以T型狹縫結構提升微帶饋入式雙倒F天線之隔離度設計

Abstract

本論文提出一個可應用於具diversity功能的無線通訊系統的T型狹縫隔離結構設計。完整的電路由兩個微帶線饋入的PIFA天線、T型狹縫和微帶線-狹縫轉接結構所組成。為了減少PIFA天線的空間尺寸，因此將PIFA天線開路端的傳輸線繞成螺旋形，而且能使得天線更加緊密可實際應用在無線手持裝置上。因為兩相鄰PIFA天線間強烈的互耦合效應造成互相干擾，因此需要設計T型狹縫的隔離結構去降低互耦合效應，而且微帶線-狹縫轉接結構在PIFA天線和T型狹縫之間提供能量的耦合。最後電磁模擬與量測結果證明T型狹縫結構提昇隔離度的同時，亦不影響原本PIFA天線的阻抗匹配。再者如原先預期的，因為在接地面上的T型狹縫結構改變了電流分佈的情況，輻射場形和峰值增益也稍有變動。理論與實驗量測的一致性對此論文的設計方法提出最佳的佐證。

A novel isolation structure based on a T-shaped slotline junction for use with diversity-capable wireless communication systems is presented. The entire circuit consists of two microstrip-fed PIFAs, a T-shaped slotline junction, and two microstrip-to-slotline transitions. For reducing the dimensions of PIFA, the typically straight open-ended transmission line is turned into a spiral such that it is more compact and practical for the wireless mobile devices. Because the intense correlation due to mutual coupling between two nearby PIFAs, we design a T-shaped slotline junction-based isolation enhancement structure to suppress the coupling effect. Moreover, the microstrip-to-slotline transitions provide the coupling of energy between PIFAs and T-shaped slotline structure. Finally, the simulated and measured results prove that T-shaped slotline structure increases the isolation without affecting the impedance matching of PIFAs. Furthermore, as expected, the radiation patterns and peak gain vary slightly as the current distribution is changed by the T-shaped slotline structure on the ground plane. Good agreements observed between theoretical and measured results confirm the validity of the proposed design in this thesis.