Broadband circularly polarized stacked patch antenna for universal UHF RFID applications

A double layer stacked patch antenna with a size of 200 × 200 × 48 mm³ is proposed in this investigation. To achieve broad CP bandwidth that can cover the universal UHF RFID applications (840-960 MHz), a slot loaded circular patch antenna fed by an L-shaped probe is applied as the lower layer (main patch), while the top layer (parasitic patch) is a simple cross slot loaded circular patch. Besides demonstrating broad 10-dB return loss bandwidth of 16% (823-966 MHz), desirable CP bandwidth (3-dB axial ratio) of 14.2% (833-960 MHz) was also measured. Furthermore, the proposed antenna has also yielded a maximum gain of approximately 8 dBic.