transponder

American  

[tran-spon-der] / trænˈspɒn dər /

Or transpondor

noun

1. a radio, radar, or sonar transceiver that automatically transmits a signal upon reception of a designated incoming signal.

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transponder British  

/ trænˈspɒndə /

noun

1. a type of radio or radar transmitter-receiver that transmits signals automatically when it receives predetermined signals

2. the receiver and transmitter in a communications or broadcast satellite, relaying received signals back to earth

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transponder Scientific  

/ trăn-spŏn′dər /

1. A radio or radar transmitter and receiver that responds to an incoming signal either by broadcasting its own predetermined signal (as in aircraft identification systems) or by relaying the incoming signal at a different frequency (as in satellite communications).

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Etymology

Origin of transponder

First recorded in 1940–45; trans(mitter) + (res)ponder

Example Sentences

Homendy added that the runway safety system ASDE-X, designed to track aircraft and ground vehicles, did not generate an alert before the crash because the fire truck was not equipped with a transponder.

From Barron's • Mar. 24, 2026

These efforts could, for example, make the International Maritime Organization’s transponder system truly universal, with important collateral health and safety benefits.

From The Wall Street Journal • Feb. 18, 2026

They said the plane was broadcasting its military number through the transponder, but the boat targeted in the strike likely lacked the equipment to read the radio signal identifying the plane.

From Salon • Jan. 13, 2026

He said that in order to fly in civilian airspace, the military helicopter would have needed to be fitted with a transponder alerting surrounding aircraft to its position.

From BBC • Jan. 30, 2025

One file held what appeared to be a list of satellite and microwave dish coordinates—longitude, latitudes, transponder frequencies.

From Underground by Dreyfus, Suelette