WATER VAPOR ATTENUATION STUDIES FOR KA AND V BAND FREQUENCIES OVER A TROPICAL REGION

The recent communication satellite systems tend to employ higher frequency (18-60 GHz) bands to satisfy the growing capacity requirements. Such wide bandwidths are valuable in supporting applications such as high speed data transmission and video distribution. The attenuation of Satellite signals due to water vapor absorption is very essential for high frequency (>10GHz) satellite communication. Using the formulae referred in Recommendations ITU-R, P.676-5, predictions of specific attenuation and path attenuation due to water vapor absorption are calculated and presented and also compared with the water vapor attenuation estimated from Radiosonde data collected from the India Meteorological Department (IMD), for the first time over tropics. The important findings of the current study includes the observation of slant path attenuation value, which is high for frequencies like 20 GHz, 24 GHz, 26 GHz, 47 GHz and () low for frequencies 18 GHz, 16 GHz, 14 GHz, and 12 GHz etc. It is also observed that for low elevation angles the slant path attenuation is maximum and its value decreases with the increase of elevation angle. For the 1200 GMT similar results are obtained indicating that there is significant diurnal change in the observed attenuation.