Low-Profile Interdigitated UHF RFID Tag Antenna for Metallic Objects

This paper presents a novel miniature interdigitated ultra-high frequency (UHF) radio frequency identification (RFID) tag antenna that can be placed on metallic objects. The tag structure comprises two horizontal strip lines, each loaded with seven identical open stubs, and an integrated circuit (IC) chip connected directly to the feed lines in the middle of the structure. The perfect match to the IC chip’s impedance is realized by adjusting the length of the loaded open stubs and the spaces between the stubs. Molding the antenna’s geometry can be applied to realize conjugated impedance with any sort of IC chip due to the flexibility of the tag structure. It is fabricated on a single Polytetrafluoroethylene (PTFE) substrate. Moreover, the proposed structure does not involve any metallic vias or shorting walls, which makes its construction simple and suitable for mass production. The tag of the size of $55.2mm\times 44.2mm\times 1.5mm$ yields a total realized gain of −4.11 dB at the North American band (902 – 928 MHz) while being placed on a $20cm\times 20cm$ metallic plate. The measured detection distance is $8.14~m$ on metallic objects and $5~m$ in the free space. A good match between the measured and simulated results is observed.