研究了双共焦波导回旋行波管高频结构的电磁特性。根据惠根斯原理的光衍射理论，分析得出双共焦波导中的两类本征模式（叠加模和环形模）对应的截止频率和场分布情况。理论分析结果与商用仿真软件CST的仿真结果一致。其中用作回旋行波管工作模式的“反相叠加TE₀₆模”的损耗明显小于其他模式，这种不同模式损耗不同的特性将有效抑制竞争模式带来的寄生振荡。双共焦波导的模式密度略大于传统单共焦波导的模式密度，但是明显小于圆波导的模式密度，因此双共焦波导适合用作回旋行波管的高频结构。

The electromagnetic characteristics of the double confocal waveguide for a gyro-TWT is investigated in details. The eigenvalue and the field distribution of two kinds of steady-state modes in a double confocal waveguide， namely the superposition mode and the ring mode， are calculated with the scalar formulation of Huygens’ Principle， the theoretical results agree well with those from the commercial CST software. When the anti-phase superposition mode TE₀₆ mode is chosen as an operating mode in a gyro-TWT， the diffractive loss of the potential parasitic modes is far greater than that of the operating mode. It means that the potential parasitic modes can be suppressed by means of its own diffractive loss in a double confocal waveguide. The mode density in a double confocal waveguide is higher than that in a single confocal waveguide， but far lower than that in a cylindrical waveguide. Compared to the single confocal waveguide， a higher beam-wave interaction efficiency can be obtained in the double confocal waveguide for a gyro-TWT， it is an appropriate choice to choose a double confocal waveguide as the beam-wave interaction structure in a gyro-TWT.