Design of a compact broadband circularly polarized RFID antenna

For problem that existing circularly polarized antenna is difficult to meet requirements of broadband and miniaturized application simultaneously, a compact broadband circularly polarized RFID antenna for global ultrahigh frequency(UHF) RFID read-write application was designed by use of a new type of power-dividing phase-shifting feed network, rotating short-circuit radiation patch and coupled patch as well as feed probe and grounding probe. The experimental results show that relative bandwidths of the antenna are 59% and 34% respectively when return loss is greater than 15 dB and axial ratio is less than 3 dB. Within the frequency band of global UHF RFID, antenna radiation gain is greater than 2.7 dB with symmetric and stable radiation direction, and half power beam width is greater than 101° which is suitable for wide angle reading and writing. By comparing performance and structure of the designed antenna with existing circularly polarized RFID antenna, it is found that the operating frequency band of the antenna not only covers global UHF RFID frequency, but also has compact structure which is in favor of design and implementation of RFID system with low cost.