Test 1 Flashcards
What is angular resolution
The ability to distinguish between targets that are close in azimuth and elevation. Function of beam width and range
Relationship between antenna and beamwidth
The bigger the antenna the more focused the beam
What is range resolution based on?
Range resolution is based on Pulse Width.
What is range resolution?
Pulse length divided by 2
**Advantages of pulse radar (Need to know 2)
Only one antenna required, good range accuracy, simple electronics, good ground mapping and weather detection
**Disadvantages of pulse radar (Need to Know 2)
Lower AOP limits detection range (low PRF), cannot filter out ground clutter without increased processing, not very accurate in velocity measurements
**CW/Doppler radar advantages (Need to know 2)
Can filter out ground clutter, high AOP increases detection range, very accurate velocity measurements, good against high aspect angle targets, simple
**CW/Doppler radar disadvantages (Need to know 2)
Two antennas required (more weight and space), no range information, susceptible to doppler notch, degraded capabilities against beam and stern targets
**Pulse Doppler radar advantages (Need to know 2)
Only one antenna required, filters out ground clutter, high output power, good all aspect capability
**Pulse Doppler radar disadvantages (Need to know 2)
Complicated electronics, susceptible to doppler notch, range measurement difficult with a HPRF PD Radar.
Describe active aircraft signature reduction
Observable emissions:
RF Signals
Acoustic
IR
Describe passive aircraft signature reduction
All observable signal resulting from external illumination:
EO/Visual
Electro-magnetic/Radar
** What is the most critical signature for most aircraft?
RCS is the most cricital signature for most aircraft because radar provides an all weather, long range detection capability (early warning) and also provides target range, azimuth, and velocity data (target tracking.
What dominates radar signature?
Shape which determines how much incident RF power is captured and sent back
What factors affect RCS signature?
Azimuth and Elevation (Target)
Frequency and Polarization (Radar)
**What four methods make an aircraft stealthy?
Shaping - Reflect energy another direction (MOST IMPORTANT)
Absorption - Turn radar into heat
Cancellation - Active/Passive cancelling out
Transparencies - Allow radar to pass thru material
List primary shaping techniques
Compound curve, Faceted shaping, Planform alignment
Describe compound curve
Replace straight edges with curved to reflect less
Describe faceted shaping
Orient flat surfaces to deflect radar
Describe planform edge alignment
Align edges to limited set of angles
Describe how surface roughness effects RCS
Fastener to panel interface increases RCS.
Reflections more significant at higher frequencies and low graze angles
See LO slides 58-62…..
DO IT or DON’T
What are some fundamental characteristics of IR?
All objects (above absolute zero) emit IR radiation
- 0 K/-273 oC - Heated externally (e.g., the Sun) or internally (e.g., engine)
Define Watts and Lumens.
- The watt is a unit of power or heat (thermal)
- The lumen is a unit of light output (brightness) or the ability to see with the eye (photometric)
** What are the three forms of interaction that can take place when energy strikes or is incident upon a surface?
- Absorption (a)
- Reflection (f)
- Transmission (t)
- Total must add up to one (100%): a + r + t = 1
Define Absorption
Incident energy not refelcted or transmitted. Transformed into another form such as heat
Define Reflection
Incident energy not absorbed or transmitted.
Define Transmission
When energy propagates through a medium, the energy not absorbed or reflected will be transmitted.
**List applications of the optical/IR detection systems.
- EO/IR imaging systems
- Detectors
- Terminal homing seekers
- Video trackers
- Automatic target recognizers
- IRCM systems
- Laser systems
- Space imaging systems
Why should you avoid the 5-8u region?
Atmospheric attenuation.
**Angular (azimuth and elevation) resolution is a function of blank and blank
Beamwidth and Range
**Range resolution is based on which paramater
Pulse width
** All objects (blank) temperature emit radaition
0K -273C*
** Thermal radiation measures (blank) in terms of (blank) (units) whereas photometic radiation measures (blank) in terms of (blank)
Power/Heat in terms of watts
Light in terms of lumens
** When planning for the use of optical/IR sensors, detectors or employment of EO weapons, there are several considerations which must be taken into consideration with regards to source heating and source viewing
- Orientation
- Season
- Sun angle
- Weather (rain, wind)
- Thermal crossover
- Approach axis
- Background
- Distance
- IR decoys
** Describe the basic passive aircraft signature reduction concepts, and list the four passive signatures
Passive signature reduction concepts counter threat detectors and trackers with aircraft design and configration. Passive aircraft signatures are the acoustic signature, the visual signature, the IR signature, and the RCS
** State the goal of radar absorbent material in aircraft design?
The goal of RAM in aircraft to design is to reduce spectacular reflections and multi bounce reflections. AND to reduce energy diffracted from trailing edges or discontinuities by absorbing energy as the wave travels along the surface.
** List three radar systems techniques that may be used to counter stealth aircraft
Low frequency radar, high frequency radar, bistatic or multistatic radar, or ultra-wide band radar.
