This research proposes a single-fed broadband circularly polarized (CP) bidirectional antenna operable in 840–960 MHz frequency band for readers of universal UHF-RFID applications. The proposed antenna is comprised of upper-layer conductor, lower-layer conductor, and wall patches. The upper-layer conductor consists of two diagonally aligned rectangular copper plates with a feeding gap at the center, and the lower-layer conductor is of two diagonally adjoined rectangular plates. The upper- and lower-layer conductors are adjoined with the wall patches. The diagonal alignment technique of the upper- and lower-layer plates was used to realize circular polarization and improve 3-dB axial ratio (AR) bandwidth. The double layers were deployed to improve impedance bandwidth (|S₁₁| < −10 dB) and achieve bidirectional radiation pattern. The simulated impedance bandwidth and 3-dB AR bandwidth were 772.19–1014.6 MHz (27.13%) and 675–1000 MHz (38.80%), and the corresponding measured results were 759–1011 MHz (28.47%) and 648–1110 MHz (52.55%). The simulated LHCP/RHCP half-power beamwidth (HPBW), 3-dB AR beamwidth, and gain were 56° – 90°/54° – 92°, 60° – 104°, and 4.94 – 5.89 dBic, while the corresponding measured results were 52° – 98°/62° – 97°, 96° – 126°, and 4.28 – 5.72 dBic. As a result, the single-fed broadband CP bidirectional antenna is applicable to universal UHF-RFID readers. Besides, the novelty of this research lies in the use of diagonal alignment of conducting plates to achieve circular polarization and wider AR bandwidth.

中文翻译：

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单馈宽带CP双向天线，带有双层对角对准板，适用于通用UHF-RFID应用

这项研究为通用UHF-RFID应用的阅读器提出了一种单馈宽带圆极化（CP）双向天线，可在840-960 MHz频带内工作。拟议的天线由上层导体，下层导体和墙贴组成。上层导体由两个对角排列的矩形铜板组成，中间有一个馈送间隙，而下层导体则由两个对角邻接的矩形板组成。上层和下层导体与壁片相连。上下层板的对角线对齐技术用于实现圆极化并提高3-dB轴向比率（AR）带宽。部署双层以改善阻抗带宽（| S ₁₁| <-10 dB）并实现双向辐射方向图。模拟的阻抗带宽和3-dB AR带宽分别为772.19–1014.6 MHz（27.13％）和675–1000 MHz（38.80％），相应的测量结果为759–1011 MHz（28.47％）和648-1110 MHz（52.55） ％）。模拟的LHCP / RHCP半功率波束宽度（HPBW），3 dB AR波束宽度和增益分别为56°– 90°/ 54°– 92°，60°– 104°和4.94 – 5.89 dBic，而相应的测量值结果为52°– 98°/ 62°– 97°，96°– 126°和4.28 – 5.72 dBic。因此，单馈宽带CP双向天线适用于通用UHF-RFID读取器。此外，这项研究的新颖性在于使用导电板的对角线对准来实现圆极化和更宽的AR带宽。