Wave attenuation through rain with different rainfall rates at millimeter wave ( $f = 77$ GHz) and low-terahertz (Low-THz) ( $f = 300$ GHz) frequencies is studied in this article. Rain has pronounced impacts on electromagnetic wave propagation and one of the well-known effects is attenuation of the transmitted wave. Attenuation at both frequencies and hydrometeor properties [rainfall rate and drop size distribution (DSD)] are measured simultaneously. The measured DSD is fit with gamma and Weibull distributions and is also compared to the frequently used distribution Marshall and Palmer (MP) model; Weibull is shown to be a better fit to the measured DSDs. Theoretical prediction of attenuation as a function of rainfall rate (up to about 20 mm/h) is determined using Mie scattering theory, and the fit gamma and Weibull, and MP distribution models; as well as using the International Telecommunications Union Radiocommunication Sector (ITU-R) recommendation. The calculations are evaluated by comparing them to the experiment. The measured results at 77 GHz best agree with the ITU-R recommendation whereas at 300 GHz, the calculation based on Mie scattering and the Weibull distribution exhibits the best fit to the measured data. The measured data that exceed the theoretical prediction are analyzed and interpreted based on their corresponding observed drop size properties, for the first time.

中文翻译：

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毫米波和低太赫兹频率下的降雨衰减

本文研究了在毫米波 ($f = 77$ GHz) 和低太赫兹 (Low-THz) ($f = 300$ GHz) 频率下不同降雨率下的降雨波衰减。雨对电磁波传播有显着影响，众所周知的影响之一是传输波的衰减。同时测量频率和水凝物特性 [降雨率和液滴尺寸分布 (DSD)] 的衰减。测得的 DSD 与 gamma 和 Weibull 分布拟合，并与常用的分布 Marshall and Palmer (MP) 模型进行比较；Weibull 被证明更适合测量的 DSD。衰减作为降雨率（最高约 20 毫米/小时）的函数的理论预测是使用 Mie 散射理论、拟合 gamma 和 Weibull 以及 MP 分布模型确定的；以及使用国际电信联盟无线电通信部门 (ITU-R) 的建议。通过将它们与实验进行比较来评估计算。77 GHz 下的测量结果最符合 ITU-R 建议，而在 300 GHz 下，基于 Mie 散射和威布尔分布的计算显示出与测量数据的最佳拟合。超过理论预测的测量数据首次根据其相应的观察到的液滴尺寸特性进行分析和解释。基于米氏散射和威布尔分布的计算显示出与测量数据的最佳拟合。超过理论预测的测量数据首次根据其相应的观察到的液滴尺寸特性进行分析和解释。基于米氏散射和威布尔分布的计算显示出与测量数据的最佳拟合。超过理论预测的测量数据首次根据其相应的观察到的液滴尺寸特性进行分析和解释。