Rain attenuation using Ka and Ku band frequency beacons at Delhi Earth Station

Abstract

Quantitative analysis and prediction of radio signal attenuation is necessary in order to improve the reliability of satellite-earth communication links and for economically efficient design. The Ka band suffers large attenuation due to rain and as most of the parts of India are situated in the tropical region, the impact of rain on Ka band propagation is severe. None of the existing ITU-R models is validated for prediction of rain attenuation over India and only a few over the tropical region and hence, it calls for a propagation experiment to validate the existing models. In this paper, study on the effect of rain attenuation on the propagation of satellite signals in Ka band has been carried out by receiving signal of frequency 20.199 GHz from the IPSTAR (Thaicom-4 Satellite) and a Ku band beacon signal of frequency 11.698 GHz from GSAT-8 satellite at Delhi Earth Station of ISRO. It has been observed that the difference between the ITU-R predicted rain attenuations and the observed rain attenuations for Ka band varies from 1.5 to 4.5 dB and that for Ku band from 2.1 to 3.7 dB. The long-term probability distribution of fade slope for any definite base value of attenuation is symmetric on both positive and negative sides and this feature is independent of frequency. This observation corroborates earlier findings.