| Abstract: | 近幾年來，行動通訊網路一直是無線通訊最廣泛的應用，伴隨著網路世界的快速發展，網路已成為應用軟體重要的搭載平台，而由固定寬頻網路發展出無線區域網路，乃是非常重要且關鍵的一步，它能使消費者可連接（access）的網路區域延伸涵蓋任何角落。不需網路線只需透過無線行動裝置即可上網，然而，在這些輕巧的行動裝置中，天線要如何整合至電子產品，則需要設計上的巧思，其中縮小天線的面積尺寸為重要的關鍵技術。
本論文首先探究基本的倒L天線結構的特性，比較原先饋入方式之實部阻抗及虛部阻抗等差異性，提出利用偏移饋入的方式，改善ILA於原基頻（1.8GHz）處的阻抗不匹配問題，但依舊保有ILA天線低剖面、體積小等先天上的優點，此一方式和傳統倒F天線（IFA）的概念完全不同。
接著，從接地面上，引進幾種不同幾何形狀的耦合strip，用來增加上述偏移饋入天線的可應用頻率範圍，以達成雙頻天線的設計，並進一步探究此類天線的特性，與原有天線之反射損耗、實部阻抗及虛部阻抗等進行比較，逐步利用耦合strip的變化來達成雙頻模態的設計目標。
最後，本論文探討了改動傳統倒F天線饋入位置的影響。模擬結果顯示，單純的移動倒F天線饋入位置，可以大幅度的移動其中心頻率，且可維持良好的阻抗匹配，這是相當有趣的現象且有其實用價值。
In recent years, mobile communication network has been the most widely used wireless application, along with the rapid development of the Internet world wide web. Nowadays, network has become an important platform to carry various software application. Furthermore, the development of wireless LAN out of the fixed broadband networks is a very important and critical step, which enables consumers to access network almost from any place. No need for the cable can one access the network via simply the wireless mobile devices. However, with these compact mobile devices the antenna should be
carefully integrated, which requires design ingenuity. Among which, technologies to reduce the antenna size are important ones .
In this thesis the characteristics of the basic inverted L antenna are examined first. As a good comparison of the original inverted L antenna, an offset-fed inverted L antenna is proposed to improve the ILA, for which the impedance mismatch problem at the fundamental frequency (1.8GHz) is resolved, but still retain the low profile, small size and other inherent advantages of the ILA antenna. The offset-fed approach is is entirely different from the design concept of the traditional inverted F antenna (IFA).
Then, associated with the ground surface, the introduction of several coupling strips of different geometrical shape is employed to increase available frequency range for the offset feed antenna. The goal is to achieve the dual-band antenna design. By exploring the characteristics of such antennas, the return loss, the real part of impedance and imaginary impedance of the original antenna were carefully compared, by which the uses of coupled strip are tested with the aim of dual-band design.
Finally, the paper investigate effect of changing the feeding position of the traditional inverted F antenna. Simulation results show that by simply changing the feeding position the resonant frequency can be substantially moved around, while a very good impedance matching is maintained, which is quite interesting and of practial use. |
