A wideband line-line dielectrometric method for liquids, soils, and planar substrates

A line-line (LL) method for measuring the permittivity of materials up to millimeter waves is proposed. It is based on a property of the well-known line-return-line (LRL) calibration technique developed for microwave circuits: the complex propagation constant of the two-line calibration standards can be extracted from the raw measurement of these two lines. Using this feature for a dielectrometric purpose, we combine this LL formulation with accurate models for the propagation constant to extract from the measured value the permittivity of the medium surrounding, or contained in, the LL calibration lines. Choosing the line topology (planar, coaxial, or waveguide) according to the nature and consistency of the material under consideration yields the permittivity of a wide variety of materials. In this paper, we demonstrate the efficiency of the method for three kinds of substances: organic liquids, soils, and planar dielectric substrates used for microwave planar circuits. Advantages particular to each application are detailed in the paper.