Improvement on the Forward-backward Iterative Physical Optics Algorithm Applied to Computing the RCS of Large Open-ended Cavities

Abstract

The equivalent impedance boundary condition and the transmission line theory are used to analyze the surface impedance and reflective coefficient of the PEC surface coated with a thin absorber layer. Then, the IPO iterative equation is deduced by combining the surface impedance and reflective coefficient with the asymptotic principles of physical optics. The method of initial value succession is introduced to the forward-backward iterative physical optics (FBIPO) algorithm. The initial residual error is reduced by inheriting the current values. Combined with a relaxation parameter, the method improves the convergence of the FBIPO algorithm for cavity scattering problems. The accuracy of RCS calculation is also enhanced by using a more precise mixed-face model. The RCS of a jet inlet model is calculated, with its results in good agreement with the experimental ones. The method is also used to calculate the RCS reduction of a circular wave guide by coating the inner wall with absorber material.