Electronic counter-countermeasures (ECCM) describes a variety of practices which attempt to reduce or eliminate the effect of Electronic countermeasures (ECM) on sensors aboard vehicles, ships and aircraft and especially seekers on weapons such as missiles. ECCM is also known as 'Electronic protective measures' (EPM), chiefly in Europe.

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 or spoofing. This originated with the British use of what they codenamed window during World War 2, which is now often referred to as chaff (see Electronic countermeasures). Jamming also may have originated with the British during World War 2, 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 weren't 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.

The other main aspect of ECCM, other than simply increasing the fidelity of sensors through techniques such as increasing power or improving discrimination, 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-forget 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. The jamming is effectively a beacon announcing the presence and location of the opposing aircraft. This makes the use of such ECM a difficult decision; it helps you by obscuring your exact location but hurts you by giving away your presence and making it easier to track you down once approached. Another type of ECCM employed on such missiles is programming the seeker logic to be able to recognise attempts at spoofing (e.g. aircraft dropping chaff during terminal homing phase) and ignore them.

Even more sophisticated applications of ECCM might be to recognise the type of ECM being used against you and be able to cancel out the signal. In addition, the use of spread-spectrum techniques allow signals to be spread over a wide enough spectrum to make jamming of such a wideband signal difficult. Frequency agility ('frequency hopping') means the jammer must 'follow' the transmitter with its frequency hops. Even if it can do this, the time required for it to re-calibrate to each new frequency might allow the sensor to perform its job anyway.

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.

References

• Raytheon ECCM-capable radio set
• Pictures of the effect of ECM and discussion of ECCM for Nike SAM