臺灣博碩士論文加值系統

為了設計出一個能與系統整合的平面結構且具有雙頻操作之單極微帶天線，本論文的做法是將單純的單極微帶天線做兩次彎摺，而第二模態的反向電流就可自行抵消，進而在與第一模態一樣只貢獻單一方向的電流，因此兩模態輻射場就可形成甜甜圈的分佈。而利用理論、模擬和實驗的數據證實設計理念之餘，結構參數的改變也用來探討天線的特性。
對於雙彎摺天線的特性，單極天線長度是針對四分之一和四分之三波長兩種模態，因在這兩模態的波長之輸入阻抗最接近50Ω，因此所設計出的天線也容易達成阻抗的匹配。而在適當的雙彎摺尺寸下，理論與模擬所得兩模態的輻射場都具有可接受的甜甜圈分佈，因此天線確實具有雙頻的操作。而在結構參數改變對特性影響的探討中，第一段微帶寬度的改變能調整頻率的間距，又特定的多彎摺結構尺寸能有的降低cross-pol.輻射進而設計的自由度可提升。
就分析方法而言，本論文將雙彎摺天線分成五個區段，這些區段所貢獻的電磁場可以運用原本未彎摺前的分析概念獲得，進而兩模態的輻射場狀況可易掌握。其中分析方法是以線電流的形式處理，因此天線的分析困難度可大大降低。而理論、模擬以及實驗數據比對的結果，除了證明設計理念的可行性外，也證實模擬方式的正確性，因此單單模擬所得的結果就可用來探討雙彎摺天線的特性。
在設計此天線中，本論文所提的理念是利用彎摺天線的方式而達到雙頻的操作，如果天線彎摺的次數增多，則多頻帶操作的功能就有可能達成。

This thesis uses the concept of double folded structure to design a dual-band monopole microstrip antenna for integration with a coplanar system. The reversed currents of the 2nd mode can cancel with each other, the dominant current becomes singly directed as that of the first mode. Thus the radiations pattern of the two modes can be similar to donut shapes. The data from theory, simulation and experiment verifies design concept, and the variation of structure is used to investigate antenna characteristics.
For this double-folded antenna, the design focuses on the two modes with quarter or three-quarter wavelength respectively, their input impedances are close to 50Ω. Therefore, the impedance of designed antenna is easy to match with appropriate dimension of double folded structure. The theoretical and simulated radiations of two modes both show acceptable donut shape patterns. According to the investigation of dimension variation, the width of the first segment can adjust band separation, and the dimension of folded extension can be used to reduce cross-pol. radiation and improve design freedom.
From the theory point of view, the double folded antenna is divided into five regions, so that the electromagnetic field from these segments can be obtained based on the unfolded one. Therefore, the radiations of two modes are easy to handle. Since the analysis is done based on line currents, the procedure becomes much more easier. The comparison between theory, simulation and experiment does not only confirm design concept, but also verify the validity of simulation. In other word, the result of simulation can be used to investigate antenna characteristic sufficiently.
In this design, the employment of double-folded structure can make an antenna operate at dual bands, the multiple-band function may be achieved if the number of folded segments increases.

摘要 I
英文摘要 II
致謝 III
目錄 IV
圖目錄 V
表目錄 VIII
第一章 1
1-1 歷史背景與研究動機 1
1-2 設計理念與研究方法 2
1-3 論文架構 4
第二章 5
2-1 傳統偶極天線 5
2-2 傳統單極天線 8
2-3 微帶式單極天線 9
2-4 結論 10
第三章 27
3-1 兩模態之之電流分佈 27
3-2 雙彎摺單極微帶天線參數之推導 28
3-3 雙彎摺單極微帶天線特性之探討 32
3-4 結論 33
第四章 52
4-1 第一段的微帶寬變化之影響 52
4-2 多彎摺結構對於天線輻射場之影響 53
4-3 結論 54
第五章 69
參考文獻 71

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