Air to Air Weapons

Air-to-Air Missile (AAM) is a missile fired from an aircraft for the purpose of destroying another aircraft (also including unmanned aircraft such as cruise missiles). Most common AAM use by USAF AMRAAM (AIM-120) and Sidewinder (AIM-9).

This illustration showcases the three primary air-to-air missiles (AAM) used in US modern aerial combat.

Semi-Active Radar-Homing Missile (Fox 1 – AIM-7 Sparrow)

Semi-active radar Homing (SARH) is a method used by missiles such as the AIM-7 Sparrow to track and destroy air targets. In this guided system, the missile does not generate its own radar signal to locate the target. Instead, it relies on an external radar source (typically the aircraft that launched the missile) to illuminate and track the target. The missile's onboard receiver then detects the reflected radar energy bouncing off the target and uses this information to home in.

How It Works

1. Target Illumination: The launching aircraft’s radar "illuminates" the target, sending a continuous radar signal towards it.
2. Reflection Detection: The missile’s seeker head picks up the radar energy reflected off the target.
3. Guidance: The missile uses the information from the reflected signal to adjust its trajectory toward the target.

Advantages

• Longer Engagement Range: Semi-active radar-guided missiles can engage targets at greater distances because the aircraft radar is typically more powerful than a missile-mounted radar.
• Simplicity in Missile Design: Since the missile doesn't have its own active radar, it is relatively simple and less expensive compared to active radar-guided missiles.

Disadvantages

• Continuous Illumination Required: The launching aircraft must keep its radar locked on the target throughout the missile's flight. This limits the aircraft's ability to maneuver or engage multiple targets at once.
• Vulnerability to Jamming: Semi-active radar systems are vulnerable to electronic countermeasures. If the target employs jamming or chaff, it can confuse the radar signal, causing the missile to lose track of the target.

Infrared-Guided Missile (Fox 2 – AIM-9 Sidewinder)

Infrared-guided (IR) missiles, like the AIM-9 Sidewinder, are also known as heat-seeking missiles because they use infrared radiation (which is essentially heat) to home in on targets. Most aircraft engines emit large amounts of heat through their exhaust, making them prime targets for infrared-guided missiles.

How It Works

1. Heat Detection: The missile has a seeker that senses infrared radiation, which is particularly strong from the hot exhaust of jet engines.
2. Target Acquisition: Once launched, the missile homes in on the strongest heat source it can detect, which is usually the rear of an enemy aircraft.
3. Guidance and Impact: The missile continually adjusts its path to intercept the heat signature of the target. Infrared missiles are typically "fire-and-forget" weapons, meaning that once launched, the missile does not require further input from the launching aircraft.

Advantages

• Fire-and-Forget Capability: Once the missile locks onto a heat source, the launching aircraft is free to maneuver or engage other targets.
• Stealthier: Since infrared-guided missiles don’t rely on active radar signals, they are less detectable by radar warning receivers on enemy aircraft.
• Low Altitude Capability: Unlike radar-guided missiles, infrared-guided systems can function well at low altitudes where radar performance may be degraded by ground clutter.

Disadvantages

• Susceptibility to Flares: Infrared-guided missiles can be confused by countermeasures like flares—decoy heat sources designed to mislead the missile’s seeker.
• Limited Aspect Use: Earlier infrared missiles could only lock onto the rear of the target (where the engine’s exhaust is hottest), know as Rear-aspect missile. However, modern variants can engage targets from all angles, know as All-aspect missile.

Active Radar-Homing Missile (Fox 3 – AIM-120 AMRAAM)

Active radar (AR)-guided missiles, like the AIM-120 AMRAAM, have their own radar system to detect and lock onto targets. This means that after the missile is launched, it can find, track, and engage the target autonomously without needing continuous radar support from the launching aircraft.

How It Works

1. Initial Launch Phase (Pre-A-Pole): The missile is launched with guidance data from the aircraft’s radar, including the target’s location and trajectory. Initially, the missile is guided using these external commands, known as mid-course guidance.
2. Active Radar Activation (A-Pole): As the missile approaches the target, its onboard active radar turns on with High Pulse Repetition Frequency radar mode and begins scanning for the target independently, known as "HPRF active".
3. Terminal Guidance (M-Pole): In the final phase, the missile locks onto the target using its own radar system, radar mode switches to Medium Pulse Repetition Frequency, known as "MPRF active", homing in to ensure an accurate hit.

Advantages

• True Fire-and-Forget Capability: Once the missile’s radar goes active, the launching aircraft is free to maneuver or engage other threats, making the missile highly versatile in combat.
• Engage Multiple Targets: Active radar-guided missiles allow aircraft to engage multiple targets simultaneously since they don’t require continuous target illumination.
• High Kill Probability: The combination of mid-course guidance (from the aircraft) and terminal active radar guidance (from the missile) gives these missiles a high probability of hitting the target, even in complex electronic warfare environments.

Disadvantages

• More Expensive and Complex: Active radar systems are more technologically advanced and expensive to produce.
• Detectability: Once the missile’s radar goes active, the target may be alerted to the incoming threat and could deploy countermeasures or evasive maneuvers.
• Vulnerability to Jamming: While more resistant than semi-active systems, active radar-guided missiles can still be affected by sophisticated electronic warfare countermeasures.

Guidance Type	Targeting Method	Advantages	Disadvantages
Semi-Active Radar (Fox 1)	Relies on aircraft radar to illuminate target	Long-range engagements, simple missile design	Aircraft must maintain radar lock, vulnerable to ECM jamming
Infrared (Fox 2)	Homes in on heat (infrared) emitted by target	Fire-and-forget, stealthy, effective at low altitudes	Vulnerable to flares, early models (ex AIM-9P) limited to rear attacks
Active Radar (Fox 3)	Missile has its own onboard radar	True fire-and-forget, can engage multiple targets	Expensive, target may detect missile when radar activates