Microwave Sensors for Dielectric Sample Measurement Based on Coupled-Line Section

In this paper, a novel class of sensors composed of coupled-line sections dedicated for complex permittivity measurements of dielectric samples have been proposed. The end-shorted and open-ended coupled-line sections have been used as sensing elements for nonresonant and nondestructive measurements allowing for characterization of dielectric samples. It has been shown that by utilization of an iterative procedure, the complex permittivity of a dielectric material under test can be determined based on the measured complex odd-mode effective permittivity of the system. Since the complex odd-mode effective permittivity is mainly related to the mutual capacitance between coupled strips, high sensitivity on the covering sample has been obtained and the measured sample can be as narrow as the spacing between the coupled strips. The proposed sensors have been theoretically investigated and experimentally validated. The obtained results have been compared and the sensors' advantages and limitations have been discussed. The obtained measurement results have proved the correctness and usefulness of the proposed approach.