实现200 km以上ALMA基线的新的时钟和定时方法
A novel clock and timing approach for achieving 200+ km ALMA baselines
摘要：
射电望远镜阵列是干涉仪，因此需要对来自被观测天文源的信号进行相干捕获和处理。在ALMA中，这是通过在每个天线处使用时钟进行下变频和数字化来实现的，该时钟通过往返相位校正技术从中央位置发送到那里，使用专门的模拟光子设备和方法。这是具有挑战性的，但在接近1 THz的ALMA频率和超过15 km的热稳定和机械稳定的埋地光纤下工作良好。对于未来的ALMA升级，这可能涉及更长的基线，因此光纤到达，这种方法可能不可行。本文深入研究了一种替代的和新的方法，“非相干时钟”（IC），其中每个ALMA天线使用自己的自由运行的本地振荡器执行操作（下变频和数字化），其随时间变化的频率测量使用所有数字方法相对于一个共同的时钟域，随后的数字化数据进行相应的校正，然后再进一步的互相关和波束形成处理。该方法旨在允许使用空中光纤和COTS数字光纤收发器将ALMA基线增加到200 km或更长。
英文摘要：
Radio telescope arrays are interferometers and thus require coherent capture and processing of the signal from the astronomical source being observed. In ALMA this is accomplished by using a clock at each antenna for down-conversion and digitization, sent there from a central location via a round-trip phase-corrected technique, using specialized analogue photonic equipment and methods. This is challenging but works well at ALMA frequencies approaching 1 THz and over ~15 km of thermally and mechanically stabilized buried fiber. For future ALMA upgrades, which may involve much longer baselines and therefore fiber reaches, such an approach may not be feasible. This paper delves into an alternative and novel method of "incoherent clocking" (IC) wherein each ALMA antenna performs operations (down-conversion and digitization) using its own free-running local oscillator, its temporally-varying frequency is measured using all digital methods relative to a common clock domain, and subsequently the digitized data is corrected accordingly before further cross-correlation and beamforming processing. This method purports to allow for increasing ALMA baselines to 200 km or more using aerial fiber and COTS digital fiber optic transceivers.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
