FDFD based measurement of permittivity using an open-ended coaxial probe

In this paper, 2D-FDFD method is applied for measuring electrical properties of dielectric materials using an open-ended coaxial probe. A SMA connector with flange is used as the coaxial probe and the reflection coefficient from probe aperture in contact with dielectric is measured by a vector network analyzer. To convert the aperture-plane reflection coefficient to dielectric permittivity, first, the coaxial probe is modeled by the 2D-FDFD method and then the genetic algorithm is employed to solve the inverse problem. The accuracy of the proposed method is investigated by measuring the dielectric properties of three known materials. The mean absolute percentage errors are below 10% and the maximum absolute percentage error is below 12%. Thus, good agreement between measured and actual values are observed.