Lecture 3 - Radar and Air Defence Flashcards
What is radar and how does it work?
Radar is short for “radio detection and ranging”. Radar systems try to assess whether an incoming noise is statistically different from a random noise. Radar reflection.
Camouflage
Relevant to hider-finder competition. The goal is to blend in with the environment by minimising the differences between it and yourself.
X-band frequency
Frequency of fire-control radars. Has a high resolution for identification, tracking and engagement (missile guidance). (slide 40)
Which travel further, low or high frequency radar waves?
Low frequency radar waves travel longer distances, but they have lower resolution. –> identical to acoustics (slide 44)
Long-range detection
Ground-based radars can have a range of up to 400km. Airborne radars can have a range of up to 600-700km.
Speed of sound vs. Speed of light
The fastest missile or aircraft travels at supersonic or hypersonic speed (faster than sound). The slowest radar signals travel at the speed of light. While this difference in speed does not guarantee that an aircraft or missile can be intercepted (let alone easily), it does mean that air defence systems can “detect, identify and track an incoming missile or aircraft and still have time to pass this information to engagement systems.
Discrimination & the Doppler Shift
Distinguishing incoming (potential) threats from other objects and random noise. One way this can be achieved is by ignoring all static targets. Since the frequency of a radar pulse changes when it illuminates a moving object (“Doppler shift”), an operator can focus on moving targets by ignoring radar returns whose frequency does not vary. Furthermore, slow-moving objects can be identified (and ignored, as they are unlikely to be incoming jet fighters).
Identification
Identifying the specific object type. When illuminating an object with a narrow beam (high-frequency) radar pulse, it will produce unique radar returns. The radar system will then compare this unique return with a library of radar returns to find a high-probability match and thus identify the object.
What is tracking?
Tracking refers to the process of following an object with a radar pulse. This entails that the radar systems automatically changes the direction of the radar pulse so that it can keep illuminating the object of interest (i.e., predict the subsequent position). Tracking is critical for engagement (you want to know. Operators of air defence systems need to know where to aim and what to aim at (and the target may be warned by a radar warning receiver that they are being tracked).
What are the different types of radars, based on tracking/missile guidance ability?
Active radar: Radar on/integrated into missile. Emits radar pulse, tracks radar return of target and follows. “Fire-and-forget” missile that allows pilot to change course after firing.
Semi-active radar: Ground-based or airborne radar (usually jet fighter or fire-control radar from the surface-to-air battery that launched missile) illuminates the target. Missile has a radar receiver that guides the missile towards the radar reflection of the target.
Passive (not radar): Sensor that follows some specific feature of an aircraft (e.g., heat-seeking missiles following large sources of heat, such as emitted by engines of jet fighters).
Radar countermeasures
Chaff: Aluminium foils that were cut of a given size to maximise radar reflection, thus creating a large radar return on enemy’s radar screens. Would remain airborne for long due to being made out of aluminium. Primarily used during WWII.
Jamming: Interfering with the enemy’s radar signal.
Due to the curvature of the earth, flying at low altitudes is an effective way of avoiding radar detection (from ground-based radars).
What is a proximity fuze?
The proximity fuze was a detonation device that activated the explosive in the munition when it got close to a large metallic object, such as an aircraft. Thus, an aircraft didn’t need to be physically hit to be damaged anymore. The proximity fuze was guided by a small radar device.
What is stealth technology?
Stealth technology is a set of technologies aimed at reducing observability/visibility to enemy sensors (primarily radar, given its long range). The shape of stealth aircrafts is such that radar waves are deflected away, rather than reflected (slide 134). By reducing the range of detection, the reaction time available to enemy air defences is reduced. By reducing the radar cross section the range of detection decreases. (slide 150)
