Design of 2.45GHz Circularly Polarized Tag Antenna

Abstract

This paper presents the design and development of a circularly polarized (CP) tag antenna to overcome the polarization mismatch between the reader antenna and the tag antenna in RFID systems. This CP antenna is designed at 2.4 GHz for radio frequency identification (RFID) applications. It consists of a simple square loop loaded with an open gap, two feeding strips, and a matching stub. The antenna is fabricated on an FR4 substrate with a dielectric constant of 4.4, a dielectric loss tangent of 0.02, and a thickness of 0.8mm. In order to achieve conjugate matching between the circular tag antenna and the tag chip, the technique of loading a matching short line on the tag chip was used. Additionally, the radiation of circular polarization (CP) was achieved by placing an open gap and two feeding strips on the square loop. Through electromagnetic simulation analysis, the antenna performance is evaluated. The reflection coefficient (S11) at 2.45 GHz is measured to be - 17.16db, indicating good impedance matching. The 3 dB axial ratio bandwidth is 0.19 GHz (7.7%), covering the frequency range of 2.34 GHz to 2.53 GHz. The 10db power reflection bandwidth is approximately 8.9% (2.33 GHz to 2.55 GHz), ensuring broad operational bandwidth. The antenna also exhibits a favorable antenna gain of 2.29dBi. This study successfully demonstrates the design and performance evaluation of a CP tag antenna for RFID applications