Near-Field Kandonian Loop Antenna With Wide Interrogation Zone for UHF RFID Applications

A near-field kandonian loop antenna with small loop array and opposite directional current (ODC) for using ultra high frequency (UHF) radio frequency identification (RFID) system is proposed. The proposed antenna is constructed by array four loop antennas smaller than the wavelength of the operating frequency. The proposed antenna expands the interrogation zone at near-field and has a uniform field distribution because each straight line at the top and bottom of the substrate in the small loop utilizes ODC to canceling current and form one large loop electrically. In addition, the proposed antenna has a lower E-field compared to the conventional single loop, which prevents detection of adjacent tags outside the interrogation zone. The proposed antenna has a maximum read range of 48 mm and the detailed characteristics of the proposed antenna are verified by comparing the simulation and measurement results.