Question
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase?
Answer Options
- A) Cardioid
- B) A figure-eight end-fire along the axis of the array
- C) A figure-eight broadside to the axis of the array
- D) Omni-directional
Correct Answer: A
Explanation
This antenna configuration involves two elements spaced rac{1}{4}-wavelength apart with a 90^\circ phase shift applied to the feed. This specific geometry creates constructive interference in one direction and destructive interference (cancellation) in the opposite direction. This is a common arrangement for directional \text{VHF} or \text{MF} arrays.
This feeding arrangement creates a Cardioid (heart-shaped) radiation pattern. The pattern has a strong, single lobe in one direction and a deep null (cancellation) in the opposite direction. This makes the array useful for direction finding (to locate a null) or for reducing interference from a known source.
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