共查询到20条相似文献,搜索用时 15 毫秒
1.
A new analysis technique for infinite phased array antennas was developed and demonstrated. It consists of the finite element method (FEM) in combination with integral equation radiation conditions and a novel periodic boundary condition for 3-D FEM grids. Accurate modeling of rectangular, circular and circular-coaxial feeds is accomplished by enforcing continuity between the FEM solution and several waveguide modes across an aperture in the array's ground plane. The radiation condition above the array is enforced by a periodic integral equation in the form of a Floquet mode summation, thus reducing the solution to that of a single array unit cell. The periodic boundary condition at unit cell side walls is enforced through a matrix transformation. That mathematically “folds” opposing side walls onto each other with a phase shift appropriate to the array lattice and scan angle. The unit cell electric field is expanded in vector finite elements. Galerkin's method is used to cast the problem as a matrix equation, which is solved by the conjugate gradient method. A general-purpose computer code was developed and validated for cases of open-ended waveguides, microstrip patches, clad monopoles and printed flared notches, showing that the analysis method is accurate and versatile 相似文献
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孙连友 《太赫兹科学与电子信息学报》2003,1(3):28-32
为了避免出现截断边界及截断边界条件,提出了开放区域上的有限单元和无限大单元相结合的区域剖分方法,并给出了无限大单元上基函数的构造。数值结果表明,该方法具有很好的计算效率和计算精度。 相似文献
3.
Awada K.A. Jackson D.R. Williams J.T. Wilton D.R. Baumann S.B. Papanicolaou A.C. 《IEEE transactions on bio-medical engineering》1997,44(8):736-752
A comparison is made of two different implementations of the finite element method (FEM) for calculating the potential due to dipole sources in electroencephalography (EEG). In one formulation (the direct method) the total potential is the unknown that is solved for and the dipole source is directly incorporated into the model. In the second formulation (the subtraction method) the unknown is the difference between the total potential and the potential due to the same dipole in an infinite region of homogeneous conductivity, corresponding to the region where the dipole is located. Both methods have the same FEM system matrix. However, the subtraction method requires an additional calculation of flux integrations along the edges of the elements in the computation of the right-hand side (RHS) vector. It is shown that the subtraction method is usually more accurate in the forward modeling, provided the flux integrations are computed accurately. Errors in calculating the flux integrations may result in large errors in the forward solution due to the ill-conditioned nature of the FEM system matrix caused by the Neumann boundary condition. To minimize the errors, closed-form expressions for the flux integrations are used for both linear and quadratic triangular elements. It is also found that FEM forward modeling errors may cause false extrema in the least-square objective function obtained from the boundary potential, near boundaries between media of differing conductivity. Multiple initial guesses help eliminate the possibility of the solution getting trapped in these false extrema 相似文献
4.
Towers M.S. McCowen A. Macnab J.A.R. 《Antennas and Propagation, IEEE Transactions on》1993,41(6):770-777
The application of finite elements to the open region associated with scattering problems necessarily requires the truncation of the solution region. This work investigates the use of infinite elements to extend the solution region beyond that of the finite elements which can be truncated by a noncircular boundary. A finite/infinite element formulated is developed in two dimensions and tested on dielectric, magnetic, and conducting scatterers with known analytic solutions 相似文献
5.
Guven I. Madenci E. Cho Lik Chan 《Components and Packaging Technologies, IEEE Transactions on》2002,25(4):684-694
Electronic packages experience large temperature excursions during their fabrication and under operational conditions. Inherent to electronic packages are the presence of geometric and material discontinuities. The regions where adhesive bond lines intersect with convective heat-loss surfaces are the most critical locations for failure initiation due to heat flux singularities and extreme thermo-mechanical stresses. Thus, accurate calculation of the flux field, as well as the temperature field, is essential in transient thermo-mechanical stress analysis. Although the finite element method (FEM) is highly efficient and commonly used, its application with conventional elements suffers from poor accuracy in the prediction of the flux field in these regions. The accuracy of the results from the boundary element method (BEM) formulation, which requires computationally intensive time-integration schemes, is much higher than that of the FEM. However, in this study, a novel boundary element-finite element coupling algorithm is developed to investigate transient thermal responses of electronic packages consisting of dissimilar materials. 相似文献
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This paper presents an application of the edge-based vector finite element method to scattering problems of anisotropic and inhomogeneous objects. Based on conventional FEM functional, a hybrid finite element-surface integral formulation is established by introducing permittivity and permeability tensors. The space domain is divided into interior and exterior regions by an imaginary surface conformal to the scatterer. Edge vector finite elements are used to model the anisotropic and inhomogeneous interior, and a surface integral equation is used to model the unbounded exterior. Compared to other hybrid techniques, the approach here retains the symmetry and sparsity of the FEM matrix and introduces only one type of unknown equivalent current in the moment matrix equation. To validate the theory, typical 2-D numerical results are first presented, which show excellent agreement with exact eigenmode expansion solutions or accurate MoM data 相似文献
8.
A hybrid finite-element-method/method-of-moments (FEM/MoM) approach is applied to the analysis of a gapped power-bus structure on a printed circuit board. FEM is used to model the details of the structure. MoM is used to provide a radiation boundary condition to terminate the FEM mesh. Numerical results exhibit significant errors when the FEM/MoM boundary is chosen to coincide with the physical boundary of the board. These errors are due to the inability of hybrid elements on the boundary to enforce the correct boundary condition at a gap edge in a strong sense. A much better alternative is to extend the MoM boundary above the surface of the board. 相似文献
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The accuracy of the finite element method (FEM) depends on the properties of the mesh which covers the problem geometry. The accuracy can usually be improved by increasing the element density in the mesh or the order of the shape functions in the elements at the expense of a significant increase in computation time. Instead, in this paper an a posteriori error reduction scheme is applied to improve the accuracy in the solution of three-dimensional electromagnetic boundary value problems. In this scheme, first the FEM, solution is generated by the use of lower-order shape functions. Then the numerical error is expressed in terms of higher-order shape functions and calculated on an element-by-element basis from information derived from the FEM solution. Finally, this error is added to the FEM solution to improve its accuracy. The degree of error reduction which is achieved with the application of this scheme is demonstrated by means of several simple electromagnetic boundary value problems 相似文献
11.
Reddy C.J. Deshpande M.D. Cockrell C.R. Beck F.B. 《Antennas and Propagation, IEEE Transactions on》1996,44(10):1327-1333
A technique using the hybrid finite element method (FEM)/method of moments (MoM) and geometrical theory of diffraction (GTD) is presented to analyze the radiation characteristics of cavity fed aperture antennas in a finite ground plane. The cavity which excites the aperture is assumed to be fed by a cylindrical transmission line. The electromagnetic (EM) fields inside the cavity are obtained using finite element method (FEM). The EM fields and their normal derivatives required for FEM solution are obtained using: (1) the modal expansion in the feed region and (2) the MoM for the radiating aperture region (assuming an infinite ground plane). The finiteness of the ground plane is taken into account using GTD. The input admittance of open-ended circular, rectangular, and coaxial line radiating into free space through an infinite ground plane are computed and compared with earlier published results. Radiation characteristics of a coaxial cavity-fed circular aperture in a finite rectangular ground plane are verified with experimental results 相似文献
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Unit cell analysis of infinite phased-arrays in the finite difference time domain (FDTD) is performed by implementation of periodic boundary conditions. The technique allows for pulse excitation and oblique scan directions in both the cardinal and intercardinal planes. To our knowledge, this is the first paper presenting FDTD computations for intercardinal pulse scanning in oblique directions. The ordinary Yee lattice is used, which makes the algorithm easy to incorporate in an already existing FDTD code. Nonperiodic boundaries are truncated by Berenger's (see J. Comput. Phys., vol.127, p.363-79, 1996) perfectly matched layer (PML). Active impedance of an infinite dipole array is calculated with the new method and validation is performed via the “element-by-element” approach, i.e., by a conventional FDTD simulation of a corresponding large finite array. Excellent agreement is found and the technique has been numerically stable in all cases analyzed 相似文献
14.
Pantic-Tanner Z. Scott Savage J. Tanner D.R. Peterson A.F. 《Microwave Theory and Techniques》1998,46(2):178-184
The finite-element method (FEM) exhibits a reduced convergence rate when used for the analysis of geometries containing sharp edges where the electromagnetic field is singular. The convergence of the method can be-improved by introducing singular elements that model analytically predicted singular behavior. A number of authors have developed singular elements that are compatible with the scalar FEM. In this paper, we propose a new singular element that is compatible with edge-based vector finite elements and can cope with any order of singularity while preserving the sparsity of the FEM equations. Edge-based singular elements more correctly model singular fields and thus require fewer unknowns, while avoiding the introduction of spurious modes in the numerical solution. Numerical results verify that the convergence of the FEM is significantly improved 相似文献
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S. E. Bankov 《Journal of Communications Technology and Electronics》2011,56(3):235-248
2D electromagnetic crystal with lumped nonlinear elements is considered. An electrodynamic model with a rectangular grid is
developed for a crystal that is infinite in one coordinate and finite in the other. In the case when the structure is excited
by a plane wave, linear boundary value problems are formulated for electromagnetic fields at multiples of the fundamental
frequency. The nonlinear problem is solved by means of the harmonic balance method. A system of nonlinear equations for the
amplitudes of voltage harmonics at nonlinear elements is derived. Results of numerical solution of the system are presented
for resistive and capacitive nonlinear elements. 相似文献
17.
Jian Gong Volakis J.L. Woo A.C. Wang H.T.G. 《Antennas and Propagation, IEEE Transactions on》1994,42(9):1233-1242
An edge-based hybrid finite element-boundary integral (FE-BI) formulation using tetrahedral elements is described for scattering and radiation analysis of arbitrarily shaped cavity-backed patch antennas. By virtue of the finite element method (FEM), the cavity irregularities, the dielectric super/substrate inhomogeneities, and the diverse excitation schemes inside the cavity may be readily modeled when tetrahedral elements are used to discretize the cavity. On the aperture, the volume mesh reduces to a triangular grid allowing the modeling of nonrectangular patches. Without special handling of the boundary integral system, this formulation is typically applicable to cavity-backed antenna systems with moderate aperture size. To retain an O(N) memory requirement, storage of the full matrix due to the boundary integral equation is avoided by resorting to a structured triangular aperture grid and taking advantage of the integral's convolutional property. If necessary, this is achieved by overlaying a structured triangular grid on the unstructured triangular grid and relating the edge field coefficients between the two grids via two narrow banded transformation matrices. The combined linear system of equations is solved via the biconjugate gradient (BICG) method, and the FFT algorithm is incorporated to compute the matrix-vector product efficiently, with minimal storage requirements 相似文献
18.
A numerical technique is presented for analysing diffraction gratings of arbitrary groove shape. The method is based on the application of finite element technique. It is suggested that this technique, thus far reserved mostly for the problems of bounded extent, may be used to advantage for analysing this problem. To this end, the infinite space is divided into two regions, one finite and the other infinite in extent. A series solution is employed in the infinite region, and in the finite one a functional is used. The two solutions are then matched on the common boundary of the two regions. The resulting equation for the field is finally solved by application of the finite element technique. The numerical results obtained for echelette gratings are favourably compared with a number of similar results reported in the literature. 相似文献
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