摘要:

The averaged field approach is used for obtaining the band structure of a photonic crystal with conducting inclusions whose dimension is small compared with the longest period of the rectangular lattice of the photonic crystal. The band structure is obtained in an explicit and simple way. The method is verified numerically by comparing with a FDTD method.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756663

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An approximate theory of scattering by nearly two-dimensional (2D) objects (plane wings, leg bones,...) is presented and implemented numerically in the case of perfectly conducting diffraction gratings slightly modulated in the direction of the grooves. Derived from the Waterman formalism, this theory leads to the solution of several problems of scattering by 2D objects, illuminated by a sum of plane waves. It is shown from numerical results that this theory is able to deal with nearly two-dimensional objects in condition where, as far as we know, the only numerical tools are based on rigorous theories of three-dimensional scattering problems.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756664

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper presents a rigorous and concise formulation of the complete eigenfunction expansions of the dyadic Green's functions for cylindrical multilayered gyrotropic bianisotropic media. The media may consist of any number of layers bounded by optional impedance/ admittance walls. Both electric and magnetic dyadic Green's functions for arbitrary field and source locations are derived simultaneously making use of the principle of scattering superposition. Based on the theory of distributions, the singularities and discontinuities associated with unbounded dyadic Green's functions are deduced directly from Maxwell dyadic equations. Using the discontinuity relations obtained, the eigenfunction expansions outside the source point are constructed in terms of an expedient set of cylindrical vector functions. For the scattered dyadic Green's functions, their scattering coefficient matrices are determined without cumbersome operations while providing good physical insights into the scattering mechanism. These coefficients are expressed in compact and convenient forms involving global reflection and transmission matrices. Corresponding to the impedance/admittance boundary walls, the global reflection matrices are related directly to the wall impedance/admittance dyadics. For illustration, the general expressions of dyadic Green's functions are applied to the configuration of a perfect conducting cylinder coated with gyrotropic bianisotropic medium.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756665

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The synthesis of conformal antenna arrays is complicated by the impossibility factorizing the analytical expression for the power pattern into an element factor and an array factor. This article describes a general method of pattern synthesis that, given a well-defined single-element power pattern, is applicable to arrays of arbitrary geometry. Essentially, the method uses simulated annealing to optimize the excitation distribution so as to minimize the difference between the power pattern it generates and the desired power pattern.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756666

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Modeling of long range propagation of pulsed fields along guiding structures poses some major difficulties with the conventional FDTD scheme, arising from the vast computer resources needed to discretize the entire domain and the accumulation of numerical dispersion error. The moving frame FDTD approach, presented in this work, overcomes these difficulties by limiting the computational grid to a window centered about the propagating pulse and moving along with it at the local wavespeed of the medium. In this work, we first present an FDTD solution of the field equations as formulated in the moving coordinate frame, and then explore such issues as the numerical dispersion, which is shown to be reduced substantially compared with the stationary formulation, the numerical stability, and the absorbing boundary conditions at the leading, trailing and side boundaries of the moving window. Numerical results of pulsed field propagation along graded index waveguides are shown, and the capability of the method is demonstrated with propagation distances exceeding the order of 104 pulse lengths. We choose initial field distributions that give rise to pulsed beam fields. The propagation characteristics of these fields along nonuniform guides are explored analytically in the Appendix. The numerical results are also checked against frequency domain adiabatic mode solutions developed in the Appendix.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756667

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The Heaviside operational calculus is known to be an effective means for obtaining first-hand solutions to various electromagnetic problems. Basic problems can often be reduced to the compact form of a pseudo-differential operator operating on the delta function. The problem is then shifted to the interpretation of the result in terms of calculable functions. The present article reviews methods helping in the interpretation process and a table of useful operational rules is given as an appendix. Operator formulation of two-dimensional multipole fields and sources is discussed with examples on the synthesis of radiation patterns by multipole sources.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756668

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An innovative miniature rectangular cavity with an infinitely thin meander line on a stratified medium is presented. It is designed to be a quarter-wave section of the shielded meander line. The dyadic Green's function for a rectangular cavity with a stratified medium is derived by a new method. Based on the simplification of the dyadic Green's function, the input impedance of the coaxial lineexcited rectangular cavity is determined by a multi-filament methodof- moments solution. Good numerical results are observed and the rectangular cavity is proved to be a quarter-wave section of shielded meander line, grounded at one end and open-circuited at the other.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756669

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The frequency-domain method of moments (MoM) has been used to analyze the induced current characteristics for an arbitrarily shaped, perfectly conducting, thin wire antenna and scatterer. The time-domain response of the current is obtained from the frequency domain data via an inverse fast Fourier transform (FFT) when the wire is excited by a Gaussian pulse. The numerical results of the transient current show that the late-time responses for both the radiation and scattering of a straight wire are almost identical, but that their early-time responses are quite different. The poles and residues of the time-domain response that contain the complex resonant frequencies of the scattering object are then extracted via the generalized pencil-of-function (GPOF) method. It is numerically demonstrated that the complex resonant frequencies of the object are their natural frequencies since they do not depend on the excitation sources. The time-domain response reconstructed by using the poles and residues is in excellent agreement with that obtained by FFT of the frequency domain data. The complex resonances for the transient scattering of an L-shaped wire are also analysed. As an application of this method to the radiation and scattering of buried bodies, the scattering from a strip on the surface of a lossy half-space is investigated and its complex resonances are recognized.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756670

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Scattering of plane electromagnetic waves from a cylindrical object of arbitrary cross-section which is buried in a geometry with parallel plane interfaces is studied. Far-zone scattered field expression is derived in a general form which contain two terms. Each term of this general form contains two factors. One factor depends only on geometry of the problem while other factor depends upon shape of the object, primary excitation and geometry of the problem. Shape dependent factor becomes independent of the geometry if it assumed that the object is deeply buried and in this situation this factor is termed as shape function. Field expression in a particular geometry for one object can be utilized for other object by inserting the shape function of desired object. Shape functions involved in field expression can be identified analytically for objects with simple shapes. It is observed that field expressions becomes quite simple for the case of a circular cylinder.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756671

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Utilizing an approximate induced current distribution, the far-zone scattered fields from a perfectly conducting, circular cylinder, which is deeply buried in a dielectric half-space are evaluated. Interpretation of these scattered fields is presented in terms of ray optics. Important scattering parameters, i.e., far-zone field patterns, 3dB beamwidth, scattering width and total scattered power are evaluated. It is found that monostatic scattering width of circular cylinder, which is deeply buried in a dielectric half-space configuration, is related to monostatic scattering width of circular cylinder in a homogeneous medium via dielectric constant times the fourth power of Fresnel transmission coefficient. Behaviour of the total scattered power as a function of depth is found to be oscillatory around a mean value which is the total power scattered from a cylinder in homogeneous medium.

ISSN:0920-5071    

DOI:10.1080/09205071.2000.9756672

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor