Achieving transparency and maximizing scattering with metamaterial-coated conducting cylinders

In this work, the electromagnetic interaction of plane waves with infinitely long metamaterial-coated conducting cylinders is considered. Different from "conjugate" pairing of double-positive (DPS) and double-negative (DNG) or epsilon-negative (ENG) and mu-negative (MNG) concentric cylinders, achieving transparency and maximizing scattering are separately achieved by covering perfect electric conductor (PEC) cylinders with simple (i.e., homogeneous, isotropic, and linear) metamaterial coatings. The appropriate constitutive parameters of such metamaterials are investigated for Transverse Magnetic (TM) and in particular for Transverse Electric (TE) polarizations. For TE polarization it is found out that the metamaterial-coating permittivity has to be in the 0< εc < ε0 interval to achieve transparency, and in the - ε0 < εc <0 interval to achieve scattering maximization. However, unlike the "conjugate" pairing of DPS-DNG or ENG-MNG cases, when the transparency for metamaterial-coated PEC cylinders are considered, the analytically found relation between εc and the ratio of core-coating radii, γ, should be modified in a sense that scattering from the PEC core is canceled by the coating. Furthermore, replacing ε by μ (and vice versa) does not lead to the same conclusions for TM polarization unless the PEC cylinder is replaced by a perfect magnetic conductor (PMC) cylinder. On the other hand, scattering maximization can also be achieved in the TM polarization case when coating permeability μc <0, whereas transparency requires large | μc | for this polarization. Numerical results in the form of normalized monostatic and bistatic echo widths, which demonstrate the transparency and scattering maximization phenomena, are given and possible application areas are discussed. © 2007 The American Physical Society

A closed-form solution to the asymptotic part of the MoM impedance matrix and the MoM excitation vector for printed structures on planar grounded dielectric slabs

In the spectral domain method of moments (MoM) solution of printed structures on planar grounded dielectric slabs, the infinite double integrals which appear in the asymptotic parts of the MoM impedance matrix and the MoM excitation vector elements, have been previously transformed to one-dimensional finite integrals, which have been numerically computed using the highly specialized "International Mathematics and Statistics Library" subroutines. In this paper, these one-dimensional integrals are evaluated in closed-form, resulting in an improved efficiency and accuracy for the rigorous investigation of printed antennas and complex millimeter and microwave integrated circuits. Numerical results in the form of mutual impedance between two expansion functions and input impedance of various microstrip antennas are presented to assess the accuracy of these closed-form expressions. © 2007 Wiley Periodicals, Inc

A comparative investigation of SRR- and CSRR-based band-reject filters: Simulations, experiments, and discussions

A comparative investigation of split-ring resonator (SRR)and complementary split-ring resonator (CSRR)-based band-reject filters is performed. These compact band-reject filters are obtained by loading simple 50-Ω microstrip lines with SRRs and CSRRs that have exactly the same shape and dimensions. Unlike the previous studies, stopband characteristics of these filters, such as resonance frequency, band-width, sharpness, and amount of attenuation in the rejection region based on the number of SRR or CSRR stages, are investigated in a detailed and comparative manner. Based on simulations that are accompanied by experimental results, it has been observed that some of the aforementioned stopband characteristics of SRR-based band-reject filters are significantly different than those of CSRR-based band-reject filters. This makes SRR- or CSRR-based filters preferable depending on applications. © 2007 Wiley Periodicals, Inc

Application of iterative techniques for electromagnetic scattering from dielectric random and reentrant rough surfaces

Stationary [e.g., forward-backward method (FBM)] and nonstationary [e.g., conjugate gradient squared, quasi-minimal residual, and biconjugate gradient stabilized (Bi-CGSTAB)] iterative techniques are applied to the solution of electromagnetic wave scattering from dielectric random rough surfaces with arbitrary complex dielectric constants. The convergence issues as well as the efficiency and accuracy of all the approaches considered in this paper are investigated by comparing obtained scattering (in the form of normalized radar cross section) and surface field values with the numerically exact solution, computed by employing the conventional method of moments. It has been observed that similar to perfectly and imperfectly conducting rough surface cases, the stationary iterative FBM converges faster when applied to geometries yielding best conditioned systems but exhibits convergence difficulties for general geometries due to its inherit limitations. However, nonstationary techniques are, in general, more robust when applied to arbitrarily general dielectric random rough surfaces, which yield more ill-conditioned systems. Therefore, they might prove to be more suitable for general scattering problems. Besides, as opposed to the perfectly and imperfectly conducting rough surface cases, the Bi-CGSTAB method and FBM show two interesting behaviors for dielectric rough surface profiles: 1) FBM generally converges for reentrant surfaces when the vertical polarization is considered and 2) the Bi-CGSTAB method has a peculiar convergence problem for horizontal polarization. Unlike the other nonstationary iterative techniques used in this paper, where a Jacobi preconditioner is used, convergent results are obtained by using a block-diagonal preconditioner. © 2006 IEEE

Analysis of finite arrays of circumferentially oriented printed dipoles on electrically large cylinders

An efficient and accurate hybrid method of moments (MoM)/Green's function technique in the spatial domain is developed for the rigorous analysis of large, finite phased arrays of circumferentially oriented printed dipoles on electrically large, dielectric-coated, circular cylinders. Basic performance metrics (in the form of array current distribution, active reflection coefficient, far-field patterns, and so forth) of several arrays have been obtained and compared with similar printed arrays on grounded planar substrates. Certain discrepancies have been observed and discussed. © 2004 Wiley Periodicals, Inc

SIW-based interdigital bandpass filter with harmonic suppression

A novel configuration of interdigital bandpass filter based on the substrate integrated waveguide (SIW) technology is proposed. In addition to the interdigital resonators in SIW that determine the main response/characteristics of the filter, narrowing the width of the SIW at the center of the filter and additional vias at its input and output parts act as two additional control mechanisms to achieve the desired filter response. Moreover, dumbbells are etched to the ground side of the microstrip feeding sections at both ends of the filter to improve its harmonic suppression. A prototype filter is designed and fabricated for verification. The measured results are in good agreement with the simulations, and the filter exhibits very good harmonic suppression. © 2015 Wiley Periodicals, Inc

Integral equation based method for the fast analysis of irregularly contoured large finite phased arrays

A fast and accurate integral equation based hybrid method that can investigate electrically large, arbitrarily contoured finite planar arrays of printed elements is developed. The method is a hybridization of the Galerkin type method of moments (MoM) and generalized forward backward method (GFBM) with the grounded dielectric slab's Green's function; and the acceleration of the resultant hybrid method by a discrete Fourier transform (DFT) based acceleration algorithm. Numerical results in the form of array current distribution are given for arbitrarily contoured as well as thinned arrays of probe fed microstrip patches where current on each element expanded by more than one subsectional basis function

Investigation of metamaterial coated conducting cylinders for achieving transparency and maximizing radar cross section

Recently, reducing the radar cross sections (RCS) of various structures to achieve transparency and obtaining resonant structures aimed at increasing the electromagnetic intensities, stored or radiated power levels have been investigated. The transparency and resonance (RCS maximization) conditions investigated in are mainly attributed to pairing of "conjugate" materials: materials which have opposite signs of constitutive parameters [e.g., double-positive (DPS) and double- negative (DNG) or epsilon-negative (ENG) and mu-negative (MNG)]. In the present work, we extend the transparency and resonance conditions for cylindrical structures when the core cylinder is particularly perfect electric conductor (PEC). The appropriate constitutive parameters of such metamaterials are investigated for both TE and TM polarizations. For TE polarization it is found out that, the metamaterial coating permittivity has to be in the 0 < epsivc < epsiv0 interval to achieve transparency, and in the -epsiv0 < epsivc < 0 interval to achieve RCS maximization. As in the case of "conjugate" pairing, transparency and resonance are found to be heavily dependent on the ratio of core-coating radii, instead of the total size of the cylindrical structure. However, unlike the "conjugate" pairing cases, replacing epsiv by mu (and vice versa) does not lead to the same conclusions for TM polarization unless the PEC cylinder is replaced by a perfect magnetic conductor (PMC) cylinder. Yet, RCS maximization can also be achieved in the TM polarization case when coating permeability muc < 0, whereas transparency requires large \muc\ for this polarization. Numerical results, which demonstrate the transparency and RCS maximization phenomena, are given in the form of normalized monostatic and bistatic echo widths

Paraxial space-domain formulation for surface fields on large dielectric coated circular cylinders

A space-domain represention for the surface fields excited by an elementary current source was discussed. Green's function was used and an approximation was made using Fourier series (FS), where FS coefficients were calculated using numerical integration. The integrals were evaluated numerically along the real axis using a Gausian quadrature algorithm. However, the developed scheme yielded field expressions that remain valid along the paraxial region for arbitraily small and large separation between observation and source points

Fast acceleration algorithm based on DFT expansion for the iterative MoM analysis of electromagnetic radiation/scattering from two-dimensional large phased arrays

An acceleration algorithm based on Discrete Fourier Transform (DFT) is developed to reduce the computational complexity and memory storages of iterative methods of moment (IMoM) solution to O(Ntot), where Ntot is the total number of elements in the array. As such, numerical results for free-standing dipoles obtained using IMoM-DFT approach are presented and compared with the conventional MoM solution