無線區域網路的波束切換天線系統之模擬與實現

Simulation and Implementation of a Switched Beam Antenna System for WLAN

鍾孟霖(Meng-Lin Chung)

指導教授 ： 李學智

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.01700

摘要

摘要
為了改善無線區域網路的通訊品質並降低多路徑衰減的效應，我們實際製作了一個應用在5 GHz 頻段的四波束切換波束天線系統。切換波束天線是智慧型天線的一種，其結構包含了天線陣列和一個由巴特勒矩陣構成的饋入網路，可以產生數個正交的波束來涵蓋整個通訊區域，其產生的波束具有高方向性、高增益，藉此來提高系統信號干擾比，並降低多路徑衰減的效應。
因為使用在5 GHz 的頻段，我們使用Rogers RO4003( = 3.38 h = 52 mil)的板材來製作天線陣列和巴特勒矩陣。在天線部分，我們使用垂直極化的雙面印刷偶極天線使得每個天線單元都是全向性的天線；在饋入網路的部分，我們使用4x4的巴特勒矩陣來產生四個正交的波束以涵蓋120度的扇形區域。我們對裝有切換波束天線的系統進行實際的通道量測並加以分析，我們也提出一個簡單的室內多路徑通道響應的模型。這個模型可以隨機產生大量的室內通道響應，方便在電腦上做進一步的模擬。從量測和模擬結果來看，如果將切換波束天線系統應用在室內環境的無線區域網路中，將導致接收信號的延遲擴散降低，這個現象會使頻率響應的變化較為平緩，讓信號受到嚴重衰落的機會降低。但在直接波受到嚴重阻擋的情況下，比起傳統的全向性天線，效能的改善並不明顯。

關鍵字

智慧型天線 ； 延遲擴散 ； 切換波束 ； 巴特勒矩陣

並列摘要

Abstract
In WLAN, the main causes of degradation of quality of communication are multipath fading and interference. To overcome these problems, we implement a 4-beam switched beam antenna system operating in the 5 GHz frequency band. Switched beam antenna is one type of smart antennas. A switched beam antenna consists of an antenna array and a feeding network based on the Butler matrix, which allows producing 2n orthogonal narrow beams to cover the communication range. Each of these beams leads to high directivity and high power gain. Thus, the SNR of the system is enhanced, and the multipath fading is suppressed.
Because of operating in the 5 GHz band, we use RO4003 board ( = 3.38, = 0.002, thickness = 1.32 mm) for fabricating the antenna array and the Butler matrix. Due to its omni-directional property, we use a twin-line dipole antenna as the antenna element; we use a 4×4 Butler matrix circuit as the feeding network to form four orthogonal beams. These beams can cover a communication range of 120o angular spread. Equipped with the designed switched beam antenna, experimental measurements were carried out to examine its performance. Besides, a simple model of the indoor multipath propagation is presented. By using this model, a large number of indoor channel responses are generated for computer simulations. From the measurement results and the simulation results, switched beam antenna can reduce delay spread in WLAN, and lead to a flatter frequency response. That means the deep fading is in lower probability. However, if the direct wave is wholly or mostly blocked, switched beam technique cannot provide a better performance than omni-directional antenna, even worse.

並列關鍵字

switched beam ； delay spread ； smart antenna ； butler matrix

參考文獻

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