ISSN:0920-5071    

DOI:10.1163/156939394X00966

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Integral equation methods have generally been the workhorse for antenna and scattering computations. In the case of antennas, they continue to be the prominent computational approach, but for scattering applications the requirement for large-scale computations has turned researchers' attention to near neighbor methods such as the finite element method, which has lowO(N)storage requirements and is readily adaptable in modeling complex geometrical features and material inhomogeneities. In this paper, we review three hybrid finite element methods for simulating composite scatterers, conformal microstrip antennas and finite periodic arrays. Specifically, we discuss the finite element method and its application to electromagnetic problems when combined with the boundary integral, absorbing boundary conditions and artificial absorbers for terminating the mesh. Particular attention is given to large-scale simulations, methods and solvers for achieving low memory requirements and code performance on parallel computing architectures.

ISSN:0920-5071    

DOI:10.1163/156939394X00975

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This article discusses general time-domain modeling in electromagnetics, considering why time-domain modeling may be worth doing and some choices to be made among the principle modeling approaches, and briefly traces the evolution of present time-domain modeling. The steps involved in developing and using a time-domain model are discussed as are some specific aspects of performing time-domain modeling using differential-equation- and integral-equation-based models. An in-depth discussion of more general issues that can arise in time-domain modeling is presented. Finally, time-domain applications are characterized with respect to computer requirements. A representative list of some available time-domain software is also presented along with some concluding comments.

ISSN:0920-5071    

DOI:10.1163/156939394X00984

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this paper, a new Finite Element Time Domain (FETD) solution algorithm, that uses Whitney's edge and face elements for the representation of the electric and magnetic fields is presented for the direct solution of Maxwell's equations. The accuracy and computational efficiency of the algorithm are discussed and illustrative numerical results are presented for a cavity problem. The method itself is equally well applicable to open region problems when employed in conjunction with the appropriate absorbing boundary conditions.

ISSN:0920-5071    

DOI:10.1163/156939394X00993

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Yee's finite difference time-domain method is widely used for numerically solving Maxwell's equations. The Yee algorithm is numerically dispersive which limits its usefulness for modeling wide-band electromagnetic phenomena. In this paper, we describe the use of flux-corrected transport for suppressing the numerical dispersion associated with the Yee algorithm. Flux-corrected transport uses the computed results from a numerically dispersive finite-difference algorithm and a numerically diffusive finite-difference algorithm at each time step to arrive at a final solution. In this case, the dispersive algorithm used is the original Yee FDTD method. Results are given comparing the accuracy of the FDTD algorithm with flux-corrected transport versus the unmodified Yee algorithm for propagating pulsed-type plane waves in two dimensional scattering problems.

ISSN:0920-5071    

DOI:10.1163/156939394X01000

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The use of several high-frequency, asymptotic techniques is explored for modeling the scattering, using higher-order diffractions, of radar targets composed of two or more parallel edges with diminishing electrical separation between them. The Uniform Theory of Diffraction (UTD) is one of the most popular and easily applied techniques; however, difficulties in accurately modeling second-order diffractions are inherent in the method due to the failure of the technique in overlapping transition regions. The effectiveness of the UTD, as the electrical size of the target decreases, is explored using a square cylinder. Other high-frequency methods for dealing with fields in overlapping transition regions are reviewed. Particularly, the Extended Spectral Theory of Diffraction (ESTD) and the Extended Physical Theory of Diffraction (EPTD) are examined, and the EPTD is applied to the scattering by a strip. Results are compared with UTD and moment method (MM) data. A hybrid method, using the UTD plus the ESTD or the EPTD, is recommended for accurately predicting the scattering of radar targets, even of small electrical size, at all observation angles.

ISSN:0920-5071    

DOI:10.1163/156939394X01019

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A closed form solution is presented for the scattering in the far zone by a vertex at the interconnection between the two edges of a plane angular sector, when it is illuminated by a plane wave. The solution is obtained as a superposition of simple interaction mechanisms between the two adjacent edges. The spectral representation of the field diffracted by the first edge is used to illuminate the second edge. The response of the latter is evaluated by applying the induction principle at the plane angular sector. In spite of the simplicity of this basic assumption, the resulting expressions recover in the pertinent directions the dominant edge ray field contributions, including second order diffraction mechanisms. The solution is cast in a very simple, compact matrix form, which explicitly satisfies reciprocity.

ISSN:0920-5071    

DOI:10.1163/156939394X01028

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Until recently, when multi-polarization radars were introduced, not all the fundamental properties of an electromagnetic wave were being exploited fully to detect and identify targets. An attempt is made, to re-unite in a single article, the complex RCS (both magnitude and phase), polarization (coherent) and depolarization signatures of two types of targets-simple and complex. The objective is to concentrate on the basic scattering components that all targets possess and to model them on the basis of their high-frequency response to an incident electromagnetic wave. Detailed equations of the scattering process and the signatures that result from them are presented. It is discussed how the amplitude, phase, polarization and depolarization signatures can be utilized in the discrimination stage of the recognition process.

ISSN:0920-5071    

DOI:10.1163/156939394X01037

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this paper, a novel spectral domain method for obtaining higher order impedance boundary conditions for the problem of electromagnetic scattering from complex coatings is described. The method is then applied to the specific case of chiral coatings on conductors. The present method for obtaining the boundary conditions is quite general, and is applicable to coatings with arbitrary constitutive relations, including anisotropic coatings, such as dielectric layers with tensor permittivity, and non-reciprocal coatings, such as magnetically biased ferrites. Multiple layers may also be handled in a systematic manner. Although the examples presented focus on boundary conditions containing tangential derivatives no higher than second order, an extension to higher order conditions is also straight forward. The standard impedance boundary condition (SIBC), tensor impedance boundary condition (TIBC), and the generalized impedance boundary conditions (GIBC), are contained as special cases of the general method described in this paper. It is also shown how the general method presented allows the effects of curvature to be included in the boundary condition. The examples presented include a number of planar chiral layers and chiral coated circular cylinders, and illustrate the accuracy of the proposed boundary conditions.

ISSN:0920-5071    

DOI:10.1163/156939394X01046

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The performance of radar absorbing material (RAM) is analyzed numerically in low-to-mid frequency range. The dielectric properties of actual absorber were measured and used in the analysis. In the analysis, the so called, Volume-Surface Integral Equation (VSIE) is modified to handle the scattering not only for side incidence but also for forward incidence (i.e., along the wedges). This results in two coupled integral equations in terms of longitudinal electric and magnetic fields. By taking advantage of geometry periodicity, the integration interval is reduced from infinite to one period using Floquet mode expansion. These integral equations are then solved numerically using a point matching technique. The computer code is verified by computing reflection from a lossy slab backed by a perfect conductor and comparing the results to those obtained from exact solution. The scattered fields of infinitely periodic lossy wedges backed by a perfect conductor are computed for a number of cases and the results are presented herein.

ISSN:0920-5071    

DOI:10.1163/156939394X01055

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor