Q.What are the different types of radiowave propagation ?

Radiowave propagation occurs mainly by three mechanisms — ground wave (along the Earth's surface), sky wave (reflection off the ionosphere), and space wave (line-of-sight, including satellite links) — each suited to a different frequency range and distance.

1. Ground wave (surface wave) propagation

Here the radio wave travels along the surface of the Earth, guided by and partly following the curvature of the ground, with the ground acting as a conductor. It is used mainly for low-frequency and medium-frequency signals (up to a few MHz), such as AM radio broadcasting. Ground waves suffer increasing attenuation as frequency increases, which limits this mode to lower frequencies and to distances of a few hundred kilometres.

2. Sky wave (ionospheric) propagation

The radio wave is directed upward into the atmosphere, where it is reflected back down to Earth by the ionosphere (the ionised upper layers of the atmosphere, roughly 50–400 km altitude). By repeated reflection between the ionosphere and the Earth's surface, sky waves can travel very long distances, even around the globe. This mode is used for shortwave (high-frequency, roughly 3–30 MHz) broadcasting and long-distance communication, and its effectiveness depends on the state of the ionosphere (which varies with time of day and solar activity).

3. Space wave propagation

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