High-Efficient Compact Folded-Patch Antenna Fed by T-Shaped L-Probe for On-Metal UHF RFID Tag Design

A compact folded-patch antenna with a dimension of 45 mm $\times45$ mm $\times3.2$ mm ( $0.137\lambda \times 0.137\lambda \times 0.0097\lambda$ ) is proposed for on-metal applications. A T-shaped L-probe is employed for feeding the top-loaded radiating folded patch. It is found that good impedance matching can be easily achieved between the tag antenna and the microchip with the use of the T-shaped feeder. Also, the maximum power transmission coefficient can be significantly enhanced from 0.45 to 1. By adjusting some of the design parameters, the tag's footprint area can be effectively reduced by 50 while maintaining considerably good read performance. The proposed tag antenna can not only radiate efficiently with a high radiation efficiency of 73.8 but also be read from a long read distance of 19 m when placed on a 20 cm $\times20$ cm metal plate with reference to a transmitting power of 4 W EIRP.