Synthesis of Filtering Structures for Microstrip Active Antennas Using Orlov's Formula

In this paper, a synthesis technique for nonuniform filtering structures to be employed in active integrated antenna layouts is presented. The idea is to suppress the higher harmonic contribution due to the presence of nonlinear components through a nonuniform transmission line properly designed via Orlov's synthesis formula. The theory presented is applied here to synthesize an amplifier-based active antenna layout for wireless local area network (WLAN) purposes working at 2.4 GHz. The numerical results presented show the capabilities of the proposed approach

Experimental demonstration of the enhanced transmission through circular and rectangular sub-wavelength apertures using omega-like split-ring resonators

Cataloged from PDF version of article.Enhanced transmission through circular and rectangular sub-wavelength apertures using omega-shaped split-ring resonator is numerically and experimentally demonstrated at microwave frequencies. We report a more than 150,000-fold enhancement through a deep sub-wavelength aperture drilled in a metallic screen. To the authors’ best knowledge, this is the highest experimentally obtained enhancement factor reported in the literature. In the paper, we address also the origins and the physical reasons behind the enhancement results. Moreover, we report on the differences occurring when using circular, rectangular apertures as well as doublesided and single-sided omega-like split ring resonator structures. (C) 2012 Elsevier B.V. All rights reserve

FSS-based approach for the power transmission enhancement through electrically small apertures

Cataloged from PDF version of article.In this paper, a novel approach, based on the employment of frequency selective surfaces, to enhance the power transmission through sub-wavelength apertures at the microwave frequencies is presented. A heuristic interpretation of the phenomenon is given, as well as an analytical model, based on the transmission line network representation. Finally, the performance of the proposed structure is validated through a set of full-wave numerical simulations. © 2011 Springer-Verlag

Temporal Rainbow Scattering at Boundary-Induced Time Interfaces

Since the dawn of modern optics and electromagnetics, optical prism is one of the most fascinating optical elements for refracting light. Exploiting its frequency dispersive behaviour, a prism is able to refract different frequencies in different directions, realizing polychromatic light rainbows. Recently, thanks to their engineerable electromagnetic response, metamaterials have been exploited for achieving novel refractive scattering processes, going beyond the classical prism effects. In this Manuscript, we report on a novel rainbow-like scattering process taking place at the interface of a boundary-induced temporal metamaterial realized by instantaneously opening the boundary conditions of a parallel plate waveguide. Changing abruptly the conductivity of one of the two metallic plates, we demonstrate that an equivalent temporal interface between two different media is realized, and the monochromatic wave propagating into the waveguide gets scattered into a polychromatic rainbow in free-space. We derive the relationships between the waveguide mode and the raising rainbow in terms of scattered amplitude and frequencies as a function of the elevation angle with respect to the waveguide axis. We apply the underlying physics to control the temporal rainbow by imposing a principal direction of scattering by design. Full-wave numerical simulations are performed for computing the rainbow temporal scattering and verifying the design guidelines for achieving controlled temporal rainbow scattering.Comment: 14 pages, 3 figures, Appendi

Optimization and tunability of deep subwavelength resonators for metamaterial applications: complete enhanced transmission through a subwavelength aperture

Cataloged from PDF version of article.In the present work, we studied particle candidates for metamaterial applications, especially in terms of their electrical size and resonance strength. The analyzed particles can be easily produced via planar fabrication techniques. The electrical size of multi-split ring resonators, spiral resonators, and multi-spiral resonators are reported as a function of the particle side length and substrate permittivity. The study is continued by demonstrating the scalability of the particles to higher frequencies and the proposition of the optimized particle for antenna, absorber, and superlens applications: a multi-spiral resonator with lambda/30 electrical size operating at 0.810 GHz. We explain a method for tuning the resonance frequency of the multi-split structures. Finally, we demonstrate that by inserting deep subwavelength resonators into periodically arranged subwavelength apertures, complete transmission enhancement can be obtained at the magnetic resonance frequency. (C) 2009 Optical Society of Americ

Miniaturized negative permeability materials

Cataloged from PDF version of article.Experimental and numerical studies of mu-negative (MNG) materials such as multisplit ring resonators (MSRRs) and spiral resonators (SRs) are presented. The resonance frequency of the structures is determined by the transmission measurements and minimum electrical size of lambda(0)/17 for the MSRRs and of lambda(0)/82 for the SRs observed. These MNG materials can be easily produced by the well developed printed circuit board and optical lithography techniques. They are promising elements for the development of high resolution metamaterial lenses and electrically small antennas. (c) 2007 American Institute of Physics

Design of Miniaturized Narrowband Absorbers Based on Resonant-Magnetic Inclusions

Cataloged from PDF version of article.In this paper, we present the design of miniaturized narrowband-microwave absorbers based on different kinds of magnetic inclusions. The operation of the proposed components originates from the resonance of a planar array of inclusions excited by an incoming wave with a given polarization. As in common absorber layouts, a 377 Omega resistive sheet is also used to absorb the electromagnetic energy of the impinging field. Since the planar array of magnetic inclusions behaves at its resonance as a perfect magnetic conductor, the resistive sheet is placed in close proximity of the resonating inclusions, without perturbing their resonance condition. In contrast to other typical absorber configurations presented in the literature, the absorber proposed in this paper is not backed by a metallic plate. This feature may be useful for stealth applications, as discussed thoroughly in the paper. The other interesting characteristic of the proposed absorbers is the subwavelength thickness, which has shown to depend only on the geometry of the basic resonant inclusions employed. At first, regular split-ring resonators (SSRs) disposed in an array configuration are considered and some application examples are presented. Absorbers based on SRRs are shown to reach thickness of the order of lambda(0)/20. In order to further squeeze the electrical thickness of the absorbers, multiple SRRs and spiral resonators are also used. The employment of such inclusions leads to the design of extremely thin microwave absorbers, whose thickness may even be close to lambda(0)/100. Finally, some examples of miniaturized absorbers suitable for a practical realization are proposed

Plasmonic Cloaking of Cylinders: Finite Length, Oblique Illumination and Cross-Polarization Coupling

Metamaterial cloaking has been proposed and studied in recent years following several interesting approaches. One of them, the scattering-cancellation technique, or plasmonic cloaking, exploits the plasmonic effects of suitably designed thin homogeneous metamaterial covers to drastically suppress the scattering of moderately sized objects within specific frequency ranges of interest. Besides its inherent simplicity, this technique also holds the promise of isotropic response and weak polarization dependence. Its theory has been applied extensively to symmetrical geometries and canonical 3D shapes, but its application to elongated objects has not been explored with the same level of detail. We derive here closed-form theoretical formulas for infinite cylinders under arbitrary wave incidence, and validate their performance with full-wave numerical simulations, also considering the effects of finite lengths and truncation effects in cylindrical objects. In particular, we find that a single isotropic (idealized) cloaking layer may successfully suppress the dominant scattering coefficients of moderately thin elongated objects, even for finite lengths comparable with the incident wavelength, providing a weak dependence on the incidence angle. These results may pave the way for application of plasmonic cloaking in a variety of practical scenarios of interest.Comment: 17 pages, 11 figures, 2 table

Equivalent-Circuit Models for the Design of Metamaterials Based on Artificial Magnetic Inclusions

Cataloged from PDF version of article.In this paper, we derive quasi-static equivalent-circuit models for the analysis and design of different types of artificial magnetic resonators-i.e., the multiple split-ring resonator, spiral resonator, and labyrinth resonator-which represent popular inclusions to synthesize artificial materials and metamaterials with anomalous values of the permeability in the microwave and millimeter-wave frequency ranges. The proposed models, derived in terms of RLC equivalent circuits, represent an extension of the models presented in a recent publication. In particular, the extended models take into account the presence of a dielectric substrate hosting the metallic inclusions and the losses due to the finite conductivity of the conductors and the finite resistivity of the dielectrics. Exploiting these circuit models, it is possible to accurately predict not only the resonant frequency of the individual inclusions, but also their quality factor and the relative permeability of metamaterial samples made by given arrangements of such inclusions. Finally, the three models have been tested against full-wave simulations and measurements, showing a good accuracy. This result opens the door to a quick and accurate design of the artificial magnetic inclusions to fabricate real-life metamaterial samples with anomalous values of the permeability