A Dual-Differential Fed Open-loop Antenna with Broadband Circular Polarization for mm-Wave Applications

A broadband circularly polarized open-loop antenna fed by dual-differential structure for millimeter-wave (mm-Wave) applications is proposed in this paper. Its radiation parts are curved on a substrate, with two reverse loops etched on the upper surface and the other two etched on the lower surface, along with a reflective ground plane printed on another substrate. The loops on the same surface are differentially fed by one-half-wavelength phase delay lines. Further, the loops on the upper and lower surfaces are also differentially fed by a substrate integrated waveguide (SIW) through a double-sided parallel-strip line (DSPSL). Results show the antenna owns an impedance bandwidth (IBW) and 3 dB axial ratio bandwidth (ARBW) of 30.4% (24-32.6 GHz) and $38.9 \%(22.4-33.2 \mathrm{GHz}$) respectively, a low profile of $0.16 \lambda_{0}$ (where $\lambda_{0}$ is the free-space wavelength at 28 GHz) and a peak gain of $\mathbf{1 0. 4} \mathbf{~ d B i c.}$