Measurements of index of refraction and signal loss due to an ice fog medium at 97 GHz using a Fabry-Perot resonator

This paper describes the measurements of the complex dielectric constants of ice fogs using a Fabry-Perot cavity. The measurements were made at a frequency of 97 GHz over the temperature interval from-30\degC to-48\degC. The tests were conducted in an environmental chamber with the fog created by the introduction of a controlled amount of steam. For comparison purposes a helium-neon laser beam (6328 Å) was transmitted through the fog and its extinction coefficient measured. Fog particle number density measurements were made with a four stage cascade impactor. The complex index of refraction of the ice fog was determined from the change in resonant frequency and the amplitude response of the cavity when the fog was introduced. The results were normalized to one dB per meter attenuation of the laser beam intensity. On this basis the fogs studied in this experiment showed refractive index changes of 1 to 2 N units and extinction coefficients varying with temperature between3 \times 10^{-6}and5 times 10^{-7}cm^-1