Low Observables

Question 1

Define Stealth

Answer 1

The act of proceeding secretly or imperceptibly

Question 2

Define aircraft survivability

Answer 2

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

Question 3

Stealth is accomplished by

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

Electro-optical / visual

Electromagnetic (radar)

Question 6

Low Probability of Intercept (LPI) methods include

Answer 6

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

Question 7

What are common acoustic signature reduction techniques

Answer 7

Engine placement
Exhaust nozzle design
Mixing engine jet with ambient air

Question 8

Engine exhaust and afterburners are examples of which type of IR

Answer 8

Near and mid IR

Question 9

Aircraft skin is an example of which type of IR

Answer 9

Far IR

Question 10

Define Radar signature

Answer 10

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

Question 11

Radar signature varies with:

Answer 11

RF wavelength and viewing angle

Question 12

Radar Cross Section (RCS) is typically measured in

Answer 12

square meters

Question 13

What is RCS

Answer 13

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

Question 14

Factors that affect RCS

Answer 14

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

Question 15

Define Projected Cross-section

Answer 15

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

Question 16

Define Reflectivity

Answer 16

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

Question 17

Define directivity

Answer 17

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

Question 18

What is specular reflection

Answer 18

The most significant form of reflection

Reduced significantly by shaping

Question 19

Define traveling wave returns

Answer 19

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

Question 20

Define Creeping wave

Answer 20

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

Question 21

Define diffraction

Answer 21

Waves striking a very sharp surface or edge are scattered

Question 22

How does polarization affect radar returns

Answer 22

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

Question 23

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

Answer 23

16

Question 24

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

Answer 24

Shaping
Absorption
Cancellation
Transparencies

Question 25

Which method to increase stealth is most important?

Answer 25

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

Question 26

What are the three primary shaping techniques

Answer 26

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

Question 27

What is RAM

Answer 27

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

Question 28

What are the two types of Radar Absorption

Answer 28

Resonant - used for a specific frequency | Nonresonant - designed to work at a range of frequencies

Question 29

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

Answer 29

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

Question 30

Reflections become more significant at ____ frequencies and ____ graze angles

Answer 30

higher frequencies; low graze angles

Question 31

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

What are characteristics of a bistatic or multistatic radar

Answer 33

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

Question 34

What are characteristics of a passive coherent radar

Answer 34

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

Question 35

What is the Nebo M Multistatic / Multiband Radar System

Answer 35

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

Question 36

Objective of LO design in stealth aircraft

Answer 36

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

Question 37

``` List whether these are active or passive: EO Comms EM Nav RADAR Engine/Prop Noise IR ```

Answer 37

``` EO – P Comms – A EM – P NAV – A RADAR – A Engine/Prop noise – A IR – A ```

Question 38

What is the most critical signature for aircraft

Answer 38

Radar

Question 39

What is the most significant form of radar reflection

Answer 39

Specular Reflections

Question 40

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

Answer 40

Shaping