Performance Comparison of TE31 to TE11 Mode Converters for an A6 Magnetron

An A6-type relativistic magnetron (RM) with a conventional diffraction output (DO) structure generates the TE31 mode that is unsuitable for antenna applications because of its poor central directivity and degraded beam focusing efficiency. To address this limitation, the TE31 mode must be converted into the fundamental TE11 mode that is known for its high directivity. In this study, we designed and comparatively analyzed three types of TE31 to TE11 mode converters using CST Microwave Studio: two converters employing a length difference method (one converter with a perpendicular and the other converter with a parallel waveguide arrangement) and one converter using a coupled slot structure. The simulation results demonstrated that the coupled slot-based converter achieved the highest conversion efficiency of 97 % and a wide bandwidth. Furthermore, among the two length difference designs, the parallel waveguide configuration exhibited a superior conversion efficiency of 90 % compared with 86 % for the perpendicular configuration.