Radio Wave Propagation (Overview of Radio Wave Propagation)

In the earth environment, electromagnetic waves propagate in ways that depend not only on their own properties but also on those of the environment itself.

The waves with frequencies above HF (High Frequency) travel in a straight line. They propagate by means of so called waves. They travel in the troposphere, the portion of the atmosphere closest to the ground.

Frequencies below the HF (High Frequency) range travel around the curvature of the earth. They are called Ground Waves or Surface Waves. All broad-casting radio signals received in day time propagate by means of surface waves.

Waves in HF (High Frequencies) ranges are reflected by the ionized layers of the atmosphere and are called sky waves. Such signals are beamed into the sky and comedown again after reflection, returning to earth.

Types of propagation can be written as:

1.      Line of Sight Propagation (Space Waves): It requires a path where both antennas are visible to one another i.e. both transmitting and receiving antennas must be within line of sight. VHF (Very High Frequencies) & UHF (Ultra High Frequencies) communication typically use this path. For example Satellite Communication, Ground Communication.

Fig1: Line of sight propagation

1.      Ground Wave Propagation (Ground Waves): Ground waves progresses along the surface of the earth i.e. the signal follows contour of the earth and can propagate considerable distances. This type of wave induces currents in the ground over which it passes and thus loses some energy by absorption. Frequencies up to 2MHz (VLF and MW uses it). For example AM Radio.

Fig2: Ground wave propagation

1.      Sky-Wave Propagation: In sky wave propagation the waves reflects back to the earth from the Ionosphere of the earth atmosphere i.e. the signal is reflected from the ionized layer of the atmosphere and travel forward with a number of hops, back and forth. For example SW Radio (HF uses it).

Fig3: Sky wave propagation