Research Of High-order Quasi-optical Mode Converter

High-power microwaves have the advantages of short wavelength and strong penetration,and are widely used in electronic countermeasures and electromagnetic pulse weapons in national defense and military fields.The most important part of high-power microwave technology is the high-power microwave source.Currently,the electron cyclotron resonance heating(ECRH)used in the tokmak device that realizes nuclear fusion requires a cyclotron oscillator that outputs energy laterally.However,as the frequency and power requirements increase,the order of the working mode of the gyrotron is getting higher and higher,and it is a high-order rotating polarization mode.However,the high-order rotating polarization mode is not suitable for long-distance low-loss transmission,and because the gyrotron needs to output energy laterally,it needs to be converted into a Gaussian beam by a quasi-optical mode converter and then output laterally.The most important part of the quasi-optical mode converter is the radiator.At present,the design of the radiator in China basically adopts the coupled wave theory for calculation and optimization.However,with the increase of the order of the working mode,because the coupled wave theory calculates the regular radiator wall disturbance,the calculated high-order mode radiator is too long,which is not conducive to the design of other parts of the gyrotron.If the scalar diffraction theory is used to distribute the field on the inner wall of the radiator,a hybrid radiator with a shorter length can be obtained.Therefore,the focus of this paper is the new algorithm for solving the field distribution of the inner wall of the radiator based on scalar diffraction integral and fast Fourier transform.The main research contents of this paper are as follows:1.Analyze the propagation characteristics of the wave in the radiator by geometric optics;derive the scalar diffraction integral by studying the scalar diffraction theory;research and derive the Fourier transform and convolution theory,and obtain the discrete Fourier transform expression and sampling correlation Case.2.Two scalar quasi-optical algorithms are obtained through scalar diffraction integral and fast Fourier transform algorithm,cylindrical wave decomposition method and dipole source diffraction method,and the radiator with working frequency of118 GHz and working mode of TE22,6 is taken as an example Calculate the inner wall field distribution of the hybrid radiator by two methods,and compare it with the field distribution calculated by the coupled wave theory for verification.3.Since the low power test of the mode converter requires a quasi-optical mode exciter,a mode exciter with a working frequency of 94 GHz and a working mode of TE63 was designed to test the radiator designed and processed in the future.The TE63 was designed The purity of the model is 97.23%.