以印刷電路板設計之平衡饋入式超寬頻對數週期天線

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。平面化對數週期偶極天線於近年提出，然而其交叉極化隔離度之效能並不理想，且仍多以同軸電纜方式饋入，因製作複雜度及重量增加，而造成使用上的諸多不便。本論文首先成功地將傳統立體結構的平衡不平衡轉換器平面化，且仍保有原先之特性，再將其應用於饋入平面化對數週期偶極天線。另外，吾人利用帶線結構來進行平面化對數週期偶極天線內的能量傳輸，使得交叉極化獲得改善。最後，本論文成功地設計出1.2GHz至3.3GHz之對數週期偶極天線，其正向增益約為1dBi，交叉極化隔離度約20dB，由實際製作電路板所做之量測與模擬結果具有一致性。

Theoretically, the log-periodic dipole antenna is a linearly polarized frequency independent antenna with stable gain patterns. Planar PCB log-periodic dipole antennas were recently proposed, while its performance on cross-polarization isolation is far from being ideal with drawbacks on feeding by a coaxial line, thus increases complexity, weight and difficulties in applications. In this thesis, we firstly planarize a traditional three-dimensional balun successfully, while keeping the original wideband characteristics and therefore suitable for feeding a planar PCB log-periodic dipole antenna. In addition, we apply a stripline structure for the energy transmission within planar PCB log-periodic dipole antennas to supress the cross-polarization. The proposed antenna is successfully simulated, built, and tested with the broadside gain about 0dB to 3dB and the cross-polarization isolation about 20dB in the 1.2~3.3GHz band. A good agreement is achieved between the measured and simulated results.