Which type of wave reaches from the transmitter antenna to the receiver antenna, limited by the horizon?

The correct choice is the direct wave. This type of wave travels in a straight line from the transmitter antenna to the receiver antenna, establishing a direct path of communication under the influence of the horizon. The characteristics of direct waves are essential in line-of-sight communication scenarios, where the transmitting and receiving antennas must be within a clear visual line, unobstructed by physical barriers such as hills or buildings.

In contrast, ground waves tend to follow the curvature of the Earth, thus not being limited to a straight-line path, while sky waves bounce off the ionosphere and can reach beyond the horizon by utilizing the atmospheric layer. Reflected waves involve interactions with surfaces that bounce back signals but do not represent a direct, line-of-sight transmission. Understanding these distinctions is essential for grasping how various wave types effectively operate in communication technology.