臺灣博碩士論文加值系統

本論文利用摺疊的結構改善具雙頻操作的T形微帶天線之頻帶受限問題，並探討摺疊結構對輻射場之影響。其中的作法是將雙摺疊的結構套用至原先之T形金屬微帶，在摺疊處的PMC面上所產生的磁流會互相反向，藉由主宰Cross-pol.輻射的磁流之互相抵銷以減弱相對應之輻射強度。對於此天線的兩模態，其可接受輻射的頻帶變多，可調整之共振長度的選擇相對的也會變多。除了以理論、模擬及實驗之數據驗證設計理念外，本文並針對三組不同頻帶間距之天線改善其輻射場，以及探討最有效益之摺疊結構安排。
對於這個雙摺疊T形天線，理論與模擬所得呈現天線輻射場不僅能維持單波束，且Cross-pol.的輻射強度也低於摺疊之前的狀況。數據也證實輻射場也會受摺疊形式而影響，其中以三等份的摺疊安排對輻射場的改善效果較佳，對主宰Cross-pol.輻射之磁流的抵銷也有實際的幫助。又在不同頻段間距下，天線輻射場都可接受，因此天線結構中的共振長度可調整的範圍就大增，此T形天線的設計彈性也大大提升。
就分析方式而言，本文是利用移動磁流的方式計算摺疊後的天線輻射，這種間接的分析方式可避免複雜且繁瑣的計算。即使天線的摺疊形式不同，只要相對的磁流的位置能掌握，摺疊後的輻射場也能求得。又理論數據與模擬結果相近，除了設計理念正確性可證實外，而利用此間接的理論方式來分析雙摺疊T形天線的做法也具有可信度。
本文所提出的摺疊結構確實改善了T形天線之輻射，而此設計理念也可套用在不同頻帶之應用。所用的理論分析簡單，對有類似問題之天線，此分析方式也能適用。

This thesis uses folded structure to improve the problem on limited operation band for T-shape dual-band microstrip antenna, and to investigate the effect on radiation of folded arrangement. As a microstrip patch is changed into a double-folded structure, the vectors of magnetic currents on PMCs will point to opposite directions with each other, the X-polarization of radiation will thus be reduced. For the two modes of this antenna, the frequency band with acceptable radiation will increase, so as the choice of resonant lengths for adjustment. In addition to the confirmation of design concept by using theoretical, simulated and experimental results, this thesis also improves the radiation for three sets of antennas with various frequency separations. Moreover, the investigation for optima folded arrangement is done.
For this double-folded T-shape microstrip antenna, the radiations obtained from theory and simulation do not only remain the shape with a single beam, but the strength of X-pol. radiation also become lower than that of the antenna before folded. The results prove that antenna radiation also vary by folded arrangement. More importantly, the arrangement with equal division offers optima improvement, the X-pol. radiation from dominate magnetic currents is reduced. The radiations become acceptable at various frequency separations, the range of resonant length for adjustment becomes so larger that the design freedom of this T-shape Microstrip antenna increases.
As the procedure for analysis, this thesis uses the concept of moving magnetic currents to compute antenna radiation, this alternative approach can avoid complicated computation efforts. For the antenna with different folded arrangement, the radiation can be still obtained without any difficulty as long as the locations of the corresponding magnetic currents is handled. Meanwhile, the agreement between results from theory and simulations does not only confirm design concept, but it also provides a reliable approach to analyze the double-folded T-shape microstrip antenna. The theoretical analysis used is simple, it is eligible for the antennas with similar problem.

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 緒論 1
1-1 歷史背景與研究動機 1
1-2 設計理念與分析方式 2
1-3 論文架構 3
第二章 雙摺疊微帶天線之探討 4
2-1 天線參數之推導 4
2-2 摺疊方式對天線特性之影響 8
2-3 結論 10
第三章 T形微帶天線特性之探討 19
3-1 天線參數之推導 19
3-2 結構尺寸對天線特性之探討 22
3-3 結論 24
第四章 雙摺疊之T形微帶天線 40
4-1 理論的輻射場之處理 40
4-2 輻射場數據之驗證 43
4-3 摺疊安排之探討 44
4-4 結論 45
第五章 總結 59
參考文獻 61

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