Coplanar-fed Planar Inverted-L Antennas (PILAs) for Miniature On-Metal RFID Tag Design

A new type of miniature tag antenna, which comprises of a pair of planar inverted-L antennas (PILAs), is proposed for designing an on-metal RFID tag. The PILAs are symmetrical to each other and they are simultaneously fed by a narrow coplanar feedline, which lies along the line of symmetry of the tag. Despite being electrically small (
$35\ \text{mm}\times 35\ \text{mm}\times 3.18\ \text{mm}$
), the proposed tag antenna can achieve high radiation efficiency of 51%, which is much higher than most of the contemporary miniature tags. As a result, the tag can achieve maximum read distance of ∼24 m on metal. Two notches are etched on the PILAs for introducing additional capacitance and inductance to the antenna's impedance for achieving conjugate match with the chip's impedance.