Which of the following lists only includes directional antennas?

Directional antennas are designed to radiate or receive radio waves more effectively in specific directions compared to non-directional antennas.

In the context of the correct choice, it consists of the loop antenna, parabolic antenna, slotted planar antenna, and helical antenna, all of which are recognized as directional antennas. The loop antenna can be designed to focus its radiated power in specific directions depending on its dimensions and configuration. The parabolic antenna is highly effective for directing signals because its parabolic shape reflects radio waves towards the focal point, creating a well-defined directional beam. The slotted planar antenna employs slots cut into a flat surface to create specific radiation patterns, which allows it to direct signals effectively in desired directions. The helical antenna, meanwhile, can produce highly directional signals and is often used in applications such as satellite communications due to its circular polarization characteristics.

The context shows that the other options include components that are not solely directional antennas, such as the dipole antenna, which is typically considered a non-directional or omnidirectional antenna, capable of radiating power equally in all directions in a horizontal plane. The sense antenna is generally used for different applications and may not be categorized strictly within directional types. Therefore, the combination in the selected answer