Low-cost planar coupled-line sensor for permittivity measurement of low-loss dielectric materials in a wide frequency range

This paper presents novel non-destructive method for dielectric sample characterization in a wide frequency range. Recently proposed sensors based on differentially excited shortended coupled-line section has been used to determine the permittivity of an unknown dielectric sample. A simplified calibration and calculation procedure is proposed in the presented approach while maintaining a good measurement accuracy. Since the sample permittivity is obtained based on the measurement of the odd-mode effective permittivity, which is mainly related to the mutual capacitance between coupled strips, high sensitivity on the covering sample is achieved. The proposed measurement technique has been theoretically investigated and experimentally verified. A good agreement between predicted and obtained from measurement results has been obtained in a wide frequency range up to 7 GHz with percent error not greater than ± 5%.