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Methods are given for estimating attenuation caused by rain during the average year, worst year and worst month of a 20-year period and during the worst month of the average year of that period. Probability distributions of point rain rates are modified by temporal and spatial factors derived from long-term and short-term rainfall records to obtain probability distributions of line rates RL, over paths up to 60 km long. Attenuation A is calculated from A = Â¿RÂ¿L, where Â¿ and Â¿ are parameters dependent on polarisation and frequency. Estimated values are compared with experimental observations at frequencies near 11, 20, 36, 60 and 110 GHz.