U-Shaped Inductively Coupled Feed UHF RFID Tag Antenna With DMS for Metal Objects

A novel U-shaped inductively coupled feed ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna with defected microstrip surface (DMS), which can be attached to a metallic surface is proposed. The proposed design consists of two symmetrical U-shaped feeder structures inductively coupled to the transmission lines that are connected to the patch surface from two opposite sides. The feed structure provides enhanced flexibility to the tag antenna as matching can be done with any type of IC chip, through the tuning of the U-shaped structure's dimensions. Implementation of DMS, attained by etching a rectangular slot, improves antenna's performance by increasing its realized gain by 5.7 dB. It is worth noting that the structure does not include any metallic vias or shorting stubs. The measured detection distance with and without being mounted on the metallic surface is 8.44 and 6.2 m, respectively. A good agreement is achieved between the simulated and measured results.