- 學位論文
應用於第四代/第五代無線通訊之寬頻四乘四巴特勒矩陣設計
Design of Broadband 4 × 4 Butler Matrix for 4th/5th Generation Wireless Communication
摘要
隨著人類對於無線通訊的需求快速激增，為了提升頻道容量、通訊品質以及頻譜使用效率，智慧型天線已被廣泛應用於各式各樣的無線通訊設備。而智慧型天線可以概分為兩個種類，分別是適應性天線以及波束切換式天線，由於整體架構簡單以及不需要過於複雜的運算過程，波束切換式天線成為目前最普遍的類型。而波束切換式天線的架構主要可以分為三大部分，分別是開關、波束形成網路以及天線陣列，其中，波束形成網路為整個架構最核心的部分，它可以根據不同的開關而產生適當的餽入訊號，再將此適當的訊號傳送至天線陣列，使整個天線陣列的主波束可以指向特定的方向。也因為波束形成網路的重要性，過去幾年有幾種種類的波束形成網路架構陸續被提出，其中又以原件少、低成本及低損耗的巴特勒矩陣最為被廣泛使用，有鑒於此，本論文主要致力於寬頻四乘四巴特勒矩陣之設計。 典型的四乘四巴特勒矩陣架構包括了三分貝耦合器、中間網路以及輸出網路，由於輸出網路的功能僅在於重新排序各個輸出口的位置，因此本論文將著重於三分貝耦合器以及中間網路的設計，其中三分貝耦合器主要是提供將能量均分的功能，而中間網路則是調整各個輸出口之間的相位差，藉此來產生適當的餽入訊號給天線陣列。 關於三分貝耦合器的設計，本論文提出一種新型的寬頻前向式方向耦合器。在奇、偶模態皆達到阻抗匹配的前提下，前向式方向耦合器的耦合量來自於這兩種模態累積的相位差異，當此相位差愈大，耦合量就愈大；除此之外，為達到寬頻的特性，如何使奇、偶模態的相位差在寬頻帶內可以維持定值，將成為另一項設計的關鍵。因此，本論文在耦合器設計方面，將以週期性結構的概念出發，提出的單元結構除了可以達到奇、偶模態的寬頻阻抗匹配，亦可提供較大的相位差異，並且使此相位差在寬頻帶內維持定值，藉此達到寬頻前向式方向耦合器，同時維持具有競爭力的小體積。 另外，本論文亦提出一種新型的寬頻中間網路，此網路將引用到指叉式電容的架構，並且搭配簡化的等效電路模型來輔助分析，藉此可以在寬頻帶內提供輸出口之間45度的相位差。最後，適當地整合本論文提出的寬頻前向式方向耦合器和寬頻中間網路，即可達到寬頻四乘四巴特勒矩陣，此電路大小約0.98λg × 1.33λg，並且在輸出口能量大小維持在7分貝正負1分貝的限制下，此電路的比例頻寬可以達到約46%。相較於文中比較的文獻，本論文提出之電路不僅可以維持小體積，並可以擁有更良好的頻寬。
並列摘要
With the demand for wireless communication increasing explosively, smart antennas have been widely applied in kinds of wireless communication devices in order to promote the channel capacity, signal quality, and the spectrum efficiency. Butler matrix is the most popular type of smart antenna due to its less components, low cost, and low loss. In view of these characteristics, this thesis dedicates to the design of broadband 4 × 4 Butler matrix. The typical 4 × 4 Butler matrix contains 3-dB couplers, a middle network, and an output network. However, this thesis focuses on the designs of the 3-dB coupler and the middle network since the output network is only used to rearrange the locations of output ports in order. Besides, the 3-dB coupler mainly provides the equal power division and the middle network is used to adjust the phase differences between the output ports. In this way, the proper feeding signals are generated for the antenna array. Regarding the design of 3-dB coupler, this thesis proposes a new type of forward-wave directional coupler. It provides a promising larger phase difference; therefore, a coupler with compact size can be achieved. In addition, in order to achieve the property of wide band, the phase difference between even and odd mode at a constant value within a broad band is necessary. Therefore, in the design of coupler, the proposed unit cell based on the concept of periodic structure not only achieves the broadband impedance matching for the two modes but also provides larger phase difference. And the phase difference can be kept at a constant value within a wide band. In this way, the broadband forward-wave directional coupler is fulfilled and it possess a competitive size simultaneously. On the other hand, this thesis also proposes a new type of broadband middle network. In addition to using the interdigital capacitor structure, the proposed middle network can provide 45o phase difference between the output ports within the broadband frequency range with the aid of simplified equivalent circuit models. Finally, the proposed forward-wave directional coupler and middle network are integrated appropriately to form the broadband 4 × 4 Butler matrix. The total size is about 0.98 λg × 1.33 λg and the frequency range where the magnitudes of the output ports are within 7 dB ± 1 dB corresponds to the fractional bandwidth of 46%. Compared with other works in related literatures, the proposed Butler matrix can achieve a larger fractional bandwidth while maintaining a compact size.