设计了一种适用于窄带高功率微波源系统的紧凑型TEM-TE11模式转换器。该结构首先将同轴波导沿角向分区使微波在各分区内相位传播常数不同，然后将相位传播常数较大的分区进行横向折叠设计以缩短系统轴向长度。分区传播的微波在模式转换器末端相位差达到180°时，合成同轴波导中TE11模式。为L波段磁绝缘振荡器设计了模式转换器，并采用数值仿真程序进行计算，在1.31 GHz中心频率上，模式转换器转换效率为95%；在1.23~1.40 GHz频率上，模式转换器效率大于90%，相对带宽13%。将模式转换器应用于磁绝缘振荡器，并测量了天线的定向辐射能力，所得结果与设计一致。

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.