A compact wideband circularly polarized square slot antenna for universal UHF RFID reader applications is proposed and tested. An L-shaped radiator at lower surface of the substrate is used to feed the proposed antenna. To achieve a broadband circular polarization (CP) and good performance, two rectangular stubs with different sizes are inserted at opposite corners of the square slot at the upper surface of the substrate. A small rectangular slit is used to improve the impedance matching of the proposed antenna. The antenna's measured <10-dB impedance bandwidth and measured 3-dB axial ratio bandwidth are 70.2% (660-1374 MHz) and 45.8% (796-1269 MHz), respectively. The proposed antenna has a dual circular polarization characteristic, wide impedance bandwidth, wide axial ratio, compact size, and maximum measured gain about 3.9 dBi. The total size of the proposed antenna is 120×120×1.6 mm3. Furthermore, the impedance bandwidth and axial ratio bandwidth of the proposed antenna cover the entire UHF RFID band easily. The proposed antenna is suitable for UHF RFID reader applications.
2. Ismail, I. and S. Norzeli, "UHF RFID reader antenna with high gain," International Journal of Electrical and Electronics System Research, Vol. 6, 46-52, 2013.
3. Farswan, A., A. K. Gautam, B. K. Kanaujia, and K. Rambabu, "Design of Koch fractal circularly polarized antenna for handheld UHF RFID reader applications," IEEE Transactions on Antennas and Propagation, Vol. 64, 771-775, 2016.
4. 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.
5. Chen, W.-S. and Y.-C. Huang, "A novel CP antenna for UHF RFID handheld reader," IEEE Antennas and Propagation Magazine, Vol. 55, No. 4, 128-137, 2013.
6. Liu, Q., J. Shen, H. Liu, Y. Wu, M. Su, and Y. Liu, "Low-cost compact circularly polarized directional antenna for universal UHF RFID handheld reader applications," IEEE Antennas and Wireless Propagation Letters, Vol. 14, 1326-1329, 2015.
7. 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.
8. Wang, Z., et al., "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, No. 4, 1066-1073, 2011.
9. Cao, R. and S.-C. Yu, "Wideband compact CPW-fed circularly polarized antenna for universal UHF RFID reader," IEEE Transactions on Antennas and Propagation, Vol. 63, 4148-4151, 2015.
10. 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.
11. Xu, B., S. Zhang, Y. Liu, J. Hu, and S. He, "Compact broadband circularly polarised slot antenna for universal UHF RFID readers," Electronics Letters, Vol. 51, 808-809, 2015.