Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Radar Systems Design > Week 1 > Flashcards

Week 1 Flashcards

1
Q

Surveillance radar

A

Scans the horizon looking for targets

Air traffic control, air defense, ships

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Tracking radar

A

Locks onto target and follows it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Law enforcement radar

A

Measures vehicle velocity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Radar acronym

A

RAdio Detection And Ranging

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

A basic type of radar can

A

Detect the presence of a target

Measure the range

Find the azimuth and elevation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Range

A

The distance between the radar and the target

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Azimuth and Elevation

A

The direction to the target using a directional antenna

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Synthetic aperture radar

A

Maps the ground with high resolution for earth resources and military purposes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Weather radar

A

Ground based - maps precipitation over wide area

Aircraft based - warns of dangerous rain areas

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Radar Applications

A

Ground probing - looking for land mines
Movement sensing - security, door openers
Terrain avoidance - low flying military aircraft
Radar altimeter - accurate measurement of aircraft height (essential for blind landing)
Space radar - detect satellites, debris, space weather
Autonomous vehicles - key sensor technology (lidar - light radar)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Radar definition

A

An electrical system that transmits RF EM waves towards a region of interest and receives and detects these EM waves when reflected from objects in that region

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Pulse radar

A

Sends out a short burst of RF energy

For a point target, the received echo is spread in time by the width of the pulse.
The echo from the point target has the appearance of the transmitted pulse but is greatly reduced in magnitude

Series of pulses, typically 10 to 50

Standard radar processing integrates over all the pulses and echoes in the series to produce a single pulse-echo combination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Mono static radar

A

TX and RX are co-located and often share an antenna

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Bistatic radar

A

Tx and Rx are in separate locations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Tx power

A

kW to MW

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Rx power

A

nW levels and lower

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Measuring range

A

Measure time for radar pulse to go to target and back

Radar measures time from transmitted pulse to received echo

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Pulses repetition interval

A

Tp

Time between pulses

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Range Ambiguity

A

Pulsed radars process the echoes (or returns) from many pulses collectively

When a successive pulse is transmitted before the echo from the previous pulse is received, the range measurement for the echo will be wrong

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Measured range is correct only for

A

R < Rua

Rua - maximum unambiguous range

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Range resolution

A

If two targets are close together, the echoes will overlap in time —> the radar will report a single target

Minimum spacing at which two targets can be separated by radar

Point targets can be separated provided their echoes are received with time delay greater than one pulse width

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

If we want to resolve targets that are closer

A

We must use a shorter pulse

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

CW radar

A

Sends out a continuous wave of RF energy

Tx and Rx operate continually

Because of the continual transmission, a mono static CW radar must be low power (to protect the receiver) —> limits CW radars to near range operations

Police radars

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Can we measure the range to a target with a CW radar

A

No, not if we use a simple waveform

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Radar transmitters are rated by

A

Pulse power

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Pulse power

A

Pt - rms output power of the transmitter while it transmits a pulse

27
Q

Time-range radar correspondences

A

1 ms - 150 km
1 us - 150 m
1 ns - .150 m = 15 cm

28
Q

Early radars operated in the bands:

A

HF: 3 to 30 MHz
VHF: 30 to 300 MHz
UHF: 300 to 1000 MHz

29
Q

Most radars today operate at

A

Microwave frequencies

- 1000 to 100,000 MHz = 1 GHz to 100 GHz

30
Q

HF Band

A

3 to 30 MHz

31
Q

VHF band

A

30 to 300 MHz

32
Q

UHF band

A

300 to 1000 MHz

33
Q

L-band

A

1-2 GHz

34
Q

S-band

A

2 to 4 GHz

35
Q

C-band

A

4 to 8 GHz

36
Q

X-band

A

8 to 12 GHz

37
Q

Ku-band

A

12 to 18 GHz

38
Q

K-band

A

18 to 27 GHz

39
Q

Ka-band

A

27 to 40 GHz

40
Q

W-band

A

75 to 110 GHz

41
Q

MHz / m radar systems

A

f[MHz]λ[m] = 300

42
Q

GHz / cm radar systems

A

f[GHz]λ[cm] = 30

43
Q

Motion of a wave

A

In the direction of the wave vector k, k = 2π/λ [rad/m]

44
Q

Coherent radar

A

Detect the amplitude of returned signal

Provides info on the phase of the returned signal, measured relative to the transmitted signal

LO, STALO - listening time

45
Q

Stable local oscillator

A

LO, STALO

Used to generate the transmit signal and to process the returned signal

46
Q

Pulse coherent radar

A

Phase ca be measured on the signal returned from successive pulses

Can measure the difference in phase between the echo and the LO reference

If the phase changes between pulses, gives rise to Doppler shift

47
Q

If the phase is changing between pulses

A

The distance to the target is changing (target is approaching or receding)

48
Q

Doppler shift

A 
ωd = dφm/dt 
fd = ωd/2π = 2vr/λ
49
Q

Sign of the Doppler shift

A

Positive for motion toward radar

Negative for away

50
Q

Resolving the Doppler frequency

A

Ambiguity can arise

If phase changes by more than π rad between pulses, can’t tell where phase is increasing or decreasing

If phase change is 2π between pulses, then dφ/dt and the apparent speed is zero

Must sample at least twice as fast as fd
-sample the phase once per pulse (sampling rate = PRF)

51
Q

Doppler shift / velocity measurement only correct for

A

|fd| < fd_max

|vr| < vr_max

52
Q

Ambiguity and PRF regimes

A

Resolving an ambiguity in range - lower PRF

Resolving an ambiguity in Doppler shift or velocity - higher PRF

53
Q

Low PRF

A

Unambiguous in range

Ambiguous in Doppler shift / velocity

54
Q

High PRF

A

Ambiguous in range

Unambiguous in Doppler shift / velocity

55
Q

Medium PRF

A

Ambiguous in both range and Doppler shift/velocity

56
Q

Radar range equation

A

Calculates the power received from a target at a given range

Calculates the max range at which a target of known radar reflectivity can be detected

57
Q

Gain generally refers to

A

The gain in the direction of peak antenna performance

58
Q

Radar cross section

A

RCS, expresses the relationship between the power density incident on the target and the power density received at the antenna from the target as a result of reflection (scattering)

59
Q

Power density at the radar receiver

A

Target has become its own transmitter, an isotropic radiator with Prefl = Pint

60
Q

Effective collective area

A

Receiving antenna scoops radio wave power out of the air over this area

61
Q

Smin

A

Minimum power needed in the receiver to reliably detect the target

Usually determined by noise in the receiver

62
Q

Max range of detection of a given target is a measure of

A

Radar sensitivity

63
Q

Losses in a radar

A

Propagation effects, losses in waveguides and components

May be as high as 20 dB

Max range of the radar will be (10^-20/10)^1/4 = 31.6% of the range predicted by the idealized equation

Radar Systems Design (6 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions