以弱色散特性的扇形金属-介质夹持杆螺旋线慢波结构的Ka波段行波管作为研究对象，进行了互作用特性仿真研究。采用螺距跳变和磁场跳变技术进一步提高了该行波管在工作频带的输出功率和电子效率，并解决了电子注散焦问题。设计结果表明：当工作电压为9 kV、工作电流为210 mA时，行波管在24~40 GHz整个频带内，各频点的增益在37.7~48.7 dB之间，电子效率在15.18%~19.42%之间，输出功率大于286 W。此结果较之均匀周期的设计结果，电子效率增幅在4.19%以上，输出功率增长率在4.3%以上，尤其在26~37 GHz范围内，电子效率增幅达到了11.8%以上，输出功率增长率达11.9%。

The interaction simulation of the fan-shaped metal-dielectric support rod helix traveling wave tube(TWT) is carried out. On the basis of simple uniform pitch design, the helix pitch step and magnetic field step are used to improve the output power and electronic efficiency of the TWT in the working frequency band, and the problem of electron beam defocusing is solved. The final design results show that, when the working voltage is 9 kV and the working current is 210 mA, the gain of the traveling wave tube in the whole frequency band of 24-40 GHz is between 37.7 dB and 48.7 dB, the electronic efficiency is between 15.18% and 19.42%, and the output power is greater than 286 W. Comparing with the results of the original design, the growth rate increases by more than 4.19% on the electron efficiency, the growth rate of output power is more than 4.3%, especially in the range of 26-37 GHz, the growth rate of electron efficiency increases by more than 11.8%, and the growth rate of output power goes up to 11.9%. The design results are helpful to design improved fan-shaped metal-dielectric support rod for high efficiency broadband millimeter wave helix TWT.