General Science

  • noun a device in an aircraft for receiving and automatically transmitting radio signals so that an air traffic control station can identify the aircraft



  • A radio or radar device that responds to a certain received signal by emitting a radio signal itself.


  • A device or system which incorporates both a transmitter and a receiver, and which emits the appropriate signals automatically when the specified trigger signals are received. Used, for instance, in satellite communications, or in radars. Also called responder (1).
  • In a communications satellite, a unit which receives a signal from one location, processes and amplifies it, and retransmits it to other locations. A single satellite may have many transponders. Also called satellite transponder.
  • synonymtransmitter-responder

Media Studies

  • noun a receiving and transmitting device in a communication or broadcast satellite that relays the signals it receives back to earth
  • noun a channel system on a satellite that allows it to send and receive many different signals simultaneously