| Summary: | A study on rainfall attenuation at 11 and 36GHz and on prediction of rain-attenuation statistics at 11, 20 and 36 GHz from point rainfall measurements is presented. Emphasis is given on the effects of raindrop size distribution and the application of a "synthetic storm" model, respectively. A "generalised gamma" distribution introduced by Deirmendjian is used for evaluating the ratio of 36.5GHz to 11 GHz attenuation, as a function of the variance of the distribution and some of the theoretical values are compared with those predicted by known drop-size distributions. Attenuation measurements simultaneously recorded at 11 and 36.SGHz (Bradford link) are compared with Laws and Parsons' drop-size distribution and are included between theoretical boundaries obtained from "generalised gamma" distribution. It is shown from this dual frequency experiment that Laws and Parsons' distribution represents on average the rain at moderate attenuations whereas at low attenuation values the actual rain consists of drops smaller than those accounted for by Laws and Parsons. Six months' statistics of rain-attenuation at 11 and 36.5GHz demonstrate that the expected traction of raining time that attenuation exceeds a specified value follow a log-normal distribution. Attenuation statistics measured from the 13.6km Bradford link at 11 and 36.5GHz are found to be in good agreement with statistics predicted from a technique based on a "synthetic storm" model. Attenuation predictions for a number of in-line partially overlapping links in East Anglia indicate the application of this technique in storms of arbitrary orientation and in short and intermediate path lengths. For relatively short links, good estimates of attenuation/time profiles, for individual events, are obtained whereas improved event correlations can be seen on longer links in case of storms moving almost parallel to the link. It is also shown that the use of individual storm velocities is not more advantageous (in terms of prediction accuracy) than the use of an average storm velocity.
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