微扰实验法测试螺旋线行波管耦合阻抗及模拟仿真

 应用有限元仿真软件HFSS，建立了准确的3维螺旋线行波管耦合阻抗仿真模型。应用该模型，对微扰实验法在微扰杆内电场所做出的4个假设和近似，进行了定量的分析和讨论：电场在轴向是均匀的，忽略掉轴向高次空间谐波的存在；电场在角向是均匀的，忽略掉角向高次空间谐波的存在；忽略掉电场中TE波部分，认为电场角向分量为零；假设微扰前后的电场是相等的。同时，对微扰杆的尺寸和介电常数与耦合阻抗的依赖关系进行了模拟分析。结果表明：当微扰法所引入的假设和近似逐步消失后，微扰法的结果最后收敛于定义法。

Perturbation experiment method for helix traveling-wave tube interaction impedance measurement

The accurate three dimensional helix travling-wave tube cold-test simulation model is presented using the electromagnetic code HFSS. For electric field in the perturbation rod,four prominent approximations of perturbation method are analyzed with the simulation model. Firstly,the electric field is supposed uniform in the axial coordinate,neglecting the higher axial space harmonics. Secondly,the electric field is supposed uniform in the azimuthal coordinate,neglecting the higher azimuthal space harmonics. Thirdly,the azimuthal electric field is supposed zero,neglecting the transverse electric field. Finally,the electric field is supposed equal before perturbation and after. Also,the affection of the perturbation rod's dimension and relative permittivity on interaction impedance is simulated. It is shown that the results of perturbation method are converging on that of definition method when the perturbation rods dimension and relative permittivity becomes small slowly.