In this paper, a tunable ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna is proposed using characteristic modes analysis. The proposed tag consists of a folded-patch and a feeding loop stacked on two substrate layers. The folded patch wrapped around 2 mm thick FR4 substrate and is optimized using characteristic modes to resonate around 915 MHz. The inductive feeding loop provides matching with RFID chip. This tag covers American RFID band form 905 MHz to 928 MHz

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... 10 dB return loss and can be tunable to European band by adding copper strips. Moreover, the proposed design is low cost, because it does not require any via or shorting pin. Furthermore, the measured read range of this tag is 3.5 m and 5 m in free space and above 200x200 m 2 metal plate respectively.