Question
In free space, how does the gain of two three-element, horizontally polarized Yagi antennas spaced vertically 1/2 wavelength apart typically compare to the gain of a single three-element Yagi?
Answer Options
- A) Approximately 1.5 dB higher
- B) Approximately 3 dB higher
- C) Approximately 6 dB higher
- D) Approximately 9 dB higher
Correct Answer: B
Explanation
When two identical antennas (like Yagis) are stacked, their feed points are typically connected to create a phased array, combining their energy. For maximum gain increase, they should be fed in phase.
When two antennas are phased correctly, the maximum theoretical gain increase over a single antenna is 3 \text{ dB} (a doubling of power). Therefore, the stacked array’s gain typically compares to the single Yagi as approximately 3 \text{ dB} higher. This technique is common for increasing effective radiated power (ERP) in the desired direction.
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