Low SAR Dual-Band Circularly Polarized Wearable RFID Antenna Using FSS Reflector with Reduced EMI

Abstract

A circularly polarized dual band wearable antenna using a frequency selective surface backed reflector for radio frequency identification reader resonating at global ultra-high frequency band (860– 960 MHz) and ISM band (2.4 GHz) is proposed in this work. For circular polarization, the corner is truncated at the opposite end of a square patch with periodic slots over the patch for getting an orthogonal electric field in both the X and Y axis directions. Another truncated inner square slot patch miniaturizes the antenna further for stable frequency response. Finally, the periodic frequency selective surface-based reflector is used for gain enhancement and crosstalk reduction. The simulated and measured results for antenna over human body are plotted against the required bandwidth. The return loss and maximum radiated gains of −31 dB and 8.30 dB are achieved at a resonating frequency of 2.4 GHz with the reading range and Specific Absorption Rate (SAR) of 6.98 m and 0.77 watt/kg, respectively. At 865 MHz, the return loss and maximum radiated gain are −23 dB and 5.31 dB with the reading range and SAR of 5.21 m and 0.65 watt/kg, respectively. The proposed Ultra-High Frequency (UHF) RFID antenna is circularly polarized with the axial ratio bandwidth less than 3 dB with approximately 15% (860–965 MHz and 2.4–2.45 GHz) range. The designed wearable antenna provides better isolation when FSS is incorporated while enhancing the gain for longer read range. The FSS reflector below the antenna reduces the SAR for on-body wearable applications. This RFID antenna can be used efficiently for WBAN applications as a portable RFID reader wearable antenna for remote sensing and real time monitoring.