Improving Radar Detection of Drones and Air Mobility Systems in Urban Areas

Drones are used for a broad series of civil and commercial applications. The cost-performance ratio, the compact size and the automation level allow several applications, such as precision agriculture, infrastructure inspection, package delivery, and search and rescue. The large variety of missions requires the definition of a set of regulation and requirements for the airspace in which the Unmanned Aerial Vehicles are supposed to fly and for the involved systems. A challenging problem for the Unmanned Aerial System Traffic Management is performing external surveillance of their travelled path during a mission. This task includes detection, identification, and tracking of drones. This is required by traffic assistance authorities worldwide to provide real time alert in case the current route of drones can be source of potential risk for people and buildings. Their operational environment is characterized by several obstacles, vehicles and objects. Radars can be an effective solution to provide independent surveillance. Anyway, the radar cross section of a drone is typically small; consequently, drones cannot be reliably detected and distinguished from other elements, even birds. Moreover, they fly close to the ground where the effect of ground clutter is degrading radar surveillance performance. To improve this gap, in this paper two solutions are prosed to enhance the radar cross section of small drones. The first one concerns the use of a passive on-board system, whereas the second one concerns the implementation of an active on-board system. Tests were performed by using an octahedral corner reflector as passive system, while a Software Defined Radio was used as active system. On-ground and in-flight tests were realized to demonstrate the feasibility of the two proposed solutions.