摘要:

Generalized effective impedance boundary conditions for an inhomogeneous thin layer coated on a perfectly conducting plane are considered. The first order and second order approximate impedance boundary conditions are derived first for a two-dimensional thin layer with TE plane wave incidence through an asymptotic expansion in power series of the thickness. Numerical results show that the second order boundary condition gives a sufficient accuracy for all incident angles. A rigorous derivation for the case of Maxwell's equations for a three-dimensional inhomogeneous thin layer is also given.

ISSN:0920-5071    

DOI:10.1163/156939397X01106

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A novel numerical technique based on the orthogonal polynomial approximation with minimum error-variance is presented for analyzing optical fibers with arbitrary refractive index profile. The developed method is verified to provide reliable solution in the case where the existing method based on the Chebyshev polynomial expansion shows instability. The usefulness of the proposed method lies in a number of desirable features viz., procedural simplicity, complete linearization of the problem, numerical stability, and more, that its application brings.

ISSN:0920-5071    

DOI:10.1163/156939397X01115

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Power distribution system in printed circuit board (PCB) in the form of conducting planes plays a critical role in ensuring proper operation of the whole PCB assembly. An effort to model the power distribution system in terms of equivalent circuit consisting of inductors and capacitors using planar circuit approach is presented in this paper. In this approach, the power planes are discretized into sub-segments. Electromagnetic fields within the planes are solved using Helmholtz wave equation. Approximating differentials with appropriate finite differences, the solutions can be interpreted as equivalent mesh of capacitors and inductors. These circuit models can be obtained in SPICE format so that simulations can be performed easily. SPICE simulation is performed for two planar circuit examples. Results from the first example of a L-patch microstrip planar circuit are compared with those from Method of Moment; while results of the second example of a rectangular stripline planar circuit are compared with those from Finite Difference Time Domain (FDTD) approach and from measurement. A third illustrative simulation example shows a possible application of the model in deriving design rules for high-speed PCB layout.

ISSN:0920-5071    

DOI:10.1163/156939397X01124

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A hybrid technique combining the shooting-and-bouncing-ray (SBR) method and the method-of moments (MoM) is presented for analyzing scattering by large conducting bodies having small, inhomogeneous protrusions. In this technique, the MoM with an approximate Green's function is used to characterize the small protrusions, yielding an admittance matrix, which, when multiplied with the incident field on the protrusions, yields the currents induced on the protrusions. The incident field in the presence of the large bodies is calculated using the SBR method. The field radiated by the currents on the protrusions is also calculated using the SBR method with the aid of reciprocity. Furthermore, an iterative approach is developed, which can reduce the error introduced by the use of the approximate Green's function. Numerical results are given to demonstrate the efficiency, accuracy, and capability of the hybrid technique.

ISSN:0920-5071    

DOI:10.1163/156939397X01133

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper describes the electromagnetic wave diffraction from a metallic Fourier grating based on the T-matrix analysis and the extended boundary condition. The grating consists of a basic sinusoidal wave and a second-harmonic wave. The analytical form of the expression of matrix elements is presented in the term of the Bessel functions. The error of power conservation versus the truncated number of the basic functions has been examined; thus a high accuracy result is obtained. Diffraction efficiencies versus incident angle, groove depth and wavelength have also been discussed for both perfect and lossy metallic (Au) gratings. Numerical results are in good agreement with those obtained from other methods and experimental values. Reasonable numerical results are presented for a groove depth per period of the grating less than 0.28.

ISSN:0920-5071    

DOI:10.1163/156939397X01142

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The analytical solution for the scattering of electromagnetic plane waves from an infinitely long homogeneous cylinder of arbitrary material, in an eccentric coating at oblique incidence, is presented. The solution is determined by solving the scalar wave equation in the cylindrical coordinates, for the various geometric regions and by applying the boundary conditions at the material interfaces. Furthermore, the translational addition theorem of Bessel functions is utilized for transferring the fields component between two cylindrical coordinate systems. Both polarizations of the incident plane wave (TM and TE with respect to the z -axis) are considered. The resulting solution consists of a system of eight coupled equations for the unknown expansion or scattering coefficients. Expressions for the extinction, scattering, and back scattering cross sections are presented. A numerical algorithm for the solution is developed, implemented, and tested for several limiting and special cases. Comparisons of the results with those reported in the literature show excellent agreements. Numerical calculations indicate that the eccentric cylinder arrangement is easily distinguishable from that of the coaxial cylinders.

ISSN:0920-5071    

DOI:10.1163/156939397X01151

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The temporal variation of millimeter wave backscatter signature of snowcover is studied based on a dense medium radiative transfer (DMRT) theory and a one-dimensional mass and energy balance model of snow named SNTHERM. The multilayer DMRT scattering model of snowcover developed in this work takes into account the reflection and refraction at the snow-snow interfaces. Appropriate boundary conditions, quadrature points and weights are selected for using the discrete-ordinate eigenanalysis method to solve the multilayer DMRT equations. It shows that the inclusion of reflection and refraction at the snow-snow interfaces may affect the model prediction. Cohesive spherical particles are applied to account for the clustering feature of snow grains. To model the time-varying behavior of snowcover, SNTHERM is employed to simulate the aging process of snow. SNTHERM provides pertinent snow parameters, such as grain size, density, liquid water content, and stratification with a high resolution in time and depth. These snow properties are then used in modeling the temporal radar signatures of snowcover. The comparisons of temporal model responses with time series polarimetric backscatter data at 35 and 95 GHz are presented. Good agreement is demonstrated between model and measurements in both timing and magnitude. The results indicated that the coupled DMRT and SNTHERM model can be useful in studying the electromagnetic interactions with time-varying snow microstructure.

ISSN:0920-5071    

DOI:10.1163/156939397X01160

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

When accounting for polarization effects in radar and communications systems, it is often necessary to transform descriptions of the polarization state of an antenna or the polarization response of a target between local (or body-centered) and global coordinate frames. Such transformations correspond to rotation of the polarization basis by a prescribed angle which is a function of (1) the coordinate transformation matrix that relates the two coordinate frames and (2) the direction of propagation. Although methods for determining the polarization rotation angle have been presented previously in the literature, they can only be applied in special cases. Here we solve the problem in the general case using methods based on spherical trigonometry and vector algebra, respectively. In order to apply these techniques, the elements of the coordinate transformation matrix must be known. Since conventional methods for determining these elements requireinformation which may be difficult to obtain in practice, we present an alternative method which requires only a pair of directions that have been expressed in terms of both coordinate frames.

ISSN:0920-5071    

DOI:10.1163/156939397X01179

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939397X01188

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor