摘要:

The paper further develops the recently introduced idea of compressing the impedance matrix by an iterative selection of expansion functions. The improved algorithm uses an overcomplete dictionary comprising bases whose inherent properties match some features of the given scattering problem. Thus, the overcomplete dictionary offers a variety of expansion functions from which a solution-oriented spanning set for the unknown current is extracted. The number of iterations in the proposed algorithm is suppressed by selecting more than one expansion function at each iteration. This latter section is facilitated by a matching pursuit process. It is shown that the compression ratio of the resultant compressed impedance matrix is superior to the one achieved by the ordinary iterative matrix compression algorithm.

ISSN:0920-5071    

DOI:10.1163/156939398X00359

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We use the localized approximation and some modified versions to study the electromagnetic field interaction of a plane wave with a slab of complex permittivity. The approximation as originally proposed is based on the localization property of the appropriate Green's function and the smooth variation of the internal field. In our one-dimensional case, the Green's function singularity degenerates into a localized peak. We apply two iterative techniques to the localized procedure in order to better simulate the internal fields. The first technique involves iterating the governing equation once before adopting the localized approximation, while the second technique involves iterating the localized approximation once. A study of other approximations based on the Born approximation is also included. In addition we present a generalization of the localized approximation using the Extended-Born approximation. We compare and contrast the performance of the various approximations in simulating the internal and external fields numerically. The localized approximation and the two modified versions are next used in one-dimensional profile reconstruction based on a least-structured version of the least-squares inversion method. We compare and contrast the performance of the approximations in profile reconstruction. A noticeable consequence of these modifications is an aggravation of the nonlinearity in the inverse problem. We investigate the consequences of this aggravation.

ISSN:0920-5071    

DOI:10.1163/156939398X00368

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this contribution the generalized exponential matrix technique in spectral domain is adopted for investigating the combined effects of chiral operation in some multilayered bianisotropic substrates, and the mathematical treatment accounts for the most generalized bianisotropic linear media characterized by four 3 x 3 constitutive tensors. Such chiral operation can be realized artificially using a certain number of bianisotropic biaxial or Faraday chiral plates in order that double or three chiralities are formed. Numerical results are presented to demonstrate the influences of changing different variables associated with the reversing of the sign of chirality parameter : the right-and left-handed spiral orientations of the axes of four constitutive tensors as well as the biasing magnetic fields in chiroferrite and chiroplasma substrates on the co- and cross-polarized far-field distribution of a dipole antenna. Some unique relations concerning the main beam direction and the co- and cross-polarized components of the far-field are found and discussed.

ISSN:0920-5071    

DOI:10.1163/156939398X00377

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

It is shown that a large class of dynamic systems with non-stationary dimensions can be solved analytically. The corresponding mathematical models of these systems are initial-boundary-value-problems for the wave equation with moving boundary conditions. The method given in a previous paper is generalized and used for solving such problems. It consists of transforming the wave equation for the domain with moving boundary into a form-invariant wave equation for a domain with fixed boundary. The transformation is accomplished through a formal change of variable, and an analytical function F(W) of a complex variable W, permitting a conformal mapping between the two domains. For the transformation to exist, F(W) has to satisfy the condition F*(W) = F(W*). We show that the solution of such systems is obtained in the form of a functional Fourier series,, and the modes are dynamical, each having an instantaneous frequency. The problem of initial conditions is also treated. Furthermore, it is shown that all possible transformation functions permitting the covariant transformation of the wave equation have to satisfy two fundamental relations. As applications, some examples of F(W) and transformation functions are given.

ISSN:0920-5071    

DOI:10.1163/156939398X00386

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Based on the eigenfunction expansion of electromagnetic waves in the reciprocal uniaxial bianisotropic medium, an extended mode-matching method is developed to study the electromagnetic scattering of a PEC circular cylinder with an inhomogeneous coating thickness of reciprocal uniaxial bianisotropic medium. Excellent convergence property of the bistatic echo width is numerically verified, which establishes the reliability and applicability of the present extended mode-matching method for two-dimensional problem of reciprocal uniaxial bianisotropic medium.

ISSN:0920-5071    

DOI:10.1163/156939398X00395

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A regularized solution of the hybrid Generalized-Multipole - Technique (GMT) / Moment-Method (MoM) method is presented in this paper. The study is focused on convergence and accuracy aspects of the solution, examining their dependence on the location and the number of the GMT and MoM sources. A Tikhonov regularization process is incorporated, which highly improves the conventional GMT-MoM solution and besides stabilizes it by reducing the condition number associated with the matrix formulation of the problem. Furthermore, the use of this regularization tool allows to overcome an important difficulty for the users of the GMT-MoM method, namely, its great dependence on the sources location. These ideas are verified by analyzing the convergence of the method for two-dimensional TE and TM polarized problems.

ISSN:0920-5071    

DOI:10.1163/156939398X00403

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An accurate and efficient numerical solution is presented for the two-dimensional electromagnetic wave scattering from multilayered resistive strip gratings. Both E- and H-waves are treated. The method is based on the integral equations combined with the moment method with regularization procedure. The numerical experiment reveals the criteria for the truncation numbers. The reflected, transmitted, and absorbed powers are computed for various grating parameters and frequencies. Special attention is paid to maximizing the absorption into the strips, and thereby the relative absorbed power amounts to more than 90%.

ISSN:0920-5071    

DOI:10.1163/156939398X00412

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents a spectral-domain analysis of a 2 x 2 microstrip antenna array fed by a microstrip line. The Galerkin Method of Moments is employed to gain insight into the characterization and performance of such a patch array antenna system, whereas the mutual coupling is taken into account in the analysis. The VSWR and the radiation pattern of the array are calculated and compared with the data of measurements made in a frequency range from 9 to 11 GHz. As a further extension of this analysis of the 2 x 2 array, the features of a 4 x 4 microstrip patch array are also investigated in this paper and some interesting results are obtained. As shown in the comparison, reasonably good agreement between theoretical analysis and experimental data is achieved.

ISSN:0920-5071    

DOI:10.1163/156939398X00421

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The extension of the Method of Auxiliary Sources (MAS) to large body scattering problems is investigated. Approximations leading to correct predictions of scattering field with minimum numerical cost are examined. After interpreting the involved physical phenomena associated with scattering field singularities, highly efficient MAS algorithms are developed. Furthermore, the same approach leads to a source visualization technique, which is of exceptional interest. As result of this analysis, an efficient "target" visualization method for large body scatterers, is proposed.

ISSN:0920-5071    

DOI:10.1163/156939398X00430

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A hybrid method consisting of employing the mode matching method in conjunction with the Fourier transform technique is used to analyze the radiation of the lowest order TM-wave from an impedance loaded parallel plate waveguide. In contrast to the classical formulations which lead to an intractable matrix Wiener-Hopf equation, the hybrid method that we will adopt reduces the related boundary value problem into a scalar modified Wiener-Hopf equation of the second kind and bypasses the most challenging step of matrix Wiener-Hopf factorization. The solution involves infinitely many unknown constants satisfying an infinite system of linear algebraic equations which can be solved approximately through numerical procedures. Some computational results showing the effects of the impedances of the plates and the plate to plate separation distance on the radiation phenomenon are also presented.

ISSN:0920-5071    

DOI:10.1163/156939398X00449

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor