Electromagnetic Characterization of Thin Dielectric Materials From Amplitude-Only Measurements

Abstract

A method is proposed for unique and accurate permittivity ( $\varepsilon _{r}$ ) extraction of low-loss thin samples from reference-plane-invariant amplitude-only measurements without resorting to the information of explicit permittivity of a sample holder. Thanks to the amplitude-only measurements, it is possible to bypass the increased phase uncertainty of scattering parameters and retrieve unique $\varepsilon _{r}$ . An uncertainty analysis is followed to investigate improved accuracy attained by our method. Waveguide measurements at the $X$ -band are next conducted to measure $\varepsilon _{r}$ of polyethylene and polyvinyl chloride samples with different lengths (the sample holder is a soda-lime glass) for validation of the method and for comparison its accuracy with other methods. From the comparison, we note that reference-plane-dependent methods necessitate precise knowledge of sample location for accurate $\varepsilon _{r}$ retrieval. Besides, it is observed that while compared reference-plane-invariant techniques either require that the sample holder does not move while positioning the sample over it or produce more than one solution for $\varepsilon _{r}$ measurement of low-loss dielectric samples, our method removes these two problems.