| In the past, methods for solving electromagnetic scattering problems in the frequency domain have been developed largely for the low-frequency (moment method) and high-frequency (asymptotic techniques) regimes. The intermediate, or resonant, frequency range has been analyzed by combinations of these two approaches or by separation of variables, when possible. This work is devoted to the development of an independent approach, viz., the "Spectral-Iterative Technique," which is capable of handling arbitrary scatterers with dimensions ranging from small to moderately large. The method takes advantage of the simplicity with which the source-field relationships are expressed in the spectral domain. The boundary conditions or constitutive relationships, on the other hand, are expressed most simply in the spatial domain. Alternating between the two domains is carried out with the aid of the FFT algorithm. Since the spectral domain includes only two independent transform variables, the third one being related to them by the dispersion relationship, the method is applied first to thin planar structures which allow the analysis to be carried out out on a plane. The generalization of the 2-D analysis to arbitrary 3-D bodies is then accomplished by sampling the current distribution on the scatterer over a number of parallel planes, and using the simple spectral-domain interaction relationships between the planes. This new approach involves no matrix inversion and is capable of analyzing scatterers whose sizes far exceed those treatable by the moment method. In addition to being arbitrarily shaped, the scatterer may be conducting, dielectric or lossy dielectric. Thus, the SIT provides an efficient approach to filling the much-needed gap between low- and high-frequency conventional techniques, e.g., the moment method and GTD, and to extending the range of applicability to dielectric scatterers, with or without loss. |
