新型任意雙頻枝幹耦合器應用於雙圓極化天線之設計

Abstract

本論文的研究方向著重於設計2.55 GHz和3.5 GHz雙頻段的新型雙頻枝幹耦合器之饋入網路並且搭配L 形電容耦合饋入式平面天線實現雙頻雙圓極化天線。傳統的枝幹耦合器只能用於單一個頻率,然而現在高傳輸資料量、高傳輸速度、傳輸高品質的時代下，設計多頻的饋入網路和多極化天線勢必為一種趨勢。本論文相對於傳統枝幹耦合器不同的是在於引用複合式左右手傳輸線的概念，在枝幹上加入開路殘段和集總的電容、電感元件，經由嚴謹的電路奇偶模分析步驟法得出正確的參數數值，進而讓枝幹耦合器達到雙頻效果，而此雙頻之操作頻段可由設計者任意選取兩頻率且無範圍限制皆可實現其效能。 實現雙頻雙圓極化天線重點在於饋入網路和天線需要有雙頻及產生圓形極化波條件的特性。尤其枝幹耦合器的設計更為重要，因為輸出端埠會隨著操作在不同頻率的變化而有不同的功率大小和相位。因此在設計的雙頻段下，輸出兩端埠需要功率大小相等、相位差為正負90度才能滿足產生圓極化波條件。接著在雙頻微帶線貼片天線部分，利用L形電容耦合饋入法饋入訊號並在平面天線的輻射體上挖置四條狹縫，此目的不僅可以產生雙頻共振條件也可與枝幹耦合器一樣具有高對稱性的結構，如此一來，將天線結合所設計出的雙頻饋入網路而形成一系統，因此達到雙頻雙圓極化天線之設計。

A design of the novel dual-band branch-line coupler applied to dual-band dual-sense circularly polarized antenna is presented in this thesis. The resonant frequency of the dual-band branch-line coupler is designed at 2.55 GHz and 3.5 GHz. Different from the conventional branch-line coupler, the concept of composite right left handed transmission line is used in this thesis by inserting open stubs and the lump elements of capacitors and inductors in the branch. In order to have a dual-band circuit, there are exact parameter values which obtained by the steps of even-odd mode analysis method. The circuit can be operated at arbitrary dual-frequency which is decided by designer. It is importance to have the properties of dual-band and producing the condition of circular polarization of the patch antenna. Especially, the novel dual-band branch-line coupler is most important because of equally power amplitude and ninety phase difference between two output ports. Also, the patch antenna is etched four slots and fed by L-shaped capacitive coupling probes so that it can produce circular polarization and more symmetry as same as the branch-line coupler. Finally, the whole configuration is combined with the circuit and the patch antenna to obtain the dual-band dual-sense circularly polarized antenna.