Large Electrical Size Research Articles

An Improved Multilevel Green's Function Interpolation Method With Adaptive Phase Compensation

An improved multilevel Green's function interpolation method (MLGFIM) with adaptive phase compensation (APC) is proposed. The difficulty in applying interpolation approaches to the fast varying phase term in the integral equation kernel for full-wave electromagnetic (EM) simulations is eradicated by using the phase compensation and adaptive direction separation (ADS). The multilevel tree structure in MLGFIM keeps the number of direction separation invariant at all levels, attributing to the recursive interpolation with multilevel phase compensation. The proposed MLGFIM-APC in conjunction with the Lagrange-Chebyshev interpolation yield an O(N log N) CPU time and O(N) computer memory requirement for surface scattering problems. By introducing a transition level, the MLGFIM-APC can adaptively incorporate interpolation techniques of conventional interpolation (CI), transition interpolation (TI) and phase-compensation interpolation (PI), corresponding to electromagnetic simulation of problems of small, moderate, and large electrical sizes, respectively. Large-scale microstrip antenna arrays are simulated to illustrate the accuracy and efficiency of the proposed method. It is found that the CPU time scales better than O(N log N) for these co-planar problems.

Sparse direct solution of the electric field integral equation using nonoverlapped localizing logos modes

AbstractA sparse direct solver for the electric field integral equation is demonstrated for electromagnetic scattering from perfectly conducting targets of fairly large electrical size. For the geometries considered, numerical experiments demonstrate that both the memory and CPU costs of the reported factorization algorithm are significantly less than those required for standard direct solution methods. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 303–307, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23068

Wavelet‐like efficient analysis of two‐dimensional arbitrarily shaped radomes using a surface formulation

Radomes are usually made of lossy dielectric materials, and their accurate analysis is often cumbersome because of their typical large electrical size and geometrical complexity. In real reflector antenna structures, there are always complex interactions between the radome, the reflector surfaces and the directional feeds, which are typically neglected for the sake of simplicity. In this paper we will consider all such interactions in a very accurate way, thus requiring a high number of unknowns for the numerical solution of the problem. To overcome such drawback, an integral equation formulation based on the Equivalence Principle in combination with the wavelet transform has been employed, obtaining finally a robust and accurate CAD tool for the rigorous analysis of arbitrarily shaped radomes containing continuous and discrete electromagnetic sources. It will be shown that the use of wavelet‐like bases substantially improves the numerical efficiency and memory requirements of the original integral equation method. For verification purposes, the results obtained with the new technique are successfully compared with examples taken from the literature. Complex antenna structures are then discussed in order to prove the usefulness of the new method.

Cloaking and transparency for collections of particles with metamaterial and plasmonic covers

Following our recently developed idea of employing plasmonic covers to cloak an isolated conducting, plasmonic or insulating sphere through scattering cancellation, here we extend this concept by investigating the possibility of cloaking multiple objects placed in close proximity of each other, or even joined together to form a single object of large electrical size. We show how the coupling among the single particles, even when placed in the very near zone of each other, is drastically lowered by the presence of suitably designed covers, thus providing the possibility of making collections of objects transparent and "cloaked" to the impinging radiation even when the total physical size of the system is sensibly larger than the wavelength. Numerical simulations and animations validate these results and give further insights into the anomalous phenomenon of transparency and cloaking induced by plasmonic materials and metamaterials.

Sensitivity analysis of iterative adjoint technique for microstrip circuits optimization

AbstractThis paper presents an accurate and efficient full‐wave method, combined with iterative adjoint technique, for analyzing sensitivities of planar microwave circuits with respect to design parameters. Method of moments (MoM) in spatial domain is utilized, and generalized conjugate residual iterative scheme is applied to solve the linear matrix equations with fast convergence. Green's functions for multilayer planar structures in DCIM form are employed to simplify the spatial domain manipulation. In the present method, a conventional integration model and the corresponding adjoint model are solved by MoM respectively. The adjoint technique, with the aid of iterative schemes, could significantly reduce the computational requirements, especially for the large electrical size device with many perturbing design parameters. Numerical results of S‐parameter sensitivities of a low‐pass microstrip filter by the present method are presented. Accuracy and efficiency are validated. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 607–609, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22204

FAST METHODS FOR EVALUATING THE ELECTRIC FIELD LEVEL IN 2D-INDOOR ENVIRONMENTS

When estimating the electric field level in an indoor environment, the usual complexity of the geometry and its large electric size make it necessary to deal with asymptotic assumptions, also known as high frequency techniques. But, even with these assumptions, the computational complexity, and the CPU-time cost, can be very high. Considering this drawback, this paper proposes the implementation of a Networks System for fast calculations of the Electric field in 2D-indoor environments. When dealing with an indoor environment, the computational complexity when using deterministic methods even if frequency techniques are considered to calculate the field level in a given area, can be extremely high. Because of it, this paper deals with the implementation of fast methods using Artificial Neural Networks, for the reduction of CPU-time and memory resources when calculating the field coverage in an indoor environment. Artificial Neural Networks (ANNs) are defined as intelligent knowledge based systems. This means that, starting from a previous knowledge or any training information, ANNs are able to solve certain complex mathematical problems. Moreover, any ANN's structures are assumed to be universal function's approximators, (as proved in (1) for Multilayer Perceptrons MLP, and in (2) for Radial Basis Function Networks RBFN). Taking into account these characteristics, it can be derived that an ANN is able to link inputs and outputs in a problem, as accurate as we want. if ANNs are Universal Approximators for known functions, why to use them in this application? One reason is that the analytical equations that describes the problems, are not known, in a general

Analysis and Design on Aperture Antenna Systems with Large Electrical Size Using Multilevel Fast Multipole Method

A full-wave procedure for designing electrically large optimized classical aperture antenna systems is analyzed using the multilevel fast mulitpole method (MLFMA). The useful design equations for optimized offset dual reflector antennas with circular apertures are also presented to allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The radiation of feed horn is first analyzed and compared with theoretical and available measurement results. The conventional reflector antennas are simulated and analyzed for aperture blockage of the feed. Finally, the offset dual reflector antennas with circular aperture are designed and validated numerically by showing that low cross polarization and spillover losses obtained. All the simulations are made by using the MLFMA which is implemented based on the method of moments (MoM) with RWG triangular patch basis function to model any shape of reflector surfaces.

Fast far‐field approximation for calculating the RCS of large objects

AbstractA fast far‐field approximation (FAFFA) is developed to estimate the RCS of conducting scatterers. This method accounts for the interaction between subscatterers in two ways, depending on the electrical distance between the subscatterers. The interactions of subscatterers separated by a large electrical distance are computed in three stages: (1) aggregation, which computes the total field at a group center due to the subscatterers of the group; (2) translation, which translates the field from one group center to another; and (3) disaggregation, which distributes the field in a group center to each subscatterer in the group. Two strategies are employed to accelerate the computation in the above three stages. One is the use of far‐field approximation to simplify the computation in the translation stage; the other is the use of interpolation and smoothing techniques, which reduces the complexity of aggregation and disaggregation. The overall computational complexity for a matrix‐vector multiplication is of the order of N1.33, and the memory requirement is of order N. Numerical results show that this method can predict a RCS that is very close to exact solution, and that the method can be applied to objects with very large electrical sizes. © 1995 John Wiley & Sons. Inc.

Far-Field Transient Backscattering by Water Drops

Abstract Approximations to the far-field, backscattering response for an electromagnetic impulse are shown for two water sphere sizes. For small electrical sizes, the scattering is described by an electric dipole; for large electrical sizes, a combination of reflection from the front interface, creeping waves, and surface currents excited as the impulse moves across the sphere is used. It is shown that transient effects are confined effectively to an equivalent space period of less than six diameters and can be neglected in all operational applications of pulse radar to rain detection.