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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
State the factors that affect Radar (8)
``` Frequency PRF PW Power Beamwidth ARP Antenna Weight ```
26
What target information can we get from Radar? (6)
``` Range Bearing Height Course Speed Shape/size/outline ```
27
State the different types of Radar Display
Plan position indicator (PPI) B-scope A-scope
28
How can height information be obtained from a circular scanning radar?
Uses 2 beams, 1 vertical and one at 45 degrees
29
How does a search radar calculate aircraft height using a V-Beam?
By measuring the time difference between illuminations in each beam The longer the time interval, the higher the target
30
What are two types of sector scan?
Bi-directional Sector scan? | Uni-directional Sector scan
31
What are the advantages of using a pencil beam?
High power Small beamwidth Good tracking information
32
Describe a Raster Scan
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
Describe a monopulse radar
Monopulse radars split the beam into parts and then compares the signal strength of the parts when they return
34
Explain the characteristics and limitations of a Co-axial cable
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
Explain the characteristics and limitations of Waveguides
Suffers almost no losses Signals are shielded Inflexible Electroplated plastics means no longer heavy
36
Explain the term 'sidelobe' in relation to the main beam
Energy reflected near to the parabola edges produce extra lobes of RF energy radiating out of the antenna
37
What are the two methods of beam steering?
Mechanical | Electronic
38
Describe Mechanical beam steering
The beams are steered by the rotation of the antenna Aircraft radar will tilt the main array to increase the radar FOV
39
List the 3 types of Electronic beam steering and its advantage
Phase Frequency Time delay Has the advantage that it is much quicker and more agile then mechanical methods
40
What is the function of a Cosecant Squared Radar?
More power at longer range to give similar size returns for the same size target at different ranges
41
What does a Cassegrain Antenna achieve and how?
It avoids the problem of a centre null (the feed) by using a sub reflector that changes polarization
42
Define beamwidth
The width of the beam in degrees measured at the -3db or half power points
43
State the main components in an antenna system
Feed Reflector Transmitting medium (co-axial or waveguide)
44
State the relationship between Antenna size and wave length
Smaller antenna = smaller wavelength
45
State the 2 main types of array
Linear | Planar
46
State 2 methods of array beam steering
Mechanical | Electrical
47
What are the different ways of measuring DOA?
Amplitude Phase Time delay
48
Explain position fixing
Multiple LOBs combined to create AOP "Ellipse"
49
Functional analysis - Frequency
Range Higher RF = Greater Attenuation = Shorter Range Antenna Size Higher RF = Smaller Antenna
50
Functional analysis - PRF
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
Functional analysis - Pulse Width
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
Functional analysis - ARP/Scan
Operating Range Fast ARP = Small Range Data Rate Fast ARP = High Data Rate
53
Functional analysis - Beamwidth
Angular Resolution Data Rate Wider beam = greater dwell time = more pulses hit the target
54
Functional analysis - Power
Detect Range High Power = Increased POI for small targets Average Power = Peak Power x (PW/PRI) Duty Cycle = (PW/PRI) x 100
55
Why is DOA important?
Fixing Emmitters De-interleaving Location of threats
56
What are the four aspects of an ellipse?
Major Axis Minor Axis Orientation Position of the centre
57
How does ESM equipment position fix?
RWR can be programmed to estimate range of emitter based on received power
58
An EM wave is made up of 2?
Fields E-field (Electrical) H-field (Magnetic)
59
x10^? Units
GHz x10^9 MHz x10^6 KHz x10^3 μs x10^-6
60
Wavelength and Frequency Forumla
``` wavelength = c/f f = c / wavelength ``` c= 3x10^8
61
Explain Polarisation
The orientation of the radio wave in respect to the Earth Determined by the Electric Field
62
What are the types of Polarisation?
Random (Static, Light) Linear (Horizontal, Vertical, Slant) Circular & Elliptical (Right and Left Hand) - 26dB for Mismatch - 3dB for Partial Match
63
Explain the three different types of scattering
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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