*Question E9B04:
What is the front-to-back ratio of the radiation pattern shown in Figure E9-2?*  

*Correct Answer is  B: 28 dB*  

### AI Response: (may contain errors)  

The front-to-back ratio of an antenna is a measure of how much more power is radiated in the forward direction compared to the backward direction. It is usually expressed in decibels (dB).

1. **Correct Answer: 28 dB**  
   - The front-to-back ratio is calculated by comparing the power radiated in the forward direction to the power radiated in the backward direction. In Figure E9-2, the forward gain is significantly higher than the backward gain, resulting in a front-to-back ratio of 28 dB. This means the forward radiation is 28 dB stronger than the backward radiation.

2. **Why the Other Choices are Incorrect:**
   - **15 dB (Choice A):** This value is too low compared to the actual front-to-back ratio shown in the figure. It would indicate a smaller difference between forward and backward radiation.
   - **3 dB (Choice C):** This is much too low and would suggest almost equal forward and backward radiation, which is not the case in the figure.
   - **38 dB (Choice D):** This value is too high, indicating a much larger difference than what is shown in the figure.

3. **Useful Formula:**
   - The front-to-back ratio in dB can be calculated using the formula:  
     $$ \text{Front-to-Back Ratio (dB)} = 10 \log_{10} \left( \frac{P_{\text{forward}}}{P_{\text{backward}}} \right) $$
   - Where $P_{\text{forward}}$ is the power in the forward direction and $P_{\text{backward}}$ is the power in the backward direction.

Understanding the front-to-back ratio helps in evaluating the directional performance of an antenna, which is crucial for minimizing interference and optimizing signal strength in the desired direction.