A compact wideband circularly polarized (CP) square slot antenna for universal ultra high frequency (UHF) RF identification (RFID) handheld reader applications is proposed, fabricated, and tested. The antenna is coplanar waveguide (CPW) fed by an inverted Z-shaped feeding line. By inserting four stubs in diagonal directions and two inverted T-shaped strips inside the square slot, broadband CP operation, wide axial ratio bandwidth, and good impedance matching are achieved. The measured < -10 dB impedance bandwidth is from 706 MHz to 1007 MHz (301 MHz, 35.1%). The measured 3-dB axial ratio (AR) is 427 MHz (745-1172 MHz, 44.5%). The maximum measured gain of the proposed antenna is 4.8 dBi. The proposed antenna has wide impedance bandwidth, wide axial ratio bandwidth, and small size. The dimensions of the antenna are only 120×120×1.6 mm3. The impedance bandwidth and AR bandwidth performances of the proposed antenna can easily cover the UHF RFID band as whole.
2. Wu, T., H. Su, L. Gan, H. Chen, J. Huang, and H. Zhang, "A compact and broadband microstrip stacked patch antenna with circular polarization for 2.45-GHz mobile RFID reader," IEEE Antennas and Wireless Propagation Letters, Vol. 12, 623-626, 2013.
3. Pan, C.-Y., C.-C. Su, G.-J. Wu, and J.-Y. Jan, "Circularly polarized monopole antenna using shortcircuited sleeve strip for UHF RFID readerCircularly polarized monopole antenna using shortcircuited sleeve strip for UHF RFID reader," Microwave and Optical Technology Letters, Vol. 56, 957-961, 2014.
4. Liu, X., Y. Liu, and M. M. Tentzeris, "A novel circularly polarized antenna with coin-shaped patches and a ring-shaped strip for worldwide UHF RFID applications," IEEE Antennas and Wireless Propagation Letters, Vol. 14, 707-710, 2015.
5. Chen, Z. N., X. Qing, and H. L. Chung, "A universal UHF RFID reader antenna," IEEE Transactions on Microwave Theory and Techniques, Vol. 57, 1275-1282, 2009.
6. Li, J., Y. Huang, Y. Wang, Q. Zhang, G. Wen, and H. Zhang, "Wideband high gain circularly polarized UHF RFID reader antenna," 2016 IEEE Conference on Antenna Measurements & Applications (CAMA), 1-3, 2016.
7. Wu, K., G. Wen, Y. Huang, J. Li, and H. Sun, "Universal UHF RFID reader antenna based on the ferrimagnetic slab with tunable operating frequency," 2014 IEEE International Conference on Communication Problem-Solving (ICCP), 60-63, 2014.
8. Fu, S., C. Li, S. Fang, and Z.Wang, "Low-cost single-fed circularly polarized stacked patch antenna for UHF RFID reader applications," 016 Progress In Electromagnetic Research Symposium (PIERS), 2031-2034, Shanghai, China, Aug. 8–11, 2016.
9. Sim, C., Y. Hsu, and G. Yang, "Slits loaded circularly polarized universal UHF RFID reader antenna," IEEE Antennas and Wireless Propagation Letters, Vol. 14, 827-830, 2015.
10. Wang, Z., S. Fang, S. Fu, and S. Jia, "Single-fed broadband circularly polarized stacked patch antenna with horizontally meandered strip for universal UHF RFID applications," IEEE Transactions on Microwave Theory and Techniques, Vol. 59, 1066-1073, 2011.
11. Wang, C. and C. Chen, "CPW-fed stair-shaped slot antennas with circular polarization," IEEE Transactions on Antennas and Propagation, Vol. 57, 2483-2486, 2009.
12. Shen, Y., C. L. Law, and Z. Shen, "A CPW-fed circularly polarized antenna for lower ultrawideband applications," Microwave and Optical Technology Letters, Vol. 51, 2365-2369, 2009.
13. Lu, J.-H. and S.-F. Wang, "Planar broadband circularly polarized antenna with square slot for UHF RFID reader," IEEE Transactions on Antennas and Propagation, Vol. 61, 45-53, 2013.
14. Pakkathillam, J. K., M. Kanagasabai, and M. G. N. Alsath, "Compact multiservice UHF RFID reader antenna for near-field and far-field operations," IEEE Antennas and Wireless Propagation Letters, Vol. 16, 149-152, 2017.
15. Abdelrahim, W. and Q. Feng, "Wideband circularly polarized slot antenna for universal UHF RFID reader," 2018 International Conference on Microwave and Millimeter Wave Technology (ICMMT), 1-3, Chengdu, China, 2018.