*Question E9E11:
What is the purpose of using multiple driven elements connected through phasing lines?*  

*Correct Answer is  A: To control the antenna’s radiation pattern*  

### AI Response: (may contain errors)  

To understand why multiple driven elements connected through phasing lines are used, let's break down the purpose and effects:

### Correct Answer: A: To control the antenna’s radiation pattern

1. **Why the correct answer is correct:**
   - **Radiation Pattern Control:** By using multiple driven elements with phasing lines, you can manipulate the direction and shape of the antenna's radiation pattern. This is achieved by adjusting the phase and amplitude of the signals fed to each element, allowing for beam steering, pattern shaping, and null placement.
   - **Phasing Lines:** These are transmission lines that introduce specific phase shifts between elements, enabling constructive and destructive interference in desired directions.

### Why the other choices are incorrect:

2. **B: To prevent harmonic radiation from the transmitter**
   - **Incorrect:** Harmonic radiation is typically managed by filters and not by the configuration of driven elements. The purpose of phasing lines is not to filter frequencies but to control the radiation pattern.

3. **C: To allow single-band antennas to operate on other bands**
   - **Incorrect:** Operating on multiple bands usually requires different techniques, such as traps, loading coils, or multiband antennas. Phasing lines do not enable a single-band antenna to operate on other bands.

4. **D: To create a low-angle radiation pattern**
   - **Incorrect:** While phasing can influence the angle of radiation, the primary purpose is broader control over the pattern, not just creating a low-angle pattern. Low-angle radiation is often achieved by antenna height and ground reflection rather than phasing alone.

### Useful Concepts:

- **Interference:** By adjusting the phase, you can create constructive interference in desired directions (increasing gain) and destructive interference in others (reducing interference or noise).
- **Beam Steering:** This is the ability to direct the main lobe of the antenna pattern in a specific direction without physically moving the antenna.

Understanding these concepts helps in recognizing how phasing lines and multiple driven elements are used to optimize antenna performance for specific applications.