Millimetre-wave rain induced attenuation: theory and experiment

The paper presents a short review of the theoretical solution for the problem of the interaction between electromagnetic radiation and rain in the frequency range 10¿¿100 GHz together with some experimental results. The raindrop shapes are assumed to be spherical. This approximation is considered valid for the small diameter raindrops which are the most important at millimetre wavelengths. Particular attention is devoted to the effect of the raindrop-size distribution on rain induced attenuation, and a comparison is made between the theoretical prediction for attenuation and phase dispersion using the Laws and Parsons and the log-normal raindrop-size distributions. Rain-induced attenuation measurements were made simultaneously at 36 GHz and 55 GHz on a common 4.1 km link and are presented for isolated rainfall events as well as in a statistical form for two separate periods of 12 and 17 months. The measurements are compared with the Laws and Parsons and the log-normal raindrop-size distribution predictions. Comparison is also made with attenuation measurements made on the same path at 36 GHz and 110 GHz.