## 1 Introduction  
Ground-based multichannel microwave radiometers (GMRs) can continuously observe atmospheric radiation brightness temperature (TB) in K- and V-bands, and provide valuable data on the temperature, water vapor, cloud liquid and humidity structures of the troposphere [1, 2, 3, 4]. The microwave radiometer is a typical remote sensing device and provides very useful data for the detection of mesoscale phenomena that require high spatial and temporal capabilities (e.g., nowcasting convective activity and heavy rain events, boundary layer meteorology, clouds and assimilating GMR data into the WRF precipitation model) [5, 6, 7]. In addition, [PERSON] et al. presented the theoretical research for the lightning TB response of a GMR [8], and [PERSON] et al. remotely sensed artificially triggered lightning events with a GMR to research the lightning heating radiation for the first time [9]. The GMR has become a popular and efficient instrument for remotely sensing the atmospheric temperature and humidity profiles. In order to obtain the fine detection atmospheric temperature and humidity profiles, GMRs have been operated in many countries for monitoring climate and meteorological phenomena in the last few decades [6]. At present, the megacities meteorological observation network of microwave radiometers is gradually being implemented in China, but they lack a unified monitor for their operational condition. In general, common practice monitoring antenna alignment, system gain and receiver stability rely on either target source or methods. For instance, we can measure the antenna pattern to determine the antenna alignment and gain in a microwave anechoic chamber. The performance of the radiometer can be assessed by comparison of the observed TBs against modeled values, and the radiative transfer model can be used to calculate the modeled values with the radiosonde sounding, and the liquid nitrogen is a good target source for calibration and assessing system stability. However, if frequent checks are required, then these methods have the drawback of greater complexity and higher costs for the observation network of microwave radiometers [6; 10]. Therefore, a simple, low-cost and automatic monitoring GMR system method is a necessary and important work. At present, solar microwave radiation observation has long been used to good advantage by radar operators as a convenient radiation source to check out radar system performance according to literature. For example, [PERSON] et al. detected the method with operational weather radars and the results showed that the solar radiation can be used for health automatic checks of a radar [11]. [PERSON] et al. made use of solar radiation to check the antenna alignment and the stability of the receiver system of a weather radar [12]. It is said that the azimuth, elevation and effective antenna system gain could be determined with 0.1\({}^{\circ}\), 0.2\({}^{\circ}\) and 1.3 dB [12]. This solar monitoring method has been implemented successfully to determine the antenna alignment, check system gain, monitor receiver stability and the differential reflectivity offset [13; 14]. Along these lines, we can see that the solar radiation method has revealed to be potentially useful for the GMR system assessment. In this paper, we attempted to apply the solar radiation method to monitor the health automatic checks of a ground-based microwave radiometer and evaluate the antenna performances; an experiment was also performed with the GMR installed at Xi'an field experimental site (N34.091\({}^{\circ}\), E108.89\({}^{\circ}\)), in China. Firstly, we introduce the theory and experiment that the solar microwave radiation was remotely sensed with the GMR. The solar radiation TB increment arriving at the antenna without atmospheric attenuation can be observed by the GMR. Secondly, this paper presents what we have done with the solar method to determine the GMR antenna pattern and to monitor antenna alignment of GMR networks operating in the field.