使用漸近線型負載邊界條件分析平面式接地介電基板上含金屬線型格柵結構的表面波與散射特性

Abstract

接地介電基板上含金屬線型格柵結構是一種傳統上被廣泛應用於天線和微波元件設計的周期性結構，然而到目前為止都還沒出現既有效率，又能獲得電磁場場型分布解析解的分析方法，本篇論文將漸近線型負載邊界條件(ASBC)應用於該結構上，發展出既快速又簡單的分析方式。 商用電磁軟體CST，在本篇論文中被用來和ASBC分析法比對，然而，CST分析結果在無窮常結構上的不一致性，在本篇論文中被討論並解決。解決CST一致性問題後，再與ASBC分析法做比對。 藉由解開從ASBC得到的特徵矩陣，任意方向的色散圖都可以被獲得包含OX、XM、MO路徑。此外藉由設計適當的入射波形表示式(TE或TM)，ASBC還可以獲得非其次系統方程矩陣，解開後即可獲得反射係數，因此ASBC除了可以解色散問題還可以用來解任意方向入射的反射問題，這是CST軟體所無法達成的。 最後，我們發現ASBC分析法在金屬線型格柵的寬度較寬時，準確性會下降。因此我們利用表面特性阻抗連續的概念，修改了純ASBC法。使修正後的ASBC法在即使是金屬線型格柵的寬度較寬的狀況下也能保有高精準度。

Metallic strip grating on grounded dielectric slab is a canonical structure applied to many kinds of microwave components and antennas. However that there is no efficient method can be used to analyze the structure and obtain field distributions in closed form until now. This thesis applies ASBC on the strip-grating structure and obtains EM properties in an easy and fast way. Commercial software CST is used to confirm the ASBC analysis result. Nevertheless inconsistency of CST simulation result occurs in infinite long structure. The problem is also be discussed and solved in this work. By solving the characteristic matrix which result from ASBC analysis all directions of dispersion diagram can be acquired including OX, XM, and MO path. Setting proper incident wave (TE and TM), and solving nonhomogeneous matrix, ASBC also can be used to figure out refection problem even for oblique azimuth planes which CST cannot do. Finally, we find that accuracy of pure ASBC analysis is not so good when the width of metal strip become wider. Therefore we combine the concept of consistency of surface impedances with pure ASBC analysis. With this correction method, ASBC is accurate even for wider metal strip cases.