電磁能隙與天線之整合設計以提升增益及頻寬

Abstract

本論文提出一種新穎的電磁能隙高增益天線架構，其組成包含一印刷微帶天線及一層週期性結構，該結構是由幾條長方型金屬片排列而成。若將這種結構製作在印刷電路板上，與平面微帶天線做整合，則可當作一種部分反射平板。經由這兩層所構成之空氣或介質共振腔，電磁波將在其間做同頻震盪，最後以等相位加成的形式輻射出來，使天線在正上方獲得增益提升。 本天線操作頻率在5GHz左右，可應用於IEEE 802.11a WLAN無線區域網路系統中。我們設定並利用FR4板來實現我們的天線設計，並將這種天線與2x2微帶天線陣列做比較，其面積皆為75mm2，厚度皆為3.2mm，遠比傳統的高增益天線薄得許多。我們共分兩種天線，第一種天線具有空氣共振腔，將其實作出來經過量測後，返回損失頻寬(小於-10dB)有20%以上，3dB及1dB增益頻寬分別達27%及12%，實際增益達到11.6dBi，其等效之槽孔效率約有70%。第二種天線則是以介質為共振腔，可實現在多層印刷電路板上，其厚度可較第一種天線更薄。經實做驗證後，返回損失頻寬有12%，實際增益約9.9dBi，而等效槽孔效率約有55%。上述天線設計之模擬與量測大部分皆有一致的結果，證實本論文所提出之天線設計為一可行的方法。

This thesis presents a novel EBG-based high gain PCB antenna. The antenna consists of a conventional printed patch antenna for the bottom layer and a superstrate with printed periodic strips for the top layer. With proper design on the periodic strips of the top layer known as partial reflective surface (PRS), the region between the two layers may form a resonant cavity that can be air or dielectric loaded. Under the optimized design of the PRS and cavity height, the coherent resonant waves may be radiated from the PRS with an in-phase sense leading to an enhanced gain at the zenith direction. We illustrate the proposed antenna design on cost-effective FR4 PCBs with operational frequency around 5GHz for IEEE 802.11a WLAN applications. The resultant antenna dimensions in this thesis have the area ranges from 70mm2 to 100mm2 and the total height from 2mm to 3.5mm. Two design examples are presented for the cavity filled by air and dielectric, respectively. The first design employs the air cavity and performs promising results including the 10-dB return loss bandwidth of 20% and the peak gain of 11.5 dBi with 3-dB and 1-dB gain bandwidth about 25% and 12%, respectively. Compared to the traditional 2x2 patch array of the same area (75 mm2), the proposed antenna improves the equivalent aperture efficiency from 46 to 70%. The other design using the dielectric loaded cavity may further reduce the antenna height to l0/30. The final antenna area is 70 mm2 with measured performances including the 10-dB return loss bandwidth of 12%, the peak gain of 9.9 dBi, and the aperture efficiency of 55%. The simulation and measurement results show very good agreement in this thesis.