Dual-Band Polarization Conversion Metasurface-Assisted Compact High-Efficiency RFID Reader Antenna Design

In this communication, a novel dual-band 0.9/2.45 GHz circularly polarized (CP) radio frequency identification (RFID) reader antenna with low-profile high-efficiency based on the polarization conversion metasurface (PCM) is proposed. At first, a dual-band linearly polarized (LP) bow-tie dipole antenna etched with two pairs of U-shaped grooves is designed as a radiator. The gradient microstrip balun feeding is employed to achieve excellent radiation performance and easy installation as a supporting structure. Then, a PCM is designed as a reflector, enabling polarization conversion and phase difference (including tracing phase difference) for CP radiation in dual frequency bands. Finally, the antenna has been manufactured and measured, resulting in an overall size of $0.42\lambda _{0} \times 0.42\lambda _{0} \times 0.09\lambda _{0}$ at 0.9 GHz. The measured impedance bandwidths for the lower and upper bands are 17.54% (0.78–0.93 GHz) and 4.94% (2.37–2.49 GHz), respectively. The axial ratio (AR) bandwidths are 6.67% (0.87–0.93 GHz) and 5.33% (2.37–2.50 GHz) in the corresponding bands. The proposed antenna can cover the UHF/2.45-GHz industrial scientific medical (ISM) dual bands of China, and the Federal Communications Commission (FCC) band of North America. Furthermore, the measured peak gains for right-handed circular polarization are more than 6.02 and 9.14 dB in the respective frequency ranges. Therefore, the antenna is very suitable for RFID applications in both UHF and 2.45-GHz ISM dual frequency bands.