中文摘要：

在高次模回旋管中，模式竞争是亟待解决的问题．本文基于广义传输线理论，得到能准确描述缓变结构谐振腔模式耦合的一阶传输线方程组；通过分析耦合系数，优化得到了一种新型光滑渐变（缓变）谐振腔．与直线连接的（折变）谐振腔相比，该腔体有更强的模式抑制能力，腔中非工作模式归一化幅值可达-100dB，输出行波段非工作模式归一化幅值可达-88．6dB．

英文摘要：

The mode competition is the problem to be solved urgently m mgh-order moae gyrotron, tlasea on me generallzea meory o： transmission line, a group of first order transmission line equations that can accurately describe the coupling modes in a gradually- varying cavity is studied. Through analysing the expressions of the coupling coefficients between the various modes, a gradual-varying cavity for a gyrotron is designed. It is proved that the power in spurious modes in this novel cavity may be kept far below that in the line-joint cavity. The normalized amplitudes of non-operating modes can reach -100 dB in cavity and -88.6 dB in travelling wave guide.