Metamaterials (MMs) are artificial materials that have received attention recently because their built-in features create collective electromagnetic effects that are otherwise impossible, such as negative refraction, and because of their exotic electromagnetic applications, namely, perfect lens and invisibility cloaks. Depending on wave propagation characteristics, MMs possessing normally weak magneto-electric coupling coefficients start to exhibit stronger bianisotropic effects. Therefore, accurate electromagnetic characterization of these MMs is important. In this study, we adapt a stepwise method based on the Nicolson-Ross-Weir technique for accurate and unique retrieval of electromagnetic properties of bianisotropic MM slabs. For this goal, we have derived explicit expressions for unique retrieval of electromagnetic properties of these slabs and compared these expressions with those in the literature in the retrieval process. From the comparison, we note that derived expressions are appropriate for unique determination of electromagnetic properties of bianisotropic MM slabs. In the performance analysis of the stepwise method for different measurement scenarios, we considered different bianisotropic MM cell configurations (split-ring and Omega-shaped resonators as well as the same resonators with wire strips) and extracted their electromagnetic properties when measured/simulated scattering parameters have some thermal noise. We note that for most of the frequencies, the stepwise method retrieves correct electromagnetic properties even when a relatively higher normally distributed noise with zero mean value and with standard deviations of 0.015 is present. In addition to the influence of thermal noise on performance of the stepwise method, we also analyzed the effect of both increasing length slab and the frequency band on retrieved electromagnetic properties of the analyzed various bianisotropic MM slabs.

Abstract-We have applied the phase unwrapping technique to resolve the phase ambiguity problem arising from complex expressions of scattering parameters, for reflection-only measurement configurations, since, at some instances, only one side of the sample under test is accessible for electromagnetic measurements. We considered two different measurement configurations for testing the applicability of the phase unwrapping technique as: 1) two identical samples with different lengths flushed by a short-circuit termination and 2) one sample shorted by a varying short-circuit termination. For each measurement configuration, the underlying expressions for the reflection scattering parameters are derived. For both cases, we evaluated the suitability of the phase unwrapping technique by considering a highly-dispersive medium (distilled water) as our test sample. We note that continuity of the real part of the complex wavelength is a key issue in the unwrapping technique for (one-port) reflection-only measurements.

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