Low probability of intercept
Encyclopedia
A low-probability-of-intercept radar (LPIR) is designed to be difficult to detect by passive radar detection equipment (such as a radar warning receiver
– RWR) while it is searching for a target or engaged in target tracking. This characteristic is desirable in a radar
because it allows finding and tracking an opponent without alerting them to the radar's presence.
Ways of reducing the profile of a radar include using wider-frequency bandwidth (wideband
), frequency hopping, using a frequency-modulated continuous-wave signal, and using only the minimum power required for the task. Using pulse compression
also reduces the probability of detection, since the peak transmitted power is lower while the range and resolution is the same.
Constructing a radar so as to emit minimal side and back lobes may also reduce the probability of interception when it is not pointing at the radar warning receiver. However, when the radar is sweeping a large volume of space for targets, it is likely that the main lobe will repeatedly be pointing at the RWR. Modern phased-array radars not only control their side lobe
s, they also use very thin, fast-moving beams of energy in complicated search patterns. This technique may be enough to confuse the RWR so it does not recognize the radar as a threat, even if the signal itself is detected. All military EM
(EM) emitters, including fighter aircraft
, naval ship
s, and missile
systems are designed for reduced electromagnetic profiles for improved stealth.
In addition to stealth considerations, reducing side and back lobes is desirable as it makes the radar more difficult to characterise. This can increase the difficulty in determining which type it is (concealing information about the carrying platform) and make it much harder to jam
.
Systems that feature LPIR include modern Active Electronically Scanned Array
(AESA) radars such as that on the F/A-18E/F Super Hornet
and the electronically steered phased array
on the S-300PMU-2 missile.
Radar warning receiver
Radar warning receiver systems detect the radio emissions of radar systems. Their primary purpose is to issue a warning when a radar signal that might be a threat is detected. The warning can then be used, manually or automatically, to evade the detected threat...
– RWR) while it is searching for a target or engaged in target tracking. This characteristic is desirable in a radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
because it allows finding and tracking an opponent without alerting them to the radar's presence.
Ways of reducing the profile of a radar include using wider-frequency bandwidth (wideband
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....
), frequency hopping, using a frequency-modulated continuous-wave signal, and using only the minimum power required for the task. Using pulse compression
Pulse compression
Pulse compression is a signal processing technique mainly used in radar, sonar and echography to increase the range resolution as well as the signal to noise ratio...
also reduces the probability of detection, since the peak transmitted power is lower while the range and resolution is the same.
Constructing a radar so as to emit minimal side and back lobes may also reduce the probability of interception when it is not pointing at the radar warning receiver. However, when the radar is sweeping a large volume of space for targets, it is likely that the main lobe will repeatedly be pointing at the RWR. Modern phased-array radars not only control their side lobe
Side lobe
In antenna engineering, side lobes or sidelobes are the lobes of the far field radiation pattern that are not the main lobe....
s, they also use very thin, fast-moving beams of energy in complicated search patterns. This technique may be enough to confuse the RWR so it does not recognize the radar as a threat, even if the signal itself is detected. All military EM
Electromagnetic radiation
Electromagnetic radiation is a form of energy that exhibits wave-like behavior as it travels through space...
(EM) emitters, including fighter aircraft
Fighter aircraft
A fighter aircraft is a military aircraft designed primarily for air-to-air combat with other aircraft, as opposed to a bomber, which is designed primarily to attack ground targets...
, naval ship
Naval ship
A naval ship is a ship used for combat purposes, commonly by a navy. Naval ships are differentiated from civilian ships by construction and purpose...
s, and missile
Surface-to-air missile
A surface-to-air missile or ground-to-air missile is a missile designed to be launched from the ground to destroy aircraft or other missiles...
systems are designed for reduced electromagnetic profiles for improved stealth.
In addition to stealth considerations, reducing side and back lobes is desirable as it makes the radar more difficult to characterise. This can increase the difficulty in determining which type it is (concealing information about the carrying platform) and make it much harder to jam
Radar jamming and deception
Radar jamming and deception is the intentional emission of radio frequency signals to interfere with the operation of a radar by saturating its receiver with noise or false information...
.
Systems that feature LPIR include modern Active Electronically Scanned Array
Active Electronically Scanned Array
An Active Electronically Scanned Array , also known as active phased array radar is a type of phased array radar whose transmitter and receiver functions are composed of numerous small solid-state transmit/receive modules . AESAs aim their "beam" by broadcasting radio energy that interfere...
(AESA) radars such as that on the F/A-18E/F Super Hornet
F/A-18E/F Super Hornet
The Boeing F/A-18E/F Super Hornet is a twin-engine carrier-based multirole fighter aircraft. The F/A-18E single-seat variant and F/A-18F tandem-seat variant are larger and more advanced derivatives of the F/A-18C and D Hornet. The Super Hornet has an internal 20 mm gun and can carry air-to-air...
and the electronically steered phased array
Phased array
In wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
on the S-300PMU-2 missile.