为了提高回旋管的工作效率，高频结构中的模式之间的竞争是急需解决的问题。从模式耦合理论出发系统地研究了回旋管中过渡渐变复合腔的高频场结构，同时考虑了TM型寄生模式对工作模式的影响。通过对耦合系数的分析，为了降低模式之间的耦合程度，采用曲线作为回旋管中高频结构的渐变段。用三维电磁仿真软件和自主开发的程序对高频结构进行计算。计算结果与传统的线性渐变段谐振腔相比，采用非线性类型的谐振腔具有更强的模式抑制能力，并且该类型腔体中能够激励起更强的场幅值。

The mode competition is a problem that should be solved urgently in the high-frequency structure in order to improve the working efficiency of the gyrotron. The impact of the spurious TM modes were considered and the high frequency structure was systematically studied for a complex cavity gyrotron with gradual transition by the mode coupling theory. In order to reduce the degree of coupling between the modes, the coupling coefficient was analyzed and it made two types of curves as the transition section of the high-frequency structure in the gyrotron. 3D electromagnetic simulation software and self-developed program were used to calculate the high-frequency structure. Compared with the traditional linear gradual transition resonant cavity, the nonlinear resonant cavity has the enhanced capability of rejecting the non-working mode, and this type of cavity could excite a stronger field amplitude.