EW6 - Electronic Protection Flashcards
State the two areas of Electronic Protection.
Technical (Electronic) EP
* Techniques within electronic circuitry of a device.
Procedural (Operational) EP
* How the device is used.
* Information security (INFOSEC).
– computer security and emanations security (EMSEC).
» communications security (COMSEC) and electronic security.
* Emission control (EMCON).
Describe the following Transmitter EP techniques: Power
Power:
** – Increase S/J ratio to overcome main lobe jamming by: **
– Transmit more average power for brief period of time.
– Dwell longer on target, concentrating energy to a sector of interest,
– Increasing antenna gain, or
– Combination of any/all of above.
Describe the following Transmitter EP techniques: Polarisation diversity
Polarisation Diversity:
– Jammers must match polarisation for effectiveness.
– Radar should have capability to change polarisation;
* to discriminate between true & deception signals.
Describe the following Transmitter EP techniques: RF diversity
RF Diversity:
– Several complementary radar transmissions at different frequencies;
* from single or several radars.
– Forces jammer to spread power over widest spectrum.
– Limited by practical considerations;
* cost, frequency management, to a finite number of frequencies.
– Stacked beam radar.
– Surveillance radar (2D) coupled with height finder.
– Spatially dispersed radars in netted configuration.
Describe the following Transmitter EP techniques: RF Agillity
RF Agility:
– Rapidly change frequency in pseudo random fashion.
– Keeps narrow instantaneous bandwidth.
– Forces jammer to cover entire possible band.
Describe the following Transmitter EP techniques: PRF agility
PRF Agility:
– Countering interference effects from jamming or other radars.
* Inter-pulse modulation.
– Staggered PRF inhibits creating false targets.
– Jittered PRF prevents creation of false targets at ranges less than target range.
Describe the following Signal Processing EP techniques: Moving Target Indicator
Moving Target Indicator.
* MTI depend on phase shift in radar echo by moving target.
– Can distinguish between fixed, slow, or high speed targets (aircraft)
-even if clutter echo is greater in power aircraft echo.
– MTI developed to neutralise effects of ground clutter & clouds.
– Properties of MTI applicable in overcoming effects of jamming;
* chaff and synchronous pulse jamming.
Describe the following Signal Processing EP techniques: Pulse Compression
Pulse Compression.
– Designed to enhance SnR.
– Achieved by transmitting a coded long pulse for receiver to ‘compress’
- optimise range resolution.
– Jammers have to imitate pulse to effectively jam;
* jamming of pulse compression is more difficult.
Describe the following Signal Processing EP techniques: Constant False Alarm Rate
Constant False Alarm Rate.
– Adaptively adjusts the sensitivity according to the power of clutter returns.
– Doppler radar returns sorted into cells of range and Doppler shift.
– Threshold of each cell set independently;
* dependant on average amount of noise received.
* Prevents noise in one cell “washing out” valid returns in other cells.
Describe the following Spatial Filtering EP techniques: Low Sidelobe Antenna.
Low Sidelobe Antenna.
– Consists of taking extra steps to minimise antenna sidelobes:
* Proper feed design,
* Selection of best aperture illumination,
* Improving engineering & manufacturing tolerances, and
* Locating antenna to minimise scattering from nearby objects - on the radar or nearby structures e.g. fences.
– Parabolic have sidelobe levels around -20dB.
– Techniques to reduce aperture block can reduce to around 30dB.
– To get -40dB and better - use flat plate array
Describe the following Spatial Filtering EP techniques: Multiple Elevation Beams.
Multiple Elevation Beams.
– Multiple beams (elevation beams of search radar) outputs are combined therefore;
– Possible to delete any beam that contains jamming.
Describe the following Spatial Filtering EP techniques: Sidelobe Cancellation.
Sidelobe Cancellation.
– Produces an array null in direction of jamming signal.
– Accomplished;
* Selecting weights applied to individual elements of a phased array, or
* Combining the output of antenna with output of added Omni-directional antenna. The outputs of the auxiliary antennas are correlated with the outputs of the main antennae.
Describe the following Tracking EP techniques: Look Through.
Look Through.
– To determine jammers own effectiveness.
– Jammers stop to “look through” to see if jamming still required.
– Victims exploit this lull period;
* use returns received during this period.
– Prevents jamming, but lowers update rate.
– Achieved by;
* Isolate Tx & Rx antenna – enables simultaneous Tx & Rx.
* Turning jammer off – low duty cycle.
Describe the following Tracking EP techniques: Anti RGPO.
Anti RGPO.
– Based on assumption that jamming return delayed from the target return by transit time of signal through repeater jammer.
– Range gate tracks only leading edge of return.
– Should not be susceptible to range gate pull-off techniques.
Describe the following Tracking EP techniques: Track on Jam.
Track on Jam.
– Attempts to locate direction of jammer through the angular resolution of the antenna.
– The ability of a missile to guide itself toward jamming source.
