A low cost circularly polarized microstrip patch antenna with low axial ratio for UHF RFID applications

Abstract

This paper presents a low cost circularly polarized microstrip patch antenna with low axial ratio (AR) and broad AR beam width for ultrahigh frequency (UHF) radio-frequency identification (RFID) applications. The proposed design utilizes the corner truncated technology along with a thicker substrate and large ground plane to achieve circular polarization and a low axial ratio. The substrate material for the antenna is FR-4, which has a dielectric constant of 𝟒. 𝟑. The antenna is fed by using a 𝟓𝟎 −𝒐𝒉𝒎 feed line. Simulations are carried out using the CST (Computer Simulation Technology) Studio Suite software. The simulation results show that the proposed antenna has a reflection coefficient of less than −𝟏𝟎 𝒅𝑩 from 𝟖𝟖𝟔. 𝟐𝟑 𝑴𝑯𝒛 to 𝟗𝟐𝟒. 𝟗𝟔 𝑴𝑯𝒛 with a bandwidth of 𝟑𝟖. 𝟕𝟑 𝑴𝑯𝒛. The antenna provides the axial ratio less than 𝟑 𝒅𝑩 for the frequency range from 𝟗𝟏𝟓 𝑴𝑯𝒛 to 𝟗𝟏𝟗 𝑴𝑯𝒛. Other antenna parameters, such as the directivity, gain, voltage standing wave ratio (VSWR) etc. are also presented and discussed. The antenna with optimized dimensions is fabricated and measured. The measured results show good agreement with simulated results. The fabricated antenna has a bandwidth of 𝟓𝟕. 𝟓𝟐𝟕 𝑴𝑯𝒛 and achieves a minimum reflection coefficient of −𝟐𝟕. 𝟗𝟕 𝒅𝑩 at 𝟗𝟏𝟒. 𝟎𝟒𝟓 𝑴𝑯𝒛