Page 241 - Radar Technology Encyclopedia
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231 jamming, self-screening [-protection] JITTER
ment by air-defense weapons systems. Self-protection jam- Stand-forward [stand-in] jamming is jamming emitted
ming may use noise jamming to deny the victim radar or from a platform located between the weapon system and the
missile seeker range information, or it may employ a reper- strike vehicle. Since the stand-forward jammer usually is
toire of deceptive jamming techniques to frustrate the vic- located within the lethal range of defensive weapon systems
tim’s angle tracking and homing guidance system. PCH for a considerable time, the use of remotely piloted vehicles
as a platform for jammer is practical. SAL
Sidelobe jamming is “jamming through a sidelobe of the
receiving antenna in an attempt to obliterate the desired signal Ref.: Skolnik (1990), p. 9.6; Chrzanowski (1990), p. 82.
received through the mainlobe of the receiving antenna at Standoff jamming is jamming emitted from a support plat-
fixed points.” SAL form (typically an aircraft) orbiting within line-of-sight of a
Ref.: Johnston (1979), p. 66. victim radar but beyond the range of the defensive system.
When the protected vehicles start their penetration of the
The jamming-to-signal ratio (JSR or J/S), is ratio of the
combat area, the support vehicle can direct jamming against
power received from a jammer (or jammers) to the target sig-
all significant radars in this area. In principle it is a generic
nal power received, as measured at a common point in the
term applied to standoff ECM, escort ECM, and cooperative
victim radar (e.g., at the radar antenna terminals). For the
ECM. The term support jamming can be applied to this or any
general noise-jamming case, this ratio can be expressed as
other offboard jamming technique. SAL
2 Ref.: Johnston (1979), p. 67.
æ P G A B F ö
j
j r r j
ç ------------------------------ ÷ 2 straddle jamming (see two-signal jamming).
2
è 4p R B L ø P G æ F öB æ 4
1
J j j aj æ j j ö j æ r ö R öL a öæö
æ
--- = ----------------------------------- = ----------- ç ------ ÷ ----- ç ------- ÷ -------- ---
èø
S 4 è P G ø 4 è B ø 2 è L ø s Support jamming is any type of jamming originating on a
t è
æ P G A sF ö t F ø j è R j ø aj
t
t r
ç ---------------------------- ÷ platform other than the radar target.
2 4
è ( 4p ) R L ø
a
surface-bounce jamming (see ground-bounce jamming).
where the radar parameters are identified in accordance with
A swept jammer is a jammer that sweeps a narrow band of
the radar range equation. Here the subscript j applies to the
electronic energy over a broad bandwidth. A transmitter in
jammer parameters, r applies to the victim radar parameters,
which a narrowband signal can be tuned over a broad fre-
F includes the relative radar antenna gain in the direction of
j
the jammer, and L represents the signal loss due to atmo- quency ban and then locked on a particular frequency is
a
spheric attenuation (one-way for the jammer, two-way for the called a sweep-lock-on jammer. SAL
radar signal). (See also barrage noise jamming, RANGE Ref.: Johnston (1979), p. 67.
EQUATION, with jamming.) PCH Two-frequency jamming is jamming emitted as two jam-
ming carriers separated by the IF of the victim radar. In this
Skirt-frequency jamming is jamming that can be used
case radar receivers that lack RF preselection are subject to
against monopulse radar based on the fact that sum and differ-
generation of spurious outputs. The effectiveness of this
ence channels must be well matched in phase so that the error
method depends on the jamming level and receiver perfor-
detector can preserve the polarity of the target error voltage.
mance, in particular on the nonlinearity of input mixers. Basi-
An error in receiver phase matching causes a shift in the
cally the technique is applied against radar seekers that must
tracking point, and if error exceeds 90° the tracking loop may
operate at very short ranges. The main ECCM is to use RF
settle on the previously unstable null, more than one beam-
preselection or amplitude comparison after envelope detec-
width away from the desired tracking axis. A jamming tech-
tion. DKB, SAL
nique that exploits this problem is called skirt-frequency
jamming, because it produces a signal lying on the skirts Ref.: Barton (1989), p. 501.
(edges) of the IF passband. DKB, SAL two-point coherent jamming (see cross-eye jamming).
Ref.: Barton (1989), p. 497.
Two-signal jamming “is a method of jamming whereby two
A smart noise jammer is a hybrid type of jammer that incor- signals are transmitted on two frequencies only slightly sepa-
porates the features of both noise and deception jamming. In rated. Effective against certain types of radars where receiver
this case, repeater-type jammer generates responsive noise in bandwidth is narrow enough to defeat noise jamming.” SAL
a transponder mode. A noise burst occurs before and after the Ref.: Johnston (1979), p. 67.
actual target return and covers the true echo. The span of
JITTER. (1) The noise-like fluctuations due to target echo
ranges where the noise is radiated is synchronized to the vic-
characteristics, propagation, or receiver thermal noise that
tim radar and the jammer may adapt its directive beam to the
degrade the tracking accuracy and result in zero-mean ran-
angles of arrivals of radar illumination. SAL
dom errors in successive target position measurements.
Ref.: Barton (1988), p. 367; Schleher (1986), p. 11.
Sometimes is termed also tracking noise. (2) “Intentional
Spot jamming is “the jamming of a specific channel or fre- variation of a radar parameter, for example, pulse interval.”
quency.” SAL SAL
Ref.: Johnston (1979), p. 67. Ref.: IEEE (1990), p. 19; Skolnik (1980), p. 167.