Rain attenuation measurements at 6.75 GHz in Malaysia

Attenuation of radio frequency signal by clouds, snow and in particular, rains have to be considered at frequencies above 10 GHz. Indeed, below 10 GHz, rain may cause severe degradation at certain threshold frequencies especially when operating in tropical regions. At high rain rates, it causes significant absorption, scattering and depolarization. Therefore, data and prediction models are required for establishing any satellite-Earth communication links. The successful development of predicted models calls for the knowledge of propagation characteristics along the signal path. Such knowledge is acquired both from theoretical studies of relevant propagation phenomena and statistical analysis of long-term propagation data bases. In view of the importance of such data the University has started to do measurements to model the slant path attenuation and the rain structure. In this paper, results of a year of measurement of radiometer and rain gauges are presented. The measured sky noise temperatures are analyzed in both event and statistical terms. The values of the sky temperature are converted into attenuation using the radiometer equation with medium temperature of 290 K. The cumulative distribution of attenuation was calculated. The rain rate measurements are made using two tipping bucket rain gauges employing one-minute integration time. Investigation of several events shows that the rain rate is not uniform over a short distance (3 km) especially at high rain rates. Comparison of rain rates and attenuation with the International Radio Consultative Committee (CCIR) proposed model shows discrepancy especially at low percentages of time. More data are required to develop a new model.