Ground-based Multichannel Microwave Radiometer Antenna Pattern Measurement using Solar Observations
Abstract. Ground-based multichannel microwave radiometers (MWRs) can provide continuous temperature and humidity profiles of the troposphere. MWR antenna pattern measurements are important for reliable and accurate antenna temperature measurement and are usually carried out in a microwave anechoic chamber. Measurement using an anechoic chamber is complex and expensive because the conventional measurement procedure requires a special situation and professional instruments. More importantly, the construction of the anechoic chamber and the installation method of the absorbing material can directly influence the performance of the anechoic chamber and the result of the antenna measurement. This paper proposes a new method of MWR antenna measurement by observing the sun, and this method can be used to measure other radar antenna patterns. During the measurement, the MWR observes the microwave radiation brightness temperature (TB) to measure the antenna pattern by high-resolution raster scanning of the azimuth and elevation of the sun under a clear sky in Xi'an, China. Analysis of the TB scanning data of the sun at four frequencies, 22.235, 26.235, 30.000 and 51.250 GHz, showed that the microwave radiation TB of the sun is strong enough to be observed by the MWR. Furthermore, the antenna pattern was illustrated and analyzed based on these data, which fully proves that the sun can be used to measure the antenna pattern. Finally, the antenna pattern derived from the solar observation was compared with the result of the far-field measurement with a point source in the microwave anechoic chamber at 30 GHz, the maximum error of the beamwidth is less than 0.1°, which showed that this pattern matched well to the pattern measurement using a point source in the microwave anechoic chamber. Therefore, the antenna pattern of the MWR can be measured by scanning the sun without a point source in the microwave anechoic chamber, and this method can be used for convenient MWR antenna measurements and can reduce the measurement complexity and cost.
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