Compact 2.5 GHz circularly polarized antenna using high permittivity substrate

The compact circularly polarized antennas by employing high-permittivity and low loss substrates are investigated. The antennas were individually fabricated on nano-Al₂O₃ (ε_r = 9.7, Q×f value of 500,000 GHz) and Al₂O₃ (ε_r = 9.7, Q×f value of 200,000 GHz) substrates and operated at 2.5 GHz. The presented circularly polarized antennas using nano-Al₂O₃ and Al₂O₃ substrates can achieve 80 MHz and 60 MHz of 3-dB axial ratio bandwidth (CP bandwidth), respectively. The application of the nano-Al₂O₃ substrate demonstrates a wider CP bandwidth and a smaller size of the antenna.