Design of UHF small passive tag antennas

We explore structures of planar tag antennas that permit high efficiency, a low profile, and reliable performance on a variety of dielectric materials. For the basic structure of the antenna, we used the inductively coupled feed concept to efficiently reduce the size of the tag antenna. We examined two different types of windings for the antenna body to achieve better performance with the given RFID tag chip. To find detailed design parameters that attain multiple design goals, we employ a Pareto genetic algorithm with an IE3D of Zealand EM simulator. The finalized designs were built on a 5 mil thick Duroid substrate with the Alien tag chip. The size of the optimal design was reduced to kr=0.2, with a readable range of 40 cm-280 cm.