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WIC 16A > 410A Radar > Flashcards

410A Radar 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.

Hz

f=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^2

Strength 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 conditions

Subrefraction 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 dish

Basic satellite dish

20
Q

Characteristics of mechanically scanned planar array antennas
MSA

A

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

21
Q

ESA Characteristics

A

Mounted in fixed position
Beam 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 processor

Active- 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
Q

Range Resolution (Pulsed Radar)

A

Radar’s ability to resolve multiple targets in a range

Range resolution is a factor of Pulse Width (PW)

26
Q

Resolution Cell (Pulsed Radar)

A

The smallest amount of 3D space in which a radar cannot distinguish between multiple targets

AZ/EL is based on BW and Range
Range Resolution based on PW

27
Q

Average Output Power (AOP)

A

AOP is peak power averaged over the PRI (Pulse Repetition Interval)

28
Q

Pulse Ranging

A

Radar transmits RF, RF reflects off target, RF echoes received
Time between transmit and receive is converted to range using this equation…Range=((T)xc)/(2)

29
Q

Range Rate

A

Is computed on the basis of change in the measured range with time - not the best method to determine target speed

30
Q

Advan/Disadvan of Pulsed Radar

A

A- only one antenna req, good ground mapping and weather detection, good range accuracy, simple electronics
D- Lower AOP limits detection range (low PRF), cannot filter out ground clutter without incresed processing, not very accurate in velocity measurments

31
Q

Impact of antenna on Radiation Pattern

A

Antenna determines beam shape and size

Large Antenna = Large Sidelobes

32
Q

Impact of Antenna on BW

A

Larger antenna = narrower BW

33
Q

Impact of antenna on angular resolution

A

Larger antenna = narrower BW = higher angular resolution in AZ/EL

34
Q

Define polarization

A

The orientation of the electric field

35
Q

CW/Doppler Characteristics

A

Accurate measuring velocity
Susceptible to ground clutter
Good at ground mapping
Can be defeated by a Doppler notch

36
Q

How CW/Doppler measure velocity

A

Measures the shift in frequency of an Em wave radiated, reflected or received by an object in motion.

37
Q

How CW/Doppler cancels ground clutter

A

By filtering out using Doppler processing

38
Q

Impact of mainbeam and Sidelobe clutter on tgt detection

A

Mainbeam clutter is the Doppler notch and normally a factor during look down.

39
Q

Advan/Disadvan of CW/Doppler radar

A

A- can filter ground clutter, high AOP increases detection range, very accurate velocity measurement, good agains high aspect targets, simple
D- two antennas more weight/space, no range information, susceptible to Doppler notch, degraded capabilities against beam/stern targets

40
Q

Pulsed Doppler radar

A

Combines advantages of pulsed and Doppler radars

41
Q

MPRF vs HPRF in pulsed Doppler radars

A

M- good all aspect tgt detection, decreased detection range compared to H

H- good long range detection for high aspect targets, difficult to determine range to target

42
Q

Advan/Disadvan of pulse Doppler radars

A

A- one antenna req, filters ground clutter, high AOP, good all aspect capability

D- complicated, susceptible to Doppler notch, range measurement is difficult

43
Q

Radar ground mapping

A

Using radar waves to create a fine resolution of topographical features an objects on the ground.

44
Q

Radar acq techniques

A

Circular scanning
Sector scan
Spiral scan
Raster scan

45
Q

Radar tracking techniques

A

Lobing
Mono pulse
Conical

WIC 16A (1 decks)

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