We report on system noise temperature estimates from the SRT site in W-band (70-116 GHz) based on recorded atmospheric data at four specific days, three-months apart, in the period 15 Oct. 2019-15 July 2020. The estimates are based on the atmospheric model described in [1] and on the feed-horn beams model and receiver noise specification of the W-band multibeam receiver being built for the Gregorian focus of the SRT.
We used different values for the antenna forward efficiency ηf to estimate the impact of such parameter on overall system noise Tsys. The beam truncation due to the 1 m diameter SRT Gregorian focus radome, which protects the receiver cabin from the atmospheric agents, is evaluated assuming that the cabin surrounding the radome contributes with a 293 K thermal noise (greater than the sky noise). The beams from the W-band receiver will be slightly truncated by the radome, especially at the lowest frequencies, where the beams are larger. We conclude that the effects of truncation on Tsys are negligible even in the scenario of lowest thermal emission from the sky, expected during winter season.
The estimated seasonal variations of the atmospheric conditions at the SRT show that, for the four specific days for which the system noise temperature was calculated, the Tsys have broad minima near the 3 mm band atmospheric window, around 85-105 GHz and achieves values of order 100 K or lower during winter. The system noise increases towards the W-band receiver band edges at 70 GHz and 116 GHz; the highest Tsys is obtained at the highest frequency of the band, 116 GHz, and reaches values beyond 200 K the 15th of October, 2019 and the 15th of July, 2020
