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Introduction to Electronic Defense Systems

1 2 3 Tho Army

The defensive task of an army is to conduct operations on the ground that will wear the enemy down by a process of attrition and repel or deter an attack. T o achieve this end, the army will make use of the usual corps: Infantry; Armored units; Artillery; Engineers.


To stop or weaken enemy forces, the army will have at its disposal ballistic or inertial-guidance SSMs and long-range artillery to strike in-depth and to prevent the enemy from taking the initiative. It will have tanks to counter enemy tanks. Those tanks will have weapon delivery systems controlled by laser rangefinders, which enable them to hit with the first shot, hopefully without having come to a halt. The army will be provided with SAM systems (Figure 1.19) to counter the enemy's ground attack aircraft, as well as with radar-guided artillery (MA) (Figure 1.20). A characteristic of army systems is their mobiliry, so

Figure 1.19 S A M systems are frequently used to defend ground forces against air raids. The photograph showsthe Soviet SA-13 battery.

Figure 120 Radar-guided anti-aircraft artillery has shown its great effectiveness. The photographs show (a) the Soviet ZSU-23.4 system and (b) the integrated point defense SKYGYARD.


Introduction to Electronic Defense Svnems

that they can easily follow troop movements and be redeployed frequently to avoid being detected and destroyed. The army will also be equipped with helicopters (Figure 1.21) able to climb swiftly and to launch wire- or infrared-guided ASMs against enemy ranks.


Thanks to as mobility, the helicopter is extremely effectiveagainn tanks. The photograph shows the A-129 antitank helicopter.

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T o help them control the battlefield, the army will use dedicated information-gathering sensors, such as radars, infrared systems, and remotely piloted vehicles (RPVs), also known as unmanned air vehicles (UAVs). The army will have antimortar radar systems capable of locating accurately the direction and hence the location from which projectiles are fired so as to be able to direct counterfire with precision to destroy the battery. More recently, weapon-locating radars (WLRs) have been developed to specifically locate the source of rockets. I have great importance. In fact, the army conIn an army, C ~systems sists of a multitude of extremely mobile units whose activities are constantly in need of coordination. T o sum up, the army will mainly draw upon the following weapon systems: C31systems, f ~ e or d mobile; SSM systems; Long-, medium- and short-range artillery systems; Search and acquisition radar systems to detect the ground attack aircraft; SAM systems;

AAA systems;
Antimortar radars and WLRs; Armored vehicles; Helicopters with wire- or infrared-guided missiles; Battlefield surveillance systems.

1.3 The Main Weapon Systems
All the operations listed above are conducted in two phases: first the detection phase, and then the response phase in which missiles or guns are used. Accordingly, the main systems employed by the armed forces against which protection is required are the following: Search systems; Missile systems; Artillery systems.


Introduction to Electronic Defense Systems

The functioning of all these systems is based on the use of electronic sensors. It has been amply proved that the effectiveness of a weapon system is destroyed by adequately jamming its sensors. The concept of electronic defense, the development of specialized equipment, and the mission it has to accomplish, are all consequences of this fact. In order to understand the way in which jamming interferes with weapon systems, it is necessary to examine in more detail how the weapon systems themselves are structured and how they operate. The performance of an air defense system depends on the capabilities of the long-range search radar associated with it. An electronic device designed to jam a detection system can interfere only with the radar sensor and its signal processing, as the ensuing data processing can take place in remote, well-protected command and control centers. As already stated, a missile system usually consists of: A medium-range search radar (acquisition radar); A number of tracking radars, each tracking one target to supply guidance data for the missile; A number of missile launchers. A missile may be guided exclusively by commands from the tracking radar (command missile) or it may be launched on the basis of data supplied by the tracking radar, and then acquire signals for self-guidance to its target (homing). Homing, therefore, can be as follows: Active, if the missile is fitted with a sensor (seeker comprising a small tracking radar); Semiactive, if the energy source is an illuminator at the missile site and the seeker is a tracking radar receiver that sees radiation reflected by the target; Passive, if the missile has a seeker that does not require any transmitter but detects the energy radiated by the target in the infrared, ultraviolet, or microwave spectrum.

An artillery system consists of:

A medium-range search radar (acquisition radar);

Electronic Defense


A number of tracking radars (sometimes the tracking is achieved by
optical means);

A number of cannon and machine guns.
Here too the search radar detects and identifies the target, then designates it to a tracking radar. The tracking radar searches, detects, acquires, and tracks the indicated target, and supplies its data to a computer that accurately computes the interceptor point and aims the weapon. T o sum up, it is apparent from this review that all of the weapon systems that we have examined employ one of the following sensors, which could be the victim of electronic jamming systems: Search radar; Tracking radar; Radio-frequency seeker; Electro-optic search systems; Infrared seeker. In Chapter 2, an analysis of the way in which the sensors operate will also indicate their weaknesses and the possibilities for interfering with them. T o show to what extent disturbance of a sensor is useful for electronic defense, Chapter 3 will analyze the way in which the weapon systems themselves operate. The armed forces coordinate among themselves by extensive use of communications systems, which can be jammed. These systems will also be examined briefly in Chapter 3.

1.4 The Objectives of Electronic Defense
In Section 1.3, the main means of defense and offense have been listed, based on "hard kill." This section deals with the electronic defense devices themselves, their military functions, and how by interfering with them "soft kills" of the enemy can be achieved.
1.4.1 The Organization of Electronic Defense

It should be remembered that the ultimate objective of electronic defense is to minimize the effectiveness of those weapon systems that draw on


Introduction to Electronic Defense Systems

electronic sensing devices for their operation. T o achieve this end, the following measures are necessary: Strategic knowledge of the enemy's electronic devices. This is obtained by monitoring and studying the signals that they emit [signal intelligence (SIGINT)]. Tactical knowledge of the enemy's devices, that is, knowledge of the distribution over an area, or around the protected point or platform, of hostile electromagnetic sources [electronic order of battle (EOB)]. This is needed both for a defensive response for self-protection or mutual protection and for an electronic offense operation suppression of enemy air defense (SEAD). Responses employing traditional weapons are not discussed here. Generation of electronic countermeasures (ECM), which has as its aim the maximum reduction of the operational capabilities of enemy electronic devices, including search radars, acquisition and tracking radars, infrared systems, laser systems, and communications systems. Adoption of electronic counter-countermeasures (ECCM). It is in fact sometimes possible to reduce or eliminate an intentionally caused disturbance or interference by incorporating filters and other special devices. The organizational display of electronic defense, as shown in Figure 1.22, is based on the above list.

1.5 Electronic Defense Systems and Their Operational Objective
The main electronic defense systems will be defined here according to their position in the table of organization (Figure 1.22). It should be remembered that an electronic defense system can consist of a collection of the equipment described next. For example, it is possible to have two separate electronic support measures (ESM) and ECM systems, or one integrated system, when both functions are performed together.
Signal Intelligence (SIGINT)

The task of SIGINT systems is the acquisition of as much data as possible about the electromagnetic emissions of a potential enemy. They can be further classified into electronic intelligence (ELINT) systems, which collect


intelligence Electronic support measures Electronic countermeasures Electronic countercountermeasures Information warfare


Electronic intelligence EL'NT


Communications intelligence





(Weapons systems) (Weapons systems)









Counter information

Counter-counter information


off-board Expendable decoys Towed decoys




(Weapons systems)




Passive ECM



Deception IRMC cources

z R ;

Figure 1.22 Electronic defense organization.


Introduction to Electronic Defense Systems

radar emission data, and communications intelligence (COMINT) systems, which collect enemy communication data. Their function is primarily a strategic one; they are essential for the identification of a potential enemy's operational procedures.

Electronic Intelligence (ELINT) This equipment must be able to define the characteristics, the time dependence, and the location of hostile electronic emissions. It should also be able to analyze the enemy's electronic signals both in time and in frequency, and to associate with them a serial number of the enemy's equipment (i.e., fingerprinting), sometimes even in a one-to-one relation, thus making it possible to follow the movement of the equipment. These systems can be airborne for deep probes into the electronic scenario of a potentially hostile country. They can also be land-based, located on sufficiently elevated mountain sites and on promontories or straits, for control of sea traffic (Figure 1.23). The collected data are usually transmitted to an analysis center, which codes them suitably, memorizes them in a database, and correlates them with the information gathered by equipment of other types, or by other organizations, or at different times.

Figure 1.23 The main purpose of an ELINT system is to intercept and analyze, for strategic purposes, all the electromagnetic radiation generated in a potentially hostile country.

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All this information, processed according to operational criteria established by the military organizations, will be used to build up special files in which all emissions and other features of enemy equipment will be listed (libraries). From these files information is compiled to be loaded into the memories of electronic defense equipment used for detection of enemy signals.
Communications Intelligence (COMINT)

These systems are similar to the preceding ones, but their task is the interception and analysis of telecommunications emissions and the identification of relevant communications networks.
Electronic Support Measures (ESM)

The main objective of equipment of this type of class is tactical interception. The simplest systems are those whose main function is to detect the presence of already known emitters by comparison of the intercepted signals with stored data. They are called radar warning receivers (RWR). This equipment, which can instead reconstruct a very complex electromagnetic scenario, including previously unknown emitters, and can therefore contribute to an attack by identifying and detecting enemy platforms, is more sophisticated. These are the ESM systems.

RWR The main features of equipment of this class are simplicity (they measure few parameters with moderate accuracy), high reliability, low weight, and low cost. They are used to detect an imminent threat, that is, the presence in a given direction of the radar of a hostile weapon system locked on to the protected platform. They are mainly committed to aircraft defense and enable the pilot to react promptly either by an evasive maneuver, or by both a maneuver and the simultaneous launching of chaff, which consists of explosive cartridges containing millions of tiny, extremely light dipoles, capable of generating a very strong radar echo that masks the platform (see Chapter 5), or by generating electronic jamming signals, or by a combination of these different techniques.

This class of equipment is characterized by medium to high complexity and sophistication. Its task is an almost real-time reconstruction of an electromagnetic scenario, which can be highly complex and previously unknown,


Introduction to Electronic Defense Systems

starting from the interception of the multitude of signals crowding into its antenna. Usually, the total "traffic" consists of pulse and continuous wave signals. Pulse signals are frequently very dense (millions of pulses per second), are dispersed on bandwidths from a few hundred megahertz to a few tens of gigahertz to millimeter waves, and make use of the most varied wave forms, including pulses, modulated pulses, and so forth. The main aim of such a system is to give a picture of the electromagnetic scenario in the environment both for self-defense, by discovering the presence of enemy platforms (ESM on a naval platform) (Figure 1.24), and for passive surveillance of a wide area (ESM on an aerial platform or landbased network of ESM systems). Reconstruction of the electromagnetic environment depends both on detection of the electromagnetic signal input to the antennas and on characterization of signals in terms of carrier frequency, direction of arrival (DOA), time of arrival (TOA), pulse width (PW), amplitude, modulation on pulse (MOP), form and modulation in time, and modulation and amplitude of continuous waves (CW). Out of this information an ESM installation must extract knowledge of the generating emitters. The process of correlating pulses and of grouping them in possible "families" is a very complex one, and is called sorting or deinterleaving. Because of the variability of the signals, automatic extraction is even more difficult. Frequently, wrong conclusions are reached: Emitters that do not really exist are created, and so false alarms are generated that reduce the reliability of the equipment.


Figure 1.24 The purpose of an ESM system is to detect the presence of enemy platforms

by intercepting their electromagnetic emissions.

Electronic Defense


In the field of military electronics, ESM automatic extraction is generally regarded as one of the most difficult problems, as the complex electromagnetic signal, which has to be extracted from a crowded and complicated background, is usually not known in advance.

The aim of these systems is to intercept all enemy communications, both for location of transmitters and radio relay systems and for detection and decoding of the messages themselves. Knowledge of enemy intentions is of the first importance to the choice of appropriate action and to the effecting of electronic countermeasures.
Infrared Warning

Enemy missiles with infrared guidance do not need to radiate any RF signals because they lock onto infrared emission naturally generated from a target. This means that the presence of an infrared missile cannot be detected by any radio frequency electronic support measure equipment. In fact, their detection is normally obtained by dedicated radar. The desire to defend a platform against missile attack, however, often conflicts with the need to keep radar turned off to avoid detection by the enemy (a "radar silence" situation). In this case, passive electro-optic sensors offer a solution. This kind of equipment is in fact capable of detecting either the aerodynamic heating or the infrared radiation produced by the booster at the time of launching. The problem with these sensors is that the background infrared radiation usually gives a much stronger signal than the signal produced by the threat to be intercepted. Systems that detect the infrared radiation emitted at launch are distinct from those that detect aerodynamic heating. Among the latter, the simpler surveillance or infrared vision systems, for example, fonvardlooking infrared (FLIR), should be distinguished from much more complex and costly systems capable of warning automatically, such as infrared search and track (IRST).
Laser Warning Receivers

The last decade has seen a proliferation of weapons either guided or controlled by a laser emitter. In tank warfare, laser rangefinders yield accurate ranges, while laser designators give precision guidance for bombs or missiles toward ground targets. The carbon dioxide laser now allows missiles to be guided toward fast-moving platforms.


Introduction to Electronic Defense Systems

Obviously, the first requirement of adequate defense against such threats is the ability to detect their presence. This is what laser warning receivers do.
Electronic Countermeasures (ECM) After this brief survey of the main types of equipment for reconnaissance of the electromagnetic environment surrounding a protected area, it is time to describe those systems whose task is the neutralization of hostile electronic systems that have been detected. Their purpose is either to conceal the protected platform or to deceive the hostile weapon system by creating spurious targets. Chaff A chaff system comprises a launcher that ejects cartridges. These cartridges explode within a certain distance of the protected platform and disperse a multitude of tiny dipoles into space. These dipoles remain suspended in space, producing a cloud that radiates back radar signals. Chaff generates wide corridors within which search radars are dazzled, and therefore cannot identify aircraft targets, even at altitudes different from those filled with chaff (Figure 1.25). T o create these corridors, aircraft flying at great heights dispense an enormous quantity of chaff over a very wide area. Sometimes chaff is launched from a platform as a defense against an attacking weapon system. In this case, the weapon system's radar is usually deceived by the strong signal produced by the chaff and is diverted from the pursuit of the true target. Stealth Techniques Naturally, the best way of preventing dangerous response is to avoid detection. Since the signal received by a radar is directly proportional to the radar cross section (RCS) presented by the platform, a drastic reduction of the strength of the radar signal produced by the protected platform is very desirable. T o this end a new technology has been developed in recent years for the study of materials and structural geometries capable of minimizing target RCS. The techniques are usually called stealth techniques. These are very promising; the supporters of the stealth aircraft in the United States call it "invisible." Noise Jammers A noise jammer generates signals of the same frequency as an opponent's radar. These signals create a disturbance equivalent to a very strong thermal

Electronic Defense


Figure 1.25 Chaff consisting of clouds of extremely light, conductive metal foil strip dipoles is used to create areas in which radar is blinded and cannot see targets.

noise in the radar receiver. Thus, the signal produced by the platform is drowned in noise and is no longer "visible" (Figure 1.26).

Figure 1.26 The purpose of a noise jammer is to mask targets by emission of signals that create confusion on the radar display.


Introduction to Electronic Defense Systems

Deception Jammers

A deception jammer generates false radar targets. In the case of search radars,
it impedes identification of the real platform. In the case of tracking radars, it ensures that the tracking and ensuing locking on of the weapon system is progressively shifted onto the false target (Figure 1.27).
Expendable Decoys

There are several types of decoy. A decoy is considered to be an object, usually ejected from the protected platform, which generates a spurious but sufficiently convincing target for enemy radar. Decoys can be passive (a corner reflector on a buoy) or active (i.e., able to return a strongly amplified radar signal).

The purpose of these systems is to generate noise signals, or interference, in order to jam the receivers of enemy telecommunications systems, thus rendering messages incomprehensible. Inability to rely on its communications systems is a major drawback for any armed force.
Infrared Countermeasures (IRCM)

These are systems that prevent infrared-guided missiles from reaching the target. Currently there are two types of system: onboard and off-board.

False target


.............'"'" True target ,.............'


Figure 1.27 The purpose of a deception jammer is to protect a platform by luring enemy radars with false targets.

Electronic Defense


The onboard type is composed of modulated infrared transmitters. Since infrared seekers are quite often based on a scanning tracking system, an amplitude-modulated infrared signal can introduce huge errors into a missile trajectory. The off-board system is a flare dispenser, which is a launcher capable of ejecting cartridges that generate an intense infrared radiation to deceive the missile heat seeker.

These systems are designed to prevent accurate rangefinding by a laser system. They either operate on the same principles as the jammers mentioned above or dispense clouds of smoke that reduce visibility.
Electronic Counter-Countermeasures (ECCM)

These devices are usually added to weapon sensors to enable them to operate in an electronically hostile environment, that is, in the presence of intentional jammers, with minimal reduction of their normal capabilities.

1.6 Information
Besides the traditional assets present in war operations, in recent years the importance of a modern information system in defense operations has emerged very clearly. It is well known that in all life aspects it is necessary for successful operations to possess the right information, especially in competitions, where the winner is normally the one that had the better information. Today this is even truer, thanks to the evolution of computer technology and the associated structured communication network (e.g., the Internet) that now allows a quick exchange, storage, classification, and manipulation of information. Everybody is witnessing the importance of information and requires more and better accessibility to that information, to the point that it has been claimed that, after the Agricultural Age and the Industrial Age, we are now in the Information Age. If information is of vital importance in civilian life, this is even truer in the military field. In fact, the information advantage is considered one of the key elements to achieve and maintain one's superiority over the enemy. Consequently, it has become very important to understand the supporting technology, that is, the information technology. Information technology can be defined as
The branch of modern technologies aimed to create new tools and methodologies to support all the phases of information management


Introduction to Electronic Defense Systems

and exploitation (acquisition, storage, dissemination, retrieval, and exploitation) in a cost-effective and secure way.
1.6.1 Information Operation (10)

All the operations that involve the gathering, dissemination, and exploitation of information are defined as the information operations (10). Therefore, a good definition of information operations can be [I] Any actions involving the acquisition, transmission, storage, or transformation of information, that enhances the employment of resources. Considering the strategic value of information, it is clear that in the military field it is of vital importance to achieve and maintain information superiority over the enemy. Besides ;he strategic value of information operations, I 0 can also have a tactical importance. In fact, I 0 can also change significantly the tactical way of conducting war operation. Examples of the tactical exploitation of I 0 include the following: The blind firing against a target with targeting coordinates provided by the information system;

A soldier in the desert or in a jungle, blind until a few years ago,
can have now in their portable computer the complete picture of the local war theatre: their position, the position of the enemy echelons, and the targets, even if they do not have any special sensor;

A ship in the middle of the ocean can receive via satellite communication the complete surrounding situation (wide area picture) even in a complete silent operation mode.
1.6.2 lnformation Warfare (IW)

As in "hard kill" war operations, where to achieve superiority it is necessary
to attack the enemy forces and reduce their capabilities, in the information field, in order to achieve information superiority, it will be necessary to attack the enemy's information systems in addition to building up a good information system. At the same time, it will be necessary to protect one's own information operation system from the enemy attacks. All the information operations that are dedicated in particular to attacking the enemy information or to protect one's own information can be

Electronic Defense


defined as information warfare. A general definition of information warfare is the following [2]: Information Warfare consists of those actions intended to corrupt, deny or destroy the enemy information or information resources, and [at] the same time to protect one's own information resources for their good exploitation. O f course, the aim of IW is the same as that of I 0 and of all other warfare operations, that is, to achieve a significant advantage, objective, or victory over an adversary. As already emphasized, in warfare operations today information operations have achieved a greater importance than in the past and represent a strategic and tactical interconnective tissue-to protect it, it is necessary to foresee a good level of information warfare (Figure 1.28).

Figure 1.28 Information operations as the "broad mean" of acting with high effectiveness.


Introduction to Electronic Defense Systems

The attacking I W [3] operations are generally oriented against the enemy's information-based processes, information systems, and computerbased networks; in general, however, for strategic purposes their targets can be even wider. In fact, today it could be necessary, for instance, to use the information to influence people and organizations through a planned use of the mass media. This book will concentrate more on the technical aspects of information operation (Chapter 3) and information warfare (Chapter 5).

1.7 Need for the Study of Weapon Systems
The main purposes of electronic defense equipment have now been described. Chapters 4 and 5 will deal with actual performance, with the technical solutions and with their distinctive characteristics. However, before contemplating action against a weapon system (the "victim" of the jamming), it is necessary to know how the weapon system operates, the principles on which it is based, its problems, and its limits. It is precisely by amplifying the problems of weapon system sensors that enemy forces can be weakened. Once the problems are known, it is easier to neutralize the system. For example, if it is known that a radar is employed to give an angular tracking accuracy of a milliradian, and that this is an absolute requirement for the performance of an artillery system, there is no need to prevent tracking entirely, that is, to achieve a "break lock." A disturbance introducing a 10-mrad error will suffice to reduce the effectiveness of the weapon system satisfactorily. Again, if it is known that a search radar guarantees valid protection only if it can detect targets at its maximum range, the use of countermeasures capable of reducing the detection range by half is enough to indicate that the objective of electronic defense has been at least partially achieved.


Allan, C. T., (Col., USAF), "Electronic Warfare: Foundation of Information Operations," Journal of Electronic Defense, October 1998.
Schwartau, W., Information Wafare, Second Edition, New York: Thunder's Mouth Press, 1996. Waltz, E., Information Wafare: Principles and Operations, Nonvood, MA: Artech House, 1998.


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