本論文研製一共平面圓極化開槽環形單極天線(coplanar circular polarization slotted annular ring monopole antenna)，有別於常見的平面式圓極化天線，如微帶貼片天線(microstrip patch antenna)、槽孔天線(slot antenna)等，其阻抗頻寬(impedance bandwidth)受到天線結構上的限制而為單一頻段且窄頻特性，無法滿足於多頻段整合之無線通訊產品，有鑑於此，在設計上採用具有寬頻特性之單極天線作為首選。天線結構主要由共平面波導(coplanar waveguide，CPW)傳輸線與環狀開槽金屬環所組成，在圓極化頻段設計上利用環狀開槽金屬環上之環形電流路徑以及接地金屬面上非對稱電流產生之輻射，使原為線性極化(linear polarization)的單極天線具有圓極化特性。天線之10dB折返損耗(return loss)操作頻帶由1.5GHz至3GHz，阻抗頻寬約為66.7%，頻帶內涵蓋了GPS、DCS、PCS、PHS、WCDMA、Bluetooth等常用無線通訊頻段，此天線在GPS頻段下為圓極化、其餘操作頻段保有線性極化特性。此外，天線設計上可利用在接地金屬面延伸出長度約為四分之一導波波長(guide wavelength)的倒L形金屬片，藉由此金屬片增加一額外的電流路徑，改善輻射電場分量之振幅差距，設計出第二個圓極化頻段，使天線具有雙頻段圓極化特性。The design and analysis of a planar, circularly polarized, and slotted annular ring monopole antenna are presented. In contrast to traditional planar circularly polarized patch antenna and slot antennas poised for narrowband applications, the presented antenna is of relatively broad operating bandwidth by exploiting the broadband monopole antenna structure. Specifically, the proposed antenna consists of a coplanar-waveguide (CPW) fed annular ring monopole with a gap near the CPW feed. The circular polarization is essentially realized with the circular current flow on the slotted annular ring and the unsymmetrical surface current on the ground plane. Furthermore, additional circularly polarized operation bands can be realized with the incorporation of stretched-out quarter-wavelength inverted-L sleeves on the ground plane edges. In this thesis, a single-band and a dual-band CPW-fed slotted annular ring monopole antennas are demonstrated. The single-band antenna features circular polarization at the L1 band, while the dual-band antenna is of circular polarization at the L1 band, as well as at 1.96 GHz. In addition, both antennas is of operating frequencies ranging from 1.5 GHz to 3 GHz for the GPS, DCS, PHS, WCDMA, and Bluetooth applications.
