A wide analysis of left-handed material (LHM) spheres with different constitutive parameters has been carried out employing different integral-equation formulations based on the Method of Moments. The study is focused on the accuracy assessment of formulations combining normal equations (combined normal formulation, CNF), tangential equations (combined tangential formulation, CTF, and Poggio-Miller-Chang-Harrington-Wu-Tsai formulation, PMCHWT) and both of them (electric and magnetic current combined field integral equation, JMCFIE) when dealing with LHM's. Relevant and informative features as the condition number, the eigenvalues distribution and the iterative response are analyzed. The obtained results show up the suitability of the JMCFIE for this kind of analysis in contrast with the unreliable behavior of the other approaches.

We propose a three-dimensional directional cloak for arbitrarily polarized incoming electromagnetic waves, motivated by the fact that there will be negligible scattering when the direction of impinging wave coincides with the axial direction of a very thin and elongated perfectly electric conducting (PEC) scatterer. The performance of the cloak under different polarizations of incoming waves are numerically investigated. The case in which the direction of incoming wave is perturbed off the ideal direction is also quantitatively studied. Numerical simulations show that the directional cloaking device is able to tolerate a large range of tilted angles of incoming waves.

An innovative radar imaging system, based on the capability of a fixed UWB array to radiate short pulses in different directions along time with the principle of electronic beam steering, is presented in this paper. To demonstrate its concept, the analysis presented in this paper is based on simulation results. As function of the use of either only one antenna or several antennas in reception, two radar imaging algorithms have been developed and are detailed in this paper. These algorithms permit to obtain an image of the analyzed scene thanks to the transient beam pattern of the array used in emission. Finally, with a same analyzed scene, these algorithms have been compared with the time reversal method and the back projection algorithm, in association with a SAR imaging system. The conditions of applicability of these methods are also discussed.

The performance degradation in traditional adaptive beamformers can be attributed to the imprecise knowledge of the array steering vector and inaccurate estimation of the covariance matrix. The inaccurate estimation of the covariance matrix is due to the limited data samples and presence of desired signal components in the training data. The mismatch between the actual and presumed steering vectors can be mainly due to the error in the look direction estimate. In this paper, we propose a novel algorithm to estimate the look direction and to reconstruct the covariance matrix so that near optimal performance without the effect of saturation can be achieved as the input SNR increases. Numerical results also show that all existing beamforming algorithms suffer from saturation effect as the input SNR increases.

The increase in mobile communications traffic has led to heightened interest in the use of ray tracing (RT) methods together with digital building databases for obtaining more accurate and efficient propagation prediction in urban microcellular environments. In this paper, a novel quasi three-dimensional (3-D) RT algorithm is presented by taking into account the advantages of both the image theory (IT) and the shooting-and- bouncing ray (SBR) method. It is based on creating a new virtual source tree in which the relationship between neighbor nodes is a left-son-and-right-brother one. Our theoretical results of the signal path loss along the streets are compared with measurements which have been reported for city streets in Tokyo and Ottawa City for various values of the propagation parameters. The good agreement with these measurements indicates that our prediction model works well for such microcellular communication applications. The proposed method can provide the reliable theory basis for radio-wave propagation prediction and network planning in urban microcellular environments.

The TM₀ surface mode in an infinitely long parallel-plate waveguide filled with a double-positive (DPS) and epsilon-negative (ENG) metamaterial bi-layer is studied. With proper constitutive parameters and thicknesses of the two layers, the slow-wave factor (SWF) for such a parallel-plate waveguide can tend to infinity as the frequency decreases. A 2-D cavity based on the DPS-ENG bi-layer waveguide is constructed and studied to evaluate the radiation ability of its corresponding patch antenna. Based on the cavity model analysis of patch antennas, we show that good efficiency for broadside radiation of such a cavity-based rectangular patch antenna can be achieved when one layer of the cavity is shielded (or partially shielded) by PEC boundaries. Taking practical loss and dispersion into consideration, a miniaturized cavity-based rectangular patch antenna is proposed as an example. With the super-slow TM₀ surface mode excited in the bi-layer by a simple coaxial line feeding, the antenna has a dimension of only 0.107λ₀×0.129λ₀×0.045λ₀. The patch antenna produces broadside radiation, and fairly good radiation efficiency is achieved. The PEC-Partially-Shielded-ENG-Cavity based rectangular patch antenna with a further miniaturization but reduced radiation efficiency is also discussed.

The homogeneity of the amplitude of one of the polarizations of the RF field B₁ is a crucial issue in Magnetic Resonance Imaging (MRI), and several methods have been proposed for enhancing this uniformity (``Shimming''). The existing approaches aim at controlling the homogeneity of B⁺₁ and limiting the Specific Absorption Rate (SAR) of the RF field by independently controlling magnitude and phase of individual excitation currents in MRI scanners, either birdcage or TEM coil system. A novel approach is presented here which allows a joint control of B⁺₁ uniformity, SAR, and purity of polarization of the total RF B₁ field. We propose a convex optimization procedure with convex constraints, and special attention has been devoted to the issue of convexity of the proposed functional. The method is applied to MRI brain imaging; numerical tests have been performed on a realistic head model at low, medium, and high RF field in order to assess the effectiveness of the proposed method. We found that maintaining a specific polarization plays an important role also in maintaining the homogeneity of B⁺₁ amplitude.

Simple normalized dispersion relations for transverse magnetic (TM) and transverse electric (TE) propagating modes in parallel-plate waveguides filled with DPS/DPS or DNG/DNG, and DNG/DPS bilayers are presented. The evanescent TE₀ mode of the waveguide filled with a DNG/DPS bilayer is characterized also by a simple normalized dispersion relation. Since an important behavior of the modes in the waveguide filled with a DNG/DPS bilayer is the existence of a turning point (TP) at which the power carried by the respective mode on the propagation direction equals zero and changes the sign, we present also implicit relations for determining the normalized parameters of the TM and TE modes at that TP. We show that the TP begins to exist at certain values of the normalized parameter v₂ characterizing the DPS layer. For both the TM and TE modes, the higher is the mode order, the greater is the v₂ parameter at which the TP begins to exist, but the behavior of the TP is different for the TM and TE modes.

In this work, we analyze modified bowtie nanoantennas with polynomial sides in the excitation and emission regimes. In the excitation regime, the antennas are illuminated by an incident plane wave, and in the emission regime, the excitation is fulfilled by infinitesimal electric dipole positioned in the gap of the nanoantennas. Several antennas with different sizes and polynomial order were numerically analyzed by method of moments. The results show that these novel antennas possess a controllable resonance by the polynomial order and good characteristics of near field enhancement and confinement for applications in enhancement of spontaneous emission of a single molecule.

Modeling of a ferroelectric interdigital capacitor (IDC) and its incorporating in composite right/left-handed (CRLH) unit cells is represented. To evaluate the capacitance of a multi-layered IDC structures, conformal mapping and partial capacitance methods are utilized. Furthermore, the partial displacement method is utilized to calculate the electric field distribution and the its relation in the ferroelectric layer to applied voltage is obtained. Using this relation in a phenomenological model, dependency of the relative permittivity of ferroelectric on the applied voltage is obtained. The designed unit cell is comprised of IDCs and spiral inductors. To alter the propagation constant of the unit cell by varying the applied voltage, a thin layer ofBa_0.5Sr_0.5TiO₃ (BST-0.5) ferroelectric is incorporated underneath an IDC, called BST-0.5 varactor. The periodic structure based on the designed unit cell leads to a CRLH LWA. The Tunability of the periodic structure with three unit cell is demonstrated by varying the relative permittivity of the ferroelectric layer.

In the present paper, we deal with the performance analysis of the Adaptive Normalized Matched Filter (ANMF) detector in compound-Gaussian clutter with inverse gamma texture model and unknown covariance matrix. First, the maximum likelihood estimate (MLE) of the covariance matrix for this clutter model is derived. The MLE is then plugged into the ANMF test and compared to the well known normalized sample covariance matrix estimate (NSCM) and the approximate maximum likelihood estimate (AML). The performance in terms of CFAR behavior and detection probability is evaluated in the presence of simulated clutter and real sea clutter data, which is collected by the McMaster IPIX radar.

A novel multipolarized sectoral antenna on a metallic electromagnetic band gap (M-EBG) surface is investigated. The M-EBG structure behaves as a partially reflecting surface (PRS) and enhances the directivity of a simple radiating source. The use of metallic structures offers a new approach to industrial partners in order to reduce costs and to facilitate design techniques. By using double layers of M-EBG structure working on orthogonal polarizations as a superstrate with a single patch feeding by two ports, multipolarization operation is achieved. This antenna provides vertical, horizontal, 0°/90°and circular polarizations with a sectoral radiation pattern in the azimuth plane. M-EBG antennas with sectoral pattern are usually designed only for vertical polarization. In order to verify the results a Bipolar M-EBG Sectoral antenna prototype for WIMAX application~[5.15-5.35] GHz is realized and measured. Finally, we study the possibility to generate circular polarization.

The simulation of nonlinear loaded high-speed microstrip interconnects by means of a convolution-based procedure is described when both, analytical and measured scattering parameters are used. Closed-form equations are employed to obtain the analytical scattering parameters. The influence of measured scattering parameters, when these are used instead the analytical ones, is investigated to know how the microstrip interconnect responses are affected. The convolution procedure is complemented by including the transmission line linear equation and the microwave circuit reflection theory. S

Electric field Discontinuity-Considered Effective-Permittivities and Integration-Tensors (DC-EP&IT) for the three-dimensional Finite-Difference Time-Domain (FDTD) method are derived using a contour-path approach that considers the jump in the electric field at the interface of two dielectric materials. This is a natural but not so obvious extension to the work by Mohammandi et al. [1] from two to three-dimensions. Proposed method is verified by comparing with the exact Mie theory as well as the staircase, volume-averaged and subpixel methods.

An enhanced particle swarm optimization (EPSO) algorithm is proposed. To improve convergence accuracy and velocity, we introduce a quadratic interpolation method and perturbation to personal best particles in EPSO. Then, a design procedure based on the EPSO is proposed for the design and optimization of equal split broadband microstrip Wilkinson power dividers (MWPDs). A set of numerical examples and fabricated samples are presented to validate the improvement of the proposed EPSO. Even-odd mode analysis is incorporated in the design procedure to calculate the scattering matrix of the MWPD on the basis of the dispersion and dissipation microstrip line model. A fitness function is then constructed according to the scattering parameters. The optimized widths and lengths of microstrip lines and values of isolation resistors are directly obtained by minimizing the fitness function. EPSO is also compared with the genetic algorithm (GA), standard particle swarm optimization (PSO) and improved particle swarm optimization (IPSO).

In this paper, an approach for the pad modeling of the test structure for Metal Oxide Semiconductor Field Effect Transistor (MOSFET) up to 40\,GHz is presented. The approach is based on a combination of the conventional equivalent circuit model and artificial neural network (ANN). The pad capacitances and series resistors are directly obtained from EM (electromagnetic) simulation of the $S$ parameters with different size of pad and operating frequency. The parasitic elements in the test structure can be modeled by using a sub artificial neural network (SANN). So the pad capacitances and series resistors can be regarded as functions of the dimensions of the pad structure and operating frequencies by using SANN. Good agreement between the ANN-based modeling and EM simulation results has been demonstrated. In order to remove the impact of the parasitic elements, the de-embedding procedure for MOSFET device using ANN-based pad model is also demonstrated.

Thinning is a technique by which the total number of active elements in an antenna array is reduced without causing major degradation in system performance. Dynamic thinning is the process of achieving this under real time conditions. Stochastic techniques have been useful in the design of thinned arrays. However while applying the technique to large 2-D arrays, under changing conditions problems arise due to the very large and rugged solution space. Also, evaluation of the objective function in such cases requires large computational resources, thus reducing the rate of convergence. This paper suggests a technique using Genetic Algorithm which is useful for overcoming these problems. After discussing the basic concept involving dynamic thinning and application methodology, simulation results of applying the technique to linear and planar arrays are presented.

Electromagnetic design problems usually involve a large number of varying parameters. A designer can use different kinds of models in order to achieve optimum design. Some models, e.g., finite-element model, can be very precise: however, it requires large computational costs (i.e., CPU time). Therefore, the designer should use a screening process to reduce the number of parameters in order to reduce the required computational time. In this paper, using the Design of Experiments (DOE) approach to reduce the number of parameters is explored. The benefits of this technique are tremendous. For example, once researchers realize how much insight and information can be obtained in a relatively short amount of time from a well-designed experiment, DOE would become a regular part of the way they approach their simulation projects. The main objective of this paper is to apply the DOE technique to electromagnetic simulations of different systems and to explore its effectiveness on a new field, namely the magnetic refrigeration systems. The methodology of the DOE is presented to assess the effects of the different variables and their interaction involved in electromagnetic simulations design and optimization processes.

Measurements of the radiation patterns from a planar array of bow-tie slot antennas coupled through an extended hemispherical lens are reported. The design operates over 10% bandwidth centred at 30 GHz with a return loss of 10 dB. A moderate directivity from the integrated lenses of 13 dB with half-power beamwidth (HPBW) of 10º is achieved. The reduced size of this design is suitable for the integration with millimetre wave circuits.

A novel route to achieve a narrowband free-space electromagnetic absorber in any range of the spectrum based on stacked subwavelength hole arrays is proposed. The absorption is obtained by means of a slow light mode inside a fishnet-like engineered structure and exploiting the unavoidable misalignments and bucklings of the free-standing stack. An incoming pulse becomes permanently trapped in the structure due to the near zero group velocity which causes an enhancement of the radiation-structure interaction that leads to a huge increment of losses arising from the finite conductivity of the metal as well as arrangement tolerances. This approach is studied not only by simulation but also experimentally under normal incidence at millimeter wavelengths. Moreover, a basic grasp about the angular dependence of the structure is given by analyzing the 2D dispersion diagram. It shows that this scheme may also display high absorption under oblique incidence for s-polarization (or TE-polarization), whereas $p$-polarization (TM-polarization) would degrade its performance.