Compact L band TEM-TE₁₁ mode converter

A compact TEM-TE11 mode converter suitable for narrow band high power microwave system was developed. The coaxial waveguide is divided into several sectorial waveguides with different phase propagation constants, and the waveguides with relatively large phase propagation constants are transversely folded to shorten their axial lengths. When the microwaves in different sectorial waveguides have a phase shift of 180 degree at the end of the mode converter, they compose a coaxial TE11 mode. A mode converter is designed for L-band 1.31 GHz magnetically insulated transmission line oscillator (MILO) system. The conversion efficiency of TEM-TE11 mode at center frequency is 95%. In the frequency range of 1.23-1.40 GHz, the conversion efficiency exceeds 90%, with a corresponding bandwidth of 13%. The directional radiation performance of the mode converter connected to L band MILO tube is tested. The experimental result reveals that the mode converter works well.