An improved coaxial probe technique for measuring microwave permittivity of thin dielectric materials

A practical coaxial probe technique for convenient, fast and accurate measu rements of thin dielectric materials is presented in this paper. The thin d ielectric samples, backed by a short circuit, are placed flush with the pro be. The complex permittivities of the samples are determined from the coaxi al aperture reflection coefficient, which is measured by a vector network a nalyser. In order to realize fast measurements, only the fundamental coaxia l mode is considered in the determination of the permittivity of a sample f rom the measured reflection coefficient. However, in calibration computatio ns, both the fundamental mode and higher-order modes are considered in orde r to ensure that the measurement system is accurately calibrated. Two pract ical measurement set-ups are specifically developed, for thin solid samples and thin liquid samples, respectively, in order to minimize various measur ement errors and to make the measurements convenient. To validate this tech nique, experimental measurements are carried out on several different diele ctric materials, including low-, medium- and high-permittivity materials. T he measured data are found to be in good agreement with the known data. The limitations of this technique are also discussed.