基于mTCA平台的射频前端板性能测试与研究

Performance measurement and study of front-end board based on mTCA

上海软X射线自由电子激光装置中C波段直线加速器的工作频率为5712 MHz。在低电平系统中,C波段的射频信号需要在射频前端板上与5686.556 MHz的本振信号进行混频后下变频为26.444 MHz的中频信号,之后由时钟频率为105.778 MHz的采样信号进行采样。针对C波段低电平的整体性能的物理设计需求,设计了基于mTCA平台的DWC8VM1板卡作为低电平控制系统的射频前端板。对射频前端板的输入端回波损耗,射频输入端口间隔离度、输入输出线性度、信号噪声、幅相稳定性、上变频通道的附加相位噪声等参数进行了实验测试,测试结果表明,端口的输入损耗大于8.63 dB,端口之间的隔离度大于63 dB,幅度和相为稳定度可达±0.04%和±0.05°,上变频通道附加相位噪声小于2 fs。该设计的射频前端板性能能很好地满足SXFEL理论设计中低电平控制系统的要求,达到国际同类装置的先进水平。

The C-band linear accelerator of Shanghai soft X-ray free electron laser facility(SXFEL)operates at 5712 MHz.In the low level radio frequency(LLRF)system,C-band microwave signals are mixed with the 5686.556 MHz local oscillator(LO)signal on the RF front-end board and down converted to 26.444 MHz intermediate frequency(IF)signal,and then sampled by 105.778 MHz clock signal.According to the physical design requirements of SXFEL,DWC8 VM1 board based on mTCA platform is selected as the RF front-end board of LLRF system.In this paper,the parameters of the RF front-end such as isolation between RF input ports,input and output linearity,amplitude and phase stability and Additional phase noise of up conversion channel were experimentally tested.The experimental results show that input return loss is more than 8.63 dB,channel-to-channel crosstalk is more 63 dB and the additional phase jitter integral of up conversion channel is 2 fs.The performance of this RF front-end(DWC8 VM1)can meet the theoretical requirement of the SXFEL.