EEE381B Aerospace Systems & Avionics

1. EEE381BAerospace Systems & Avionics Electronic Warfare Ref: Moir & Seabridge 2006, Chapter 6 Dr Ron Smith

2. Outline • Introduction • Signals Intelligence (SIGINT) • Electronic Support Measures (ESM) • Electronic Countermeasures (ECM) • Defensive Aids • Jam resistant radar design • Exercises EEE381B

3. 1. Introduction EEE381B

4. 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. EEE381B

5. 1.2 The EW spectrum EEE381B

6. 1.3 The intelligence cycle • The picture below depicts the typical, continuous cycle of intelligence gathering and application. EEE381B

7. 1.4 EW elements EEE381B

8. 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) EEE381B

9. 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). EEE381B

10. 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. EEE381B

11. 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. EEE381B

12. 2.4 Typical COMINT/ELINT architecture EEE381B

13. 3. Electronic Support Measures • Similar to an ELINT system, an Electronic Support Meausres (ESM) system’s 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 EEE381B

14. 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. • Canada’s 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 EEE381B

15. 4. Electronic Countermeasures • Electronic countermeasures (ECM) involve taking actions to interfere with or deceive the enemy’s 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. EEE381B

16. 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 EEE381B

17. 4.1.1 Effects of noise jamming EEE381B

18. 4.1.1.1 Effects of noise jamming [2] EEE381B

19. 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. EEE381B

20. 4.1.2.1 Burnthrough depicted EEE381B

21. 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 EEE381B

22. 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. EEE381B

23. 4.2.1.1 Range gate pull-off (RGPO) EEE381B

24. 4.2.1.2 Range gate pull-off (RGPO) EEE381B

25. 4.2.1.3 Range gate pull-off (RGPO) EEE381B

26. 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. EEE381B

27. 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) EEE381B

28. 4.3.1 Airborne jamming platforms [2] EEE381B

29. 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 EEE381B

30. 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. EEE381B

31. 5.1.1 A typical RWR architecture EEE381B

32. 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. EEE381B

33. 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 EEE381B

34. 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. EEE381B

35. 5.3.1.1 Chaff EEE381B

36. 5.3.2 Flares EEE381B

37. 5.3.3 Towed decoys EEE381B

38. 5.4 F/A-18E/F Defensive EW EEE381B

39. 5.5 Modern active decoys EEE381B

40. 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 EEE381B

41. 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 EEE381B

42. 7. In-class exercises EEE381B

43. 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? EEE381B

44. 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? EEE381B

45. 7.3 Quick response # 3 • How could knowledge of a radar’s scan pattern and antenna characteristics be used to effectively jam the radar? EEE381B

46. 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" EEE381B