UHF RFID reader antenna using oppositely directed group currents for large identification area

In this paper, an antenna with one excited element and several parasitic elements is proposed to expand the identification area. The currents along the excited element and parasitic ones are oppositely directed, which is called oppositely directed group currents (ODGCs). The near-field magnetic field surround the antenna is affected by the phase and amplitude of the currents. The distances between arbitrary two elements and the lengths of the parasitic elements affect the phase difference greatly, which will be analyzed in this paper. All these analysis are of great significance to design the near-field radio-frequency identification (RFID) antenna formed by the ODGCs at UHF band.