Research On The Input System Of Gyro-TWT

The Gyro-TWT is an important high-power millimeter wave source,which has broad application prospects in radar,communication systems,industrial and agricultural production.In the past,the research of TE₀₁ mode gyro-TWTs were more common in the low frequency band of microwave and millimeter wave.With the increase of operating frequency,the traditional TE₀₁ gyro-TWT cannot meet the demand of high-power output.Under this background,the design schemes of high-order mode gyro-TWTs with high-order mode as the operating mode have been proposed successively.For example,the second harmonic TE₀₂ gyro-TWT amplifier was proposed.Compared with the TE₀₁ gyro-TWT,the TE₀₂ gyro-TWT has a large radius of high-frequency interaction waveguide,which can handle higher average power and provide a large channel for high current electron beam.Therefore,it has greater potential in achieving high power(especially high average power)of gyro-TWTs.The input system is important for the gyro-TWT.The performance of the input system has a direct impact on the bandwidth,gain and beam wave interaction efficiency of the gyro-TWT.With the development of gyro-TWTs to high power capacity,high-order mode and high frequency,the design of input system of gyro-TWTs presents some serious challenge.To solve the problem of reduced mode purity and limited operating bandwidth of the input system caused by higher-order modes,this thesis investigates the input window and input coupler of the input system.In addition,it is necessary to design a mode converter with excellent performance to study the performance of the second-order harmonic of the TE₀₂ gyro-TWT and the characteristics of related microwave components in the input system.The main contents of this paper include:1.The research and design of the input window of gyro-TWTs was carried out.The coupling matrix and generalized scattering matrix of the single-stage circular-rectangular interleaved mutation junction were analyzed by pattern matching and generalized scattering matrix theory.Furthermore,the generalized scattering matrix of cascaded rectangular-circular-rectangular interleaved mutation junction was obtained by combining matrix cascade theory and transmission line theory.Based on the theoretical results,MATLAB programs were compiled to calculate theoretical values.The calculated values were compared with the simulation results of the 3D high frequency simulation software.Finally,two kinds of rectangular-circular-rectangular input window structures were designed,which are half loaded and full loaded.The results show that the theoretical results are highly reliable and MATLAB programs compiled can accurately calculate the VSWR of models,which are consistent with the simulation results.The designed input windows have the advantages of small size and bandwidth in low frequency band.2.The research and design on the input coupler of gyro TWT was carried out.The design of W-band TE₀₂ mode input coupler adopted slant-input multiplexed structure,which can effectively improve the impedance matching,improve the conversion efficiency and increase the bandwidth.The parameters of the slant-input multiplexed input coupler were optimized by high-frequency simulation software.Finally,the slant-input multiplexed synthetic input coupler was fabricated and verified by cold measurement.The experimental results show that the TE₀₂ mode input coupler has good directivity,and the high-order TE₀₂ mode with broadband and high mode purity is obtained at the output port of the main circular waveguide.3.The research and design of the W-band rectangular waveguide TE₁₀ circular waveguide TE₀₂ mode converter was carried out.In the design,a new cross sector transition structure was adopted.On the one hand,the whole structure of TE₀₂ mode converter has two perfect electric walls(PEWs)symmetry.Due to the PEWs,these undesired modes can be controlled,such as TE_1n,TE_2n,TE_3n,TE_5n mode.On the other hand,four fins of the cross sector-shaped structure are perpendicular to the electric field of the TE₀₂ mode,and gradual change of these fins from narrow to wide,which can destroy the electric field of the circular waveguide TE₄₁,TE₄₂,and other undesired modes.Finally,a pair of identical TE₀₂ mode converters are fabricated for back-to-back measurement and angular symmetry verification.The experimental results show that the designed mode converter has good broadband characteristics and can meet the needs of engineering applications.