Analytical modeling of open-ended coaxial probe - a review

Abstract

An open-ended coaxial probe is a probe consists of inner and outer conductors with radius, respectively. The open end of the coaxial line is terminated by a semi-infinite sample on a ground plane. In general, the medium between the conductors is filled by free space or lossless materials. The application is based on the principle that a reflected signal through the coaxial opening will carry the desired information about the material sample at terminal surface. Thus, if the aperture admittance or reflection coefficient characteristics can be precisely formulated then, it can be used as a probe for the characterization of material samples. Nevertheless, there exists no completely analytical relationship between the reflection coefficient and the permittivity of the material under test. Various methods have been used to relate the reflection coefficient data to the dielectric properties of the sample in the past. Subsequent considerable efforts were made to further improve these models. The methods range from simple closed-form equivalent circuit model to rigorous analytical technique. In this chapter, the closed-form equivalent circuit admittance models and rigorous integral admittance models is reviewed and used as a function to relate the reflection coefficient and the permittivity of the material under test.