Sekundaarradar

Sekundaarradar is a term that translates from Swedish as "secondary radar." It refers to a type of radar system that relies on transponders. Unlike primary radar, which detects reflected radio waves from an object, secondary radar interrogates a transponder carried by the target. The transponder then transmits a coded signal in response, providing additional information beyond just the target's location. This information can include identity, altitude, speed, and other operational data.

The fundamental principle of secondary radar involves an interrogator, typically a ground-based radar station, sending out a specific radio frequency pulse. This pulse triggers a transponder on an aircraft, ship, or other equipped vehicle. The transponder then replies with a coded signal on a different frequency. This coded reply is what the secondary radar receiver detects and decodes.

Secondary radar systems are widely used in air traffic control (ATC) for identifying and tracking aircraft. The Mode S transponder, for example, is a common standard in aviation that enables selective interrogation, allowing ATC to communicate directly with individual aircraft. It plays a crucial role in ensuring air safety by providing a reliable means of identifying friendly aircraft and distinguishing them from other radar contacts. Other applications include maritime surveillance and military identification friend or foe (IFF) systems. The reliance on transponders means that secondary radar is dependent on the target being equipped with and actively transmitting from such a device.