An NRW Extension For Dielectric Characterization of Arbitrary Length Low-Loss Materials

In this paper, we propose an extension for the Nicolson-Ross-Weir (NRW) method that enables the retrieval of the electrical parameters of low-loss materials that are thicker than one-half wavelength $(\lambda g/2)$. The proposed extension overcomes the NRW intrinsic limitation that causes a divergence of results at frequencies where the material thickness is an integer multiple of $\lambda g/2$. The method is tested on different sample materials, and is proven to provide a stable permittivity estimation, with no divergence at frequencies corresponding to integer multiple of $\lambda g/2$.