Secondary surveillance radar is partly a communication system between aircraft and air traffic controllers on the ground; a limited amount of information (aircraft height and flight identification number) is requested by an interrogator on the ground and automatically supplied by a transponder on the aircraft. In the future, this flow of information will increase. Secondary surveillance radar also acts as a radar system because the position of the aircraft is found by measuring the range (from the time delay between interrogation and reply) and the azimuth, as measured by an antenna on the ground. Many of the early problems with SSR have now been solved, and the system is in widespread use throughout the world.

Chapter Contents:

• 7.1 Introduction
• 7.2 Basic principles
• 7.3 Problems with secondary surveillance radar
• 7.4 Multipath
• 7.5 Mode S and the future
• 7.6 Summary
• 7.7 References
• 7.8 Problems

Inspec keywords: airborne radar; transponders; distance measurement; antennas; search radar; air traffic control

Other keywords: transponder; air traffic controller; communication system; aircraft; secondary surveillance radar; antenna; range measurement

Subjects: Radar equipment, systems and applications; Air traffic control and navigation; Spatial variables measurement; Single antennas