Electromagnetic Waves-Types of Propagations-Ground Propagation

Waves that can travel through space, without being dependent on any support system for their movement, are known as electromagnetic waves. A clear point of distinction between electromagnetic waves and mechanical waves is that mechanical waves require the support of a material system to enable them to travel from location to location. Sound waves and light waves are examples of mechanical and electromagnetic waves, respectively.

Propagations of electromagnetic waves:

Based on the concept that Electromagnetic waves are not dependent upon any specific material medium to propagate and move through the atmosphere. It is imperative to understand the different categories of propagation of electromagnetic waves. These are:

• Ground Wave Propagations
• SkyWave Propagations
• Space wave Propagations

Ground propagation definition:

Ground wave propagation is a type of signal propagation in which the signal travels over the ground’s surface; hence majorly, it is used to provide geographic coverage on the long and medium wave frequency band.

What is ground propagation?

Radio frequency propagation along the earth’s surface for communication purposes, using low frequencies of the electromagnetic spectrum. Surface wave propagation is another name for it. Ground wave propagation is the accumulation of these electromagnetic waves along the earth’s surface, and the concentration of the waves reduces with an increase in distance. This happens, due to the effect of loss of power through the absorption of these waves by the ground.

Radio waves from the transmitter travel across the surface of the planet to reach the receiver antenna in ground propagation. To emit signals efficiently, the devices used for transmission purposes should have adequate compatibility. Depending upon the frequency and distance of the propagations, the size and location of the devices should be used.

Ground wave propagation is critical in the low- and medium-frequency bands of transmissions. Ground wave radio propagation is used to provide regional coverage, especially for radio frequencies that need to cover a specific area.

Attenuation of ground waves:

• Attenuation here refers to the loss of efficient transmission of electromagnetic waves.
• In ground wave propagations, this loss happens while travelling along the surface of the earth, as some frequencies get absorbed by the earth.
• In these propagations, the attenuation increases as the frequency of EM waves grows.
• These propagations are most suitable for transmitting frequencies of up to 3 megahertz.
• Attenuation here depends upon many factors that include the size of the area for propagations.

Ground wave and Earth’s surface

• The curves of the earth’s surface affect the ground wave propagations as the em waves travel along the surface of the earth.
• A ground that is of a conductive nature is best suited for these propagations.
• Seawater that is salty in nature is regarded as best suited for ground wave propagations
• Sandy regions are regarded as least efficient for ground waves.

Polarisation:

Polarisation refers to the direction of flow of the electric field of the EM waves Propagation.

• Ground propagations have effects on the use of antenna type and the way it is polarised
• Losses in ground propagation with respect to polarisation states that, when vertical, there is a lesser loss in comparison with the case of horizontal polarisation.
• Change in polarisation can be there in the case of atmospheric pressures.
• Horizontal polarisation can lead to a short circuit.

Application of Ground Wave Propagations:

• Communicative support used by the military.
• Effective communication in sea vessels.
• Television
• Radio

Positives of Ground Propagations:

• It is not dependent on the conditions of the atmosphere.
• With the injection of required power, ground wave propagations can be used for transmissions of EM waves between two points
• Vertical polarisation of these waves acts as a protective environment in safeguarding against the risk of short circuits.

Negatives of ground Propagations:

• Change in the atmospheric conditions, there can be changes in polarisation.
• Polarisation changes to horizontal ones can be a cause of a short circuit.
• Limitations of Distance

Ground Wave Propagations Key points:

• As implied by the name, these electromagnetic waves propagate from one point to another, moving over the earth’s surface.
• These propagations occur through the antennas placed between the two-point, with transmitter and receiver devices installed as required.
• The EM waves are transmitted  and received between the antennas
•  Depending upon the required efficacy of the Electromagnetic waves, different sizes of antennas are required at sending and receiving ends.
• There is a loss of power when EM waves propagate through the ground, the larger the distance these waves have to cover, the greater can be the loss. For the same reason, ground wave propagations are recognized to be most effective when they are used for a shorter distance of propagations.
• Ground wave propagations are generally used in relay of television from satellite antennas, radio antennas, etc.
• Ground waves can be further classified into three types:
  • Surface waves
  • Direct Waves
  • Earth reflected waves

Conclusion: 

The efficacy of the ground wave propagation keeps on declining with the incremental absorption of energy by the surface of the earth. This simply implies that for optimal use of ground waves, it should be used for a shorter distance. Additionally, the losses in case of a higher frequency of transmissions are higher, so a lower frequency is more advisable. Ground Wave Propagations have accordingly established their use and are used optimally for the desired purposes. To overcome the shortcomings of ground waves, sky waves and space waves are used.