Feedlines - Matching and Antennas
radiation resistance, antenna efficiency, beamwidth
What is meant by the radiation resistance of an antenna?
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The resistance in the atmosphere that an antenna must overcome to be able to radiate a signal
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The specific impedance of an antenna
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The combined losses of the antenna elements and feed line
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Correct AnswerThe equivalent resistance that would dissipate the same amount of power as that radiated from an antenna
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Why would one need to know the radiation resistance of an antenna?
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To measure the near-field radiation density from a transmitting antenna
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To calculate the front-to-side ratio of the antenna
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Correct AnswerTo match impedances for maximum power transfer
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To calculate the front-to-back ratio of the antenna
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What factors determine the radiation resistance of an antenna?
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Correct AnswerAntenna location with respect to nearby objects and the conductors length/diameter ratio
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Transmission line length and antenna height
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Sunspot activity and time of day
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It is a physical constant and is the same for all antennas
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What is the term for the ratio of the radiation resistance of an antenna to the total resistance of the system?
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Beamwidth
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Effective Radiated Power
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Radiation conversion loss
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Correct AnswerAntenna efficiency
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What is included in the total resistance of an antenna system?
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Radiation resistance plus transmission resistance
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Correct AnswerRadiation resistance plus ohmic resistance
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Transmission line resistance plus radiation resistance
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Radiation resistance plus space impedance
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How can the approximate beamwidth of a beam antenna be determined?
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Draw two imaginary lines through the ends of the elements and measure the angle between the lines
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Correct AnswerNote the two points where the signal strength is down 3 dB from the maximum signal point and compute the angular difference
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Measure the ratio of the signal strengths of the radiated power lobes from the front and side of the antenna
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Measure the ratio of the signal strengths of the radiated power lobes from the front and rear of the antenna
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How is antenna percent efficiency calculated?
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(radiation resistance / transmission resistance) X 100
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(total resistance / radiation resistance) X 100
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(effective radiated power / transmitter output) X 100
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Correct Answer(radiation resistance / total resistance) X 100
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What is the term used for an equivalent resistance which would dissipate the same amount of energy as that radiated from an antenna?
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Correct AnswerRadiation resistance
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"j" factor
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Antenna resistance
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"K" factor
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Antenna beamwidth is the angular distance between :
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Correct Answerthe points on the major lobe at the halfpower points
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the maximum lobe spread points on the major lobe
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the 6 dB power points on the major lobe
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the 3 dB power points on the first minor lobe
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If the ohmic resistance of a half-wave dipole is 2 ohms, and the radiation resistance is 72 ohms, what is the antenna efficiency?
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74%
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72%
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Correct Answer97.3%
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100%
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If the ohmic resistance of a miniloop antenna is 2 milliohms and the radiation resistance is 50 milliohms, what is the antenna efficiency?
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52%
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Correct Answer96.15%
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25%
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50%
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