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  • 1
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    A finite element conjugate gradient FFT method for scattering (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Validated results are presented for the new 3D body of revolution finite element boundary integral code. A Fourier series expansion of the vector electric and mangnetic fields is employed to reduce the dimensionality of the system, and the exact boundary condition is employed to terminate the finite element mesh. The mesh termination boundary is chosen such that is leads to convolutional boundary operatores of low O(n) memory demand. Improvements of this code are discussed along with the proposed formulation for a full 3D implementation of the finite element boundary integral method in conjunction with a conjugate gradiant fast Fourier transformation (CGFFT) solution.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Task Reports on Developing Techniques for Scattering by 3D Composite Structures and to Generate New Solutions in Diffraction Theory Using Higher Order Boundary Conditions; 26 p
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Radiation from a homogeneous sphere mounted on a waveguide aperture (1975)
    In:  Other Sources
    Details
    Publication Date: 2011-08-16
    Description: The results of an experimental and theoretical study of the effects of placing a dielectric sphere over the aperture of a circular waveguide are presented. A dielectric sphere excited by a Huygens' source is used as the theoretical model to interpret the experimental results. Calculations based on this model show good overall agreement with experimental patterns and directivity measurements. It is concluded that dielectric loaded antennas such as the dielectric sphere excited by a waveguide can produce directivities in excess of that obtained by a uniformly illuminated aperture of the same cross section, particularly for dielectric objects with dimensions of two wavelengths or less. Measurements of the coupling between these antennas show that they, in general, are not as closely coupled as plain apertures without dielectric object loading.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation; AP-23; Sept
    Format: text
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  • 3
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    A class of hybrid finite element methods for electromagnetics: A review (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Integral equation methods have generally been the workhorse for antenna and scattering computations. In the case of antennas, they continue to be the prominent computational approach, but for scattering applications the requirement for large-scale computations has turned researchers' attention to near neighbor methods such as the finite element method, which has low O(N) storage requirements and is readily adaptable in modeling complex geometrical features and material inhomogeneities. In this paper, we review three hybrid finite element methods for simulating composite scatterers, conformal microstrip antennas, and finite periodic arrays. Specifically, we discuss the finite element method and its application to electromagnetic problems when combined with the boundary integral, absorbing boundary conditions, and artificial absorbers for terminating the mesh. Particular attention is given to large-scale simulations, methods, and solvers for achieving low memory requirements and code performance on parallel computing architectures.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-192631 , NAS 1.26:192631 , UMICH-028918-4-T
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  • 4
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    Investigation of finite element: ABC methods for electromagnetic field simulation (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The mechanics of wave propagation in the presence of obstacles is of great interest in many branches of engineering and applied mathematics like electromagnetics, fluid dynamics, geophysics, seismology, etc. Such problems can be broadly classified into two categories: the bounded domain or the closed problem and the unbounded domain or the open problem. Analytical techniques have been derived for the simpler problems; however, the need to model complicated geometrical features, complex material coatings and fillings, and to adapt the model to changing design parameters have inevitably tilted the balance in favor of numerical techniques. The modeling of closed problems presents difficulties primarily in proper meshing of the interior region. However, problems in unbounded domains pose a unique challenge to computation, since the exterior region is inappropriate for direct implementation of numerical techniques. A large number of solutions have been proposed but only a few have stood the test of time and experiment. The goal of this thesis is to develop an efficient and reliable partial differential equation technique to model large three dimensional scattering problems in electromagnetics.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-196837 , NAS 1.26:196837 , UMICH-031155-2-T
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  • 5
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    A finite element boundary integral formulation for radiation and scattering by cavity antennas using tetrahedral elements (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A hybrid finite element boundary integral formulation is developed using tetrahedral and/or triangular elements for discretizing the cavity and/or aperture of microstrip antenna arrays. The tetrahedral elements with edge based linear expansion functions are chosen for modeling the volume region and triangular elements are used for discretizing the aperture. The edge based expansion functions are divergenceless thus removing the requirement to introduce a penalty term and the tetrahedral elements permit greater geometrical adaptability than the rectangular bricks. The underlying theory and resulting expressions are discussed in detail together with some numerical scattering examples for comparison and demonstration.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-189491 , NAS 1.26:189491 , UMICH-028918-1-T
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  • 6
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    General aviation aircraft antennas for the global positioning system (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Several antenna designs that utilize the NAVSTAR Global Positioning System in a low-cost system for general aviation aircraft were evaluated. Experimental investigations were made of crossed-dipoles, various types of crossed-slots, and microstrip antennas with modifications to improve their coverage. Principal plane radiation patterns for several of these antennas were measured on a one-seventh scale model of a Gates Lear Jet.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-TM-83212
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  • 7
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    Edge-based finite elements and vector ABCs applied to 3D scattering (1992)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An edge based finite element formulation with vector absorbing boundary conditions is presented for scattering by composite structures having boundaries satisfying impedance and/or transition conditions. Remarkably accurate results are obtained by placing the mesh a small fraction of a wavelength away from the scatterer.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-190352 , NAS 1.26:190352 , UMICH-025921-29-T
    Format: application/pdf
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