近年來無線通訊技術發展迅速，能夠提供使用者更高速率的傳輸，以及更寬的頻寬，IEEE標準協會制定了新的無線網路標準802.11ac，此無線網路標準是透過5 GHz頻段來提供高通量的無線區域網路(WLAN)，能夠支援最多8個多重輸入多重輸出(Multi-input Multi-output, MIMO)空間串流。因此在本論文中提出了適用於IEEE 802.11ac的MIMO天線，此MIMO天線可放置於室外無線基地台(access point, AP)中，利用低頻段的全向性場型提供Wi-Fi給移動中的使用者，在高頻段除了指向性場型還加入了場型可調(pattern-reconfigurable)的功能，本設計的場型切換功能是利用頻率選擇表面(frequency selective surface)，能夠提供靜止的裝置與裝置之間高資料傳輸率(throughput)的點對點的傳輸。
首先提出能夠操作於2.4 GHz以及5 GHz頻段的偶極天線(dipole antenna)，利用一天線本身的迴圈(loop)結構反射高頻輻射場型，使天線擁有低頻全向性和高頻指向性的輻射場型。接著在天線下方置放一接地面，將雙極天線結構等效為單極天線(monopole antenna)；第二部分提出一MIMO天線，將單極天線的結構於接地面上方鏡射，並且共用兩天線用來反射高頻場型的迴圈結構，以及加大接地面使MIMO天線操作頻段與單天線相同，也依然擁有高低頻的全向性以及指向性場型；第三部分為提出增加低頻隔離度(isolation)的方法，因為經過鏡射後的MIMO天線低頻單極天線距離小於半個波長，在阻抗匹配以及輻射場型上會有干擾的情況。因此參考文獻，在天線接地面上設計接地面電流扼流結構(ground current choke)，連接上層的金屬結構以及下層的槽孔結構形成一電感電容諧振電路，改善隔離度。第四部份在MIMO天線兩側天線加上頻率選擇表面，並在頻率選擇表面上加上PIN二極體(PIN diode)，使頻率選擇表面可切換為穿透板或是反射板，因此每一個天線皆能有三種輻射場型可切換，並且在低頻擁有全向性場型。

In recent years, the development of the wireless communication systems have grown rapidly. The higher the data rate and the wider the bandwidth can be provided to users. The IEEE’s newer wireless local area network (WLAN) standard, 802.11ac, is used for providing high throughput WLAN at 5 GHz band. It is also capable of supporting up to 8 MIMO spatial streams. In this thesis, a Multi-Input Multi-Output (MIMO) antenna suitable for 802.11ac standard is proposed. This MIMO antenna can be placed in an outdoor access point(AP) to give Wi-Fi for moving users by using the omni-directional radiation pattern in the lower band. In the higher band, the antenna has the directional radiation pattern and the function of pattern reconfigurability in the higher band by using frequency selective surfaces (FSS). The high throughput can be provided by means of Peer to Peer (P2P) transmission to the devices.
Firstly, a dual-band dipole antenna operating at 2.4 GHz and 5 GHz is designed. This antenna has the omni-directional pattern at the lower band and directional pattern at the higher band. In the antenna design, a loop structure can reflect the radiation pattern in the higher band. By placing a ground structure perpendicular to the antenna, the dipole antenna becomes a modified monopole antenna. Secondly, a MIMO antenna is formed by mirror duplicating the existing monopole. Thirdly, the solution of the isolation problem in the lower band is proposed. A current choke is designed on the top and bottom sides of the substrate of the ground to improve the isolation. It is equivalent to an LC resonator by a patch on top side connected to a slot on bottom side. Fourthly, the four FSS with PIN diodes are placed beside the MIMO antenna to either act as reflectors or to remain non-reflective. Three radiation patterns of each port can be steered at 5.8 GHz, and the omni-directional radiation pattern at 2.4 GHz.

論文審定書i
碩士論文公開授權書ii
致謝iii
摘要v
Abstract vi
目錄viii
圖次x
表次xiv
第一章 緒論1
1.1 研究背景與動機1
1.2 文獻回顧2
1.3 研究方法3
1.4 研究目標3
第二章 雙頻MIMO天線設計5
2.1 偶極及單極天線介紹5
2.2 雙頻天線設計8
2.3 雙頻MIMO天線設計18
2.4 雙頻MIMO天線隔離度增強25
第三章 場型可調雙頻MIMO天線35
3.1 頻率選擇表面介紹35
3.2 場型可調天線設計36
第四章 天線實作及量測45
4.1 天線之S參數量測45
4.2 天線場型量測48
4.3 MIMO天線封包相關係數量測53
第五章 結論57
參考文獻58

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