Propagation experiment at 140 GHz through simulated rainfall

Measurements of rainfall attenuation of a millimeter wave at 140 GHz were conducted through simulated rain using a large scale rainfall installation. By this installation, rainfalls with different drop-size distributions were realized without varying the rainfall rate. It was experimentally verified that the rainfall attenuation at the millimeter wave band is strongly affected by the raindrop size distribution. A method of inference of the raindrop size distribution from the simultaneous measurements of the attenuation and the rainfall rate was newly proposed. This method was applied to those experimental results. The inferred drop-size distribution showed fairly good agreement with those measured directly. The polarization dependence of attenuation and the depolarization were also measured. The effects of raindrop distortion from spherical shapes were found to be too small to be detected by the experimental system.