Excess Attenuation Caused by Antenna Wetting of Terrestrial Microwave Links at 32 GHz

Excess attenuation of microwave radio links caused by the wet antenna effect is addressed. Long-term measured attenuation of two commercial microwave links (816 m 611 m long) at 32 GHz is compared to theoretically predicted rain attenuation. The theoretical prediction is calculated using a kR
^α
relationship where k and α are constants derived from a local disdrometer measurement, and rain rate R is available from rain gauges placed at both ends of the links to obtain the distribution of rain rate along the path length. From this comparison, excess attenuation caused by antenna wetting is derived. A new model describing wet antenna attenuation (WAA) as a function of rain rate is suggested where excess attenuation reaches approx. 3 dB per antenna for a rain rate of 100 mm/h. Statistics of theoretically predicted rain attenuation, including the WAA term, is compared with statistics of measured attenuation on a set of three other links working at the same frequency. Adding the wet antenna term to the rain attenuation calculation significantly improves the accuracy of the rain attenuation prediction.