How do surface-to-air missile systems use radar to intercept aircraft?

Surface-to-air missile (SAM) systems integrate radar to detect, track, and intercept aircraft through several sophisticated guidance methods. These systems typically utilize a central control unit that coordinates radar sighting, target identification, and missile guidance.1

The primary ways radar facilitates interception include:

• Semiactive Homing: The launch site illuminates the target with radar energy. A seeker in the missile detects the energy reflected off the aircraft and uses it to home in on the target, often measuring the Doppler shift to calculate an intercept trajectory.2
• Command Guidance: The system tracks both the target and the missile from the ground. It then transmits steering commands to the missile via radio or radar impulses. A specialized form, "track-via-missile," involves the missile itself tracking the target and relaying data to the ground, where computers calculate the optimal path.3
• Active Homing: Some missiles carry self-contained radar systems, allowing them to track the target independently during the terminal phase of flight.4
• Beam Riding: The missile senses a radar beam pointed at the target and automatically adjusts its flight path to remain within that beam.3

Additionally, radar-based proximity fuzes are often employed to trigger the warhead when the missile is within an effective range of the aircraft.56