*Question E9C08:
What is a folded dipole antenna?*  

*Correct Answer is  C: A half-wave dipole with an additional parallel wire connecting its two ends*  

### AI Response: (may contain errors)  

A folded dipole antenna is a specific type of dipole antenna that has an additional wire connecting its two ends, which effectively increases its impedance and bandwidth.

### Correct Answer Explanation:
- **C: A half-wave dipole with an additional parallel wire connecting its two ends**  
  This is correct because a folded dipole consists of a standard half-wave dipole (which is typically $L = \frac{1}{2} \lambda$, where $\lambda$ is the wavelength) with an extra wire that connects the ends. This configuration increases the antenna's impedance (typically to around 300 ohms) and can improve its bandwidth.

### Incorrect Answer Explanations:
- **A: A dipole one-quarter wavelength long**  
  This is incorrect because a folded dipole is not one-quarter wavelength long; it is a half-wave dipole. A quarter-wave dipole is a different type of antenna, known as a monopole, which is not the same as a folded dipole.

- **B: A center-fed dipole with the ends folded down 90 degrees at the midpoint of each side**  
  This is incorrect because folding the ends down at 90 degrees does not describe a folded dipole. A folded dipole maintains a straight configuration with an additional parallel wire connecting the ends.

- **D: A dipole configured to provide forward gain**  
  This is incorrect because a standard folded dipole does not inherently provide forward gain. It is primarily designed for improved impedance matching and bandwidth, not for gain. Gain is typically associated with directional antennas, such as Yagi or log-periodic antennas.

### Useful Formulas and Rules of Thumb:
- The length of a half-wave dipole antenna can be calculated using the formula:  
  $$L = \frac{468}{f}$$  
  where:
  - $L$ = length in feet
  - $f$ = frequency in megahertz (MHz)

- The impedance of a standard half-wave dipole is approximately 73 ohms, while a folded dipole typically has an impedance of about 300 ohms due to the parallel configuration.

Understanding these concepts will help you grasp the characteristics and applications of folded dipole antennas for your Extra Class exam.