What causes the loss of energy of a radio wave because of the spreading of the wavefront as it travels from the transmitter?

The loss of energy of a radio wave as it travels is primarily due to free space loss. This phenomenon occurs because as a radio wave propagates, it spreads out over a larger area. The power of the radio wave remains constant; however, as it covers more distance, the energy becomes distributed over a broader wavefront, resulting in a decrease in signal strength at any given point of that wavefront. The further the wave travels from the transmitter, the more it spreads, causing the signals to weaken—this is directly related to the inverse square law, where the signal strength diminishes with the square of the distance.

Other losses like diffraction, refraction, and clutter are more context-dependent. Diffraction involves bending around obstacles, refraction is the bending of waves due to changes in medium, and clutter refers to the presence of physical objects that scatter the wave. These factors can impact signal strength but are not the primary cause of energy loss due to the inherent spreading of the wavefront as it travels through free space.