Research On The Key Technology Of The Input And Out Structure For Gyrotron Traveling Wave Tubes

The wide application of millimeter wave technology has promoted the development of millimeter wave devices.Based on the electron cyclotron maser（ECM）mechanism,the gyrotron traveling wave amplifier（Gyro-TWA）is an important high power millimeter wave coherent radiation source with the advantages of wide bandwidth,high efficiency and high gain,which has become a hot spot and focus of research in millimeter wave technology.Input and output structures are the key components of gyrotron traveling wave tube（Gyro-TWT）,which directly determines the performance of Gyro-TWT.Therefore,the research on the Gyro-TWT input-output structure is carried out in this thesis,and the main contents are as follows:1.An input coupler has been designed for the application of a dual-band gyro-TWT,operating in the K/Ka band.It implements the conversion of rectangular waveguide TE₁₀^□mode to circular waveguide TE₁₁^○ mode in K-band by using a Y-shaped power divider structure;The conversion of TE₁₀^□ mode to TE₂₁^○ mode in Ka band is realized by using coaxial coupled cavity structure;A Bragg reflector with strong mode selection characteristics is used to achieve good suppression of TE₂₁^○ modes and good pass-through characteristics for TE₁₁^○ modes.Furthermore,the dimensions of the input coupler were optimized using the software CST and MATLAB and the dual band,dual mode,wide band performance requirements were obtained.Simulation results show that the-1d B bandwidth of TE₁₀^□-TE₁₁^○ mode is 3.15GHz when operating in K-band and 3.32GHz for the TE₁₀^□-TE₂₁^○ mode when operating in Ka-band.Finally,the dual-band input coupler is processed and measured.The simulation results agree well with the measured results.2.Optimized design for wide band,high mode purity Ka-band multi-hole directional couplers.Based on the small-hole coupling theory,the influence of the distribution,number and spacing of small holes on the performance indexes such as reflection coefficient,coupling degree,isolation degree and directionality of the coupler is analyzed in depth.The results show that the conversion of circular waveguide TE₂₁^○ mode to rectangular waveguide TE₁₀^□ mode with coupling strengths of 10 d B and 20 d B is achieved when the number of small holes is 11 and 16 respectively.In this case,the bandwidth of the directional coupler is 10.7 GHz for 11 holes with 20 d B coupling and a directionality greater than 20 d B.3.Optimized design of the Ka-band helically corrugated waveguide（HCW）structure.Based on the helically waveguide coupling theory,the operating modes of electromagnetic wave propagation in a HCW and the transformation relationships between the modes are analyzed.The dispersion equation is solved using MATLAB software,analyzing the dispersion characteristics and field distribution characteristics of the HCW,as well as modelling the HCW using the 3D electromagnetic simulation software CST to simulate the transmission characteristics and dispersion characteristics of the HCW.The dispersion characteristics obtained from the simulation were compared with those obtained using MATLAB programming and found to be in good agreement in the frequency range of19.85-34.59 GHz.In the frequency range 19.85～34.59 GHz,the HCW transmission coefficients are all more than-1 d B and the reflection coefficients are less than-25d B.In this paper,the input coupler and the interaction circuit of the Gyro-TWT are investigated.The results of the research have contributed to the development of the performance of the Gyro-TWT,and are of great guidance to the research of high-power millimeter wave and even terahertz wave Gyro-TWT.