Active radar homing
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Active radar homing is a missile guidance method in which a guided missile contains a radar transceiver and the electronics necessary for it to find and track its target autonomously. NATO brevity code for an active radar homing missile launch is Fox Three.
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.
There are three major disadvantages to active radar homing:
- Since the missile has to contain an entire radar transceiver and electronics, it was until recently difficult to fit all of this into a missile without unacceptably increasing its size and weight. Even with today's miniaturisation making this possible, it is quite expensive to make these missiles since the sophisticated electronics within the missile are inevitably destroyed upon impact.
- There is very little chance that targets with capable modern radar warning receiver would be unaware that an incoming missile is approaching them. This gives them sufficient time to take evasive action and deploy countermeasures. However, given the accuracy of this homing method, unless the target is especially maneuverable or the missile is not, there may not be much they can do to avoid being intercepted.
- ARH-type missiles lose their effectiveness the closer the target is. Therefore, these types of missiles with this mounted equipment are only effective in long range confrontations.
Passive radiation homing 
Many missiles employing this type of guidance have an extra trick up their sleeves; If the target does attempt to use noise jamming, they can in effect turn into an anti-radiation missile and home in on the target's radiation passively. This makes such missiles practically immune to noise jamming, in addition to removing the second disadvantage. Since they already have the radar receiver on board, this should not be a difficult feature to add (at least, it requires extra processing logic but little extra hardware).
Active radar homing is rarely employed as the only guidance method of a missile. It is most often used during the terminal phase of the engagement, mainly because since the radar transceiver has to be small enough to fit inside a missile and has to be powered from batteries, therefore having a relatively low ERP, its range is limited. To overcome this, most such missiles use a combination of command guidance with an inertial navigation system (INS) in order to fly from the launch point until the target is close enough to be detected and tracked by the missile. The missile therefore requires guidance updates via a datalink from the launching platform up until this point, in case the target is maneuvering, otherwise the missile may get to the projected interception point and find that the target is not there. Sometimes the launching platform (especially if it is an aircraft) may be in danger while continuing to guide the missile in this way until it 'goes active'; In this case it may turn around and leave it to luck that the target ends up in the projected "acquisition basket" when the missile goes active. It is possible for a system other than the launching platform to provide guidance to the missile before it switches its radar on; This may be other, similar fighter aircraft or perhaps an AWACS.
List of missiles 
Examples of missiles known to use active radar homing (all in their terminal phase) include:
- MBDA Meteor air-to-air missile (With contribution from France, Germany, Italy, Spain, Sweden and United Kingdom)
- DRDO-Astra BVRAAM air-to-air missile
- Type 80 Air-to-Ship Missile
- Type 81 Surface-to-air Missile (SAM-1C only)
- Type 88 Surface-to-Ship Missile
- Type 90 Ship-to-Ship Missile
- Type 91 Air-to-Ship Missile
- Type 99 air-to-air missile (Mitsubishi AAM-4, AAM-4Kai)
- Type 03 Medium-Range Surface-to-Air Missile
- Type 11 Surface-to-air Missile
- NPO Novator and DRDO R-172 long range air-to-air missile
- Vympel NPO R-37 (AA-13 Arrow) long range air-to-air missile
- Vympel NPO R-77 (AA-12 Adder) medium range air-to-air missile
- Vympel NPO R-27 (AA-10 Alamo) medium range air-to-air missile (R-27AE version only)
- Tactical Missiles Corporation Kh-31 (AS-17 Krypton) anti-shipping missile (Kh-31A only)
- Raduga Kh-15 (AS-16 Kickback) air-to-surface missile (Kh-15S only)
- Raduga Kh-59 (AS-13 Kingbolt) air-to-surface missile (Kh-59MK only)
- Tactical Missiles Corporation Kh-25 (AS-10 Karen) air-to-surface missile (Kh-25MA only)
- Raduga KSR-5 (AS-6 Kingfish) anti-shipping missile
- Raduga KSR-2 (AS-5 Kelt) anti-shipping missile
- Raduga Kh-22 (AS-4 Kitchen) anti-shipping missile
- KBM Khrizantema (AT-15 Springer) anti-tank missile (9M123-2 and 9M123F-2 variants only)
- NPO Almaz S-400 Triumf (SA-21 Growler) surface-to-air missile
- NPO Mashinostroyeniya P-500 Bazalt (SS-N-12 Sandbox) anti-ship missile
- NPO Mashinostroyeniya P-700 Granit (SS-N-19 Shipwreck) anti-ship missile
- Raduga P-270 Moskit (SS-N-22 Sunburn) anti-ship missile
- Tactical Missiles Corporation Kh-35 (SS-N-25 Switchblade) anti-ship missile
- NPO Mashinostroyeniya P-800 Oniks (SS-N-26) anti-ship missile
- NPO Novator 3M-54 Klub (SS-N-27 Sizzler) anti-ship missile
South Africa 
- Sky Sword II air-to-air missile
United States 
- Boeing Harpoon anti-ship missile
- Lockheed Martin AGM-114L Hellfire Longbow air-to-surface missile
- Lockheed Martin MIM-104 PATRIOT surface-to-air missile (PAC-3 version only)
- Raytheon AIM-120 AMRAAM air-to-air missile and surface-to-air missile
- Raytheon RIM-174 Standard ERAM (Standard Missile 6) surface-to-air missile
- The U.S. Navy's Bat radar-guided glide bomb of World War II, world's earliest munition design known to use an active radar homing system.
- ausairpower.net: "Active and Semiactive Radar Missile Guidance" (retrieved 6 April 2010)
- designation-systems.net: "Directory of US Military Rockets and Missiles" (retrieved 6 April 2010)