IMPROVEMENT OF THE Q FACTOR MEASUREMENT IN RF CAVITIES
IMPROVEMENT OF THE Q FACTOR MEASUREMENT IN RF CAVITIES
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射频腔中 Q 因子测量的改进
DOI：
10.2172/1061590
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发表时间：
2013
影响因子：
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通讯作者：
H. Hahn
中科院分区：
文献类型：
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作者：
Wencan Xu;S. Belomestnykh;I. Ben;H. Hahn
射频谐振腔中高阶模的Q值通常由网络分析仪在-3dB水平下测量的谐振带宽来计算。谐振曲线失真是由制造公差和RF端口引起的椭圆度引起的谐振分裂引起的。因此，测量的Q值通常低于模拟或理论Q值。在某些情况下，只有一个模式的Q值可以用-3 dB方法测量。这可能有两个原因。一个原因是一个模式被强激发，而相邻的分裂模式接近90 °偏振，因此被弱激发;另一个原因是一个模式的谐振曲线被另一个模式扭曲得太厉害，以至于无法测量-3 dB水平。在本文中，我们解决了这个问题，通过研究的RF测量设置，包括腔，输入耦合器和拾波耦合器，从等效电路和波的角度来看。使用HOM数据的铜原型的BNL 3腔，我们比较了测量和模拟的结果。
The Q values of Higher Order Modes (HOMs) in RF cavities are usually calculated from the resonance bandwidth measured at -3 dB level by a network analyzer. The resonant curve distortion is caused by the resonance split due to the ellipticity caused by manufacturing tolerances, and RF ports. Therefore, the measured Q values are usually lower than the simulated or theoretical Q values. In some cases, only one mode’s Q can be measured with the -3 dB method. There may be two reasons for this. One is that one mode is excited strongly, while the neighboring split-mode is close to 90o polarized and thus excited weakly; the other reason is that the resonant curve of one mode was distorted by the other mode too much to measure the -3 dB level. In this paper, we resolve this issue by looking into the RF measurement setup, including cavity, input coupler and pick-up coupler, from the equivalent circuit and wave point of view. Using HOM data for a copper prototype of the BNL3 cavity, we compare the results from measurements and simulations.