## 5 Conclusions  
The microwave T\({}_{\rm B}\) observation experiment with the upgraded GMR was carried out at the Xi'an field experiment site, where we made an attempt to observe the sun with a GMR. The two solar eclipse events happened on 26 December 2019 and on 21 June 2020 and were observed at three frequencies (22.235, 25.0 and 30.0 GHz). We observed and studied the variation of the intensity of the solar radiation arising from the eccentricity of the earth's orbit with the GMR for the first time, and the results from the data analysis were herein presented.  
1. We provided a new method to observe and monitor the process of the solar eclipse with a GMR. This method develops and extends the application possibilities of the GMR. The observation results showed that the GMR can accurately respond to the variations of solar radiation, and we analyzed the variation features of solar radiation by combining the solar phase during two solar eclipses. During the solar eclipse, the effective radiation region of the sun was shadowed by the moon and the observed T\({}_{\rm B}\) increment were in good agreement with the percentage of the shadow of the solar eclipse. The two solar eclipses gave us the unique possibility to observe and study the varying features of solar radiation.
2. More importantly, we found that the GMR could respond to the variation of the solar radiation arising from the Earth-Sun distance. Therefore, a good experimental determination of the eccentricity of earth orbit by using GMR has been described and the estimated eccentricity of the earth's orbit is 0.0169, which is in relatively good agreement with the 0.0167 found in the literature.
3. In addition, we also estimated the average variation of the Earth-Sun distance and the intensity of the incident solar radiation with the GMR, and the results showed that the variations are 3.44% and 6.6% throughout the year, which supports previous theoretical and observational results.  
In future work, we will continue to observe the long-term variation of the solar microwave radiation with the GMR, so that a possible study regarding the features of solar activity and their effects on the earth's atmosphere can be carried out.  
Conceptualization, L.L., J.L. and Z.W.; methodology, L.L., J.L., Z.W. and Y.M.; software, L.L.; validation, L.L., Z.R.C. and J.Q.; formal analysis, L.L. and Y.M.; resources, L.Z. and R.C.; data curation, L.L.; writing--original draft preparation, L.L., Z.W. and Y.M.; writing--review and editing, L.L., Y.M. and Z.W.; project administration, Z.W. and J.L.; funding acquisition, Z.W. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China (NO. 41675028), the Natural Science Foundation of Shanxi Province, China (NO. 2020 JM-718), the Xi'an Science and Technology Project of Shanxi Province, China (NO. 20 SFSF0015).  
Data Availability Statement: The data presented in this study are available on request from the corresponding author.  
We are grateful to the Shanxi Provincial Atmospheric Sounding Technical Support Center and the Xi'an Meteorological Observation Center of Shaanxi Province, China, for the radiometer installation and for their support.  
The authors declare no conflict of interest.