An antenna

Options

A. Converts AF wave to RF wave
B. RF signal into electromagnetic energy
C. Converts the guided em waves into free space em waves and vice versa
D. Super imposes AF wave on RF wave.

Answer

### Step-by-Step Solution:

1. **Understanding the Function of an Antenna**:
- An antenna is a device that converts electrical energy into radio waves and vice versa. It plays a crucial role in communication systems by allowing the transmission and reception of signals.

2. **Analyzing the Options**:
- The question provides four options regarding the function of an antenna:
1. Converts AF (Audio Frequency) to RF (Radio Frequency) wave.
2. Converts RF signal into electromagnetic energy.
3. Converts guided electromagnetic wave into free space electromagnetic wave and vice versa.
4. Superimposes AF wave into RF wave.

3. **Evaluating Each Option**:
- **Option 1**: This option suggests the conversion of AF to RF waves. While antennas can work with RF signals, they do not specifically convert AF to RF.
- **Option 2**: This option implies that antennas convert RF signals into electromagnetic energy. This is somewhat misleading because antennas radiate RF signals as electromagnetic waves rather than converting them into energy.
- **Option 3**: This option states that antennas convert guided electromagnetic waves into free space electromagnetic waves and vice versa. This accurately describes the primary function of antennas, as they facilitate the transition between guided waves (like those in cables) and free space waves (like radio waves).
- **Option 4**: This option suggests that antennas superimpose AF waves into RF waves, which is not a primary function of antennas.

4. **Conclusion**:
- After evaluating all options, the correct answer is **Option 3**, as it correctly describes the function of an antenna in converting guided electromagnetic waves into free space electromagnetic waves and vice versa.

### Final Answer:
The correct option is **Option 3: Converts guided electromagnetic wave into free space electromagnetic wave and vice versa**.