Development of secondary surveillance radar for air-traffic control

With the increasing volume of air traffic, radar aids to air-traffic control are becoming essential, not only in the vicinity of airports but in any fairly congested area. For secondary surveillance radar (s.s.r.) it is necessary to have similar airborne equipments in aircraft of all the nationalities requiring service from the system. A standard specification for s.s.r. has been agreed on by the International Civil Aviation Organisation.