*Question G9C07:
What does “front-to-back ratio” mean in reference to a Yagi antenna?*  

*Correct Answer is  C: The power radiated in the major lobe compared to that in the opposite direction*  

### AI Response: (may contain errors)  

The "front-to-back ratio" of a Yagi antenna is a measure of how well the antenna can focus energy in one direction (the front) while minimizing radiation in the opposite direction (the back). This is important for reducing interference from signals coming from behind the antenna.

1. **Correct Answer: C**  
   The front-to-back ratio is defined as the ratio of the power radiated in the major lobe (the main direction the antenna is pointed) to the power radiated in the opposite direction (180 degrees from the main direction). This is typically expressed in decibels (dB). A higher front-to-back ratio indicates better performance in terms of rejecting signals from the rear.

   - **Formula**:  
     If $P_{\text{front}}$ is the power in the major lobe and $P_{\text{back}}$ is the power in the opposite direction, the front-to-back ratio in decibels is given by:  
     $$\text{Front-to-Back Ratio (dB)} = 10 \log_{10} \left( \frac{P_{\text{front}}}{P_{\text{back}}} \right)$$

2. **Why the other choices are incorrect**:
   - **Choice A**: The number of directors versus the number of reflectors does not define the front-to-back ratio. These elements influence the gain and directivity of the antenna but are not directly related to the front-to-back ratio.
   - **Choice B**: The relative position of the driven element with respect to the reflectors and directors affects the antenna's impedance and pattern but does not define the front-to-back ratio.
   - **Choice D**: The ratio of forward gain to dipole gain is related to the antenna's overall gain compared to a reference dipole, not specifically to the front-to-back ratio.

Understanding the front-to-back ratio helps in designing and selecting antennas for applications where minimizing interference from unwanted directions is crucial.