What type of radar signal does a transponder respond to?

A transponder is a device on an aircraft that receives specific signals and responds by sending back information. The type of radar signal that a transponder responds to is known as interrogating radar signals. These signals are typically sent out by ground-based radar systems that are designed to engage with the transponder to obtain data such as the aircraft’s identification and altitude.

When an interrogating radar signal is transmitted, the transponder on the aircraft recognizes this signal and activates, sending back its own data. This interaction provides air traffic control with more detailed information about the aircraft, which is crucial for tracking and safety in busy airspace.

Other types of radar signals, such as ground radar or primary radar signals, do not induce this specific response from the transponder. Ground radar signals might be used for different purposes, such as tracking the position of an aircraft on the ground, while primary radar involves the detection of reflected signals without any specific interaction from a transponder. Weather radar signals are used to detect weather conditions and do not engage with transponders in the same manner.