A fast and simple parameter estimation algorithm, joint azimuth angles, elevation angles and polarization parameters of incident sources for an arbitrary conformal array is proposed. Based on 2-D Discrete Fourier Transform (2-D DFT), the computational complexity can be reduced significantly compared with traditional 2-D space-search MUSIC or polynomial rooting (search-free) methods. The antenna elements can be mounted on arbitrary curved surfaces or platforms. Conformal array characteristics, such as directional radiation patterns of the elements and polarization are taken into consideration. Numerical simulations based on real-world conformal arrays are provided to demonstrate the performance of the proposed method.

Multiwalled carbon nanotubes display dielectric properties similar to those of graphite, which can be calculated using the well known Drude-Lorentz model. However, most computational softwares lack the capacity to directly incorporate this model into the simulations. We present the finite element modeling of optical propagation through periodic arrays of multiwalled carbon nanotubes. The dielectric function of nanotubes was incorporated into the model by using polynomial curve fitting technique. The computational analysis revealed interesting metamaterial filtering effects displayed by the highly dense square lattice arrays of carbon nanotubes, having lattice constants of the order few hundred nanometers. The curve fitting results for the dielectric function can also be used for simulating other interesting optical applications based on nanotube arrays.

A proximity-fed MIMO (multiple-input-multiple-output) antenna with two printed IFAs (inverted-F antennas) and a wideband T-shaped neutralization line is presented. Each element printed IFA is fed by a proximity-fed structure which provides a parameter to control the return loss without effect on the isolation of the two IFAs. The wideband T-shaped neutralization line, which consists of two meandered branches and a rectangular grounded branch, can enhance the isolation of the two IFAs over a wide operation band (2.35-3.75 GHz). The two meandered branches are connected to the two IFAs, respectively, and the rectangular branch is connected to the ground plane. There are two parameters to adjust the isolation without effect on the return loss. Therefore, the operational bandwidth and the isolation of the proposed antenna can be controlled independently. A bandwidth of 46% with VSWR ≤ 2 and isolation ≥ 20 dB from 2.35 to 3.75 GHz is achieved. The MIMO antenna of compact size 40 x 14 mm² is suitable for application in mobile phones. Moreover, the ground plane size can be changed for applying the proposed antenna in different handsets. The results, including S-parameters, radiation pattern, mean effective gain (MEG), radiation efficiency, complex correlation coefficient and the effects of human hand and head, indicate the proposed MIMO antenna can provide spatial and pattern diversity.

The excitation of ion azimuthal surface oscillations with extraordinary polarization by light ion beam is studied analytically. Beam-plasma system consists of a cylindrical metal waveguide filled partially by cold magnetized plasma and light ion flow rotating around the plasma column. Dependencies of the beam instability growth rate on the system parameters (plasma and beam densities, value of the external axial magnetic field, radius of the plasma column, width of the gap between the plasma column and the waveguide wall, absolute value and sign of the azimuthal wave number) are analyzed numerically.

This paper deals with a group velocity dispersion issue and a peak reflectivity issue in a non-uniform fiber Bragg gratings (FBG) due to an arbitrary refractive index profile along the length of grating. The paper shows that by using more complicated refractive index profile one can significantly reduce the group velocity dispersion and side lobes intensity and that in main lobe the bandwidth of reflectivity would also increase substantially due to a complicated refractive index profile. To the authors' knowledge, there has not been any work reported in this direction. Generally, coupled mode theory is used to analyze the uniform fiber Bragg grating (UFBG). The analysis results in two coupled first order ordinary differential equations with constant coefficients for which closed form solutions can be found for appropriate boundary conditions. Most fiber gratings designed for practical applications, however, are non uniform. The main reason for using non uniform grating is that it reduces the side lobes in the reflectivity spectrum. Due to the complexity of analysis, no particular method for an analysis of the non-uniform fiber Bragg grating would be found. The two standard approaches for calculating the reflection and transmission spectra of a non uniform FBG are direct numerical integration of coupled mode equations and piecewise uniform approximation approach. The former is more accurate but computationally intensive. In this paper, piecewise uniform approximation approach is used to study a dispersion characteristic due to an arbitrary refractive index profile. The usefulness in FBG based sensors has been demonstrated.

Scattering of electromagnetic plane wave from an infinitely long circular DB cylinder placed in chiral and chiral nihility metamaterials is studied, and the results are compared with that of scattering from DB cylinder placed in free space. The discussion is further extended by considering coating of DB cylinder with chiral/chiral nihility metamaterial. For DB cylinder placed in unbounded free space/chiral/chiral nihility metamterial, only co-polarized scattered fields are obtained, whereas, for chiral/chiral nihility metamaterial coated case, both co- and cross-polarized scattered fields are noted. Numerical results are presented for different values of chirality parameter.

The total-field/scattered-field (TF/SF) formulation is a popular technique for incorporating sources into electromagnetic models like the finite-difference frequency-domain (FDFD) method. It is versatile and simplifies calculation of waves scattered from a device. In the context of FDFD, the TF/SF formulation involves modifying all of the finite-difference equations that contain field terms from both the TF and SF regions in order to make the terms compatible. While simple in concept, modifying all of the equations for arbitrarily shaped TF/SF regions is tedious and no solution has been offered in the literature to do it in a straightforward manner. This paper presents a simple and efficient technique for implementing the TF/SF formulation that allows the TF/SF regions to be any shape and of arbitrary complexity. Its simplicity and versatility are demonstrated by giving several practical examples including a diffraction grating, a waveguide problem, and a scattering problem with a cylindrical wave source.

In this paper, we present a new model using a Four-dimensional (4D) Element-Oriented physical concepts based on a topological approach in electromagnetism. Its general finite formulation on dual staggered grids reveals a flexible Finite-Difference Time-Domain (FDTD) method with reasonable local approximating functions. This flexible FDTD method is developed without recourse to the traditional Taylor based forms of the individual differential operators. This new formulation generalizes both the standard FDTD (S-FDTD) and the nonstandard FDTD (NS-FDTD) methods. Moreover, it can be used to generate new numerical methods. As proof, we deduce a new nonstandard scheme more accurate than the S-FDTD and the known nonstandard NS-FDTD methods. Through some numerical examples, we validate this proposal, and we show the power and the advantage of this Element-Oriented Model.

In this paper, a tree-shaped power distribution network is designed based on constructal theory for planar EBG structure power plane on PCB, in order to optimize DC performance. Planar EBG structures suppress noise, and the network provides currents to them. This network is composed of hierarchical metal paths. The geometric parameters can be optimized based on the concept of constructal theory. The optimal performance consists of constructing the given area in a sequence of building blocks from the smallest size toward larger sizes hierarchically. In the meantime, a PCB power plane is developed with 2nd order tree-shaped constructal network. Analysis illustrates that EBG power plane with constructal tree shaped network has multifunctions of low voltage drop, current equidistribution and effective noise isolation.

Unidirectional carbon/epoxy composite laminates are highly orthotropic, with their conductivity and permittivity being strongly dependent on the incident angle relative to the fibre orientation. This paper presents a novel frequency selective polarizing subreflector manufactured from unidirectional carbon fibre reinforced polymer (CFRP), placed a certain distance from a conducting ground also made from CFRP laminate. Theoretical analysis, computational simulation, and experimental measurements are conducted to investigate the effects of separation offset, laminate thickness and incident angle on the performance of a reflector manufactured from a unidirectional IM7/977-3 CFRP. The results show that this new reflector reduces the cross polarization at S-band by 13 dB while remaining a good reflector at X-band and the incident angle has minimal effect on the frequency response of the polarizer. The single reflector can support two orthogonal polarized frequencies, unlike traditional wire grid polarizer screens.

In this work, a new method is introduced to model the excitation and loading for antennas composed of arbitrarily shaped conducting surfaces treated by the elctric field integral equation method described by Raw-Wilton-Glisson (RWG). Instead of using a single non-boundary edge to represent a zero-width exciting gap according to the conventional method, the proposed method uses either single or multiple pairs of facing boundary edges to form a real gap of arbitrary shape and width. The new method has many advantages over the conventional (zero-width) source/load representation considering the flexibility in shaping the gap to fit the antenna surface and the accuracy of the obtained results especially for the antenna input impedance and the input current distribution. The new method is described mathematically in detail. Modified basis functions are described for the gap source/load. Numerical results are obtained to investigate the dependence of the antenna input impedance and the current distribution along the gap length on the gap width, the geometrical shape of the gap and the surface segmentation resolution along the gap length.

For dielectric periodic gratings, we propose the combination of a spectral-domain volume integral equation and Fourier factorization rules to address the Gibbs phenomenon caused by jumps in both the fields and the permittivity. From a theoretical point of view we discuss two ways to overcome the computational complexity caused by the inverse rule by changing the fundamental unknowns of the underlying electromagnetic problem. The resulting numerical system is solved iteratively and the corresponding matrix-vector product has an O(NMlogM) complexity, where M is the number of Fourier modes and N is the number of sample points in the longitudinal direction.

Reconfigurable antenna arrays are often capable of radiating multiple patterns by modifying the excitation phases of the elements. In this paper a method based on Firefly Algorithm (FA) has been proposed to obtain dual radiation pattern from a concentric ring array of isotropic elements, by finding out two different combinations of states for the switches, which are assumed to be connected with the rings of the array, along with optimum set of 4-bit radial amplitude and 5-bit radial phase distributions of the array elements for the specific switch combinations. The optimum excitations of the array elements in terms of discrete amplitudes and discrete phase, and the different switch combinations for the specific excitations are computed using Firefly Algorithm. To illustrate the effectiveness of Firefly Algorithm, the two beam pairs have been computed by the same procedure from the same array, using Particle Swarm Optimization (PSO) algorithm, without changing their design criteria. Results clearly show the superiority of the Firefly Algorithm over Particle Swarm Optimization to handle the proposed problem.

This paper presents the design of a crossed oval-ring microstrip slot antenna to achieve triple-frequency operation for WLAN/WiMAX applications. The proposed antenna is composed of a rectangular microstrip feed line and a ground plane on which three crossed oval-ring slots are etched. The three crossed slot loops finally excite three resonant modes and the resonant frequencies of the proposed antenna are mainly controlled by the dimensions and locations of the slot loops. The antenna prototype is fabricated and the characteristics are experimentally verified. The measured impedance bandwidths for triple operating bands can reach 840/670/940 MHz with return losses larger than 10 dB, which is enough for WLAN/WiMAX communication. In addition, good radiation characteristics with moderate peak gains are obtained and the measured and simulated results show a good agreement.

Multi-band microwave filters are important for multifunctional and miniaturization requirement of portable communication equipment. In this paper, tri-section split ring stepped-impedance resonator is analyzed, and new compact dual-band and tri-band bandpass filters are proposed by using split ring stepped-impedance resonators, and the designs are demonstrated by measurement. The new dual-band filters operate at about 2.4 and 5.5 GHz which meet IEEE 802.11 application requirements, and the new tri-band filters operate at about 2.4-2.6, 3.3-3.6 and 5.2-5.6 GHz, and filter sizes are greatly reduced compared with relative reports. The designed filters have advantages of compact and miniature structures, low passband insertion losses and good frequency selectivity, all these have prospect to be applied in wireless communication systems.

A full-wave analysis for determining the resonant frequency, quality factor and far-zone radiation patterns of a circular disk and annular ring microstrip patches, printed on a uniaxial anisotropic substrate is presented. Green's functions of the structure are determined in Hankel transform domain (HTD) using Hertz potential vectors. Galerkin's method, together with parsval's relation in Hankel transform domain is then applied to compute the resonant frequency and quality factor. The far-zone radiation patterns are expressed in terms of Hankel transforms of the tangential fields on the substrate. Wave equation is solved in cylindrical coordinates for the structure to estimate the basis function. The numerical results show that there are substantial deviations in calculated resonant frequency and quality factor when substrate dielectric anisotropy is considered. Furthermore, significant variations are seen in the radiation patterns of the structures due to substrate anisotropy. The variations of resonant frequency, quality factor and radiation patterns of the structure, with respect to anisotropy ratio of the substrate, for several values of substrate thickness and patch radius are presented.

We establish the exact formulas of multipole expansion in Cartesian coordinates for the most general distribution of charges and currents (including toroidal sources).

In this paper, a differential wavelet-based operator defined on an interval is presented and used in evaluating the electromagnetic field described by Maxwell's curl equations, in time domain. The wavelet operator has been generated by using Daubechies wavelets with boundary functions. A spatial differential scheme has been performed and it has been applied in studying electromagnetic phenomena in a lossless medium. The proposed approach has been successfully tested on a bounded axial-symmetric cylindrical domain.

Magnetic induction tomography (MIT) attempts to image the passive electromagnetic properties (PEP) of an object by measuring the mutual inductances between pairs of coils placed around its periphery. In recent years, there has been an increase in applications of non-contact magnetic induction tomography. When finite element-based reconstruction methods are used, that rely on the inversion of a derivative operator, the large size of the Jacobian matrix poses a challenge since the explicit formulation and storage of the Jacobian matrix could be in general not feasible. This problem is aggravated further in applications for example when the number of coils is increased and in three-dimension. Krylov subspace methods such as conjugate gradient (CG) methods are suitable for such large scale inverse problems. However, these methods require use of the Jacobian matrix, which can be large scale. This paper presents a matrix-free reconstruction method, that addresses the problems of large scale inversion and reduces the computational cost and memory requirements for the reconstruction. The idea behind the matrix-free method is that information about the Jacobian matrix could be available through matrix times vector products so that the creation and storage of big matrices can be avoided. Furthermore the matrix vector multiplications were performed in multiple core fashion so that the computational time can decrease even further. The method was tested for the simulated and experimental data from lab experiments, and substantial benefits in computational times and memory requirements have been observed.

This paper explores the optimal conditions for wave propagation on a microstrip line loaded by a Schottky diode. Investigations are undertaken by studying the transmitted power versus frequency, power and place of injection of a continuous sine high frequency aggression signal. The aggression is injected in a near-field mode. Coupling conditions between the aggression signal in the 500 MHz-3 GHz frequency band and the system is thus determined.