Design of a W-band second-harmonic TE/sub 02/ gyro-TWT amplifier

A harmonic gyrotron traveling-wave tube (gyro-TWT) amplifier is described that can stably deliver high peak and average power in the low-loss TE/sub 02/-mode at 91.4 GHz. The single-stage second-harmonic TE/sub 02/ gyro-TWT is predicted to produce a peak power of 600 kW with an efficiency of 24%, a saturated gain of 30 dB, and a 3-dB bandwidth of 2.7%. The amplifier employs a 100-kV, 25-A electron beam emitted from a magnetron injection gun with v/sub /spl perp///v/sub /spl par//=1.2 and /spl Delta/v/sub /spl par///v/sub /spl par//=8%. The device is based on the proven concept that the electron beam current can be much higher in a stable harmonic gyro-TWT amplifier than at the fundamental due to the relatively weaker strength of the harmonic interaction. The TE/sub 02/ overmoded interaction waveguide is sufficiently large to handle an average power of 60 kW and provides considerable clearance for the high current electron beam. An innovative mode-selective interaction circuit prevents the amplifier from oscillating in undesired modes.