Stable and Broadband Extraction of Permittivity and Permeability of Low-loss Dielectric Material using Rectangular Waveguide System

Electric permittivity and magnetic permeability are the two main parameters used to describe the electromagnetic properties of materials. Determination of these complex constitutive parameters is imperative for many applications (radar, acoustic, EM interference, automotive, microwave circuit design, etc) [1]. Several experimental techniques and algorithms have been developed over the years to measure and extract the EM properties of the materials. The rectangular waveguide system is one of the most commonly used systems. The material under test (MUT) is placed inside the waveguide, and the S-parameters are measured. However, an accurate determination of the permittivity and permeability from this measurement is more delicate. The Nicolson Ross Weir (NRW) algorithm has been proposed in the literature for this purpose [2]. This technique is known to suffer from divergence, resulting from phase ambiguities, when the thickness of the sample is an integer multiple of the half-guided wavelength [3]. A new stable algorithm to correct the divergence is proposed in this paper. To validate the approach, two different and known samples of polystyrene based materials of different densities and carbon-loaded concentrations were tested. The thickness of the samples is 9.6 mm.