Page 166 - Radar Technology Encyclopedia

156 ECCM, search radar ELECTRONIC COUNTERMEASURES (ECM)

main ECCM technique against chaff is discrimination of real of the electromagnetic spectrum.” It is one of the three com-
and false returns on the basis of doppler processing (e.g., ponents of electronic warfare. In radar applications its main
MTI). Antiradiation missiles are threats to search radars. One objectives are to deny or to falsify information (detection,
of the best methods of defence is to use a blinking network of measurement, discrimination, and classification data) that the
radars. SAL radar tries to obtain. There are a number of ways to classify
Ref.: Skolnik (1990), p. 9.25; Neri (1991), pp. 418–436; Chrzanowski ECM tactics and techniques. From the point of view whether
(1990), pp. 81, 99. electromagnetic energy is radiated or not, ECM is divided
Tracking radar ECCM is employed in radars whose pur- into active and passive. From the standpoint of what main
pose is to provide good resolution and precise measurement parameters of radar information are influenced, ECM is
of targets parameters. It is based on antenna-, transmitter-, divided into angle-measurement ECM, range-measurement
receiver- and signal-processing-related ECCM techniques. ECM, and velocity-measurement ECM. From the viewpoint
Practically all measures referred to as search radar ECCM, of the types of jammed radars, it is primarily divided into
including maximizing the radiated energy delivered to the tar- ECM versus search (surveillance) radars and ECM versus
get and minimizing the jammer signal entering signal-pro- tracking radars. From the viewpoint of the ECM systems
cessing circuits, are helpful to counter noise jamming in location, onboard and offboard ECM are distinguished. As to
tracking radars. A more threatening ECM technique against tactics of ECM combat employment, typically five classes
tracking radars is deception jamming. Typically, it is decep- can be identified: escort ECM, cooperative (mutual-support)
tion in angle (angle-gate stealing), range (range-gate stealing ECM, self-protection (self-screening) ECM, stand-forward
or range-gate pull-off) and velocity (speedgate stealing or ECM, and stand-off ECM. Some authors include defence sup-
velocity-gate pull-off). Angle-gate stealing is especially pression as an ECM, although others consider it a separate
effective against radars employing conical scanning and ingredient of electronic warfare.
sequential lobing, so monopulse tracking, inherently insensi- ECM is primarily based on jamming: both noise jam-
tive to angle deception jamming from a single point, must be ming and deception jamming. Modern ECM systems are
used in radars where good ECCM efficacy against jamming designed to cope with different types of radars, and they have
in angle is required. Using of leading-edge tracker, tracking to operate in a dense threat environment that requires com-
of both real and false targets in both range and doppler, using puter control of the system. Typical parameters of an
PRF jitter, the mode of multiple PRF operation (low, high and advanced, self-protection active ECM system designed for
medium PRF) and frequency agility are the usual measures fighter-type aircraft are given in Table E1. SAL
against deception jammers in range and doppler domains. Ref.: Schleher (1986), pp. 109–198; Barton (1991), pp. 12.2–12.9; Skolnik
(1990), p. 9.4; Wiegand (1991); Chrzanowski (1990); Neri (1991),
SAL
pp. 337–416; VanBrunt (1978), (1982), (1995).
Ref.: Skolnik (1990), p. 9.25; Neri (1991), pp. 436–438; Chrzanowski
(1990), p. 127.
Table E1
Transmitter-related ECCM is based on the property of a Typical Advanced Self-Protection Jammer Parameters
radar transmitter to control the frequency, power, and wave- Frequency coverage 0.7 to 18 GHz
form of the radiated signal to reduce the effectiveness of
System response time 0.1 to 0.25 sec
ECM. Increasing of the transmitter frequency is analogous to
Receiver-processor:
increasing the antenna aperture in a fixed-frequency system,
narrowing the antenna beamwidth and in turn improving the (a) Dynamic range 50 dB
spatial resolution (see antenna-related ECCM). Control of (b) Sensitivity - 71 dBm
frequency involves primarily frequency agility and frequency (c) Resolution 5 MHz
diversity. The objective of frequency agility and frequency (d) Instantaneous bandwidth 1.44 GHz
diversity is to force the jammer to spread its energy over the
(e) Pulsewidth 0.1 m s (min)
wider bandwidth and to reduce the power density of jamming
(f) Input pulse amplifier 20 dBm (max)
at the radar input. The methods of power control are based
mainly on the brute-force approach of increasing radar trans- (g) False alarm rate 5/h (max)
mitter power or more flexible approaches based on manage- (h) Signal detection capability Pulsed, CW, PD, agile
ment of power in time and space. The control of the Jammer:
waveform includes using waveform coding based on intra- (a) Peak power 58 to 63 dBm
pulse modulation that enables increased signal bandwidth,
(b) Pulse-up capability 5 to 7 dB
shaping of the transmitted radar pulse, and coding of various
(c) Set-on accuracy ± 0.5 to ± 20 MHz
parameters of radar signal (e.g. PRF jitter and PRF stagger).
SAL (d) Duty cycle 5 to 10%
Ref.: Skolnik (1990), p. 9.16; Farina (1992), p. 8. (e) Jamming capability 16 to 32 signals
(f) Modes Noise, deception
ELECTRONIC COUNTERMEASURES (ECM) are
“actions taken to prevent or reduce the enemy’s effective use (from Schleher, 1986, p. 169).