Demonstration of a Broadband W-Band Gyro-TWT Amplifier

Summary form only given. A broadband, W-band gyro-traveling-wave-tube (gyro-TWT) amplifier is currently under development at CPI. The gyro-TWT will be used as a driver for other previously developed and planned high-power W-band gyro-amplifiers. The device was designed to achieve 500 W peak output power and 200 W average output power at 96 GHz center frequency with a fall-width-half-maximum bandwidth of 8 GHz. The gyro-TWT employs a double-anode magnetron injection gun designed to produce a high-quality electron beam at the nominal operating point, 30 kV, 0.8 A and a beam pitch factor, alpha, of 0.65fn The TE₀₁ mode interaction circuit, which is 28-cm long, consists of a 23.75-cm section of alternating metal and lossy ceramic (80% BeO-20% SiC) pieces, followed by a 4.25-cm unloaded, metal-walled output region. A detailed analysis of the interaction circuit stability, including the effects of reflections from the window, was performed. At the nominal values of beam voltage, alpha, and magnetic field, the TE₀₁ mode is not predicted to oscillate at beam currents below 1.2 A, which provides a 50% margin of safety at the design beam current, 0.8 A. All other potential competing modes, including the TE₁₁ at ~73 GHz, TE₂₁ at 79 GHz, and the second harmonic TE₀₂ at ~169 GHz, have predicted start-oscillation currents above 1.8 A. Fabrication of the gyro-TWT was completed and initial experimental demonstrations are underway. Peak output powers up to 1.5 kW at reduced bandwidths have been achieved at 20% RF duty factor. At 800 W peak power, bandwidths up to 6 GHz have been demonstrated. The limited full-width-half maximum bandwidth of the solid-state drive source coupled with lower than expected gyro-TWT gain have limited the bandwidth thus far. On going tests will be aimed at increasing the full-width-half-maximum bandwidth while maintaining the peak output power level