The influence of load mismatch on resonant frequency, gap impedance and external Q factor of klystron output circuit has been studied by using microwave equivalent circuit and 3D electromagnetic software. And the influence of load mismatch on the efficiency of klystron was calculated by 1D large signal klystron code. The calculation results of C band klystron indicate that for single-gap output cavity, the change of resonant frequency caused by load mismatch is smaller and the changes of gap impedance and equivalent external Q factor are bigger. When the voltage standing wave ratio(VSWR) of load is 1.5, the resonant frequency changes about 35 MHz, the real part of gap impedance varies from 3 660 Ω to 7 998 Ω, the external Q factor varies from 36.9 to 93.5, and the efficiency at central frequency decreases about 4.6％. For filter-load output circuit, the mismatch of load will lead to larger variation of impedance-frequency characteristics and efficiency-frequency characteristics. When the load VSWR is 1.5, the efficiency at central frequency decreases 11.2％. When the load VSWR is smaller than 1.2, the mismatch of load has a small effect on the performance of klystron.%采用微波等效电路和3维电磁场计算软件研究了负载不匹配对大功率速调管输出腔的谐振频率、间隙阻抗和外观品质因数的影响.并采用1维大信号计算软件研究了负载不匹配对速调管效率的影响.对C波段速调管的研究表明:对于单间隙输出腔,负载不匹配对谐振频率影响较小,对间隙阻抗和等效外观品质因子影响较大,当负载驻波比为1.5时,谐振腔的谐振频率变化约35 MHz,间隙阻抗实部最大值变化为3660～7 998 Ω,等效外观品质因子变化为36.9～93.5,中心频率处的效率下降4.6%.对于滤波器加载输出电路,负载不匹配对阻抗-频率特性和效率-频率特性有较大影响,当负载驻波比为1.5时,中心频率处的效率下降11.2%.当负载驻波比小于1.2时,负载失配对速调管性能的影响较小.
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