Semi-active radar homing (SARH) is a common type of missile guidance system, perhaps the most common type for longer-range air-to-air and surface-to-air missile systems. The name refers to the fact that the missile itself is only a passive detector of a radar signal – provided by an external (“offboard”) source — as it reflects off the target(in contrast to active radar homing, which uses an active radar: transceiver). Semi-active missile systems use bistatic continuous-wave radar. The NATO brevity code for a semi-active radar homing missile launch is Fox One.