摘要:

The finite element method of Monte Carlo simulations of random rough surface scattering is extended to plane and tapered wave scattering from random metallic surfaces at optical frequencies. The backscattering enhancement associated with these rough surfaces is studied for both TE and TM incident waves. Numerical results of the finite element method are presented and compared with those of the tapered wave integral equation method. In all the cases considered, both the TE and TM incident waves show backscattering enhancement. The lossy surfaces scatter more power for TE incident waves than those of TM due to the TM surface waves. No TE surface wave is supported by rough surfaces simulated in this paper.

ISSN:0920-5071    

DOI:10.1163/156939394X00876

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Kelvin's well-known and Neumann's lesser known image theories for the sphere, valid for static sources outside the sphere, are extended to low-frequency current sources involving a nondispersive dielectric, by expressing known field integrals as arising from suitable image currents. The image of a radial current element is seen to consist of a radial line current between the center of the sphere and the Kelvin point plus a dipole at the Kelvin point. The image of a transverse current element is a combination of a transverse current strip plus a radial bifilar line current between the center and the Kelvin point. These image currents can be interpreted as image charges of the corresponding static problem in harmonic motion. The theory is tested by known limiting cases.

ISSN:0920-5071    

DOI:10.1163/156939394X00885

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper presents a spatial filtering method for reducing ill-effects of atmospheric turbulence on holographic imaging using airborne radars. The method is based on the spatially weighting of amplitudes of received waves and is examined by showing graphically the average strip-image which is holographically reconstructed by using exponential weight functions. The introduction of the weight functions yields fairly good restoration of images degraded by atmospheric turbulence and may be useful for image reconstruction in the case of extremely strong turbulence.

ISSN:0920-5071    

DOI:10.1163/156939394X00894

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The purpose of this paper is to give solid ground to rigorous studies of open-waveguide-related scattering problems. In the core of the difficulties associated with them there lies the presence of infinite but penetrable boundaries. This calls for a revision of the condition of radiation, and to the necessity of justifying the limiting absorption principle. The analysis is based on the Fourier-transform approach and study of the analytic properties of transform functions with respect to a parameter. Except for simple 2-D geometries, regularized integral equations and operator theory theorems are used. The result differs from the free-space expression and involves the guided natural modes spectrum. It reveals also that the direction of power flow associated with each particular mode is to be taken into account. The obtained expressions validate the intuitively clear equations of power conservation and reciprocity. A numerical example is given and extension to more complicated open waveguides is discussed.

ISSN:0920-5071    

DOI:10.1163/156939394X00902

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A resonance effect of transient fields on a thin conducting wire is described. Based on the analysis of the wire's characteristic spectrum, its backscatter, bistatic, and specular scattering are investigated in response to a one-cycle sine waveform. The responding waveforms are discussed in terms of traveling waves. It is found that the resonance effect is directly associated with the excitation of a very strong traveling wave.

ISSN:0920-5071    

DOI:10.1163/156939394X00911

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A general formula is derived, within the framework of the low frequency transmission line formulation, for the internal impedance per unit length of good conductors in terms of the surface electric field. This is used to partition the internal impedance per unit length into a part resulting from the perfectly conducting surface current distribution and corrections resulting from local surface features such as sharp corners. The two electrical properties, skin depth and surface impedance divided by the product of frequency times external magnetic permeability, must be small compared to other distances in the problem (for example the distance between local features such as corners) for this partitioning to be useful. The concept of how the sizes of these two electrical parameters and the ratio of internal-to-external magnetic permeabilities influence the use of approximations, such as the surface impedance approximation, is discussed and illustrated on the problem of a current filament above a conducting half space. The general results obtained in this paper are applied in future papers to obtain the local impedance corrections for right angle corners with arbitrary ratios of internal-to-external magnetic permeabilities.

ISSN:0920-5071    

DOI:10.1163/156939394X00920

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This study presents a newly developed technique for obtaining the theoretical scattering characteristics of the Luneberg lens. Generally, such calculations are approximated by using multi-layered, concentric sphere models. Here the Fredholm Integral Method (FIM) has been applied to the scattering problem, involving a single inhomogeneous sphere, where the refractive index of the sphere varies with radial distance from its centre. Comparisons are presented between scattering from the Luneberg lens, modeled by 3-, 5- and 10-layered spheres and by the FIM technique, for k0a values in the range 1.0 to 5.0. A comparison is also given, at k0a = 5.0 , with a differential equation solution.

ISSN:0920-5071    

DOI:10.1163/156939394X00939

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00948

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00957

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor