AdvancedA-007-004-009
In a half-wave dipole, where does minimum voltage occur?
C
Answer
Interference, EMC, and safety
Type
A
Both ends
B
It is equal at all points
C
The centre
D
At the right end
Answer Notes
A half-wave dipole operates as a resonant antenna, which creates a standing wave pattern of voltage and current along its length. Because the power distribution is relatively constant, voltage and current are inversely related along the wire.
The highest current in this standing wave is found at the feedpoint, which is at the center of the dipole. Conversely, the voltage drops to its absolute minimum at this exact same central location. As you move away from the center toward the tips, the current decreases and the voltage increases.
Options suggesting that the minimum voltage is at the ends or is equal everywhere ignore this fundamental standing wave distribution. The physical ends of the wire actually experience the maximum voltage.
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The impedance of a half-wave antenna at its centre is low, because at this point:
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In a half-wave dipole, where does the minimum current occur?