凹槽电磁散射的高频分析

High Frequency Analysis of EM (Electro-Magnetic) Scattering by Groove

基于高频近似方法——改进一致性绕射理论 ( UTD) ,分析了凹槽的电磁散射。应用改进的一致性绕射系数得到凹槽边缘的绕射场 ,并考虑了边缘之间的高阶绕射效应作为必要补充。凹槽内部的场应用射线 -模式耦合理论表示成模式场的传输形式 ,反复迭代得到其内部的辐射场。算例结果和其他方法相比较 ,取得了良好的一致性。

Groove structure (Fig.1) is quite common in analyzing the EM character of an airplane and it can evidently influence the whole EM character. EM scattering by groove was completely analyzed via Improved Uniform Theory of Diffraction (IUTD) and ray modal theory. In high frequency region, making use of the local effect of scattering, we can separate the whole structure into different parts and analyze these parts independently. In the same way, we can separate the groove from the airplane, and further separate the scattering by groove into two parts: edge and interior. Edge diffracted field includes diffraction to the incident field and high order diffraction to the diffracted field from other edges, both of these fields are computed through IUTD coefficient (Eq.5). Field coupled into interior is expanded as modal field via the ray modal theory (Eq.8), then the modal field propagates to the groove bottom and reflects back to the aperture. Some field will reenter the interior for the discontinuity of the aperture and they are expanded as modal field repeatedly to acquire more exact solution from the interior. Sum of edge diffraction and interior radiation give the complete scattering feature of the groove. Since higher order fields from both the edge and interior are considered, exact solution at wide range can be expected. Numerical calculations are carried out and results as given in Figs.3 and 4 are in good agreement with exact low frequency method [5] .