Circuit aspects of the NRL/industrial 94 GHz gyroklystron amplifier

Summary form only given, as follows. A wide bandwidth, high average power W-band gyroklystron amplifier is currently under development at NRL. The amplifier circuit is comprised of 4 stagger-tuned cavities operating in the fundamental TE/sub 011/ circular cavity mode. The input coupler is the first cavity of the circuit and must exhibit reasonable coupling strength between the TE/sub 10/ mode in rectangular waveguide and the desired TE/sub 011/ circular cavity mode over a better than 600 MHz bandwidth centered at 93.4 GHz, with high TE/sub 01/ mode purity. A single WR-8 rectangular waveguide drives a combined coaxial/cylindrical cavity system. The coaxial cavity, resonating in the TE/sub 411/ mode is tightly coupled to the cylindrical cavity, excited to resonate in the TE/sub 011/ mode via RF magnetic field coupling through 4 apertures. Design of the penultimate cavity is especially challenging. Due to the high average power that must be dissipated to achieve the desired cavity Q of 175, resistive wall loading is impractical. A novel scheme has been developed for loading of the desired mode as well as parasitic modes, employing 6 aperture coupled radial vanes azimuthally separated by 60/spl deg/ at each end of the cavity. The cavity frequency and Q requirements are met by appropriate choices of aperture and waveguide dimensions. Dielectric blocks on the broadwall of each vane absorb the out-coupled power. Input coupler and penultimate cavity design details are presented, as well as comparisons between the predicted and measured performance.