近年來，隨著無線通訊系統將頻譜切割成不同頻段提供特定用途，例如900/1800/2100MHz行動通訊、2.4/5.2-GHz無線區域網路(WLAN)、和2.5/3.5-GHz WiMAX等。由於頻譜的需求與使用率日益增加，在資源有限的情況下，必須找出有效提升頻譜使用率的方法，其中感知無線電系統就是一個突破此困境的重要技術。感知無線電被視為具有發展性的技術，主要歸功於利用「頻率可重置能力」與「感測能力」兩大功能提升頻譜的使用率。將這兩個能力實現於天線設計上，我們必須設計出能夠調整諧振頻率的「頻率可重置天線」，以及具有寬頻偵測頻譜使用情形的「寬頻感測天線」。另一方面，多重輸入多重輸出(MIMO)天線系統一直以來被視為提升通訊品質與傳輸資料量的技術。上述兩種技術在各自領域都有許多的研究與探討，但目前為止將兩種技術合併與應用以提升通訊品質的研究成果較為少見。
在本論文中，我們設計一個應用於感知無線電系統之頻率可重置多重輸入多重輸出單極天線，並包含寬頻感測功能。本天線設計包含兩支頻率可重置的單極天線，以及共平面波導(CPW)饋入之寬頻感測天線。在多天線無線傳輸系統中，天線彼此之間會有耦合的現象發生，因此天線隔離度將是在設計時的重要議題。本設計中，我們將寬頻感測天線放置在兩支單極天線的正中央位置，除了可以縮小天線整體體積之外，最大的目的是將寬頻感測天線做為提升單極天線隔離度的金屬結構。我們應用兩顆變容二極體改變單極天線之電氣長度以達成頻率可重置之特性，經由適當設計可以在2GHz至5.8GHz做窄頻寬頻帶切換。另外寬頻天線也能在相同頻率範圍內感測無線環境之頻譜使用狀況，將資訊回報給用戶端，再將多重輸入多重輸出之單極天線切換至頻譜間隙做窄頻寬高資料量的傳輸。本天線設計建立完整天線平台提供使用者於感知無線電系統之應用。

Recently, radio spectrum is in high demand as the usage of the spectrum increases day by day at an enormous rate; there is a need to find a solution to efficiently utilize these insufficient resources. Cognitive radio is a huge step towards this goal. Cognitive radio has become a promising technology thanks to its inherent spectrum sensing capability and frequency-agile radio functions for efficient spectrum utilization. In order to achieve a cognitive radio antenna system, we have to design a frequency reconfigurable antenna and a wideband sensing antenna. On the other hand, a multiple-input-multiple-output (MIMO) antenna system is a well-known technique to enhance the performance of wireless communication systems. Quite a few research has been available in each individual field but very few approaches are found in literature where both are combined and utilized.
A cognitive radio MIMO antenna is presented in this paper. The proposed antenna consists of two reconfigurable printed monopole antennas and a coplanar waveguide (CPW) fed wideband sensing antenna located between the two antennas. The structure is specially designed for antenna miniature. For multi-channel wireless communication systems, it is essential that the designed multi-antenna would have high isolation between the antenna ports. To this end, the wideband antenna at the middle is utilized as a structure to enhance the isolation of two monopoles. When properly designed, the MIMO antenna can be electronically tuned over the lower ultrawideband (UWB) frequency band (2300–6300 MHz) using two pairs of varactor diodes. The wideband sensing antenna is used to cover a wide range frequency band from 2.2 GHz to more than 7 GHz. The proposed antenna elements develop a complete antenna platform for cognitive radio (CR) applications. The overall size of the antenna is set to be 60 × 40 mm2.

論文審定書 i
摘要 ii
ABSTRACT iii
目錄 iv
圖次 vi
表次 x

第一章　　序論 1
1.1　　研究動機 1
1.2　　研究方法 2
1.3　　相關研究概況 3
1.4　　論文大綱 5

第二章　　感知無線電系統 6
2.1　　感知無線電系統介紹 6
2.2　　感知無線電天線設計 8

第三章　　寬頻感測天線設計 11
3.1　　共平面波導饋入之寬頻單極天線設計 11
3.2　　槽孔改善寬頻天線阻抗匹配之設計 14
3.3　　天線實作與量測結果 17

第四章　　頻率可重置之多重輸入多重輸出單極天線設計 23
4.1　　雙頻單極天線設計 23
4.2　　應用變容二極體實現頻率可重置之雙頻天線設計 27
4.3　　頻率可重置之三頻單極天線設計 32
4.4　　多重輸入多重輸出天線系統與隔離度設計 37
4.5　　直流偏壓系統設計 42
4.6　　天線實作與模擬探討 45

第五章　　結論 58

參考文獻 59

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