How do air-to-air missiles such as the Sidewinder and Sparrow use different guidance systems?

Air-to-air missiles like the AIM-9 Sidewinder and the AIM-7 Sparrow utilize fundamentally different guidance technologies to track and intercept targets.

• Sidewinder (Infrared Homing): The Sidewinder is a heat-seeking missile. It uses a seeker head sensitive to infrared radiation, allowing it to home in on the thermal emissions—specifically the exhaust—from a target aircraft’s engines. While early models were restricted to rear-aspect attacks, later versions feature sophisticated seekers capable of detecting emissions from the side or front of an aircraft.1
• Sparrow (Semiactive Radar Homing): The Sparrow employs semiactive radar guidance. In this system, the target is illuminated by radar energy from an external source, typically the launching aircraft. The missile’s onboard seeker detects the radar energy reflected off the target and uses that signal to compute an intercept trajectory.12

Because these systems rely on different physical phenomena—thermal radiation versus reflected radar waves—fighter aircraft are often armed with both types to maintain tactical flexibility across various combat situations.1