How does radar work?

Radar is an acronym for Radio Detection And Ranging. An environment is searched for objects by transmitting and receiving radio waves. Using the received radio waves, the size, direction, distance, height and speed of the object can be determined.

After the discovery of electromagnetic waves by James Maxwell in 1865, it was Christian Hülsmeyer who first developed a radar in 1904. This radar, then called a Telemobiloscope, could transmit, reflect and receive radio waves and thus detect metal objects. At that time, aviation was still in its infancy, which meant that the first radar installations would be built on ships. The first demonstration of the Telemobiloscope was able to detect ships up to three kilometers away. Despite great interest from the shipping world, Hülsmeyer was unable to build a properly functioning installation. The first radar prototypes were not developed until 1939 by the Dutch engineer Max Staal. These radars used a pulse system as it is still used today

A radar works by means of a transmitting and a receiving antenna. The transmitting antenna emits a radio wave, when it is reflected by an object the radio wave is picked up again by the receiving antenna. Because electromagnetic waves move through the air at a constant speed, the distance can be determined by the time difference between transmitting and receiving.

The constant speed of these electromagnetic waves is equal to the speed of light, rounded up to 300,000 kilometers per second. The time between the pulses of the radars is called the frequency, this frequency is expressed in Hertz (Hz). The number of Hertz indicates the number of pulses per second.

The distance of the object can be determined by the following equation;
R (distance) = (C0 x t) / 2
Where C0 = speed of light (3*108 m/s) and t = transit time (s)

This distance can then be plotted in a radar screen. This provides insight into where a detected object is located. A plot of a 270 degree setup looks like this.

Ground surveillance

This radar principle is perfect as an alarm for outdoor detection. Radio waves are not affected by weather factors and smaal movements. In addition, radio waves can be filtered so that only large objects can be detected. By forwarding the radar detections to the cameras, they will only record and forward to the control room after a reliable detection. Due to these reliable detections, false reports can be reduced and therefore also the associated costs to control rooms and security services.