利用一維電磁帶隙結構設計之五頻近地印刷型單極天線

Abstract

隨著筆電無線通訊的發展，運用於筆電的內嵌式五頻天線的需求逐漸增長。在筆電內嵌式天線運用中，天線的寬度被筆電邊緣寬度所限制，所以需要一個近地且狹小的天線設計。然而，當天線非常接近地平面時，因為受到地面反向鏡像電流的影響，天線的效率勢必會減少。為了解決這個問題，我們將電磁能隙結構運用於地面邊緣處，如此可以改善接地面鏡像電流所造成的阻抗匹配、天線增益退化等問題，因此可將天線直接放置於具有高阻抗電磁表面的金屬接地面之上，而不影響原有天線特性。 本論文提出一種一維電磁能隙結構，不同於傳統的電磁帶隙結構，此一維電磁能隙結構採用印刷方式實現並聯LC共振電路，能有效縮小結構體積並有利於簡單製作。根據上述優勢，本論文提出兩種利用一維電磁能隙結構所設計的平面印刷近地天線，此兩種天線皆可用低成本的FR4基板製造。首先提出一個利用一維電磁能隙結構設計之高效率近地偶極天線，該天線與地面之間的距離只有10毫米，整體尺寸10毫米× 153毫米。此天線擁有良好的效能，量測的天線輻射效率在GSM (824 MHz-960 MHz) 頻段中皆有55.6％以上。接著提出一個利用一維電磁能隙結構設計之五頻（GSM850/900/1800/1900/UMTS）近地單極天線。在此我們結合兩種不同的一維電磁能隙結構來提供較寬的電磁能隙結構共振頻寬，如此一來可以將單極天線近地放置且在GSM (824 MHz-960 MHz)頻段中仍維持良好的天線效能。在較高的頻段(1710 MHz-2170 MHz)中，一部份的一維電磁能隙結構能夠產生新的電流路徑並有效的輻射，達成五頻天線的需求。相較於之前的設計，第二個天線擁有較小的尺寸和更大的頻寬。此天線尺寸為10毫米× 63毫米，且在五頻頻段中皆有超過51.5％的輻射效能。鑑於此一維電磁能隙結構擁有縮小的面積和良好的設計的靈活性，因此很適合運用於近地印刷式天線設計，以符合商業天線應用。

The demand for compact internal WWAN (Wireless Wide Area Network) antenna embedded in the laptop computer for penta-band operation has seen growing attention. For laptop computer applications, the width of the antenna is limited to the overall width of the edge of laptop computers, which results in narrow and low profile needs. However, when the antenna is very close to the ground plane, it is bound to reduce the antenna efficiency. To solve this problem, the EBG structure is applied to the ground plane, which behaves as a high impedance surface at the resonance frequency of the EBG structure. Thus, the antenna can placed close to the ground plane while maintaining the antenna performance. The new 1-D EBG structure is proposed in this thesis. Unlike the conventional EBG structures, the proposed 1-D EBG structure utilizes a printed parallel LC circuit, which is more compact and easy to fabricate. According to the advantages shown above, two antenna applications base on the 1-D EBG structure are presented. Both of them are fabricated on low cost FR4 substrate of 0.4 mm. First, a high efficiency ground-proximity dipole antenna using 1-D EBG structure is designed. The distance between antenna and the ground plane is only 10 mm with the overall size of 10 mm × 163 mm. The good radiation properties are obtained with the measured radiation efficiency over 55.6% for GSM (824 MHz-960 MHz) applications. Secondly, the penta-band (GSM850/900/1800/1900/UMTS) ground-proximity printed penta-band monopole antenna is achieved with different 1-D EBG structures combined together. These 1-D EBG structures are combined to provide wider EBG operation bandwidth for GSM (824 MHz-960 MHz), so the monopole antenna and ground plane can be placed in close proximity without affecting the antenna performance in the lower band. In the higher band (1710 MHz-2170 MHz), the 1-D EBG structures can be viewed as efficient radiators, which create additional two resonances and penta-band is thus achieved. Compared to the previous design, the second antenna has a smaller size of 10 mm × 63 mm. The radiation performance is still maintained, which is all above 51.5% in penta-band. Given the design flexibilities and compactness, the antenna designed with 1-D EBG structures is feasible to commercial applications.