Modeling Antenna Noise Temperature Due to Rain Clouds at Microwave and Millimeter-Wave Frequencies

Abstract—A characterization of the antenna noise temperature due to precipitating clouds at Ku band and above is described by deriving a closed-form solution of the scalar radiative transfer equation. Following the so called Eddington approximation, the analytical model is based on the truncated expansion of unpo-larized brightness temperature angular spectrum in terms of Legendre polynomials. The accuracy of the sky-noise Eddington model (SNEM) is evaluated by comparing it with an accurate numerical solution, taking into consideration a wide variability of medium optical parameters as well as a typical rain slab model. The effect of the antenna pattern for ground-based antennas is also quantified. Physically-based radiative cloud models, characterized by a vertically-inhomogeneous geometry, are also introduced. Hydrometeor optical parameters are calculated and modeled for a large set of beacon channel frequencies. Nimbostratus and cumulonimbus models are finally applied to SNEM for simu-lating slant-path attenuation and antenna noise temperatures for ground-based antennas. Results are compared with ITALSAT satellite receiver measurements and co-located radiometric data between 13.0 and 49.5 GHz for various rain events during 1998. Index Terms—Antenna noise temperature, clouds and rainfall, radio propagation, scattering, sky noise temperature. I