摘要:

A simple, efficient and rapidly convergent algorithm for evaluating the cutoff wavenumbers and the field of propagating modes inside circular waveguides with one or two inner strip conductors is presented. The formulation leads exactly to a Carleman-type singular integral equation (S.I.E.) for the surface current density (-ties) on the strip(s); the solution is based on Neumann's expansion of the Hankel-function kernel of the S.I.E. and is particularly suited for wide as well as narrow strips. Numerical results for the cutoff wavenumbers, both TM and TE, are presented for various waveguiding configurations and the efficiency of the algorithm is amply demonstrated.

ISSN:0920-5071    

DOI:10.1163/156939392X00265

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We outline the analytical basis of a scheme to excite a specified geometric form of the sub-surface field from the surface of a conducting half-space. The inversion or migration process is exact for the azimuthally symmetric model assumed. The numerical integration to determine the surface aperture field is straightforward. It is shown that, if the sub-surface field is too limited in lateral extent, the required aperture field distribution has a severe oscillatory character.

ISSN:0920-5071    

DOI:10.1163/156939392X00274

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We consider the problem of the diffraction of a plane electromagnetic wave by a square array of perfectly conducting cylinders of finite length. We outline a method of generating a modal solution of this problem. The finding of modes necessitates the evaluation of a set of dynamic lattice sums over the square array. We consider two methods of evaluating the lattice sums, which do not converge absolutely. The first of these methods is that of Ewald summation, while the second relies on a set of identities among the lattice sums. We show that the results of the two methods agree, and that the second method is both the easier of the two to implement, and is capable of generating accurately the values of a large set of lattice sums.

ISSN:0920-5071    

DOI:10.1163/156939392X00283

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Coherent propagation of polarized millimeter waves through falling nonspherical hydrometeors is considered on the basis of Foldy's approximation. It is assumed that the distribution of hydrometeors over orientations is locally axially symmetric, the axis of symmetry being given by the local direction of air flow around the hydrometeors. An efficient rigorous method is described to compute the orientationally averaged forward-scattering amplitude matrix. This method is based on Waterman's T-matrix approach and fully exploits rotational properties of the T-matrix. First, the T-matrix is analytically averaged over hydrometeor orientations in the local coordinate system with the Z-axis along the direction of local air flow. Then, the elements of the forward-scattering amplitude matrix with respect to the local and laboratory coordinate systems are calculated via simple analytical expressions. Analytical solutions of the propagation equation for the coherent electric field are discussed. Cross polarization of the coherently transmitted linearly polarized wave is computed for canting spheroidal raindrops at 34.8 GHz, and the effects of the scatter of raindrop canting angles on the cross polarization are discussed. In particular, it is shown that the scatter of raindrop canting angles reduces the cross polarization considerably as compared with that of equioriented raindrops.

ISSN:0920-5071    

DOI:10.1163/156939392X00292

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Scattering of bound surface waves by dielectric obstacles along planar dielectric waveguide is studied. An asymmetric planar dielectric waveguide is formed by the tri-layered substrate/film/cover environment, typical of integrated circuits for millimeter and optical wavelengths. An electric Green's function (believed new) is constructed for the TE field maintained in either the film or cover layers by currents immersed in those regions. Using a direct complex analysis approach, the Green's function is expanded in the discrete and continuous propagation spectrum components for the asymmetric planar waveguide. This electric Green's function is exploited to study scattering of TE surface waves by uniform dielectric discontinuity placed arbitrarily along the asymmetric waveguide. A polarization EFIE description of the discontinuity region is developed. Scattering coefficients are subsequently calculated in terms of the induced field. Method of moment (MOM) numerical solutions are implemented for slice discontinuities along an asymmetric slab waveguide.

ISSN:0920-5071    

DOI:10.1163/156939392X00300

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Modal propagation in chirowaveguides with perfect electric walls is studied. Both the circular cylindrical and the two parallel plate chirowaveguides are considered. Mode bifurcation in the circular chirowaveguide is demonstrated by showing that each mode pair with exp (imØ) and exp (-imø) azimuthal variations have the same cutoff frequency but different phase constants at higher frequencies. In the two parallel plate chirowaveguide, a pair of an odd mode and the next even mode start at the same cutoff frequency, in agreement with the results presented by Engheta and Pelet. We show, however, that the lowest order even mode has no odd counterpart and is therefore the dominant mode in a two parallel plate chirowaveguide.

ISSN:0920-5071    

DOI:10.1163/156939392X00319

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The vector circuit theory developed for isotropic and chiral slabs and multilayered structures is generalized for biisotropic (non-reciprocal chiral) media slabs and multilayered structures. The theory appears to be similar to that used for reciprocal structures and enables one to study plane wave reflection and transmission for arbitrary polarized waves coming at oblique angles of incidence. The numerical examples clarify the combined effect of chirality and non-reciprocity of the media on reflection and transmission characteristics of biisotropic layers.

ISSN:0920-5071    

DOI:10.1163/156939392X00328

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The inverse scattering of a buried imperfectly conducting cylinder is investigated. Assume that a conducting cylinder of unknown shape and conductivity is buried in one half-space and scatters the field incident from another half-space where the scattered field is measured. By giving the scattered field, we can reconstruct both the shape and the conductivity of the object. The Newton-Kantorovitch algorithm and the moment method are used to transform the nonlinear integral equations into matrix form. Then these matrix equations are solved by the pseudoinverse transformation to obtain a stable approximate solution. In addition, the condition number of the matrix is also discussed. Computer simulations show that with multiple incident directions good reconstruction of shape and, to a lesser extent, conductivity is obtained even in the presence of noise in measured data.

ISSN:0920-5071    

DOI:10.1163/156939392X00337

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The present paper studies beyond-the-horizon propagation of SHF in an evaporation duct in the presence of strong anisotropic fluctuations of the refractivity index. An effective technique to obtain numerically complex constants of propagation is suggested. On the basis of this approach, the modelling method of SHF propagation in media with layer fluctuations of refractivity index is formed. Finally, the paper considers some examples of the influence of fluctuations on beyond-the-horizon propagation. A generalization of the adiabatic approximation for opening systems with a complex spectrum of eigenvalues and indefinite eigenfunctions is suggested. On this basis of the rough solution obtained for the atmosphere with nonuniformity in the horizontal direction is revised. The mechanism of exiting the evaporation duct by the high-located SHF source is also discussed.

ISSN:0920-5071    

DOI:10.1163/156939392X00346

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939392X00355

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor