A component model approach for the RCS validation of an electrically large open-ended cylindrical cavity

Abstract

The electromagnetic scattering of large open-ended cavity structures is an important problem in both military and civilian applications primarily for target characterization and radar cross section (RCS) reduction. For example, a complex-shaped cavity such as a jet engine inlet of an aircraft typically produces a major RCS contribution at a head-on view which is a key target identification feature and also vital to the RCS calculation of the entire aircraft [1].A variety of analytical (exact, modal, etc.) and numerical techniques [geometric optics (GO) and geometric theory of diffraction (GTD); shooting and bouncing rays (SBR); physical optics (PO) and physical theory of diffraction (PTD); integral-equation methods; finite element methods; differential-equation methods; hybrid techniques, etc.] have been developed and explored by researchers in an effort to generate accurate, efficient radar signatures for both simple and complex cavity geometries [2]. The particular technique chosen to solve a cavity scattering problem is dependent on many factors such as the size of cavity (electrically large versus small), the complexity of the cavity geometry (simple versus complex), the accuracy desired, the computer memory, time, and storage limitations, and the scattering phenomena that one wishes to ultimately capture in the radar signature. The RCS of a jet engine is difficult to compute due to the large and complex 3D structure, the multiple interactions between the cavity walls, and all the deficiencies of the various methods are encountered. The only alternative to these techniques is to collect measurements on a full size or scaled target which tends to be costly, time consuming, and typically will not include all radar viewing angles and frequencies.Currently no single prediction code can simultaneously meet all accuracy and computational time requirements required for the image generation (Nyquist sampling requirement) of electrically large complex targets (large asymmetric 3D targets with small features, cavities, dielectric materials, multiple interactions, etc.) with a time dependent motion. In this paper we present a novel RCS component prediction model approach to producing both fast and accurate scattering from an electrically large open-ended cylindrical cavity (circular cross section). The component model is a hybrid approach which easily permits individual scattering mechanisms to be coherently combined to produce a high fidelity signature. For this problem, the component model included scattering 2471 1-4244-0878-4/07/$20.00 ©2007 IEEE produced from the interior of the cavity calculated via the waveguide modal approach combined with the scattering produced from the cavity's finite thick rim opening (i.e., annulus) computed via the Method of Moments (MoM) and finally combined with the cavity's external base ring edge diffraction computed via PTD. Narrowband and wideband signature analysis for the circular cylindrical cavity configuration are presented to validate the component prediction model with static...