甚长基线干涉测量数字基带转换器子通道时延影响分析

Impact Analysis of the Sub-channel Delay in Very Long Baseline Interferometry Digital Baseband Converter

为提高甚长基线干涉测量(VLBI)带宽综合处理精度,在接收系统各通道时延一致的情况下,对数字基带转换器(DBBC)子通道时延对带宽综合精度的影响进行了分析。通过理论推导,首次发现在单站群时延测量中,子通道时延会使不同子通道之间产生"相位阶梯",引入带宽综合处理误差;在双站时延差测量中,当两个观测站相应子通道本振频率差不相同时,也会出现"相位阶梯",降低带宽综合处理精度。针对不同数字基带转换器结构,讨论子通道时延的影响域,提出通过子通道时延补偿消除"相位阶梯"。仿真结果表明,子通道时延补偿可以有效消除"相位阶梯",使带宽综合处理精度至少提高一个量级以上。

The effect of Digital BaseBand Converter （DBBC） sub-channel delay on bandwidth synthesis precision is analyzed under the condition of the consistent receiving system channel delay in order to improve the accuracy of bandwidth synthesis. Through a theoretical derivation, it is for the first time to discover that the sub-channel delay could induce“phase step”phenomenon among the different sub-channels in the group delay measurement of a single station. And in the delay difference measurement of different stations, the“phase step”phenomenon could occur when the frequency differences of different stations’ corresponding sub-channel Local Oscillator （LO） are different. The “phase step” could deteriorate the precision of bandwidth synthesis. The impact domain of the sub-channel delay is discussed for different DBBCs, suggesting that the “phase step” can be eliminated by a sub-channel delay compensation. The simulation results show that the sub-channel delay compensation can effectively remove the“phase step”and the precision of bandwidth synthesis can be improved by at least one order of magnitude or more.