Unmanned aerial vehicles (UAVs) are gaining ground for civil and military applications, with their growing numbers emphasizing the importance of reliable communications links between operators and UAVs. For that purpose, researchers from several educational institutions in Spain developed a lightweight, embedded folded printed quadrifilar helix antenna (FPQHA) with wide-angle coverage for telemetry and remote-control systems in UAVs. The compact antenna and its feed network were designed for integration into the inner part of the UAV’s tail fuselage to reduce aerodynamic drag.
The antenna was designed for use at UHF, from 865 to 871 MHz with left-handed circular polarization (LHCP) and an omnidirectional radiation pattern. Target design specifications included an axial ratio (AR) of less than 3, a 3-dB beamwidth of 180 deg. (−90 to +90 deg.), more than 2.5 dB gain, and more than 15.3 dB cross-polarization discrimination. The antenna was constructed with low-loss, lightweight materials to reduce weight without compromising performance. It consists of a folded, printed, four-helix, radiating section and a compact feed network. It was designed with the aid of commercial 3D electromagnetic (EM) simulation software—CST Microwave Studio from Computer Simulation Technology—with a prototype fabricated according to the dimensions detailed in Microwave Studio.
The antenna was built and integrated inside the UAV’s fiberglass tail fuselage and measured in a spherical anechoic chamber. The antenna structure was fabricated on 0.127-mm-thick, low-loss commercial circuit substrate material with permittivity (εr) of 2.17. The feed network was formed of commercial 90-deg. hybrid circuits from Mini-Circuits on 0.4-mm-thick FR-4 PCB material. A number of measurements were performed on the prototype antenna, including radiation pattern, AR versus theta and versus frequency, gain, and S-parameters. The UAV’s fiberglass fuselage was found to have minimal effect on the antenna’s performance, which includes high gain across the frequency range and consistent axial ratio with frequency.
The embedded FPQHA provides wide-angle coverage from within the tail fuselage of a UAV, operating at UHF to provide telemetry and remote-control functions while adding little weight and volume to the UAV. The 50-Ω antenna and feed network feature less than 13.5-mm radius, length of less than 230 mm, and weight of less than 15 g. The compact antenna can be produced by means of low-cost manufacturing processes, making it a viable solution for UAV telemetry applications in civil and military areas.
See “An Embedded Lightweight Folded Printed Quadrifilar Helix Antenna,” IEEE Antennas & Propagation Magazine, Vol. 59, No. 3, June 2017, p. 69.