A-007-08: Radiation resistance, antenna efficiency, beamwidth
What is meant by the radiation resistance of an antenna?
The equivalent resistance that would dissipate the same amount of power as that radiated from an antenna
The resistance in the atmosphere that an antenna must overcome to be able to radiate a signal
The specific impedance of an antenna
The combined losses of the antenna elements and feed line
Why would one need to know the radiation resistance of an antenna?
To match impedances for maximum power transfer
To measure the near-field radiation density from a transmitting antenna
To calculate the front-to-side ratio of the antenna
To calculate the front-to-back ratio of the antenna
What factors determine the radiation resistance of an antenna?
Antenna location with respect to nearby objects and the conductors length/diameter ratio
Transmission line length and antenna height
Sunspot activity and time of day
It is a physical constant and is the same for all antennas
What is the term for the ratio of the radiation resistance of an antenna to the total resistance of the system?
Effective Radiated Power
Radiation conversion loss
What is included in the total resistance of an antenna system?
Radiation resistance plus ohmic resistance
Radiation resistance plus transmission resistance
Transmission line resistance plus radiation resistance
Radiation resistance plus space impedance
How can the approximate beamwidth of a beam antenna be determined?
Note the two points where the signal strength is down 3 dB from the maximum signal point and compute the angular difference
Draw two imaginary lines through the ends of the elements and measure the angle between the lines
Measure the ratio of the signal strengths of the radiated power lobes from the front and side of the antenna
Measure the ratio of the signal strengths of the radiated power lobes from the front and rear of the antenna
How is antenna percent efficiency calculated?
(radiation resistance / total resistance) X 100
(radiation resistance / transmission resistance) X 100
(total resistance / radiation resistance) X 100
(effective radiated power / transmitter output) X 100
What is the term used for an equivalent resistance which would dissipate the same amount of energy as that radiated from an antenna?
Antenna beamwidth is the angular distance between:
the points on the major lobe at the half-power points
the maximum lobe spread points on the major lobe
the 6 dB power points on the major lobe
the 3 dB power points on the first minor lobe
If the ohmic resistance of a half-wave dipole is 2 ohms, and the radiation resistance is 72 ohms, what is the antenna efficiency?
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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