*Question G9C02:
What is the approximate length of the driven element of a Yagi antenna?*  

*Correct Answer is  B: 1/2 wavelength*  

### AI Response: (may contain errors)  

In a Yagi antenna, the driven element is typically a dipole, which is designed to be resonant at the frequency of operation. The resonant length of a dipole antenna is approximately half of the wavelength of the frequency it is designed to receive or transmit.

### Explanation:

1. **Correct Answer: 1/2 wavelength**
   - The driven element of a Yagi antenna is usually a half-wave dipole. This means its length is approximately half of the wavelength of the frequency it is intended to operate on. This is because a half-wave dipole is naturally resonant, making it efficient for transmitting and receiving signals.

2. **Why Other Choices Are Incorrect:**
   - **1/4 wavelength (Choice A):** A quarter-wave length is typically used for monopole antennas, not for the driven element of a Yagi, which is a dipole.
   - **3/4 wavelength (Choice C):** A three-quarter wavelength is not a standard length for a resonant dipole. It would not be efficient or resonant for a Yagi driven element.
   - **1 wavelength (Choice D):** A full wavelength is too long for a resonant dipole in a Yagi antenna. It would not provide the desired impedance characteristics for efficient operation.

### Useful Formula:

The length of a half-wave dipole can be calculated using the formula:

$$
L = \frac{468}{f}
$$

where:
- $L$ is the length of the dipole in feet.
- $f$ is the frequency in megahertz (MHz).

This formula provides a good approximation for the length of the driven element in a Yagi antenna.