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Core 1 20B > Low Observables > Flashcards

Low Observables Flashcards

1
Q

Define Stealth

A

The act of proceeding secretly or imperceptibly

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2
Q

Define aircraft survivability

A

The ability of an aircraft to avoid and/or withstand a hostile engagement and still accomplish the mission

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3
Q

Stealth is accomplished by

A

Reducing active and passive signatures to make an aircraft less “visible”

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4
Q

Active signatures are all the observable emissions from an aircraft and include:

A

RF Signals (communications, navigation, radar)
Acoustic (engine or propeller noise)
Infrared (engine exhaust, skin temperature)

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5
Q

Passive signatures are all of the observable signals from an aircraft resulting from external illumination (reflection) and include:

A

Electro-optical / visual

Electromagnetic (radar)

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6
Q

Low Probability of Intercept (LPI) methods include

A 
Power management
Maximum frequency bandwidth
Frequency agility
Emission time control
Signal directionality
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7
Q

What are common acoustic signature reduction techniques

A

Engine placement
Exhaust nozzle design
Mixing engine jet with ambient air

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8
Q

Engine exhaust and afterburners are examples of which type of IR

A

Near and mid IR

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9
Q

Aircraft skin is an example of which type of IR

A

Far IR

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10
Q

Define Radar signature

A

the measure of a target’s ability to reflect RF signals in the direction of the radar receiver

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11
Q

Radar signature varies with:

A

RF wavelength and viewing angle

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12
Q

Radar Cross Section (RCS) is typically measured in

A

square meters

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13
Q

What is RCS

A

The amount of energy scattered back to a radar by a target

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14
Q

Factors that affect RCS

A 
Projected cross-section
Reflectivity
Directivity
Specular reflections
Traveling wave returns
Creeping wave returns
Diffraction
Radar frequency
Signal polarization
Surface smoothness
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15
Q

Define Projected Cross-section

A

Projected area the target presents to the radar

Similar to aerodynamics, a lower amount of drag is similar to a lower amount of projected cross-section

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16
Q

Define Reflectivity

A

Fraction of intercepted power that is reflected by the target, regardless of direction

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17
Q

Define directivity

A

The ratio of power that is backscattered in the direction of the radar that would have been backscattered in that direction if the scattering were uniform in all directions

18
Q

What is specular reflection

A

The most significant form of reflection

Reduced significantly by shaping

19
Q

Define traveling wave returns

A

Incident wave strikes the aircraft body at a very slight incident angle.
The wave propagates on the surface and scatter is increased when discontinuities (surface gaps or shape changes or material changes) occur

20
Q

Define Creeping wave

A

Form of traveling wave that does not encounter surface discontinuities and allows the wave to travel back to the radar. Common in tubular surfaces and not stealth aircraft

21
Q

Define diffraction

A

Waves striking a very sharp surface or edge are scattered

22
Q

How does polarization affect radar returns

A

Horizontal Polarization gives significant return from leading edges
Vertical Polarization gives significant return from trailing edges

23
Q

To reduce detection range by half, the RCS must be reduced by a factor of:

A

16

24
Q

What are the four basic methods to make an aircraft stealthy?

A

Shaping
Absorption
Cancellation
Transparencies

25
Q

Which method to increase stealth is most important?

A

Shaping. Design surfaces to that radar energy is reflected in directions other than back at the radar

26
Q

What are the three primary shaping techniques

A

Faceted Shaping - Orient flat surfaces to deflect radar energy away from threat radar
Compound Curve - Replace straight edges with curved edges to reflect less radar energy
Planform Alignment - Return a radar signal in a very specific direction, away from emitter into narrow spikes

27
Q

What is RAM

A

Radar Absorbent Material, Used to reduce specular reflections and absorb energy as the wave travels over the surface

28
Q

What are the two types of Radar Absorption

A

Resonant - used for a specific frequency

Nonresonant - designed to work at a range of frequencies

29
Q

What are the three types of RAM and what are their characteristics?

A 
Resonant dielectric (E-RAM) - narrowband, thick, light
Nonresonant magnetic (MagRAM) - broadband, thin, heavy
Nonresonant large volume (RAS [Radar Absorbing Structures]) - broadband, thick, light
30
Q

Reflections become more significant at ____ frequencies and ____ graze angles

A

higher frequencies; low graze angles

31
Q

What are characteristics of a low-frequency radar (<1 GHz)

A

Long wavelength
Half-wave resonance can generate a significant return
Limitation - Few freqs available and heavy clutter
Limitation - Poor range resolution

32
Q

What are characteristics of a high-frequency radar (>40 GHz)

A

Short wavelength
Exploits scattering produced by surface irregularites
Limit - Short range
Limit - Atmospheric attentuation

33
Q

What are characteristics of a bistatic or multistatic radar

A

Separate transmitter / receiver
Reduces effectiveness of LO shaping
Limit - synchronization
Limit - Widebeam antenna or long scan time

34
Q

What are characteristics of a passive coherent radar

A

Detect by processing reflections from noncooperative sources (radio, tv transmissions, cell phone towers)
Reduces LO design effectiveness
Difficult to jam
Limit - reliance on third-party illuminators
Limit - azimuth and range only

35
Q

What is the Nebo M Multistatic / Multiband Radar System

A

Three discrete radars covering the VHF, L-band, and X-band controlled by a command van

36
Q

Objective of LO design in stealth aircraft

A

To increase the survivability by reducing the probability of detection and exposure to engagement by threat system

37
Q 
List whether these are active or passive:
EO
Comms
EM
Nav
RADAR
Engine/Prop Noise
IR
A 
EO – P
Comms – A
EM – P
NAV – A
RADAR – A
Engine/Prop noise – A
IR – A
38
Q

What is the most critical signature for aircraft

A

Radar

39
Q

What is the most significant form of radar reflection

A

Specular Reflections

40
Q

There are four basic methods to make an aircraft stealthy to radars. Of the four, which is most important?

A

Shaping

Core 1 20B (5 decks)

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