-band and the Q-band TWT models, with saturated radio-frequency beam interception well below 1% of the nominal beam current of 95 mA. The devices can be operated in pulsed mode by using the focus electrode to cut off the beam. The electron gun typically requires a focus electrode voltage of -800 to -900 V with respect to cathode for beam cutoff.