Compact Dual-Band Circularly-Polarized Cross-Dipole Antenna for Portable RFID Readers

This paper presents a dual-band circularly-polarized cross-dipole antenna for RFID readers. The proposed configuration is comprised of two crossed dipole pairs, with each pair consisting of orthogonal elements designed on front and back sides of the substrate. Double quarter wavelength delay lines are used to connect the dipole elements and introduce a 90° phase difference, resulting in circular polarization in both bands. The impedance bandwidth of the antenna is 13.16 % in the 900 MHz band and 13.6 % in the 2450 MHz band. The axial ratio bandwidth of the antenna is 3.08 % in the 900 MHz band and 1.63 % in the 2450 MHz band. Coaxial cable is used to feed the structure, which eliminates the need for complicated feeding networks. The antenna configuration has an overall size of $(65 \times 65 \times 1.6)$ mm3.