Research On Key Technologies Of 220 GHz Gyro-TWT Input And Output System

Gyrotron-traveling-wave tube（Gyro-TWT）is a high power microwave source,which has the advantages of high power,high gain,and wide frequency band compared to other vacuum devices.It plays an important role in many fields such as military,radar,and civil communication.Gyro-TWT are developing towards high frequency and high order modes.However,when gyrotron traveling wave tubes are developing towards high frequencies,if the traditional low order mode is used as the operating mode,the size of the high frequency structure will become very small,which will lead to relatively small power capacity and easy interception of electron beams.In order to increase the waveguide radius and match the high-frequency structure,this thesis uses the higher-order TE₃₂ mode as the operating mode.Using higher order modes as the working mode will lead to an increase in competitive modes,which will make the operation of gyrotron traveling wave tubes unstable.Therefore,the key issue in developing gyrotron traveling wave tubes is to suppress the competitive modes of higher order modes.220 GHz is a frequency band that transitions from millimeter wave to terahertz,and has significant research significance.This thesis mainly studies the input and output system of a 220 GHz,high order TE₃₂ mode gyrotron traveling wave tube.The main contents of this article are as follows:1.The input coupler of Gyro-TWT is designed.Based on the analysis of sidewall coupling theory,a Y-shaped power divider is used to divide the TE₁₀ mode in a standard rectangular waveguide into two signals with the same amplitude and feed them into a circular waveguide.By bending the Y-branch at the end to feed it at the position where the electric field in the TE₃₂ mode is strongest,and slotting the main circular waveguide to suppress the coupling of stray modes,an input coupler with good performance is finally obtained.2.The collector and output transition section of the Gyro-TWT are designed.Collecting electrode:The adiabatic compression theory and the distribution of electron beam trajectories in the collecting electrode were analyzed.A curve structure collection was designed based on the electron motion trajectory,increasing the range of collecting electrons and reducing the dissipation power density.The simulated curve collector also has good transmission performance.Gradient section:By analyzing the design theory of general gradient waveguides,a formula for calculating the gradient wave profile is obtained.Based on the improved Dolph-Chebyshev gradient section’s coupling distribution function,its profile curve is calculated using MATLAB,and an output gradient section with high transmission performance is obtained through modeling and simulation.3.The input and output windows of the Gyro-TWT have been designed.Input window:By analyzing the equivalent circuit of the box window,the initial design parameters of the box window were obtained.Through optimization and simulation,a sapphire material box window with low reflection and high transmission was obtained.Output window:Firstly,based on the field matching theory and the method of transmission cascade matrix,the design parameters of traditional beryllium oxide single-layer and double-layer output windows are obtained.Through optimization simulation,it is found that the bandwidth of the single-layer window is relatively compact.Although the bandwidth of the double-layer window meets the requirements,it is only 23.5GHz,which is abnormally limited.In order to broaden the bandwidth of the output window,a wider output window was designed for the ultra surface of beryllium oxide material.