本論文第一部分首先研究自平衡及非平衡天線，由於非平衡的平面倒F形天線主要的輻射來自於接地面，因此針對平面倒F形天線產生的強接地電流作探討以及提出改善方式。而在自平衡天線如環圈天線以及偶極天線中，完美差動訊號饋入是必要的，然而在實際應用常常以採用單端饋入。文中探討此方式造成天線的特性變化以及連接到纜線上所產生的影響。第二部分利用耦合饋入改變平面倒L形天線的虛部阻抗以降低其四分之三波長的諧振頻率，並提出採用耦合饋入達成用於MIMO天線的內建式隔離機制，其特點為不需要額外低加入隔離元件，可有效利用空間。接著將此隔離機制應用於WLAN 2.4 GHz頻帶的USB Dongle天線設計上，由於為內建式的設計，因此所需面積相當小，在2.4 GHz頻帶內的隔離度皆大於15dB，最佳處達到22 dB。最後並結合前面所發現的耦合饋入改變單極天線的特性，完成應用於WLAN 2.4/5 GHz雙頻MIMO天線的設計，在2.4 GHz頻帶內隔離度皆大於10 dB，最佳處達到25 dB，而在5 GHz頻帶內皆大於15 dB，最佳處達到55 dB。

The first part of this thesis analyzes the self-balanced and unbalanced antennas. Because PIFA (Planar Inverted-F Antenna) is an unbalanced antenna, and its ground contributes to the most radiation pattern of the entire antenna, uncontrollable system ground currents could degrade system performance. To reduce the ground currents, an improved protruding ground structure is proposed. In the self-balanced antenna, such as loop and dipole antennas, perfect differential signal feed is necessary; however single-ended feed is often used. The effects of single-endedly fed loop antenna were investigated. The antenna mode currents were found and validated. In the second part of this thesis, we employed a coupling feed to modify the imaginary part of the PILA (Planar Inverted-L Antenna) impedance to reduce second resonate frequency, and we found such feed exhibited a built-in isolation characteristic for MIMO antenna configuration. Unlike usual isolation structure, this coupling feed doesn’t need additional isolation element and is suitable for small-sized MIMO antenna. Then, a WLAN 2.4 GHz USB dongle MIMO antenna which employs this isolation mechanism is designed. Due to the built-in mechanism, the antennas have small size and good isolation. In all the operation frequencies, the overall isolation reaches 15 dB, with the best isolation being 22 dB. Finally, a dual-band MIMO antenna, which combines the both properties (modifying imaginary impedance and built-in isolation) was proposed, fabricated and validated. In lower operation frequencies, the overall isolation reaches 10 dB, with the best isolation being 25 dB. In higher operation frequencies, the overall isolation is better than 15 dB, with the best isolation being 55 dB.

論文審定書 I
誌 謝 II
摘 要 III
Abstract IV
目 錄 V
圖 次 VII
表 次 X
第一章 緒論 1
1.1研究背景及動機 1
1.2章節概要 2
第二章 自平衡與非平衡小天線之研究 3
2.1探討PIFA對於接地電流之影響 3
2.1.1 PIFA擺放位置對於接地電流之影響 4
2.1.2利用突出式接地控制接地電流分佈 5
2.1.3接地電流對於輻射場型之影響 9
2.2非平衡饋入對於環圈天線之影響 9
第三章 多輸入多輸出通訊系統 18
3.1多輸入多輸出通訊架構 18
3.2隔離機制介紹 20
3.3微波混響室介紹 21
第四章 電容耦合饋入天線之研究 26
4.1倒L形天線 26
4.2直接饋入與耦合饋入之倒L形天線探討 31
4.3具有內建隔離機制之MIMO天線 34
4.3.1天線架構 34
4.3.2模擬及隔離機制分析 35
第五章 使用內建隔離機制設計用於USB Dongle 之微小化MIMO天線設計 37
5.1天線設計與原理 37
5.2天線實驗與量測結果 39
第六章 適用於USB Dongle 之微小化雙頻MIMO天線設計 48
6.1天線設計與原理 48
6.2天線實驗與量測結果 50
第七章 結論與未來工作 57


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