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In this paper, we show how metallic plate inclusions can be used to enhance the coupling values of microstrip directional couplers. The analysis and the design of symmetrical coupled microstrip lines with high values of forward-wave coupling with a coupling length very small are presented. A quasi-static circuit model of the structure is developed and physical insights on the operation of the proposed component and on the role of Epsilon NeGative (ENG) material slab loading are also given. Full wave numerical simulations are shown for different geometries. Index Terms--Microstrip couplers, plasma media, power dividers.

In this contribution, we present a proper extension of the finite-element method based on a variational formulation which is able to take into account the effects of nonconventional materials in the evaluation of the electromagnetic field inside a cavity bounded by both closed and open boundary conditions. As a numerical application, we show how nonconventional materials like, for instance, metamaterials can be used in the design of integrated circuits, in order to reduce the proximity effects among planar transmission lines. Index Terms--Anisotropic media, crosstalk, finite-element method (FEM), microstrip couplers.

Recent theoretical studies have shown that circular patch antennas loaded by an inhomogeneons substrate partially filled with a [mu]-negative (MNG) metamaterial may in principle support a resonant radiating mode, even if the total size of the radiator is significantly smaller than the wavelength of operation. In those theoretical analyses, MNG metamaterials have been assumed as continuous, isotropic and readily available materials, characterized by a proper dispersion in frequency and by inherent ohmic losses. The fabrication of such compact antennas, however, would require the major effort of designing proper subwavelength inclusions that realize the MNG behavior of the substrate, and consequently a careful design of their geometry, location and orientation. The fabrication of a fully isotropic MNG sample to reside underneath the sub-wavelength patch, moreover, may be challenging with the current technological limitations. In this paper, we first show that the proposed sub-wavelength radiator may operate even when the fabricated MNG sample is not isotropic, due to the specific polarization of the magnetic field in the MNG region. Then, we propose a complete design of the magnetic inclusions, presenting full-wave numerical simulations of the structure, which effectively supports the expected resonant mode, despite the small size of the antenna. The comparisons among analytical results of the patch loaded by: (a) the ideal MNG sample applying a simple cavity model; (b) full-wave numerical simulations of the same antenna considering the presence of the feed; and (c) full-wave numerical simulations of the antenna loaded by the proposed magnetic inclusions, show how our design effectively simulate the presence of an MNG sample, allowing the realistic design of a sub-wavelength metamaterial patch antenna with satisfactory matching and radiating features. This may open up new venues in the realization of efficient metamaterial radiating components for practical purposes. Index Terms--Integrated antennas, magnetic inclusions, metamaterials.

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. Index Terms--Artificial magnetic inclusions, labyrinth resonators, metamaterials, miniaturization, multiple split-ring resonators, split-ring resonators.

We present the design of miniaturized resonant inclusions to be employed in the practical realization of metamaterial samples with anomalous values of the real part of the permeability. Such inclusions, in fact, can be employed in the design of both [micro]-negative (MNG) materials and artificial magnetodielectrics (with negative and high-positive values of the real part of the permeability, respectively). The inclusions here considered are the multiple split-ring resonators (MSRRs), that represent a straightforward extension of the commonly used split-ring resonators (SRRs), and the spiral resonators (SRs) that enable a greater miniaturization rate. Some physical insights on the resonance mechanism and on the inherent saturation of the resonant frequency when increasing the number of the rings of the MSRRs and the number of the turns of the SRs are given in the paper. New and accurate analytical design formulas, based on a quasi-static model, for both MSRRs and SRs are derived and tested through a proper comparison with the existing formulas and full-wave numerical results. Both MSRRs and SRs are shown to be useful to reduce the electrical dimensions of the resonant inclusions when synthesizing artificial metamaterials. Index Terms--Metamaterials, [micro]-negative (MNG) metamaterials, resonant magnetic inclusions, split ring resonators.

The detailed theory of a single subwavelength conformal radiator that exploits the resonant properties of thin cylindrical metamaterial shells supporting leaky waves is presented. It is shown and reviewed analytically and numerically how a circularly symmetric resonant leaky mode may be supported by a properly designed subwavelength homogenous cylindrical shell of low negative permittivity. Some physical insights are provided and numerical simulations with a feed point, considering also the finiteness of the antenna in the longitudinal direction, are presented and discussed. Moreover, possibilities and limitations of a practical realization of this setup are mentioned, considering in details the possible anisotropies in the metamaterials. Index Terms--Conformal antennas, cylindrical antennas, leaky waves, metamateriais.

We analyze the matching and radiation properties of subwavelength resonant patch antennas filled with double-negative, double-positive, and/or single-negative metamaterial blocks. Analyzing the theoretical limits inherently present when loading such common radiators with metamaterials, we show how these configurations may exhibit in principle an arbitrarily low resonant frequency for a fixed dimension, but they may not necessarily radiate efficiently when their size is electrically small. However, interesting possibilities are suggested to overcome these limitations by employing circular or more complex patch geometries in order to select specific modes that, when appropriate loading ratios between the filling materials are chosen, also ensure radiation performance comparable qualitatively with a regular patch radiator of standard dimensions. Realistic numerical simulations, considering material dispersion, losses and the presence of the antenna feed are presented, showing how a practical realization is foreseeable. This may open novel venues in the design of small-scaled radiators with enhanced performance, which is of interest for many applications. Index Terms--Metamaterials, miniaturized antennas, patch antennas.

Recently, there has been an increased interest in the problem of wave transmission through sub-wavelength apertures, following successful experimental demonstration by several groups for enhancing optical power transmission through nano-scale holes in metallic screens due to properly designed periodic corrugation. Oliner, Jackson, and their co-workers explained and justified this phenomenon as the result of the excitation of the leaky waves supported by the corrugated screen. Here we discuss in detail the mechanism and analysis for another setup we have recently proposed, in which metamaterial layers with special parameters may be utilized as covers over a single sub-wavelength aperture in a perfectly electric conducting (PEC) flat screen in order to increase the wave transmission through this aperture, and we provide a detailed physical insights and analytical explanation for this aperture setup that may lead to similar, potentially even more pronounced effects when the proper metamaterial layers are used in the entrance and the exit face of the hole in the flat PEC screen with no corrugation. Some numerical results confirming this theory are presented and discussed. We also investigate the sensitivity of the transmission enhancement to the geometrical and electromagnetic parameters of this structure. Index Terms--Aperture coupling, aperture enhancement, leaky wave, metamaterials, polariton, sub-wavelength aperture.

An effective design of polygonal patch antennas with multifrequency or broad-band operation modes for wireless communications is presented in this paper. It is shown how polygonal patches with suitable features may be obtained after a proper perturbation of conventional rectangular geometries, which inherently present poor bandwidth performances. These perturbed irregular geometries may support multiple resonances and, thus, may present a broad-band or multifrequency operation mode, even employing conventional patch antennas with a single dielectric substrate. These polygonal patches are efficiently analyzed through a numerical code based on the method of moments, with entire domain basis functions that accurately describe the radiation mechanism. After the presentation of the analysis and design techniques, some antenna layouts for modern wireless communication systems will be proposed. Such antennas are designed for both universal mobile telecommunication system and wireless local area network portable equipment with real-life finite ground planes. Index Terms--Integrated antennas, mobile terminals, polygonal patches, wireless communications.

This paper presents a generalization of the method of lines (MoL) numerical algorithm for the analysis of integrated structures with a finite local curvature. Starting from the derivation of the generalized transmission line equations in a generic orthogonal reference system and in a bianisotropic material, it is shown the possibility of solving the electromagnetic problem associated to an integrated structure with arbitrary curvature and/or loaded by complex dielectric materials via a MoL approach. The introduction of new algorithms that extend and complete the original method is required in the most general case. A detailed description of this new extended version of the MoL is presented through the paper and its full coincidence with the original algorithm in the case of structures with simple loading materials is also shown. Finally, some numerical results obtained analyzing microwave conformal antennas and resonators are presented and compared with analyzes performed employing other numerical methods and available in the literature. Index Terms--Conformal antennas, integrated antennas, method of lines (MoL).

The generalized transmission line equations for bianisotropic materials are derived in this paper. These equations are obtained in a general orthogonal curvilinear reference system, taking properly into account the metric factors and decomposing the field vectors into two components: a transverse component and a longitudinal one, both with respect to a reference coordinate direction. Such a general formulation is very useful in order to analyze metallic/dielectric uniform bended waveguides. On the other hand, it is very appropriate when studying conformal integrated circuits by using the method of lines (MoL). Finally, the formulation here presented leads to a straightforward derivation of the transmission line equations in the spectral domain when studying conformal integrated antennas. As particular cases of the theory here presented, transmission line equations in orthogonal curvilinear coordinates are also derived for anisotropic, bi-isotropic, and isotropic materials. Index Terms--Complex media, conformal structures, transmission line equations.

Exploiting a rigorous variational formulation, the main effects of a chiral cover on a cavity backed microstrip patch antenna are pointed out in this paper. An hybrid finite element-boundary integral method is employed to numerically solve the electromagnetic problem modeled by a variational functional. The dependence of the resonance frequency on the cover thickness and on the chirality admittance of the material is first investigated. More in detail, it is demonstrated that a chiral cover permits to reduce the antenna dimensions, compared to an isotropic one, for a fixed working frequency. Then, the variation of gain properties, cross-polarization levels, radiation resistance, radiation efficiency, and radar cross-section is also investigated through several numerical examples. Index Terms--Chiral materials, covered patch antennas, microstrip antennas.

In this paper, we propose an analytical study in the spectral domain of inhomogeneoas layers that are characterized in terms of transmission matrices leading to an equivalent circuit representation of the whole multilayered structure. Within the framework of this two-port formalism, we present a new contribution to the computation of the Green's function arising in the analysis of multilayered integrated antennas loaded with inhomogeneous materials. Such materials offer new degrees of freedom and, besides, may allow of pattern control, frequency shifting, and enlargement of the bandwidth. We propose, also, an analytical study of the shielding effectiveness of isotropic inhomogeneous materials located in multilayered configuration. The expression of the shielded fields sustained both by plane wave and arbitrary sources is deduced in a closed analytical form. Numerical results are also presented showing the effects of the electromagnetic parameters on radiation pattern, matching properties and radar cross section of the integrated structure. Index Terms--Green's dyad, inhomogeneous media, layered media, shielding effectiveness.

In this paper, we present an application of the method of lines (MoL) for the analysis of a finite array of microstrip patch antennas loaded with dielectric layers on a cylindrical structure. New formulas are given in cylindrical coordinates to describe multiple, stacked layers without causing an increase in the difficulty or complexity of the analysis. We show that this model is not only numerically efficient, compared with other numerical methods, but also, shows a very good accuracy with respect to experimental results and has no limitation on antenna array geometry and excitation. Finally, some numerical results for both radiation and mutual coupling are presented. Index Terms--Conformal antennas, mutual coupling, nonhomogeneous media.

Method of line (MoL) procedure is very useful in the analysis of radiative and transmissive microwave components, but its standard version does not allow for the study of elements with complex substrates. In this work, we first show that components integrated into materials exhibiting the magneto-electric effect (bi-isotropic and general bianisotropic media) cannot be analyzed following a standard MoL algorithm. Next, we derive an extended MoL numerical tool, which allows for the analysis of components in the presence of any linear medium (even inhomogeneous, bianisotropic and lossy). Such an extension is based on the generalization of the transmission-line equations for a general linear medium, which, in the case in point, are not necessarily decoupled. Furthermore, we present the full coincidence of this new method with the standard MoL in the case of simpler media (i.e., not exhibiting the magneto-electric effect) and, finally, we show some numerical results, obtained analyzing microwave antennas and resonators with bianisotropic and chiral substrates. Index Terms--Bianisotropic materials, chiral materials, Method of line (MOL), microwave components.

The analysis of patch antennas residing in cavities filled by general inhomogeneous and lossy bianisotropic substrates is presented in this paper. The theoretical study is based on a variational formulation associated with the boundary value problem under analysis, and a hybrid finite element-boundary integral method is employed to numerically solve the electromagnetic field inside and outside cavities. Initially, the general formulation presented here is applied to some particular cases known in the literature. Then, the main scattering and radiation features of cavity backed patch antennas with chiral, anisotropic, and bianisotropic materials are presented. Particularly, it is shown that complex media allow for frequency control and for a reduced antenna size at a given operating frequency. Index Terms--Complex materials, finite-element method, patch antennas.

A novel design method for lossy Blass matrix beam-forming networks (LBMBFNs) is presented. Compared to those formerly developed, the new method allows the design of an LBMBFN in order to generate not only two simultaneous beams but also an arbitrary number of them. This skill is obtained by means of a new approach to minimize losses that allows one to transform a nonlinear multivariable programming problem into a linear one-variable problem. The solution of such a design problem, then, can be carried out in a very straightforward way by applying Gram--Schmidt orthogonalization. Such a design method takes into account also the limited availability of coupling values of directional couplers. Numerical results obtained through the application of such a design method are then presented. The ease, accuracy, and efficiency of this novel method for the design of LBMBFN make it very useful in modern applications of multibeam antenna arrays. Index Terms--Array signal processing, multibeam antennas.

In this paper we find the solution of telegrapher's equations for a non-homogeneous medium applying the theory of hypergeometric functions. Also we show that such a medium is described by means of a stratified structure, so we can use the developed theory for microwave components. We find the behavior of the reflection coefficient and compare it with other known results present in literature. Moreover, we show how an Exponentially Tapered Non Uniform Transmission Line (ETNUTL) can be treated as a high-pass filter. It is found that the exponential profile improves the performance of the filter and the normalized transmission coefficient is given for different values of tapering factor. Finally, we find a lumped equivalent circuit for the filter, whose elements are dependent on the tapering factor. The high-pass characteristics of an ETNUTL are verified with techniques in the frequency domain. Index terms - Non Uniform Transmission Lines, Spectral Full-Wave Analysis, Kummer's Equations.

A new extended finite element formulation for finding radiation patterns, Radar Cross Section (RCS) and input impedance of planar integrated circuits on a very general bi-anisotropic grounded slab with finite size is presented. The approach is based on a hybrid Finite Element Method (FEM) wherein the electromagnetic fields in the FEM region are coupled to the fields outside by a surface integral equation. Because of the local nature of the FEM, this formalism allows inclusion of the inhomogeneities in the problem domain. Numerical results are compared and agree well with existing published data for various conventional configurations. Index Terms - Hybrid finite element method, bi-anisotropic media, open integrated structures.

A method, based on the Full Wave Analysis (FWA) is presented to treat analytically and evaluate numerically the electromagnetic field sustained by an electric point-source inside an electrically biisotropic chiral grounded slab embedded in an isotropic homogeneous half-space in presence of a perfectly conducting finite patch located at the interface. The expression of the electric field in each region of the space in terms of the spectral electric Green's dyad is given. The use of the boundary conditions allows us to determine a Spectral Electric Integral Equation (SEIE) for the electric current density induced on the scatterer's surface. The solution of the SEIE is carried out in the general case of location of the electric sources with the patch parallel to the interface. Numerical results for the input impedance of the structure and the radiated far-field with noteworthy information about the radiation on the horizon plane and constraints on the electromagnetic parameters, thickness of the slab, working frequency and source position are presented and discussed.

This paper presents the application of non-linear neural optimization networks to the analysis of arbitrarily shaped microstrip patch antennas with a very general bianisotropic grounded slab. A neural network approach is presented to solve in a new and efficient way the integral equation which describes, from the electromagnetic point of view, the planar integrated structure.

A method, based on the Full Wave Analysis (FWA) is presented to treat analytically and evaluate numerically the electromagnetic field sustained by an electric source inside an electrically biaxial grounded slab embedded in an isotropic homogeneous half-space in presence of a perfectly conducting finite patch located at the interface. As a prerequisite to this approach, the electric spectral (Fourier) dyadic Green's function of the structure is first developed and fully derived via the transmission-line analogy. Then the expression of the electric field in each region of the space in terms of the spectral electric Green's dyad is given. The use of the boundary conditions allows us to determine a Spectral Electric Integral Equation (SEIE) for the electric current density induced on the scatterer's surface. The solution of the SEIE is carried out in the general case of location of the electric sources with the patch parallel to the interface. Numerical results for the radiated far-field, for the structure without the patch, with noteworthy information about the radiation on the horizontal plane and constraints on the electromagnetic parameters, thickness of the slab, working frequency and source position are presented and discussed. Finally, a numerical solution for SEIE, in order to evaluate the electric current densities induced on the patch, is shown.

In this paper, we present the theoretical analysis and the design of cylindrical multilayered electromagnetic cloaks based on the scattering cancellation technique. We propose at first the analysis and the design of bi-layered cylindrical shells, made of homogenous and isotropic metamaterials, in order to effectively reduce the scattered field from a dielectric cylindrical object. The single shell and the bi-layered shell cases are compared in terms of scattering reduction and loss effects. The comparison shows that the bi-layered configuration exhibits superior performances. The scattering cancellation approach, is, then, extended to the case of generic multilayered cylindrical shells, considering again homogeneous and isotropic metamaterials. The employment of the proposed technique to the case of cloaking devices working at multiple frequencies is also envisaged and discussed. Finally, some practical layouts of cylindrical electromagnetic cloaks working at optical frequencies are also proposed. In these configurations, the homogenous and isotropic metamaterials are replaced by their actual counterparts, obtained using alternating stacked plasmonic and non-plasmonic layers. The theoretical formulation and the design approaches presented throughout the paper are validated through proper full-wave numerical simulations.

The metamaterial concept is used for designing, implementing and characterizing electrically thin microwave absorbers. The split-ring resonator (SRR) and multiple SRR (MSRR) magnetic metamaterial back plates are used for showing that the absorber electrical thickness can be further reduced as the electrical size of the metamaterial unit cell has decreased.