An Accurate Method for Measuring the Sheet Impedance of Thin Conductive Films at Microwave and Millimeter-Wave Frequencies

A simple and accurate method to measure the complex sheet impedance of thin conductive films on dielectric substrates is reported. This method allows for accurate extraction of the sheet impedance without characterizing the substrate (thickness and permittivity) beforehand, within a wide range of frequencies and sheet complex impedances. In this method, the sample is placed between two rectangular waveguide flanges, creating a discontinuity. The discontinuity is modeled by an equivalent Pi-circuit, and the sheet impedance is found from measured circuit parameters of the sample and bare substrate. We propose two retrieval approaches using different circuit parameters, examine their extraction accuracy with various substrate thicknesses and sheet impedances, and determine the most reliable extraction method. Uncertainty analysis under random perturbations of measured scattering parameters is also performed to investigate the robustness of the technique. Experimental studies are carried out to demonstrate the validity of the proposed approach for the impedance measurements of thin conductive ink films supported by both thin or thick (up to 0.28 times the wavelength in the dielectric) substrates.