摘要:

The scattering problem for a bi-isotropic object of arbitrary shape is considered. Boundary integral equations are derived in a rigorous way through the dyadic Green's functions for the bi-isotropic medium. The boundary integral equations are solved numerically by the method of moment with a triangular patch modeling and numerical results are presented. In particular, the numerical results for a bi-isotropic sphere are compared with an explicit solution which is derived through the expansions of the spherical vector wave functions.

ISSN:0920-5071    

DOI:10.1163/156939398X00485

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The fields refracted by circular symmetric hyperbolic lens illuminated by a linearly polarized wave incident obliquely on the aperture are calculated from the induced surface currents. It is shown that the fields in the axial region approximate to the fields in the aperture of corrugated horn under balanced hybrid condition. The image structures for different focal ratio are compared with the classical Airy pattern, deduced by scalar analysis, of optical focusing systems. The coupling between the lens and a corrugated horn at different position on focal plane are presented. The fields distributions on focal surface besides of the focal plane are also calculated.

ISSN:0920-5071    

DOI:10.1163/156939398X00494

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents a novel approach for constructing the complete eigenfunction expansions of electric and magnetic dyadic Green's functions for general linear bianisotropic media. The eigenfunctions are expressed in terms of linear combinations of commonly employed solenoidal and irrotational vector wave functions. Based on the theory of distributions, the source point singularities required for complete expansions of the dyadic Green's functions are derived directly from Maxwell dyadic equations without any integration. Apart from the singularities, the discontinuities associated with the eigenfunction expansions across the source point are also obtained as by-products. These discontinuity relations constitute the fundamental equations from which the eigenfunction expansions outside the source point can be constructed. This approach is parallel to the utilization of Lorentz reciprocity theorem for relating eigenwaves with sources and it is applicable directly to both nonreciprocal as well as reciprocal media. Furthermore, the discontinuity relations also yield directly the jump conditions for electric and magnetic fields across a current sheet.

ISSN:0920-5071    

DOI:10.1163/156939398X00502

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Scattering by a perfectly conducting strip which is buried in an infinite grounded dielectric layer is considered. It is assumed that the strip is far away from interfaces of the grounded dielectric layer. This assumption is utilized to simplify the work by considering that the scattered field, which is reflected more than once by any interface or reflected by both the interfaces of grounded dielectric layer, has no interaction with the buried strip. Dominant contribution of the reflected scattered field which interacts with the strip is calculated asymptotically, for large separation of the strip from boundaries of the grounded dielectric layer. Far-zone field expression, for region above the grounded dielectric layer, is derived taking into account the effects of interaction of reflected scattered field with the strip. This expression is derived in a general form which can be applied to any arbitrary cylindrical obstacles. Some numerical results are given for the case of perfectly conducting circular cylinder buried in this geometry.

ISSN:0920-5071    

DOI:10.1163/156939398X00511

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The physical peculiarities of the wave propagation in coupled cylindrical slot lines are studied in the context of a rigorous electromagnetic theory. The mode analysis is performed. The approximate dispersion equations of the lowest waves in symmetrically coupled cylindrical slot lines are derived and the splitting of the wave spectrum is considered. The numerical analysis of the rigorous dispersion equation yields the wave dispersion characteristics depending on geometrical and constitutive parameters. The calculation results of the field structure of the modes are presented. A New peculiarity of the phenomenon of the waves mutual transformation is discussed.

ISSN:0920-5071    

DOI:10.1163/156939398X00520

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A rigorous and efficient method for characterizing rectangular waveguide junctions is presented. Using the image theory, in this method, the junction problem is transformed into an aperture problem in a uniform rectangular waveguide. The fields in the cavity region expressed by Fourier integrals are matched to those on apertures expanded by the normal modes of arm-waveguides. Then a system of linear equations with very fast convergence is obtained to determine scattering parameters of the junction. The scattering parameters are calculated for right-angle corner bends, symmetric E- and H-plane T-junctions, asymmetric E- and H-plane T-junctions, and asymmetric series E-plane T-junctions, which agree very well with literatures.

ISSN:0920-5071    

DOI:10.1163/156939398X00539

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this paper we propose using wideband measurement techniques to determine propagation mechanisms. The factors that can affect the accuracy of the measurements are analyzed. The delay profiles can be obtained by applying inverse fast Fourier transforming (IFFT) on the measured frequency response. To avoid range ambiguity in the delay profile, the frequency response should be finely sampled. The peak values sampled in the delay profiles can be used to represent certain scattering mechanisms such as reflection coefficients or edge diffraction coefficients. To obtain accurate peak value, enough zeros will be padded to the frequency domain measurement data before applying IFFT. In this paper we also propose a calibration procedure so that the ordinate value in the delay profile can represent the propagation loss relative to that at the reference position. Wideband measurement techniques will be employed to determine wall reflection coefficients and edge diffraction coefficients. Consistency between the experimental and simulation results shows the effectiveness of the proposed methods.

ISSN:0920-5071    

DOI:10.1163/156939398X00548

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The electromagnetic eigenfrequencies fnsmin a perfectly conducting spheroidal cavity are determined analytically. The analytical determination is possible in the case of small values of h = d/(2a), (h « 1), where d is the interfocal distance of the spheroidal cavity and 2a the length of its rotation axis. In this case exact, closed-form expressions are obtained for the expansion coefficients g(2)nsmand g(4)nsmin the resulting relation fnsm(h) = fns(0) [1 + h2g(2)nsm+ h4g(4)nsm+ O(h6)]. Analogous expressions are obtained with the use of the parameter v = 1- a2/b2(for |v| << 1) , where 2b is the length of the other axis of the spheroidal cavity. The electromagnetic field is expressed in terms of spheroidal eigenvectors. Numerical results are given for the lower-order modes.

ISSN:0920-5071    

DOI:10.1163/156939398X00557

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A method is described which optimizes the performance of antenna arrays with defective elements, by numerically finding a new excitation for the remaining ones. Two approaches for recovering the pattems have been investigated. In the first, new excitations are obtained by changing their amplitude distribution, whereas in the second, only the phase distribution is modified while keeping the original amplitudes. These optimum values for new excitations are calculated by the application of the simulated annealing technique. Examples for both sum and shaped beam patterns are presented to illustrate the optimal results obtained.

ISSN:0920-5071    

DOI:10.1163/156939398X00566

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The most widely used model for Inverse Synthetic Aperture Radar (ISAR) signal processing and image reconstruction is the point scatterer model. Instead, a line scatterer model is proposed and used in this paper for estimating significant states of a target, as well as to reconstruct a good image of the target. The line scatterer model is shown to contain information regarding the inclination angle and length of the target. Simulation studies for an aircraft show that the model also provides a good reconstructed image of the aircraft. It is shown that the line scatterer model offers a unified approach to the state estimation and imaging of a target.

ISSN:0920-5071    

DOI:10.1163/156939398X00575

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor