Rapid and accurate interferometric measurements of the complex permittivity of medium loss liquids at millimeter and centimeter wavelengths

Dielectric relaxation has proved itself a useful tool for studying molecular motions or very fast chemical kinetics in the liquid phase.1 For a large number of experiments it is essential to carefully investigate the frequency region 3–300 GHz where radio techniques merge with optical techniques. The aim of our paper is to show that a broad band Michelson interferometer, featuring oversized rectangular waveguide (RG49/U) is suitable for rapid but accurate complex permittivity measurements over the whole 15–300 GHz frequency range. Some complementary data can be obtained in the X-band (7–12 GHz) from a similar but standard waveguide (RG52/U) arrangement using a magic tee as beam divider. Typical interferograms as well as Cole-Cole plots of some liquids will be reproduced. Also encouraging is the coherence of our results with far ir data.