Radar, which emits and measures reflections of electromagnetic waves to detect and locate objects, is used for a variety of UAV and drone-related applications in both civil and military contexts.
Surveillance radar systems used for tracking unmanned aircraft in civil airspace may be either primary surveillance radar (PSR) or secondary surveillance radar (SSR).
PSR – Primary Surveillance Radar
Primary surveillance radar uses echolocation via high-power electromagnetic pulses, capturing reflected waves from targets in the airspace. PSR systems operate completely independently of the target aircraft, but cannot directly identify the targets.
SSR – Secondary Surveillance Radar
Secondary radar relies on UAVs being fitted with a radar transponder, which when interrogated by a radar pulse will broadcast information such as aircraft ID. SSR systems can provide more detailed information, but rely on targets being equipped with drone transponders.
Detection & Tracking Radar
Drone tracking radar can be used to protect against drone threats, either from hostile operators or from drone pilots who accidentally allow their aircraft to fly too close to sensitive sites such as airports or government buildings. Drone surveillance radar is often used as part of a comprehensive anti-drone solution, complementing other devices such as RF sensors and cameras. The layering of different counter-UAV technologies into a single solution helps provide more comprehensive threat protection and also reduces the likelihood of false positive alarms. These sensors may also be integrated with a variety of drone countermeasures such as jammers, nets and lasers.
Smart detection capabilities allow drone radars to classify drones as distinct objects without mistaking them for birds or other flying objects. Radar signatures can be compared against a database of known drone types, and artificial intelligence and machine learning software can be used to further improve the accuracy of results. Micro-doppler radar can also be used, which is able to detect the speed differences between different moving parts of an object, and can thus identify drones by their propellers.
UAV radars can operate independently of weather and lighting conditions, unlike many electro-optical sensors. They are able to detect autonomous drones, while RF sensors must rely on detecting the signals sent between manually-operated drones and their pilots. The ease with which a UAV can be detected by a radar depends on its radar cross section (RCS), which is a function of the size of the UAV and how much reflective material it contains. Drones with larger RCS can be detected at greater distances.
Ground Surveillance Radars
In many jurisdictions, aircraft flying in civilian airspace are required to have some way of seeing and avoiding other aircraft – a capability that for manned aircraft is provided by the pilot onboard. One solution for unmanned aircraft is to use ground-based sense and avoid (GBSAA) systems, which may utilise ground surveillance radars and do away with the need for human spotters or manned chase planes.
GBSAA surveillance radars can detect airspace traffic, and are able to provide real-time tracking based on the known GPS coordinates of the radar and the distance and angle of the target. This information can be transmitted to the drone operator, providing situational awareness for safe flight at all times.