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A near-optimal design of a log-periodic dipole array (LPDA), suitable for digital video broadcasting-terrestrial (DVB-T) reception (470–790 MHz), is presented. The LPDA is required to provide low standing wave ratio as well as high-gain radiation pattern with sufficient gain flatness over the entire passband, and concurrently achieve low gain for frequencies above 800 MHz to reject LTE800 signals and thus improve the reception quality in the DVB-T band. All the above requirements are better satisfied by applying a novel particle swarm optimization (PSO) variant, called PSO with velocity mutation (PSOvm). PSOvm induces mutation on the velocities of those particles, which are unable to improve their fitness. As shown in this paper, PSOvm comes closer to the above requirements compared to four well-known optimization methods and outperforms the traditional LPDA design method proposed by Carrel. The LPDA geometry chosen for optimization is not the conventional one, and therefore the dipoles are not considered to be included inside a specified angle as proposed by Carrel. Thus, the dipole lengths and distances as well as the boom dimensions are independently optimized. The PSOvm-based LPDA sufficiently meets all the above requirements and thus is suitable for DVB-T reception without the use of an external LTE-band rejection filter.

Nature-inspired metaheuristics of the swarm intelligence field are a powerful approach to solve electromagnetic optimization problems. Ant lion optimizer (ALO) is a nature-inspired stochastic metaheuristic that mimics the hunting behavior of ant lions using steps of random walk of ants, building traps, entrapment of ants in traps, catching preys, and re-building traps. To extend the classical single-objective ALO, this paper proposes four multiobjective ALO (MOALO) approaches using crowding distance, dominance concept for selecting the elite, and tournament selection mechanism with different schemes to select the leader. Numerical results from a multiobjective constrained brushless direct current (DC) motor design problem show that some MOALO approaches present promising performance in terms of Pareto-optimal solutions.

A versatile and straightforward human body model, comprising simple geometric structures, is consistently developed in this study for the precise electromagnetic field exposure assessment owing to mediated lightning strikes. The proposed model incorporates a realistic set of frequency-dependent media, approximated by a 4-Cole-Cole scheme, while every body part is considered to be occupied by the most dominant medium. For the reliable evaluation of all related electromagnetic quantities, the featured implementation is systematically discretised by means of an efficient finite-difference time-domain algorithm and all results are compared to those of a circuit-based approach, simulated via an electronic circuit software. Moreover, to minimise comparison errors, the most critical human body dimensions are carefully optimised. Finally, the model, so constructed, is employed for the study of a side flash impact and the investigation of a lethal electric discharge possibility through the disruptive effect technique. The benefits of the proposed realisation in the successful prediction of mediated lightning effects are thoroughly validated in terms of various real-world scenarios, which, among others, reveal that the impact on humans is inversely proportional to its distance from the stroked object.

In this paper, an efficient integral equation method is developed for the response and scattering characteristics of cloaked 2-D planar microstrip receiving antennas. The featured technique combines Green’s function for the strip-free structure with the decomposition of the strip into cylindrical thin wires and a radiation integral evaluation for the scattered field. In essence, the desired low-profile operation of the antenna is achieved by overlaying a superstrate slab atop the antenna. Moreover, an optimization process determines the constitutive parameters and thickness of the slab, so that a significantly reduced scattering behavior is obtained. Finally, the performance of the receiving antenna is investigated for a specific range of frequencies around the operating one, while the accuracy of the proposed algorithm is successfully verified through several numerical simulations.

Incorporating standard high-order spatial approximations in the alternating-direction implicit (ADI) finite-difference time-domain method does not suffice for improving the technique’s accuracy, as these operators are capable of reducing spatial errors only. We herein develop an alternative design procedure, which results in the construction of finite-difference expressions that ameliorate the combined space–time flaws. In essence, it is shown that three error formulas are derived from the individual implicit equations, provided that the ADI updates are treated as a single-step process. Then, more efficient spatial expressions can be extracted through proper manipulation of these formulas and subsequent application of error-controlling concepts.

An aperiodic reconfigurable microstrip antenna array is designed to serve as a DVB-T base station antenna operating in a single broadcasting channel. The antenna array is optimized at 698 MHz (center frequency of DVB-T channel 49) to concurrently achieve a particular radiation pattern shaping with high forward gain, main lobe tilting and null filling inside the service area, as well as low sidelobe level outside the service area, and low standing wave ratio at the inputs of all the array elements. To concurrently satisfy all the above requirements, both the geometry dimensions and the array feeding weights (amplitudes and phases) are optimized, thus leading to a complex multi-variable and multi-objective problem. The problem is solved by applying a recently developed particle swarm optimization (PSO) improved variant, called PSO with velocity mutation, in conjunction with the CST software package, which is employed by the PSOvm every time a full-wave analysis is required. Furthermore, all the optimization methods found in the CST environment are compared with the PSOvm. The results show that the PSOvm is capable of producing an antenna array geometry, which is closer to the predefined requirements than the geometries derived by the rest of the optimizers, in the least amount of computational time.

The finite-difference time-domain method is herein combined with polynomial-chaos expansions for the study of axially-symmetric structures featuring material uncertainties. By exploiting the problem's periodicity, we reduce the high computational burden of fully 3D simulations, and reliably extract the necessary statistical information from a single simulation.

A finite-difference time-domain (FDTD) method for simulating wave propagation in Havriliak-Negami (H-N) dispersive media is presented. In an H-N medium, the time-domain polarization relation involves a fractional differential operator, whose analytical evaluation is troublesome. Moreover, if the fractional differential operator is approximated by a sum of fractional time derivatives, the numerical treatment of the polarization relation results in significant memory storage demands, because fractional derivatives are not local. However, by an appropriate approximation of the Grunwald-Letnikov definition of fractional derivatives, an FDTD scheme with reasonable memory requirements is feasible. In particular, the coefficients that appear in the Grunwald-Letnikov definition are approximated by sums of decaying exponentials. As a result, the FDTD scheme is based on recursive equations, while a limited number of auxiliary vectors need to be stored. The proposed scheme has been applied successfully to the simulation of the excitation of an H-N medium by a wideband Gaussian electromagnetic pulse.

We present here a 3-D E-B linear eigenmode formulation for the analysis of periodic structures, including lossy periodic waveguides, photonic crystals, and metamaterials. The proposed finite-element formulation utilizes proper H (curl) vector basis functions for the electric field and H (div) vector basis functions for magnetic flux density. The resulting eigenmode problem is linear, and it enforces periodic boundary conditions in a simple manner via appropriate field transformations and does not exhibit spurious modes. Moreover, it can provide accurate complex-k dispersion diagrams, in terms of both propagation and attenuation constant, while it is also able to deal with either propagating or evanescent modes, including those with oblique propagation directions.

The consistent modeling of microwave components with random fluctuations regarding their electromagnetic material parameters is performed in this paper via a 3-D stochastic finite-difference time-domain method. The featured formulation provides precise numerical results with a considerably smaller computational cost compared to the extensively resource-consuming Monte Carlo approach. Numerical simulations of microstrip transmission lines with media uncertainties are conducted in order to verify the accuracy of the proposed technique along with its effectiveness to investigate the operation of complicated microwave structures in a stochastic environment.

The propagating modes on a magnetically biased curved graphene microstrip are thoroughly examined in the present work by means of an efficient finite element modal solver. The influence of the anisotropic surface conductivity due to the magnetic bias is carefully addressed and investigated through a multitude of numerical results, including the effective index and the electric field distribution of the dominant modes.

Aiming at the minimization of numerical dispersion effects in finite-difference time-domain (FDTD) simulations, we investigate the potential of introducing frequency-dependent coefficients in the approximations of differential operators. The proposed methodology exploits some previous results on optimized finite-differences, but initially avoids the necessity for selecting a specific optimization point. Herein, the operators' coefficient formulae are approximated by a low-order polynomial, which is transformed into a finite-difference counterpart using the Helmholtz equation. This modifies the initial spatial stencil and improves performance over all frequencies, which can be further controlled with the least-squares method, leading to various new FDTD schemes of augmented reliability.

We present and validate a computational approach that enables the quantification of time-dependent uncertainty in axially symmetric electromagnetic (EM) problems, in the context of a unique simulation. In essence, the finite-difference time-domain (FDTD) method, adapted to model bodies of revolution (BOR), is combined with truncated polynomial-chaos (PC) expansions of the involved field components, so that the stochastic nature of the latter is modelled reliably, when media with random electric properties need to be considered. The developed approach features two distinct advantages: First, by exploiting the azimuthal periodicity of the investigated problems' geometry, the high computational burden of three-dimensional (3D) simulations is reduced. Second, the large number of simulations that are normally required by Monte-Carlo (MC) methodologies for the extraction of statistical features is avoided, thanks to the integrated PC approximations. A number of numerical tests are conducted, in order to verify the validity and performance of the suggested stochastic algorithm.

The performance of periodic-grating resonant structures, which find various applications as optical devices, is highly dependent on their geometric features. This Letter investigates the response of such wideband configurations, when a non-trivial number of random geometric variables are considered. To avoid computationally expensive solutions, we develop sparse Polynomial-Chaos (PC) approximations for the quantity of interest, using a limited number of basis functions. Initially, the size of the PC series is reduced by excluding terms that describe highly complex interactions. Then, the most significant terms are computed via the Orthogonal-Matching-Pursuit algorithm, in the context of compressed sensing. The latter necessitates only a few deterministic model evaluations, and produces sparse, yet accurate, PC formulae. Numerical results for a broadband grating filter verify the proposed two-step approach, and display the structure's performance variability under uncertainty conditions.