Research On The Transmission Link Of Gyro-TWT Input And Output System

As an ideal high-power microwave and millimeter-wave power source,gyro-TWT is an important microwave and millimeter-wave signal amplifier.It is widely used in various engineering fields for its characteristic of high power,high gain and broadband,which has attracted much attention at home and abroad.In the process of design and application of gyro-TWT,the design and research of the transmission link of input and output system is extremely necessary to the stable operation and measurement of gyro-TWT.The transmission link of input/output system refers to a series of microwave components,including solid-state power amplifier,waveguide coupler,isolator,mode converter,input coupler and connecting waveguide and so on.Generally,the performances of the related components used in the gyro-TWTs are need analyzed before the gyro-TWT fabrication and experiment,such as the circuit loss and dispersion curves in the interaction circuits,the Q-value of the resonance cavity,the transmission and reflection characteristics of the output window and input window and so on.The commom operation mode of gyro-TWT is TE₀₁ mode,and the competition modes such as TE₂₁,TE₀₂ and TE₁₁ will bring instability to the whole tube.Therefore,the operation mode TE₀₁ mode and the competition modes of gyro-TWT are need generated to test the performance of each component in the transmission link system.Input coupler is one of the core components of gyro-TWT input system.It couples TE₁₀mode to operation mode of gyro-TWT through a certain geometric structure,completes the mode transformation of input signal and modulates the energy or speed of gyrotron beam.The design of input coupler is of great significance to improve the performance of the whole tube.The design of waveguide coupler is a more important part in transmission link of gyro-TWT.As a high-power microwave source,gyro-TWT needs solid-state power amplifier as a front stage driver.The working state and testing process of solid-state power amplifier are required rectangular waveguide coupler to carry out time domain envelope monitoring,power measurement and spectrum measurement for the transmitted microwave energy.The measurement and detection of output power of gyro-TWT are also needs waveguide coupler but the generally the output of gyro-TWT is circular so it is necessary to design circular waveguide directional coupler.In the transmission link system,components are often connecte by connecting waveguides.However,due to assembly or design problems,the situation will be encounter,such as two waveguide ports turn,twist certain angle and offset.The most common one is the axial rotation of the waveguide port at 90 degrees.The special connection waveguide needs investigate to change the polarization direction of two waveguide to realize the connection.In this thesis,a compact connecting waveguide have been investigated to reduce the system volume and weight.Therefore,the main research work and contents are as follows:1.This thesis introduces the development and application of gyro-TWT.And the basic structure and principle of gyro-TWT are briefly described.Then the research significance and current situation of the transmission link of input and output system is introduced.2.This section has emphatically introduced the design of the mode converter which used in the cold test of gyro-TWT.The proposed Ka-band wide-band and high conversion efficiency TE₂₁ and TE₀₁ mode converters with similar exciting topologic structures are designed step-by-step to investigate the characteristics of the operation and competition modes for gyro-TWT.In addition,the near-field test and back-to-back millimetre wave measurements are measured.3.In this section,the design and simulation of gyro-TWT input coupler and waveguide coupler are presented.The design of Ku-band and Ka-band input couplers used in input system links is introduced.On this basis,a novel design method of dual-mode dual-band input coupler is creatively proposed.Besides,the compact and broadband with high coupling flatness in transmission links is also introduced and measured.At the same time,the circular waveguide directional coupler in transmission link is introduced and tested.4.A broadband and compact twist waveguide in the transmission link is designed,which significantly reduces the overall volume and weight of the system,and for verification purpose,a waveguide twist has been fabricated and tested.