*Question T9A03:
Which of the following describes a simple dipole oriented parallel to Earth's surface?*  

*Correct Answer is  B: A horizontally polarized antenna*  

### AI Response: (may contain errors)  

To understand why the correct answer is "B: A horizontally polarized antenna," let's break down the options:

1. **Correct Answer: B - A horizontally polarized antenna**
   - A simple dipole antenna oriented parallel to the Earth's surface radiates electromagnetic waves that are polarized in the horizontal plane. This means that the electric field of the radiated waves is oriented horizontally, which is characteristic of horizontally polarized antennas.

2. **Why the other choices are incorrect:**
   - **A: A ground-wave antenna**
     - Ground-wave antennas are designed to propagate radio waves along the surface of the Earth, typically at lower frequencies. While a dipole can be used for ground-wave propagation, the term "ground-wave antenna" does not specifically describe the polarization of the dipole.
   
   - **C: A travelling-wave antenna**
     - A travelling-wave antenna is designed to support the propagation of waves along the length of the antenna, such as a long wire or a Yagi. A simple dipole does not fit this description, as it primarily radiates waves from its ends rather than supporting a travelling wave along its length.
   
   - **D: A vertically polarized antenna**
     - A vertically polarized antenna has its electric field oriented vertically. Since the dipole in question is oriented parallel to the Earth's surface, it cannot be classified as vertically polarized.

3. **Useful concepts:**
   - **Polarization**: The orientation of the electric field of the radio wave. For a dipole oriented horizontally, the polarization is horizontal.
   - **Dipole Antenna**: A basic antenna type that consists of two conductive elements. Its radiation pattern and polarization depend on its orientation relative to the ground.

In summary, a simple dipole oriented parallel to the Earth's surface is classified as a horizontally polarized antenna due to the orientation of its electric field.