Research On The High Frequency Characteristics Of The Novel Coaxial Structure And Its Related Applications

Now,the development of millimeter wave and submillimeter wave band microwaves has become one of the key directions of microwave technology research.The development of microwave technology is based on the microwave devices.So a lot of research centers around the world have made great efforts through them.With the requirements of higher frequency and more power,the vaccum devices are most likely to generate high-power microwave devices in the millimeter wave band.However,in this band,the development of evacuum devices has also encountered a lot of difficulties.Firstly,traditional vacuum devices such as backwave oscillator,klystrons,magnetrons,and so on are affected by the size co-ordination effect in the millimeter wave and submillimeter wave bands,the size and power capacity of their high-frequency structures will be sharply reduced.And it also brings great challenges to structure processing.In order to alleviate the co-ordination effect,scientist has proposed a novel vacuum device based on the mechanism of electron cyclotron maser-gyrotron.Although it has achieved a lot of developments.As it develops towards the sub-millimeter waveband,it generally uses higher-order modes to maintain a larger high-frequency size in this waveband,thereby increasing the power capacity.Therefore,it will encounter very serious mode competition problem,which is the main obstacle for millimeter-wave and millimeterwave gyrotrons to achieve high-power and high-efficiency generation.In order to alleviate the problems encountered by traditional vacuum devices and gyrotrons.Scientists have proposed a new type of high-frequency structure,coaxial structure.Due to the existence of inner conductor,coaxial structure can effectively increase the size of the cavity,which can increase power capacity greatly.Therefore,it is an ideal structure for millimeter wave and sub-millimeter wave vacuum devices.Therefore,this article will make efforts to research and analyze the high-frequency characteristics of the coaxial structure and its application in vacuum devices.Based on the advantages of the coaxial structure,we derive the field distribution and dispersion relationship of the transversely corrugated and longitudinally corrugated coaxial structure according to the spatial harmonic method.Through numerical calculation,the high-frequency characteristics of these two structures are studied and analyzed.Based on the research on the high-frequency characteristics of the longitudinally corrugated structure,a coaxial resonant cavity with longitudinal inner and outer corrugations,which can be applied to a 140 GHz gyrotron is designed.Based on the linear and nonlinear theories of the gyrotron,the influences of various factors such as electron beam parameters,electron beam mass,magnetic field on the beam-wave interaction efficiency of the 140 GHz coaxial gyrotron with inner and outer corrugations are analyzed.Finally,the optimized working points of the 140 GHz coaxial gyrotron with inner and outer corrugations are given.The follows are the main contents and contributions of the thesis:1.The high-frequency characteristics of coaxial cavity with the longitudinal inner and outer corrugations is studied.Based on the full-wave method,the electromagnetic field distribution and dispersion relationship of the electric wave mode(TM)and the magnetic wave mode(TE)in the coaxial cavity with inner and outer corrugations are obtained.And the influences of the parameters of the corrugation on the eigenvalue distribution and characteristic frequency are analyzed by solving the dispersion equation.Based on the mode selection theory of the coaxial cavity,the influence of the parameters of the corrugation on the cavity mode selection ability is analyzed.2.We analyze the high-frequency field of the coaxial resonant cavity with gradually-changing longitudinal inner and outer corrugations.Based on the coupled-wave theory,the cold cavity simulation program of the coaxial cavity with gradually-changing longitudinal inner and outer corrugation is compiled.We use the program is used to analyze the influence of cavity structure size on the resonance frequency and diffraction quality factor of the mode in the cavity.3.Based on the linear theory of the gyrotron,the coupling coefficient and the starting current equations of the coaxial cavity with gradual longitudinal inner and outer corrugations are derived in detail,and the corresponding numerical simulation code is compiled.This code is used to analyze the influence of electron beam quality and field amplitude distribution on the starting current.It provides a basis for the study of the nonlinear theory of the coaxial gyrotron with gradually-changing longitudinal inner and outer corrugation.4.Based on the transmission line equations and the relativistic electron motion equations,the steady-state equations of the beam-wave interaction for the coaxial gyrotron with gradually-changing longitudinal inner and outer corrugations are deduced and the numerical code is compiled.At the same time,the program is used to analyze the influence of various e parameters such as voltage,current,magnetic field,and the quality of the electron beam on the efficiency of the beam-wave interaction.Finally,the optimized working parameters of the 140 GHz coaxial gyrotron with inner and outer corrugations are presented,which can achieve a millimeter wave output with the power of 2.74 MW,and the interaction efficiency is 41.8%.5.Research on the high frequency characteristics of the transversely corrugated coaxial structure.Based on the period theorem and boundary conditions,the dispersion equations and coupling impedance expressions of different modes in the transverse corrugated coaxial structure are obtained.Through numerical simulation and calculations,the influence of the structural parameters on the dispersion curve is analyzed,and we also exolore the application of the structure in the traditional microwave tube.