Modes of a planar nonlinear-metamaterial waveguide

Modes of a planar dielectric waveguide are investigated. The waveguide is made from a nonlinear metamaterial with a negative permittivity and a negative permeability. The mode wavenumbers and field distributions are calculated for structures with parabolic permittivity and permeability profiles. It is shown that anomalously high field intensities can be observed in such a structure. The dependences of the mode propagation coefficients on the electric field are analyzed for the case of nonlinear media. The effect of nonlinearity saturation is considered.     

Excitation of an electrically thick metamaterial waveguide of a finite length

The problem of diffraction of a cylindrical wave by a plate whose medium has a negative refractive index (a metamaterial) is numerically solved. The near and far fields are investigated for the case when a cylindrical wave source is located near the narrow butt-end of a long plate and when the metamaterial of the plate has various values of the permittivity and permeability. The results obtained are interpreted in terms of the geometric optics. It is shown that a plate made from such a metamaterial can be applied for fabricating antennas with multi- and single-lobe patterns.     

Resonance transformation of the field of a linear source into multipole radiation with the help of a cylindrical metamaterial layer

A hollow circular metamaterial cylinder with a negative permittivity and a negative permeability is considered. The 2D problem of excitation of the cylinder by a filament source is numerically investigated. It is found that, when the relative permittivity and permeability are close to minus unity, high-Q resonances exist in hollow cylinders of an electrically small diameter. It is shown that, when the cylindrical wave source is situated inside the cavity, omnidirectional radiation is transformed at the resonance frequency into multipole radiation with a large number of identical lobes in the pattern. Near- and far-field patterns are calculated. The influence of loss on the resonance characteristics is investigated.     

The dispersion characteristics of metamaterial waveguide modes

The eigenmodes and noneigenmodes of a planar metamaterial dielectric waveguide are investigated. The dispersion dependences and field distributions of the modes are calculated for structures with step and parabolic profiles of the permittivity and permeability. It is shown that the magnetic field can exhibit an anomalously large increase in a waveguide with variable permittivity and permeability profiles. The effect of the nonlinearities of media on the mode propagation coefficients is studied.     

Microstrip Sierpinski fractal carpet for slot antenna with metamaterial loads for dual-band wireless application

The compact microstrip antennas with the dual-band characteristic and reconfigurable qualification have been noticed and investigated in this paper. We have developed the slot microstrip antenna with Sierpinski carpet and Minkowski formations and then the metamaterial loads are placed on this antenna in the slot area. The reflection/transmission method has considered to obtain the permittivity and permeability of the split ring resonator (SRR) as a metamaterial. Finally, we show that by using some junction in the metamaterial layer, we can obtain reconfigurable characteristic. Both antennas have dual-band characteristic where the first antenna has two resonances at 3.2 and 4.5 GHz and in the second antenna by altering the metamaterial layer both resonances are occurring at 3.5 and 5.8 GHz. We show that the antenna has two resonance frequencies that matched with the metamaterial Double Negative (DNG) characteristic. Both antennas are printed on FR-4 also we compared measurement and simulation results together. Aforementioned antennas cover the main wireless, WiMAX and LTE bands with sufficient gain and high efficiency (more than 80% typically) with a bi-directional radiation pattern for the indoor application. Here, the metamaterial is used for controlling the resonances and Sierpinski carpet is developed for matching.     

超介质覆层在偶极子天线上的应用

以研究超介质覆层对天线为目的,基于超介质理论中细导线阵列尺寸与等离子体工作频率关系的数学模型,将一个理想偶极子嵌入到周期性细导线圆阵列构成的超介质覆层中,设计了一种超介质覆层加载的高增益全向天线。该天线辐射特性的仿真结果表明,在1.57~1.65 GHz频段范围内,理想偶极子的增益从2.4 dBi提高到7.7 dBi,并呈现出高收敛性及全向性。所采用的数学模型计算出的理论结果与该天线的仿真结果基本吻合,验证了将该数学模型应用于天线设计的正确性,利于缩短天线开发周期,并对分析细导线阵列的负介电常数、负折射率的产生机理具有一定指导意义,对设计性能更完善的超介质覆层加载的天线提供了理论依据。     

Radar absorbers based on metamaterials

Application of metamaterials for creation of new types of radar absorbers (RAs) is investigated. Typical frequency dependences of the permittivity and permeability of composites fabricated from various inclusions employed in designing RAs are considered. It is shown that the structures of RAs can contain metamaterials with both positive and negative values of the real parts of permittivity and permeability. An RA having a low reflection coefficient over a wide range of the incidence angles of an electromagnetic wave for both wave polarizations is developed. It is based on a metamaterial with negative values of the permittivity and permeability.     

High-Q resonanaces of surface waves in thin metamaterial cylinders

The 2D problem of excitation of a circular metamaterial cylinder by a filament source is numerically investigated. It is found that, when the relative permittivity and permeability are close to minus unity, high-Q resonances occur in cylinders of an electrically small diameter. Near- and far-field patterns are calculated. It is discovered that, under resonance conditions, a multilobe scattering pattern typical of superdirective antennas is formed. The influence of loss on the resonance characteristics is investigated.     

Low-frequency resonances in hollow metamaterial cylinders

The 2D problem of excitation of a hollow circular metamaterial cylinder by a filament source is analytically and numerically investigated. It is found that, when the relative permittivity and permeability are close to minus unity, high-Q resonances exist in hollow cylinders of an electrically small radius. Near- and far-field patterns are calculated. It is found that, under resonance conditions, a multilobe scattering pattern typical of superdirective antennas is formed. The influence of loss on the resonance characteristics is investigated.     

Investigation of a frequency-selective surface based on a planar mushroom-shaped metamaterial with an electronically tunable stopband

A design of a band-stop frequency-selective surface based on a planar mushroom-shaped metamaterial with an electronically tunable stopband has been proposed and investigated. The results of numerical simulation and experimental measurements of the parameters of a finite section of the metamaterial with mounted varicaps are presented. These results illustrate the shift of the structure stopband occurring simultaneously with a change in the capacitance of the lumped elements. Frequency dependences of the inherent dielectric parameters have been obtained. They indicate the presence of negative values of the effective permittivity and effective permeability of the proposed structure and the presence of the surface impedance that significantly exceeds the free-space characteristic impedance and is frequency-tunable.     

Design of Arbitrarily Controlled Multi-Beam Antennas via Optical Transformation

The design of arbitrarily controlled multi-beam antennas is investigated by using the technique of optical transformation. Based on the optical transformation, cylindrical waves emitted from a line source can be converted to plane waves through a metamaterial layer which has a circular shape in the inner outline and a polygon shape in the outer outline. Hence the line source together with the metamaterial layer constructs a high-performance multi-beam antenna. The number of sidelines and the shape of polygon are used to control the number and directions of beams. Analytical formulas of the permittivity and permeability tensors are presented for the metamaterial layer in the antenna. The designed multi-beam antennas are validated by full-wave simulations using the finite-element method. The proposed multi-beam antennas will be very useful in the intelligent traffic system.      

The effect of subwavelength localization of the electromagnetic field on the surface of a circular metamaterial cylinder

The 2D problem of excitation of a circular metamaterial cylinder by a filamentary source is numerically investigated. It is found that, for the minus one values of the relative permittivity and permeability, the field on the surface of the cylinder concentrates in a region that is located on the illuminated surface of the cylinder and that is small compared to the wavelength.     

Measurement of the effective relative permittivity of unshielded coplanar waveguides

The dependence of the effective relative permittivity of coplanar waveguides is measured as a function of frequency in the frequency range from 3?12 GHz and is compared with the computed values.     

Microstrip Filter Designing by SRR Metamaterial

In this paper planar and compact band stop filter using split ring resonator (SRR) metamaterial is proposed. Band stop type attenuation is presented from L-to X-band. Low insertion loss in the pass band and high attenuation in the stop band can be considered as the advantage of this filter. Filter characteristics of SRR is presented using microstrip line. Here SRR is introduced in the substrate layer of microstrip line. It has been observed that the rejection level of the filter in stop band goes on increasing as we increase the number of SRR in the structure. Size of SRR is much less than the operating wavelength thereby several SRR can be introduced in substrate layer to provide a compact structure with high rejection level in the stop band. The frequency of filtering depends on the dimensions of SRR. The effect of varying the dimensions of SRR on the filtering frequency is also presented in this paper. It has also been observed by Nicolson-Ross-Weir approach that at the filtering frequency, value of relative permeability as well as relative permittivity for this structure is negative. This confirms that this structure behaves as a Left Handed medium.     

Shielding Properties of a Wire-Medium Screen

The shielding performance of a planar metamaterial wire-medium (WM) screen under plane-wave illumination is studied. The screen consists of a finite number of periodic layers of thin conducting cylinders embedded in a dielectric matrix; in the low-frequency limit and for waves with the electric field polarized along the wire direction, such a screen can be modeled as a homogeneous slab with a plasma-like dispersive permittivity. In particular, well below the plasma frequency, the effective relative permittivity is negative and very large in absolute value, giving rise to high values of the shielding effectiveness. A comparison with a conventional planar metal screen is reported, showing how the proposed structure can be designed to be advantageous in terms of low density and weight saving. In order to be effective against arbitrarily polarized waves, the original structure is modified, adding a second WM screen with wires orthogonally oriented with respect to the first one. Numerical results are provided that illustrate the validity of the homogenized model in predicting field levels both near to and far from the screen and show the shielding performance attainable with the proposed metamaterial screen in both single- and double-layer configurations at normal incidence.     

Q-Based Design Equations and Loss Limits for Resonant Metamaterials and Experimental Validation

Practical design parameters of resonant metamaterials, such as loss tangent, are derived in terms of the quality factor Q of the resonant effective medium permeability or permittivity. Through electromagnetic simulations of loop-based resonant particles, it is first shown that the Q of the effective medium response is essentially equal to the Q of an individual resonant particle. This implies that by measuring the Q of a single fabricated metamaterial particle, the effective permeability or permittivity of a meta-material can be estimated simply and accurately without complex simulations, fabrication, or measurements. Experimental validation shows that the frequency-dependent complex permeability analytically estimated from the measured Q of a single fabricated self-resonant loop agrees with the complex permeability extracted from S parameter measurements of a metamaterial slab to better than 20 %. This Q equivalence reduces the design of a metamaterial to meet a given loss constraint to the simpler problem of the design of a resonant particle to meet a specific Q constraint. The Q-based analysis also yields simple analytical expressions for estimating the loss tangent of a planar loop magnetic metamaterial due to ohmic losses. It is shown that tan delta ap 0.001 is a strong lower bound for magnetic loss tangents for frequencies not too far from 1 GHz. The ohmic loss of the metamaterial varies inversely with the electrical size of the metamaterial particle, indicating that there is a loss penalty for reducing the particle size at a fixed frequency.     

The effect of chirality on the existence of backward waves in metamaterials made from resonance planar chiral elements

Artificial media made from lattices of resonance planar chiral elements (RPCEs), such as planar double open rings and plane spirals, are considered. The effect of chirality on the electromagnetic properties of such media is investigated theoretically. It is shown that, when RPCEs are identically oriented, backward waves do not propagate in the medium, although there is a region where permittivity ? and permeability μ are negative simultaneously. However, such a metamaterial exhibits chirality and, hence, the refractive index turns out to be imaginary even when energy dissipation is disregarded. It is found that a medium with the opposite orientation of neighboring RPCEs is nonchiral; in such a medium, the resonance property of ? and μ is retained; the refractive index is real; and backward waves are present at frequencies at which both ? and μ are negative. For these media, it is found that there are regions where the directions of propagation of the wave energy and phase coincide (right-handed passbands), a region where these directions are opposite (left-handed passbands), and regions of evanescent waves.     

Radiation characteristics of coaxial waveguides as a small primary feed

The radiation patterns of coaxial waveguides with a TE11 exciting mode are computed numerically. It is shown that by a proper selection of the coaxial aperture dimensions the symmetry of the copolar patterns can be improved considerably. Coaxial radiators can therefore be designed as a useful small primary feed for paraboloid reflector antennas.     

Effects of leaky-wave propagation in metamaterial grounded slabs excited by a dipole source

In this paper, dispersive propagation and radiation properties of leaky waves on metamaterial grounded slabs are investigated. The proper or improper nature of leaky modes supported by such structures is shown to be related to the metamaterial being /spl epsi/-negative, /spl mu/-negative, or double-negative, and to field polarization, giving rise to backward or forward radiation depending on the frequency range of operation. These spectral features and the associated frequency scan of the radiated beam are illustrated by considering the field excited by a dipole source in the presence of an infinite metamaterial grounded slab. The possibility to achieve nearly equal values for the phase constants of a TE and a TM leaky mode on a large frequency range is shown; this allows us to obtain a conical radiation pattern and, also, for suitable values of the attenuation constants, the radiation of a pencil beam at broadside. Conditions for achieving maximum power density at broadside are derived, when one constitutive parameter is much smaller than the other. In order to illustrate these novel features, numerical results based on experimentally tested dispersion models for permittivity and permeability of the metamaterial media are provided, concerning leaky-wave modal properties and near and far fields excited by a dipole source.     

Experimental evaluation of bend radiation losses in millimetric dielectric waveguide

A crucial parameter in the design of compact dielectric waveguide integrated circuits is the minimum bend radius below which radiation losses become prohibitive. It is shown that, for waveguides with a relative permittivity of 10, values of bend radii down to four guide wavelengths are acceptable.