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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), afive-channel design centered around the 22 GHz water vapor line. Fluctuationsin precipitable water vapor cause fluctuations in atmospheric brightnessemission, which are assumed to be proportional to phase fluctuations of theastronomical signal seen by an antenna. Water vapor radiometry consists ofusing a radiometer to measure variations in the atmospheric brightness emissionto correct for the phase fluctuations. The CWVR channel isolation requirementof < -20 dB is met, indicating < 1% power leakage between any two channels.Gain stability tests indicate that Channel 1 needs repair, and that thefluctuations in output counts for Channel 2 to 5 are negatively correlated tothe CWVR enclosure ambient temperature, with a change of ~ 405 counts per 1degree C change in temperature. With temperature correction, the single channeland channel difference gain stability is < 2 x 10^-4, and the observable gainstability is < 2.5 x 10^-4 over t = 2.5 - 10^3 sec, all of which meet therequirements. Overall, the test results indicate that the CWVR meetsspecifications for dynamic range, channel isolation, and gain stability to betested on an antenna. Future work consists of building more CWVRs and testingthe phase correlations on the VLA antennas to evaluate the use of WVR for notonly the VLA, but also the Next Generation Very Large Array (ngVLA).

A Study of the Compact Water Vapor Radiometer for Phase Calibration of the Karl G. Janksy Very Large Array