Abstract-It is always a challenge to predict Radar Cross Section (RCS) of a full scale military platform with a good accuracy. Most of the time antennas and cavities are the main contributors of aircrafts RCS. Several methods have been developed to compute the RCS of cavities such as analytical methods (modal methods) and asymptotic methods (geometrical optics (GO) methods and physical optics (PO) methods). This article presents the Iterative Physical Optics (IPO) method which consists in an iterative resolution of the Magnetic Field Integral Equation (MFIE) to compute the currents on the inner walls of the cavity. This method allows computing arbitrarily shaped cavity with a good accuracy even for cavity with a depth inferior to the wavelength. Comparisons of IPO results with Rays and Finite element methods show a better accuracy of IPO than Rays especially for cross polarization. But computation time represents one of the main limitations of the IPO method. We present here a new formulation of the Segmented IPO method which coupled with the generalized reciprocity theorem decreases significantly the complexity of the method and consequently the computation time. The S-IPO method has been validated by comparisons with Modal method and measurements. We have observed that the repartition of the electric currents density on the inner walls of the cavity is quite the same with IPO and S-IPO computations. Lastly we propose an evolution of the IPO method we have developed to compute the RCS of cavities under radome. This method has been validated by comparison with finite element results.

Abstract-In this paper, we present a fast method to predict the monostatic Radar Cross Section (RCS) in high-frequency of a cavity, which can be modeled as a succession of bent waveguides of the same cross section and stuffed by a perfectly-conducting termination. Based on a modal analysis combined with the Kirchhoff Approximation, this method allows us to obtain closed-form expressions of the transmission matrix at each discontinuity. In addition, to improve the efficiency, a selective modal scheme is proposed, which selects only the propagating modes contributing to the scattering. Compared to the Iterated Physical Optics (IPO) method and the Multi-Level Fast Multipole Method (MLFMM, generated from the commercial software FEKO), this approach brings good results for cavities with small tilt angles of the bends, typically smaller than 2 degrees.