Design and Fabrication of Miniaturized Fractal Antennas for Passive UHF RFID Tags

Abstract

Generally, passive RFID tags consist of an integrated circuit (RFID chip) and an antenna. Because the passive tags are batteryless, the power transfer between the RFID's chip and the antenna is an important factor in the design. The increasing of the available power at the tag will increase the read range of the tag which is a key factor in RFID tags. The passive RFID tag antennas cannot be taken directly from traditional antennas designed for other applications since RFID chips input impedances differ significantly from traditional input impedances of 50 Ω and 75 Ω. The designer of RFID tag antennas will face some challenges like: • The antenna should be miniaturized to reduce the tag size and cost. • The impedance of the designed antenna should be matched with the RFID chip input impedance to ensure maximum power transfer. • The gain of the antenna should be relatively high to obtain high read range. Fractal antennas gained their importance because of having interesting features like: miniaturization, wideband, multiple resonance, low cost and reliability. The interaction of electromagnetic waves with fractal geometries has been studied. Most fractal objects have self-similar shapes, which mean that some of their parts have the same shape as the whole object but at a different scale. The construction of many ideal fractal shapes is usually carried out by applying an infinite number of times (iteration) an iterative algorithms such as Iterated Function System (IFS). The main focus of this chapter is devoted to design fractal antennas for passive UHF RFID tags based on traditional and newly proposed fractal geometries. The designed antennas with their simulated results like input impedance, return loss and radiation pattern will be presented. Implementations and measurements of these antennas also included and discussed.