Research Of Quasi-optical Mode Converter And Broad- Band Directional Coupler Of High Power Gyrotron

High-power microwave system has a broad application prospect in the world, and it is becoming a challenge to achieve the transmission and measurement of high power.Quasi-optical mode conversion is a key point for the power transmission of microwave and millimeter waves. Meanwhile, the broadband directional coupler can make up for the defects in the link of microwave experiment because of low precision measurement.Under the background of high power microwave source, especially gyrotron,this paper selects quasi-optical mode converter and broadband directional coupler of transportation and measuring system as the research direction respectively, and it is proved to be valuable both in theory and in practice.Quasi-optical mode converter:First, this paper expounds the spread of the waveguide mode in the radiator by using geometrical optics theory. The Denisov radiator is studied in this paper. The pattern synthesis method of the gaussian beam and the structural design principle are introduced in Denisov radiator. The rules between modes in the radiator are discussed by using the coupled wave theory. At last, a Denisov radiator working at 140 GHz is analyzed and designed, the power change of patterns and the radiation field distribution on the waveguide wall are respectively shown when only primary disturbance,secondary disturbance or their combination. The simulation gives that a good gaussian beam has been presented on the waveguide wall. At the same time, three kinds of Vlasov radiator with different structures are described. On the basis of vector diffraction theory, a Vlasov converter working at 170 GHz is designed by numerical simulation calculation, which output mode is02 TE, and the distribution of the radiation field on the parabolic mirror and observation mirror are both shown respectively.Calculation results indicate that a gaussian beam has been formed on the observation mirror perpendicular to the emergent wave.Broadband directional coupler:Based on the theory of small aperture coupling, a Ka-band01 10TE-TE? ?multiaperture array directional coupler was designed to measure the output power and monitor the spectrum for Gyro-TWT. The radius of circular waveguide and the distance between adjacent coupling apertures are determined according to the principle offorward superposition and backward offset.Some numerical calculation about the change of coupling degree and directivity with coupler’s size have been done. The analysis shows that increasing the number, reducing the thickness of coupling aperture and enlarging the radius of hole can improve the coupling degree, and that increasing the number also can raise directivity within a certain working frequency band. At the same time, the optimal parameters of 16-apertures directional coupler are given and simulated by the electromagnetic simulation software CST, the results of simulation agree with numerical calculation approximately. The coupling is-35dB±0.9dB and the directivity is over 20 dB within 6GHz bandwidth. At last, the experimental sample is made, and cold test shows that the cold test results meet the requirement of design.