Page 170 - Radar Technology Encyclopedia

ECM, range measurement ECM, velocity-measurement 160

waveform permits a frequency shift to produce an early out-
Table E2
put from the pulse compression filter).
ECM against Search Radar
Against sophisticated trackers the apparent target accel-
eration of the repeater pulse must be maintained within the Effects of ECM
ECM type ECCM techniques
limits that can represent an intended target. In the third phase, on radars
when the target echo is not contributing to the output of the
Barrage noise:
gate, angle deception modulations may be applied to the
repeater pulse in an attempt to introduce an error in angle · SOJ Prevent target Low-sidelobe anten-
tracking rate. In the fourth phase, the repeater pulse is turned detection and acqui- nas, sidelobe
sition cancellation, coher-
off, breaking the tracking loops. If sufficient angle rate has
ent integration
been introduced into the tracking loops, the beam may drift
· SSJ and ESJ
off the target before the receiver gain is increased and reac- Prevent target Jammer strobe pro-
quisition of the target is attempted. This will force the radar to detection and acqui- cessing, coherent
reinitiate its complete acquisition scan process, during which sition integration
time the target is not under track. In the absence of a signifi- Spot noise:
cant angle rate, the range gate can be swept to reacquire the
· SOJ Prevent target Same as barrage
target within fractions of a second. SAL, DKB detection and acqui- noise SOJ plus fre-
Ref.: Schleher (1986), pp. 143–145; Chrzanowski (1990), pp. 71–86, 114– sition quency agility
117; Lothes (1990), pp. 114–119.
As above, plus Same as barrage
ECM versus search radar is used to prevent detection and · SSJ and ESJ receiver saturation noise SSJ, plus fre-
acquisition of the target. To achieve this goal all main meth- quency agility, wide
ods of active and passive jamming may be employed, includ- dynamic range
ing noise jamming, deception jamming, and use of chaff and receivers
decoys. The main types of ECM and relevant ECCM tech- Swept noise Same as barrage Guardband con-
niques are cited in Table E2. SAL noise, plus false tar- trolled blanking
Ref.: Barton (1991), p. 12.15; Chrzanowski (1990), pp. 51–109. get generation
Self-screening ECM is “conducted by individual combat ele- Repeater (SSJ False target genera- Multiple track file
1
ments to deny acquisition, tracking, or fire-control data to and ESJ) tion, track file maintenance , side-
1
hostile weapon system.” Typically, it requires that the single saturation lobe blanking (ESJ)
aircraft penetrating through an air defence system rely upon Decoys:
its own ECM capabilities. SAL · Active False target genera- Multiple track file
1
Ref.: Schleher (1986), p. 13; Skolnik (1990), p. 9.6 repeater tion, track file maintenance , target
· Passive saturation 1 analysis
Stand-forward ECM is the ECM tactic “in which the jam-
ming platform is located between the weapon systems and the Chaff Prevent target Doppler filtering and
detection and acqui- MTI
strike vehicles and jams the radar to protect the strike vehi-
sition, false target
cles.” In this case only remotely piloted vehicles can meet the
generation
safety requirements as the platform with the jammer is usu-
1 Assumes track-while-scan (TWS) operation
ally located within the lethal range of defensive weapon sys-
tem for a long period of time. SAL from Barton (1991), p. 12.16.
Ref.: Skolnik (1990), p. 9.6.
Velocity-measurement ECM is used to disrupt the measure-
Stand-off ECM is the ECM tactic in which missions are
ment of velocity based on doppler shift measurement with a
“conducted outside the lethal zones of hostile weapon-control
doppler filter bank. In this case, deception jamming has a
systems to provide ECM support for friendly forces subject to
preference over noise jamming, as the latter has to spread its
hostile fire.” Typically, the stand-off ECM system must pro-
energy over the expected range of frequencies of possible
vide high-power noise jamming able to jam the victim radar
radar returns (that may be tens of percent of the carrier fre-
through the sidelobes at long ranges. SAL
quency), resulting in very high requirements of effective radi-
Ref.: Schleher (1986), p. 12; Skolnik (1990), p. 9.6.
ated power. The main type of deception jamming against
ECM versus tracking radar is used to prevent or delay doppler radar is velocity-gate pull-off (VGPO), which is a
acquisition of the target and to disrupt the tracking function of deceptive jamming technique, often used by self-protection
the radar (or at least introduce intolerable measurement airborne jammers against coherent tracking radars or missile
errors). The primary types of ECM against tracking radar and seekers, to produce erroneous target doppler measurement
relevant ECCM techniques are cited in Table E3. SAL and ultimately to cause break-lock of the doppler-tracking
Ref.: Barton (1991), p. 12-17; Chrzanowski (1990), p. 109-164. loop. The jammer is either a true repeater or a transponder
repeater that captures the victim radar or missile seeker veloc-
.