An MNG-TL loop antenna for UHF near-field RFID applications

A loop antenna is designed and fabricated for ultra-high frequency (UHF) near-field radio frequency identification (RFID) readers. The artificial mu-negative transmission line (MNG-TL) structure has been applied to the antenna design, which will help the current distribution along the loop to keep in phase even with the perimeter of the loop more than two operating wavelengths. Thus the antenna can generate strong and uniform magnetic field with a large interrogation zone. Simulation results indicate that a relatively large impedance bandwidth from 762.2MHz to 1004.8MHz has been obtained. The overall size of the antenna is 216mm×216mm and a large interrogation zone with uniform and strong magnetic field distribution of up to 187.2mm × 187.2mm has been achieved.