利用頻率選擇面設計雙頻可切換場型之波束天線

Abstract

隨著無線通訊的發展，有限的頻寬不斷地被數量眾多的無線通訊設備使用及分割，因此，如何有效地使用通訊頻寬並將其他干擾減至最低將是目前無線通訊設備在設計上一個重要的課題。可變換場型並集中能量的智慧型天線是一個解決此問題的好選擇。 在本論文中，我們提出一種新型的雙頻的智慧型天線。利用可改變特性的頻率選擇平面當做主要的反射面架構，並配合直角反射面天線的運作原理及電路開關的狀態，設計出三個雙頻的智慧型天線，可使用於2.45 GHz 及 5.25 GHz 的頻段中。藉由各面上開關的組合，此天線可以包括許多不同的場型。 第一個天線的反射面只能運作在某一個頻率，因此，對於雙頻的智慧型天線來說，雙層的反射面設計是必需的，同時也增加了使用體積；而第二個天線的設計中，將單一反射面設計成可操作在雙頻，如此可減少天線體積，並可減少開關的使用數量；在第三個天線中，一種更為簡單的雙頻反射面架構被提出，在每一邊僅用一個長方形的環形共振器，如此可更加簡化天線的複雜度及開關的設計。而在實際的應用當中，全向性場型跟單一方向性場型的切換是最重要的，因此在以上的設計中，我們主要專注研究在此兩種場型的特性與切換。

With the development of the wireless communication, more and more devices share the limited bandwidth for communication. Therefore, how to reduce the interference from other devices and environment and use the limited bandwidth efficiently is one of the important subjects. A smart antenna which can change radiation patterns and focus the patterns is a good candidate to solve those problems. In this thesis, a novel dual-band smart antenna is developed. By the switching frequency selective surface, the principle of a right angle corner reflector antenna, and the operation of switches, three dual-band pattern reconfigurable antennas are investigated. The operating frequencies in our design are 2.45 GHz and 5.25 GHz. Through combinations of switches on reflecting walls, multiple radiation patterns can be obtained. Each reflecting wall of the first proposed pattern reconfigurable antenna operates only at one frequency; therefore, Two-layer reflecting walls are needed here. However, the volume of the completed antenna is about one-wavelength of 2.45 GHz square due to the principle of the corner reflector antenna. In the second proposed antenna, a reflecting wall can operate at two frequencies. As a result, the size of the antenna can be reduced, and the amount of switches can be decreased too. Finally, a dual-band pattern reconfigurable antenna with a simpler structure such as a rectangular loop is developed without the damages to the original properties belonging to the second antenna. Since omni-directional and directional patterns are the most important in application, we mostly focus on those two patterns in our design.