Invariance of accumulation time factor of Ku-band signals in the tropics

Simultaneous measurements of Ku-band attenuation and rain-rate give A 0.01 and R0.01 as 9.7 dB and 54mm/hr respectively, Unlike the monotonous variation predicted by the ITU-R model, breakpoints were observed in both the rain-rate and Ku-band attenuation exceedances. Similar observations were reported from other stations in the tropics. The accumulation time factor measured at the breakpoints remained almost a constant in these stations. Using this it is predicted that for stations with high elevation angle receivers, at breakpoint rain-rates, one rain-cell intercepts the propagation path of the signal. It is estimated that, in the tropics, the diameter of a rain-cell is a??1.5km when the rain-rate begin to saturate.