A reflection‐only method for characterizing PEC‐backed anisotropic materials using waveguide higher order modes

This paper presents a new reflection‐only set‐up for characterizing the properties of an anisotropic PEC‐backed materials. Albeit, the reflection‐only methods are established long ago, they are not elaborated appropriately for retrieving industrial anisotropic materials. In spite of other researches, this method is capable to determine tensors of both permittivity and permeability of an anisotropic PEC‐backed material. In contrast to similar researches, this method is mathematically simple and easy to implement. Tensors of epsilon and mu of PEC‐backed sample are characterized by rotating sample and measuring reflection coefficient in various configuration. Not measuring the transmission, in order to provide enough equations, the higher order mode of the waveguide is employed. A three‐port probe is designed for this goal and optimized to excite the TE₁₀ and TE₂₀ modes simultaneously. Good agreement of retrieved parameters from experimental measurements with those of actual ones shows the reliability of this set‐up for characterization of PEC‐backed anisotropic composites.     

A new FDTD scheme analysis for the characteristics of the magnetic‐anisotropic EBG structure

In this article, the new grid finite‐difference time‐domain (NG‐FDTD) method is applied to calculate the dispersion curves of electromagnetic band‐gap structures, and the dispersion characteristics of three magnetic‐anisotropic medium EBG structure are obtained using the NG‐FDTD method. According to these results, we can conclude that the EBG structure of a magnetic‐anisotropic medium, in which the permeability of nondiagonal elements is real, has a much larger band‐stop than that of isotropic EBG. Other magnetic‐anisotropic EBG structures can also increase the first band‐stop. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.     

Glyphs for Asymmetric Second‐Order 2D Tensors

Tensors model a wide range of physical phenomena. While symmetric tensors are sufficient for some applications (such as diffusion), asymmetric tensors are required, for example, to describe differential properties of fluid flow. Glyphs permit inspecting individual tensor values, but existing tensor glyphs are fully defined only for symmetric tensors. We propose a glyph to visualize asymmetric second‐order two‐dimensional tensors. The glyph includes visual encoding for physically significant attributes of the tensor, including rotation, anisotropic stretching, and isotropic dilation. Our glyph design conserves the symmetry and continuity properties of the underlying tensor, in that transformations of a tensor (such as rotation or negation) correspond to analogous transformations of the glyph. We show results with synthetic data from computational fluid dynamics.     

Electromagnetic scattering by arbitrarily shaped stratified anisotropic media using the equivalent dipole moment method

The equivalent dipole moment method, which was used to model the isotropic media, is extended and applied to the analysis of the electromagnetic scattering characteristics of arbitrarily shaped multilayer electric anisotropic media in this work. The initial motivation to put forward this method is based on the intrinsic physical properties of the electric anisotropic media whose constitutive parameter permittivity is a tensor matrix that can be modeled as equivalent electric dipole moment. This method employs the method of moments to solve the electric field volume integral equation (VIE) formulated by discretizing the scattering body into tetrahedral volume elements, in which the electrical parameters are assumed constant in each element. Then the VIE is solved directly to obtain the scattered field. Numerical results are given to validate the accuracy and efficiency of this method. © 2010 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

Non‐destructive recognition of dielectric coated conducting objects by using WD type time–frequency transformation and PCA‐based fusion

This article demonstrates the applications of a non‐destructive electromagnetic target recognition method, called Wigner distribution‐principal component analysis (WD‐PCA) method, to dielectric coated conducting spheres. These spheres are chosen to be highly similar having the same overall size but slightly different permittivity and thickness values in coating layers. Four different classifiers are simulated by using the WD‐PCA method for varying sizes of object libraries under different noise conditions. High correct decision rates are demonstrated even for challenging classifier libraries containing a large number of coated conductors while the method is also shown to be highly robust against noise both in design and test stages. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Both transversal negative permeability and backward‐wave propagation in X‐Band waveguide with double‐side SRR metamaterials

In this article X‐band rectangular waveguides partially filled with the double‐side single ring resonator (DSRR) array are investigated for miniaturization, stop‐band, and multi‐band filters applications. Several rectangular waveguides loaded with the DSRR array in 2–10 GHz frequency band have been studied and optimized. We observe both the transversal negative permeability presented above the cutoff frequency and the backward‐wave located below the cutoff frequency with the DSRR array in X‐band waveguide. Both simulation and measurement results of DSRR array are with good agreement. The DSRR array provides better performance of the transversal negative permeability and the backward‐wave than the split‐ring resonator array. The physical explanation of backward‐wave is presented. The power loss distributions are clearly presented for the negative permeability attenuation and the backward‐wave propagation. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:240–246, 2016.     

Iterative solution of scattering by surface‐treated targets

An efficient iterative technique has been developed to compute the scattering behavior of the radar cross section of a conducting circular cylinder coated by a dielectric loaded with periodic metallic strips. This method is based on the concept of waves. It consists of establishing a relationship between electromagnetic fields and the incident‐reflected waves. The numerical results for a number of scattering geometries are given to illustrate the efficiency and versatility of the present approach. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 206–214, 2003.     

Scattering characteristics of an anisotropic medium sphere

Based on the invariable displacement current of anisotropic media, a theoretical model for electromagnetic reconstructing anisotropic media and a basic method for selecting electromagnetic field are proposed. Taking the gypsum crystal as an example, the analytical solution of bi‐axial medium scattering is presented by using the spherical vector wave function of electromagnetic field. The electromagnetic wave scattering of the anisotropic medium spheres are simulated in radiation of electromagnetic waves of different frequency. The electromagnetic analysis of the simulation results shows that the electromagnetic mechanism is consistent with the results of relevant literature. When the anisotropic medium degenerates to the isotropic medium, the results obtained by the model are completely consistent with those obtained by Mie theory.     

A triangular MIMO array antenna with a double negative metamaterial superstrate to enhance bandwidth and gain

Multiple‐input‐multiple‐output (MIMO) array antenna integrated with the double negative metamaterial superstrate is presented. The triangular metamaterial unit cell is designed by combining two triangular elements positioned in complementary on the same plane at different sizes. Such design with more gaps is used to excite rooms for more capacitance effects to shift the resonance frequency thus enlarging the bandwidth of the MIMO antenna. The unit cell is arranged in 7 × 7 periodic array created a superstrate metamaterial plane where the C_stray exists in parallel between the two consecutive cells. It is found that the existence of C_stray and gaps for each unit cells significantly influenced the bandwidth of the MIMO antenna. The higher value of the capacitance will lead to the negativity of permittivity. The superstrate plane is then located on top of the 4 × 2 MIMO with a gap of 5 mm. The integration resulted in improving the bandwidth to 12.45% (5.65‐6.4GHz) compared to only 3.49% bandwidth (5.91‐6.12GHz) of the MIMO antenna itself. Moreover, the negative permeability characteristic is created by a strong magnetic field between the complementary unit cells to have 14.05‐dBi peak gain. Besides that, the proposed antenna managed to minimize the mutual coupling and improve the mean effective gain, envelope correlation coefficient, and multiplexing efficiency.     

Inverse scattering of dielectric cylindrical target using dynamic differential evolution and self‐adaptive dynamic differential evolution

The inverse problem under consideration is to reconstruct the characteristic of scatterer from the scattering E field. Dynamic differential evolution (DDE) and self‐adaptive dynamic differential evolution (SADDE) are stochastic‐type optimization approach that aims to minimize a cost function between measurements and computer‐simulated data. These algorithms are capable of retrieving the location, shape, and permittivity of the dielectric cylinder in a slab medium made of lossless materials. The finite‐difference time‐domain (FDTD) is employed for the analysis of the forward scattering. The comparison is carried out under the same conditions of initial population of candidate solutions and number of iterations. Numerical results indicate that SADDE outperforms the DDE a little in terms of reconstruction accuracy. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Improved approach using symmetric microstrip sensor for accurate measurement of complex permittivity

A novel symmetrical planar sensor based on splitter/combiner microstrip sections with a pair of interdigital capacitors (IDCs) and 2 complementary split ring resonators (CSRRs) structure is presented. A high sensitivity area to the dielectric property of surrounding materials has been established by locating IDC unit on the top‐plane while a rectangular CSRR structure etched out on the ground plane. The symmetrical circuit makes the sensitivity further improved to the introduction of sample to be tested because of the destruction of the symmetry. The complex permittivity of the dielectric samples has been evaluated from the actual experimental scattering parameters by using back propagation neural network techniques. The proposed methodology is validated by fabricating the sensor on Rogers5880 substrate and testing various standard dielectric samples viz. PVC, Glass epoxy, FR4, and Glass in C‐band. The measured complex permittivity of the test specimens is found to be in close agreement with their values available in literature with maximum error of <5%.     

q-Families of CVD(MPFA) Schemes on General Elements: Numerical Convergence and the Maximum Principle

In this paper, families of flux-continuous, locally conservative, finite-volume schemes are presented for solving the general geometry-permeability tensor pressure equation on structured and unstructured grids in two and three dimensions. The schemes are applicable to the general tensor pressure equation with discontinuous coefficients and remove the O(1) errors introduced by standard reservoir simulation (two-point flux) schemes when applied to full anisotropic permeability tensor flow approximation (Edwards and Rogers in Multigrids Methods, vol. 1, pp. 190–200, 1993; Edwards and Rogers in Proceedings: 4th European Conference on the Mathematics of Oil Recovery, 1994; Edwards and Rogers in Comput. Geom. 2:259–290, 1998). Full tensors arise when the local orientation of the grid is non-aligned with the principal axes of the tensor field. Full tensors may also arise when fine scale permeability distributions are upscaled to obtain gridblock-scale permeability distributions. In general full tensors arise when using any structured or unstructured grid type that departs from K-orthogonality.     

A hexa‐band dual‐sense circularly polarized antenna for WLAN/Wi‐MAX/SDARS and C‐band applications

In this article, a compact single fed hexa‐band circularly polarized (CP) monopole antenna using split ring resonators (SRRs) on the partial ground plane is designed and experimentally investigated. The loaded SRR elements generate multiple circularly polarized bands along with a reduction in antenna size. The multiband can be controlled by changing the configuration of SRRs and their position on the ground plane without altering the monopole radiator. To illustrate the CP mechanism and multiband operation of the proposed configuration, the surface current density has been studied. The antenna is fabricated on RT Duroid 5880 substrate of permittivity 2.2 with a total size of 47 × 40 × 1.57 mm³. Compared with the existing antenna designs, the proposed structure is compact and demonstrates improved multiband performance with circular polarization.     

Novel ultra‐compact two‐dimensional waveguide‐based metasurface for electromagnetic coupling reduction of microstrip antenna array

A novel ultracompact two‐dimensional (2D) waveguide‐based metasurface is proposed herein and applied for the first time to reduce mutual coupling in antenna array for multiple‐input multiple‐output applications. The unit cell of the proposed 2D waveguide‐based metasurface is ultracompact (8.6 mm × 4.8 mm, equal to λ₀/14.2 × λ₀/25.5) mainly due to the symmetrical spiral lines etched on the ground. The metasurface exhibits a bandgap with two transmission zeros attributing to the negative permeability in the vicinity of magnetic resonance and the negative permittivity in the vicinity of electric resonance. Taking advantage of these two features, a microstrip antenna array is then designed, fabricated, and measured by embedding an 8 × 1 array of the well‐engineered 2D waveguide‐based metasurface elements between two closely spaced (9.2 mm, equal to λ₀/13.3) H‐plane coupled rectangular patches. There is good agreement between the simulated and measured results, indicating that the metasurface effectively reduces antenna mutual coupling by more than 11.18 dB and improves forward gain. The proposed compact structure has one of the highest reported decoupling efficiencies among similar periodic structures with comparable dimensions. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:789–794, 2015.     

3D‐printed cylindrical Luneburg lens antenna for millimeter‐wave applications

A 3D‐printed cylindrical Luneburg lens antenna working at 26 GHz is proposed in this article. The antenna consists of a feeding waveguide, a 3D‐printed cylinder, and a pair of printed metal grids which are stuck on the side faces of the cylinder. 3D‐printed structure ensures the convenience for processing and structural integrity of the Luneburg lens. Hole drilling technology is utilized for the design of the cylindrical lens. In the E‐plane, conversion of spherical waves into planar waves is achieved based on the gradient refractive index which is realized by the gradient equivalent relative dielectric constant. The main part of the lens contains a hole drilling region to realize the desired equivalent permittivity from 1.23 to 2, while another gradual‐thickness region realize the permittivity ranges from 1.23 to 1. H‐probe method is utilized for the optimization of the gradual‐thickness region in this article. And for the H‐plane, with the grids, H‐field distribution is optimized compared with the Luneburg lens antenna without the loading grids. Thus, the side lobe level (SLL) in H‐plane could be reduced. Meanwhile, a narrower half power beamwidth (HPBW) in H‐plane will be obtained due to the metal grids. Experiment results illustrate the feasibility and validity of the proposed 3D‐printed cylindrical Luneburg lens antenna.     

A new method of establishing the scale model of target

In this article, a method of establishing a scaled model for a full‐size target composed both of medium and conductive material is proposed. The scattered characteristics of the dielectric sphere, conductor sphere, and its coated medium sphere etc. are estimated with this proposed method. All the estimated results by the scaled model have a good agreement with the accurate solutions of the full‐size target. Simulation shows that the effectiveness of the method used to the target of lossy medium is better than that of the principle of similitude used to the target. The method has the advantage of being free from the operating frequency, the target permittivity, and the target permeability.     

A dual‐band single‐layer circularly polarized reflectarray composed by elements having variable rotation angles

A dual‐band single‐layer circularly polarized reflectarray composed by elements with variable rotation angles is presented in this article. Orthogonal dipole elements etched on the substrate are designed to operate at 10 and 13.5 GHz, respectively. By introduction of element rotation technique, the proposed reflectarray has a good isolation between the two operating bands and obtains excellent performance of circular polarization compared with the conventional design. All the simulated and measured results demonstrate the advantages of the proposed reflectarray. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:39–47, 2015.     

A novel design of dual broadband,single‐layer circularly polarized reflectarray

A single‐layer dual‐band circularly polarized reflectarray antenna composed by split double rings for higher band and cross dipoles for lower band is presented in this letter. By adjusting the length of the cross dipole and rotation angle of split double ring, two classes of elements achieve the required reflection phase. Then, a reflectarray with these two types of elements is fabricated and tested. It is worth noting that the designed reflectarray obtains broadband performance at both bands. Measurement results demonstrate that the fabricated reflectarray obtains a 1 dB gain bandwidth of more than 14% for both bands and a 3 dB axial ratio bandwidth of 22.9% for the lower band and 40% for the upper band. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:364–369, 2015.     

The study of relative phase-permeability functions for anisotropic media

Properties of relative phase-permeability functions for different characteristic configurations of a medium with anisotropic filtration properties are studied using the numerical-analytical method. The anisotropy may be related to fracturing created, e.g., as a result of a brittle rupture. Correlations between tensors of the phase and absolute permeabilities are analyzed on the assumption of capillary equilibrium. Examples of relative phase-permeability functions are obtained for media with orthotropic and monoclinic symmetry of filtration properties. The influence of the property of connectivity on the found functions is shown, and the dependence of the position of the principal axes of the phase-permeability tensor on saturation is also investigated. Thereby, the misalignment of the tensors of the phase and absolute permeabilities is shown. The results qualitatively agree with the experimental data.     

The improved technique of electric and magnetic parameters measurements of powdered materials

This paper presents the measurement technique that allows to determine the relative permittivity and permeability of powdered materials. Measurements are realized in a coaxial transmission line which guarantees the broad band frequency characterization. Calculations utilize the scattering matrix parameters of the two-port formed by the sample of powdered material supported by two dielectric walls. The proposed measurement procedure is demonstrated in the example of ferrite powder - Yiitrium Garnet YIG class ferrite for which the relative permittivity (??^′,??^″) and permeability (??^′,??^″) are determined in the frequency range of 200-1200 MHz.