在鐵道環境中，要提供穩定且快速的無線通訊是一個挑戰，車廂會對基地台傳送的訊號造成嚴重的衰減，使得通訊品質不佳，在車廂外部設置天線，接收基地台發射的訊號是解決這項問題的方法之一。長期演進技術(Long Term Evolution, LTE)是現今能夠提供最高傳輸速率的無線通訊技術，多重輸入多重輸出(Multiple-Input Multiple-Output, MIMO) 的通訊架構亦可提升資料傳輸速率。鐵道環境對於天線性能的要求，並能同時涵蓋LTE所有頻段和WLAN頻段，對天線設計是一大挑戰，特別是在低頻之LTE-700 MHz頻段。
本論文設計寬頻、全向性、MIMO天線，操作頻率從690MHz~6000MHz，頻率比為8.7:1，我們將Return Loss設計在15dB以上、天線高度為56mm(0.13〖 λ〗_700MHz)。首先，我們整合單極天線和支撐機制；第二部分，將天線設計成MIMO、利用指叉式電容的概念降低姿態，並利用袖套天線(sleeve antenna)的概念達成阻抗匹配，接著在兩天線間加入隔離器改善隔離度；最後一部分，討論模擬和實作的誤差並且改善之。

It is a challenge to provide a stable and high data rate transmission in railway wireless communication. The radio signal of base station decays seriously and reduces the communication quality when propagating through train carriages. To overcome this disadvantage, we can mount antennas on the roof of trains to receive the radio signal. Long Term Evolution (LTE) can provide the highest data rate transmission, and multiple-input multiple-output (MIMO) system can also support the high data rate of transmission. Meeting the requirement of rigorous antenna performance in railway applications, as well as covering all the LTE and WLAN bands, are big challenges, especially at the lower frequency band of LTE 700 MHz.
In the thesis, we design wide band omnidirectional MIMO antennas, which operate at a frequency range of 690-6000MHz with ratio frequency about 8.7:1. Also we design the antennas with return loss higher than 15 dB and its height is 56mm which is approximately 0.13 wavelength of 700 MHz. First, we co-design monopole antenna and fixing mechanism. Secondary, we design MIMO antennas and use the concept of both interdigital capacitor and sleeve antenna to lower the profile and enhance the impedance matching of antennas. An isolator is placed between the antennas. By using this parasitic element, a better isolation is achieved. Final part of this thesis, we discuss the difference between the results of simulations and implementation and further improve performance of implemented antennas.

論文審定書 i
誌謝 ii
摘要 iii
Abstract iv
目錄 v
圖次 vii
表次 xi
第一章 緒論 1
1.1 研究動機及背景 1
1.2 相關研究概況 2
1.3 論文大綱 3
第二章 寬頻天線設計 4
2.1 寬頻原理介紹 4
2.2 寬頻天線設計 6
第三章 MIMO天線設計與隔離度探討 19
3.1 MIMO通訊架構 19
3.2 MIMO天線設計與降低天線姿態 20
3.3 MIMO天線隔離度改善 35
第四章 天線實作與量測 41
4.1單天線實作及量測 41
4.2 MIMO天線實作及量測 46
第五章 結論 57
參考文獻 58

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