Design of Compact Microstrip Patch Antennas for RFID Reader Applications

Abstract

This thesis work presents the design of a RFID reader antenna using microstrip antenna design technology. Microstrip antennas have many advantages as compared to conventional microwave antennas and therefore cover a broad microwave frequency range i.e 100 MHz to 100 GHz. The microstrip antennas have very low cost, light weight, and thin profile configuration which can be made conformal and can be easily integrated with microwave integrated circuits. These antennas can be made dual polarized. So a circularly polarized microstrip patch antenna working UHF band has been proposed in this thesis. The UHF frequencies typically offer much better read range (inches to 50+ ft. depending on the RFID system setup) and can transfer data faster (i.e. read many more tags per second) than lowand high-frequencies.
To fulfill the requirements, a very low cost easily fabricated slotted microstrip antenna has been designed on low cost easily available FR4 substrate. A compact microstrip circularly polarized slotted antenna is presented in this paper. The antenna is having wider operational bandwidth from 740 MHz to 1560MHz. The antenna is designed with Coplanar waveguide (CPW) feed with T-shaped feeding line. To obtain proper impedance matching two L-shaped lines are inserted into the circular slot in the ground plane. It shows simulated 70% fractional bandwidth centered at 1150 MHz. The peak gain of the antenna is 4dB. The antenna has 3-dB axial ratio bandwidth of around 383 MHz ie from 1155 MHz to 1438 MHz. The fabricated antenna has been tested using Agilante ENA 710C vector network analyzer The dimension of the antenna is 0.28λ × 0.28λ × 0.019λ , where λ corresponds to the wavelength of the lowest cutoff frequency. This antenna is suitable for ultrahigh frequency (UHF) radio-frequency identification (RFID) reader applications.