In this paper, a low-profile, dual-band, unidirectional, tag antennais proposed for ultra-high frequency band (UHF) radio frequency identification (RFID) applications. The antenna consists of a compact printed dipole, a metasurface of 4 × 4 periodic metallic plates, and a metallic reflector. The dipole antenna is fed by a modified T-matching network for a conjugate impedance matching with the UCODE G2XM chip. The metasurface is designed to work as an artificial magnetic conductor surface, which allows low-profile configuration and unidirectional radiation. More interestingly, the finite-sized metasurface generates extra resonance for the antenna system, which is combined with the dipole resonance for the dual-band operation. For an easy realization and low cost, the dipole and metasurface are built on the top and bottom sides of a thin FR-4 substrate, respectively. The final design with overall size of 190 mm × 190 mm × 15.8 mm (0.532λ × 0.532λ × 0.044λ at 840 MHz) yields a simulated |S11| < -10 dB bandwidth of 840-855 MHz and 916-932 MHz and a unidirectional radiation with a directivity of 7.0 dB and 5.8 dB at 925 MHz and 845 MHz, respectively. The antenna has been fabricated and tested. The measured readable range agrees rather closely with the predicted values. The measurements result in the maximum readable range of 6-m and 4.4-m at standard frequency bands of FCC (902-928 MHz) for North America and IN (840-845 MHz) for India, respectively.
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