| Recent interest in new materials, including metamaterials and magneto-dielectrics, for RF applications provided strong impetus for measurement techniques to characterize associated permittivity, permeability, and loss factors. Traditional measurement techniques are not readily available to characterize these engineered composites. For example, conventional resonant cavity methods are known to be narrowband and require careful sample preparation. For metamaterials and magneto-dielectrics, broadband characterization is particularly necessary to observe their dispersive properties. Also, a challenge with new materials, such as layered composites, is the restriction in measurable shape, size and thickness. Often, small and irregularly shaped samples are available, making their characterization challenging.;With these issues in mind, this dissertation is aimed at developing new characterization techniques for novel engineered composites. Specifically, four techniques are presented to characterize textured metamaterial volumetric structures, magneto-dielectric mixtures and films, and highly conductive metallo-dielectric films. One of the presented techniques is based on a Gaussian beam illumination. In this method, the Gaussian beam is used to illuminate the center of layered material samples to avoid diffraction from sample edges. In contrast to generating the Gaussian beam using bandwidth-limited lenses, the beam was reconstructed by scanning a probe over a virtual aperture much like the synthetic aperture radar process. This approach was successfully employed at X-band (8 to 12 GHz) for the characterization of slow-wave propagation in a layered metamaterial slab. However, the Gaussian beam method is not feasible at low frequencies as it requires a large sample aperture (> lambda in size). The second characterization method was, therefore, developed to measure smaller samples (< lambda/4) in lower frequencies (100 MHz to 4.8 GHz). More specifically, a stripline fixture, supporting transverse electromagnetic wave propagation, was designed to characterize permittivity and permeability of ferrite mixtures. This approach is suitable for reasonably thick samples but not accurate for extremely thin samples (thickness t < 1 mm). For thin material composites, we employed a planar microstrip line based structure for accurate measurements. Furthermore, a new de-embedding process based on full-wave simulations was developed to avoid uncertainties in conventional quasi-static de-embedding process. The last and 4th presented method was developed for material samples with high conductivity. As compared to the low-conductive materials presented already, of interest with these materials is the characterization of conductivity and resistivity. Using a 1-port re- flection coefficient measurement set-up, these quantities were extracted for multilayer metallo-dielectric films over broadbandwidth (100 MHz to 15 GHz). |
