小型水汽辐射计用于卡尔G. Janksy甚大天线阵
A Study of the Compact Water Vapor Radiometer for Phase Calibration of the Karl G. Janksy Very Large Array
摘要：
我们报告的紧凑型水蒸气辐射计（CWVR）的NSF的卡尔G原型的实验室测试结果。Jansky甚大阵列（VLA），一个围绕22 GHz水蒸气线的五通道设计。可降水量的波动会导致大气亮度的波动，这被认为是成比例的相位波动的天文信号所看到的天线。水蒸气辐射测量包括使用辐射计来测量大气亮度发射的变化以校正相位波动。满足< -20 dB的CWVR通道隔离要求，表明任何两个通道之间的功率泄漏< 1%。增益稳定性测试表明，通道1需要维修，通道2至5的输出计数波动与CWVR外壳环境温度呈负相关，温度每变化1 ℃，计数变化约为405。经过温度校正后，单通道和通道差增益稳定度< 2 x 10^-4，在t = 2.5 - 10^3 s内可观测增益稳定度< 2.5 x 10^-4，均满足要求。总体而言，测试结果表明，CWVR满足动态范围，通道隔离和增益稳定性的规格，以在天线上测试。未来的工作包括建造更多的CWVR和测试VLA天线的相位相关性，以评估WVR不仅用于VLA，而且用于下一代超大型阵列（ngVLA）。
英文摘要：
We report on laboratory test results of the Compact Water Vapor Radiometer (CWVR) prototype for the NSF's Karl G. Jansky Very Large Array (VLA), a five-channel design centered around the 22 GHz water vapor line. Fluctuations in precipitable water vapor cause fluctuations in atmospheric brightness emission, which are assumed to be proportional to phase fluctuations of the astronomical signal seen by an antenna. Water vapor radiometry consists of using a radiometer to measure variations in the atmospheric brightness emission to correct for the phase fluctuations. The CWVR channel isolation requirement of < -20 dB is met, indicating < 1% power leakage between any two channels. Gain stability tests indicate that Channel 1 needs repair, and that the fluctuations in output counts for Channel 2 to 5 are negatively correlated to the CWVR enclosure ambient temperature, with a change of ~ 405 counts per 1 degree C change in temperature. With temperature correction, the single channel and channel difference gain stability is < 2 x 10^-4, and the observable gain stability is < 2.5 x 10^-4 over t = 2.5 - 10^3 sec, all of which meet the requirements. Overall, the test results indicate that the CWVR meets specifications for dynamic range, channel isolation, and gain stability to be tested on an antenna. Future work consists of building more CWVRs and testing the phase correlations on the VLA antennas to evaluate the use of WVR for not only the VLA, but also the Next Generation Very Large Array (ngVLA).
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