A Circularly-Polarized Reconfigurable 360°- Scanning Phased Array for UAV Communication

In this paper, a circularly-polarized reconfigurable 360°-scanning array antenna is proposed for unmanned aerial vehicles (UAV) communication. Reconfigurable 360° scanning can be achieved by flexibly adjusting the excitation of two backto-back rotated linear arrays to switch between broadside and endfire radiation modes. Specifically, this array contains 2 × 8 omnidirectional circularly-polarized elements built by a metalcavity dipole and a simple power-divider feeding structure. Thereby, horizontal and vertical electrical-field components of the cavity-dipole element can be excited simultaneously with 90° phase difference, thus generating circularly-polarized radiation in azimuth plane. It is also noted that three S-shaped slots are etched on these metal cavities to effectively obtain good axial ratio of less than 3 dB in entire azimuth plane. By adjusting the position of the antenna elements to form a back-to-back rotated antenna elements pairs to realize half-space omnidirectional radiation, ensuring the gain variation lower when scanning at low elevation angle, enhancing front-to-back ratio to achieve single-beam scanning and avoiding grating lobes in the array without adding reflectors. To verify the proposed design, an array prototype is fabricated and tested, with measured results consistent well with simulations. The array can realize reconfigurable 360° beam scanning with the gain variation less than 1.7 dB and axial ratios less than 3 dB. With advantages of circular polarization and reconfigurable 360° beam scanning, the proposed array has great potential usage in UAV communication.