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A method based on high frequency asymptotic techniques is described for rapid radar cross section (RCS) computation of arbitrary convex axisymmetric objects whose geometry is described in a computer-aided design (CAD) format. A modified version of the physical theory of diffraction (PTD), which is free from divergence problems at caustics and shadow boundaries and yields good accuracy even for low RCS objects, is employed. The spurious contributions due to sudden truncation of the physical optics (PO) currents on the shadow boundary, which yield nonphysical results, are removed, and the accuracy of the PTD is enhanced by adding the contributions due to the creeping waves and the fringe-wave currents for discontinuities in the curvature. This modified version of the PTD not only yields results that are consistent with the geometrical theory of diffraction (GTD) when the stationary phase evaluation of the fields from the induced currents is valid, but also allows us to compute the RCS for the entire range of incidence angles, even for those for which there is a breakdown of the conventional GTD. The results obtained by using this approach have been validated by a comparison with those computed with an integral equation code, and good agreement has been found.

The design of a thin, light weight and broadband radar absorber is a problem of considerable interest and is cast in this paper as a minimization problem of the following quantities, namely the reflection coefficient at the set of frequencies [{f.sub.1, f.sub.2, ... , f.sub.n}] and the thickness (or surface mass) of the absorber. We attempt to synthetize an absorber with a undefined number of layers and assume we have the freedom to choose the permittivity and the permeability of the material in each layer from a set of m specified value of [epsilon.sub.k](f) and [mu.sub.k](f). The usual approach to the design problem is to consider classical types of absorbers, such as Dallenbach or Jaumann layers [1]. In this paper, we present a design procedure based upon an Optimal Control method, that simultaneously determines both the material properties of the different layers as well as their thicknesses, to minimize at the same time the reflection coefficient over a prescribed range of frequencies and surface mass or thickness. Illustrative examples of multilayer absorbers synthetized with this method are presented and the results are compared with those designed by using the Simulated Annealing method.

Abstract: The feedback control algorithm is applied to provide stable propagation of the shock waves for nonlinear isothermal Euler equations even if the desired profile and velocity of the wave do not correspond to their analytical solution. Also the control algorithm helps to suppress scheme oscillations on the shock wave solutions, this is studied on an example of the Lax‐Wendroff second‐order scheme. [ABSTRACT FROM AUTHOR]

We review the characteristic current decomposition, first introduced by Garbacz (1968, A generalized expansion for radiated and scattered field. Ph.D. Dissertation, Ohio State University, Columbus) and then by Harrington & Mautz (1971, Theory of characteristic modes for conducting bodies. IEEE Trans. Antennas Propag., AP-19, 622–628). Our approach is based on the study of the scattering operator, or scattering matrix, the unitarity property of which plays a central role. The spectral decomposition of this operator leads to a particular characteristic far fields (or eigenfar-fields), from which a set of characteristic currents can be derived. These currents are those of Garbacz, Harrington and Mautz. They satisfy a generalized eigenequation involving usual integral operators split according to the regular/singular decomposition of the free space Green kernel. We provide proof of existence, denseness and orthogonality for these sets of characteristic modes (both currents and far fields). In addition to its theoretical interest, our analysis is motivated by its application to radar cross-section (RCS) analysis, where this particular decomposition turns out to be a powerful tool, especially for objects of small dimensions compared with the wavelength of the incident wave. Numerical computations are presented for a general three-dimensional object and the electrical field integral equation, including the first characteristic currents and their analyses in terms of their impact on the monostatic RCS. [ABSTRACT FROM AUTHOR]