High power microwave(HPM) sources usually employ overmoded output waveguide to obtain higher power capacity. In designing feeder of beam waveguide and reflect antenna, THE mode needs to be convert to HEH mode to radiate a qua-si-Gaussian beam with quite low side lobe. RF breakdown will occur in corrugate gap when traditional corrugated THE-Hen mode converter is used in HPM field. In order to solve this problem, a method to design over-moded smooth-wall THE-HEH converter was investigated. Using an iterative synthesis method based on coupled-mode theory, a 9. 4 GHz, Φ70 mm over-moded smooth-wall Ten-Hen converter was designed, and contrast to electro-magnetic simulation result, the scalar Gauss ratio of the output beam is higher than 99. 5% from 9. 1 GHz to 9. 7 GHz, the power capacity is as high as 4. 9 GW.%采用半径微扰的光滑壁圆波导产生HE11模,避免了常规微波领域中采用的波纹渐变转换器在高功率微波领域应用时易发生齿间打火的不足.采用基于模式耦合理论的迭代综合方法优化了不规则的半径渐变轮廓,使输出产生组成HE11模的混合模式.并通过全电磁波仿真软件进行了对比,输出波束标量高斯含量在9.1～9.7 GHz范围内均高于99.5％,功率容量4.9 GW.
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