Compact Circularly Polarized Metasurface Antennas for RFID Readers

Developing a circularly polarized (CP) antenna with a compact size while achieving good radiation characteristics for handheld radio frequency identification (RFID) readers is a very challenging task. This paper presents two CP antennas with compact size, high gain, and high front-to-back ratio characteristics. These proposed designs consist of a 2$\times$ 2 unit-cell metasurface and are excited by a Y-shaped patch. The first antenna has compact overall dimensions of 0.45$\lambda$$\times$ 0.45$\lambda$$\times$ 0.02$\lambda$, where $\lambda$ is the guided wavelength at the center frequency. The operating bandwidth is about 2.0%, the broadside gain is about 6.5 dBi, and the front-to-back ratio is about 22.8 dB. The second design has a more compact size of 0.36$\lambda$$\times$ 0.36$\lambda$$\times$ 0.02$\lambda$. This antenna has an operating bandwidth of 0.8%, a broadside gain of 5.9 dBi, and a front-to-back ratio of 11.8 dB.