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Classic's Class > Antenna Theory & Identification > Flashcards

Antenna Theory & Identification Flashcards

1
Q

What is an antenna?

A

An antenna is a transducer, as it converts electromagnetic energy to radio frequency energy.

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2
Q

What is the “Rule of Reciprocity”?

A

The “Rule of Reciprocity” is that a good transmit antenna is a good receive antenna.

Note: this does not mean that a good receive antenna is a good transmit antenna.

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3
Q

What is one of the most important considerations when selecting an antenna?

A

It is imperative to consider an antenna that enables us to focus on enemy activity.

Note: because of this, we must also be able to identify the type(s) of antennas used by the enemy.

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4
Q

What is resonant length?

A

Resonant length is the length of the antenna.

Note: the length of the antenna will vary based on the specific frequency it is designed for.

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5
Q

What is the equation used to measure an antenna’s main element?

A

Full-Wave: 936 (MHz) / Frequency (MHz) = Length (Ft) of Antenna.

Half-Wave: 468 (MHz) / Frequency (MHz) = Length (Ft) of Antenna.

Quarter-Wave: 234 (MHz) / Frequency (MHz) = Length (Ft) of Antenna.

Note: it is common practice to utilize the half-wave equation when constructing an antenna.

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6
Q

What are the seven (7) parts of a radio link?

A
  1. Transmitter
  2. Power Supply
  3. Transmission Lines
  4. Transmitting Antenna
  5. Propagation Path
  6. Receiving Antenna
  7. Receiver
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7
Q

What does a transmitter do?

A

The transmitter generates a radio signal.

Note: a transmitter generates radio frequency energy on a desired frequency and modulates the energy to convey information.

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8
Q

What does the power supply do?

A

The power supply supplies power for the operating voltage of the radio.

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9
Q

What does the transmission line do?

A

The transmission line delivers the signal from the transmitter to the antenna.

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10
Q

What does the transmitting antenna do?

A

The transmitting antenna converts electromagnetic energy into radio frequency energy, and focuses the energy into desired directions [gain].

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11
Q

What is a propagation path?

A

The propagation path is the path in space that the radio signal follows as it goes towards the receiving antenna.

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12
Q

What does the receiver do?

A

The receiver processes [demodulates] the radio signal so that the human ear can hear it.

Note: a receiver also filters out and ignores signals of undesired frequencies and amplifies the weak received signal sufficiently to allow processing.

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13
Q

What is a radiation pattern of an antenna?

A

The radiation pattern of an antenna describes the relative strength of the radiated field in various directions from the antenna at a set distance.

Note: the radiation pattern of an antenna must be known to determine the coverage of the antenna.

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14
Q

What are the three (3) types of radiation patterns?

A
  1. Isotropic
  2. Omni-Directional
  3. Directional
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15
Q

What is an isotropic radiation pattern?

A

An isotropic radiation pattern is an imaginary pattern that radiates equal power in all directions.

Note: it is used as a reference for directive characteristics of actual antennas.

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16
Q

What is an omni-directional radiation pattern?

A

An omni-directional radiation pattern is a pattern which is non-directional in terms of azimuth [directional degree].

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17
Q

What is gain?

A

Gain is the increase in effective radiated power in the desired direction of the major lobe.

Note: gain is expressed in dB, as it is the comparison of the antenna pattern to a standard.

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18
Q

What is a directional radiation pattern?

A

A directional radiation pattern is a pattern with greater gain in one or more directions.

Note: the radiation [transmit] pattern is a reception pattern as well, as the “Rule of Reciprocity” is considered.

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19
Q

What does the suffix of dBi mean?

A

The suffix of dBi [isotropic] is for the forward gain of an antenna compered with an isotropic [imaginary] antenna.

Note: isotropic antennas uniformly distribute energy in all directions.

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20
Q

What does the suffix of dBd mean?

A

The suffix of dBd [dipole] is for the forward gain of an antenna compared with a half-wave dipole antenna.

Note: 0 dBd = 2.15 dBi

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21
Q

What does the suffix of dBm mean?

A

The suffix of dBm [milliwatt (mW)] is the standard unit for measuring levels of power in relation to a 1-milliwatt reference signal.

Note: 0 dBm = 1 mW

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22
Q

Solve these common dBm to milliwatts conversions:

  1. 0 dBm = ? mW
  2. 10 dBm = ? mW
  3. 30 dBm = ? mW
  4. 37 dBm = ? mW
  5. 47 dBm = ? mW
A
  1. 0 dBm = 1 mW
  2. 10 dBm = 10 mW
  3. 30 dBm = 1,000 mW [1 W]
  4. 37 dBm = 5,000 mW [5 W]
  5. 47 dBm = 50,000 mW [50 W]
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23
Q

What occurs to the beam of a radiating signal as gain increases?

A

The beam of a radiating signal becomes more tightly focused with more intense signal strength.

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24
Q

What is directivity?

A

Directivity is the consideration that all antennas exhibit directive effects in that the intensity of radiation is not the same in all directions [azimuth] from an antenna.

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25
Q

What is the reason for the decibel [dB]?

A

The reason for the decibel [dB] is because it is a ratio that can conveniently represent a very large (or small) number.

Note: it is a relative measure of two different power levels.

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26
Q

Solve these common “3 dB Rule” assumptions:

  1. -6 dB = ? power level
  2. -3 dB = ? power level
  3. 0 dB = ? power level
  4. +3 dB = ? power level
  5. +6 dB = ? power level
A
  1. -6 dB = 1/4 power level
  2. -3 dB = 1/2 power level
  3. 0 dB = 1 power level
  4. +3 dB = 2 power level
  5. +6 dB = 4 power level
27
Q

What is beamwidth?

A

Beamwidth is the width, in degrees, of the major lobe between the two directions at which the relative radiated power is equal to one-half [50%] its value at the peak of the lobe.

Note: beamwidth is measured until it is 50% of the original strength at the center.

28
Q

What is front-to-back ratio?

A

Front-to-back ratio is the ratio of difference in gain between the maximum forward gain and the gain taken directly 180 degrees from that forward bearing.

29
Q

What is polarization?

A

Polarization is the direction of the electric field [e-plane] of an antenna relative to the earth’s surface.

30
Q

What are the four (4) types of polarization?

A
  1. Horizontal
  2. Vertical
  3. Elliptical
  4. Left / Right-Handed Circular
31
Q

What is bandwidth?

A

Bandwidth is the width of the range of frequencies that an electronic signal occupies on a given transmission medium.

Note: bandwidth can also measure how much frequency can be varied while still obtaining an acceptable transmission.

32
Q

What is VSWR?

A

VSWR is the voltage standing wave ratio, and it numerically describes how well the antenna is impedance-matched to the radio (or feedline) it is connected to.

Note: the smaller the number, the better.

33
Q

What is EIRP?

A

EIRP is the effective isotropic radiated power (level), which is measured in dBm.

Note: in order to solve for EIRP, add the power at antenna input [dBm] with the relative antenna gain [dBi].

34
Q

What is ERP?

A

ERP is the effective radiated power (level), which is measured in dBm.

Note: in order to solve for ERP, add the power at antenna input [dBm] with the relative antenna gain [dBd].

35
Q

What is a monopole antenna?

A

A monopole antenna is a vertical (or horizontal) radiator that operates against a ground plane.

Note: a monopole antenna has a typical gain of two (2) to six (6) dB, and is either vertically or horizontally linearly polarized (depending on antenna set-up).

36
Q

What is an AM tower?

A

An AM tower is an insulated tower that is mounted on a large insulator at its base.

Note: the insulator of an AM tower isolates the tower from the ground.

37
Q

What is relevant regarding the relationship between an AM tower and lightning?

A

Pertaining to lightening specifically, AM towers have spark gaps that are used to provide a means for discharge where those lightning strikes (and large static build-ups) will flash across the gap without compromising the loss of the radio frequency energy as well.

38
Q

What are a couple key features of an AM tower?

A

AM towers are base-insulated monopoles that typically broadcast in the upper range of the low frequency [LF] spectrum of 30 kHz to 1,700 kHz.

39
Q

What is a dipole antenna?

A

A dipole antenna is a radiating element, made of two (2) separate elements of a specific wavelength, that is connected to a feed at the physical direct center.

40
Q

What are a couple key features of a dipole antenna?

A

A dipole antenna has a typical gain of one (1) to three (3) dB, and is considered the building block for many antenna systems.

41
Q

What is a “V” antenna?

A

A “V” antenna is a variation of a dipole where the center feed is typically (vertically) higher than its two ends, and where its directive radiation pattern properties are determined based on the arrangement of the two conductor’s specific angle, length, and height above the earth.

42
Q

What are a couple key features of a “V” antenna?

A

A “V” antenna has a typical gain of two (2) to seven (7) dB, and has a frequency range from the high [HF] to ultra-high frequency [UHF] of 3 MHz to 500 MHz.

43
Q

What is a log-periodic antenna?

A

A log-periodic antenna [LPA] is a multi-element, broad-band, directional, narrow-beam antenna that can be used from the high frequency [HF] range up to the ultra-high frequency [UHF] range, but is most commonly used for large frequency bandwidth transmissions in the very-high frequency [VHF] and ultra-high frequency [UHF] range.

44
Q

What are a couple key features of a log-periodic antenna?

A

A log-period antenna has a typical gain of three (3) to eight (8) dB, and only a small part of the whole structure of the transmitting antenna is active at any given frequency.

45
Q

What is a “Yagi-Uda” antenna?

A

A “Yagi-Uda” antenna is a dipole antenna that is very widely used at frequencies up to 2.5 GHz and consisting of only one driven element with many parasitic reflectors and directors (which are used to increase directionality).

Note: the simplest “Yagi-Uda” antenna consists of a reflector, driven element, and director.

46
Q

What are a couple key features of a “Yagi-Uda” antenna?

A

A “Yagi-Uda” antenna has a typical gain of five (5) to 15 dB, as additional gain is achieved by adding more (parallel dipole) directors; with this in mind, the director elements will always be shorter than the driven element, as the longest element will always be the reflector.

47
Q

What is a “Moxon” antenna?

A

A “Moxon” antenna is a simple and mechanically robust two-element parasitic array antenna with a rectangular design.

Note: One half of the rectangle design is being driven, while the other half is a reflector.

48
Q

What is a ground plane antenna?

A

A ground plane antenna consists of a radiating element with a surface (either natural or artificial) acting as the missing half of a two-element dipole antenna.

Note: for example, in very-high frequency [VHF] mobile communications, the metal of a vehicle body acts as a form of ground plane.

49
Q

What is a “Discone” antenna?

A

A “Discone” antenna is an omni-directional, vertically polarized, wideband antenna that is excellent as a receiving antenna frequently utilized by government / military agencies because of its bandwidth characteristics and non-directional coverage.

50
Q

What is a “Biconical” antenna?

A

A “Biconical” antenna is a broadband dipole that consists of two conical conductors that have a common axis and vertex.

Note: A biconical antenna has a typical gain of zero (0) to four (4) dB, and is frequently used for electromagnetic interference [EMI] testing.

51
Q

What is a stacked dipole antenna?

A

A stacked dipole antenna is an omni-directional, multi-band vertical array of dipoles mounted on a pole or tower.

Note: a stacked dipole antenna is commonly utilized for commercial and private base station very-high frequency [VHF] and ultra-high frequency [UHF] broadcast applications.

52
Q

What is a helix antenna?

A

A helix antenna is a circularly-polarized antenna that is only used from the very-high frequency [VHF] range and higher, and is commonly used for satellite tracking and spaceship communication.

Note: a helical [helix] antenna has a typical gain of up to 10 dB.

53
Q

What is a horn antenna?

A

A horn antenna is a directional, wideband antenna that consists of a flaring metal waveguide (shaped like a horn) to direct radio waves in a beam.

Note: because a horn antenna lack resonant elements, it enables it to operate over a wide range of frequencies [wideband antenna] with a typical gain of five (5) dB to 20 dB.

54
Q

What is a loop antenna?

A

A loop antenna is a magnetic dipole antenna which consists of a loop of wire connected to a balanced transmission line, and usually employed as a receive-only antenna.

Note: a loop antenna has a typical gain of negative two (-2) dB to two (2) dB, and is most commonly utilized for AM radio or direction finding [DF] because it is relatively unaffected by nearby trees, buildings, weather, etc.

55
Q

What is a rhombic antenna?

A

A rhombic antenna is a diamond-shaped, directional, broadband antenna most commonly used in high frequency [HF] range, with a typical gain of two (2) dB to 7 dB.

Note: being leveled at a height of one-half wavelength, all four horizontal “legs” of a rhombic antenna must also be the same length (of half-wavelengths).

56
Q

What is a parabolic antenna?

A

A parabolic antenna is a highly-directive antenna that uses a parabolic “dish” reflector to direct its waves; because of this high directivity, it has a typical gain of 10 to 30 dB.

Note: a parabolic antenna is utilized for high-gain, point-to-point satellite communication, WLAN links for data communication, and can also be utilized for radar antennas for airplanes and ships.

57
Q

What is a microwave system?

A

A microwave system is a telecommunication system that can utilize several types of antennas, most commonly parabolic antennas, specifically for transmitting microwaves.

Note: microwave energy is focused into a very narrow beam [high directionality] and aimed at the receiving antenna.

58
Q

What is a “Radome”?

A

A “Radome” is a form of antenna shielding that provides environmental survivability without compromising the radiation pattern.

Note: these “Radome” shields can be constructed from nylon or polymer-based fabrics or even hardened materials such as fiberglass or plastic.

59
Q

What is a corner reflector?

A

A corner reflector is a reflecting object consisting of two (2) [dihedral] or three (3) [trihedral] intersecting conducting surfaces, made of mesh or solid material, in order to “boost” gain up to 10 dB.

60
Q

What are a couple key features of an FM broadcast tower?

A

An FM broadcast tower is composed of vertically-stacked radiating elements designed for side-mounting to a steel pole; with this in mind, these elements are designed to concentrate energy at a low radiation angle in order to prevent energy from radiating above the horizon and into space.

Note: commercial radio stations traditionally operate on evenly-spaced 200 kHz channels from 88.1 MHz to 107.9 MHz.

61
Q

What are a couple key features of a cellular antenna?

A

Cellular antennas traditionally are located on existing infrastructure, and, can be easily identified by the 360 degree, 3-panel patten placed on said infrastructure.

62
Q

What are a couple key features of a “Pico-Cell”?

A

A “Pico-Cell” is a cellular-band antenna commonly used in areas where there is either a high population density or a lack of coverage.

Note: consider locations such as shopping malls, sports stadiums, and transportation tunnels as common locations for a “Pico-Cell.”

63
Q

What are six (6) types of log-periodic antennas?

A
  1. Medium Range HF LPA
  2. Multimode Spiral LPA
  3. Rotatable LPA
  4. Shortwave Broadcast LPA
  5. Super High Gain LPA
  6. Vertically Polarized LPA

Classic's Class (8 decks)

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