Radar Fundamentals Flashcards

1
Q

Define wavelength

A

Physical distance of one complete wave

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2
Q

Define frequency

A

Number of cycles that the RF energy completes per second.Hzf=c/wavelength

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3
Q

Define phase

A

A 360 degree cycle of an Em wave.The degree to which individual cycles of a wave coincide with those of a reference wave of the same frequency

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4
Q

Define polarization

A

Orientation of the electrical field in an Em wave.Vertical, Horizontal, Spiral

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5
Q

Define BW, Beamwidth

A

BW is angular measurement of the size of the mainbeam, normally expressed in degrees.

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6
Q

Define PW, Pulse Width

A

PW is the time radar is transmitting each pulse.Units Time

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7
Q

Define PL, Pulse Length

A

PL is the distance between the leading and trailing edges of a pulse. Units Distance

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8
Q

Define PRF, Pulse Repetition Frequency

A

Rate at which pulses are transmitted. Measured in pulses per second.

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9
Q

Lower Frequency Radar Characteristics

A

Long Wavelength; large antenna; components able to generate high transmit power; low atmospheric attenuation; good long range detection capability, but poor precision; best long range for EW radars

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10
Q

Medium Frequency Radar Characteristics

A

Smaller wavelengths allow smaller antennas; components cannot handle as much power, therefore less detection range; some atmospheric attenuation; used by ASR, HF, GCI, SAM, and ADA acquisition radars.

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11
Q

Higher Frequency Radar Characteristics

A

Higher frequencies have shorter wavelengths and smaller antennas; smaller components allow less power with shorter detection range; high precision; atmospheric attenuation more of a problem; fire control radars for fighters, SAM and ADA.

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12
Q

Linear Polarization

A

Horizontal, vertical, slant

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13
Q

Circular Polarization

A

Right hand, left hand waves whose polarization rotates through 360 degrees in every wavelength

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14
Q

Radar Power

A

Strength of radar signal hitting a target = 1/R^2Strength of radar signal sent/received by a radar = 1/R^4

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15
Q

Radar Reflection

A

The process of reradiating an incident radio wave.

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16
Q

Radar Refraction

A

The bending of Em energy through different materials.

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17
Q

Radar Ducting

A

The bending of radar rays due to atmospheric conditionsSubrefraction decreases radar LOS by bending the radar beam upward.Superrefraction increases radar LOS detection by bending the radar beam downward.

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18
Q

Radar Diffraction

A

Phenomenon observed when a radio wave spreads around objects whose size is comparable to its wavelength and bend around the edges of larger objects. Diffraction increases with wavelength.

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19
Q

Characteristics of Parabolic Antenna

A

Large Sidelobes (disadvantage)Easiest and cheapest to manufacture (advantage)Transmitter in front of dishBasic satellite dish

20
Q

Characteristics of mechanically scanned planar array antennasMSA

A

Flat-faced antenna mechanically scanned in AZ and ELConsists of an array of many individual radiators of equal phase distributed over a flat surfaceSlots cut in the walls of a complex of waveguides behind the antennas faceDesigned to distribute the radiated power across the array so as to minimize sidelobes

21
Q

ESA Characteristics

A

Mounted in fixed positionBeam is steered by individually controlling the phase of the radio waves transmitted and received by each radiating element

22
Q

Passive vs Active ESA

A

Passive-beam is steered by an electronically controlled phase shifter placed behind radiating element, controlled by BSA or central processorActive- Instead of a phase shifter, a small T/R module is placed behind radiating element

23
Q

Limitations of ESA

A

FOR-Apparent size of antenna decreases with off boresight; results in increased beam width and decrease in efficiency; limits maximum look angle to +-60 degrees (BW doubles, power half)Electronically complex

24
Q

Advantages/Disadvantages of CW Radar(Continuous Wave)

A

Continuously Transmits- separate transmitter vs receiver (disadvantage), High AOP (advantage)Greater detection range (Hight AOP)- unable to determine range (disadvantage)

25
Range Resolution (Pulsed Radar)
Radar's ability to resolve multiple targets in a rangeRange resolution is a factor of Pulse Width (PW)
26
Resolution Cell (Pulsed Radar)
The smallest amount of 3D space in which a radar cannot distinguish between multiple targetsAZ/EL is based on BW and RangeRange Resolution based on PW
27
Average Output Power (AOP)
AOP is peak power averaged over the PRI (Pulse Repetition Interval)
28
Pulse Ranging
Radar transmits RF, RF reflects off target, RF echoes receivedTime between transmit and receive is converted to range using this equation...Range=((T)xc)/(2)
29
Range Rate
Is computed on the basis of change in the measured range with time - not the best method to determine target speed
30
Advan/Disadvan of Pulsed Radar
A- only one antenna req, good ground mapping and weather detection, good range accuracy, simple electronicsD- Lower AOP limits detection range (low PRF), cannot filter out ground clutter without incresed processing, not very accurate in velocity measurments
31
Impact of antenna on Radiation Pattern
Antenna determines beam shape and sizeLarge Antenna = Large Sidelobes
32
Impact of Antenna on BW
Larger antenna = narrower BW
33
Impact of antenna on angular resolution
Larger antenna = narrower BW = higher angular resolution in AZ/EL
34
Define polarization
The orientation of the electric field
35
CW/Doppler Characteristics
Accurate measuring velocitySusceptible to ground clutterGood at ground mappingCan be defeated by a Doppler notch
36
How CW/Doppler measure velocity
Measures the shift in frequency of an Em wave radiated, reflected or received by an object in motion.
37
How CW/Doppler cancels ground clutter
By filtering out using Doppler processing
38
Impact of mainbeam and Sidelobe clutter on tgt detection
Mainbeam clutter is the Doppler notch and normally a factor during look down.
39
Advan/Disadvan of CW/Doppler radar
A- can filter ground clutter, high AOP increases detection range, very accurate velocity measurement, good agains high aspect targets, simpleD- two antennas more weight/space, no range information, susceptible to Doppler notch, degraded capabilities against beam/stern targets
40
Pulsed Doppler radar
Combines advantages of pulsed and Doppler radars
41
MPRF vs HPRF in pulsed Doppler radars
M- good all aspect tgt detection, decreased detection range compared to HH- good long range detection for high aspect targets, difficult to determine range to target
42
Advan/Disadvan of pulse Doppler radars
A- one antenna req, filters ground clutter, high AOP, good all aspect capabilityD- complicated, susceptible to Doppler notch, range measurement is difficult
43
Radar ground mapping
Using radar waves to create a fine resolution of topographical features an objects on the ground.
44
Radar acq techniques
Circular scanningSector scanSpiral scanRaster scan
45
Radar tracking techniques
Lobing Mono pulseConical