印刷式微帶偶極天線的設計及其於2.4GHz無線區域網路與智慧型天線系統的應用

Abstract

本文中我們使用動差法（Moment Method）對於描述印刷天線的表面電流與滿足邊界條件的積分方程式（Integral Equation）求解，作為解析天線元件的工具。此外，分別選定1.88GHz為智慧型天線的中心頻率，2.45GHz為無限區域網路天線的中心頻率，設計對應的尺寸，模擬分析探討其應用的可行性。印刷式微帶偶極天線在設計上有其頻寬和效率的限制，如果能夠在設計階段加以審慎評估材料與結構的電磁場效應，仍舊能夠獲得良好的特性。 智慧型天線基本上可以視為多個元件天線所組成的天線陣列而且可以切換掃瞄天線的波束場型，所以天線元件的選擇與設計對智慧型天線的功能有重要的影響。此外，基於商業的考量，我們選用廉價的材料(FR4)做電路基板，發展1.88GHz為中心頻率的印刷式微帶偶極天線技術，作為智慧型天線元件設計的材料。其次是多元件天線所組成的天線陣列，因為元件之間會存在耦合現象，造成天線元件的電氣與輻射特性有所失真，進一步影響智慧型天線的功能。所以本文將在後面的章節描述排除此一不利因素的可行方式。另外天線的排列方式與波束掃瞄控制，都有進一步研究的必要，因為較好的排列方式，可以降低耦合現象；最後提出一種可行的方法，測試天線波束掃瞄時，每個天線元件所需的激發訊號強度與相角。 在無線區域網路天線的應用方面，我們將發展中心頻率為2.45GHz的印刷式微帶偶極天線技術，並且加以實作測試天線元件；因為電波傳播的環境在室內，整體而言十分複雜，所以特別加入"變化性"(Diversity)的設計，我們將使用兩支互相垂直的天線元件結合偏壓線路，以確保天線有更好的收發效果，最後，將此天線搭配無線區域網路卡作實地量測。

In this article, a mixed potential integral equation (MPIE) is first derived and then solved by the method of moment (MOM). We use moment method to analyze the printed dipole antenna and to estimate some phenomenon caused by coupling effect. Besides, we develop two similar prototypes of the printed dipole antenna. One has the resonant frequency of 1.88GHz for Smart Antenna System application. The other's resonant frequency is 2.45GHz for Wireless Local Area Network (WLAN) interface card. A Smart Antenna System has several element antennas and it is able to steer its main radiating beam. Thus, to ensure the antenna array working well, the performance of a single antenna element is very important. For cheaper and more available PCB substrate source, the FR4 PCB substrate is chosen to layout the element antenna. Since the Smart antenna system is a multi-element array, the coupling effect existing between each element antenna can affect the antenna impedance and distort the radiation pattern. A proper countermeasure is taken to reduce the coupling effect. The arrangement of each antenna element position also have the influence of the coupling effect .We provide a suitable arrangement to reduce the effect. It is necessary to control the amplitude and the electric phase of each element, then the array can steer its radiation beam. We suggest a possible method to collect the amplitude and the electric phase respective to each scanning angle. In the application of WLAN card, the consideration of the antenna "Diversity" has to be cared because of the complexity of the indoor radio propagation environment. Thus, we develop a switch circuit combined with two identical printed dipoles. This design can improve the transmitting and receiving ability of the antenna. Finally, we realize the antenna for WLAN card and test it on personal computers.