Question
What type of radiation pattern is created by two ¼-wavelength vertical antennas spaced ½-wavelength apart and fed 180 degrees out of phase?
Answer Options
- A) Cardioid
- B) Omni-directional
- C) A figure-eight broadside to the axis of the array
- D) A figure-eight oriented along the axis of the array
Correct Answer: D
Explanation
Antenna arrays combine multiple elements to synthesize a specific directional pattern. The resulting pattern depends on three factors: the spacing between the elements, the phase relationship of the signals fed to them, and the orientation of the elements.
When two quarter-wave vertical antennas (which are omnidirectional individually) are spaced ½-wavelength apart and fed 180° out of phase, the array acts as an end-fire system. This combination creates a figure-eight oriented along the axis of the array, with maximum radiation pointing off the ends of the array, perpendicular to the elements themselves.
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