摘要:

The solution of a hybrid finite element method (HFEM) problem is considered. It is shown that a suitable ordering of the FEM mesh results in a canonical HFEM matrix system. This linear system can be solved in O(N1.5) cost when sparse direct methods are used. This cost is comparable to FEM methods using approximate boundary conditions and a similar sparse solution method.

ISSN:0920-5071    

DOI:10.1163/156939397X00404

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this contribution, the Discretized Mie-Formalism (DMF) for plane wave scattering by irregularly shaped objects is presented in both cylindrical and spherical co-ordinates. Besides the direct method we discuss an iterative procedure which results in less computational effort and a higher numerical stability. This makes the DMF applicable to aspect ratios and size parameters which have only been treated by use of the Extended Boundary Condition Method so far. The iterative DMF is a Method of Moment scheme applied to the continuity condition of the tangential electromagnetic field components at the scatterer surface. Based on the differential equation formulation, the DMF can be considered to be the numerical generalization of the Mie theory to particles with non-spherical boundaries. By use of a special Finite Difference technique, the so-called Method of Lines, the Helmholtz equations for the Debye potentials, related to the scattering process, can be transformed into an uncoupled system of ordinary differential equations depending only on the radial coordinate. This system can be solved analytically by taking the radiation condition into account. In this way, the final calculation can be restricted to the surface of the scatterer as known from surface integral approaches. Additionally, a decoupling of the orientation of the scatterer with respect to the incident field from its geometrical and physical configuration is achieved. The theoretical description is completed by an application to scatterers with different shapes, and in different size parameter regions.

ISSN:0920-5071    

DOI:10.1163/156939397X00413

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this paper, a full wave approach is used to analyze the propagation parameters of two coupled symmetric microstrip transmission line on dielectric multilayer substrate with dielectric overlay and a notch between the strips. The purpose of this analysis is to examine the validity of previously reported quasi-static techniques to higher frequencies for applications in the millimeter wave frequency range. The objective is to reduce the distortion of a transmission line that consists of two parallel microstrip lines on two dielectric substrates with a notch and a dielectric overlay. The distortion in such a transmission line is produced due to the difference in the phase velocities of the even and odd dominant modes. Techniques based on controlling the dielectric constant, height and width of the notch and the overlay are used to reduce distortion. The semi-analytical method of lines (MoL) technique is applied here to solve for the normalized phase velocities of the dominant even and odd modes for this planar microstrip transmission line configuration. The numerical results provide a detailed analysis of the transmission line controlling parameters for frequencies up to 100GHz .

ISSN:0920-5071    

DOI:10.1163/156939397X00422

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The work physically models wide-band radio propagation for urban line-of-sight (LOS) micro-cellular mobile and personal communications, including two contributions. First, a more explicit narrow-band channel transfer function for a six-ray model is presented. Second, the corresponding wide-band propagation characteristics are calculated, by extending an existing and validated method originally for rural environments and making it applicable to urban LOS micro-cellular environments. These characteristics are described by time-domain path loss, wide-band path loss, and relative power in frequency domain. Comparisons of these parameters with results calculated by using two-ray model are presented, since the experimental validation of the entire wide-band modeling for two-ray model was made previously. The time-domain path loss interprets power-delay profiles. The wide-band path loss is on the order of narrow-band path loss at a carrier frequency. The relative power in frequency domain ranges a finite bandwidth set by the radio system.

ISSN:0920-5071    

DOI:10.1163/156939397X00431

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A study of the propagation of localized waves in collisionless plasma media is undertaken. It is shown how such pulsed wavefields can be generated from finite-time dynamic apertures. We demonstrate that localized waves exhibit an unusual robustness when they propagate in a plasma medium modeled by the Klein-Gordon equation. The decay rates of the centroids of such pulses are comparable to those of localized waves traveling in vacuum. Furthermore, when a parameter controlling the spatiotemporal coupling of the spectral components of the localized wave is tuned to the plasma frequency, the decay of the centroid of the radiated field becomes slower than that of a localized wave traveling in vacuum. We provide an explanation of this behavior based on the unusual depletion of the spectral components of the finite-time localized waves.

ISSN:0920-5071    

DOI:10.1163/156939397X00440

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The homogenization method is applied to solve a scattering problem for a periodic grating when the period is small compared to the wavelength. A planar infinite grating becomes a planar stratified structure after the homogenization. The differential equations and boundary conditions for the higher order correction terms are derived, and numerical results are presented. The case of a curved and finite grating is also considered.

ISSN:0920-5071    

DOI:10.1163/156939397X00459

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The sensitivity of certain near field antennas and the power handling capability of high frequency transmission lines are limited by similar geometric considerations. In particular, unwanted spatial concentrations of the electromagnetic fields lead to increased ohmic losses, to dielectric losses and to dielectric breakdown. Three dominant mechanisms by which such current concentrations occur may be enumerated: (1) The shape effect, which is exemplified by the divergence of the electromagnetic field at sharp corners of conducting parts. (2) The proximity effect which relates to concentration and eventual divergence of the electromagnetic field between two metal parts at different potential. (3) The ferrite effect, which refers to the field concentrations that result from the presence of highly permeable materials. In the past, proximity effects in parallel cylindrical conductors and shape effects in isolated conductors have been studied. This paper shows that a different picture emerges when the effects of the proximity, shape and ferrite are combined, as can easily be the case in a practical antenna. In particular, these effects may be played off against each other in order to reduce undesirable field concentrations. The argument is illustrated using exact solutions available from conformal mapping and numerical solutions calculated by a boundary element technique.

ISSN:0920-5071    

DOI:10.1163/156939397X00468

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The reflectivity of quasi-randomly distributed gratings of fibers is analyzed by means of an integral representation of the scattered field. The results are compared with those obtained from two homogenization methods and used to investigate the accuracy of the latter. Both TE and TM polarizations are considered and the reflectivity is investigated as a function of the wavelength and the angle of incidence.

ISSN:0920-5071    

DOI:10.1163/156939397X00477

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Analyses of power in radiation fields are nearly universally based upon the complex Poynting theorem, CPT, yet the scientific basis for its use is not well established. The time dependent Poynting theorem, TDPT, is seldom used yet its scientific basis is well established. We use Hansen's method to obtain a generalized modal expansion for all possible electromagnetic fields that can originate within a confined volume and travel infinitely outward, combine the modal expansions and both Poynting theorems to determine the power expressions, and contrast results. The TDPT shows that the characterization of power in a sinusoidal field requires three numbers. Therefore it cannot be fully described by only real and reactive values. We conclude that the CPT is intrinsically an insufficient basis for a full description of power in a radiation field. We compare TDPT and CPT solutions for several idealized antenna designs. Comparative analyses show that the TDPT provides solutions that correspond to reality in all cases and the CPT does not. Proofs that electrically small antennas cannot be efficient are based upon the CPT; we re-examine these proofs using the TDPT and find that certain mixed modal configurations may surpass the generally accepted small antenna rules.

ISSN:0920-5071    

DOI:10.1163/156939397X00486

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Exact image theory for the vertically layered ground, previously introduced by the second author and collaborators, is simplified through the equivalent source concept. In particular, the image for a horizontal source can be derived by replacing the source by an equivalent vertical source and applying simpler theory for the vertical source. The resulting vertical image, again, can be replaced by an equivalent horizontal image. The equivalent source method circumvents the more complicated dyadic analysis applied previously. The layered half space may have any isotropic or bi-isotropic structure represented by four reflection operators. As an example, image expressions are derived for the horizontal dipole above a slightly chiral half space, applying the theory derived previously for the vertical electric and magnetic dipoles.

ISSN:0920-5071    

DOI:10.1163/156939397X00495

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor