What does diffraction refer to in radio wave propagation?

Diffraction refers to the bending of waves around obstacles or the spreading of waves as they pass through openings. In the context of radio wave propagation, this phenomenon is crucial because it enables radio signals to reach areas that would otherwise be blocked by physical structures such as buildings or hills. When radio waves encounter a barrier, some of the energy can bend around the edge, allowing the signal to propagate into areas that lie behind the obstacle.

This property is particularly important in urban environments, where signals often need to navigate around various structures. The ability of waves to diffract contributes to the reliability of communications systems, as it helps maintain signal strength and quality in the presence of physical obstructions.

In other contexts, the other options represent different aspects of wave behavior but do not accurately describe diffraction. For example, the expansion of waves into multiple frequencies refers more to the concept of frequency modulation rather than diffraction. Similarly, the slowing down of waves in dense mediums is a description of refraction, not diffraction, and absorption deals with how surfaces can weaken or eliminate wave energy rather than influencing its bending behavior.