A Dual Circularly Polarized RFID Reader Antenna With Wideband Isolation

This letter presents a dual circularly polarized microstrip antenna with wideband isolation for radio frequency identification (RFID) reader application. The proposed antenna consists of a radiating patch and ground plane with a branch-line coupler (BLC) fed by separate Tx/Rx ports. The BLC is located underneath ground and can provide dual circularly polarized radiation coupled to the radiating patch through H-shaped slots. The prototype antenna was fabricated and shows S11 ≤ -18 dB and axial ratio AR ≤ 2 dB from 860 to 940 MHz. The -25-dB isolation characteristic between Tx and Rx ports achieves wide bandwidth of 65 MHz (864-929 MHz), which covers both Europe (865-869 MHz) and USA (902-928 MHz) RFID bands.