摘要:

Two-dimensional scattering by conducting circular cylinders of small to moderate size in wavelengths in the presence of local directive sources is rigorously analyzed. The sources are both extended apertures, represented by arrays of complex source point (CSP) beams and by single CSP beams. From scattering patterns the latter are shown to accurately represent cosine squared aperture distributions as sources and with less accuracy other symmetrically tapered distributions. Scattering cross sections calculated show that for E-polarized local sources the cross section first decreases and then increases with increasing directivity whereas for H-polarized sources the reverse occurs. An explanation for this unexpected behavior is offered.

ISSN:0920-5071    

DOI:10.1163/156939399X00646

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This work presents a new formulation for conducting bodies of revolution (BOR) in layered media. It is derived using magnetic field integral equation (MFIE). The discrete complex image method is used to transform the Sommerfeld integrals into closed form solutions. For large closed objects, the use of the magnetic field formulation is shown to be more advantageous than the electric field integral equation (EFIE) concerning the convergence of the solution. The obtained formulation is applied to the contiguous half-spaces case. Results of both the magnetic and electric field integral equation formulations are presented.

ISSN:0920-5071    

DOI:10.1163/156939399X00655

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Some general statements for theory of wave multiple scattering in a three-dimensional inhomogeneous layered dielectric medium are established using the composition rule of the scattering (T-matrix) operators to show that the problem of wave scattering from dielectric interface may be studied similar to the problem of volume wave scattering. The medium is thought as being a stack of n layers, each of them is confined by perpendicular to the z axis planes and consists of a three-dimensional discrete or continuous inhomogeneous medium. The layers do not intersect between them and are embedded into a homogeneous background. A result of the paper is a mixed system of exact operator equations (transfer relations) for the operator wave reflection and transmission coefficients of the medium and the operator wave amplitudes of waves in splits between layers. It is shown that the transfer relations lead to a separate recurrent system of operator equations, which describe the incremental change of the operator wave reflection and transmission coefficients of stack of n - 1 layers upon attachment of a n's layer to the stack. We derive from this recurrent equations a generalized Riccati equation for the operator wave reflection coefficient of the medium and an corresponding equation for the operator wave transmission coefficient of the medium, the coefficients of the Riccati equation and the corresponding equation being expressed in terms of the operator wave reflection and transmission coefficients of a thin slice of the medium and embedding parameter being taken along the z axis. The derived Riccati equation is applied to the problem of electromagnetic wave reflection from a periodic one-dimensional interface of two dielectric half-spaces, the interface being varied in the x axis direction and the wave electric field vector being parallel to the y axis. A solution to the Riccati equation for this problem is found numerically, taking into account with the aid of the Bloch (Floquet) theorem both the propagating and evanescent waves and not invoking the Rayleigh hypothesis. A resonant effect related to the Wood anomalies is discussed.

ISSN:0920-5071    

DOI:10.1163/156939399X00664

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper addresses the issue of target detection in Gaussian noise for wideband radar systems. Through the use of the parsimonious singularity expansion method (SEM) representation of the late-time transient radar return and Bayesian detection theory, an aspect independent detection method based on a generalized likelihood ratio test (GLRT) is developed. The resulting decision rule has a non-central Χ2distribution which is used to analyze the performance of the GLRT in terms of the probability of detection (PD) and the probability of false alarm (PF) . Results illustrating the performance of the GLRT for two different thin wire targets are displayed in the form of receiver operating characteristics. Simulation results are generated to verify the analytical receiver operating characteristics.

ISSN:0920-5071    

DOI:10.1163/156939399X00673

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper deals with the problem of finding a correct way of restricting the computational domain in the FDTD-method in its application to the analysis of transient wave processes in infinite homogeneous regions containing compact inhomogeneities. The formulation of the explicit ABCs (Absorbing Boundary Conditions) in such a way that they do not distort the physical model simulated by the mathematics, and the incorporation of these ABCs in the computational scheme form the basis of the approach presented here. A number of numerical results are given, illustrating in particular the performance of the exact ABCs in comparison with lower order approximations.

ISSN:0920-5071    

DOI:10.1163/156939399X00682

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

in this paper, a statistical study on correlative many electromagnetic (abbr., EM) interferences is given mainly from a theoretical viewpoint on the basis of random walk problem in multi-dimensional signal space, along to the same study line as in our previous paper. First, a joint multi-variate characteristic function of Hankel transform type matched to many kinds of EM environmental fluctuation waves is introduced especially in an extended form (in space and time domains) of D. Middleton's basic result. Then, a joint multivariate probability density function (abbr., pdf) is explicitly derived for correlative many kinds of EM random fluctuations with a power scaled variable (or an effective value) observed by many receivers of mean square operation type, especially by laying emphasis upon a derivation of explicit pdf expression for correlative two kinds of EM fluctuation waves. The effectiveness of the proposed method is experimentally confirmed through an acoustic type simulation experiment with joint space-time non-Poisson interference as one of the same wave motion type environment as EM environment and an application to the actual EM environment.

ISSN:0920-5071    

DOI:10.1163/156939399X00691

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Approximate boundary conditions for an inhomogeneous nonlinear thin layer coated on a perfectly conducting plane are derived through an asymptotic expansion of the field in power series of the thickness. Numerical results show that the second order approximate boundary condition gives a sufficient accuracy for all incident angles when the coating thickness is much smaller than the wavelength. The case when the nonlinear thin layer is coated on a curved metallic surface is also considered.

ISSN:0920-5071    

DOI:10.1163/156939399X00709

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The class of decomposable bi-anisotropic media was recently defined to consist of media in which any electromagnetic field can be decomposed in two individual electromagnetic fields satisfying certain conditions for the electromagnetic fields. Also it was shown that, for a medium in this class, the fourth-order Helmholtz determinant operator governing the basic electromagnetic fields can be factorized, i.e., expressed as a product of two second-order operators. In the present paper, plane-wave propagation in the general decomposable medium is studied. Analytical solutions are derived for the dispersion equation and the polarizations of the eigenwaves are also determined in analytic form. As a check the expressions are applied to a medium with previously known solutions. In an appendix, conditions for the medium dyadics of the decomposable bi-anisotropic medium are derived for the case when the medium is lossless.

ISSN:0920-5071    

DOI:10.1163/156939399X00718

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The purpose of this paper is to study the effective permittivity behavior of dry snow in the 18 to 90 GHz range. The empirical values of the effective permittivity of dry snow are derived from experimental data on the extinction coefficient of the dry snow. The range of the validity of strong fluctuation theory model for dry snow effective permittivity is examined by comparing the model predictions with experimental data-based values. The effective permittivity values as a function of mean grain size, frequency and temperature are numerically evaluated. Several empirical and theoretical mixing models for dry snow are also considered in this study.

ISSN:0920-5071    

DOI:10.1163/156939399X00727

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An approximate method to obtain the line parameters of multiple coupled microstrip lines based on the full-wave analysis is presented. The technique uses the coupled-mode equations for the amplitudes of currents on each line. The coupling matrix in the equations, expressed by overlap integrals between the eigenmode fields of each isolated single line, characterizes the electromagnetic natures of the coupled lines. The eigenvalues and eigenvectors of the matrix yield the propagation constants, the ratios of line currents, and the characteristic impedances of the coupled modes. The proposed method is applied to two nonidentical coupled lines and three nonidentical coupled lines in a single plane, and two identical coupled lines in dual planes. The numerical results for the mode propagation constants and characteristic mode impedances are compared with those obtained by the direct numerical solution method for the coupled lines. Both results show a good agreement.

ISSN:0920-5071    

DOI:10.1163/156939399X00736

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor