Modified rain attenuation model for tropical regions for Ku-Band signals

Attenuation measurement on Ku- band satellite signal in a tropical site, Fiji is presented. Rain-attenuation prediction by ITU-R and the Crane Global models showed noticeable deviation to the measured values. Unlike the monotonic decrease predicted by these models, exceedance of rain-rate and attenuation in Fiji and other tropical regions showed the presence of breakpoints. For Suva, the breakpoint in rain-rate and attenuation were at 58 mm/h and 9.4 dB with exceedances of 0.009 and 0.018%, respectively. Modifications to the ITU-R model are proposed in this paper, for adopting it in the tropics. These modifications are based on the properties that in the tropics (i) the accumulation time factor at the breakpoints is an invariant (ii) for elevation angles < 60 degrees and at high rain rates multiple rain cells intersect the slant path. The attenuation exceedance is predicted by two expressions similar to the ITU-R model, one for rain-rates lower than the breakpoint rain-rate and the other above it. The modified prediction model show remarkable agreement with the measured Ku-band attenuation in seven tropical sites. Copyright (c) 2006 John Wiley & Sons, Ltd.