Large NF UHF RFID Segmented Loop Antenna with Parasitic Coplanar Slot Loop

This work proposes an enlarged segmented loop antenna for ultra-high frequency (UHF) near field (NF) radio frequency identification (RFID) applications. The proposed antenna is based on a compact interdigital capacitor embedded periodically into a groundless loop. A coplanar slot loop is also deployed as a parasitic element enabling the loop antenna to generate a strong uniform magnetic field within a perimeter of up to 3.22 times the free space operation wavelength lambda at 0.915 GHz. A practical prototype of a rectangular loop with an interrogation area 1.027 lambda x 0.44 lambda was fabricated for experimental testing. The measurements concluded a 100% read range of 26 mm above the antenna surface for commercially available loop-based UHF RFID tags.