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Electronic counter-countermeasures (ECCM) is a part of
electronic warfare Electronic warfare (EW) is any action involving the use of the electromagnetic spectrum (EM spectrum) or directed energy to control the spectrum, attack an enemy, or impede enemy assaults. The purpose of electronic warfare is to deny the opponen ...
which includes a variety of practices which attempt to reduce or eliminate the effect of electronic countermeasures (ECM) on electronic
sensor A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon. In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
s aboard vehicles, ships and aircraft and weapons such as
missile In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocket i ...
s. ECCM is also known as electronic protective measures (EPM), chiefly in
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
. In practice, EPM often means resistance to jamming. A more detailed description defines it as the electronic warfare operations taken by a radar to offset the enemy's countermeasure.


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 ECM is
radar jamming Radar jamming and deception is a form of electronic countermeasures that intentionally sends out radio frequency signals to interfere with the operation of radar by saturating its receiver with noise or false information. Concepts that blanket the ...
or spoofing. This originated with the Royal Air Force's use of what they codenamed ''Window'' during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, which Americans referred to as ''
chaff Chaff (; ) is the dry, scaly protective casing of the seeds of cereal grains or similar fine, dry, scaly plant material (such as scaly parts of flowers or finely chopped straw). Chaff is indigestible by humans, but livestock can eat it. In agri ...
''. It was first used during the
Hamburg (male), (female) en, Hamburger(s), Hamburgian(s) , timezone1 = Central (CET) , utc_offset1 = +1 , timezone1_DST = Central (CEST) , utc_offset1_DST = +2 , postal ...
raid on July 24-25, 1943. The night fighters outfitted with ''Window'' had prong antennae stuck out from their noses, allowing their radars a range of four miles in a 70 degree cone. Jamming also may have originated with the British during World War II, when they began jamming
German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmit ...
communications. These efforts include the successful British disruption of German Lutwaffe navigational radio beams. 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 may refer to: Signal blocking devices * Radar jammer, a device used in radar jamming and deception * Radio jammer, a device used in radio jamming * Radio-controlled Improvised Explosive Device jammer, a counter-IED device * Mobile phon ...
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 is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
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 Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consists ...
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. The technology powering modern sensors and seekers allow all successful systems partly due to ECCM designed into them. Today, electronic warfare is composed of ECM, ECCM and, electronic reconnaissance/intelligent (
ELINT Signals intelligence (SIGINT) is intelligence-gathering by interception of ''signals'', whether communications between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly used in communication ( ...
) activities. Examples of electronic counter-countermeasures include the American Big Crow program, which served as a Bear bomber and a standoff jammer. It was a modified Air Force NKC-135A and was built to provide capability and flexibility of conducting varied and precision electronic warfare experiments. Throughout its 20-year existence, the U.S. government developed and installed over 3,143 electronic counter-countermeasures to its array of weapons. There is also the BAMS Project, which was funded by the Belgian government since 1982. This system, together with advanced microelectronics, also provided secure voice, data, and text communications under the most severe electronic warfare conditions.


Specific ECCM techniques

The following are some examples of EPM (other than simply increasing the
fidelity Fidelity is the quality of faithfulness or loyalty. Its original meaning regarded duty in a broader sense than the related concept of ''fealty''. Both derive from the Latin word ''fidēlis'', meaning "faithful or loyal". In the City of London f ...
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 compression Pulse compression is a signal processing technique commonly used by radar, sonar and echography to increase the range resolution as well as the signal to noise ratio. This is achieved by modulating the transmitted pulse and then correlating th ...
technique is boosting the apparent signal strength as perceived by the radar receiver. The outgoing radar pulses are
chirp A chirp is a signal in which the frequency increases (''up-chirp'') or decreases (''down-chirp'') with time. In some sources, the term ''chirp'' is used interchangeably with sweep signal. It is commonly applied to sonar, radar, and laser system ...
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

Frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
agility ("
frequency hopping Frequency-hopping spread spectrum (FHSS) is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. The changes are controlled by a code known to both tra ...
") 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 switch in frequency quickly enough or predict the next hop frequency, and switch their own jamming frequency accordingly during the receiving time window. The most advanced jamming techniques have a very wide and fast frequency range, and might possibly jam out an antijammer. This method is also useful against
barrage jamming Barrage jamming is an electronic warfare technique that attempts to blind (" jam") radar systems by filling the display with noise, rendering the broadcaster's ''blip'' invisible on the display, and often those in the nearby area as well. "Barrag ...
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 equipment at any one time. The use of
spread-spectrum In telecommunication and radio communication, spread-spectrum techniques are methods by which a signal (e.g., an electrical, electromagnetic, or acoustic signal) generated with a particular bandwidth is deliberately spread in the frequency dom ...
techniques allow signals to be spread over a wide enough spectrum to make jamming of such a wideband signal difficult.


Sidelobe blanking

Radar jamming Radar jamming and deception is a form of electronic countermeasures that intentionally sends out radio frequency signals to interfere with the operation of radar by saturating its receiver with noise or false information. Concepts that blanket the ...
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
omnidirectional antenna In radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis (elevation angle), declining t ...
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 polarization, the jamming signal will incur a loss that reduces its effectiveness. The four basic polarizations are linear horizontal, linear vertical, right-hand circular, and left-hand circular. The signal loss inherent in a cross polarized (transmitter different from receiver) pair is 3 dB 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 polarization and comparing the signals received on each. This effect can effectively eliminate all jamming of the wrong polarization, although enough jamming may still obscure the actual signal.


Radiation homing

Another practice of ECCM is to program sensors or seekers to detect attempts at ECM and possibly even to take advantage of them. For example, some modern
fire-and-forget Fire-and-forget is a type of missile guidance which does not require further external intervention 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 targe ...
missiles like the
Vympel R-77 The Vympel NPO R-77 missile ( NATO reporting name: AA-12 Adder) is a Russian active radar homing beyond-visual-range air-to-air missile. It is also known by its export designation RVV-AE. It is the Russian counterpart to the American AIM-120 ...
and the
AMRAAM The AIM-120 Advanced Medium-Range Air-to-Air Missile, or AMRAAM (pronounced ), is an American beyond-visual-range air-to-air missile (BVRAAM) capable of all-weather day-and-night operations. It is 7 inches (18 cm) in diameter, and employs ...
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 An anti-radiation missile (ARM) is a missile designed to detect and home in on an enemy radio emission source. Typically, these are designed for use against an enemy radar, although jammers and even radios used for communications can also be ...
s" (ARMs). The jamming in this case effectively becomes a beacon announcing the presence and location of the
transmitter In electronics and telecommunications, a radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna (radio), antenna. The transmitter itself generates a radio frequency alternating current, which i ...
. This makes the use of such ECM a difficult decision – it may serve to obscure an exact location from non-ARMs, but in doing so it must put the jamming vehicle at risk of being targeted and hit by ARMs.


See also

* Jamming *
Electronic warfare Electronic warfare (EW) is any action involving the use of the electromagnetic spectrum (EM spectrum) or directed energy to control the spectrum, attack an enemy, or impede enemy assaults. The purpose of electronic warfare is to deny the opponen ...
**
Electronic warfare support measures In military telecommunications, electronic support (ES) or electronic support measures (ESM) gather intelligence through passive "listening" to electromagnetic radiations of military interest. They are an aspect of electronic warfare involving ac ...
* Wartime reserve mode


References

{{Reflist
Raytheon ECCM-capable radio set


* Electronic countermeasures Electronic warfare Military technology Military communications Missile technology Radar signal processing Electronic counter-countermeasures