Showing papers in "Electromagnetics in 2002"
TL;DR: In this paper, a semianalytical algorithm for the determination of eigenmodes and for the analysis of longitudinally varying structures is presented. But the results prove stability of the algorithm, and comparisons with other methods show the accuracy.
Abstract: Algorithms for the determination of eigenmodes and for the analysis of longitudinally varying structures are presented. The media may be anisotropic and the devices may consist of an arbitrary number of layers or waveguide sections, respectively. Starting with generalized transmission line equations, suitable expressions are derived which are implemented in the method of lines, a semianalytical algorithm. To ensure the numerical stability, a transformation of the reflection coefficient is performed. Numerical results are presented for a Bragg-grating with a very high number of periods, for an electro-optical switch, and for an anisotropic groove waveguide. The results prove stability of the algorithm, and comparisons with other methods show the accuracy.
48 citations
TL;DR: In this paper, the problem of spurious solutions in finite-element methods for electromagnetics is discussed with the explicit aim to re-open the discussion on this much debated subject.
Abstract: The problem of spurious solutions in finite-element methods for electromagnetics is discussed with the explicit aim to re-open the discussion on this much debated subject. First, an overview is given of existing ideas about the causes of spurious solutions together with the solutions that are proposed. Subsequently it is concluded that the cause of spurious solutions may differ from what is usually suggested or claimed, and an alternative cause for spurious solutions is proposed. Finally, suggestions are given about how a finite-element method should be designed that is free of spurious solutions.
23 citations
TL;DR: The analysis contained herein compares and contrasts the MORe techniques by not only considering the nature of the individual algorithms, but also solving several illustrative numerical examples.
Abstract: In this paper, an analysis of some model order reduction (MORe) techniques is presented. More precisely, this paper considers asymptotic waveform evaluation (AWE), Galerkin asymptotic waveform evaluation (GAWE) with a short-term vector recurrence relation, multipoint Galerkin asymptotic waveform evaluation (MGAWE) also using a short-term recurrence, and matrix-Pade via Lanczos (MPVL). These techniques are applied to matrix equations resulting when the enite element method (FEM) is used to model electromagnetic wave propagation problems. The reduced order model equations can then be solved repeatedly to obtain a wideband frequency simulation with a reduction in total computation time. The analysis contained herein compares and contrasts the MORe techniques by not only considering the nature of the individual algorithms, but also solving several illustrative numerical examples. These examples show how, for a MORe technique, a radiation and scattering problem might have to be treated very differently. In addition, it is noted that the unknown(s) desired as output(s) from the FEM mesh can ineuence which MORe technique is more efecient. The solutions obtained through the MORe techniques are compared to an LU decomposition at each frequency point of interest to benchmark their accuracy and efeciency.
20 citations
TL;DR: In this article, P-adaptive schemes are proposed for use with recently developed vector edge elements up to order 4 in computing the scattering matrices of microwave devices, and tested on three problems: a capacitively terminated parallel-plate waveguide, a metal post in a rectangular waveguide and a two-cavity rectangular waveguarantee filter.
Abstract: P-adaption improves the quality of a finite element solution by selectively increasing the polynomial order of the elements. P-adaptive schemes are proposed for use with recently developed vector edge elements up to order 4 in computing the scattering matrices of microwave devices. The schemes are tested on three problems: a capacitively terminated parallel-plate waveguide, a metal post in a rectangular waveguide, and a two-cavity rectangular waveguide filter.
16 citations
TL;DR: This paper presents a new approach based on multilayered perceptrons (MLPs) to compute the characteristic impedance and the effective permittivity of the micro-coplanar strip.
Abstract: This paper presents a new approach based on multilayered perceptrons (MLPs) to compute the characteristic impedance and the effective permittivity of the micro-coplanar strip. Only one neural model is used to calculate the both parameters of the strip. An extended delta-bar-delta algorithm is used to train the MLP. The results obtained by using the MLP model are in very good agreement with the theoretical and experimental results reported elsewhere.
14 citations
TL;DR: In this article, the response of uniaxial bianisotropic slabs to obliquely incident electromagnetic waves is studied, and the exact solution of this boundary-value problem is derived.
Abstract: The response of uniaxial bianisotropic slabs to obliquely incident electromagnetic waves is studied, and the exact solution of this boundary-value problem is derived This includes the calculation of all characteristics of reflected and transmitted waves The study is relevant to recent experimental studies of arrays of parallel spirals The present theory gives an analytical model of such artificial bianisotropic media
14 citations
TL;DR: In this paper, a model for the electromagnetic properties of a dielectric half-space covered by a regular array of planar bianisotropic particles is described, and the model allows us to homogenize the structure, presenting it as a half space covering by a finite-thickness layer of bisotropic medium.
Abstract: A model for the electromagnetic properties of a dielectric half-space covered by a regular array of planar bianisotropic particles is described. The model allows us to homogenize the structure, presenting it as a half-space covered by a finite-thickness layer of bianisotropic medium. The array particles' mutual coupling is studied within the frame of the assumption of "electric and magnetic dipole," which implies the rather sparse arrays of particles, though the presented approach can be generalized to the case of dense arrays taking into account the higher multipoles. The model is numerically tested for the case of a bianisotropic array in free space.
13 citations
TL;DR: In this article, a stable variational formulation for full-wave analysis of waveguides is presented, which applies to a wide class of vector finite elements, including two families of Nedelec (1980, 1986) and their generalization, hp-edge elements.
Abstract: A new stable variational formulation for full-wave analysis of waveguides is presented. Reported theoretical results apply to a wide class of vector finite elements, including two families of Nedelec (1980, 1986) and their generalization, hp-edge elements (Demkowicz & Vardapetyan, 1998; Vardapetyan & Demkowicz, 1999a). Numerical experiments show that the method remains stable at very low frequencies.
13 citations
TL;DR: The analysis and design of microwave filters obtained by the insertion of cylindrical posts in a rectangular waveguide is implemented by a neural network approach, suitable to analyse a cascade of multiple posts and to provide a solution for the synthesis of such a filtering device.
Abstract: The analysis and design of microwave filters obtained by the insertion of cylindrical posts in a rectangular waveguide is in this paper implemented by a neural network approach. The neural architecture is able to give an accurate description of the filtering device behaviour in almost real time, whereas the full wave simulator would take several minutes. This kind of approach is suitable to analyse a cascade of multiple posts and to provide a solution for the synthesis of such a filtering device.
13 citations
TL;DR: In this article, the finite element-boundary integral method with hierarchical TVFEs for tetrahedra is used for analysis of infinite, doubly periodic antenna arrays, and it is shown that accurate prediction of array scanning properties can be obtained by using higher order TV FEs in the regions where large fields and rapid field variations are expected and lowest order TVFes elsewhere.
Abstract: Hierarchical mixed-order tangential vector finite elements (TVFEs) for tetrahedra are attractive for accurate and efficient analysis of a wide class of electromagnetic radiation and scattering problems. They provide versatile geometrical modeling and accurate field representation by allowing combination of lowest and higher order TVFEs. In this paper, the finite element-boundary integral method with hierarchical TVFEs for tetrahedra is used for analysis of infinite, doubly periodic antenna arrays. It is shown that accurate prediction of array scanning properties can be obtained by using higher order TVFEs in the regions where large fields and rapid field variations are expected and lowest order TVFEs elsewhere. This type of multi-resolution modeling is applied to several array configurations to demonstrate the accuracy and capabilities of the technique. Adaptive Integral Method (AIM) for the acceleration of the boundary integral is discussed and results regarding the speed-up are also given. Applications ...
10 citations
TL;DR: In this paper, a hybrid approach of the forward-backward method (FBM) with spectral accelerate algorithm (SAA) to solve the magnetic field integral equation is developed.
Abstract: In order to numerically simulate bistatic scattering from a fractal rough surface at low grazing angle (LGA) incidence, a hybrid approach of the forward-backward method (FBM) with spectral accelerate algorithm (SAA) to solve the magnetic field integral equation is developed. Numerical bistatic scatterings from one-dimensional perfectly conducting fractal rough surface with and without a regular object presence are accomplished. Accuracy and efficiency of FBM/SAA are discussed. Numerical simulations demonstrate functional dependence of bistatic scattering upon fractal geometry, especially at LGA. The linear relationship between the envelope slope of bistatic scattering pattern and fractal dimension is discussed.
TL;DR: In this paper, a new numerical method, called Robin Boundary Condition Iteration (RBCI), was proposed for the finite element solution of electromagnetic scattering problems, adapted to the numerical computation of antenna parameters.
Abstract: A new numerical method, called Robin Boundary Condition Iteration (RBCI), recently devised by the authors for the finite element solution of electromagnetic scattering problems is adapted to the numerical computation of antenna parameters. In RBCI the unbounded domain is truncated to a bounded one by means of a fictitious boundary that contains the antenna and on which a suitable nonhomogeneous Robin (mixed) boundary condition is assumed for the Helmholtz equation in the bounded domain. The Robin condition is expressed by means of an integral formula (the 2nd Green identity) in terms of the field in the interior of the bounded domain, the integration surface being strictly enclosed by the truncation boundary. The discretized differential and integral equations are then coupled together to solve the problem. A simple and effective iterative solving scheme is described. The computation of the antenna impedance in postprocessing is discussed. Examples are also provided to explain the method.
TL;DR: In this article, an iterative method based on the concept of waves is applied to the computation of the scattering behavior of spherical and cylindrical surfaces, and an example of multiple scattering by N parallel circular conducting cylinders of arbitrary radius and distribution is also presented.
Abstract: An iterative method based on the concept of waves is applied to the computation of the scattering behavior of spherical and cylindrical surfaces. An example of multiple scattering by N parallel circular conducting cylinders of arbitrary radius and distribution is also presented. The method allows a unified numerical solution procedure to be implemented for the foregoing hierarchy of the scatterers. Representative numerical results for a number of scattering geometries are given to illustrate the efficacy and the versatility of the present approach.
TL;DR: In this article, an unconventional model of electromagnetic field computation is presented, which aims at being as close to the physics as possible for the class of strongly heterogeneous and/or anisotropic media.
Abstract: An unconventional model of electromagnetic field computation is presented. It aims at being as close to the physics as possible for the class of strongly heterogeneous and/or anisotropic media. The electric field strength, the magnetic field strength, the electric flux density, and the magnetic flux density are computed separately. Consistently linear edge expansion functions are employed for the discretization of the field strengths and consistently linear face expansion functions are employed for the discretization of the flux densities. The model imposes the exact satisfaction, for each element, of the space-time discretization, of the space-time integrated field equations and compatibility relations, combined with the least-square satisfaction, for each such element, of the space-time integrated constitutive relations.
TL;DR: In this paper, the distribution of the total field when the height of the surface changes in a random way is presented, together with a comparison with the distribution obtained when a plane wave is incident on a finite flat surface of the same size, having a height varying in an arbitrary manner.
Abstract: The field due to a plane wave with a Gaussian profile incident on a perfectly conducting one-dimensional smooth random rough surface with finite size is studied. The distribution of the total field when the height of the surface changes in a random way is presented, together with a comparison with the distribution of the field obtained when a plane wave is incident on a finite flat surface of the same size, having a height varying in a random manner. The results show that the two cases are equivalent.
TL;DR: In this paper, a boundary value problem of electrostatic potential penetration into two circular apertures in a thick conducting plane is solved rigorously, where the scattered potentials are represented in terms of discrete and continuous modes by using the Hankel transform and superposition principle.
Abstract: A boundary-value problem of electrostatic potential penetration into two circular apertures in a thick conducting plane is solved rigorously. The scattered potentials are represented in terms of discrete and continuous modes by using the Hankel transform and superposition principle. The boundary conditions are enforced to obtain a set of simultaneous equations for the discrete modal coefficients. The electric polarizability is represented in fast convergent series which is amenable to computation. The electric polarizability is evaluated for various aperture geometries to show the characteristics of electrostatic potential penetration.
TL;DR: In this paper, the electromagnetic characteristics of symmetric and asymmetric modes in a disk-loaded structure have been investigated and the impact of the geometry on the EM characteristics is presented and some simple analytic relations have been developed based on simulations.
Abstract: The electromagnetic (EM) characteristics of symmetric and asymmetric modes in a disk-loaded structure have been investigated. The study focused on those EM characteristics that affect the dynamics of electrons in amplifier. Two different frequency bands have been considered, X-band and Ka-band, referring to two main activities at Stanford Linear Accelerator Center and Cornell University. The impact of the geometry on the EM characteristics is presented and some simple analytic relations have been developed based on simulations.
TL;DR: In this paper, the propagation of electromagnetic waves along earth-space paths in forest environments is analyzed, where the transmitter is placed in the air region above the vegetation, while the receiver may be in the aerial region or within the vegetation.
Abstract: Propagation of electromagnetic waves along earth-space paths in forest environments is analyzed in this paper, where the transmitter is placed in the air region above the vegetation, while the receiver may be in the air region or within the vegetation. This propagation model considers the forest as a horizontally stratieed, anisotropic medium of canopy and trunk, bounded by ground below and air above. Dyadic Green’s functions in their eigenfunction expansion forms for planarly layered anisotropic media are applied to analyze this problem. The analytical close forms of these electric eelds are then obtained by using the saddle point techniques and branch cut integrations in the complex plane and, hence, expressed in terms of direct wave, multiply reeected waves, and lateral waves. Propagation mechanisms of these waves are studied and radio losses in a typical forest are calculated numerically.
TL;DR: In this article, the surface fields diffracted by an impedance wedge are determined and studied for the case of skew incidence plane wave, using the Maliuzhinets method, based on available approximate solutions of the coupled difference equations for the spectrum functions.
Abstract: The surface fields diffracted by an impedance wedge are determined and studied for the case of skew incidence plane wave, using the Maliuzhinets method. These surface fields are based on available approximate solutions of the coupled difference equations for the spectrum functions. Derived surface fields recover the available surface fields which are valid for normal incidence and based on exact solution of the difference equations. These surface fields may be utilized to determine the transition currents to supplement the physical optics currents.
TL;DR: In this paper, a new error estimator for design sensitivities is proposed for finite-element analysis of microwave devices, based on derivatives of C with respect to position for internal nodes in the mesh (not on any parameterized boundaries or interfaces).
Abstract: A new error estimator for design sensitivities is proposed for finite-element analysis of microwave devices. A function of scattering parameters, C, varies with parameter g. By the adjoint method, the sensitivity dC/dg can be found. A new estimate of the error in dC/dg is based on derivatives of C with respect to position for internal nodes in the mesh (not on any parameterized boundaries or interfaces). It is shown that these estimates of the error are close to the actual errors for a variety of test cases. The estimator is tested using a p-adaptive finite-element method.
TL;DR: In this paper, a numerical method called Davidenko's method is presented to search the complex roots of the dispersion relation of a lossy asymmetric moving waveguide and the propagation characteristics of the guided TE waves are examined.
Abstract: This paper presents a numerical method called Davidenko's method to search the complex roots of the dispersion relation of a lossy asymmetric moving waveguide. The propagation characteristics of the guided TE waves are examined. The effects of variation of the mode, the core thickness, the dielectric constant of the substrate, and the velocity of waveguide on the attenuation of the waves are also calculated.
TL;DR: In this paper, an analytical perturbation determination of power dependent attenuation of TE waves propagation in a very thin metal film bounded by nonlinear media is presented, and simple analytic formulas are deduced which give accurate results that are in a good agreement with those of the numerical methods of solving the eigenvalue equation in the complex plane.
Abstract: An analytical perturbation determination of power dependent attenuation of TE waves propagation in a very thin metal film bounded by nonlinear media is presented. Simple analytic formulas are deduced which give accurate results that are in a good agreement with those of the numerical methods of solving the eigenvalue equation in the complex plane.
TL;DR: This paper tests an iterative solver for magnetic field integral equation (MFIE) developed for scattering problems of electrically large bodies and finds that GMRES on the normal equation typically possesses higher convergence rates than the GM RES on the original MFIE.
Abstract: This paper tests an iterative solver for magnetic field integral equation (MFIE) developed for scattering problems of electrically large bodies. GMRES (generalized minimum residual or Krylov subspace method) is applied to MFIE written in the normal form. The results for the perfectly conducting (PEC) sphere and other PEC structures demonstrate the solver performance. The surface current distributions and absolute convergence rates for the sphere are controlled by direct comparison with the Mie series calculated for the surface current. Both nonresonant and resonant frequencies of the internal cavity are considered. A low-order boundary element model is implemented, with the surface current being constant across each element. Results are compared to the conjugate gradient method on the normal equation (CGNE) and to the GMRES on the original nonsymmetric MFIE. It is found that GMRES on the normal equation typically possesses higher convergence rates than the GMRES on the original MFIE. GMRES on the normal e...
TL;DR: In this paper, a finite element magnetostatic solver is used to develop modified slab shapes, which reduce high magnetic flux concentrations in the corner regions, to increase operating bandwidths and provide better stability in high-power devices.
Abstract: Nonuniform magnetization occurs in nonellipsoidal ferrite shapes such as rectangular slabs used in microwave phase shift and control components. A finite element magnetostatic solver is used here to develop modified slab shapes, which reduce high magnetic flux concentrations in the corner regions. Microwave finite element calculations show that similar phase shift performance is obtained in the standard and modified geometries. The proposed differential phase shifter cross sections should increase operating bandwidths and provide better stability in high-power devices.
TL;DR: In this article, four conditions must be satisfied by the constitutive parameters of a linear, homogeneous, bianisotropic medium for it to support the propagation of a circularly polarized plane wave along a fixed axis.
Abstract: Derived here are four conditions that must be satisfied by the constitutive parameters of a linear, homogeneous, bianisotropic medium for it to support the propagation of a circularly polarized plane wave along a fixed axis.
TL;DR: A model based on a solution of DGF (dyadic Green's function) in spherical coordinates that will describe the field distributions inside a biological head is analyzed and shows that this method correlates well with other techniques.
Abstract: The accurate modeling of electromagnetic (EM) effects is now an increasingly important design requirement for the advancement of PCS (personal communication services). Also, possible adverse effects of EM fields, especially on the brain and the nervous system, are of increasing concern, particularly with reference to mobile transceivers held close to the head. The spherical head model, while not accurate, provides easy and reasonably effective means for the estimation of the "worst case SAR (specific absorption rate)" either through modeling or experimentation. The purpose of this work is to analyze a model based on a solution of DGF (dyadic Green's function) in spherical coordinates that will describe the field distributions inside a biological head. Numerical results from analytical expressions are computed for the problem of the spherical head model (multilayered homogeneous lossy dielectric spherical model) in close proximity to a dipole antenna and then compared with the results from the same model u...
TL;DR: In this paper, a 3D FDTD subgridding scheme based on a finite element (FE) formulation to solve the Maxwell equations is presented, derived from a variation formulation of two coupled problems with the use of Lagrange multipliers and mass lumping.
Abstract: A 3D FDTD subgridding scheme based on a finite element (FE) formulation to solve Maxwell equations is presented. Derived from a variation formulation of two coupled problems with the use of Lagrange multipliers and mass lumping, an FDTD subgridding scheme is proposed and analyzed. The stability is discussed with the help of a discrete energy conservation. Some results demonstrate the efficiency and validity of the proposed method.
TL;DR: This paper is focused on the creation of an efficient electromagnetic model of MEMS switches which operates at microwave frequencies and a scalable lumped circuit model is extracted to allow easy implementation of the switch model into commercial microwave CAD software.
Abstract: This paper is focused on the creation of an efficient electromagnetic model of MEMS switches which operates at microwave frequencies. The switches are first characterized using a full wave analysis based on a finite element method to extract the S-parameters of the switches for different geometrical dimensions. From the S-parameter database, a scalable lumped circuit model is extracted to allow easy implementation of the switch model into commercial microwave CAD software. The lumped circuit model results are compared with published measured data as validation of our model.
TL;DR: In this paper, anisotropic layers with real permittivity and permeability tensors are used to enclose the computational domain for vectorial modal analysis of dielectric waveguides through the finite element method.
Abstract: Anisotropic layers with real permittivity and permeability tensors are used to enclose the computational domain for vectorial modal analysis of dielectric waveguides through the finite element method. The approach does not require any iterative procedure. It is computationally efficient and reliable, it can directly calculate many modes at the same time, and it is very accurate in providing both the vectorial field distribution and the propagation constant. Analysis of performances is provided for different dielectric waveguides by varying the constituent parameters of the layers.
TL;DR: In this article, the authors considered the problem of scattering by a cylindrical obstacle in a rectangular waveguide and proposed an accurate and rapidly converging algorithm based on the efficient series representation of the field in the rectangular interaction region.
Abstract: The canonical problem of scattering by a cylindrical obstacle in a rectangular waveguide is rigorously reexamined in the framework of the domain product technique. An accurate, rapidly converging algorithm is based on the efficient series representation of the field in a rectangular interaction region. It is shown that the fast convergence of the numerical approximation is stipulated by mathematical properties of the matrix operator arising from the boundary value formulation. The solution is also validated by comparison with the data of other authors. The approach proposed can be applied to the analysis of scattering by real metallic or dielectric posts placed parallel to the narrow or broad wall of the guide, in the theory of the circular-rectangular coaxial waveguide and the theory of other structures containing circular obstacles in the rectangular coupling region.