Directional Energy-Efficient Metasurface-Backed RFID Reader Antenna for Minimizing Tag-Detection Uncertainty in IoT Networks

In this paper, a 2.45/5.8 GHz circularly polarized RFID antenna backed with a dual-band artificial magnetic conductor (AMC) is presented for tagged-object detection in Internet of things (IoT) networks. RFID systems require a long-range reader to maintain energy-efficient communication with the tagged devices. An efficient reader antenna is presented to increase the interrogation distance of the reader, and decreasing the uncertainty of tagged-object detection. The proposed RFID antenna consists of two dipole pairs, are printed on both sides of the substrate to obtain 2.45 GHz and 5.8 GHz bands, connected by feed delay lines in a cross-dipole arrangement. To increase the range of the reader, the cross-dipole antenna is supported by a $5\times5$ AMC surface placed $0.042{\lambda }_{0}$ beneath the antenna, where ${\lambda }_{0}$ is the wavelength calculated at the lowest resonant frequency. In measurement, the metasurface backing results in gain enhancements of 4.1 dBi in the 2.45 GHz band and 4.6 dBi in the 5.8 GHz band, which improves the read range of the reader. The measurement also shows an improvement in RFID band coverage in terms of impedance bandwidth, 2.32–2.57 GHz in the 2.45 GHz band and 5.48-6 GHz in the 5.8 GHz band, reducing tag-detection error. The axial ratio bandwidth of the reader antenna configuration is 2.385–2.485 GHz and 5.77–5.88 GHz in the 2.45 GHz and 5.8 GHz bands, respectively.