Dielectric Spectroscopy of Liquids by De-Embedding Two-Port Measurements

In this article, we present a calibration approach for a microwave sensor aimed for dielectric spectroscopy of liquids. The sensor consists of a T-junction terminated with an interdigitated electrodes (IDE) structure. Therefore, the calibration technique involves de-embedding a 3-port network (i.e., the T-junction) by using only three known materials. The sensor is calibrated for 1–2 GHz frequency range using three samples of ethanol/water mixtures with 20%, 50%, and 80% ethanol content, respectively, and the permittivity extraction approach is validated using four different samples. The retrieved complex permittivity results in a 1.8% and 6.4% average relative error for the real and imaginary parts compared to coaxial probe measurements for all samples, which shows the great performance of the proposed calibration technique.