Combining FDTD simulations with measurements of microstrip ring resonators for characterization of low- and high-k dielectrics at microwaves

This paper shows how the dielectric constant of alumina and rutile substrates at microwave frequencies can be accurately determined by fitting the simulated S-parameter spectra of microstrip ring resonators, generated via the finite-difference time-domain (FDTD) method, to experimentally measured data. The proposed method does not require the determination of the effective dielectric constant and the approximate closed-form expressions to find the true permittivity of the substrate. This is essential for the characterization of high-K dielectric materials at high frequencies when the closed-form expressions are invalid.