Spiral resonator loaded S-shaped folded dipole dual band UHF RFID tag antenna

A miniaturized UHF dual-band passive RFID tag antenna operating in the 866-869 and 950-956 MHz bands is proposed. It consists of an S-shaped Folded Dipole Antenna (FDA) resonating at 912 MHz, which is intermediary between the two required frequencies. To obtain dual-band response perturbation method is employed. The electrical length of the FDA changes on loading a 2-turn spiral resonator (2-SR) to it. The 2-SR splits the tag resonance at 912 MHz into two resonance frequencies (867 and 956 MHz). The proposed design is simulated using HFSS and then fabricated. Measured reflection coefficients at 867 and 956 MHz are -13.25 and -13.34 dB, respectively, exhibiting a 10 dB bandwidth of 11 MHz from 859 to 869 MHz and a 5 MHz 10 dB bandwidth from 953 to 957 MHz. Maximum read ranges of 5 m in 866-869 MHz and 3.3 m in 950-956 MHz band have been measured.