Electromagnetic Characterization of Thin Dielectric Materials From Amplitude-Only Measurements

A method is proposed for unique and accurate permittivity (epsilon(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 epsilon(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 epsilon(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 epsilon(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 epsilon(r) measurement of low-loss dielectric samples, our method removes these two problems.