Page 239 - Radar Technology Encyclopedia

229 jamming, ground-bounce jamming, noise

times this kind of countermeasure is called surface-bounce provided with an objective of determining its own effective-
jamming or terrain-bounce jamming. SAL ness, for example, correct tuning and sufficient power level.
Ref.: Barton (1989), p. 530; Schleher (1986), p. 160; Chrzanowski (1990), This is usually accomplished by using an intercept receiver
p. 155. that can be an integral part of or complement the jammer
Image-frequency jamming is jamming penetrating a itself. SAL
receiver through the radar image channel, separated by twice Ref.: Schleher (1986), p. 133.
the intermediate frequency from the intended response. As an Mechanical jamming is the term sometimes used for chaff.
ECCM, use of RF preselector is successful. SAL SAL
Ref.: Barton (1988), p. 499. Ref.: Johnston (1979), p. 63.
Imitative jamming is “the jamming technique of transmit- Modulated jamming is a jamming signal obtained by modu-
ting a signal identical to the original guidance signal.” This is lating a CW signal. The main types of modulation used in
accomplished through the use of a repeater jammer. SAL jamming are pulse modulation, sinusoidal modulation, and
Ref.: Johnston (1979), p. 61. sawtooth modulation. SAL
Ref.: Johnston (1979), pp. 63, 65, 66.
Intermittent jamming is jamming that is not continuous.
Intermittent jamming may occur unintentionally as a conse- Multiple-source jamming is jamming employing spatially
quence of electromagnetic interference (EMI) from one or dispersed jamming sources. The phase characteristics of these
several sources of RF energy at the victim radar frequency or jammers may be either coherently or noncoherently related.
one of its harmonics. Intentional jamming sources that may In the first case a deterministic or synchronized relationship
be intermittent in nature include frequency-swept jamming between the phase of multiple jammers is implied, and the
and other jamming techniques designed to attack one or more term multiple-source coherent jamming is used. The repre-
functions of a fire control radar that may be sequential or sentative of such a technique is cross-eye jamming. When the
periodic in nature, such as those functions related to weapon relationship among jamming sources is random, the technique
system guidance and control. is termed multiple-source noncoherent jamming. The major
One type of intermittent jamming is single-source blink- representatives of this technique are blinking jamming and
ing jamming, consisting of periodic bursts of rectangular formation jamming. In Russian radar literature, this type of
pulses radiating by the same jamming transmitter. This type jamming is called multipoint jamming. SAL
of jamming affects the receiver with AGC using the transient Ref.: Schleher (1986), pp. 154–159; Maksimov (1979), p. 54.
processes that take place in an AGC system when its input is
Multitarget generator jamming refers to use of a special
acted upon by strong pulse signal. It overloads the receiver
generator to produce numerous targets designed to saturate
and interrupts the transmission of information to the tracking
the tracking capability of a radar. It is controlled by comput-
channel reducing the average gain of an angle tracking sys-
ing when to transmit false targets at the radar’s frequency on
tem. The main ECCM solution to this type of jamming is to
the basis of information about a radar’s pulse repetition fre-
extend the dynamic range of the receiver to the value over
quency, scan rate, and antenna pattern. SAL
which useful output can be obtained, and to use fast AGC or
Ref.: Johnston (1979), p. 63.
logarithmic amplifiers to minimize the time spent in satura-
tion mode. PCH, SAL Noise jamming has the objective of masking the actual sig-
nal. In principle, noise jamming increases the radar receiver
Ref.: Barton (1989), p. 496; Maksimov (1979), p. 57.
noise level and the optimum jamming signal has the charac-
Intermediate frequency jamming is “the form of continu-
teristics of receiver noise (that in practice may be difficult to
ous-wave jamming that is accomplished by transmitting two
achieve). From the point of view of the occupied bandwidth,
CW signals separated by a frequency equal to the center fre-
noise jamming is classified as barrage noise jamming when
quency of the radar receiver IF amplifier.” SAL
the bandwidth extends over the entire tuning band of the vic-
Ref.: Johnston (1979), p. 62.
tim radar, and spot noise jamming when the bandwidth is less
Inverse-gain jamming is jamming that repeats the replica of than that of the radar and power is concentrated at the radar
the received signal with an induced amplitude modulation signal frequency. From the viewpoint of waveform, noise
that is the inverse of the victim radar’s combined transmitting jamming is divided into continuous noise jamming and pulse
and receiving antenna scan patterns. It was designed to be noise jamming. Continuous noise jamming in its turn can be
used against conical-scan radars where it inserts an effect categorized as direct noise jamming (when random noise is
similar to positive feedback, and this effect pushes antenna amplified and radiated directly), and modulated noise jam-
away from the target rather than to the target. The jammer ming (amplitude- or frequency-modulated). Pulse jamming
employing such a technique is called an inverse-gain repeater may be represented as a burst of RF pulses with a given duty
jammer. (See also GAIN, inverse). SAL factor and random change of pulse amplitude, duration and
Ref.: Skolnik (1990), p. 9.6; Johnston (1979), p. 62; Schleher (1986), p. 11. the spaces between the adjacent pulses (random pulse noise
jamming which is difficult to produce in practice), and jam-
Jammer look-through is the mode of jammer operation
whereby periodic monitoring of the threat environment is