Study of complex mode converter for 3mm-wave complex cavity Gyrotron

A complex mode converter consisting of waveguide and quasi-optical mode converters is proposed to utilize high mode-transforming efficiency of the former and compact size of the latter. Radiation patterns of quasi-optical mode converter with TE_0n modes as its feeds are got by numerical calculation method based on the theory of vector diffraction integral. These patterns show that the radiation pattern is more similar to the wanted Gauss pattern when the feed takes the mode TE₀₁. So the conclusion is that the complex mode converter, transforming TE_0n mode to TE₀₁ mode by waveguide converter and then TE₀₁ mode to good Gauss pattern, is helpful to hold higher converting efficiency and smaller size than waveguide or quasi-optical one alone.