What is electromagnetic wave propagation?

Electromagnetic wave propagation refers to how radio waves travel from transmitter to receiver through different media. The main propagation modes are: Ground wave (follows Earth's surface, used for AM radio), Sky wave (reflects off ionosphere, used for HF communication), Line-of-sight (direct path between antennas, used for VHF/UHF and above), and Space wave (combination of direct and ground-reflected waves). Propagation characteristics depend on frequency, terrain, atmospheric conditions, and distance. Higher frequencies generally require line-of-sight paths.