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FAA Radar Concepts > Module 2 > Flashcards

Module 2 Flashcards

1
Q

yb The complex impedance value of a(n) ______ and ______ is purely imaginary, having a real part equal to 0. Select all that apply.

A

capacitor and inductor

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2
Q

Ohm’s Law can be represented by the equation ________.

A

V = IR

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3
Q

At microwave frequencies used in radar applications, characteristic impedance can be found by dividing _______ by ________.

A

inductance, capacitance

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4
Q

According to Ohm’s Law, ZL is equal to VL/_______.

A

IL

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5
Q

Alternating current values are written in ______ letters.

A

lowercase

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6
Q

Impedance in ac circuits is analogous to ______ in DC circuits

A

resistance

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7
Q

A circuit branch consisting of a resistor in series with an inductor would have a total ZT consisting of the ________ of the two impedances

A

Sum

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8
Q

In a load matched system, Zin is ________ ZT.

A

equal to

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9
Q

Transmission lines are similar to waveguides at _______ frequencies.

A

microwave

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10
Q

Z0 at radar frequencies maintains a ______ value over the length of the line.

A

constant

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11
Q

Using a λ/4 stub is one method for keeping the inner and outer conductors separated in a _____ transmission line.

A

rigid coaxial

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12
Q

Transmission lines may propagate in _____ mode(s).

A

2 modes

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13
Q

_____ mode is not usable at lower frequencies. Select all that apply

A

Transverse electric and Transverse magnetic

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14
Q

Coaxial cables use _____ mode

A

TEM (Transverse Electromagnetic)

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15
Q

For an ac current at high frequencies, the magnitude of the current _____ as it gets further from the conductor surface.

A

decreases exponentially

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16
Q

In a flexible transmission line, the outer conductor is covered with _____ to protect it against moisture.

A

Plastic

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17
Q

H/m is the unit of _____ in a transmission line

A

inductance

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18
Q

When a dielectric is present, it determines the _____ per unit length in a transmission line.

A

capacitance

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19
Q

A(n) ___ load has zero load resistance.

A

short-circuit

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20
Q

_____ can be used to find a point of damage in a transmission line.

A

Reflections

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21
Q

The _____ is used to calculate the amplitude of a reflected signal.

A

reflection coefficient

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22
Q

A standing wave occurs when the _____ of the power source does not match the load impedance.

A

characteristic impedance

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23
Q

Coaxial cables propagate signals in the _______ mode

A

transverse electromagnetic

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24
Q

Magnetic fields form circles around the center conductor in the _____ mode.

A

transverse electromagnetic

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25
Q

The skin depth of a material _____ as frequency increases.

A

decreases

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26
Q

For an AC current at high frequencies, _____ is at its maximum value at the surface of the conducting material

A

current density

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27
Q

What are disadvantages of using a rigid coaxial transmission line? (3 answers)

A

Susceptible to moisture
Limited line length at extremely high frequencies
Prevents unwanted noise

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28
Q

What are the functions of a waveguide

A

Keeps the transmitted power out of the receiver.
Routes the received pulse to the receiver.
Routes transmitted pulse energy to the antenna.

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29
Q

Waveguides have lower transmission losses than coaxial cables because they contain a(n) _______ dielectric.

A

air

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30
Q

Readings from the ________ are used to calculate VSWR.

A

directional coupler

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31
Q

In a two wire transmission line, a /4 stub appears as a(n) _______on the line at microwave frequencies

A

open

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32
Q

On a two-wire transmission line, an attached stub will be seen as a ______ below the cutoff frequency.

A

short

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33
Q

The _____ prevents the transmitter from emitting unwanted frequencies

A

spurious radiation filter

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34
Q

The _____ allows the transmitter to radiate without sending RF waves through the antenna.

A

dummy load

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35
Q

The ______ takes the received energy collected by the reflector and sends it down the waveguide to the receiver.

A

feed horn

36
Q

Connecting a shorted λ/4 stub to a two-wire transmission line makes it appear as ______ above the cutoff frequency

A

an open

37
Q

Transmission lines and ______ work in transverse electric mode.

A

waveguides

38
Q

The E-field and the ______ lines are always perpendicular to each other.

A

H-Field

39
Q

H-field lines are measured in _______ per meter.

A

amperes

40
Q

A _____ uses the magnetic properties of iron oxide to manipulate the magnetic fields in a waveguide.

A

ferrite device

41
Q

The _____ is a solid-state device located just before the receiver in the waveguide run

A

T/R limiter

42
Q

The duplexer used by the FAA is also called a ________.

A

circulator

43
Q

A frequency-steering device that allows two radar channels to connect to the same antenna simultaneously is called a _____.

A

diplexer

44
Q

Diplexers consist of _____ that route each channel’s frequency from the antenna to the correct receiver

A

frequency filters

45
Q

Radar systems differentiate between aircraft and weather targets through the use of a

A

Polarizer

46
Q

The direction of a reflection’s rotation changes when a target is illuminated by a linearly polarized wave.

A

False

47
Q

A waveguide component that gradually expands the dimensions of a waveguide so that its impedance matches that of free space is called a _____.

A

Feedhorn

48
Q

A _____ reduces a specific microwave frequency while allowing others to pass through the waveguide.

A

ferrite attenuator

49
Q

The waveguide component that absorbs energy in a waveguide and dissipates it as heat is called a __________.

A

dummy load

50
Q

When using a diplexer, channel frequencies should be separated by at least _____ MHz in order to prevent transmitter outputs from interfering with the other channel’s receiver.

A

60

51
Q

If reflected power increases at a particular azimuth, it normally indicates _____ malfunction

A

rotatory joint

52
Q

When a _____ object is illuminated by a circularly polarized wave, the reflected wave will rotate in the same direction

A

round

53
Q

The final component of a waveguide system traveling towards the antenna is the _____.

A

feedhorn

54
Q

Radar signals are transverse electromagnetic waves, just like infrared and ultraviolet light except for _____.

A

frequency

55
Q

Electromagnetic fields comprise two __________ oscillating fields which travel together __________.

A

perpendicular, in-phaseper

56
Q

Microwave antennas communicate at __________ frequencies. (2 Answers)

A

radar and radio

57
Q

Gain in a parabolic antenna depends on ________. (3 answers)

A

dish diameter
distance to target
feed illumination

58
Q

In receive mode, solid state array antennas permit a better determination of a target’s ________ than would be possible from antenna position alone.

A

azimuth

59
Q

The passive element method shifts the phase of a microwave signal with a binary signal that varies the _________ around the _________.

A

magnetic field . ferrite

60
Q

What standard point of measurement is most often used to determine horizontal beamwidth?

A

The point of maximum power in the main lobe

61
Q

What determines vertical beam patterns? (2 answers)

A

The angle a feed assembly uses to illuminate the reflector
The antenna angle itself

62
Q

The difference between RF propagation and light propagation is partially due to ______ and ______ factors being more impactful for microwave frequencies

A

Water vapor
Atmospheric Pressure

63
Q

The number of oscillations or cycles per unit of time is a wave’s __________.

A

frequency

64
Q

The distance between similar features of a waveform, such as two successive peaks, is a wave’s __________.

A

wavelength

65
Q

What is radio wave attenuation?

A

a reduction in apparent power

66
Q

Microwave systems use ________ and ______ reflectors.

A

dipoles and parabolic reflectors

67
Q

When an antenna is fed by a transmission line, __________ acts as an impedance matcher between the line and free space.

A

the feedhorn

68
Q

What is antenna gain?

A

The concentration of power into a single direction

69
Q

Electromagnetic field polarity is always in the direction of the __________ field vector.

A

magnetic

70
Q

feedhorn provides impedance transformation between a __________ and free space

A

waveguide

71
Q

What is the function of phase shifters in a solid state array antenna? (2 answers).

A

Detect targets off the boresite
Ensure all signals reach a target in phase

72
Q

In a solid state array antenna, the active element method uses ______ to select the path RF signals are directed to.

A

TR Switches

73
Q

With regard to antennas, the azimuth gating circuit _____ coverage while ______ ground reflections

A

improves . minimizing

74
Q

Vertical lobing depends on _______. (3 answers)

A

antenna tilt and height
terrain surface

75
Q

vertical lobing is caused by _______ from the target combining with the _______ ______

A

Reflections . direct wave

76
Q

We can create circularly polarized waves by first splitting the linearly polarized wave into a horizontal component and a vertical component, and then delaying one component by ________.

A

90°

77
Q

Which of the following does the Inductosyn use to generate improved azimuth change pulses (IACP) and azimuth change pulses (ARP) (2 answers)

A

Rotor with one winding
Stator with two windings

78
Q

The number of hits per scan on a target depends on the _________. (3 answers)

A

antenna Pulse Repetition Frequency (PRF)
antenna beamwidth
antenna RPM

79
Q

We can minimize the negative impact of misplaced echoes by changing the __________ between two or more values each time the transmitter fires.

A

Pulse Repetition Frequency (PRF)

80
Q

An antenna’s pedestal and reflector are designed to withstand ________ within tolerance.

A

wind

81
Q

The __________ couples RF energy between the stationary waveguide from equipment and the rotating portion of the antenna.

A

Rotary Joint

82
Q

An azimuth-sensitive VSWR increase is a classic indication of __________ problems

A

Rotary Joint

83
Q

We can determine the wave polarization by looking at the direction of ___________.

A

the E-field vector

84
Q

An E-field vector perpendicular to the line of propagation indicates the wave is

A

linearly polarized

85
Q

The amount of time a target is within beamwidth decreases as _______ increases

A

rotational speed

86
Q

What can cause holes in radar coverage? (3 answers)

A

PRF too low
RPM too fast
Beamwidth too narrow

87
Q

A second-time around echo will cause a target’s _____________ to be processed incorrectly

A

range

FAA Radar Concepts (8 decks)

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