Dual-Chip UHF RFID Tag Antenna for Distinction of Movement Directions

This paper proposes a dual-chip RFID tag antenna with two radiating tags operating in the 915 MHz UHF band. A reflector is added between the tags to control their radiation patterns. The antenna is designed based on the differential beam concept allowing a convenient power-based distinction between the directions of the tagged object. This solution is significantly cheaper and simpler compared to dual-reader systems that offer comparable distinction. The design is simulated using CST MWS with an input impedance of 23+j224 Ω to match the impedance of NXP UCODE G2iL RFID chip. The radiation patterns show a good separation between the two beams, where the main beams are oriented at theta = ±90° with the radiation efficiency of 56.48 %. The antenna is also studied when placed over a 20 x 20 cm
²
planar metallic surface, which mimic the surface of an indoor cart that is being traced. This allows to adjust the direction of the main beams, which are pointed theta = ±21°.