The overmoded circular waveguide can achieved high power capacity,which will inevitably lead to high order mode.In order to monitor the output power and frequency spectrum of the X-band long pulse high power microwave source,an X-band high power microwave broadband mode selection directional coupler was designed by the simulation of CST software, which is used to couple TM01 mode and suppress the TM02 and TE11 mode.The sizes of waveguide and coupling hole were decided by the small coupling theory and phase superposition principle.At the central frequency range of 9.0-9.8 GHz,the simulation re-sults show that the coupling degree of the coupler is about (-59.08±1)dB,the directivity of TM01 mode is more than 30 dB, the suppression of TE11 mode is more than 15 dB,and the suppression of TM02 mode is more than 30 dB,the power handling capacity is 2.5 GW.%过模圆波导在提高功率容量的同时,不可避免地会造成微波源中同时存在多种模式.为了监测X波段长脉冲高功率微波源TM01模的输出功率和频谱,采用CST软件仿真设计了X波段高功率宽带选模定向耦合器,在耦合TM01模的同时可实现对TM02和TE11模的抑制.波导腔体及耦合孔的尺寸以小孔耦合理论和相位叠加原理为基础并结合切比雪夫分布函数计算确定.仿真结果表明:该高功率宽带选模定向耦合器在9.0～9.8 GHz的带宽范围内,耦合度为(-59.08±1)dB,定向性大于30 dB,对TE11模的抑制度大于15 dB,对TM02模的抑制度大于30 dB,功率容量大于2.5 GW.
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