Question
What happens to the radiation pattern of an unterminated long wire antenna as the wire length is increased?
Answer Options
- A) Fewer lobes form with the major lobes increasing closer to broadside to the wire
- B) Additional lobes form with major lobes increasingly aligned with the axis of the antenna
- C) The elevation angle increases, and the front-to-rear ratio decreases
- D) The elevation angle increases, while the front-to-rear ratio is unaffected
Correct Answer: B
Explanation
A simple long wire antenna is defined as a straight wire whose length is many half-wavelengths long. The radiation pattern of a long wire is complex, consisting of multiple lobes, rather than the simple figure-eight of a half-wave dipole.
As the wire length is increased, the radiation pattern changes in two ways: Additional lobes form, meaning the pattern becomes more complex, and the major lobes become increasingly aligned with the axis of the antenna (off the ends of the wire). This effect concentrates the energy more along the wire’s length, making very long wires highly directional off their ends, a characteristic often used for long-distance \text{HF} communication.
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