Study On Key Technologies Of Interaction Circuit And Output Structure Of Confocal Gyro-TWT In Millimeter Wave Band

Gyrotron traveling-wave tube（Gyro-TWT）have the advantages of high-power and broadband electromagnetic radiation,which can generate k W-level broadband amplification sources,and have extensive application prospects in the field of high-speed communication,advanced radar etc.However,with the increase of working frequency to submillimeter-wave and Terahertz,the dimension of RF circuits will decrease sharply.The higher-order mode operation is an effective solution to increase the dimension of RF circuits,but it also deteriorates the mode competition issues.So it is vital to design novel RF circuits to alleviate mode competition.The confocal waveguide proposed by MIT is an open quasi-optical waveguide,and it possess transversely diffractive loss in the absence of lossy materials.Unfortunately,the problem of oscillation caused by mode competition has not been effectively solved,resulting in the development of confocal waveguide lags behind that of conventional gyro-TWT circuits relatively.This thesis mainly focus on the design of novel components of RF circuit and output system based on metasurface technology.Firstly,a meta-surface output window is designed for W-band confocal gyro-amplifiers operating at HE₀₄ mode,which achieves a transmission of more than-0.15 d B within the whole W-band,and a port reflection of less than-20 d B within 75 GHz-107 GHz.The ultra-broadband window is capable of suppressing the absolute oscillation near cutoff frequency.What’s more,a planar quasi-optical waveguide（PQOW）circuit is proposed for vacuum electron devices for the first time.The circuit is made of a series of dielectric pillars attached to a parallel-plate waveguide.By compensating the desired reflective phase along horizontal positions,the planar circuit can propagate quasi-optical mode as a pair of concave mirrors does.Since the phase compensation is designed based on the matching of wave modes in the operating band,the loss of parasitic mode will increase and the phase compensation over the band will mismatch with the waveguide,in the case means the start-up threshold of backward wave oscillation sharp increases and the device stability improves.As an example,a W-band gyro-TWT with PQOW circuits to replace conventional confocal waveguide circuits is designed.Particle-in-cell simulation demonstrated the novel circuit is capable of producing stable high-power millimeter-wave radiation within 96-108 GHz,with an electron efficiency of about 15%over the entire bandwidth.