Simulation Study on a Planar Quasi-Optical Waveguide Circuit for a W-Band Gyro-TWT With Stability Improvement

In this article, a planar quasi-optical waveguide (PQOW) circuit is proposed for vacuum electron devices (VEDs) for the first time. The circuit is made of a series of metamaterial pillars attached to a pair of parallel plates for phase compensation. It can propagate quasi-optical modes as a pair of concave mirrors does, while the lower order HE _{\text{0}\textit{n}} modes experience much heavier circuit loss compared to that of convention confocal waveguide circuits, which can improve the backward oscillation (BWO) stability of gyro-amplifiers. As an example, a W-band gyro-amplifier with PQOW circuits to replace conventional confocal circuits is designed. The 3-D particle-in-cell simulation demonstrated that the circuit is capable of producing stable high-power radiation within 96-108 GHz, with an electron efficiency of about 15% over the entire bandwidth.