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1.INTRODUCTIONIn present article was introduced the ELINT Subsystem (ES) which is a part of EW Training Range (the SSPWE system), making up on basis of contract of realization of developmental project with National Centre of Research and Development (NCBR). The SSPWE system be designed to support of process of training aircraft crews in conditions of electronic warfare (EW) across creation approximate to real, microwave electromagnetic environment, and to obtain the information about reaction of crew on linked by conditions also. The SSPWE system will offer a real opportunity to be the complete system in the future, capable to ensuring approximate to real microwave threats for aircraft crews in time of flight. Further, are presented some radar jamming which are applied to electronic dazzling/disruption preliminary search and tracking radars used by missile/the anti-aircraft artillery and airborne radars mounted on board the multi-role fighter aircraft. Moreover, the conception of jamming classification by ELINT Subsystem was introduced. This concept is based on unique recorded features, attributed to the individual kinds of radar jamming. 1.1.Basic description of the ELINT SubsystemWithin the SSPWE system are three basic functional items [1]:
ELINT Subsystem is a part of the Surveillance - Measuring Unit. The Generation of Threats Unit (JGZ) will include:
The Surveillance - Measuring Unit (JOP) will include:
The Management and Cooperation Unit (JZW) will include:
It is supposed that staff of projected SSPWE system will execute all tasks during a training from Management and Cooperation positions whereas other items will be remotely controlled. The Microwave MIZAR sets receivers which are the main part of ELINT Subsystem allows a large frequency range (e.g., 2 to 18 GHz) to be covered in bands. Their main task is to register activity of source of emission (using monitoring channel) as well as the parametric estimation and bearings (direction finding) of indicated sources of emission (using location channel). Registered data will be sent after processing to the Management and Cooperation Unit as auxiliary data for training evaluation process. 2.REVIEW OF SELECTED JAMMING TECHNIQUESActive jamming used to suppress/dazzling the enemy’s electromagnetic signals emitted from radars can divide on two principle kind: 2.1.Cover JammingThe object of cover jamming is to reduce the quality of the signal output. There are following techniques inside cover jamming:
where: Bj – jamming noise bandwidth Br – radar intermediate-frequency bandwidth, matched to radar pulse width. Figure 2 shows the comparison between of jamming band emission for wideband signal to target pulse band in intermediate-frequency channel. The aims of this kind of jamming are mainly to:
By reason of large energy consumption and a considerable dimensions of a transmitter unit, this type of interferences does not use in the self-protection systems at present. It is a part of the systems for a different purpose like onboard Airborne Electronic Attack - AEA system.
Figure 3 illustrates a comparison of the narrow-band noise with an IF return pulse band. Generally this type of jamming is applied to older, non-coherent or pseudo-coherent generation of emitters without advanced moving target indication systems. It also applied in electronic attack systems equipped with large gain transmitting antennas and which are distinguished by a high power jamming signals [5]. 2.2.Deception JammingDeception Jamming - (basic type of jamming used in Self-protection Systems) are intentional jamming imitating real return signals on victim radar’s scope. Undoubtedly, the main advantage of using the deception jamming is the reduced capability of radar receiving systems to filter out this type of jamming signals. Matching of false waveforms in terms of carrier frequency and (in the case of using DRFM) the instantaneous phase, significantly impedes the possibility of separating the false targets from the real targets. Due to the frequency and phase matching, the requirements for the J/S ratio [5] are reduced. There are many types of deception jamming. This article is presented selected types [8]:
2.2.1.Numerous range false targets (RFT)RFT technique involves the synchronous generation of series of pulses on the carrier frequency of a threat signal with a similar pulse duration. RFT technique is mainly used for: 2.2.2.Range Gate Pull Off, Range Gate Pull InThe RGPO, RGPI techniques are based on delaying (RGPO) or accelerating (RGPI) the generated pulse relative to the actual return of the tracked target. Figure 5 shows the principle of generating the RGPO technique. False target pulse responsible for “gate stealing” is generated with increasing time delay in every pulse repetition interval. The system generating the range gate error signal compares amount of energy within “Early Gate” and in the “Late Gate”, then the system initiates a movement of the tracking gate towards the further gate to compensate the energy level [6]. This process continue until the gate leaves the range of the radar resolution cell of the target. As a result of breaking the tracking process the radar is forced to change the operational mode to the target search mode. “Pushing” the range gate closer the tracking radar in a similar way mentioned above is called RGPI technique. The only difference is the opposite direction of the changes. The RGPI technique enforce having sufficiently large knowledge about the transmitting characteristics of the victim radar and onboard emission tracking systems (Pulse Repetition Interval Tracker) to predict the arrival time of subsequent threat pulses [5]. 2.2.3.Angular deception jamming (Square Swept Wave)The angular deception jamming technique implementation (also known as Swept Wave Modulation) base on rectangular wave with the constant or modulated frequency and/or duty cycle. Figure 8 illustrates rectangular wave with the constant frequency and duty cycle equal 50 %. Figure 9 illustrates Rectangular Wave with the constant frequency and modulated duty cycle. Such modulated amplitude is implement in combination with range deception jamming techniques, noise jamming techniques or continue wave noise techniques. The effectiveness of the angular deception jamming mainly depends on side lobes level of the radar receiving antennas, presence of side lobes compensation systems or additional reference antennas. Angular deception level are mainly used for:
3.RADAR JAMMING SIGNAL DETECTION AND CLASSIFICATIONThe nature of jamming signals generated from a typical Airborne Electronic Attack or Self-Protection device is not similar to typical radar signals. Detection of such signals with a classic ELINT system is a demanding process. Proper measurement of jamming signals is possible only with particular and special care for the configuration parameters of the ELINT receivers (appropriate LIN/LOG amplifiers, fine thresholds and optimal IF bandwidths). Detection of amplitude/angle deception signals may be complicated due to high dynamic level. Classification of detected jamming signals bases on two data streams:
3.1.Monitoring channel dataIt is assumed that the bandwidth occupation analysis should be done first. According to Figure 10 it is assumed that the masking and deception jamming signals are distinguished on the basis of bandwidth occupancy coefficient. Due to ability of generating various techniques variable with time, it is necessary to define a sliding window with variable width. The bandwidth occupancy analysis will be executed again after the sliding window reached to the end of the registered sequence. Such process will allow to detect various mixed (masking and deception) jamming signals. 3.2.DF channel dataIf the jamming signal within the sliding window is classified as a deception jamming, it is necessary to analyze the DF channel data stream. It is assumed that the Range Deception analysis should be done first. 3.2.1.Range Deception jamming techniquesClassification of Range Deception jamming signals bases on the Pulse Group Repetition Interval (PGRI) analysis. Figure 12 shows the graphic interpretation of PGRI. It is defined as time between the last pulse rising edge from the preceding group and the first pulse rising edge from the succeeding group. Higher values of the bars shown in the Figure 13 are related to the Pulse Group Repetition Interval. Lower values of the bars are related to pulses inside the pulse group. It is assumed that the pulse repetition interval of pulses inside the group is constant and equal. The pulse group repetition interval of Range False Targets (RFTs) may be described as [7]: where: ε means admissible time measurement error. Figure 14 shows the PGRI difference during the Range Gate Pull Off technique being registered. Gradient coefficient α defined as [4, 7]: is positive. Value of the coefficient is dependent on the gate stealing linear rate. Figure 15 shows the pulse repetition interval of the Range Gate Pull In technique. The gradient coefficient α is negative. 3.2.2.Amplitude/Angle Deception jamming techniquesThe final step of the jamming analysis is the detection and classification of Amplitude/Angular Deception jamming techniques. Such techniques appear generally with the Range Deception techniques. The frequency of the square wave used in angular deception techniques usually does not exceed the scanning frequency of the radar antenna beam. The assumed range of detected square wave frequencies is from 2 Hz to 200 Hz. The idea of angular deception technique detection bases on the Fast Fourier Transform of envelope of the pulses stored in the Pulse Descriptor Word. It is assumed that it is necessary to detect the odd harmonic frequencies of the square wave. The angular deception signal exists when:
Figure 16 shows a square wave in time and spectra domain. The frequency of this square wave is constant and equals to 40 Hz. The duty cycle of the wave is constant and equals to 50%. In the range of 6 Hz to 1000 Hz a lot of odd frequency exists. Figure 17 shows a modulated square wave in time and spectra domain. As in previous case, the strongest is the 40 Hz base frequency. A lot of odd harmonic frequencies exists. Due to the modulated duty cycle from 50% to 30% a lot of even harmonic frequencies exists. 4.SUMMARYIn the presented article the basic direction of work carried out during the development and implementation of the ELINT ESM subsystem is described. It will be one of the key elements of the system for assessing the correctness of the Aircraft Self-Protection system. At present, it will enable the validation of interference techniques generated on board the F-16 aircraft. In the future, its usefulness for the evaluation of interference generated on board the F-35 aircraft is also assumed. The presented list of interference is not complete, in the case of the F-16 aircraft it includes several possible generation techniques, for which the basic criterion of use is the detected type of threat signal. REFERENCESE. Jasiński, M. Masiewicz, J. Wiśniewski, ITWL, Warszawa,
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