Abstract-Recently, we have presented a novel approach to design metamaterial-inspired notch filters that can be integrated within horn antennas of receiving systems to mitigate the effects of narrowband interfering signals. The filter module consists of a single Split Ring Resonator (SRR), whose rejection band needs to be matched to the bandwidth of the particular interfering signal we want to suppress. Extending our previous work, we show here how it is possible to control the bandwidth of such a filtering module by using different metamaterial-inspired resonators. In particular, we show that, while a reduction of the rejection band can be easily obtained by increasing the miniaturization rate of the resonator, the enlargement of the rejection band cannot be obtained in the same way by simply reducing the resonator quality factor. We show that a solution of the latter problem can be worked out by applying the "critical coupling" concept and considering the filtering module to be made of two equal SRRs with a proper optimal separation. The effectiveness of the approach is demonstrated trough proper full-wave simulations and experiments on a fabricated prototype. The proposed technique, used here to design a filtering module for a specific radiating system, has a more general relevance and can be applied to all cases where the operation bandwidth of a component is limited by the resonant nature of a single metamaterial-inspired particle.
Abstract-In this work, a metasurface consisting of an array of circular holes in a metal conducting sheet with a sub-wavelength periodicity is considered. The surface partially reflects the incident field according to the shape and geometrical dimensions of the inclusions and, due to this property, is widely employed in antenna systems to improve the radiation pattern of regular radiators. Since the reflection properties of the metasurface are determined by the current density distribution on the metal, we inspect this distribution and coherently develop a new, easy, and accurate analytical model to describe the grid impedance of the metasurface. In order to validate the model, we compare the reflection coefficient of the array obtained through our approach to the one resulting from full-wave numerical simulations and to other accurate analytical methods available in the open technical literature.
Abstract-In this paper, we propose a new retrieval technique to estimate the dielectric permittivity of the sub-soil materials of a stratified structure. The core of the retrieval procedure is a proper electromagnetic circuit model representing the realistic stratified media as a cascade of transmission line segments. Exploiting the analogies between the electrical parameters of the transmission line segments and the constitutive parameters of the materials of the multilayer structure, the propagation of the Ground Penetrating Radar (GPR) signal is equivalently represented as a pair of voltage and current waves propagating in the transmission line network. The effectiveness of the proposed retrieval technique is confirmed by proper experimental results. In particular, the retrieved electromagnetic parameters of the sub-soil materials are found to be consistent with the ones obtained by a direct characterization of the same materials. These results suggest that the proposed method can be successfully applied to the material characterization able to monitor several macroscopic properties of sub-soil materials.
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