Question
How does the feed point impedance of a 1/2 wave dipole change as the feed point is moved from the center toward the ends?
Answer Options
- A) It steadily increases
- B) It steadily decreases
- C) It peaks at about 1/8 wavelength from the end
- D) It is unaffected by the location of the feed point
Correct Answer: A
Explanation
The current distribution along a resonant half-wave dipole is highest at the center and drops to nearly zero at the ends. Since the feed point impedance (Z = V/I) is determined by the ratio of voltage and current at the feed point, moving the feed point to a place with less current increases the impedance.
If the feed point is moved from the center (where current is maximum, Z \approx 70 \text{ ohms}) toward the ends (where current is minimum), the current decreases, and thus it steadily increases. At the very end of the radiator, the impedance can be several thousand ohms.
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