Electromagnetic Water Drop Model for Wet Antenna Attenuation Based on Near-Field Measurements

In order to better understand the wet antenna attenuation (WAA) effect in opportunistic rainfall estimation using commercial microwave links (CMLs), near-field measurements of a standard CML antenna under test (AUT) are performed under dry and wet conditions, and equivalent surface currents (ESCs) on the antenna radome are reconstructed. The far field of the wet AUT shows an overall reduced electric field magnitude around the boresight direction compared to the dry AUT. We deduce a simple and intuitive absorption-based electromagnetic drop model for corresponding local manipulations of the dry antenna ESC distribution at individual drops and show consistency of the modeled WAA with corresponding measurements. After validation, the model is applied to synthetic but realistic drop distributions as they accumulate during rain and dew. For both cases, justifiable WAA values are obtained, and a linear relation between WAA and the approximate radome area occupied by drops is demonstrated.