Statistical Behavior of Rain Attenuation*

Thirty-one sets of experimental data on the statistics of microwave rain attenuation at frequencies above 10 GHz, in the U.S.A., England, Japan, Italy, and Canada, indicate that: (i) the distribution of rain attenuation α, in dB, is approximately lognormal with a standard deviation σ α of log 10 α ranging from 0.46 to 0.71 for earth-space paths, and from 0.33 to 0.86 for terrestrial paths; (ii) the distribution of the rain fade duration τ is also approximately lognormal with a standard deviation σ τ of log 10 τ ranging from 0.44 to 0.76 for both earth-space paths and terrestrial paths. We propose a theory to explain this general behavior. A theoretical upper bound for the fade duration distribution in the tail region is also given. The findings in this paper simplify the determination of rain attenuation statistics needed for the design of earth-satellite radio links and terrestrial radio links.