Uni-directional Broadband Circularly Polarized Slot Antennas

• Main Authors: Lee, Yong-Ting, 李勇廷
• Other Authors: 許崇宜
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/2jj8mv

碩士 === 國立雲林科技大學 === 電機工程系 === 102 === The antenna proposed in this study was designed starting from a very primitive structure. The specifications were achieved through changing the structures step by step, systematically analyzing the performance data, and then summing up the design rules. First, the first circularly polarized (CP) operating band was obtained by making the ground plane asymmetric; next, a second CP band was produced when a pair of bent slits were embedded in the ground; third, the deteriorated axial ratio around the middle of the operating band was lowered by narrowing the front portion of the feedline, making that feedline a stepped-impedance structure; and finally, the axial ratios around the upper and lower edge frequencies of the CP band were improved after a thin slot was added to extend the upper-right slit. The achieved CP bandwidth was as large as 61%. The design rules developed for the L-band CP antenna were also applied to successfully design CP antennas at other frequencies, including the X-band and the band required by DTV applications. In order to enhance the antenna gain, an open cavity (with four side walls) was placed below the already designed bidirectional CP antenna, an action leading to unidirectional radiation but, unfortunately, degraded CP performance. By appropriately adding metal patches on the open surface of the cavity, the CP performance achieved by the cavity-less bidirectional CP antenna alone was recovered. As compared with the bidirectional CP antenna, not only was the backward radiation of the unidirectional CP antenna suppressed by more than 20 dB, but the peak antenna gain was raised by more than 3 dB as well.