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Title: SCATTERING AND ABSORPTION OF ARBITRARILY ORIENTED DIPOLES WITH FINITE CONDUCTIVITY
Abstract: Plane wave scattering of lossy dipoles oriented arbitrarily in space is analyzed with the NECAE2 code. Modification of the code allows computing not only the radar cross section but also scattering and absorption cross section. With these electromagnetic characteristics it is possible to describe the relation between reradiated and absorbed power of the scatterer as a function of frequency and conductivity. A comparison with the results obtained with other codes (MININEC, Richmond) shows substantial differences at higher resonances of the dipoles. [Vol. 4, No. 2, pp. 2-15 (1989)]
Author(s): H. Dominik
File Type: Journal Paper
Issue:Volume: 4      Number: 2      Year: 1989
Download Link:Click here to download PDF     File Size: 481 KB

Title: COMBINED-FIELD FORMULATION FOR CONDUCTING BODIES WITH THIN COATINGS
Abstract: A Galerkin method-of-moments (MM) formulation is developed for the problem of electromagnetic scattering from a conducting body with a thin coating. The formulation incorporates both the electric-field integral equation (EFIE) and magnetic-field integral equation (MFIE) formulations on the conductor and the dielectric surfaces. The formulation is developed in terms of generalized Galerkin matrix operators which allow for straightforward implementation into existing computer codes for coated bodies. The analysis allows a surface coating of nonuniform thickness that is characterized by complex permeability and permittivity; the analysis can be easily extended to the case of a thin multilayered body. Standard MM formulations for coated bodies, based on either the EFIE or the MFIE at the conductor surface, fail as the coating thickness approaches zero. The combined-field integral equation (CFIE) also fails in the limit of zero thickness. The present thin-coating formulation (TCF) wiU be shown to remain valid as the coating thickness approaches zero. In the limit, the matrix equation for the TCF reduces to a self- consistent set of equations for scattering from a conducting body, independent of the dielectric coating parameters. The TCF has been implemented for the case of scattering by a conducting body of revolution (BOR) with a thin dielectric layer. Examples are presented comparing the present formulation to other MM formulations. The TCF is demonstrated near internal resonant frequencies, and for some limiting cases for both bistatic and monostatic scattering. [Vol. 4, No. 2, pp. 15-26 (1989)]
Author(s): J. M. Putnam
File Type: Journal Paper
Issue:Volume: 4      Number: 2      Year: 1989
Download Link:Click here to download PDF     File Size: 374 KB

Title: A 2-D FINITE ELEMENT MODEL FOR WAVE PROPAGATION INTO ARBITRARY INHOMOGENEOUS MATERIALS
Abstract: A finite element program called FEAST, coded in FORTRAN, provides a frequency domain (sinusoidal steady state) solution to Maxwell's equations in cylindrical coordinates. By imposing a radiation or impedance boundary condition at the far boundary of the finite element mesh, FEAST models the near fields of axially symmetric antennas in arbitrary inhomogeneous materials. The program has been validated by reproducing the driving point impedances and current distributions of several antenna configurations for which theoretical and experimental results are available in the published literature. [Vol. 4, No. 2, pp. 27-48 (l989)]
Author(s): E. Sumbar, F. S. Chute, F. E. Vermeulen
File Type: Journal Paper
Issue:Volume: 4      Number: 2      Year: 1989
Download Link:Click here to download PDF     File Size: 866 KB

Title: AN ANISOTROPIC TWO-DIMENSIONAL SCATTERING CODE
Abstract: A computer code has been developed to predict radar return from two- dimensional cylindrical targets composed of anisotropic, lossy, and inhomogeneous materials. A moment method formulation uses point matching with rectangular domains of pulse basis functions for volumetric elements. Targets may also be composed of thin films including conducting sheets. Particular attention is paid to problems associated with close coupling which involve numerical integration over neighboring domains of basis functions, rectangles which may be very close together as in the case of thin layers of material. Examples are used to show that analytical integration of singularities associated with close coupling gives results which are superior to the numerical approximations used in typical moment method The results are of interest for problems involving isotropic as well as anisotropic targets. For example, when a code which calculates close couplings with numerical approximations is applied to a hollow, conducting cylinder, computed radar return may be distorted by introducing conducting elements close to the interior wall of the cylinder. With analytical treatment of singularities, however, there is no distortion. In another example results from codes are compared for the case of a right circular cylinder coated with anisotropic material. Results in good agreement with a series solution taken from the literature are achieved when analytical treatment of singularities is considered. Finally, for the example of a conducting plate it is shown how analytical treatment of singularities makes good results possible for a minimum number of basis functions. [Vol. 4, No. 2, pp. 49-58 (1989)]
Author(s): J. P. Heaton
File Type: Journal Paper
Issue:Volume: 4      Number: 2      Year: 1989
Download Link:Click here to download PDF     File Size: 548 KB

Title: A HYBRID FINITE ELEMENT FOR CONDUCTORS WITH THIN DENSE COATINGS
Abstract: A hybrid method of using finite elements and boundary integral methods to compute scattering from two dimensional coated conductors is presented. Finite elements are used in and around an electrically dense coating where high sampling rates are required. Since the matrix equations they generate are sparse, they can be quickly solved. The finite element sampling rate is reduced with distance from the scatterer to a very low rate where the boundary integral method provides the exact near field radiation condition. The boundary integral generates a dense matrix which is small due to the reduced sampling. This technique is compared for accuracy and efficiency with series solutions and with method of moments. [Vol. 4, No. 2, pp. 59-72 (1989)]
Author(s): Willlam E. Boyse, Andrew A. Seidl
File Type: Journal Paper
Issue:Volume: 4      Number: 2      Year: 1989
Download Link:Click here to download PDF     File Size: 982 KB

Title: SOME CONSIDERATIONS ON THE USE OF NEC FOR COMPUTING EMP RESPONSE
Abstract: This paper concerns the use of a frequency domain code such as the Numerical Electromagnetics Code (NEC) for computing the time domain EMP response of structures such as antennas, aircraft or communication shelters. The effects of the choice of a proper model for the excitation and of the selection of an appropriate number of frequencies for taking an inverse FFT and obtaining a correct time domain EMP response are studied. Guidelines are given for obtaining a correct time domain response with efficient use of computer time. [Vol. 4, No. 2, pp. 73-89 (1989)]
Author(s): M. Dion, S. Kashyap
File Type: Journal Paper
Issue:Volume: 4      Number: 2      Year: 1989
Download Link:Click here to download PDF     File Size: 544 KB