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 a strong and uniform magnetic field distribution in the near field of the antenna can be generated. The simulated and measured results indicate that a relatively large impedance bandwidth from 762 MHz to 1048 MHz has been obtained. The overall size of the antenna is 216 mm×216 mm×0.4 mm, and a large interrogation zone with uniform and strong magnetic field distribution of up to 187.2 mm×187.2 mm has been achieved.
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