Design of multi-layered polygonal helix antennas for RFID readers in UHF band

A new type of printed helix antenna, called the multi-layered polygonal helix antenna, is proposed as an RFID reader antenna in the UHF band. The wire of the antenna has vertical bends on multi-layered polygons, and the antenna was optimized for various antenna characteristics, such as bandwidth, CP bandwidth, efficiency, antenna size, readable range to tag, and directivity, using the Pareto GA. Based on tests of the optimal designs, the two-layered structure shows superiority over the one-layered structure in terms of the limit of gain within all antenna sizes. To verify our investigation, we fabricated the optimal two-layered polygonal helix and printed it on a cardboard substrate. The fabricated antenna. with kr = 3.2. exhibited 27.63% impedance bandwidth, 16.8% CP bandwidth, and a readable range of nearly 9 m/sup 2/.