Semi-active radar homing is a form of radar guidance, generally used for missiles, though it can be used for large-caliber gun rounds as well. In this mode, the firing platform, which can be an aircraft, a ship or a SAM emplacement, illuminates the target with a fire control radar. The missile then homes in on the reflected radar energy from the target.

Unlike beam-riding guidance or command guidance, the missile gets a clearer image the closer it gets to the target, and thus becomes more accurate at range, rather than less. Also, the radar of the launch platform, especially that of a large warship like a Slava class cruiser, can put out much more power than the seeker of a missile, allowing the illuminator to burn through some forms of jamming. The downside, however, is that most SARH missiles must have the target illuminated for the entire flight. This means that a single launcher can only engage as many units as it has illuminators. Also, in the case of an aircraft, the plane must hold its course to maintain a radar lock on the target. This makes it vulnerable to counterattack. Also, the constantly running guidance radar gives the enemy warning of an incoming missile and opens the launcher to counterattack with anti-radiation missiles.

Some more advanced SARH missiles, like the RIM-66 SM2-MR or the SA-N-6 Grumble var. Favorit only need illumination in the last few seconds of flight. Still others, like the aforementioned SM2, or the SA-N-20 Gargoyle have secondary infrared seekers for use in high-jamming environments and to compensate for lost radar locks.

Semi-active homing is most common on anti-air missiles, though some anti-tank missiles have used it as well.

Well-known examples of SARH missiles:

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