A compact and broadband circular TE01-mode oversized deformed waveguide bend for high-power transmission line is proposed in this article. In order to obtain a circular TE01 mode with high purity output, a deformed waveguide structure, entitled quad-polar waveguide, which can destroy the degeneration between the TE01 and TM11 modes and weak mode conversion inside waveguide bend is introduced. The characterization of quad-polar waveguide and its influence of deformation on the mode spectrum are analyzed. The mode coupling coefficients of quad-polar waveguide are theoretically deduced to investigate the mode conversion inside the waveguide bend. Based on the multimode coupling theory, a broadband oversized waveguide bend with propagation efficiency over 95% from 27.6 to 34.1 GHz is designed. A prototype is fabricated and measured. The average transmission efficiency is over 93% according to the S-parameter measurement. The TE01 mode with high purity output is demonstrated by the near-field test. The high-power performance is investigated by connecting it with a gyrotron traveling-wave tube (gyro-TWT), and the waveguide bend works stably under a maximum output power of 140 kW. In addition to high power and broadband, the proposed waveguide bend features compact, simple structure, and easy to machine.

中文翻译：

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紧凑型宽带 TE₀₁ 超大变形波导弯头的理论和实验研究

本文提出了一种用于大功率传输线的紧凑型宽带圆形 TE01 模式超大变形波导弯管。为了获得具有高纯度输出的圆形TE01模式，引入了一种名为四极波导的变形波导结构，该结构可以破坏TE01和TM11模式之间的退化和波导弯曲内的弱模式转换。分析了四极波导的特性及其变形对模式谱的影响。理论上推导了四极波导的模式耦合系数，以研究波导弯曲内的模式转换。基于多模耦合理论，设计了一种在27.6-34.1GHz范围内传播效率超过95%的宽带超大波导弯头。制造和测量原型。根据 S 参数测量，平均传输效率超过 93%。近场测试证明了TE01模式具有高纯度输出。通过将其与回旋行波管（gyro-TWT）连接来研究大功率性能，波导弯曲在最大输出功率为140 kW下稳定工作。除了高功率和宽带之外，所提出的波导弯曲还具有紧凑、结构简单、易于加工的特点。