Primary/Secondary Surveillance Radar (PSR/SSR)

PSR and SSR radars constitute air traffic surveillance systems. The main feature of PSR is that it works with passive echoes. The high frequency pulses sent are reflected from the target and are received again by the radar device.

SSR also send high frequency pulses. However, these incoming pulses are not simply reflected by the target, they are received by the transponder located on the target and processed there. The transponder then prepares a response telegram at a different frequency and sends it to the radar.