*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 (F/B ratio) is a measure of how well an antenna can direct its radiation in the forward direction compared to the backward direction. It is expressed in decibels (dB) and is calculated using the formula:

$$
F/B \text{ ratio (dB)} = 10 \log_{10} \left( \frac{P_{\text{front}}}{P_{\text{back}}} \right)
$$

where:
- $P_{\text{front}}$ = power radiated in the forward direction
- $P_{\text{back}}$ = power radiated in the backward direction

### Explanation of the Correct Answer (28 dB):
- The correct answer, 28 dB, indicates that the antenna radiates significantly more power in the forward direction compared to the backward direction. This is a desirable characteristic for many applications, as it enhances the signal strength in the intended direction while minimizing interference from the rear.

### Explanation of Incorrect Choices:
- **15 dB**: This value suggests a moderate front-to-back ratio, which may not provide sufficient directivity for many applications. It implies that the antenna is not effectively suppressing radiation in the backward direction.
  
- **3 dB**: A 3 dB front-to-back ratio indicates that the power radiated in the forward and backward directions is nearly equal. This is generally undesirable for directional antennas, as it means the antenna is not effectively focusing energy in one direction.

- **38 dB**: While a 38 dB ratio indicates excellent directivity, it is likely an unrealistic value for most practical antennas. Such a high ratio would suggest an extremely narrow beamwidth, which is not typical for the antenna depicted in Figure E9-2.

### Summary:
- The front-to-back ratio is crucial for understanding antenna performance.
- The correct answer (28 dB) reflects a good balance of directivity and practical application.
- Lower values (15 dB and 3 dB) indicate less effective antennas, while an excessively high value (38 dB) is likely impractical. 

Understanding these concepts will help you answer similar questions on the Extra Class exam effectively.