Design of a Fractal-Based Circularly Polarized UHF RFID Reader Antenna

Abstract— The coplanar waveguide (CPW) fractal antennas have been given importance in recent days at lower frequencies by considering its advantage of obtaining wider bandwidth. Presently, RF domain is mainly concentrating on design of circularly polarized (CP) antennas for RFID applications as the reader can access the tag information regardless of its polarization. This mainly improves the reading capabilities of RFID reader, which is a major design constraint in whole RFID domain. This project presents the design of a coplanar waveguide (CPW) circularly polarized antenna for the central frequency 900 MHz, it comes in handy for radio frequency identification(RFID) short-range reading applications within the band of 902–928 MHz where the axial ratio of proposed antenna model is less than 3 dB. The proposed design has an axial-ratio bandwidth of 36 MHz (4%) and impedance bandwidth of 256 MHz (28.5%). The proposed design includes monopole a CPW structure concept to provide larger bandwidth at lower frequency 900 MHz, which comes to be an enormous increment typically from 4% to 5% for a general square patch (FR-4) substrate antenna to greater than 20% for CPW monopole structure. It includes fractal antenna concepts to achieve compactness as well as circular polarization.

Keywords— circular polarization, coplanar waveguides (CPWs), fractal antennas, radio frequency Identification (RFID), ultrahigh frequency (UHF).

INTRODUCTION

Radio frequency identification (RFID) is a wireless data access technology that uses two components for information exchange, it relies on tag for product information transmission and reader for data reception. The RFID system consists of two main components tags and reader. The reader always interrogates the tags which is equipped with antenna, transceiver and processor (along with software). The tags (transponder) are powered by and read at short distance ranges via magnetic field such as electromagnetic induction. The tags may use an on-board power source such as a battery, which is called active tag.
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