廣角回波週期性結構之分析與設計

Abstract

本論文旨在分析和設計一個廣角回波二維金屬週期性結構，使能克服智慧型汽車防撞系統中一般車體只能有正向回波散射場的缺陷。此結構全長二十公分，入射波為垂直偏振平面波(TE wave)，頻率為77GHz。 首先利用導體反射板上的切線電場為零的邊界條件，配合混合電位積分方程、動差法和週期性結構之格林函數來求得反射板上的感應電流；接著再以反射板上的感應電流及遠場格林函數來計算其遠場回波散射場值。最後藉著將平板彎曲成為「曲面板」，增加回波散射場每個旁波的角度寬，而達到廣角回波的目的。

In this paper, we analyze and design the geometry of a two dimensional periodically metallic structure for producing high echos over a large range of field incidence angles retrodirectivity. This structure is expected to overcome the disadvantage that only near normal directions to the vehicle body's surface can a high reflected field be obtained for automotive collision avoidance system. The incidence field is a TE plane wave with frequency of77GHz. The total length of the periodical structure is chosen to be 20cm. By incorporating the boundary condition on the conductor and using the method of moment, the mixed potential integral equation, and the periodic Green's function, we get the induced current density on the periodical conducting structure. Then, according to the current density and the far field free space Green's function (Hankel function of the second kind), the monostatic scattering far field can be calculated. Finally, it is found that, by bending the conducting structure surface, the grating lobe beamwidths of the monostatic scattering field are increased, thus resulting in a wide retrodirective beam.