摘要:

A new hybrid method is proposed for the numerical solution of integral equations describing transient scattering problems. The basic idea behind the method is to first discretize in space, and then solve the resulting system of linear time-domain equations by carrying out a temporal Laplace transformation. This approach combines the efficiency of the marching-on-in-time method with the stability and the accuracy of frequency-domain techniques. Numerical results are presented for the scattering of E-polarized, pulsed waves by a one-dimensionally inhomogeneous, lossy dielectric slab located in between two homogeneous, lossless dielectric half-spaces, and by a radially inhomogeneous, lossy dielectric circular cylinder embedded in vacuum. For these problems, the hybrid method turns out to be more powerful than existing solution techniques.

ISSN:0920-5071    

DOI:10.1163/156939389X00188

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A simple moment solution is given for the problem of electromagnetic scattering from two dimensional structures consisting of multiple perfectly conducting and lossy dielectric cylinders of arbitrary cross-section. The system is excited by a plane wave polarized transverse electric to the axis of the cylinders. The equivalence principle is used to replace the cylinders by equivalent electric and magnetic surface currents radiating into an unbounded medium. Two different sets of coupled integral equations involving the surface currents are obtained by enforcing the boundary conditions on the tangential components of the total electric and magnetic fields. The method of moments is used to solve the integral equations. Pulses are used for both expansion and testing functions. Some of the limitations of the method are briefly discussed. Results for the surface currents and the scattering cross sections are presented. Results computed using the E- field and/or the H- field formulation are in very good agreement with the exact or other available published data.

ISSN:0920-5071    

DOI:10.1163/156939389X00197

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A rigorous field analysis of the problem of scattering from a dielectric cylinder partially embedded in a perfectly conducting ground plane, and excited by a magnetic or electric line current in the free space outside the dielectric cylinder, is given in this paper. The dielectric medium is assumed to be linear, homogeneous, isotropic, although not necessarily free from losses. A field equivalence theorem is utilized to derive, for each excitation, an integral equation for the equivalent magnetic current on the dielectric interface, which is later solved using Galerkin's method. The equivalent magnetic currents are then used to determine the scattered field everywhere outside and inside the dielectric cylinder. Numerical results for the equivalent magnetic currents and far scattered field patterns are given. The resonances of the partially embedded dielectric cylinder are also defined and computed for both polarizations.

ISSN:0920-5071    

DOI:10.1163/156939389X00205

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Analytical and experimental investigations into the radiation characteristics of a high gain antenna feed system with a variable beamwidth facility are reported. The antenna consists of a homogeneous dielectric sphere placed in front of, but displaced from, the aperture of a dielectric coated conical horn. First the analysis of the fields in the dielectric coated conical horn is presented briefly using spherical hybrid modes, and the characteristic equation for the separation constant is derived. The condition for the support of balanced hybrid modes that contribute to low cross polarization is also derived. Then the theoretical expressions for the radiated far field components of the feed system are derived by treating the homogenous dielectric sphere as a scatterer of electromagnetic waves based on scattering theory approach, and also by treating the displaced dielectric sphere as a microwave lens illuminated by an aperture source. There is good overall agreement between the theoretical and experimental results. It is concluded that the test feed system has improved radiation characteristics with increased gain and directivity at reduced sidelobe levels. The low cross polarization nature of this horn makes it an attractive feed for satellite communications and radio astronomy applications.

ISSN:0920-5071    

DOI:10.1163/156939389X00214

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

In this paper, we investigate the problem of inverting a two-layer earth when the probing (by simulation) is carried out by vertical magnetic dipoles and the received signal is contaminated by noise. The mutual impedance between two probes is formulated in terms of a set of unknown parameters of the medium. The search for these parameters is then carried out until the response of the trial medium agrees, within a certain tolerance, with the received response. The search procedure is based on iterative optimization techniques, and the Hankel transform integrals are evaluated using techniques of the digital linear filter theory.

ISSN:0920-5071    

DOI:10.1163/156939389X00223

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939389X00232

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor