A Compact Slot-Based Bi-Directional UHF RFID Reader Antenna for Far-Field Applications

This research introduces a novel circularly polarized compact antenna designed for universal ultrahigh-frequency (UHF) radio-frequency identification (RFID) handheld readers for Bi-directional RFID Far-field Applications. The antenna features a microstrip feed positioned at the center opposite a slot-based square ground. The ground plane is perturbed to include a thin horizontal and vertical stub on the left side, along with a thick rectangular slot at the right side of the square ground plane to achieve circular polarization. The simulated antenna provides a 3-dB axial ratio bandwidth (ARBW) of 42 MHz (831–873 MHz), a 10 dB impedance bandwidth of 15% (814–945 MHz), and a peak gain of 5.0 dBi. The antenna is fabricated on both layers of an affordable FR4 substrate, measuring $81\times 81\times 1.6~{\mathrm { mm}}^{3}$ and its measurement results are in close agreement with simulated. The application of this antenna is made with a commercial UHF RFID reader module. The obtained read range and field of view confirm that this proposed antenna is a promising option for compact universal UHF RFID handheld reader applications and other Internet of Things (IoT) based applications.