Space Wave Propagation

Space wave propagation takes place when the radio waves from a transmitting antenna propagate through the space around the earth to reach a receiving antenna. The radio waves here can propagate either directly or after reflection from the ground or in the troposphere. Hence, to understand the term space wave propagation, we first need to know a bit about radio wave propagation.


What is Radio Wave Propagation?

Radio wave propagation defines how radio waves propagate or travel from one point to another. Besides defining the behaviour of waves as they are transmitted from one point to another, radio wave propagation also showcases the way radio waves are affected by the medium along which they propagate, and in particular, how they travel in various parts of the atmosphere. The mode of radio wave propagation in free space and atmosphere can be classified in different categories, and space wave propagation is one which we often notice. 


What is Space Wave Propagation?

Space wave propagation is defined as a category of radio wave propagation for the radio waves that occur within the 20kmfrom the earth’s surface, i.e., the troposphere. It comprises of direct or reflected waves. It is also known by two other names: 

  • Tropospheric propagation as the waves here can propagate directly from the earth's surface to its troposphere surface.  

  • Line-of-sight propagation as the waves travel in a straight line and cover a minimum distance of sight. It means the waves propagate to a distance up to which one can see with the naked eye.

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Space Wave Propagation Depends on Three Components:

  1. Direct Waves: The radio waves that, when transmitted from the transmitting antenna, reach the receiving antenna directly.

  2. Ground Reflected Waves: The radio waves that reach the receiving antenna after reflection from the ground. 

  3. Tropospheric Wave: The radio waves that reach the receiving antenna after reflection from the troposphere. 

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As the figure depicts, space wave propagation, i.e., line-of-sight propagation is not always smooth. It means this mode of propagation can face obstacles that result in attenuation or loss of signal strength. Therefore, to prevent these issues, there is a need to adjust the height of both the transmitting and receiving antennas and the distance between them. The below formula appears helpful in this:

DM = (2RhT) + (2RhR)


DM: Distance between the two antennas

R: Radius of the earth

hT: Height of transmitting antenna

hR: Height of receiving antenna 


Applications of Space Wave Propagation

Space wave mode of propagation has its application in various systems like:

  • Line-of-sight communication

  • Satellite communication

  • Radar communication

  • Television broadcast

  • Microwave linking

Note: Space waves are used for very high-frequency bands ranging from 30 MHz to 300 MHz, ultra-high frequency (UHF) bands, and microwaves. It is because, at such high frequencies, both the skywave propagation and ground wave propagation fail. 

The antennas at these frequencies are comparatively smaller and can be placed at heights of several wavelengths above the ground. Due to the line-of-sight nature of this propagation, the waves here get blocked by the curvature of the earth. That's why if one wants to receive the signal beyond the horizon, then he/she needs to ensure that the receiving antenna possesses a height enough to intercept the line-of-sight waves.

Hence, we can conclude that the space wave propagation is limited to the line of sight distance, which is defined as the distance amid the transmitting and receiving antenna at which both can view each other. It is also known as the range of communication, which can be increased by increasing the heights of both the antennas. Besides, the curvature of the earth is another aspect by which space wave propagation gets affected.  

Example: Calculate the maximum distance up to which the signal transmitted from a tower with a height of 80m can be received?

Space wave propagation is defined as the mode of propagation in which the radio waves transmitted from the transmitting antenna reach the receiving antenna after travelling or propagating through space. It is why the waves here are also known as space waves and propagation as line-of-sight communication. Space wave propagation is suitable for UHF (Ultra High Frequency) and VHF (Very High Frequency) regions. Hence, TV broadcast, microwave links, and satellite communication are some of its examples. 

Based on this definition, the maximum distance (d) up to which the signal transmitted from transmitting antenna having height 80m will be:

Given, h = 80 m, R = Radius of the earth = 6400 km

d = √2Rh

 = √2x6400x1000x80

 = 32000m = 32km

Hence, the required distance will be 32km.