M-Shaped Folded-patch Antenna for On-Metal UHF RFID Tag Design

A new M-shaped UHF' RFID tag on metal which has a small footprint of 40 x 24 x 1.1 mm(3) (0.122 lambda x 0.073 lambda x 0.003 lambda at 915 MHz) has been proposed. The tag consists of an M-shaped patch, three short wires and a ground. The tag is made on folded flexible substrate and has a simple structure. It can be easily fabricated on thin flexible PET sheet substrates. There are 3 design parameters to change, the impedance and the resonant frequency of the antenna can be changed finely by changing the parameters, so the tag can achieve different degrees of conjugate matching. An equivalent circuit is built to estimate the input impedance of the antenna. And the results show that the impedance conjugate matching between the tag antenna and the chip can be easily achieved by using the M-shaped feeder. In the simulation, the antenna has a high power transmission coefficient (similar to 1). With an EIRP (effective isotropic radiated power) of 4 W, the tag can achieve a long reading distance of 6.9 m on metal surfaces.