Characterization of Rain Attenuation for Millimeter Wavelengths for Realistic Nonrotational Symmetric Drop Shapes

ABSTRACT The use of frequencies above 30 GHz (millimeter waves) for communication purposes is nowadays a necessity, both for terrestrial (e.g., 5G/6G) and satellite links. One reason is the need for more bandwidth and the fact that “traditional” frequency bands are already fully occupied. Furthermore, the realizable antenna gain, as well as the potentially smaller antenna sizes that come with higher frequencies, is certainly advantageous for a variety of applications. The challenges of using millimeter waves mainly arise because of tropospheric propagation effects. Precipitation leads to considerable signal impairments that in general increase with frequency. The prediction of rain attenuation is one of the fundamental aspects to consider when planning both satellite and terrestrial communication links. Even more so for frequencies greater than 30 GHz, where the wavelength is less than 1 cm and thus just in the range of the diameter of raindrops. When determining the scattering and attenuation of microwaves due to rain, so far, rotationally symmetric raindrops are considered. In turbulent weather situations, however, a significant number of drops exhibit no rotational symmetry. The reason can, e.g., be found in the collision of drops that can lead to asymmetric modes of drop oscillation. In this study, therefore, raindrops are modelled as realistic as possible using drop shape information from a specialized video disdrometer (2DVD) that provides shape information for both the front and the side of every detected precipitation particle. For this purpose, the drop‐size distributions during severe rain events were analyzed and the individual drop shapes were fully reconstructed in 3D. By calculating the scattering parameters of a great number of individual drops with the use of a commercial electromagnetic solver, the effect of nonrotational symmetric drop on rain attenuation at millimeter wavelengths is characterized.