1290_04a - Electronic Intercept Systems 4.1 Introduction...

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Electronic Intercept Systems 4.1 Introduction Electronic defense intercept systems [I] are used for timely detection of the presence in the operational scenario of one or more of the weapon systems described in Chapter 3. In this chapter the following will be analyzed: Radar warning receivers (Rm): used to detect an enemy radar before it is able to give firing instructions to its associated weapons; Electronic support measures (ESM) systems: used to detect the presence of an enemy platform in the intercepted electromagnetic scenario before it has had time to detect the defended platform; Electronic intelligence (ELINT) systems: used to gather strategic data drawn from deep inside the territories of potentially hostile nations; Inpared warning receivers (IRm): used to detect the presence of enemy platforms by their infrared emissions; Laser warning receivers: used to detect the presence of a laser illumi- nator or laser range finder; Communications intercept systems: used to intercept and locate the enemy emissions for tactical purposes and communication intelli- gence (COMINT) equipment used to discover strategic information concerning enemy communications systems.
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284 Introduction to Electronic Defense Systems It is worthwhile to emphasize that in the last 10 years, radar and missile systems exploiting LPI waveforms have been recognized as one of the major problems to be solved. In order to do this, more sensitivity in RWESM intercept systems is required, but this makes the problem of false alarms worse due to overlapped pulses and interferences. In fact, by increasing the sensitivity, the traffic intercepted by the receiver increases considerably, as does the probability of performing wrong measurements due to overlapped signals or to interferences. Therefore, more complex receiving architectures (channelized receivers) became mandatory. Besides this, modern operational needs increasingly require that RWESM systems are capable of providing pilots with a comprehensive situation awareness that implies not only more accurate emitter identifica- tion but also a very accurate passive emitter location (ranging). 4.2 The Equation of a Passive System The first requirement of an intercept device is adequate sensitivity. In order to evaluate the degree of sensitivity needed by such a device [2, 31, (4.1), which expresses the power of a radar signal intercepted by an antenna with gain G, may be used: where 4 is the propagation factor (which in free space is equal to unity), and L, are polarization losses arising from the fact that since the radar polariza- tion is not known a priori, the intercept system will need antennas capable of receiving all polarizations and is therefore not always perfectly matched to that of particular emitters.
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1290_04a - Electronic Intercept Systems 4.1 Introduction...

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