Compact broadband circularly polarized UHF RFID tag antenna for metallic mounting

ABSTRACT

We report a broadband ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna of compact size mounted on a metallic object in a near field communication (NFC) RFID system. One half of the square radiation patch has a semi-annular strip feedline embedded inside a semicircle-shaped slot to improve the antenna bandwidth and gain, and the other half of the radiation patch has an L-shaped slot and a shorting pin to increase the circular polarization (CP) bandwidth and reduce the antenna size. The resonant input impedance of the tag antenna can be tuned easily by varying the length of the semi-annular feedline, and the gap between the feedline and the etched semicircular slot. The proposed tag antenna has a wide measured impedance bandwidth (−10-dB |Γ|) covering the whole operating frequency range of 181 MHz (from 790 to 971 MHz) for a UHF RFID system. The measured 3-dB axis ratio (AR) bandwidth is 43 MHz (from 895 to 938 MHz), which is much larger than those of the CP tag antennas reported in the literature for metallic objects. Further experiment has shown that the proposed tag antenna can provide a stable reading range when mounted on metal plates of various sizes.

KEYWORDS:

• Radio frequency identification
• tag antenna
• circular polarization
• broadband
• metallic object

Acknowledgment

The authors are grateful to Dr. Julian Evans for helpful discussions. This work was partially supported by the National Key Research and Development Program of China (No. 2018YFC1407503) and National Natural Science Foundation of China (No. 11621101).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The authors are grateful to Dr. Julian Evans for helpful discussions. This work was partially supported by the National Key Research and Development Program of China [grant number 2018YFC1407503] and National Natural Science Foundation of China [grant number 11621101].

Notes on contributors

Hui Liu

Hui Liu was born in Zhumadian, China. He received the M.S. degree in electromagnetic field and microwave technology from South China Normal University in 2013, the Ph.D. degree in Microelectronics and Solid State Electronics from Centre for Optical and Electromagnetic Research, Academy of Advanced Optoelectronics, South China Normal University in 2018. He is currently a Post-Doctoral Researcher with the Center for Optical and Electromagnetic Research, Zhejiang University. His research interests include antenna, RF circuit and microwave component.

Cheng Liu

Cheng Liu was born in Xinyang, Henan, China in 1992. He received the B.S. degree in electronic and information engineering from Tianjin University of Technology, Tianjin, China, in 2014 and the M.E. degree in optics from Centre for Optical and Electromagnetic Research, Academy of Advanced Optoelectronics, South China Normal University, Guangzhou, Guangdong, China, in 2017. He joined in the Dongguan R&D Center, Huaqin Communication Technology Co., Ltd. in 2017. He current research interests include antenna and RF circuit.

Qingchong Liu

Qingchong Liu was born in Jiangxi, China. He received the B.S. degree in physics from Nanjing Normal University, Nanjing, China, in 2012. He is currently pursing the Ph.D. degree with the Centre for Optical and Electromagnetic Research, Zhejiang University, Hangzhou, China. His current research interets include antenna design, metamaterial, and metasurface.

Yuefeng Lu

Yuefeng Lu is an undergraduate major in physics in The College of Physics and Electronic Information Engineering, Zhejiang Normal University, Zhejiang, China. Currently his interests include mathematical modeling and analysis of antenna and RF systems.

Sailing He

Sailing He received the Licentiate of Technology and the Ph.D. degree in electromagnetic theory from the Royal Institute of Technology (KTH), Stockholm, Sweden, in 1991 and 1992, respectively. Since then he has worked in Royal Institute of Technology as an Assistant Professor, an Associate Professor, and a Full Professor. He is also with Zhejiang University as a distinguished professor of a special program, as well as a joint research center between KTH and ZJU. His current research interests include electromagnetic metamaterials, optoelectronics, microwave photonics, and biomedical applications. He has first-authored one monograph and authored/coauthored about 400 papers in refereed international journals. He has given many invited/plenary talks in international conferences, and has served in the leadership for many international conferences. Prof. He is a Fellow of IEEE, Optical Society of America (OSA), the International Society for Optical Engineering (SPIE) and the EM Academy.