723 research outputs found
A hierarchical preconditioner for the electric field integral equation on unstructured meshes based on primal and dual Haar bases
No full textBuilt-up terrain wave propagation by Fourier split-step parabolic wave equation-ray optical techniques
No full text8 S.Fourier split-step (FSS) solutions of the parabolic wave equation (PWE) represent wave fields in terms of plane wave decompositions. However, those field solutions are usually only valid in the air space above built-up terrain, whereas field predictions for modern wireless systems often require knowledge of the fields on a street level. Since FSS PWE solutions with large step sizes are not applicable for field computations between irregular scattering obstacles such as buildings, this problem is overcome by a two-step approach combining the FSS solution of the PWE with ray optical techniques to compute the fields at ground level in wooded and urbanized areas. To account for the great variety of propagation effects in a statistical sense, direct rays, reflected rays, diffracted rays and attenuated rays at typical receiver locations are included into the considerations. Comparisons to a wide variety of measured data show that this two-step approach produces better results than state of the art semiempirical field prediction techniques.38Nr.
A Multilevel Fast Multipole Method with Spherical Harmonics Expansion of the k-Space Integrals
No full textAdvances in semi-empirical terrestrial wave propagation modeling for macrocellular environments
No full textS.907-910In this work, we concentrate on semi-empirical wave propagation modeling for macrocellular environments where the transmitter antenna is located quite above any surrounding buildings or vegetation. Also. focus on two-dimensional propagation along the great circle path between transmitter and receiver positions. Such methods are useful in flat and moderately undulating terrain as found in most inhabited areas
Modelling of integrated antenna - scatterer configurations by hybrid finite element - boundary integral - multilevel fast multipole methods
No full textS.1
Iterative near-zone preconditioning of iterative method of moments electric field integral equation solutions
No full textS.101-102A preconditioning operator for the iterative solution of the electric field integral equation as applied to metallic scattering objects is iteratively computed employing the generalized minimal residual algorithm (GMRES). Using the strongest method of moments matrix elements only (typically in the near zone), iteration of the sparse preconditioner converges very quickly. In contrast to direct factorization of the near-zone matrix, no matrix fill-ins need to be handled. Excellent convergence of the preconditioned system using GMRES again is demonstrated by scattering computations for a rectangular metallic plate and a metallic cube.
Terrestrial wave propagation: combination of fourier split-step parabolic wave equation solutions an
No full text
Iterative-solver convergence for loop-star and loop-tree decompositions in method-of-moments solutions of the electric-field integral equation
No full textS.80-85Method-of-moments (MoM) solutions of the electric-field integral equation using Rao-Wilton-Glisson (RWG) basis functions suffer from the so-called low-frequency breakdown. Introduction of loop-tree or loop-star decompositions of the basis functions can effectively solve this problem, and a number of papers have been published discussing various aspects with respect to these techniques. Several papers imply that loop-tree or loop-star decompositions may help to improve iterative-solver convergence for the solution of the resulting linear-equation systems. Since only a few results with respect to this issue are available, a study of the frequency-dependent iterative-solver convergence for RWG, loop-tree, and loop-star basis functions was performed. Two metallic scattering objects, with meshes comprising up to 21060 unknowns, were considered. RWG functions were found to provide the best convergence behavior, as long as the frequency considered was high enough to prevent the low-frequency breakdown. Among the loop-tree and loop-star bases, the loop-tree functions were found to be superior to the loop-star functions. The loop-tree functions resulted in good and stable convergence behavior if the number of subdivisions per wavelength was larger than a few hundred. Moreover, it is shown that the so-called loop-tree decomposition can also be viewed as a loop-cotree decomposition if an alternative tree of edges connecting the free vertices of the mesh is constructed.46Nr.
Irregular terrain wave propagation by a Fourier split-step wide-angle parabolic wave equation technique for linearly bridged knife-edges
No full text12 S.A novel Fourier split-step algorithm for the solution of the parabolic wave equation is proposed. The derivations are based on a two-dimensional linearly bridged knife-edge terrain model that considers ideally conducting as well as dielectric lossy ground together with a dielectric lossy layer as macroscopic representation of vegetation and buildings. The boundary condition at the terrain interface is formulated in the spectral domain, and it is shown that waves with a very wide angular spectrum with respect to the horizontal can accurately be modeled as long as the dominant portion of energy propagates above the terrain. Validation results are given for an ideally conducting as well as lossy dielectric wedge and an ideally conducting rounded obstacle. Also, real-world propagation curves show good agreement with measured data.37Nr.
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