結論 (Conclusion) - 新型多頻印刷偶極天線與縮小化印刷摺疊偶極天線設計

本論文「新型多頻印刷偶極天線與縮小化印刷摺疊偶極天線設計」中提出了兩個新穎的天線設計概念，第三、四章為多頻帶新型印刷偶極天線設計，第五、六章為縮小化摺疊偶極天線設計。在多頻帶偶極天線設計部分，本論文提出以環形微帶線分合波器作為天線的饋入網路，實現由兩端饋入訊號之新型態偶極天線架構，藉由在環形分合波器中心頻率饋入一對振輻相同、相位差180 度的平衡訊號，以及在其他頻率饋入一對振幅、

相位差不同的非平衡訊號，可以在兩斜向偶極臂上激發不同的共振模態，成功實現印刷偶極天線多頻段、寬頻帶的操作。在縮小化摺疊偶極天線設計部分，本論文提出一天線縮小化新方法，透過圍繞所設計之摺疊偶極天線適當大小形狀的環形寄生金屬，產生感應之映像電流延長輻射路徑，並在環上形成環形天線模態共振輻射。同時藉由結構產生的電感性電抗補償低頻時電容性的偶極天線，成功達到大幅降低天線共振頻率之目標。

第三章設計出結合改良式三埠微帶線環形分合波器之新型印刷偶極天線， 2~6GH 量測反射損耗中共有四個共振頻率與兩個操作頻帶，低頻帶操作頻寬可以達到1.4GHz，

高頻帶也有620MHz，不過受到環形分合波器加總端埠接上晶片電阻產生的損耗以及本身的結構因素，造成高頻輸出功率分配不足，而直接影響了天線增益。為了改善此問題，

第四章以改良式開路三埠環形微帶線分合波器取代原本的饋入網路，成功使得高頻增益從0~1dBi 大幅提高至 4~5dBi，中高頻增益也提高至 3~4dBi。同時，為了增加天線實用價值，本章進一步將共振頻率作頻帶規劃，設計出雙頻、三頻及多頻之印刷偶極天線，

其操作頻帶能夠函蓋各常用通訊系統頻段。

第五章首先設計一共振頻率 1.4GHz 之單邊繞折印刷摺疊偶極天線，透過圍繞適當內半徑與寬度之圓環形寄生金屬，成功將摺疊偶極天線共振頻率降到 0.995GHz。同時藉由史密斯圖證明圍繞環形寄生金屬即是在低頻作阻抗匹配，可以以串聯電感與電阻的等效電路模型來表示。並且由等價電流分佈設計出整合平衡非平衡轉換器之等效縮小化印刷摺疊偶極天線，透過模擬與實作量測驗證所提出之天線縮小化概念。第六章中繼續研究不同環內徑對降頻的影響與造成的因素，由於方形結構在固定與中心距離時具有較長的周長，當環緊縮時其等效環形天線共振頻率不至於太高，在進一步降頻的同時能夠提供恰當的串聯電阻給摺疊偶極天線，因此提出以方形環結構取代圓環結構來的改良設計，由模擬與整合平衡非平衡轉換器之等效結構量測結果，證明成功將共振頻率降低至 0.87GHz，且在共振頻率仍維持良好的反射損耗特性。

近幾年由於無線通訊的相關技術蓬勃發展，單一天線設計具有可雙頻段、多頻段或

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寬頻帶操作逐漸成為主流，以及伴隨輕薄短小之天線需求愈亦增加的趨勢下，本論文即針對此兩大方向分別進行天線設計研究，成功設計出可雙頻、三頻及多頻之印刷偶極天線，以及共振頻由1.4GHz 降至 0.87GHz 之縮小化摺疊偶極天線，縮小化指數可達到 1.609 之高。在未來的研究中，將繼續改良作為天線饋入網路之環形分合波器，希望可以結合極化掃描的技術，針對不同頻率的需求來提供相位差 90 度且垂直饋入的兩輸出訊號，

以達到不同頻率不同極化操作的目標。同時將針對所提出之天線縮小化方法，繼續朝向與多頻帶天線整合的設計，並設法改善降頻後頻寬變小的缺點。

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