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18A Core I Test 1 Final > Radar Fundamentals > Flashcards

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

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3
Q

Lower freq radar characteristics

A 
Long wavelength
Large antenna
Components generate high transmit power
Low atmospheric attenuation 
Good long range detection capability 
Best long range for EW Radars
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4
Q

Med freq radar characteristics

A

Smaller wavelength allow smaller antenna
Components cannot handle much power—less detection range
Some atmospheric attenuation
Used by ASR, HF,GCI,SAM and ADA Radars acquisition radars

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5
Q

High freq radars characteristics

A

Shorter wavelength and smaller antennas
Smaller components allow less power—shorter detection range
High precision
Atmospheric attenuation more of a problem
Fire control radars- SAM and ADA

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6
Q

Define amplitude

A

The electromagnetic signal strength

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7
Q

Define Phase

A

A compete 360 degree cycle of an EM wave

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8
Q

Define polarization

A

Orientation of the electrical field in an EM wave

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9
Q

Define Beam Width

A

An angular size of the mainbeam, normally expressed in degrees

Technically the width in degrees between the points where the mainbeam decreases to half power

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10
Q

Define Pulse Width (Obj 9)

A

The time radar is transmitting each pulse (Tao)

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11
Q

Define Pulse Length (Obj 9)

A

The distance between the leading and trailing edge of a Pulse

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12
Q

Define PRF (Obj 9)

A

The rate at which pulses are transmitted

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13
Q

Discuss polarization

A

Linear: horizontal, vertical and slant

Circular: right hand, left hand waves whose polarization rotates thru 360 degrees in every wavelength

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14
Q

Discuss power

A

Strength of a radar signal:

Signal hitting a tgt: 1/r^2

Signal received by a radar: 1/r^4

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15
Q

Discuss reflection

A

The process of reradiating an incident radio wave

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16
Q

Discuss refraction

A

The bending of an Em wave

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17
Q

Discuss diffraction

A

Phenomenon observed when a radio wave spreads around objects whose size is comparable to its wavelength and bends around the edges of larger objects; it increases with wavelength

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18
Q

Discuss subrefraction ducting

A

Decreases radar LOS by bending the radar beam upward, decreasing its detection range

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19
Q

Discuss superrefraction ducting

A

Increase radar detection range by bending the beam downward, increasing the radar horizon and overcoming the masking caused by the earth’s curvature

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20
Q

Discuss the impact of the antenna on the radar pattern, BW, and angular resolution

A

Antenna determines beam shape and size

Larger antenna = narrower BW

Narrower BW = higher angular resolution in AZ/EL

21
Q

Characteristics of parabolic antennas

A

Large sidelobes
Easiest and cheapest to manufacture
Transmitter/receiver at focus of parabola

22
Q

Discuss the characteristics of mechanically scanned planar array antennas (Obj 6)

A

Flat faced antenna mechanically scanned in AZ/EL

Consists of an array of many Indiv 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

23
Q

Discuss ESA characteristics. (Obj 7)

A

Mounted in a fixed position

Beam is steered by individually controlling the Phase of the radio waves transmitted and received by each radiating segment

24
Q

Discuss passive ESA (Obj 7)

A

Operates in conjunction With the same type of central transmitter as an MSA

Beam is steered by an electronically controlled Phase shifter placed behind each radiating element

25
Discuss active ESA (Obj 7)
Instead of a Phase shifter, a small T/R module is placed behind each radiating element
26
Discuss ESA limitations (Obj 7)
Field of Regard (FOR) - Apparent size of the antenna decreases when viewed from angles off-bore sight Electronically complex
27
Advantages of Continuous Wave (CW) Radar (Obj 8)
High Average Output Power (AOP) with greater detection range
28
Disadvantages of CW Radar (Obj 8)
Separate transmitter and receiver Unable to determine range
29
Discuss Average Output Power (Obj 9)
Peak power averaged over the PRI
30
Discuss pulse ranging (Obj 9)
Range accuracy is good Radar transmits an RF signal, RF reflects off a tgt, RF echoes are received
31
Discuss range resolution (Obj 9)
Is determined by tau Pulse length/2
32
Discuss range rate (Obj 9)
Computed on the basis of change in the measured range with time *Not the best method to determine tgt speed
33
Discuss resolution cell (Obj 9)
The smallest amount of 3D airspace in which radar cannot distinguish between multiple tgts * AZ/EL resolution is based on BW and range to the tgts * range resolution is based on tau
34
Advantages of pulsed radar (Obj 10)
Only one antenna required Good range accuracy Simple electronics Good Ground mapping and weather detection
35
Disadvantages of pulses radar (Obj 10)
Lower AOP limits range detection Cannot filter out ground clutter without increased processing Not very accurate in velocity measurements
36
How does CW/Doppler measure tgt velocity (Objective 11)
Measures the shift in freq of an EM wave radiated reflected or received by an object in motion
37
How CW/Doppler cancels ground clutter (Objective 11)
Filtered out using Doppler processing
38
Discuss the impact of mainbeam and sidelobe clutter on tgt detection (Objective 11)
Mainbeam clutter is good for ground mapping, bad when searching for aircraft - normally a factor only during lookdown - Sidelobes are lower in amplitude due to power output - Sidelobes have less Doppler shift due to angular difference between velocity of the radar and LOS to the ground
39
Characteristics of PD radars (Objective 13)
Pulsed radar allows for one antenna; simpler, lighter system Accurate range measurement (*time Domain) Doppler allows for accurate measurement of tgt velocity, all aspect detection and tracking and ground clutter rejection (*frequency Domain) Combine the capabilities of pulsed and Doppler radars
40
*Advantages of CW/Doppler radar (Objective 12)
Can filter out ground clutter High AOP increase detection range Very accurate velocity measurement Simple Good against high aspect angle tgts
41
*Disadvantages of CW/Doppler radar (Objective 12)
Susceptible to Doppler notch Two antenna required; more weight and space No range information Degraded capabilities against beam and stern targets
42
Impact operating PRF has on MPRF and HPRF PD radars (Objective 13)
MPRF - good all aspect detection - decreased detection range compared to HPRF (lower AOP) HPRF - good long range (higher AOP) detection for high-aspect tgts - difficult to determine range to tgt - Time to listen for return target echoes limited - PD allows look-down, shoot-down capability - Complicated electronics
43
*Advantages of PD radars (Objective 14)
Only one antenna required Filters out ground clutter High output power Good all aspect capability (MPRF)
44
*Disadvantage of PD radars (Objective 14)
Complicated electronics Susceptible of Doppler notch Range measurement difficult with an HPRF radar
45
Discuss radar ground mapping considerations (Objective 15)
Objective is to make radar maps of sufficiently fine resolution so that topographical features and objects on the ground can be recognized Resolution distance (dr) = range resolution; function of tao. Real beam antenna: Based on BW and range to target To improve (dr), PW must be decreased - Decreasing PW decreased AOP - negatively impacts radar detection range - How much PW can be decreased is a trade-off in desired detection range da is limited to the physical size of the antenna - larger antenna improves da - physical limit to aircraft's radar size
46
Discuss radar acquisition techniques (Objective 16)
Circular Sector Spiral Raster
47
*Discuss SAR considerations (Objective 15)
* Side looking radar system which utilizes the forward motion of the platform to simulate an extremely large antenna or aperture electronically * Requires time and compute power. * Radar must be pointed to the side. * The beam of the antenna must be wide enough for the area/target to fall within the beam for every position of the antenna in the entire length of an array da min = 1/2 length of real antenna (for a radar position at a fixed angle relative to the flight path
48
Discuss tracking techniques (Objective 16)
Monopulse - Angular traking information derived from one reflected pulse Conical
49
Angular resolution
Based off BW and range to the targets

18A Core I Test 1 Final (5 decks)

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