ECM01A

ELECTRONIC WARFAREELECTRONIC COUNTER MEASURE ( ECM )

ELECTRONIC COUNTER MEASURE ( ECM )Electronic Counter Measure encompasses all actions taken to introduce signals into an electronic system which degrades the performance of that system so that it is unable to perform its intended mission.ECM

Passive ActiveChaff DecoyNoise Deception ECM (DECM) # Spectral #Spatial #Temporal

ELECTRONIC COUNTER MEASURE ( ECM )Type of Jamming1.Self Protection2.Escort3.Stand Off

Noise Jamming(Denial / Obstruction )1. Barrage Injects an interference signal into the enemys electronic 2. Sweep equipment such that the actual signal is completely3. Spot submerged by the interference. Optimum jamming signal4. Smart should have the characteristics of victim receiver noise. Minimum details of victim radar is required.

ELECTRONIC COUNTER MEASURE ( ECM )Barrage JammingJammer instantaneous RF ( X - Band ) BW- 1 GHzVictim radars IF BW- 10 MHzJammer power output ( Noise Energy )- 1000 WNoise Spectral Power Density- 1000 = 1W 1x 109 1x 106Jammer Ant Gain - 13dBi Effective Radiated Power Spectral Density - 20 W/ MHz Effective Radiated Power at IF BW( Noise Power) - 20 x10 = 200 W Spot JammingInst RF BW- 10 MHzSpot Noise Power Spectral Density - 1000W = 100 W/MHz 10Jammer Ant Gain - 13dBi ERP at IF ( Noise Power ) - 20, 000 W

ELECTRONIC COUNTER MEASURE ( ECM )Spatial ( Ref Fig 3.2 )1.Main Lobe JammingStand Off or R2 Vs R42.Side Lobe JammingSupport Jamming Reduction in Radar Range Vs Jamming ERP Spectral DensitySelf - Screening Jamming - Main LobeSpot Noise BW10 MHzRx IF BW 1 MHz Jammer Ant Gain 6 dBiERP Spectral Density reqd for reduction ofRadar range to 10% of nominal range ( from curve in fig 3.2 )0.3W/MHz ERP for 10 MHz BW3 W/ MHzSince Ant Gain is 6dBi (4) Power O/P at Tx3/4 W/MHzIf Radars Rx is broad banded of the order of 1 GHz then Broad band jamming power reqd = 3x1000/43000/4= 750 W

ELECTRONIC COUNTER MEASURE ( ECM )Stand Off JammingJammer at 50 nm from Radar and works through side lobesFor reduction in range to 30% of nominal range jamming ERP spectral density reqd ( from fig 3.2 )650 W / MHz Jammer ant gain 13dBiTx ERP Spectral density reqd32.5 W/ MHzSpot Jamming Power Reqmnt ( 10 MHz )325 W

If Power O/P of Stand - Off Jammer is 2000 WJammer Ant Gain13 dBiThen ERP of Jammer is40 kWERP density for 10 MHz BW at Tx -40 x 103 W/ 10 MHz = 4 x 103 W/MHzRange reduction is 17% at 50 nm, 25%at 100nm, 57% at 50nm for ulta low side lobe, for 100MHz BW 83% and for 1GHz 96%.

ELECTRONIC COUNTER MEASURE ( ECM )

ELECTRONIC COUNTER MEASURE ( ECM )# RCS of Jammer aircraft broadside > end on ( x5)# Limitd power availability# SPJ are therefore are designed for front and tail.Factors Affecting Noise Jammers Effectiveness1. Antenna Polarisation a. Slant / Circular Vs Vertical / Horizontal - 3 dB b. RHC Vs LHC -15 to -20 dB2. Quality of Jammer noise a. Ideal noise - Gaussian noise b. Poor quality noise - 17 dB c. Direct Noise amplification DINA Band limited Gaussian noise ( Rx or thermal noise ) d. Baseband generation and hetrodyned to RF , power amplified and radiated.

ELECTRONIC COUNTER MEASURE ( ECM )

ELECTRONIC COUNTER MEASURE ( ECM ) e. Peak power limited TWTs resulting in clipped noise wave form(Used where the jammer BW>> victim emitter BW ) f. Quasi-linear mode TWT operation - Full noise wave formFrequency / Phase Modulation1. FM / PM is not affected by power amplification saturation2. Freq/Phase modulate noise waveform to obtain max power O/P fromjamming Tx3. Use Gaussian distributed process to Freq modulate jammer Tx with wide phase deviation then O/P spectral density will have an approx Gaussian shape.Gaussian distributed freq control wave form when passed through non-linear amplifier becomes uniformly distributed random wave form. 4. Apply Combined sawtooth and noise waveform with large freq deviation ( Wide Band FM. Mod Inex>>1 ).

ELECTRONIC COUNTER MEASURE ( ECM )5.If victim Rxs impulse response duration ( inversely proportional to Rx BW ) is much greater than Jammers sweep rate, then a number of randomly spaced , independent overlapping impulse responses will be added together to form the victim Rxs O/P wave form. This results in declaration of False targets.6. Narrow Band FM produces many randomly spaced spurious targets and creates confusion. However since these randomly occurring impulse respones do not overlap as in the case of wide band, the real targets are not obscured and can be extracted by appropriate temporal ECCM fix.7. Digital Noise can be generated by regenerative Shift Register techniques. Digital noise can be synchronised to victim radars waveformThis facilitates Spot Jamming / Smart Noise jamming against multiple threats by programming the jammers transmission. This avoids gain capturing in jammers TWT when multiple emitters are simultaneously jammed. Helps in power management of jammer.

ELECTRONIC COUNTER MEASURE ( ECM )Jammer Look -Through Jammers radiation needs to be controlled :-To save powerNot to reveal / compromise safety of jammer platformJammers operate on Look - Through mode interlaced with the jamming transmissions so that intercept receiver can operate with full sensitivity while the jammer is turned off to determine jammers effectiveness such as correct tuning and adequate power level.Emitter signal -85 dBmJammers power level + 63 dBmLook through mode involves separation in -Spatial domain Antenna isolation + Active cancellation (an attenuated sample of transmitted signal is combined in phase opposition with the leakage signal)

ELECTRONIC COUNTER MEASURE ( ECM )Temporal Domain Average switching rate of 20 Hz between intercept Rx and Jammer Tx. Gating of jammer for CW signals. Switches in transmitting and receiving paths of Repeater Jammer to avoid Ring Around EffectSpectral DomainMis -Tuning jammers central Freq by hetrodyning +Dummy Load

ELECTRONIC COUNTER MEASURE ( ECM )Power Management( ECM Resource Management )Need for power management:-1. High Density threat environment Vs Limited power availability of SPJ2. Expanding Types of different types of advanced RADARS Pulse Compression Builds up the signal coherently with respect to Pulse Doppler background noise Spread Spectrum 3. Effective and efficient jamming through integration and automationElements of ECM power management ;-1. ESM Rx - To intercept threat signals and measurement of attributes

ELECTRONIC COUNTER MEASURE ( ECM )2. Digital ComputerTo analyse and interpret threatTo compare with threats in the memoryTo develop an optimum strategyTo employ available jamming assets3. JammerTo radiate jamming pulses as per the strategydeveloped by the digital computer There is a need to define rules of engagement that can cope with a wide variety of military situations and new types of radar threats. Based on apriori information about location, type and operating mode of threat emitters, program ( rules of engagement) should evaluate threat priority,choice of type of jamming ( Noise or Deception ) select specific method of operation and ERP levels ( including antenna directivity ), cope with momentary threats and also monitor the effect / reaction of threat emitter to jamming.

ELECTRONIC COUNTER MEASURE ( ECM )Power management is carried out in Temporal, Spectral, Spatial and Amplitude domains Temporal :- Time sharing of jamming assetsConcentration of jamming energy in a time interval surrounding the time threat pulse is received by RWRRequires apriori knowledge of victim Radars characteristicsTypical Jam Window is of the order of 10% of PRIAnticipation of arrival of emitter pulse ( Tracking )Precise control of Txs and antennae on pulse to pulse basisDeterministic Vs Random pulse waveformsSpectralFunction of freq measurement accuracyNeed to know threat emitters BWTo decide whether Spot or Barrage jammingCoherent threat signals requires coherent storage ( memory )

ELECTRONIC COUNTER MEASURE ( ECM )SpatialUse of narrow fan beam in azimuth provides high ERP in thedirection of threatElectronically steerable phased array antenna - high ERP + ability to engage multiple emitters by rapidly by switchingbeam ( of the order of secs)AmplitudeTo achieve a J/S ( Jamming to Signal) ratio of 10 to 13 dB requires knowledge of DOA of threat signal, RCS in that direction to determine the target amplitude received by the radar.Also determine jammers transmitting and receiving antennagain in that direction to arrive at power required to achieve the desired J/S ratio

ELECTRONIC COUNTER MEASURE ( ECM )Deception Electronic Counter Measure ( DECM )# Objective is to mask the real signal by injecting a suitably modified replica of the real signal in to the victim radar systemUsed by SPJ against Tracking Radars ( terminal threats ) as noise jamming can only deny range information but can be tracked in angle and is susceptible for attack/destruction by radiationseeking and other type of guided missiles. DECM attempts to jam victim radar both in range and in angle. Some DECM also attempt to jam velocity tracking circuits to prevent cross checking between doppler measurements and differentiated range measurement.* DECM requires less energy as compared to equivalent noise jammer which makes it possible to simultaneously jam a number of radars from a single DECM* DECM employs a waveform for which radar Rx is matched. Hence develops additional processing gain in radars using coherent processing

ELECTRONIC COUNTER MEASURE ( ECM )# Advantages over noise jammer : -1. DECM operate at a duty cycle consistent with that of victim radar2. As DECM signal has the properties of a bonafide signal experiences full processing gain of the victim radar.Repeater Jammer :- Radiates replicas of the victim radars signal, possibly delayed in time , modulated in amplitude and shifted in doppler freq as is appropriate to the jammer mode selected. ( Refer Fig 3.4). A memory loop consisting off a delay line and an in line TWT forms the core of repeater jammer. A switch to gate off Rx from the Tx and to connect the signal to the output TWT for transmission, a preamp TWT for reception of weak signal a detector to sense presence of incoming signal and to activate the control circuitary for gating functions. In line TWTs are of CW type while output TWTs are of Pulse type. Delay line is implemented using either a co-axial line or a SAW device. Loop delay must be less than the min expected pulse width. Typical loop delay is of the order of 150 to 250 ns which includes 12- 20ns delayof the loop TWT

ELECTRONIC COUNTER MEASURE ( ECM )Problems :-1.Isolation between Rx and Tx to prevent self oscillation - Ring around-80 to 90 dB isolation. Separation between Tx and Rx antennae 50 dB at 3 GHz and10 feet separation and 62 dB at 10 GHz. Ant coverage restricted.2.Noise capture when no signal is present. Gating of inline TWT or by opening the memory switch.3.Phase discontinuity due to loop delay not being integral multiple of carrier RF period.4. Gradual deterioration due to noise build up and dispersion in the loop delay line. Max storage time limited to 10secs min delay 100ns lags behind real skin target echoes5. Cannot accept intrapulse modulated signals.

ELECTRONIC COUNTER MEASURE ( ECM )

ELECTRONIC COUNTER MEASURE ( ECM )Digital RF Memory ( DRFM ) :- Based on the principle of sampling a video signal at a rate which is twice the highest freq component of interset and storing the digitised samples in a memory and recreating the the signal at a later time using the stored sample. This concept can be extended to complex or RF signals by storing both in phase and quadrature components.A reference oscillator whose O/P freq is same as that of centre freq of the signal and a 900 phase shifted version of the same are mixed ( hetrodyned ) with the signal and the filtered output is stored as in-phase and quadrature base band components. To get back the original signal baseband digitised signal is converted into analog signals again mixed with ref signals and combined with a 900 phase shift.For multiple signsls ref osc freq varies from respective centre freq. Hence the BW involved in the digital storage is not the signal BW but the max freq difference between the ref osc and the extreme freq component of the signal of interest. For example if a 10 MHz video BW radar signal is

ELECTRONIC COUNTER MEASURE ( ECM ) mixed with a ref osc freq of 9.5 GHz , total BW stored must be 510 MHz and not 10 MHz.DRFM operation is independent of storage time and no deterioration of signal fidelity with delay time.Multiple simultaneous signals can be stored and replicated on command.Intra pulse modulated signal such as Pulse Compression and Phase coded signal can be stored and replicated.Doppler shifts can be induced onto the replicated signal by simply offsetting the freq of the ref osc at the DRFM input, which translates the signal to baseband, and ref osc at the output which translates the signal to RF.The memory consists of high speed RAM digital devices. The memory size is a function of the pulsewidth to be stored and the sampling rate determined by the instantaneous BW. The instantaneous BW is typically positioned about the local oscillsators centre freq.

ELECTRONIC COUNTER MEASURE ( ECM )Typical Digital RF Memory Specification

RF OutputsFrequencyInput 1 kHzPulsewidthInput 40nsLevel-12 4dBm over RF bandRF inputsInstantaneous BW400 MHzTuning Range5.4 to 5.9 GHzDynamic Range- 30 dBm to 0 dBmMemoryPulsewidth Capacity100 ns to 27 sec