基於平行板狹縫模型之金屬光柵天線二維分析與設計

Abstract

本篇論文提出一新方法，用來最佳化一薄型金屬光柵天線之效能並分析其工作原理。基於單條細狹縫之分析，本文先將金屬光柵問題分解成一基礎問題：平面波以任意角度入射至平行板波導中無窮長之單一狹縫。藉由計算所需之二維格林函數，我們得到平面波以任角度入射狹縫之反射及穿透係數，並由全波模擬得到良好的驗證。此方法得到之結果可廣泛應用於平面微波電路架構，導波與漏波結構皆適用。本文並演示其中數種，包含平行及垂直傳播方向之介質構裝波導，接地面之共平面波導，含接地面之共平面帶線。本研究發現許多有趣且獨特現象：例如垂直傳播方之狹縫對介質構裝波導造地的全反射及輻射截止頻率，以及無平板模態損耗之接地面共平面波導。 依據次此隙縫分析，我們可將此光柵天線簡化成一串接電路。天線分析被分為兩切面獨立討論，分別以均勻性及週期性漏波模型計算場型，並進一步得到天線指向性做參數分析。最佳化後的光柵而後加上實際的饋入結構，本文演示槽孔及電感饋入兩種。槽孔饋入天線操作於5GHz，單一元件可有11dBi以上增益，四元件及八元件陣列則分別有16dBi及19dBi增益，但阻抗頻寬僅1%，故本論文提出另一電感饋入天線於2.35GHz，單一元件同樣11dB以上增益，四元件陣列則亦有16dBi，頻寬則增加至3%。 本文提供一完整且一致性的方法，有系統且快速有效率的分析並最佳化一金屬光柵天線。除天線以外，本方法可適於導波結構，來解決由平面及狹縫構成的問題，特別在細狹縫，全波模擬較難處理的問題中，有良好的效果。

We developed a novel approach to analyze and design a thin metal-strip grating (MSG) antenna. Starting from the basic element, we decomposed and transformed the MSG antenna problem into a fundamental topic - the scattering of a single slit on a parallel plate waveguide (PPW) with an oblique incident TEM wave. By deriving the 2-D Green's functions of the problem, the reflection and transmission properties of the slit were successfully calculated and validated by full-wave simulations. The proposed 2-D slitted PPW model was then applied to several planar guided-wave structures, such as the substrate integrated wavequide (SIW) with transverse or longitudinal slits, the grounded co-planar waveguides (CPW), and the grounded co-planar striplines. We found and discussed some interesting and unique phenomena in these structures, such as the ``transmission-zero frequency' and the ``radiation-cut-off frequency' in transversely slitted SIW and the 'leakage-free structure' in a grounded coplanar waveguide (GCPW). With the developed 2-D slitted PPW model, a MSG antenna was analyzed using cascaded equivalent circuits for the periodic slits. We divided the antenna problem into H-plane and E-plane cases and evaluate far-field patterns with the uniform and the periodic leaky wave models, respectively. We successfully predicted the antenna directivity and then used the validated model to optimize a finite-size thin MSG antenna. Additionally, we demonstrated the realistic design, implementation, and measurement of printed MSG antennas in terms of two feeding structures. The slot-fed design at 5GHz provided the antenna gain about 11dBi for the element, and 16dBi and 19dBi for 2x2 and 4x2 arrays, respectively. The inductor-fed design at 2.35GHz provided the antenna gain about 11dBi for the element, and 16dBi for 2x2 arrays with an enhanced impedance bandwidth of 3% . This comprehensive study covers the antenna theory, design, and experimental test. The work provides a self-consistent approach to analyze and design a thin MSG antenna. In addition to the antenna problem, the developed 2-D slitted PPW model may also efficiently solve the guided-wave problems with slit-based planar structures, especially with narrow slits where the meshing-based full-wave simulator is inept.