平面式雙頻雙圓極化非對稱十字形偶極天線

Abstract

本論文探討金屬和槽孔兩種型態的十字形偶極圓極化天線等效電路模型，並以此為基礎提出平面式雙頻雙圓極化非對稱十字形天線之新設計。此天線設計可藉由調整偶極長度，可使其同時操作在雙頻；而輻射圓極化波的正上方極化情形，則可由天線架構上偶極所擺放的相對位置來進行設計。 在本論文中所設計與驗證的雙頻雙圓極化天線，其高低頻的極化方向皆設計為相反極化(即一左圓極化，一右圓極化)。但金屬與槽孔兩種平面式雙頻雙圓極化非對稱十字形天線，其兩操作頻帶皆可任意調整其正上方之圓極化方向，並不限定須相反；此外，在本論文中金屬型態之平面式雙頻雙圓極化非對稱十字形天線設計，其高低頻頻率比(frequency ratio)可達3.3:1。 為了實際應用考量，吾人亦加上了反射面進行設計，使輻射場型由雙向輻射變為單向輻射，減少實際應用時天線與環境之間的可能干擾，同時天線正上方輻射增益也因此而增加。這些特性使得本論文所提出之設計更加適合應用於現今之無線系統上，如全球定位系統(Global Position System, GPS)或點對點通訊。

Design of dual-frequency dual-sense circularly polarized asymmetric crossed-dipole antennas is proposed in this thesis. The antenna design of conductive dipole and slot dipole are inspired by the developed two different circuit models, which are in shunt and series forms, respectively. By selecting the proper lengths of the arms, the proposed antenna may operate in two different frequency bands. Furthermore, by arranging the positions of the arms, the senses of the circular polarized (CP) radiation can be adjusted arbitrarily in the two bands. In this thesis, the proposed dual-band dual-sense CP antennas are designed and fabricated. The experimental results only show the case of the CP antennas in the same senses (both LHCP or RHCP). On the dual-band performances, the frequency ratio of the proposed antenna of conductive crossed-dipole achieves 3.3:1 in this thesis. Lastly, for practice applications, such as GPS or point-to-point wireless communication, a planar reflector is added the proposed antennas to improve the radiation performance in terms of the enhanced zenith gain and unidirectional patterns.