Re-configurable Near-Field Antenna with Uniform Three-Dimensional Field Distribution

This paper presents a novel near-field antenna design to address the coupling and polarization sensitivity issues encountered by ultra-high frequency (UHF) radio frequency identification (RFID) near-field reader antennas during tag interrogation. The proposed antenna is characterized by uniform distributions of three-dimensional electric fields (Ex, Ey, Ez) and magnetic fields (Hx, Hy, Hz). Utilizing switches to control the feeding phase of four branches in a circularly polarized microstrip unit array, the antenna is capable of transitioning between normal field mode (NFM) and tangential field mode (TFM). Simulation results indicate that the antenna achieves S11 < -10 dB across the 820-960MHz frequency band, while demonstrating strong and uniform distributions of electric and magnetic field components in all directions. This design can facilitate reliable near-field reading capabilities for UHF RFID applications.