*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)  

The correct answer to the question about the purpose of using multiple driven elements connected through phasing lines is:

**A: To control the antenna’s radiation pattern.**

### Explanation of the Correct Answer:
- **Controlling the Radiation Pattern**: 
  - Multiple driven elements can be used in antenna designs, such as Yagis or phased arrays, to manipulate the direction and shape of the radiation pattern. By adjusting the phase and amplitude of the signals fed to each element through phasing lines, you can create constructive and destructive interference, which shapes the overall radiation pattern. This allows for enhanced gain in specific directions and reduced radiation in others.

### Why the Other Choices are Incorrect:
- **B: To prevent harmonic radiation from the transmitter**: 
  - While good antenna design can help mitigate harmonic radiation, the primary purpose of multiple driven elements is not to prevent harmonics. Harmonics are typically managed through filtering and proper transmitter design rather than through the use of multiple driven elements.

- **C: To allow single-band antennas to operate on other bands**: 
  - This statement is misleading. While some antennas can be designed to operate on multiple bands (like multiband antennas), using multiple driven elements connected through phasing lines does not inherently allow a single-band antenna to operate on other bands. This typically requires specific design considerations, such as traps or resonant elements.

- **D: To create a low-angle radiation pattern**: 
  - While certain configurations can indeed produce low-angle radiation patterns, this is not the primary purpose of using multiple driven elements. The main goal is to control the radiation pattern, which can include low-angle, high-angle, or other configurations depending on the design and phasing.

### Useful Formulas or Rules of Thumb:
- **Phasing and Gain**: The gain of an antenna array can be approximated by the formula:
  $$ G = 10 \log_{10}(N) + G_0 $$
  where:
  - $G$ = total gain of the array in dBi
  - $N$ = number of elements
  - $G_0$ = gain of a single element in dBi

- **Inter-element Spacing**: For optimal performance, elements in a phased array are often spaced at a distance of about $\frac{\lambda}{2}$ (half a wavelength) apart, where $\lambda$ is the wavelength of the operating frequency.

This understanding of multiple driven elements and their purpose will help you in both the exam and practical applications in amateur radio.