Question

Explain the ground wave propagation and space wave propagation of electromagnetic waves through space.

Answer 1

Ground wave propagation:
If the electromagnetic waves transmitted by the transmitter glide over the surface of the earth to reach the receiver, then the propagation is called ground wave propagation. The corresponding waves are called ground waves or surface waves.

Both transmitting and receiving antennas must be close to the earth. The size of the antenna plays a major role in deciding the efficiency of the radiation of signals. During transmission, the electrical signals are attenuated over a distance.

                                  Ground wave

Some reasons for attenuation are as follows:

1. Increasing distance: The attenuation of the signal depends on

1. power of the transmitter
2. frequency of the transmitter
3. condition of the earth surface

2. Absorption of energy by the Earth: When the transmitted signal in the form of an EM wave is in contact with the Earth, it induces changes in the Earth and constitutes a current. Due to this, the earth behaves like a leaky capacitor which leads to the attenuation of the wave.

3. Tilting of the wave: As the wave progresses, the wavefront starts gradually tilting according to the Skywave curvature of the Earth. This increase in the tilt decreases the electric field strength of the wave. Finally, at some distance, the surface wave dies out due to energy loss.

The frequency of the ground waves is mostly less than 2 MHz as high-frequency waves undergo more absorption of energy at the earth’s atmosphere. The medium wave signals received during the daytime use surface wave propagation. It is mainly used in local broadcasting, radio navigation, ship-to-ship, ship-to-shore communication and mobile communication.

Space wave propagation:
The process of sending and receiving information signals through space is called space wave communication. The electromagnetic waves of very high frequencies above 30 MHz are called space waves. These waves travel in a straight line from the transmitter to the receiver. Hence, it is used for line of sight communication (LOS).

                                    Space wave

For high frequencies, the transmission towers must be high enough so that the transmitted and received signals (direct waves) will not encounter the curvature of the earth and hence travel with less attenuation and loss of signal strength. Certain waves reach the receiver after getting reflected from the ground.