Active radar homing
Active radar homing (ARH) is a missile guidance method in which a missile contains a radar transceiver (in contrast to Semi-active radar homing, which uses only a receiver) and the electronics necessary for it to find and track its target autonomously. NATO brevity code for an air-to-air active radar homing missile launch is Fox Three.
Advantages
There are two major advantages to active radar homing:
Because the missile is tracking the target, and the missile is typically going to be much closer to the target than the launching platform during the terminal phase, the tracking can be much more accurate and also have better resistance to ECM. Active radar homing missiles have some of the best kill probabilities, along with missiles employing track-via-missile guidance.
Because the missile is totally autonomous during the terminal phase, the launch platform does not need to have its radar enabled at all during this phase, and in the case of a mobile launching platform like an aircraft, can actually exit the scene or undertake other actions while the missile homes in on its target. This is often referred to as fire-and-forget capability and is a great advantage that modern air-to-air missiles have over their predecessors.