覆背式共面波導饋入平面對數週期天線之研製

Abstract

對數週期偶極天線在理論上是屬於一種非頻變且具有穩定增益的線性極化天線。本論文針對平面化對數週期偶極天線提出改良的設計結構並加以論述。平面化對數週期偶極天線於近年提出，然而其交差極化隔離度之效能並不理想。本論文提出利用帶線型態之饋入結構將能量傳輸到天線，藉由接地面屏蔽之效果使得其交差極化隔離度可以明顯地獲得改善。另外，為了實現完全平面化的饋入結構，吾人更進一步使用覆背式共面波導傳輸線結構來轉接至此平面化對數週期偶極天線。本論文成功設計出1GHz至5GHz之對數週期偶極天線，其側向增益約為1dBi，交差極化隔離度約20dB，由實際製作電路板所做之量測與模擬結果具有一致性。最後，我們並利用反射板來達成單一方向輻射場型之目標，其側向之平均增益增加至4dBi。

Theoretically, the log-periodic dipole antenna is a linearly polarized frequency independent antenna type with stable gain patterns. In this thesis, we investigate and propose a new design of the planar log-periodic dipole antenna. The planar PCB log-periodic dipole antenna was proposed recently, however the cross-polarization isolation performance is not sufficient. In this study, we conquer this problem by using a stripline type feeding structure with shielding ground plane to improve the cross polarization isolation performance. In addition, we extend the design with a conductor-backed coplanar waveguide transmission line to realize the fully planar feeding structure. The proposed antenna is successfully simulated, built, and tested with the broadside gain about 1dBi and cross polarization isolation about 20dB around broadside in the 1~5GHz band. A good agreement is achieved between the measured performances and the simulated results. At last, we employ a slanted reflector to improve the antenna gain performance up to 4dBi with a preferred unidirectional pattern.