The History of Radar | Radar History: Isle of Wight Radar During The Second World War | Radar: The Basic Principle
Radar Technology: Main Components | Radar Technology: Side Lobe Suppression | Radar Technology: Airborne Collision Avoidance
Radar Technology: Antennas | Radar Technology: Antenna Beam Shapes | Radar Technology: Monopulse Antennas | Radar Technology: Phased Array Antennas | Radar Technology: Continuous Wave Radar | Theoretical Basics: The Radar Equation
Theoretical Basics: Ambiguous Measurements | Theoretical Basics: Signals and Range Resolution
Theoretical Basics: Ambiguity And The Influence of PRFs | Theoretical Basics: Signal Processing | Civilian Radars: Police Radar | Civilian Radars: Automotive Radar | Civilian Radars: Primary and Secondary Radar
Civilian Radars: Synthetic Aperture Radar (SAR) | Military Applications: Overview | Military Radars: Over The Horizon (OTH) Radar
How a Bat's Sensor Works | Low Probability of Intercept (LPI) Radar | Electronic Combat: Overview | Electronic Combat in Wildlife
Radar Countermeasures: Range Gate Pull-Off | Radar Countermeasures: Inverse Gain Jamming | Advanced Electronic Countermeasures
Electronic Combat1 has been the black art throughout the whole history of radar. In a modern army, radars are providing early warning, collect the air situation picture and are used for guiding weapons. Depriving an opponent of these functions renders him blind - incapable of making proper and timely decisions because of the lack of essential information. Retaining one's own capabilities despite an opponent's efforts is equally important. Successful Electronic Combat requires the knowledge of which equipment an opponent has, where it is deployed, where its weaknesses are, and how to make use of these.
Electronic Combat is, therefore, divided into four disciplines:
Electronic Intelligence (ELINT)
Dedicated equipment is employed to scan the whole electromagnetic spectrum for all kinds of radar signals. ELINT assets can be ground based, shipborne, airborne or even carried on satellites. The findings are collected in huge signal databases. Because radar signals are well adapted to the purpose of the devices which use them, they can be sorted and classified (say, attributed as belonging to a long range surveillance radar). The resulting database forms the raw data input for the other disciplines.
Additional information may be derived from sales brochures or possession of the hardware itself: see the Bruneval event of 1942, when a British task force acquired essential parts of a German air defence radar. The exploitation of these parts led to the development of dedicated jamming methods.
Electronic Protection Measures (EPM)
Also known as electronic counter-countermeasures (ECCM), this is the general expression for all efforts which are undertaken in order to harden one's own radar equipment against any hostile attempt to take it out of combat. These measures may consist of:
Modification of the radar itself (for example, by frequency-hopping or improving the signal processor so that it can discriminate true targets from the fake returns of a jammer),
Choosing appropriate procedures of operation within a radar network - for example, using several different radars for a given purpose and switching between them in fast succession,
Additional equipment like Side Lobe Suppression circuitry or decoy transmitters.
The most sophisticated class of radars, in terms of their EPM features, is called Low Probability of Intercept radar (LPI).
Electronic Support Measures (ESM)
Basically employing the same methods as ELINT and combining this information with location fixes (as derived from direction finding), ESMs serve to build an electronic order of battle (EOB). Radar Warning Receivers (RWR) and Missile Approach Warners (MAW) on board of attack aircraft are used to give alerts and devise measures for survival of the craft in a given tactical situation.
Electronic Countermeasures (ECM)
This is the part of actually jamming or even destroying an enemy's radar. There is a wealth of techniques available, of which Inverse Gain Jamming and Range Gate Pull-Off are only two examples that are described in more detail.
Self Protection Jamming (SPJ)
Techniques like Inverted Gain Jamming or RGPO are some of the features which are commonly combined in a set which is either built into an aircraft or carried below a wing, as a pod like the AN/ALQ-126. There is one property which they have in common: they are only suitable for protecting this one aircraft because there is no great deal in employing these techniques from some point outside the victim radar's beamwidth. The techniques mentioned here are suited best against ground-based tracking radars which are used for gun-laying or missile guidance. An aircraft's SPJ equipment may also be able to carry out some techniques against missile-seeker heads which are covered in the entry Advanced ECM.
Mutual Protection Jamming
'Blinking' is a jamming technique for mutual protection of pairs of aircraft against missile-seekers with a home-on-jam capability. The jammers of the jets are switched on in an alternating fashion. The effect is somewhat like mum and dad playing with the dog: dad throws a stick, and Fido fetches it. When Fido returns, dad starts shouting 'bring it here!' Once the dog has turned into dad's direction, mum starts shouting 'bring it here!' Then it is dad's turn again. Rather than heading for either mum or dad, Fido will follow some wiggly course and end up completely confused in the middle between the two. This is precisely the idea behind the blinking technique: with some luck, an anti-aircraft missile aimed at the pair of aircraft will pass between them without causing any damage.
Protecting a whole group of aircraft by giving each one a self-protection jammer is expensive and consumes considerable amounts of payload capacities. The task of protecting a group is better performed by dedicated aircraft which are either escort jammers or standoff jammers. Escort jammers are part of the group - they are exposed to the same signal environment but also to the same threat. Standoff jammers operate from a safe distance, but need to compensate for their weaker efficiency by emitting much more jamming power. Both types of jammers usually employ simple but powerful noise jamming - that is, they literally floodlight an area with noise which covers all frequency ranges that ESM means have detected as being in use by hostile devices.
The ultimate ECM is to physically destroy a radar. This is the task of Anti Radiation Missiles (ARM) such as HARM. They are provided with a passive radar-homing head which guides the missile down the radars beam and, upon impact, activates a warhead.
Electronic combat is the interworking of all the techniques listed here, although they have been presented in sequential order. As the air strike preceding the 1991 Gulf War has shown, it is the combination or rather 'orchestrating' of all the means and techniques that is essential for success.
Electronic combat is an example of a cat and mouse game, or rather, an endless loop. Say a new jamming method has been found - upon employing it in a conflict, hostile ELINT and ESM are made aware of it, and some appropriate EPM are applied to the radars. These changes are detected by own ELINT, and an improved ECM is being called for. Once this ECM is used, the opponent is again made aware of it, and so on.
History: Overview | Isle of Wight Radar During WWII
Technology: Basic Principle | Main Components | Signal Processing | Antennae | Side Lobe Suppression | Phased Array Antennae | Antenna Beam Shapes | Monopulse Antennae | Continuous Wave Radar
Theoretical Basics: The Radar Equation | Ambiguous Measurements | Signals and Range Resolution | Ambiguity and PRFs
Civilian Applications: Police Radar | Automotive Radar | Primary and Secondary Radar | Airborne Collision Avoidance | Synthetic Aperture Radar
Military Applications: Overview | Over The Horizon | Low Probability of Intercept | How a Bat's Sensor Works
Electronic Combat: Overview | Electronic Combat in Wildlife | Range Gate Pull-Off | Inverse Gain Jamming | Advanced ECM | How Stealth Works | Stealth Aircraft