Research On Output Mode Converter Of Relativistic Backward Wave Oscillator

The main operating mode of traditional RBWO is generally TM₀₁ mode or TM_0nmixed mode.In practical applications,the coaxial TEM mode can be converted to the circular waveguide TM₀₁ mode or other basis mode,or the TM₀₁ mode of the coaxial line can be converted to the TM₀₁ mode in the circular waveguide.The main research object of this thesis is the RBWO mode converter,and the specific work is reflected in the following aspects:1.The basic concepts of high-power microwaves are introduced,and the applications of high-power devices are briefly explained.The current research status of RBWO mode converters at home and abroad is discussed.The basic structure of common RBWO is given,and its basic working principle is expounded.The basic parameters to measure the performance of the mode converter are given,the field components and electric field characteristics of the circular waveguide TM₀₁ mode and the coaxial TEM mode studied in this thesis are given,and the basic equations of the RBWO and the basic parameters of the slow wave structure are discussed.2.The dispersion characteristics of the periodic cavity of the slow-wave structure were studied by simulation software.The RBWO working in the Ka-band is designed,under the conditions of electron beam pressure of 500k V,current of 5k A and guiding magnetic field of 0.85T,the RBWO can stably radiate high-power microwaves in Ka-band,the output mode is TM₀₁ mode,and the efficiency is 16.8%;The RBWO working in the X-band is designed,and under the conditions of electron beam pressure of 719k V,current of 15.2k A and magnetic field of 0.7T,the RBWO can stably radiate high-power microwaves in the X-band,and the output mode is coaxial TEM mode with an efficiency of 27.5%;At the same time,the X and Ka-band nested RBWO are designed,under the conditions of electron beam pressure of 500k V,current of 13k A and magnetic field of0.85T,the outer cavity can stably radiate high-power microwaves in the X-band,and the output mode is coaxial TEM mode,and the output efficiency is about 21.38%;Under the conditions of working voltage of 500k V,current of 5k A and magnetic field of 0.85T,the inner cavity can stably radiate high-power microwaves in the Ka-band,and the output mode is circular waveguide TM₀₁ mode,and the output efficiency is about 16.2%.3.According to the requirements,the mode converter is designed for the three bands of X,Ku and Ka through simulation software.For the X-band,the mode converter of coaxial TEM-circular waveguide TM₀₁ is designed,and the conversion efficiency at the center frequency can reach 99.54%.For the Ku and Ka bands,the mode converter of coaxial TM₀₁-circular waveguide TM₀₁ is designed,and the conversion efficiency at the center frequency can reach 99.69%and 99.59%,respectively.The influence of relevant dimension parameters on the conversion efficiency of the mode transformer is discussed.The antenna output structure of corresponding sizes is designed for the X and Ka bands,and the X and Ka nested output antennas are designed for the output of dual-frequency nested RBWO.