摘要:

This paper considers conceptual aspects of different numerical methods for solving eigenvalue and scattering problems in electrodynamics. We will focus on the separation of variables method, the method of lines as a special finite-difference technique, and surface integral equation methods. It will be shown that there are interrelations between these different methods, and that it is possible to derive a general mathematical description based on the separation of variables method. The method of lines is used as a starting point. Its concept is developed up to the Green's function belonging to the homogeneous Helmholtz equation with inhomogeneous boundary conditions prescribed on surfaces which doesn't coincide with a constant coordinate line in one of the coordinate systems in which the Helmholtz equation becomes separable. With this Green's function we are able to derive a corresponding surface integral equation. Finally, the limiting behavior of the method of lines for an infinite number of discretization lines is considered. This results in a generalization of the separation of variables method.

ISSN:0920-5071    

DOI:10.1163/156939399X00330

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A mirroring mechanism, dubbed retrodirection (as opposed to (simple) reflection) was recently introduced in connection with polarimetric measurements in chiral or in gyrotropic media [1]. It has been shown that a specular return from a number of mirrors, combined with the nature of the individual mirrors (being individually reflectors or retrodirectors), and the materials involved, determines the overall systemic properties for the returned electromagnetic waves, i.e., whether polarimetric effects are enhanced or canceled.The present study focuses on the relevant properties of corrugated and cylinder lined surfaces. An exact analytic solution for these geometries is not available, hence two strategies are employed here for relevant limiting cases: For large (compared to wavelength) cylinder radii or large corrugation steps, a specular model is used. Single specular scattering then

ISSN:0920-5071    

DOI:10.1163/156939399X00349

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper presents a method for linear array pattern synthesis with multiple suppressed sectors using phase-only control of the antenna elements. Large phase perturbations are obtained by solving the nonlinear problem using an iterative procedure with linear programming. This technique can impose symmetrical and non-symmetrical suppressed sectors in the perturbed pattern. The full phase-only control is accomplished as well as the partial control of the edge elements. The partial control leads to a significant reduction in the number of phase shifters used for sector suppression as compared to the full control implementation.

ISSN:0920-5071    

DOI:10.1163/156939399X00358

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The goal of this paper is to expose the existence of extremely narrow bandwidth (high Q) resonances in infinitely periodic Frequency Selective Surfaces (FSS) composed of Perfect Electric Conductors (PEC). These narrow bandwidth resonances occur when the current induced on the elements of the FSS has an odd (antisymmetric) distribution. For such resonances of odd current distributions, it is shown that as the incident plane wave approaches normal incidence, the bandwidth approaches 0 Hz (Q approaches ∞). The resonance bandwidth becomes identically 0 (infinite Q) at normal incidence. The currents sustaining such high Q resonances are of very large magnitude. PEC do not dissipate any power, but a small amount of surface resistance of real metals can dissipate enough power (due to the large currents) to completely dampen the high Q resonances. Numerically, as the resonant bandwidth decreases, the condition number of the matrix resulting from the Method of Moments (MoM) formulation increases. For normal incidence (zero bandwidth), the matrix is singular. It is shown that the matrix is ill-posed because of a loss of stability, which comes about in the sense that a small change in the frequency yields a large change in the result.

ISSN:0920-5071    

DOI:10.1163/156939399X00367

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

It is the aim of this work to develop a two-dimensional (2-D) analysis for the electromagnetic field distribution in distributed feedback (DFB) structures. This analysis is based on an equivalent network for the 2-D wave equation which must be satisfied by the components of both electric and magnetic field. The parameters of the equivalent network are determined from the physical parameters of the DFB structure in a straightforward manner. The zero-input response of this equivalent network leads to the dispersion relation for the modes guided by the DFB structure. The method has been applied to a number of optical components utilizing a DFB structure like DFB lasers, optical filters, and multi quantum well DFB lasers. A comparison with common methods of analysis shows that the network modeling yields accurate numerical results. At the same time its computational efficiency can be maintained quite high.

ISSN:0920-5071    

DOI:10.1163/156939399X00376

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In part I of this paper we analyze which statistical properties of a random surface are necessary to describe a wave scattering cross section from this surface. We develop such a mathematical model of sea surface that allows us to find scattering cross section. This model corresponds to statistically homogeneous rough surface that satisfies the following conditions: (1) It has the given two-dimensional (anisotropic) spectrum. (2) It has the given (non-Gaussian) joint probability distribution function (PDF) of two principal slopes at any fixed point. (3) It allows us to obtain in an explicit form the joint probability distribution (characteristic function) for an arbitrary number (N) of differences in of the surface. (4) It allows us to find in an explicit analytical form any mean scattering cross sections appearing in any theory of wave scattering from rough surface. (5) In describing the non-Gaussian PDF we use, instead of the cumulant expansion, another approach: decomposition of the multivariate non-Gaussian PDF in the sum of multivariate Gaussian PDF having different positions and different variances and correlation coefficients. In part II of this paper, we calculated in the Kirchhoff approximation the scattering from a perfectly reflecting rough surface, having non-Gaussian PDF of slopes and anisotropic spectrum.

ISSN:0920-5071    

DOI:10.1163/156939399X00385

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In part I of this paper we analyzed which statistical properties of a random surface are necessary to describe a wave-scattering cross section from such a surface. We develop amathematical model of a sea surface that allows us to find a scattering cross section. In part II of this paper, we calculate in the Kirchhoff approximation scattering from a perfectly reflecting rough surface, having non-Gaussian PDF of slopes and an anisotropic spectrum (they correspond to experimental data for wind-driven waves on the water's surface). In the Kirchhoff approximation we obtained significant differences between Gaussian and non-Gaussian cases with the same spectrum, especially in the range of small grazing angles. The azimuthal dependence of the radar cross-section highly depends on the wind speed. It was found that the ratio of radar cross sections in upwind and crosswind directions strongly depends on the wind speed and can serve as a method of measuring this value.

ISSN:0920-5071    

DOI:10.1163/156939399X00394

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

In this paper, we present an exact analysis of parallel plate-fed slot antennas loaded by a dielectric cylinder. The primary excitation is taken to be either a TE incident mode of the parallel-plate waveguide or an incident E-polarized plane wave. The followed formulation technique leads to singular integral or integrodifferential equations of the first kind which are discretized using quasi-analytical methods. The matrix elements of the resulting system of linear algebraic equations are given either in closed form or via rapidly converging single series. This, in conjunction with the small matrix size required, enables one to obtain very accurate results with low computational cost. Typical numerical results are presented to bring to light the effect of the cylindrical load on the characteristics of the antenna.

ISSN:0920-5071    

DOI:10.1163/156939399X00402

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An exact analysis is presented for investigating parallel plate-fed slot antennas loaded by a dielectric cylinder. The primary excitation is taken to be either a TM incident mode of the parallel-plate waveguide or an incident H-polarized plane wave. The analysis combines singular integral equations with separation of variables techniques. The resulting integral equations are discretized using quasi-analytical methods, which lead to computationally efficient expressions for all matrix elements. This, in conjunction with the small matrix sizes required, leads to very accurate results with low computational cost. The numerical results presented reveal the effect of the load on the characteristics of the antennas.

ISSN:0920-5071    

DOI:10.1163/156939399X00411

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The transient electromagnetic field scattered by a perfectly conducting cylinder located above an infinite, perfectly conducting, periodic surface is computed for TM polarization. A decomposition technique is used to form a set of coupled electric field integral equations for the current on the cylinder and that portion of the surface most strongly interacting with the cylinder. Use of this technique for studying the transient multipath phenomenon of a target located above a sinusoidal surface is discussed.

ISSN:0920-5071    

DOI:10.1163/156939399X00420

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor