Measurements of rain attenuation in 15 and 18 GHz converging links

Attenuation due to rain is a major impairment to the performance of radio links operating at frequencies above 10 GHz. Several methods, mostly based on experimental data generally obtained in temperate climate regions, have been developed to predict the cumulative distribution of rain attenuation in terrestrial links. These methods, including the one currently recommended by the ITU-R, usually show poor accuracy when applied to sites in tropical and equatorial regions. Also, for links with path lengths larger than 25 km, which can be affected by more than one rain cell during heavy rain events, the methods fail to predict the attenuation even in temperate regions. This paper presents the results of point rainfall rate and rain attenuation in six terrestrial line-of-sight microwave links with a common end at Sao Paulo, in the tropical region of Brazil.