Ham Radio General Class Practice Test

Which of the following is true about the gain of a log periodic antenna?

1. It is constant across all frequencies

2. It increases with frequency

3. It decreases with frequency

4. It varies logarithmically with frequency

The correct answer is: It varies logarithmically with frequency

The gain of a log periodic antenna is designed to vary logarithmically with frequency. This characteristic is a key feature of log periodic antennas, which are constructed with elements that are spaced and sized according to a specific logarithmic scale. As the frequency of the signal increases, the length and spacing of the antenna elements are designed to also increase, allowing the antenna to maintain a relatively stable gain across its operating bandwidth but with variations that fit a logarithmic model. This logarithmic relationship helps the log periodic antenna to efficiently cover a wide range of frequencies while providing gain that isn't constant but adjusts in a controlled manner. It gives users the advantage of having a predictable increase in gain as they operate toward higher frequencies within the antenna's design specifications. In contrast, options that imply constant gain across frequencies or that gain simply increases or decreases linearly do not accurately describe the behavior of this type of antenna. The uniqueness of the log periodic design specifically hinges on its logarithmic relationship with frequency, which enhances its versatility in various communication scenarios.