Co-Circularly Polarized and In-Band Full-Duplex Cavity-Backed Slot-Antenna Pair Within Shared Cavity for RFID Application

In this article, a novel cavity-backed slot-antenna (CBSA) antenna pair designed with shared radiator is proposed for radio frequency identification (RFID) systems. The CBSA pair is co-circularly polarized, meanwhile exhibiting in-band full-duplex (IBFD) capability and good radiation pattern consistency in the RFID band. The near-field mode superposition method is employed to achieve isolation between the transmitting and receiving ports. Additionally, a patch is designed inside the cavity to reshape the original cavity’s electric field distribution, thus enhancing the mode superposition and improving isolation performance. Further regulation of the feeding ports’ positions and introduction of cross slots achieve the circular polarization. The proposed CBSA pair was fabricated and measured. The prototype achieves an overlapping bandwidth of 916.5–925.4 MHz, where the impedance matching, −20-dB decoupling, and −3-dB axial ratio (AR) criteria are simultaneously satisfied, effectively covering the RFID frequency range (920–925 MHz). Notably, the maximum decoupling level within this band reaches 27.4 dB. The proposed CBSA pair has advantages in compact size, co-circularly polarized, and IBFD performance; can serve as a good candidate for compact, high-performance RFID reader applications; and is well suited for RFID systems requiring high-density target inventorying.