Multi-Excited Split-Ring Resonator Antenna With Autonomous Linear Polarization Rotation

This paper presents a novel antenna that autonomously rotates its linear polarization (LP) orientation with carrier frequency, a critical advancement for ultrahigh-frequency (UHF) radio-frequency identification (RFID) to mitigate tag collisions. The antenna’s unique capability to adjust polarization without external control is enabled by integrating an X-slot and a pair of concentric split-ring resonators (SRRs) with off-center splits. A key innovation lies in the multi-excitation mechanism: the SRRs are simultaneously activated at their corners via the X-slot, inducing distinct resonant modes through phase-shifted currents. Unlike conventional single-port designs, this multi-excitation generates dynamic current distributions in the SRRs, which act as a feedback network to reshape the X-slot’s field and drive polarization rotation. Remarkably, the prototyped antenna achieves a 126-degree polarization rotation within a narrow 30 MHz bandwidth (900–930 MHz), demonstrating precise frequency-dependent control. The antenna has a compact area of 0.157λ20 while attaining a peak gain of 4 dBi. Under identical test conditions, the proposed antenna achieves a read rate of 57.64 tags/s, representing a 65% improvement over conventional CP antennas. RFID communication tests confirm its effectiveness in enhancing polarization diversity and reducing tag collisions by aligning polarization with tags’ orientations as frequency shifts. The synergy of multi-excitation and SRR feedback underpins this breakthrough, offering a scalable solution for adaptive RFID systems and frequency-reconfigurable antennas.