AdvancedA-007-004-011

In a half-wave dipole, where does the minimum impedance occur?

A
Answer
Interference, EMC, and safety
Type
A
At the centre
B
At both ends
C
At the right end
D
It is the same at all points

Answer Notes

Impedance at any point along an antenna is determined by the ratio of voltage to current (Z = V / I) at that specific location. On a resonant half-wave dipole, the standing wave pattern causes these values to vary dramatically from the center to the tips. The center point of a half-wave dipole experiences the highest current and the lowest voltage. Applying Ohm's Law, dividing a low voltage by a high current yields a low impedance. Therefore, the minimum impedance is found exactly at the center, which makes it ideal for connecting low-impedance feedlines like 50-ohm coaxial cable. At the ends of the antenna, the situation is reversed: current is zero and voltage is high, which creates an extremely high impedance. Thus, any option suggesting the ends or a uniform impedance is incorrect.
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