Reflection Coefficient Analysis of Open-Ended Coaxial Probes Based on Geometrical Parameters

Dielectric spectroscopy is a widely used technique for investigating the frequency-dependent electrical properties of materials. In this study, the influence of probe geometry on the reflection coefficient at the tip of an open-ended coaxial probe (OECP) was systematically examined. Full-wave simulations were conducted in Ansys HFSS over the 0.5-20 GHz frequency range, with methanol serving as the test medium. The probe length (13, 23, and 26 mm), diameter values halved and doubled, and immersion depth (0,3, and 6 mm) were varied across different configurations (a total of nine simulations across four different scenarios). The results showed that immersion depth variations led to changes of approximately 16-18% in the reflection coefficient, probe length extensions caused deviations exceeding 260%, and larger probe diameters introduced differences of up to 135%. These findings highlight the strong dependence of OECP performance on geometric parameters and optimization in probebased measurement systems.