This paper introduces a novel technique for efficiently combining implicit space mapping (ISM) with method of moments (MoM) for the synthesis of antenna arrays and explores several example applications of the ISM approach. The antenna arrays geometric parameters are extracted to be optimized by ISM, and a fitness function is evaluated by MoM simulations to represent the performance of each candidate design. A coarse-mesh MoM and a fine-mesh MoM solver are used for the coarse and the fine models, respectively. To achieve the parameter extraction, the auxiliary parameter is selected and the approximation between the two models is accomplished by particle swarm optimization (PSO). The results show that the running time of the ISM algorithm is 2~3 times faster than that of other optimization algorithms (e.g. PSO).
The goal of this work is to look for a technique of optimization making it possible to improve the optical performances of materials with photonic band gap by reducing of the Kiessig fringes. The techniques of apodization and smoothing were used. The combination of these two techniques made it possible to reduce the Kiessig fringes up to 95%.
A fundamental relation between the cross sectional confinement of an arbitrary mode of a general waveguide and its propagation length is found. It is shown that due to material loss of the waveguide, the propagation length shrinks as the confinement of the mode increases. Normalized second central moment of magnetic energy density in the cross section plane of the waveguide is used as a measure of mode size and it is found that for a given mode size, there is a limit for the waveguide propagation length. This limit depends solely on permittivity of the waveguide material and its surrounding medium. As an application, this result provides a lower bound for propagation loss in subwavelength optical confinement in plasmonic waveguides which are of special interest for their nano-meter mode dimensions.
Phased array antennas are a viable solution to a number of problems related to radio communications applications. In this work, the multi-objective stochastic MOPSO algorithm is used to optimize the spatial configuration of a symmetric phased linear array. The defined optimization goals were the suppression of the radiation pattern sidelobes at a specified maximum scan angle as well as the minimization of the induced voltages correlation at the receiver frontend in order to maximize diversity performance. Non-linear constraints were enforced on the solution set, related to the multi-antenna system aperture efficiency and related to the mismatching when the array is scanned. The obtained optimized configurations for an array composed of 16 dipoles resulted in reducing the sidelobes up to 2.5 dB, when scanned 60° away from broadside, compared to a linear array with elements spaced λ/2 apart. Furthermore, the optimized dipole arrays were characterized by a maximum element correlation of 0.12 to 0.43. The performance of obtained configurations was shown to be tolerant to feed phase variations that appear in realistic implementations. The arrays were analyzed employing the Method of Moments (MoM).
Extinction and backscattering from thin curved fibers of finite conductivity are computed by solving the Pocklington integro-differential equation using the Moment Method with point matching scheme. For simplicity of interpretation these computations were performed at long wavelengths, in the Drude domain. The effect of the degree of curvature on the cross sections is examined for high and low fiber conductivities, and for two incident geometries: normal and parallel to the plane of the curved fiber. The computations show a narrowing and decreasing cross sections with increased fiber curvature for both low and high conductivities. The normal geometry produces larger cross sections than the parallel case.
A method for modeling and designing of coupled resonators photonic crystal (PC) filters for wavelength division multiplexing (WDM) systems is presented. This proposed method is based on coupling coefficients of intercoupled resonators and the external quality factors of the input and output resonators based on the circuit approach. A general formulation for extracting the two types of parameters from the physical structure of the PC filters is given. At last, we redesign a third-order Chebyshev filter which has a center frequency of 193.55 THz, a flat bandwidth of 50GHz, and ripples of 0.1 dB in the pass-band. The filter's structure derived from the proposed method is more compact.
The fields inside a rectangular waveguide with an internal coating of chiral nihility metamaterial are determined. These fields are then fractionalized utilizing the fractional curl operator to find the fields for the intermediate geometries which are also termed as the fractional order geometries. It is noted that no electric field exists inside the chiral nihility coating backed by perfect electric conductor (PEC) surface. The fractional order geometries are related through the principle of duality. The behavior of the fields with respect to the fractional parameter, α is analyzed.
A rigorous modal theory of conical diffraction from curved strip gratings is presented. In this approach, the C-method with adaptive spatial resolution is used in conjunction with the combined boundary conditions. The method is successfully validated by comparison with a case where the solution can also be obtained in the Cartesian coordinate system.
The broadcast nature of the wireless medium makes the communication over this medium vulnerable to eavesdropping. In this paper, we propose a directional sensitive modulation signal transmitted by Monopulse Cassegrain antenna for physical (PHY) layer security transmission. The main idea is that the sum beam transmit communication signal, simultaneously, and two difference beams transmit artificial noise to guarantee secure transmission of the sum beam. The eavesdropper's channel is degraded by artificial noise, but the desired receiver's channel does not affect because of the spatial orthogonality between the sum beam and two difference beams. In this way, the desired receiver can demodulate the communication signal while the eavesdroppers learn almost nothing about the information from its observations. A closed-form expression of the secrecy capacity is also derived for this practical transmit scheme from the viewpoint of information theoretic. Finally, simulation results show that the proposed signal can significantly improve the performance of secure wireless communications.
The performance assessment of maritime microwave communications and radar systems requires accounting simultaneously for the non-homogeneous propagation medium over the sea and the rough sea surface scattering. The tropospheric ducting, specific for over water propagation, is one of the most difficult to treat propagation mechanisms. The proposed work combines a recently published in the literature phase correction, responsible for the shadowing effects, to the Ament rough surface reflection coefficient and the Parabolic Equation method (as implemented in the Advanced Propagation Model) to simulate the microwave propagation over the sea under evaporation duct conditions. Propagation factor and path loss results calculated for phase-corrected Ament, non-phase-corrected Ament and the other widely used, Miller-Brown, rough surface reflection coefficient are compared and discussed. The main effects from the accounting of the shadowing result in the shift of the interference minima and maxima of the propagation factor, changes in the path loss pattern and destruction of the trapping property of the duct.
The time domain modeling and simulation of electromagnetic (EM) waves interaction with nanodevices, at high spatial and time resolution, requires high computational power. For the first time, in this paper we present an effective implementation of the Hertzian Potential Formulation (HPF) on the Graphics Processing Units (GPUs), through the NVIDIA's CUDA (Compute Unified Device Architecture) programming model. It accelerates the nanodevice EM simulations at nanometer scale harnessing the massive parallelism of the GPU based systems. This study is useful for similar electromagnetic codes including the Finite Difference approaches. The results demonstrate that this GPU tool outperforms the CPU based HPF implementation, reaching a speedup from 30× to 70×.
This paper presents an extension of the recently-developed efficient semi-analytical method, namely scaled boundary finite element method (SBFEM) to analyze quadruple corner-cut ridged circular waveguide. Owing to its symmetry, only a quarter of its cross-section needs to be considered. The entire computational domain is divided into several sub-domains. Only the boundaries of each sub-domain are discretized with line elements leading to great flexibility in mesh generation, and a variational approach is used to derive the scaled boundary finite element equations. SBFEM solution converges in the finite element sense in the circumferential direction, and more significantly, is analytical in the radial direction. Consequently, singularities around re-entrant corners can be represented exactly and automatically. By introducing the "dynamic stiffness" of waveguide, using the continued fraction solution and introducing auxiliary variables, a generalized eigenvalue equation with respect to cutoff wave number is obtained without introducing an internal mesh. Numerical results illustrate the accuracy and efficiency of the method with very few elements and much less consumed time. Influences of corner-cut ridge dimensions on the cutoff wave numbers of modes are examined in detail. The single mode bandwidth of the waveguide is also discussed. Therefore, these results provide an extension to the existing design data for ridge waveguide and are considered helpful in practical applications.
A simple and efficient joint algorithm of finite difference time domain (FDTD) and periodic boundary condition (PBC), called as the direct spectral FDTD method, has been investigated to study three-dimensional (3D) periodic structures with oblique incidence, where both the azimuth angle φ and the elevation angle θ are varying. The number of sampling points for the horizontal wave number can be determined by using an adaptive approach. As numerical results, the transmission and reflection coefficients from split-ring resonators (SRRs) and a dielectric grating slab are computed to validate the accuracy and efficiency of the direct spectral FDTD method. The computed results are in good agreement to the published ones obtained by other methods.
Finite edge geometrical theory of diffraction (FEGTD) approach is a new and latest improvement in GTD technique. This FEGTD technique is applied to the H-plane and E-plane horn radiation problems with spherical source excitation. The horn patterns obtained with the FEGTD approach are found to be in good agreement with measured results.
Breast cancer detection using Ultra Wideband Radar has been thoroughly investigated over the last decade. This breast imaging modality is based on the dielectric properties of normal and cancerous breast tissue at microwave frequencies. However, the dielectric properties of benign and malignant tumours are very similar, so tumour classification based on dielectric properties alone is not feasible. Therefore, classification methods based on the Radar Target Signature of tumours need to be further developed to classify tumours as either benign or malignant. Several studies have addressed the issue of tumour classification based on the size, shape and surface texture of the tumour. In general, these studies examined the performance of classification algorithms in primarily dielectrically homogeneous breast models. These relatively simplistic models do not provide a realistic test platform for the evaluation of tumour classification algorithms. This paper examines the classification of tumours under realistic dielectrically heterogeneous conditions. Four different heterogeneous scenarios are considered, with varying levels of heterogeneity and complexity. In this paper, the performance and robustness of tumour classification algorithms under these realistic conditions are examined and discussed.
This paper investigate the near-field interaction between the coupling slot and the radiating ones in a dielectric-covered waveguide slot array environment. This interaction can strongly affect the array aperture distribution and input match, mainly when each radiating guide contains few slots or the slot offsets are small. We propose a full-wave Method of Moments approach, taking also into account the waveguide wall thickness, to evaluate this interaction. The use of entire domain basis functions allows to get a small and well-conditioned linear system. The results presented in this paper show that the coupling due to high-order modes in the region of the junction can significantly modify the radiating slot voltage, mainly when the offset is small, and also the array input match, though to a lesser extent.
The scattering analysis from metallic Grid FSS consisting of rectangular perforations on a thick metallic screen illuminated by an oblique incident plane wave is presented. The grid structure is analyzed using Scale Changing Technique (SCT) which is based on the partition of the grid-plane into planar sub-domains defined at various scalelevels. Electromagnetic interaction between subsequent scales is modeled by mutually independent Scale-Changing Networks and finally the complete structure is simply represented by a cascade of these networks. Very good agreement is obtained between simulation results from SCT and the Finite Element Method (FEM) when computing the reflection/transmission coefficients and electromagnetic field backscattered by thick and finite size frequency selective surfaces. The computation time is significantly reduced when using SCT-based software compared with the FEM simulation tool.
A 3-bit phase array system including phase shifter blocks and antenna elements has been developed on a coplanar waveguide (CPW) using micro electromechanical system (MEMS) technology. The non Euclidean Koch fractal geometry has been used to improve the frequency behavior of the entire system. It is shown that the fractal geometry makes the design to have lower profile, wider frequency bandwidth, and lower mutual coupling effects. It also decreases the actuation voltage of the MEMS switch elements. The fabrication process has been fully described and the measured values regarding every single block is presented.
In this paper, for the very first time, a general algorithm for designing rectangular microstrip patch antenna, partially loaded with SNG (Single Negative) (MNG (µ Negative) and ENG (ε Negative)) metamaterial has been proposed to achieve better radiation performance. Then, applying our proposed algorithm, theoretically we have predicted novel dual band miniaturized rectangular patch antennas (loaded with MNG metamaterial) for two different bands using unconventional interface resonance mode under fundamental TM010 mode. Then we have proposed a complete design of magnetic inclusions, presenting full wave numerical simulations of the structure, which effectively supports the theoretical expected resonant modes as well as satisfactory radiation pattern performance. Prior to our current work, impossibility of sub-wavelength or electrically small rectangular patch antenna has been demonstrated using ENG metamaterial. However, in this paper, we have indicated a direction towards the real-life implementation of possible miniaturized rectangular patch antennas partially loaded with MNG metamaterial. The algorithm proposed in this paper is the key to choose the appropriate material parameter to design all such antennas.
Light concentrating structures with three-dimensional photonic crystals (3D PhCs) for solar cell applications are investigated via simulation. The 3D opal PhCs are suggested as an intermediate layer in the concentrator system for solar cells. It is found that the light absorption is significantly enhanced due to the adding of diffractive effects of PhCs to the concentrator. Three types of PhCs are considered in four scenarios to verify the absorption enhancement by such a light concentrating structure. Our calculations show that the face-centered cubic PhC can create an absorbing efficiency superior to the others under a specified lattice orientation pointing to the sun, which results in an enhancement factor of 1.56 in absorption for the 500--1100 nm spectral range.