A Multilevel Fast High Frequency Scattering Method From Electrically Large Multi-Layer Coated Scatterers

A multilevel fast high frequency (MLFHF) scattering method from multi-layer coated scatterers is presented. The wideband and wide angle radar cross section (RCS) analysis of thin multi-layer coated scatterers requires dense sampling in frequency angle space, making accurate and efficient modeling of coating-induced multiple reflections challenging in practice. These coating effects are modeled by a branchwise generalized equivalent reflection (GER) embedded in a surface current formulation in this work. Multilevel schemes then reduce the computational cost by interpolating scattered fields from sparse samples, but their accuracy is limited by phase-reference misalignment. On wavelength-scale quadratic patches, the region-center reference can deviate from branch-dependent stationary-phase centers, causing interpolation errors and oversampling. To address this, a physics-guided equivalent phase compensation (EPC) scheme is developed that selects branchwise equivalent phase centers from relevant critical points and forms a coherent phase reference. Numerical examples demonstrate accurate wideband and wide angle RCS prediction for five-layer coated scatterers with electrical sizes up to 1,167$\lambda$. At comparable accuracy, the MLFHF-EPC framework achieves a speedup factor of 6.79 over conventional multilevel methods.