An extremely low profile, compact, and broadband tightly coupled patch array

A tightly coupled patch array (TCPA) is introduced to realize small-size, extremely low profile planar antennas with broadband performance. Past approaches have used frequency selective surfaces (FSSs) as part of the substrate or ground plane (i.e., in passive mode) for also realizing low-profile antennas. In contrast, the proposed TCPA employs an FSS aperture as the radiating structure (i.e., array antenna). A key aspect of the TCPA is the exploitation of differences in FSSs when operating in radiating and passive modes. Tight element coupling and periodic excitation are the keys for achieving broadband operation. In this paper, a small-size, finite array is designed along with a very thin and compact feeding network. The designed TCPA resonated at 2.07 GHz with 5.6% impedance bandwidth (|S 11| \u3c-10 dB), 4.4 dB realized gain (86% efficiency), and 23% gain bandwidth (3 dB drop). Of importance is that the overall aperture dimensions were only γ 0/3 × γ 0/3 and γ 0/42 thick (including feeding network) at the midfrequency of operation. A preliminary TCPA antenna prototype was fabricated and tested. Both simulated and measured data show enhanced bandwidth as compared to the conventional microstrip patch antennas of the same size and thickness. However, as common for such extremely low profile microstrip antennas, the conductivity losses were augmented. Thus, the measured TCPA efficiency (50%) was smaller than computed. Copyright 2012 by the American Geophysical Union

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

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

Determining the effective constitutive parameters of finite periodic structures: photonic crystals and metamaterials

Cataloged from PDF version of article.A novel approach to find the effective electric and A novel approach to find the effective electric and magnetic parameters of finite periodic structures is proposed. The method uses the reflection coefficients at the interface between a homogenous half-space and the periodic structure of different thicknesses. The reflection data are then approximated by complex exponentials, from which one can deduce the wavenumber, and the effective electric and magnetic properties of the equivalent structure by a simple comparison to the geometrical series representation of the generalized reflection from a homogenous slab. Since the effective parameters are for the homogenous equivalent of the periodic structure, the results obtained are expected to be independent of the number of unit cells used in the longitudinal direction. Although the proposed method is quite versatile and applicable to any finite periodic structure, photonic crystals and metamaterials with metallic inclusions have been used to demonstrate the application of the method in this paper. © 2008 IEEE

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

Investigation of planar and conformal printed arrays for MIMO performance analysis

MIMO channel capacity of printed arrays with dipole elements is analyzed. A MIMO channel model based on electric fields is used. The effects of mutual interactions among the array elements through space and surface waves are included into the channel matrix using a full-wave hybrid Method of Moments (MoM)/Green's function technique in the spatial domain. MIMO capacity of printed arrays is then compared with that of free standing thin wire dipole arrays. Results show better performance of printed arrays