EEE381B Aerospace Systems

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EEE381BAerospace Systems Avionics

• Electronic Warfare
• Ref Moir Seabridge 2006, Chapter 6
• Dr Ron Smith

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Outline

• Introduction
• Signals Intelligence (SIGINT)
• Electronic Support Measures (ESM)
• Electronic Countermeasures (ECM)
• Defensive Aids
• Jam resistant radar design
• Exercises

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1. Introduction
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1.1 Electronic Warfare Roles

• Electronic warfare (EW) plays both a strategic
  and tactical role in any modern military
  operation.
• Assets are employed in supportive, protective and
  offensive measures.
• Specific capabilities and equipment
  specifications are usually highly classified.

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1.2 The EW spectrum
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1.3 The intelligence cycle

• The picture below depicts the typical, continuous
  cycle of intelligence gathering and application.

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1.4 EW elements
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2. Signals Intelligence (SIGINT)

• Military intelligence typically involves the
  following sources
• human intelligence (HUMINT)
• image intelligence (IMINT)
• photographic intelligence (PHOTINT)
• signals intelligence (SIGINT)
• SIGINT is further broken down into
• communications intelligence (COMINT)
• electronic intelligence (ELINT)

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2.1 COMINT

• Communications intelligence operations involve
  the collection of

• the locations and numbers of specific
  communication transmissions,
• their signal characteristics,
• their messages, as well as
• any communication patterns (including silence).

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2.2 ELINT

• Electronic intelligence operations involve the
  collection of the source and direction of arrival
  (DOA) of a broad range of radar emitters.
  Signals are analyzed for such things as

• frequency,
• pulse and PRF,
• signal strength,
• modulation schemes,
• scan parameters, and
• usage patterns.

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2.3 Airborne intelligence gathering

• A typical airborne intelligence operation
  involves high-flying specialized aircraft
  gathering emissions data on long patrol flights
  along national borders and outside missile
  engagement range.

• In the 1980s and 1990s Canada employed CE144
  Challengers in a national ELINT role
• one specially equipped aircraft commonly referred
  to as the Manitou was operated by the CF.

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2.4 Typical COMINT/ELINT architecture
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3. Electronic Support Measures

• Similar to an ELINT system, an Electronic Support
  Meausres (ESM) systems role is to detect and
  classify received radar emitters. The difference
  being that an ESM is generally employed
  tactically (for use against immediate threats).
• An effective ESM will identify the location, type
  of transmitter, mode of operation (search, track,
  engaged) and level of threat of each emitter.
• Real-time signal analysis is performed against
  received signals, comparing them with known
  emitter characteristics stored in its threat
  library
• the library having been developed based upon
  intelligence data

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3.1 ESM employment

• Electronic support measures may be employed in
  formation support role aircraft such as that of
  an AWACs or a coastal patrol aircraft.
  Alternatively, it may be employed tactically in a
  radar warning mode such as in an attack aircraft.
• Canadas CP140 Aurora Incremental Modernization
  Program (AIMP) includes the fitment of the
  AN/ALQ-217 ESM suite in block 3 of the program.
  This suite will be used in both formation support
  and self-defence roles.
• 50M (US) for 24 systems

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4. Electronic Countermeasures

• Electronic countermeasures (ECM) involve taking
  actions to interfere with or deceive the enemys
  radar system.
• Electronic counter-countermeasures (ECCM) involve
  taking actions to interfere with or deceive the
  countermeasures so as to restore radar use.
• and so on, and so, in a classic cat and mouse
  game.

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4.1 Noise Jamming

• Active noise jamming involves the transmission of
  high power white noise directed at the enemy
  radar with the intent of interference.
• Effectiveness is based upon such parameters as
• jammer power
• antenna gain
• transmitter bandwidth
• Typical types of noise jamming techniques
  include
• barrage jamming
• swept-spot jamming
• multiple-spot jamming

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4.1.1 Effects of noise jamming
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4.1.1.1 Effects of noise jamming 2
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4.1.2 Burnthrough range

• With any noise jamming technique there is some
  range at which the strength of the radar echo
  becomes stringer than the jamming noise, this is
  known as the burnthrough range.
• The range of the radar return is a function of
  1/R4, whereas the range of the jamming signal is
  a function 1/R2.
• Therefore the closer the jammer gets to the
  radar, the more likely it is that the radar
  breaks through the noise signal this is depicted
  on the graph in the next slide.
• A radar with low gain and poor sidelobes is
  susceptible to jamming, conversely a high power
  noise jammer becomes a target and is
  susceptible to home-on-jamming attacks.

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4.1.2.1 Burnthrough depicted
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4.2 Deception Jamming

• Radar deception techniques are more sophisticated
  and can often be achieved without the radar
  (operator) knowing that jamming is being used.
  Typical techniques include
• false target generation
• range gate stealing
• velocity gate stealing
• angle track breaking

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4.2.1 False targets range gate stealing

• By knowing the radar pulse parameters, false
  targets can be injected into a radar by
  replicating or repeating well timed pulses so as
  to appear as spurious random targets.
• Range gate stealing (RGS) is a similar deception
  jamming technique that begins by transmitting a
  strong enough signal to mask the true radar
  return. Once this is achieved the pulse is
  walked off the echo range until the radar loses
  accurate range information. Jamming may then stop
  and repeat the process making it difficult for
  the radar to gain lock.

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4.2.1.1 Range gate pull-off (RGPO)
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4.2.1.2 Range gate pull-off (RGPO)
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4.2.1.3 Range gate pull-off (RGPO)
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4.2.2 Other deception techniques

• Velocity gate stealing (VGS) works much the same
  as range gate stealing except that the
  transmitted jamming signal contains false Doppler
  frequency shifts causing errors in the radars
  velocity calculations.
• Angle track breaking requires knowledge of the
  radar tracking method and scan parameters
  (perhaps from an on-board ESM, or previous
  intelligence). Angle track can then be affected
  by appropriate signal modulation (as the case of
  conscan). Other techniques include terrain
  bouncing, cross-polarization, and sidelobe
  jamming.

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4.3 Airborne jamming platforms

• Airborne jammers (and their platforms) are
  generally employed in one of two common modes
• Self-screening mode is provided by on-board
  jammer(s) as protection suites. These systems
  are generally highly integrated into the mission
  suite.
• Escort and stand-off mode is provided by support
  aircraft, with stand-off aircraft usually
  operating outside harms way. These systems are
  generally stand-alone and often more powerful and
  capable than self-screen ones.

The EA-6B Prowler is being replaced with the
EA-18G Growler (escort / stand-off role)
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4.3.1 Airborne jamming platforms 2
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5. Defensive Aids

• When operating in a hostile environment an
  aircraft must be equipped with appropriate
  self-defence measures.
• In Canada these are collectively referred a
  defensive electronic warfare (DEW) suite
• Common threats faced by aircraft include
• Small arms fire
• Radar guided anti-aircraft missiles (AAA)
• Shoulder-launched surface-to-air missiles (SAM)
• SAM from ground sites, vehicles or ships

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5.1 Radar warning receiver (RWR)

• The goal of an RWR is to detect the presence of a
  hostile radar prior to the radar detecting you.
• A typical architecture includes 4 sensors located
  at the wing tips with each providing up to 90
  conical coverage.
• A typical antenna would be a spiral with 75
  beamwidth and 10 dB gain.

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5.1.1 A typical RWR architecture
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5.2 Other warning receivers

• A missile warning receiver (MWR) is designed to
  detect the infrared (IR) or ultraviolet (UV)
  emissions of a missile.
• This system may employ up to 6 sensors, each with
  110 of coverage (providing front and rear
  protection.
• Similarly a laser warning receiver (LWR) provides
  detection against missiles that emit signals in
  the laser band.

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5.3 Countermeasure dispensers

• While warning receivers are designed to detect
  the presence of a threat, countermeasure
  dispensers offer a defence against an imminent
  (launched) attack. Typical dispensers include
• Chaff
• Flares
• Towed Decoys

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5.3.1 Chaff

• Chaff is the oldest form of radar EW, dating back
  to WWII, then known as window.
• Chaff consists of tiny pieces of reflective metal
  foil or plastic. It is cut into ½ wavelength
  strips and dispensed in cloud bursts behind the
  aircraft, thus forming a brief but large RCS so
  as to break the lock of an incoming missile.
• Usually used in conjunction with evasive
  manoeuvres.

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5.3.1.1 Chaff
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5.3.2 Flares
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5.3.3 Towed decoys
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5.4 F/A-18E/F Defensive EW
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5.5 Modern active decoys
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6. Jam resistant radar design

• Modern radar designs include features which make
  them less vulnerable to traditional EW techniques
  including
• Low antenna sidelobes
• Sidelobe blanking
• Wide dynamic range with fast automatic gain
  control
• Constant false alarm rate (CFAR) reduction

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6.1 Jam resistant radar design

• Modern radars also include low probability of
  detection techniques in order to prevent being
  detected (before any EW can begin). Typical
  techniques include
• A purposeful reduction in peak power
• Frequency agility along with an increase in
  receiver bandwidth (with advanced low loss, low
  noise floor receivers)
• Very high gain antennas 55dB above the first
  sidelobe

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7. In-class exercises
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7.1 Quick response 1

• How might a frequency agile radar be able to
  defend itself against spot noise jamming?
• What noise jamming mode will the jammer have to
  resort to and at what cost?

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7.2 Quick response 2

• Range gate pull-off (RGPO) injects false targets
  at ranges beyond that of the jammer. How could
  false targets be injected between the jammer and
  the radar?
• What key radar parameter must be known for this
  to work?

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7.3 Quick response 3

• How could knowledge of a radars scan pattern and
  antenna characteristics be used to effectively
  jam the radar?

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References

• Moir Seabridge, Military Avionics Systems,
  American Institute of Aeronautics Astronautics,
  2006. Sections 2.6 2.7
• Radar in an Active Target Environment, student
  laboratory manual, 38542-00, Lab-Volt (Quebec)
  Ltd, 2006.
• David Adamy, EW101 - A First Course in Electronic
  Warfare, Artech House, 2000. Chapters 3,4 6
• George W. Stimson, Introduction to Airborne
  Radar, Second Edition, SciTch Publishing, 1998.
• Mark A. Hicks, "Clip art licensed from the Clip
  Art Gallery on DiscoverySchool.com"