Low-THz Transmission Through Water-Containing Contaminants on Antenna Radome

In this paper, signal reduction due to the presence of water content formed on a radome has been studied at low-THz frequencies. The effect of obscurants on signal reduction has been characterized by measuring the ratio of reflected signals from a reference target through the radome, with contaminant and without contaminant. All the measurements have been compared to theoretical models, demonstrating a reasonable agreement. Water is the most common obscurant in outdoor applications and the main cause of performance deterioration in rainy, snowy, and foggy weather. This paper concentrates on the attenuation caused by different forms of distribution of water as a radome contaminant. Both a thin uniform layer of water and randomly distributed water droplets are studied at 150 and 300 GHz. The results show strong signal reduction due to the presence of uniform thickness of water and higher signal reduction with increasing frequency. However, the measured transmissivity through distributed water droplets, which occur in practice due to the surface tension of water, shows lower transmission loss at the shorter wavelength, due to transmission through the distribution of gaps between droplets.