电子战讲座Electronic Warfare.ppt

1、EEE381BAerospace Systems 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,4.1.2.1Burnthrough depicted,EEE381B,4.2 Decepti

2、on 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,4.2.1 False targets & ra

3、nge 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

4、 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,4.2.1.1 Range gate pull-off (RGPO),EEE381B,4.2.1.

5、2 Range gate pull-off (RGPO),EEE381B,4.2.1.3 Range gate pull-off (RGPO),EEE381B,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 vel

6、ocity 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

7、, cross-polarization, and sidelobe jamming.,EEE381B,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

8、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

9、(escort / stand-off role),EEE381B,4.3.1 Airborne jamming platforms 2,EEE381B,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 threa

10、ts 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,5.1 Radar warning receiver (RWR),The goal of an RWR is to detect the presence of a hostile radar prior to the radar

11、 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,5.1.1 A typical RWR architecture,EEE381B,5.2 Other warning receivers,A missile warning recei

12、ver (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

13、laser band.,EEE381B,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,5.3.1 Chaff,Chaff is the oldest fo

14、rm 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 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. Usual

15、ly used in conjunction with evasive manoeuvres.,EEE381B,5.3.1.1 Chaff,EEE381B,5.3.2 Flares,EEE381B,5.3.3 Towed decoys,EEE381B,5.4 F/A-18E/F Defensive EW,EEE381B,5.5 Modern active decoys,EEE381B,6.Jam resistant radar design,Modern radar designs include features which make them less vulnerable to trad

16、itional EW techniques including: Low antenna sidelobes Sidelobe blanking Wide dynamic range with fast automatic gain control Constant false alarm rate (CFAR) reduction,EEE381B,6.1 Jam resistant radar design,Modern radars also include low probability of detection techniques in order to prevent being

17、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,7.In-class exercises,E

18、EE381B,7.1Quick 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,7.2Quick 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,7.3Quick response #