Electronic counter-countermeasures
Encyclopedia
Electronic counter-countermeasures (ECCM) is a part of electronic warfare
which includes a variety of practices which attempt to reduce or eliminate the effect of electronic countermeasures
(ECM) on electronic sensor
s aboard vehicles, ships and aircraft and weapons such as missiles. ECCM is also known as electronic protective measures (EPM), chiefly in Europe
. In practice, EPM often means resistance to jamming
.
is radar jamming or spoofing
. This originated with the Royal Air Force
use of what they codenamed window during World War II
, which is now often referred to as chaff
. Jamming also may have originated with the British during World War II, when they began jamming German
radio
communications.
In perhaps the first example of ECCM, the Germans increased their radio transmitter power in an attempt to 'burn through' or override the British jamming, which by necessity of the jammer
being airborne or further away produced weaker signals. This is still one of the primary methods of ECCM today. For example, modern airborne jammers are able to identify incoming radar
signals from other aircraft and send them back with random delays and other modifications in an attempt to confuse the opponent's radar set, making the 'blip' jump around wildly and be impossible to range. More powerful airborne radars means that it is possible to 'burn through' the jamming at much greater ranges by overpowering the jamming energy with the actual radar returns. The Germans were not really able to overcome the chaff spoofing very successfully and had to work around it (by guiding the aircraft to the target area and then having them visually acquire the targets).
Today, more powerful electronics with smarter software for operation of the radar might be able to better discriminate between a moving target like an aircraft and an almost stationary target like a chaff bundle.
With the technology going into modern sensors and seekers, it is inevitable that all successful systems have to have ECCM designed into them, lest they become useless on the battlefield. In fact, the 'electronic battlefield' is often used to refer to ECM, ECCM and ELINT activities, indicating that this has become a secondary battle in itself.
of sensors through techniques such as increasing power or improving discrimination):
technique, is boosting the apparent signal strength as perceived by the radar receiver. The outgoing radar pulses are chirp
ed, that is, the frequency of the carrier is varied within the pulse, much like the sound of a cricket chirping. When the pulse reflects off a target and returns to the receiver, the signal is processed to add a delay as a function of the frequency. This has the effect of 'stacking' the pulse so it seems stronger, but shorter in duration, to further processors. The effect can increase the received signal strength to above that of noise jamming. Similarly, jamming pulses (used in deception jamming) will not typically have the same chirp, so will not benefit from the increase in signal strength.
agility ('frequency hopping') may be used to rapidly switch the frequency of the transmitted energy, and receiving only that frequency during the receiving time window. This foils jammers which cannot detect this frequency switch quickly enough, and switch their own jamming frequency accordingly during the receiving time window.
This method is also useful against barrage jamming
, in that it forces the jammer to spread its jamming power across multiple frequencies in the jammed system's frequency range, reducing its power in the actual frequency used by the radar at any one time. The use of similar spread-spectrum techniques allow signals to be spread over a wide enough spectrum to make jamming of such a wideband signal difficult.
antenna is used for a comparison signal. By comparing the signal strength as received by both the omnidirectional and the (directional) main antenna, signals can be identified that are not from the direction of interest. These signals are then ignored.
Aside from power loss to the jammer, radar receivers can also benefit from using two or more antennas of differing polarity and comparing the signals received on each. This effect can effectively eliminate all jamming of the wrong polarity, although enough jamming may still obscure the actual signal.
missiles like the Vympel R-77
and the AMRAAM are able to home in directly on sources of radar jamming if the jamming is too powerful to allow them to find and track the target normally. This mode, called 'home-on-jam', actually makes the missile's job easier. Some missile seekers actually target the enemy's radiation sources, and are therefore called "anti-radiation missile
s" (ARM). The jamming in this case effectively becomes a beacon announcing the presence and location of the transmitter
. This makes the use of such ECM a difficult decision; it may serve to obscure an exact location from a non-ARM missile, but in doing so it must emit signals which can be exploited by an ARM type missile.
Electronic warfare
Electronic warfare refers to any action involving the use of the electromagnetic spectrum or directed energy to control the spectrum, attack an enemy, or impede enemy assaults via the spectrum. The purpose of electronic warfare is to deny the opponent the advantage of, and ensure friendly...
which includes a variety of practices which attempt to reduce or eliminate the effect of electronic countermeasures
Electronic countermeasures
An electronic countermeasure is an electrical or electronic device designed to trick or deceive radar, sonar or other detection systems, like infrared or lasers. It may be used both offensively and defensively to deny targeting information to an enemy...
(ECM) on electronic sensor
Sensor
A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...
s aboard vehicles, ships and aircraft and weapons such as missiles. ECCM is also known as electronic protective measures (EPM), chiefly in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
. In practice, EPM often means resistance to jamming
Radio jamming
Radio jamming is the transmission of radio signals that disrupt communications by decreasing the signal to noise ratio. Unintentional jamming occurs when an operator transmits on a busy frequency without first checking whether it is in use, or without being able to hear stations using the frequency...
.
History
Ever since electronics have been used in battle in an attempt to gain superiority over the enemy, effort has been spent on techniques to reduce the effectiveness of those electronics. More recently, sensors and weapons are being modified to deal with this threat. One of the most common types of ECMElectronic countermeasures
An electronic countermeasure is an electrical or electronic device designed to trick or deceive radar, sonar or other detection systems, like infrared or lasers. It may be used both offensively and defensively to deny targeting information to an enemy...
is radar jamming or spoofing
Spoofing attack
In the context of network security, a spoofing attack is a situation in which one person or program successfully masquerades as another by falsifying data and thereby gaining an illegitimate advantage.- Spoofing and TCP/IP :...
. This originated with the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
use of what they codenamed window during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, which is now often referred to as chaff
Chaff (radar countermeasure)
Chaff, originally called Window by the British, and Düppel by the Second World War era German Luftwaffe , is a radar countermeasure in which aircraft or other targets spread a cloud of small, thin pieces of aluminium, metallized glass fibre or plastic, which either appears as a cluster of secondary...
. Jamming also may have originated with the British during World War II, when they began jamming German
History of Germany during World War II
The history of Germany during World War II closely parallels that of Nazi Germany under Adolf Hitler. He came to power in Germany in 1933. From that point onward, Germany followed a policy of rearmament and confrontation with other countries...
radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
communications.
In perhaps the first example of ECCM, the Germans increased their radio transmitter power in an attempt to 'burn through' or override the British jamming, which by necessity of the jammer
Jammer
Jammer may refer to:* Jammer keyboard* Jammer, a device used in radar jamming and deception, a technique in electronic warfare to inhibit or halt the transmission of signals* Swim jammer, a type of male competitive swimwear...
being airborne or further away produced weaker signals. This is still one of the primary methods of ECCM today. For example, modern airborne jammers are able to identify incoming 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...
signals from other aircraft and send them back with random delays and other modifications in an attempt to confuse the opponent's radar set, making the 'blip' jump around wildly and be impossible to range. More powerful airborne radars means that it is possible to 'burn through' the jamming at much greater ranges by overpowering the jamming energy with the actual radar returns. The Germans were not really able to overcome the chaff spoofing very successfully and had to work around it (by guiding the aircraft to the target area and then having them visually acquire the targets).
Today, more powerful electronics with smarter software for operation of the radar might be able to better discriminate between a moving target like an aircraft and an almost stationary target like a chaff bundle.
With the technology going into modern sensors and seekers, it is inevitable that all successful systems have to have ECCM designed into them, lest they become useless on the battlefield. In fact, the 'electronic battlefield' is often used to refer to ECM, ECCM and ELINT activities, indicating that this has become a secondary battle in itself.
Specific ECCM techniques
The following are some examples of EPM (other than simply increasing the fidelityFidelity
"Fidelity" is the quality of being faithful or loyal. Its original meaning regarded duty to a lord or a king, in a broader sense than the related concept of fealty. Both derive from the Latin word fidēlis, meaning "faithful or loyal"....
of sensors through techniques such as increasing power or improving discrimination):
ECM detection
Sensor logic may be programmed to be able to recognize attempts at spoofing (e.g., aircraft dropping chaff during terminal homing phase) and ignore them. Even more sophisticated applications of ECCM might be to recognize the type of ECM being used, and be able to cancel out the signal.Pulse compression by "chirping", or linear frequency modulation
One of the effects of the pulse compressionPulse 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...
technique, is boosting the apparent signal strength as perceived by the radar receiver. The outgoing radar pulses are chirp
Chirp
A chirp is a signal in which the frequency increases or decreases with time. In some sources, the term chirp is used interchangeably with sweep signal. It is commonly used in sonar and radar, but has other applications, such as in spread spectrum communications...
ed, that is, the frequency of the carrier is varied within the pulse, much like the sound of a cricket chirping. When the pulse reflects off a target and returns to the receiver, the signal is processed to add a delay as a function of the frequency. This has the effect of 'stacking' the pulse so it seems stronger, but shorter in duration, to further processors. The effect can increase the received signal strength to above that of noise jamming. Similarly, jamming pulses (used in deception jamming) will not typically have the same chirp, so will not benefit from the increase in signal strength.
Frequency hopping
FrequencyFrequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
agility ('frequency hopping') may be used to rapidly switch the frequency of the transmitted energy, and receiving only that frequency during the receiving time window. This foils jammers which cannot detect this frequency switch quickly enough, and switch their own jamming frequency accordingly during the receiving time window.
This method is also useful against barrage jamming
Barrage jamming
Barrage jamming: jamming accomplished by transmitting a band of frequencies that is large with respect to the bandwidth of a single emitter. Barrage jamming may be accomplished by presetting multiple jammers on adjacent frequencies, by using a single wideband transmitter, or by using a transmitter...
, in that it forces the jammer to spread its jamming power across multiple frequencies in the jammed system's frequency range, reducing its power in the actual frequency used by the radar at any one time. The use of similar spread-spectrum techniques allow signals to be spread over a wide enough spectrum to make jamming of such a wideband signal difficult.
Sidelobe blanking
Radar jamming can be effective from directions other than the direction the radar antenna is currently aimed. When jamming is strong enough, the radar receiver can detect it from a relatively low gain sidelobe. The radar, however, will process signals as if they were received in the main lobe. Therefore, jamming can be seen in directions other than where the jammer is located. To combat this, an omnidirectionalOmnidirectional antenna
In radio communication, an omnidirectional antenna is an antenna which radiates radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. This radiation pattern is often...
antenna is used for a comparison signal. By comparing the signal strength as received by both the omnidirectional and the (directional) main antenna, signals can be identified that are not from the direction of interest. These signals are then ignored.
Polarization
Polarization can be used to filter out unwanted signals, such as jamming. If a jammer and receiver do not have the same polarity, the jamming signal will incur a loss that reduces its effectiveness. The four basic polarities are horizontal, vertical, right-hand circular, and left-hand circular. The signal loss inherent in a cross polarized (transmitter different from receiver) pair is 3 decibels for dissimilar types, and 17 dB for opposites.Aside from power loss to the jammer, radar receivers can also benefit from using two or more antennas of differing polarity and comparing the signals received on each. This effect can effectively eliminate all jamming of the wrong polarity, although enough jamming may still obscure the actual signal.
Radiation homing
The other main aspect of ECCM, is to program sensors or seekers to detect attempts at ECM and possible even to take advantage of it. For example, some modern fire-and-forgetFire-and-forget
Fire-and-forget is a third-generation method of missile guidance. The military uses the term for a type of missile which does not require further guidance after launch such as illumination of the target or wire guidance , and can hit its target without the launcher being in line-of-sight of the...
missiles like the Vympel R-77
Vympel R-77
The Russian R-77 Missile is a medium range, air-to-air, active radar-guided missile system. It is the Russian counterpart to the American AIM-120 AMRAAM missile, thus gaining a nickname: Amraamski....
and the AMRAAM are able to home in directly on sources of radar jamming if the jamming is too powerful to allow them to find and track the target normally. This mode, called 'home-on-jam', actually makes the missile's job easier. Some missile seekers actually target the enemy's radiation sources, and are therefore called "anti-radiation missile
Anti-radiation missile
An anti-radiation missile is a missile which is designed to detect and home on an enemy radio emission source. Typically these are designed for use against an enemy radar, although jammers and even radios used for communication can also be targeted in this manner.- Air-to-Ground :Most ARM designs...
s" (ARM). The jamming in this case effectively becomes a beacon announcing the presence and location of the transmitter
Transmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
. This makes the use of such ECM a difficult decision; it may serve to obscure an exact location from a non-ARM missile, but in doing so it must emit signals which can be exploited by an ARM type missile.
See also
- JammingRadio jammingRadio jamming is the transmission of radio signals that disrupt communications by decreasing the signal to noise ratio. Unintentional jamming occurs when an operator transmits on a busy frequency without first checking whether it is in use, or without being able to hear stations using the frequency...
- Electronic warfareElectronic warfareElectronic warfare refers to any action involving the use of the electromagnetic spectrum or directed energy to control the spectrum, attack an enemy, or impede enemy assaults via the spectrum. The purpose of electronic warfare is to deny the opponent the advantage of, and ensure friendly...
- Electronic warfare support measuresElectronic warfare support measuresIn military telecommunications, the terms Electronic Support or Electronic Support Measures describe the division of electronic warfare involving actions taken under direct control of an operational commander to detect, intercept, identify, locate, record, and/or analyze sources of radiated...