Microwave instrument for simultaneous wet antenna attenuation and precipitation measurement

Attenuation data from microwave links can be used to derive important near-ground precipitation estimates which complements observations from rain gauges and weather radars. Wetness on the cover of the microwave link antennas can, however, lead to additional attenuation, resulting in an overestimation of rainfall rates. To investigate the impact of this wet antenna attenuation (WAA) effect, a versatile microwave field experiment was built. It is based on a two-port vector network analyzer and equipped with six dual-polarized commercial microwave link antennas at different frequencies between 18 and 40 GHz. To a measurement frequency range of 150 MHz, range gating enables simultaneous measurement of antenna reflection coefficient and total path attenuation. An optical camera is integrated for visual inspection of the antenna covers. Appropriate housing and active temperature control makes the device weather-proof and enables all-season operation. Several supplementary meteorological instruments at the installation site provide information about the actual weather conditions. They can be used as the ground truth for evaluation. The presented instrument is a unique setup to study the WAA effect, by simultaneously providing measurements of the total path attenuation together with reliable WAA estimations, directly derived from measurements of the antenna reflection coefficient. Its data will give insights into WAA magnitude and temporal evolution in relation to meteorological variables. This will help developing improved WAA estimation algorithms, which will result in improved rainfall estimation from microwave links.