For the first time, a planar and low-profile magnetic loop antenna is proposed for designing an omnidirectional metal-mountable radio frequency identification (RFID) tag antenna. The proposed tag antenna, which consists of an annular slot exciter, a shorted patch, two shorting stubs, and four notches, can be easily made on one side of a flexible polyimide film. It has a dimension of 38 mm $\times \,\, 38$ mm $\times \,\, 1.6$ mm ( $0.116\lambda \times 0.116\lambda \times 0.0049\lambda$ ). The tag antenna is able to generate stable omnidirectional read patterns when placed on metal. The notches are not only employed for bringing down the tag’s resonant frequency to the ultrahigh (UHF) RFID band, but they can also be used for effectively reducing the gain fluctuation in the azimuth plane. Good maximum power transmission of ~90% is attainable. Measurements are conducted with reference to a transmitting power of 4W EIRP, and it has been shown that the proposed tag antenna is able to generate omnidirectional radiation patterns with a stable read distance of 5.29–5.65 m on metal in all directions in the azimuth plane. The tag’s resonant frequency is also very stable with a maximum fluctuation of only 0.22%.

中文翻译：

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用于全向金属上 UHF 标签设计的紧凑型磁环天线

首次提出了一种平面低剖面磁环天线，用于设计全向金属安装射频识别 (RFID) 标签天线。所提出的标签天线由一个环形缝隙激励器、一个短路贴片、两个短路短截线和四个凹口组成，可以很容易地在柔性聚酰亚胺薄膜的一侧制作。它的尺寸为 38 毫米 $\times \,\, 38$ 毫米 $\times \,\, 1.6$ 毫米 （ $0.116\lambda\times 0.116\lambda\times 0.0049\lambda$ ）。标签天线放置在金属上时能够产生稳定的全向读取模式。凹口不仅用于将标签的谐振频率降低到超高 (UHF) RFID 频段，还可以用于有效降低方位平面的增益波动。可实现约 90% 的良好最大功率传输。测量是参考 4W EIRP 的发射功率进行的，结果表明，所提出的标签天线能够在金属上在方位平面的所有方向上产生 5.29-5.65 m 的稳定读取距离的全向辐射图。标签的谐振频率也非常稳定，最大波动仅为 0.22%。