摘要:

Conditions for the most general bi-anisotropic medium in which any electromagnetic field can be decomposed into two uncoupled partial fields were recently introduced by one of the present authors. In the present paper it is shown that any electromagnetic source in this class of media can be decomposed into two sources creating uncoupled partial fields. Further, it is shown that for each of the problems the original bi-anisotropic medium can be replaced by a simpler equivalent medium for which an analytic Green dyadic can be found. This makes it possible to solve both decomposed problems in integral form.

ISSN:0920-5071    

DOI:10.1163/156939398X00016

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Multichip and flip chip technology has become increasingly popular in the past years. It employs a series of chips flipped and connected through metallic bumps. A study for improving the performance of flip chip interconnects is recently presented by Ghouz and El-Sharawy for frequencies up to 50 GHz. In that study, the idea of staggering the signal line interconnect with respect to the ground plane bumps to reduce reflection and insertion loss is introduced. In this paper concentration is put on re-shaping the discontinuity region in order to provide a better impedance match between the CPW-motherboard and the CPW-chip, and thus reducing reflection at the input terminals. Several approaches are tested to accomplish lower return loss, among them, the use of bumps of different thickness located at different positions, the use of tilted bumps or "ramps", and the use of dielectric loading on the bumps. The results indicate that the performance of these flip chips is greatly enhanced and extended to frequencies beyond 100 GHz.

ISSN:0920-5071    

DOI:10.1163/156939398X00025

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this work, the effects of the ohmic losses on the radiation properties are extensively evaluated for the general class of the traveling-wave antennas. For arbitrary aperture distributions, rigorous analytical approaches have been developed to take into account the dissipation in conductors and/or dielectrics that can adversely affect the basic design parameters, such as efficiency and leakage constant. Consequently, fundamental information is achieved both to quantify the alterations in the antenna performances due to misappreciation of the ohmic losses and, above all, to appropriately correct the synthesis procedures for improved radiation patterns. Important applications of this analysis refer to topologies of leaky-wave antennas.

ISSN:0920-5071    

DOI:10.1163/156939398X00034

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A moment-method based analysis of arbitrarily shaped zero-thickness obstacles in rectangular waveguide is presented. The method is discussed in two well-known formulations, and for both of them an efficient Green's functions representation is introduced. The representation is obtained by extracting suitable terms representing the asymptotic behaviour of the TE and TM part of Green's dyad. Two different sets of basis functions are then compared in terms of accuracy of the numerical results obtained: rooftops and bilinear. It is shown that the higher order set of bilinear basis function leads to spurious results, whereas no such effect appears using rooftops. A very good efficiency of the overall algorithm was observed.

ISSN:0920-5071    

DOI:10.1163/156939398X00043

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Splitting of a linearly polarized electromagnetic Gaussian beam into two opposite circularly polarized Gaussian beams by a chiral prism is investigated. The prism is made of homogeneous chiral material and has an isosceles triangle base with angles - It is shown that by proper choice of chirality in relation to the splitted beams can be made to emerge from different faces of the prism with small crosspolarization ratio.

ISSN:0920-5071    

DOI:10.1163/156939398X00052

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A time domain method building on the concept of wave splitting is used to study direct wave propagation phenomena in weakly nonlinear media. The starting point is the linear wave equation with time-dependent coefficients. This means that the studied nonlinear medium in some sense has to be approximated with a nonstationary medium which changes while the wave passes through. For the nonstationary equation homogeneous as well as particular solutions can be obtained. Two different iterative procedures to find the nonlinear solutions are discussed. They are illustrated by two problems fetched from different research fields of current interest. In the first case, the nonlinear term is linearized using the Fréchet derivative. This leads into a truly nonstationary, mixed initial boundary value problem with a linear equation characterized by both time-dependent coefficients and source terms. In this example a semiconductor device used for switching in high-frequency applications is considered. It can be described as a coplanar waveguide loaded with distributed resonant tunnel diodes. In the other example, wave propagation in Kerr media is considered. Then Taylor expansion transforms the nonlinear equation into a linear one with nonstationary source terms. In this case the nonlinearity does not lead to time-depending coefficients in the equation. The way to obtain the solution is a nonlinear variant of the Born approximation.

ISSN:0920-5071    

DOI:10.1163/156939398X00061

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An effective hybrid method is proposed, which combines the method of moments (MoM), the finite element method (FEM) and the wavelet transform method (WTM) (referred to as MoM/FEM/WTM method) for efficient solutions of scattering problems involving inhomogeneous media. The hybrid technique applies the equivalence principle to transform the original problem into interior and exterior problems which are coupled on the shared boundary through the continuity conditions of the tangential electric and magnetic fields. The MoM and the WTM are used for efficient solutions of the exterior problem and the FEM for the interior problem. In contrast to other traditional hybrid techniques, the new hybrid method, which combines the advantages of the MoM, the FEM and the WTM, can always produce highly sparse moment matrix equations which can be solved efficiently. This is of particular importance for large-size electromagnetic problems. Numerical results are given to demonstrate the merit of the method.

ISSN:0920-5071    

DOI:10.1163/156939398X00070

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The aim of this paper is to deal with the problem of numerical solution of Fredholm integral equation of the first kind. First, a new kind of basis functions has been proposed based on multiscale method and wavelet-like basis. Second, by using this basis, the multiscale moment method for solving Fredholm integral equation of the first kind in one dimension has been proposed. Furthermore, the adaptive algorithm of the multiscale moment method has been presented according to the characteristics of the integral equation. Many numerical simulations are carried out to test the feasibility of the multiscale method and the implemented adaptive algorithm. It is found that the two multiscaling algorithms can provide good results. The adaptive algorithm can reduce the orders of linear equations constructed by multiscale moment method for Fredholm integral equation. It is a very effective algorithm to solve integral equations.

ISSN:0920-5071    

DOI:10.1163/156939398X00089

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

After briefly reviewing the properties of the squared amplitudes of radiated fields, a simple and effective necessary condition to test if a source of given size and structure can radiate or not a power pattern lying in a given mask is furnished. The criterion is shown to be also sufficient for linear arrays, thus allowing to reduce the overall problem to the synthesis of a nominal pattern.Then, new synthesis procedures, strongly relying on the properties of squared amplitude distributions and on the quadraticity of the operator relating the source to the power pattern, are introduced. They are implemented and tested in the cases of linear and planar uniform arrays, showing that thanks to a full exploitation of the properties of quadratic operators and of those of squared amplitude distributions, they allow one to achieve very efficient solutions to mask constrained synthesis problems.

ISSN:0920-5071    

DOI:10.1163/156939398X00098

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939398X00106

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor