*Question E9B01:
What is the 3 dB beamwidth of the antenna radiation pattern shown in Figure E9-1?*  

*Correct Answer is  B: 50 degrees*  

### AI Response: (may contain errors)  

To determine the 3 dB beamwidth of an antenna radiation pattern, you need to understand what the 3 dB beamwidth represents. It is the angular width of the main lobe of the antenna pattern where the power is at least half of the maximum power. This is often referred to as the "half-power" beamwidth.

### Explanation:

1. **Correct Answer: 50 degrees**
   - The 3 dB beamwidth is the angle between the points on the radiation pattern where the power falls to half of its peak value. In the context of the exam question, Figure E9-1 would show a radiation pattern with markers indicating these points. The angle between these markers is the 3 dB beamwidth.
   - In this case, the correct answer is 50 degrees, which means the angle between the half-power points on the radiation pattern is 50 degrees.

2. **Why Other Choices Are Incorrect:**
   - **75 degrees (Choice A):** This angle is too wide and would indicate a broader beamwidth than what is shown in the figure.
   - **25 degrees (Choice C):** This angle is too narrow and would suggest a more focused beam than what is depicted.
   - **30 degrees (Choice D):** This angle is also narrower than the correct beamwidth, indicating a more focused beam than the actual pattern.

### Useful Rule of Thumb:

- The 3 dB beamwidth is a critical parameter for understanding how an antenna directs its energy. It helps in determining the coverage area and the antenna's directivity.
- Remember that a smaller beamwidth indicates a more focused beam, which is useful for long-distance communication, while a larger beamwidth covers a wider area but with less focus.

By understanding these concepts, you can interpret antenna radiation patterns and determine the 3 dB beamwidth accurately.