The primary objective of this paper is to design a high-gain, circularly polarized patch antenna suitable for Radio Frequency Identication (RFID) readers that operate in the FCC and ETSI bands (865-928 MHz). These designs will be used in a healthcare application to provide tag identification for thousands of medicines stored on shelves inside a pharmaceutical warehouse. Consequently, it is important that these antennas provide sucient electromagnetic coverage and polarization diversity in order to boost tag readability and minimize item identification errors. The proposed RFID reader antenna design begins with a single patch with truncated corners on air substrate in order to help us understand the effect of various geometrical parameters on critical antenna figures of merit. A stub is introduced in order to improve the impedance matching characteristics of the antenna. The wideband characteristic of the design, for both impedance matching and axial ratio, is achieved by a second truncated-corner patch antenna positioned on top of the first one. An optimum design is achieved by changing the heights of the main and parasitic patches, the size of the truncated corners, and the probe position. The final antenna designs are verified by comparing measurement and simulation results.
2. Polycarpou, A. C., A. Dimitriou, A. Bletsas, P. C. Polycarpou, L. Papaloizou, G. Gregoriou, and J. N. Sahalos, "On the design, installation, and evaluation of a radio-frequency identi¯cation system for healthcare applications," IEEE Antennas Propag. Magazine, Vol. 54, No. 4, 255-271, 2012.
3. Sharma, P. C. and K. C. Gupta, "Analysis and optimized design of single feed circularly polarized microstrip antennas," IEEE Trans. Antennas Propag., Vol. 31, No. 6, 949-955, 1983.
4. Sim, C.-Y.-D. and C-.J. Chi, "A slot loaded circularly polarized patch antenna for UHF RFID reader," IEEE Trans. Antennas Propag., Vol. 60, No. 10, 4516-4521, 2012.
5. Li, J., Y. Huang, Y. Wang, Q. Zhang, G. Wen, and H. Zhang, "Widebang high gain circularly polarized UHF RFID reader antenna," 2016 IEEE Conference on Antenna Measurements and Applications (CAMA), 1-3, 2016.
6. Chen, Z. N., X. Qing, and H. L. Chung, "A universal UHF RFID reader antenna," IEEE Trans. Microw. Theory Techn., Vol. 57, No. 5, 1275-1282, 2009.
7. Sim, C.-Y.-D., Y.-W. Hsu, and G. Yang, "Slits loaded circularly polarized universal UHF RFID reader antenna," IEEE Antennas Wireless Propag. Lett., Vol. 14, 827-830, 2015.
8. Nasimuddin, Z., N. Chen, and X. M. Qing, "Asymmetric-circular shaped slotted microstrip antennas for circular polarization and RFID applications," IEEE Trans. Antennas Propag., Vol. 58, No. 12, 3821-3828, 2010.
9. Lee, J. M., N. S. Kim, and C. S. Pyo, "A circular polarized metallic patch antenna for RFID reader," Proc. Asia-Paci¯c Commun. Conf., 116-118, Perth, WA, 2005.
10. Kovitz, J. and Y. Rahmat-Samii, "Using thick substrate and capacitive probe compensation to enhance the bandwidth of traditional CP patch antennas," IEEE Trans. Antennas Propag., Vol. 62, No. 10, 4970-4979, 2014.
11. Wu, J., X. Ren, Z. Wank, and Y. Yin, "Broadband polarized antenna with L-shaped strip feeding and shorting-pin loading," IEEE Antennas Wireless Propag. Lett., Vol. 13, No. 9, 1733-1736, 2014.
12. 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 application," IEEE Trans. Microw. Theory Techn., Vol. 59, No. 4, 1066-1073, 2011.
13. Herscovici, N., Z. Sipus, and D. Bonefacic, "Circularly polarized single-fed wire-band microstrip patch," IEEE Trans. Antennas Propag., Vol. 51, No. 6, 1277-1280, 2003.
14. Chung, K. L. and A. S. Mohan, "A systematic design method to obtain broadband characteristics for singly-fed electromagnetically coupled patch antennas for circular polarization," IEEE Trans. Antennas Propag., Vol. 51, No. 12, 3239-3248, 2003.
15. Yang, W., J. Zhou, Z. Yu, and L. Li, "Single-fed low pro¯le broadband circularly polarized stack patch antenna," IEEE Trans. Antennas Propag., Vol. 62, No. 10, 5406-5410, 2014.
16. Ta, S. X. and I. Park, "Low-profile broadband circularly polarized patch antenna using metasurface," IEEE Trans. Antennas Propag., Vol. 63, No. 12, 5929-5934, 2015.
17. Balanis, C. A., Antenna Theory, Analysis and Design, 3rd Ed., Wiley, New Jersey, 2005.