Coaxial probe dielectric measurements: Practical dotting “i's” and crossing “t's”

The open-ended coaxial probe is widely used to measure the dielectric properties of materials. In a recent detailed study of an SMA open-ended probe, where we examined issues of interface higher-order modes, probe lift-off and repeatability, we found several experimental issues to be important. In the study, we do not provide sufficient information on these issues or attempt to define measurement limitations. In this paper, we report on common-mode (CM) currents associated with the probe and specific low-level perturbations seen throughout our data-sets. We discuss practical matters, such as cable stability and lift-off, with the consequences on material property estimation. We conclude with a discussion on the lowest measurable loss tangent obtained by coaxial probe methods.