Dual‐Sense Circularly Polarized Quad‐Port MIMO RFID Antenna Backed With Electromagnetic Band Gap Structure for Enhanced Axial Ratio and Mutual Coupling Reduction

In the existing radio frequency identification (RFID) system, a single reader antenna is used to identify and share data with the tag. In a large complex environment with dense packing of tag users, a single antenna often leads to a collision and delay due to having a limited data rate and poor coverage. To address the current issues, a dual‐sense circularly polarized (CP) quad‐port multi‐input multioutput (MIMO) reader antenna is proposed that provides an opposite sense of rotation at diagonal pairs in this work. It introduces multipath propagation due to spatial diversity to enhance the RFID performance. Orthogonal modes of the proposed single‐element antenna are evaluated using characteristic mode analysis. In the MIMO layout, a pair of U‐shaped microstrip lines and a series of electromagnetic bandgap (EBG) structures are placed at the bottom side of the substrate for isolation improvement and axial ratio enhancement. The dispersion characteristics of the EBG cell justify the bandgap properties over the operating range. It displays an invariable response of a 10 dB impedance bandwidth of 21.3% (0.77–0.954) and a 3 dB axial ratio bandwidth of 18.8% (0.80–0.97) at all ports, covering the entire RFID band. The antenna maintains more than 25 dB isolation over the operating region of any pair of antenna ports, keeping the interelement spacing of 0.02 λ 0 . λ 0 is the free‐space wavelength at the midpoint operating frequency. Envelope correlation coefficient (ECC) lies below 0.0003, and channel capacity loss (CCL) is 0.0001 bits/s/Hz. The key features of the proposed antenna are suitable for a RFID application to read multiple tags in a crowded tag area with low latency.