A Simple Correction to Physical Optics Solution for the Estimation of the Scattering Components of a Finite Metallic Cone

Abstract

This paper describes the contributions of tip scattering, first-order rim diffraction and tip-rim interaction to the high-frequency scattering from a finite perfectly conducting right-circular cone. Empirical correction factors are introduced to the classical physical optics (PO) approximation. It is shown that the contribution due to tip scattering as obtained from physical optics approximation, with a correction factor included, closely matches with Felsen's result for small angle cones and for a wide range of aspect angle. It is also shown for axial incidence that the firstorder diffraction from the rim is expressible in terms of the PO integral after incorporating a correction factor. Axial radar cross section measurement results on narrow and large angle cones are presented and compared with the results of the modified PO result thus obtained in this paper and geometrical theory of diffraction (GTD). The contribution of the proposed tip-rim interaction is subsequently discussed and it is shown that this interaction is significant only for narrow angle cones. Backscattering measurement results on two cones over a wide range of aspect angle are also compared with the classical results of PO and GTD. From this comparison, it is inferred that for large angle cones, second order diffraction mechanisms contribute insignificantly when the incident wave is vertically polarized. This shows that PO can be a reasonably accurate analytical tool for large angle cones and for vertical polarization, except at axial incidence. At axial incidence, the correction factor introduced in this paper has to be used in the PO solution to make it match with experiment.

Indexing terms:

• Cone
• Physical optics
• Tip-scattering
• Rim diffraction
• Radar cross section
• Measurement