A Broadband Circularly Polarized Dipole Antenna with High 1-dB Gain Flatness

A novel wideband circularly polarized (CP) dipole antenna is presented. The proposed antenna is configured with three horizontal layers of an electrical dipole, two parasite Π-strips, and a ground, where the electrical dipole is fed by a vertical microstrip balun, resulting in three CP modes. The 180º rotationally symmetric dipole generates two CP modes in the middle- and high-frequency bands. In order to improve the CP bandwidth, two 180º rotationally symmetric Π-strips are introduced and excite the third CP mode in the low-frequency band. The antenna prototype is fabricated, and the measured results show that the -10 dB impedance bandwidth is 1.63 - 3.98 GHz (83.78%), the 3-dB axial ratio bandwidth (ARBW) is 1.70 - 3.11 GHz (58.63%), the realized gain is 7.34 ± 0.32 dBi, and the average radiation efficiency is 80.61%. As a result, the 1-dB gain bandwidth is overlapped with the ARBW, and the realized gain has a high flatness over the ARBW. Therefore, the proposed antenna is a promising candidate for broadband CP wireless communication system applications.