Millimeter-wave (MMW) characterization of low-loss dielectric materials of unknown thickness from free-space measurements

In last several decades, the free-space measurement methods have been popularly employed to characterize dielectric materials at microwave frequencies. The conventional methods based on transmission and/or reflection scattering parameter measurements for test materials with vector network analyzers (VNAs) derive complex permittivity in broadband frequency ranges assuming that dimensions of samples are precisely known prior to measurements.