Compact Wideband Circularly Polarized Dipole Antenna Using Modified Quadrature Hybrid Couplers

In this communication, we propose a novel circularly polarized (CP) dipole antenna fed by modified quadrature hybrid couplers (QHCs). In a conventional CP antenna, such as a sequentially rotated structure, the electrical length of the line connecting the radiating elements changes as the frequency changes. This characteristic produces a narrow axial ratio (AR) bandwidth and changes the radiation patterns of the array antenna at different frequencies. A modified QHC with minimal variation in the phase and amplitude difference between the output ports over a wide frequency range is used to achieve wide AR bandwidth and stable radiation patterns. The −10 dB impedance bandwidth of the proposed antenna is 4.1–7.6 GHz (58.3%), and the 3 dB AR bandwidth is 4.8–7.4 GHz (43.3%). The maximum gain is 4.4 dBic, and the 3 dB gain bandwidth is 5–7.5 GHz (40%). The antenna size is
$21\times 21\times0.2032$
mm
³
(
$0.42\times 0.42\times 0.004\lambda _{o}^{3}$
at 6 GHz).