Research On Millimeter Wave Gyrotron Quasi-optical Mode Converter

In this paper,through the theoretical analysis,electromagnetic simulation and cold measurement experiments,the quasi-optical mode converter of millimeter-wave gyrotron used for millimeter-wave imaging is studied,and the step-cut Vlasov quasi-optical mode converter and Cassegrain antenna system are designed.The article starts from the general,introduces the development status of millimeter wave imaging and gyrotron at home and abroad,and the development experience of quasi-optical mode converter.Based on the theory,based on the geometric optics theory and the vector diffraction theory,the types of radiators and the selection of cutouts,as well as the selection of the type of reflecting mirror of the mirror system,the determination of the mirror equations and parameters,and the local and global coordinates are explained.Transformation relationship.In addition,the theory of Cassegrain's double mirror is also explained in detail.Through theoretical analysis,a Vlasov quasi-optical mode converter with an operating frequency of 220 GHz,a feed waveguide radius of 5 mm,and a mode of is designed.Without the Cassegrain double mirror,the system was modeled and simulated in FEKO,and a simulation result was obtained with a scalar Gaussian content of 97%,a horizontal radiation angle of less than 5,and a horizontal gain of 30 dBi.The simulation results after loading the Cassegrain double mirror show that the parallel light output can be achieved but the sidelobe gain also reaches 20 dBi,which has a certain impact on the system.Finally,through the construction of the experimental platform,the power distribution measured by the power meter loaded on the electric displacement platform was used to verify the availability of the stepped-cut Vlasov quasi-optical mode converter designed in this paper,The experiment of the mirror is still not ideal,which is also a difficult problem to be solved urgently in the future work.