Frequency-Dependent Variations of the Antenna Reflection Coefficient Due to Different Wetness Conditions on the Antenna Radome

Abstract. It is investigated how the antenna reflection coefficient (ARC) of directional radio link antennas changes over time when the antenna radome gets wet and dries off afterwards. A hand sprayer is used to deposit droplets on antenna radomes manually. Next, ARC measurements are performed repeatedly using a vector network analyzer and the ARC variation over time and frequency during the drying process is recorded into consecutive frequency response data sets. These vividly demonstrate a continuous drift from the altered, i.e., wet state back to the initial dry state. Previous work has shown that the ARC is a very useful reference for determining the wet antenna attenuation (WAA) that occurs during and also after rain events. It did, however, not explain the observed significant differences in the relation between ARC and WAA with different antennas and at individual frequencies. Inverse Fourier transforms of the recorded frequency domain ARC show a clustered concentration of variations within the unambiguous range in the near vicinity of the antenna. This supports the assumption that the changes in ARC are exclusively caused by moisture on the radome. Our findings match with measurements from previous investigations, reaffirm the expedient value of ARC to support WAA estimates, and explain why different antennas exhibit very different ARC-WAA relations.