Secondary radar

4-3-010

Radar in which the target is fitted with a transponder (4-3-420) to re-transmit automatically on the same frequency as the interrogating frequency, or a different frequency. The response may be coded or delayed by a known duration (or both) to provide identification, and to allow the range to be measured.

Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)