LAUSR

A zero-phase-shift line (ZPSL) grid-loop antenna backed by an artificial magnetic conductor (AMC) is proposed to realize a uniform and strong magnetic field distribution over an electrically large interrogation zone for near-field wireless systems. The grid-loop configuration is able to achieve a uniform magnetic field distribution over an enlarged interrogation zone by enhancing the magnetic field in the central portion of the ZPSL loop. Moreover, an AMC comprised of four-arm spiral unit cells is designed to back the ZPSL grid-loop antenna for a directional field distribution and enhanced magnetic field intensity. The proposed antenna is exemplified as a reader antenna for ultrahigh frequency near-field radio frequency identification systems. By using an Impinj Speedway reader with an output power of 30 dBm, a 100% detection rate of Impinj J41 tags is achieved up to 90 mm over an interrogation zone of $200 \times 200$ mm2.