Radar systems are complex but the below section will explain the three main radar types in simplistic terms for ease of understanding. The choice of a drone radar will depend on the detection range requirements, location, size of the facility to be protected, and the capital outlay.
Active Radar: A conventional radar uses a rotating antenna to sweep the sky, sending out radio pulses and detecting those which are reflected back from objects such as aircraft or drones. By measuring the time taken for the reflected signal to return, and its frequency shift, it is possible to determine the range, position and speed. To be effective at long range, radar systems require high power, often in the megawatt range. Active radars are more costly than passive and compact radars.
Passive Radar: Unlike an active radar, a passive radar system does not emit a radio wave but receives transmitted signals from other sources such as commercial broadcast and communications signals. When the signal it is receiving, is interrupted or reflected by an aircraft or drone, it causes a time delay between the arrival of the original broadcast signal and the reflected signal at the radar’s receiving antennae. By measuring the time difference, the frequency shift, the direction of the signal, the objects location, heading and speed can be calculated. Compared to active radar, passive radars have a lower procurement cost, lower maintenance costs due to the lack of transmitter and moving parts, are physically small and hence easily deployed in places where conventional radars cannot be, and lower operating costs as it relies on signals already in the air.
Compact Surveillance Radars: Compact surveillance radars have been traditionally used for the detection of ground targets. However, they have been enhanced by some manufacturers to specifically detect drones at ranges of 700 meters and across a wide field of view. These compact surveillance radars are cost effective, light weight, and compact which permits them to be mounted in many locations. However, they have limited range and capability and will not be suited to all facilities or locations.
The challenge for aircraft radars is that they are designed to detect large, fast moving objects, not drones with a small profile, that are flying slowly, and at low altitude. Drone radars are challenged with differentiating between a bird and a drone that results in false positives.