利用漁網結構之人造介質材料設計空間波束分歧器

Abstract

本論文提出使用二維漁網組成的週期性結構，來設計四向之空間波束分歧器。經過適當設計漁網結構的週期和槽孔的大小，使此人造介質材料具備近零折射係數。由Snell定律，知道當波由近零折射係數的介質傳播至折射係數大於一的介質，其折射波將垂直於兩介質之交界面。基於此特性，我們將線性激發源置入人造介質材料內，激發出四個垂直於矩形人造介質材料的輻射波束。為了增加指向性，在四個開口加上E-plane的號角開口。本論文的主要貢獻如下：(1)系統化的計算出二維週期性結構的色散和相位關係，用以解釋波在近零折射係數的人造介質材料之異常傳播特性；(2)實作與量測驗證計算的結果。最後，理論與實驗結果具有相當的一致性。

In this thesis, we presented a 4-way spatial beam splitter consisting of two-dimsnsional fishnet-based periodic structure. By properly designing the periods and aperture size of the fishnet, the periodic medium can possess a effective refractive index close to zero. Furthermore, from Snell’s law we know that the refractive wave outgoing from a medium with refractive index near zero will tend to be perpendicular to its interface connecting to a medium with refractive index greater than unity. Based on this principle, we put a line source in the metamaterial to excite the four beams normally radiating from the four sides of the rectangle-shaped metamaterial. To enhance the radiation directivity, each of the openning is equipped with a E-plane horn type structure. The major contribution of this theses contains twofolds: (1) the dispersion and phase relations of the two-dimensionally periodic structure was systematically calculated to explain the extraordinary propagating characteristics of waves in the metamaterial with near-zero effective refractive index, and (2) in addition to the theoretical calculation, the experimental measurements were carried out to verfy the theoretical studies. Last but not the lease, a good agreement between the theoretical and experimental results was obtained.