Page 165 - Radar Technology Encyclopedia

ECCM, antenna-related ECCM, search radar 155

dom scanning to prevent deception jammers from Range gate pull-off ECCM applies to measures taken, either
synchronizing with the antenna scan rate, and other relevant with radar operator support or automatically through ECM
measures. Reduction of beamwidth increases the angular res- sensing and response circuits, to defeat the range gate pull-off
olution and is a valuable feature of any radar operating in a (RGPO) type of jamming employed by deceptive ECM
dense ECM environment. It should be kept in mind, however, (DECM) repeater jammer systems. Nondoppler measuring
that the reduction of beamwidth, for a given aperture size, radars may use a human operator to identify the occurrence of
results in increasing the sidelobe level that worsens a radar’s RGPO, in which case the operator can manually maintain the
antijamming capability, so the reasonable compromise should radar tracking cursor over the correct target. If a victim of
be found in specifying the antenna radiation pattern. The RGPO jamming is netted to another tracking radar, true target
main sidelobe-related techniques are usage of low- and ultra- range may be derived through triangulation. Doppler radars
low sidelobe antennas, sidelobe blanking (SLB) and sidelobe can compare target doppler with range rate derived from
cancellation (SLC). The generalization of SLC techniques in range data differentiation and thus determine which is the cor-
combination with adaptive processing technique is the con- rect target. This ECCM tactic may be frustrated if the jammer
cept of adaptive arrays. This technique is very promising as it also employs velocity gate pull-off (VGPO) techniques, but
is based on advanced methods of digital beam-forming and other ECCM procedures can be invoked to deny the effective-
digital signal processing and permits superresolution capabil- ness of VGPO (see velocity gate pull-off ECCM). RGPO is
ities that can be very useful for ECCM. seldom effective against modern radars when used alone, and
Polarization selection takes advantage of electromagnetic to be effective, a radar ECCM strategy must be devised that
wave polarization features for discrimination of useful signals deals with the several combined forms of range, angle, and
at the interference background. In this case, if only signals doppler jamming techniques that the radar may encounter.
with copolarization are useful, the cross-polarized response PCH
should be kept as low as possible to protect against cross- Ref.: Schleher (1986), pp. 115, 124–125.
polarized jamming. In more complex cases the two orthogo-
Receiver- and signal-processing-related ECCM is ECCM
nally polarized components may be used by the antenna to
based on the properties of the receiver and signal processing
discriminate the useful signal from those received from jam-
to reduce the influence of ECM on radar performance. The
mers and chaff. SAL
main technique associated with receivers is using a wide
Ref.: Skolnik (1990), pp. 9.7–9.16; Farina (1992), p. 6.
dynamic range to avoid saturation of signal-processing chains
The ECCM improvement factor is “the power ratio of the by a jamming signal. Logarithmic and linear-logarithmic
ECM signal level required to produce a given output signal- receivers are normally used to avoid the saturation. Other
to-interference ratio from a receiver using an ECCM tech- techniques often used in radar receivers (e.g., constant-false-
nique to the ECM signal level producing the same output sig- alarm-rate circuits, automatic gain control, fast-time- constant
nal-to-interference ratio from the same receiver without the circuits, etc.) may be useful to prevent saturation, although
ECCM technique.” SAL normally they are not referred as to ECCM techniques.
Ref.: IEEE (1990), p. 15; Johnston (1979), p. 58; Skolnik (1990), p. 9.29. Dicke-Fix devices and various kinds of limiters also can be
used to counter jamming. The main type of signal processing
Electro-optic counter-countermeasures are “the actions
that can significantly reduce the effectiveness of ECM is
taken to ensure the effective friendly use of the electro-optic
coherent signal processing. In modern radars it is imple-
spectrum despite the enemy’s use of countermeasures in this
mented in the form of coherent digital signal processing,
spectrum.” SAL
including digital MTI. SAL
Ref.: Johnston (1979), p. 59.
Ref.: Skolnik (1990), p. 9.18; Farina (1992), p. 9.
Human-factors ECCM is the “ECCM technique that covers
Search radar ECCM is employed in a radar whose purpose
the ability of an air-defence officer, a radar operator, a com-
is to search a large volume of space and locate the position of
manding officer, and/or any other air defence associated per-
detected targets. The major ECM techniques that are threats
sonnel to recognize the various kinds of ECM, to analyze the
for such radars are noise jamming, deception jamming,
effect of ECM, to decide what the appropriate ECCM should
decoys, chaff, and antiradiation missiles. The main tech-
be and/or to take the necessary ECCM actions within the
niques that can be employed against noise jamming are based
framework of the person’s command structure.” SAL
on the concepts of maximizing radar energy delivered to the
Ref.: Skolnik (1990), p. 9.22.
target of interest (burnthrough mode) or/and minimizing the
Operational ECCM is the combination of operational modes amount of jamming energy received by the radar (ultra- and
of the radar in response to a specific ECM threat. This group low-sidelobe antennas, sidelobe blanking and cancellation,
of techniques can be subdivided into those involving methods frequency agility and frequency diversity, use of coded wave-
of operation, radar deployment tactics, work of radar opera- forms). Techniques employed against the deception jamming
tor, and friendly electronic support measures in aid of ECCM. can use PRF stagger and jitter or measurement and analysis of
SAL angular, doppler or polarization characteristics of radar ech-
Ref.: Farina (1992), p. 6; Skolnik (1990), p. 9.21-9.22. oes to discriminate between real and false-target returns. The