無線區域網路之雙頻濾波器與天線設計

Design of dual-band filters and antennas for WLAN applications

蔡尚儒(Shang-ju Tsai)

指導教授 ： 丘增杰

國立中央大學/資訊電機學院/電機工程學系/碩士(2007年)

摘要

在本論文中將介紹涵蓋無線區域網路頻帶(ISM 2.4-2.5GHz和UNII 5.15-5.85GHz)的雙頻濾波器與天線。在文獻上，兩頻帶頻寬差異很大的濾波器設計存在三個主要的問題：兩個頻帶插入損耗(insertion loss, )通常過大(超過3dB)、阻抗匹配普遍不佳(僅-10dB左右)、與選擇(selectivity)的不佳。本文中將針對以上問題提出兩種新的改善方法。利用不對稱饋入3條耦合線的寬頻特性，結合雙重行為共振器(Dual-Behavior Resonator, DBR)來控制兩個頻帶的中心頻率與不同的頻寬，再加入缺陷接地結構(Defected Ground Structure, DGS)而使匹配改善。文中一共提出二階的不對稱分枝與指叉分枝濾波器兩種結構，使用的板材為厚度1.6mm的FR4基板。不對稱分枝的結構兩個頻帶的插入損耗值和反射損耗值在2.45GHz為-1.42dB及-13.8B，在5.5GHz則分別為-1.7dB及-10dB，指叉分枝的結構則改善了不對稱分枝結構中的選擇度和匹配，在兩個頻帶也達到了-1.6dB與-1.99dB的插入損耗，-15.13dB與-15.7dB的反射損耗。簡而言之，在不對稱分枝的結構中達成了好的插入損耗，指叉分枝的結構則在總面積與不對稱分枝幾乎相同下達成兩個頻帶良好的選擇度與匹配。
天線設計的特點在於體積微型化，實際大小僅6x6x3.2 mm³，但仍能提供最高超過0 dBi的輻射增益。利用平面式倒F天線(Planar Inverted-F Antenna, PIFA) 為基本架構，包含一個特別設計的饋入網路以及兩個三維曲折電流路徑，由此達成雙頻操作的目的並縮小天線體積，獨特的饋入網路配合不同的接地電感元件，可以只調整5GHz頻段的操作點而不會影響到2.4 GHz，提高了天線實際應用的便利性，若把接地電感元件捨去而直接接地，則天線只操作在2.4GHz頻段，可作為藍芽天線使用。

關鍵字

缺陷接地結構 ； 平面式倒F天線 ； 雙重行為共振器 ； 雙頻天線 ； 雙頻濾波器

並列摘要

Dual-band filters and antennas designed for wireless Lan (ISM 2.4-2.5GHz and UNII 5.15-5.85 GHz) applications will be presented in this thesis. Generally, there are three main problems for filters with relatively large ratio of passband center frequencies: high insertion loss (more than 3dB), high return loss (less than -10dB) and bad selectivity. Two new methods are proposed to improve the problems based on the following structure. This structure is basically composed of three parts. Firstly, the coupler with three asymmetrical short-circuit lines is constructed for wide band filter response. Secondly, Dual-Behavior Resonator (DBR) is used to control passband center frequencies and different bandwidths. Finally, the Defected Ground Structure (DGS) is introduced for impedance matching enhancement. The second-order filter with asymmetrical short stubs and fork branches based on previous structures are also proposed to provide good selectivity. Good results are achieved even when high-loss FR4 substrates are used. The measured insertion loss and return loss in asymmetrical short stub structure are -1.42dB and -13.8dB at 2.45GHz, and -1.7dB and -10dB at 5.5GHz. The fork branch structure further improves the selectivity and impedance matching of the previous structure. The practical measured results are -1.6dB and -15.13dB at 2.45GHz, and -1.99dB and -15.7dB at 5.5GHz.
A technique for compact antenna design is also proposed in the thesis. Based on the structure as Planar Inverted-F Antenna (PIFA), unique matching network, and two resonators rolling in 3D, extremely compact size, which is 6x6x3.2 mm³ for FR4 substrate, is obtained. High frequency band can be adjusted freely by tuning the value of inductor. The peak gain of the proposed antenna is more than 0dBi. In Bluetooth application, the antennas can also be used without the inductor.

並列關鍵字

dual-band antenna ； DBR ； DGS ； PIFA ； dual-band fulter

參考文獻

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