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COMMS > ANTENNAS -2 > Flashcards

ANTENNAS -2 Flashcards

1
Q

A metallic conductor system capable of radiating and capturing electromagnetic energy

A

Antenna

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2
Q

Couples energy from a transmitter to an antenna or

from antenna to a receiver

A

Transmission Lines

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3
Q

A special type of transmission line that consists of a
conducting metallic tube through which high-frequency
electromagnetic energy is propagated

A

Waveguide

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4
Q

Electrical energy that has escaped into free space in the

form of transverse electromagnetic waves

A

Radio Waves

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5
Q

The plane parallel to the mutually perpendicular lines of

the electric and magnetic fields.

A

Wavefront

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6
Q

The ratio of radiated to reflected energy

A

Radiation Efficiency

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7
Q

Antenna wherein two conductors are spread out in a straight line to a total length of one quarter wavelength.

A

Quarter Wave Antenna

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8
Q

Another name for quarter wave antenna.

A

Vertical Monopole or Marconi

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9
Q

A half-wave dipole

A

Hertz Antenna

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10
Q

A special coupling device that can be used to

direct the transmit and receive signals and provide the necessary isolation

A

Diplexer

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11
Q

A polar diagram or graph representing field strengths or power densities at various angular positions relative to an antenna.

A

Radiation Pattern

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12
Q

Radiation pattern plotted in terms of electric field

strength or power density

A

Absolute Radiation

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13
Q

Radiation pattern plots field strength or power density

with respect to the value at a reference

A

Relative Radiation Pattern

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14
Q

The primary beam of an antenna.

A

Major lobe

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15
Q

The major lobes that propagates and receive

the most energy.

A

Front Lobe

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16
Q

Lobes adjacent to the front lobe.

A

Side lobes

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17
Q

The secondary beam of an antenna.

A

Minor Lobes

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18
Q

Lobes in a direction exactly opposite the front lobe

A

Back Lobe

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19
Q

The ratio of the front lobe power to the back lobe

power.

A

Front to Back Ratio

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20
Q

The ratio of the front lobe to a side lobe.

A

Front to Side Ratio

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21
Q

The line bisecting the major lobe; or pointing from
the center of the antenna in the direction of maximum
radiation.

A

Line of Shoot or Point

of Shoot

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22
Q

Antenna that radiates energy equally in all directions

A

Omni-directional Antenna

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23
Q

The primary beam of an antenna.

A

Major Lobes

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24
Q

Radiates power at a constant rate uniformly in all

directions.

A

Isotropic Radiator

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25
Q

The direction in which an antenna is always pointing.

A

Maximum Radiation

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26
Q

It is defined as an equivalent transmit power. It stands

for Effective Isotropic Radiated Power.

A

EIRP

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27
Q

The equivalent power that an isotropic antenna would have to radiate to achieve the same power density in the chosen direction at a given point as another antenna.

A

Effective Radiated Power (ERP) or (EIRP)

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28
Q

The power density in space and the actual power that a receive antenna produces at its output terminals.

A

Captured Power Density

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29
Q

It describe the reception properties of an antenna

A

Capture Area

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30
Q

Another name for capture area

A

Effective Area

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31
Q

The relationship of captured power to the received
power density and the effective capture area of the
received antenna.

A

Directly Proportional

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32
Q

It refers to the orientation of the electric field radiated

from the antenna.

A

Polarization

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33
Q

The angular separation between the two half-power
(-3dB) points on the major lobe of an antenna’s plane
radiation pattern.

A

Antenna Beamwidth

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34
Q

The frequency range over which antenna operation is satisfactory.

A

Antenna Bandwidth

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35
Q

Another name for antenna input terminal

A

Feedpoint

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36
Q

The feedpoint presents an ac load to the transmission

line.

A

Antenna Input Impedance

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37
Q 
The simplest type of antenna.
Another names for elementary doublet
? Short Dipole;
? Elementary Dipole
? Hertzian Dipole
A

Elementary Doublet

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38
Q

Any dipole that is less than one-tenth wavelength

A

Electrically Short

39
Q

Hertz antenna is name after him and he was the first
to demonstrate the existence of electromagnetic
waves.

A

Heinrich Hertz

40
Q

A single pole antenna one quarter wavelength long; mounted vertically with the lower end either connected directly to ground or grounded through the antenna coupling network.

A

Marconi Antenna

41
Q

Main disadvantage of Marconi Antenna.

A

Must be close

to the Ground

42
Q

A technique use to increase the electrical length of

an antenna

43
Q

A coil added in series with a dipole antenna which

effectively increases antenna’s electrical length.

A

Loading Coil

44
Q

A loading coil approximately increases the radiation resistance of the antenna

45
Q 
An individual radiator; such as a half or quarter
wave dipole.
Two types of antenna elements
? Driven
? Parasitic
Two Elements of a single antenna
? Two Wire
? Folded Dipole
A

Antenna Element

46
Q

Its purpose is to increase the directivity and concentrate

the radiated power within a smaller geographic area.

47
Q

Elements that are directly connected to the transmission

line and receive power from the source.

48
Q

Elements are not connected to the transmission line;
they receive energy only through mutual induction with
a driven element.

49
Q

parasitic element that is shorter that its associated

driven element.

50
Q

Radiation pattern depends on the relative phase of feeds.

51
Q

The simplest type of antenna arrays

A

Broadside Arrays

52
Q

A widely used antenna commonly uses a folded dipole
as the driven element and named after two Japanese
scientists.

53
Q

Typical directivity of a yagi-uda antenna.

A

7 dB and 9 dB

54
Q

Formed by placing two dipoles at right angles to each other.

A

Turnstile Antenna

55
Q

A class of frequency-independent antennas.

A

Log Periodic

56
Q

A broadband VHF or UHF antenna that is ideally suited
for applications for which radiating circular rather than
horizontal or vertical polarized electromagnetic waves
are required.
Modes of propagation:
? Normal
? Axial

A

Helical Antenna

57
Q 
Antennas having half power beamwidths on the order
of 1o or less.
Three important characteristics:
? Front-to Back Ratio;
? Side-toSide Coupling
? Back-to-Back Coupling
A

Microwave Antenna

58
Q

Antenna that provides extremely high gain and
directivity and are very popular for microwave
and satellite communications link.
Two main part
? Parabolic Reflector
? Feed Mechanism

A

Parabolic Reflector Antenna

59
Q

The effective area in a receiving parabolic antenna

and is always less than the actual mouth area.

A

Capture Area

60
Q

The most commonly used transmission

line is a

61
Q

A receiver-transmitter station used to
increase the communications range of
VHF; UHF; and microwave signals is
called a(n)

62
Q

Microwave signals propagate by way of

the

A

Direct wave

63
Q

The type of radio wave responsible for
long-distance communications by
multiple skips is the

64
Q

The ionosphere has its greatest effect

on signals in what frequency range?

A

3 to 30 MHz

65
Q

The ionosphere causes radio signals to

be

66
Q

Ground-wave communications is most

effective in what frequency range

A

300 kHz to 3 MHz

67
Q

A wide-bandwidth multielement driven

array is the

A

Log-periodic

68
Q

antenna has a unidirectional

radiation pattern and gain

69
Q

The radiation pattern of collinear and

broadside antennas

A

Bidirectional

70
Q

Conductors in multielement antennas
that do not receive energy directly from
the transmission line are known as

A

Parasitic elements

71
Q

In a Yagi antenna; maximum direction of

radiation is toward the

72
Q

The horizontal radiation pattern of a

vertical dipole is

73
Q

A direction antenna with two or more

elements is known as a(n)

74
Q

The impedance of a dipole is about

75
Q

The horizontal radiation pattern of a

dipole is a

A

figure of 8

76
Q

An antenna that transmits or receives

equally well in all directions is said to be

A

Omnidirectional

77
Q

The magnetic field of an antenna is
perpendicular to the earth. The
antenna’s polarization

A

is horizontal

78
Q

A popular vertical antenna is the

A

Ground plane

79
Q

A popular half-wavelength antenna is

the

80
Q

A shorted half-wave line at the operating

frequency acts like a(n)

A

Series Resonant Circuit

81
Q

A shorted quarter-wave line at the

operating frequency acts like a(n)

A

Parallel Resonant

82
Q

At very high frequencies; transmission

lines are used as

A

Tuned Circuits

83
Q

This vertical angle; measured upward from the

ground

A

angle of elevation

84
Q

gain of an antenna with losses ignored

have losses

A

Directivity

85
Q

angle measured upward from the horizon. Used to

describe antenna patterns and directions

A

angle of elevation

86
Q

combination of several antenna elements

87
Q

angle between points in an antenna pattern at which

radiation is 3 dB down from its maximum

88
Q

any antenna with two sections

89
Q

an antenna used as part of an array

90
Q

distance from an antenna great enough to avoid local
magnetic or electrical coupling; and great enough for the antenna to
resemble a point source

A

far-field region

91
Q

an antenna with only one conductor; generally using ground

or a ground plane to represent a second conductor

92
Q

the region of space close to an antenna; where the
radiation pattern is disturbed by induced; as well as radiated; electric
and magnetic fields

A

near-field region

93
Q

representation of energy lost from an antenna by

radiation as if it were dissipated in a resistance

A

radiation resistance

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