Three Dual-Band and Dual-Linearly Polarized Antenna Configurations for UHF-RFID and WLAN Applications

This paper presents three dual-band, dual-linearly polarized antenna configurations for UHF-RFID and WLAN applications. The first configuration consists of a square patch with outer ring which exhibits two resonances at 865MHz and 2.45GHz respectively. At both these frequencies, the antenna has its main beam along the +z axis (broadside direction). Two superstrates, S3 and S4, are designed to be used separately with this antenna. Both S3 and S4, when placed above the antenna separately, shift the first resonance from 865MHz to 905MHz without affecting the 2.45GHz resonance. Placing S3 5mm above the antenna gives rise to a bi-directional radiation pattern (±z-axis) while replacing S3 with S4 generates a main beam along the -z axis (opposite broadside direction) at 905MHz. The radiation pattern remains unperturbed at 2.45GHz for both configurations. The first antenna configuration works within the European UHF-RFID band whereas the antenna + S3 and antenna + S4 configurations work within the North-American UHF-RFID band. Additionally, all three configurations also operate within the 2.45GHz WLAN band. Both the antenna-superstrate configurations have very low profiles of $\lambda _{0}$ / $24.4~(\lambda _{0} \,\, {=}$ free space wavelength at 2.45GHz). The antenna can thus be used with/without the superstrates as an RFID reader depending upon requirements. The information received from the tags can then be transmitted via the WLAN channel.

I. Introduction

Radio Frequency Identification (RFID) is used in many different sectors worldwide, including the healthcare, retail, security and manufacturing sectors to name a few [1]. Many different frequency bands are used by RFID systems. Two of the most popularly used UHF-RFID bands are the European UHF-RFID band (865-868MHz) and the North American UHF-RFID band (902-928MHz). Any RFID system is incomplete without an RFID tag and an RFID reader. The tags, connected to the objects to be tracked, are interrogated by the RFID reader. This information is then stored in the reader or wirelessly transmitted to another base/control station. For wireless transmission, the 2.45GHz WLAN channel is the most popular. Many such dual-band RFID readers have been proposed and presented which can also operate within the WLAN band [2], [3], [4], [5], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16].