This letter presents an analysis of wet antenna attenuation (WAA) from an electrodynamic perspective. The WAA is a relevant part of the path attenuation determined from the received signal level (RSL). In the case of extracting rain rates from path attenuation, as it is done with data from country-wide commercial microwave link (CML) networks, the WAA is a significant error source and leads to overestimation of rainfall. To handle this effect, a model, based on the three antenna parameters, reflectivity, efficiency, and directivity, is developed. The model allows the variation of those three parameters depending on the degree of wetness and shows that WAA is composed of variations of antenna impedance, antenna efficiency, and antenna directivity. The suitability of the theoretical model was assessed by a full-wave numerical simulation of a pyramidal horn antenna at 18 GHz with homogeneous water film on the surface of the antenna cover. The result of this simulation is a quantification of these three subeffects. For verification of the simulation, an antenna, similar to the antenna in the simulation, was manufactured and a controlled sprinkler device to generate a water film was built. The adjustable water flow rate determines the thickness of the water film. The parameters were generated by measuring the near field and the reflectivity of the antenna in an anechoic chamber, with a near-field scanning system and a vector network analyzer, under different flow rates equaling different water film thicknesses. From these results, the reflectivity, directivity, and efficiency were computed and compared with the results of the full-wave simulation. It is found that the reflectivity is linked to water film thickness in a such way that the WAA can be deduced from monitoring the antenna reflectivity.

中文翻译：

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用于微波链路降水估计的湿天线衰减建模

这封信从电动力学的角度对湿天线衰减 (WAA) 进行了分析。WAA 是根据接收信号电平 (RSL) 确定的路径衰减的相关部分。在从路径衰减中提取降雨率的情况下，正如使用来自全国商业微波链路 (CML) 网络的数据所做的那样，WAA 是一个重要的误差源并导致降雨量的高估。为了处理这种影响，开发了一个基于三个天线参数（反射率、效率和方向性）的模型。该模型允许这三个参数根据潮湿程度发生变化，并表明 WAA 由天线阻抗、天线效率和天线方向性的变化组成。理论模型的适用性是通过在 18 GHz 的锥形喇叭天线的全波数值模拟来评估的，天线罩表面具有均匀的水膜。该模拟的结果是对这三个子效应的量化。为了验证模拟，制造了与模拟中的天线类似的天线，并构建了可产生水膜的受控喷水装置。可调节的水流量决定了水膜的厚度。这些参数是通过测量天线在消声室中的近场和反射率产生的，使用近场扫描系统和矢量网络分析仪，在不同的流速下，等于不同的水膜厚度。根据这些结果，反射率、方向性、计算和效率，并与全波模拟的结果进行比较。发现反射率与水膜厚度相关，WAA 可以通过监测天线反射率推导出来。