Rain Attenuation of Millimeter Waves Investigated from Drop Size Distributions

Millimeter waves are expected to be among the main radio resources used in future 5G+ and 6G technologies. Rain attenuation is one of the most relevant propagation effects in these bands, compromising the maximum distance and/ or availability achievable at these frequencies. The scarcity of experimental measurements, especially above 40 GHz, can be mitigated by research based on detailed long-term meteorological data and physical models to predict rain attenuation. An investigation of this kind is presented in this paper, using a 14-year database of rain DSD gathered in Madrid, Spain, with a laser disdrometer and values of extinction cross-sections of drops with the normalized diameters of the disdrometer obtained with electromagnetic simulations for H and V polarization and a model for non-spherical raindrops. The results of the research are used to assess the predictions of the ITU-R model of specific attenuation versus rain rate, to analyze the impact of using this approach instead of the conventional use of that ITU-R model in the design of millimeter-wave links, and to validate, as far as possible, the procedures by the comparison with some available measurements from the same site.