*Question E9B02:
What is the front-to-back ratio of the antenna radiation pattern shown in Figure E9-1?*  

*Correct Answer is  D: 18 dB*  

### AI Response: (may contain errors)  

To determine the front-to-back ratio of an antenna, you need to compare the strength of the signal radiated in the forward direction (front) to the strength of the signal radiated in the opposite direction (back). This is typically expressed in decibels (dB).

### Explanation:

1. **Correct Answer: 18 dB**

   - The front-to-back ratio is calculated using the formula:
     $$ \text{Front-to-Back Ratio (dB)} = 10 \log_{10} \left( \frac{P_{\text{front}}}{P_{\text{back}}} \right) $$
     where $P_{\text{front}}$ is the power in the forward direction and $P_{\text{back}}$ is the power in the backward direction.
   - In the context of the exam question, the figure (not shown here) would provide the necessary power levels or dB values to calculate this ratio.
   - The correct answer, 18 dB, indicates that the power in the forward direction is significantly greater than the power in the backward direction, specifically by a factor of about 63 times (since $10^{1.8} \approx 63$).

2. **Why the Other Choices are Incorrect:**

   - **36 dB (Choice A):** This would imply an extremely high front-to-back ratio, suggesting the forward power is 4,000 times the backward power ($10^{3.6} \approx 4,000$). This is typically much higher than what is common for most practical antennas.
   
   - **14 dB (Choice B):** This ratio suggests the forward power is about 25 times the backward power ($10^{1.4} \approx 25$). While possible, it does not match the given correct answer of 18 dB.
   
   - **24 dB (Choice C):** This would mean the forward power is about 251 times the backward power ($10^{2.4} \approx 251$). Again, this is higher than the correct answer and does not match the expected value.

### Key Points:

- The front-to-back ratio is a measure of how well an antenna can focus energy in one direction compared to the opposite direction.
- A higher dB value indicates better directivity and less power wasted in the backward direction.
- Understanding how to read and interpret antenna radiation patterns is crucial for determining these values.