Miniature Folded Modified Log-Periodic Shaped Tag Antenna for Metal Mountable UHF RFID

A miniature and compact folded radio frequency identification (RFID) tag antenna, which consists of a modified log-periodic shaped patch is proposed. The patch is shorted to the ground using a narrow stub, where the inductive thin stub is used for frequency tuning. The proposed tag is designed using a flexible polyethylene terephthalate substrate with a very compact size of only 30 mm × 35 mm × 1.71 mm (0.092λ × 0.108λ × 0.005λ at 922 MHz). The proposed tag antenna has a compact and novel structure, and it is also able to provide sufficient resistance and inductive reactance to enable conjugate match with the chip. The proposed tag antenna is capable of achieving a power transmission coefficient of ~1 and a maximum read distance of 8.87 m when mounted on a 20 cm × 20 cm metallic surface.