Ham Radio General Class Practice Test

How do two 3-element horizontally polarized Yagi antennas spaced vertically 1/2 wavelength apart typically compare in gain to a single 3-element Yagi?

1. Approximately 1.5 dB higher

2. Approximately 3 dB higher

3. Approximately 6 dB higher

4. Approximately 9 dB higher

The correct answer is: Approximately 3 dB higher

The gain of antennas can be influenced by various factors, including their arrangement and spacing. In the case of two 3-element horizontally polarized Yagi antennas spaced vertically 1/2 wavelength apart, the combination of these antennas typically results in an increase in gain compared to a single 3-element Yagi. This enhanced gain is due to the constructive interference of the signals received from both antennas when they are properly phased. When two antennas are configured in this manner, the gain increases primarily because they not only work together but also because the vertical spacing helps to create a pattern that can enhance signal strength in the desired direction. The standard theoretical improvement in gain from vertically stacking identical antennas at this spacing is generally around 3 dB. This is a common benchmark in antenna theory and practice, meaning that the effective gain of the two antennas working together can be approximately double that of a single antenna, resulting in a 3 dB increase. This concept is essential for amateur radio operators aiming to boost signal reception and transmission capabilities. Understanding the principles of how antenna configurations enhance gain is vital for optimizing performance in various operating conditions.