Research On Key Technologies Of High-power Microwave Waveguide Mode Converter

In recent years,the application of high-power microwave technology in national defense has become more and more extensive.It can be seen that this technology is becoming more and more important.It is also the research focus of various countries in the field of high-tech,and the focus of scientific and technological competitiveness between countries.The high power microwave transmission system plays an important role in the high power system,so the working efficiency of microwave transmission devices such as waveguide mode converter and transition has a great influence on the overall high power microwave system.The main object of this thesis is waveguide mode converter.In order to be suitable for different application scenarios,circular waveguide mode converters and elliptical waveguide mode converters are designed with different cross sections in this thesis.The main contents of this thesis are arranged as follows.1.Based on the coupled wave theory and the Maxwell equations in frequency domain,the coupled wave equation and the coupling coefficient of the circular waveguide with the curved axis and the constant radius are derived.Furthermore,the coupled wave equation and the coupling coefficient of the elliptic waveguide with the curved axis are derived by combining the Mathieu function.Then the relationship between coupling capacity and coupling coefficient is analyzed by the coupled wave equation.2.The idea of solving differential equations by Runge Kutta method is studied and this method is used to write a program to solve the coupled wave equation and coupling coefficient.The optimization idea of simulated annealing algorithm is studied,and the control parameters of axis structure curve is optimized.Finally,the relative power conversion process of each mode is obtained.The numerical calculation results show that the conversion efficiency of TE₀₁-TE₁₁ circular waveguide mode converter with a radius of 26mm in X-band is 99.33%at the center frequency of 10GHz,and the length is855.98mm.After CST simulation calculation,the conversion efficiency at the center frequency is 99.1%.TE₀₁-TE₁₁ circular waveguide mode converter with radius of2.388mm in G-band has a conversion efficiency of 99.05%at the center frequency of220GHz and a length of 147.64mm.After CST simulation calculation,the conversion efficiency at the center frequency is 98.5%.3.The main coupling modes TE₀₁ mode and TE₁₁^o mode in elliptic waveguide are determined by studying the Mathieu function.The appropriate eccentricity is selected according to the coupling coefficient between the modes under different eccentricity,so that the size of the cross section is determined that 14mm for the long semi-axis and9.998mm for the short semi-axis.Then the simulated annealing algorithm is written to optimize the coupling structure combining sine and cosine functions.Finally,the conversion efficiency of the mode is calculated by writing a program.The numerical calculation results show that the Ka-band conversion efficiency of TE₀₁-TE₁₁^o elliptic waveguide mode converter is 99.13%and the length is 219.58mm at the center frequency of 32GHz.After CST simulation calculation,the conversion efficiency at the center frequency is 98.1%.