*Question G9D07:
Which of the following describes a log-periodic antenna?*  

*Correct Answer is  A: Element length and spacing vary logarithmically along the boom*  

### AI Response: (may contain errors)  

A log-periodic antenna is a type of antenna that is designed to operate over a wide range of frequencies. Let's break down the question and the choices:

### Correct Answer: A
**Element length and spacing vary logarithmically along the boom.**

- **Explanation**: In a log-periodic antenna, the lengths of the elements and the spacing between them increase logarithmically. This design allows the antenna to maintain a relatively constant impedance and gain over a wide frequency range, making it effective for applications that require multi-band operation.

### Why the Other Choices are Incorrect:
- **B: Impedance varies periodically as a function of frequency**  
  - **Explanation**: While the impedance of a log-periodic antenna does change with frequency, it does not vary in a periodic manner. Instead, it is designed to have a relatively stable impedance across its operational bandwidth, which is a key feature of its logarithmic design.

- **C: Gain varies logarithmically as a function of frequency**  
  - **Explanation**: The gain of a log-periodic antenna does not vary logarithmically. Instead, it typically remains fairly constant over its operational frequency range, with some variation at the edges of the band. The gain is more related to the design and number of elements rather than a logarithmic function of frequency.

- **D: SWR varies periodically as a function of boom length**  
  - **Explanation**: The Standing Wave Ratio (SWR) is not dependent on the length of the boom in a periodic manner. SWR is influenced by the matching of the antenna to the transmission line and the frequency of operation, but it does not have a periodic relationship with boom length.

### Summary
- A log-periodic antenna is characterized by its logarithmic variation in element length and spacing, which allows it to function effectively across a wide frequency range. Understanding this design principle is crucial for recognizing the unique properties of log-periodic antennas in amateur radio applications.