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Advanced EW Week 1 > Revision > Flashcards

Revision Flashcards

1
Q

Explain the EW Family Tree

A

EA
Jamming, Deception, Neutralisation

ES
Warning = RWRs, MWS, LWRs
SIGINT = COMINT, ELINT

EP
Active & Passive EPM = EMCON, Masking, Hardening, Wartime Reserve Modes

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2
Q

Explain the military’s main uses of the EM Spectrum

A

Radio communications
Primary and Secondary Radar
IR Detection
Ultraviolet Seekers

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3
Q

What does Radar stand for?

A

Radio Detection and Ranging

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4
Q

What is the speed of light?

A

3 x 10^8 m per second
162000 nm per second
186000 miles per second

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5
Q

Explain the relationship between wavelength and frequency

A

Inversely proportional

The longer the wavelength, the lower the frequency
The shorter the wavelength, the higher the frequency

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6
Q

Polarisation is determined by the orientation of which field?

A

Electric Field

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7
Q

State the relationship between power density and range

A

Power density will decrease as range from the source increases

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8
Q

State the two forms of atmospheric attenuation

A

Absorption

Scattering

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9
Q

Explain Atmospheric Absorption

A

Occurs when the energy from the EM wave dissipates as it interacts with gas molecules

The molecules absorb the radiation

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10
Q

Explain Atmospheric Scattering

A

Occurs when EM waves hit molecules in the atmosphere and change their direction as a result

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11
Q

State what an ES receiver should do

A

Intercept
Measure
Identify
Display

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12
Q

Describe Amplitude Comparison

A

The measurement of the relative amplitude of a signal intercepted by the gain patterns of antennas, that are orientated at different angles with respect to the target

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13
Q

Explain the Block Schematic for an ES Rx:

A

Antenna –> Amps –> Receivers –> Processor –> Outputs

Receivers –> DOA (direction of arrival) Resolver –> Outputs

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14
Q

Describe unintentional pulse modulation and how it is used

A

Caused by system noise and/or different operation / installation of components

helps with Specific Emitter Identification (SEI)

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15
Q

Explain the term Signal to Noise Ratio (SNR)

A

The ratio that describes a radar’s ability to see targets in the presence of noise

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16
Q

Explain the term Bandwidth

A

The difference between the upper and lower frequencies in a continuous set of frequencies

Typically measured in Hertz (Hz)

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17
Q

Describe external factors effecting signal quality

A

Interference
Jamming
Weather Clutter
Ground Clutter

or

Distance from the source
Atmospheric Conditions, Sun Spot Activity
No line of sight, multi-path interference
Jamming

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18
Q

What are the 3 elements of Internal Noise?

A

Equipment noise
Transmission Line Noise
Antenna Noise

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19
Q

Explain Diffraction in relation to propagation

A

The bending of waves around the edges of objects such as buildings and mountains
Longer wavelengths are diffracted more than shorter wavelengths

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20
Q

What are the different wave types?

A 
Ground Wave (Surface and Space)
Sky Wave
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21
Q

State the factors affecting a Space Wave

A

Attenuation = Absorption and Scattering
Average path length is restricted to around 25-40km
For longer distances relay station are required

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22
Q

Which layers of the earth’s atmosphere have a major effect on the performance of EM waves?

A

Ionosphere

Troposphere

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23
Q

Describe a Radar System

A

Synchroniser -> Modulator -> Transmitter -> Switch (Duplexer) -> Antenna
Antenna -> Switch (Duplexer) -> Receiver -> Display -> Synchroniser

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24
Q

List the 3 types of radar transmitter

A

Magnetron (Oscillator)
Travelling Wave Tube (Amplifier)
Field effect transistor (Amplifier)

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25
Q

State the factors that affect Radar (8)

A 
Frequency
PRF
PW
Power
Beamwidth
ARP
Antenna
Weight
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26
Q

What target information can we get from Radar? (6)

A 
Range
Bearing
Height
Course
Speed
Shape/size/outline
27
Q

State the different types of Radar Display

A

Plan position indicator (PPI)
B-scope
A-scope

28
Q

How can height information be obtained from a circular scanning radar?

A

Uses 2 beams, 1 vertical and one at 45 degrees

29
Q

How does a search radar calculate aircraft height using a V-Beam?

A

By measuring the time difference between illuminations in each beam

The longer the time interval, the higher the target

30
Q

What are two types of sector scan?

A

Bi-directional Sector scan?

Uni-directional Sector scan

31
Q

What are the advantages of using a pencil beam?

A

High power
Small beamwidth
Good tracking information

32
Q

Describe a Raster Scan

A

The beam sweeps across each bar to the horizontal limit and then drops or rises to the adjacent vertical bar to continue the next horizontal sweep

This pattern continues until the beam has travelled the vertical extent of the search area

Then the beam returns to the start of the raster ‘frame’ and begins the next sweep

33
Q

Describe a monopulse radar

A

Monopulse radars split the beam into parts and then compares the signal strength of the parts when they return

34
Q

Explain the characteristics and limitations of a Co-axial cable

A

Not suitable for high frequency - over 1 GHz problematic, over 36GHz high attenuation
Not suitable for high power - Flashover and arcing can occur
Internal impedance losses can be high

Flexible

35
Q

Explain the characteristics and limitations of Waveguides

A

Suffers almost no losses
Signals are shielded
Inflexible
Electroplated plastics means no longer heavy

36
Q

Explain the term ‘sidelobe’ in relation to the main beam

A

Energy reflected near to the parabola edges produce extra lobes of RF energy radiating out of the antenna

37
Q

What are the two methods of beam steering?

A

Mechanical

Electronic

38
Q

Describe Mechanical beam steering

A

The beams are steered by the rotation of the antenna

Aircraft radar will tilt the main array to increase the radar FOV

39
Q

List the 3 types of Electronic beam steering and its advantage

A

Phase
Frequency
Time delay

Has the advantage that it is much quicker and more agile then mechanical methods

40
Q

What is the function of a Cosecant Squared Radar?

A

More power at longer range to give similar size returns for the same size target at different ranges

41
Q

What does a Cassegrain Antenna achieve and how?

A

It avoids the problem of a centre null (the feed) by using a sub reflector that changes polarization

42
Q

Define beamwidth

A

The width of the beam in degrees measured at the -3db or half power points

43
Q

State the main components in an antenna system

A

Feed
Reflector
Transmitting medium (co-axial or waveguide)

44
Q

State the relationship between Antenna size and wave length

A

Smaller antenna = smaller wavelength

45
Q

State the 2 main types of array

A

Linear

Planar

46
Q

State 2 methods of array beam steering

A

Mechanical

Electrical

47
Q

What are the different ways of measuring DOA?

A

Amplitude
Phase
Time delay

48
Q

Explain position fixing

A

Multiple LOBs combined to create AOP “Ellipse”

49
Q

Functional analysis - Frequency

A

Range
Higher RF = Greater Attenuation = Shorter Range

Antenna Size
Higher RF = Smaller Antenna

50
Q

Functional analysis - PRF

A

Maximum Ambiguous Range (MUR) (1/2 c /PRF or 1/2 c x PRI
High PRF = Smaller Interval = Shorter MUR

Data Rate
High PRF = High Data Rate

51
Q

Functional analysis - Pulse Width

A

Maximum Detection Range
Large PW = More Average Power = Greater Range

Minimum Range
Large PW = Large Minimum Range

Range Resolution
Large PW = Poor Range Resolution

52
Q

Functional analysis - ARP/Scan

A

Operating Range
Fast ARP = Small Range

Data Rate
Fast ARP = High Data Rate

53
Q

Functional analysis - Beamwidth

A

Angular Resolution

Data Rate
Wider beam = greater dwell time = more pulses hit the target

54
Q

Functional analysis - Power

A

Detect Range
High Power = Increased POI for small targets

Average Power = Peak Power x (PW/PRI)

Duty Cycle = (PW/PRI) x 100

55
Q

Why is DOA important?

A

Fixing Emmitters
De-interleaving
Location of threats

56
Q

What are the four aspects of an ellipse?

A

Major Axis
Minor Axis
Orientation
Position of the centre

57
Q

How does ESM equipment position fix?

A

RWR can be programmed to estimate range of emitter based on received power

58
Q

An EM wave is made up of 2?

A

Fields
E-field (Electrical)
H-field (Magnetic)

59
Q

x10^? Units

A

GHz x10^9
MHz x10^6
KHz x10^3

μs x10^-6

60
Q

Wavelength and Frequency Forumla

A 
wavelength = c/f
f = c / wavelength

c= 3x10^8

61
Q

Explain Polarisation

A

The orientation of the radio wave in respect to the Earth

Determined by the Electric Field

62
Q

What are the types of Polarisation?

A

Random (Static, Light)

Linear (Horizontal, Vertical, Slant)

Circular & Elliptical (Right and Left Hand)

  • 26dB for Mismatch
  • 3dB for Partial Match
63
Q

Explain the three different types of scattering

A

Circumference of sphere is smaller then wavelength = little energy scattered

Circumference of sphere is similar to wavelength = large amounts of energy of varying large values scatters

Circumference of sphere is bigger then wavelength = constant high-level of energy scatters

Advanced EW Week 1 (4 decks)

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