Axial Ratio (AR) Bandwidth Enhancement of a Circularly Polarized Crossed-Dipole Antenna Using Tapered Vacant-Quarter Ring

A technique to enhance the axial ratio (AR) bandwidth of a circularly polarized (CP) crossed-dipole antenna is proposed in this paper. The proposed crossed-dipole antenna structure has two sets of bowtie-shaped dipole elements oriented in an orthogonal configuration, four parasitic metallic elements, a metallic cavity, and a coaxial feeding. Each crossed-dipole pair is connected by a tapered vacant-quarter ring to generate wideband axial ratio (AR) performance. To further extend the AR bandwidth, four rectangular-shaped parasitic elements are included diagonally. Simulation results show that the proposed tapered vacant-quarter ring based crossed-dipole antenna structure achieves a wide impedance bandwidth from 10-23GHz (78.78% fractional bandwidth) and the 3dB axial ratio bandwidth is about 74.85% (10.15-22.29GHz). The antenna has a relatively stable CP gain patterns with a broadside gain value of (8.2-10.3dBi) over the operating frequency range.