Millimeter-Wave Conical Beam Antennas for Drone and Vehicle Communications

In this contribution, novel designs of circular planar antennas capable of generating conical beam (CB) radiation patterns for millimeter-wave (mmWave) drone and vehicle communications are presented. The antenna comprises of a circular patch surrounded by 18 quarter wavelength bent stubs/corrugations and fed from the underside using a coaxial feed. The antenna supports the TM01 mode and produces a narrow-band linearly polarized (LP) CB radiation pattern. To increase the antennas’ bandwidth, six radial line slots were strategically placed in the top-patch, each oriented at 60° with respect to each other and rotated by 30° along the axis alignment. This configuration significantly improved the antenna’s bandwidth and maintains the beam at a constant angle. Through optimization of the physical dimensions of the design, the LP-CB antenna achieved a peak gain of 9.2 dBi with less than 1.5 dB variation across the bandwidth between 24.2 to 30 GHz. Moreover, gain patterns are circularly symmetric with very low-ripple at different elevation angles. By using the same top layer, and introducing three rings of tilted slots (6, 12 and 12 slots in each ring) in the ground plane, a second antenna is designed which is circularly polarized (CP) with a 3 dB axial ratio (AR) bandwidth from 27.5 to 30.8 GHz. Across the operating band, the beam points at the elevation angle of $24^{\circ } \pm ~1^{\circ }$ for both the antennas. The simulated and measured results demonstrate that both proposed antennas can achieve a -10 dB impedance bandwidth (IBW) of more than 22.2% for the LP design, 10.5% in the CP design, and exhibit stable and consistent radiation patterns with efficiency better than 80%. Excellent agreement between simulations and measurements was achieved. A simple planar geometry with wide bandwidth, high gain, and good CB radiation performance makes the designs promising candidates for 5G mmWave communications.