The Factors Affecting Ground Wave Propagation

Key Takeaways

• The electromagnetic spectrum in the frequency range from 3 kHz up to 300 GHz can be called the radio spectrum.

• Ground waves are divided into three components: surface waves, direct waves, and earth reflected waves. 

• The factors that affect ground wave propagation are the nature of the ground, weather, polarization, and signal frequency. 

Ground wave propagation utilizes radio waves in the range of 50 kHz to 250 kHz

Applications such as wireless computer networks, communications satellites, radio navigation, amateur radio communications, and international shortwave broadcasters all use radio waves, which is why signal propagation can be called radio wave propagation. Radio propagation can be described as the way in which radiofrequency waves travel or propagate when they are transmitted from a transmitter to receiver.

Radio propagation is classified into three types: free ground wave propagation, space propagation,  and skywave propagation. Ground waves propagate over the earth’s surface and are effective for frequencies in the range of 50 kHz to 250 kHz. Ground wave propagation is often used for signal transmission between the earth’s surface and the ionosphere. In this article, we will explore radio wave propagation, with a specific focus on ground wave propagation. 

Types of Radio Wave Propagation 

The electromagnetic spectrum in the frequency range from 3 kHz up to 300 GHz is the radio spectrum. Radio waves can transmit information from one point to another without the aid of interconnections, transmission lines, wires, or cables, enabling wireless communication.

Depending on the frequencies, radio wave propagation is classified into three types:

1. Ground wave propagation - When radio waves from the transmitting antenna propagate along the earth’s surface to the receiving antenna. This can also be called surface wave propagation.

2. Free space propagation - When the radio waves transmitted from the transmitting antenna propagate through free space and around the ground to reach the receiving antenna directly or by ground reflection. This type of propagation can also be called line of sight propagation.

3. Skywave propagation - Radio waves transmitted from the transmitting antenna propagate through the sky to the receiving antenna directly or by ground reflection. This can also be called ionospheric wave propagation.

Let’s explore ground wave propagation a little further. 

Ground Wave Propagation 

Ground wave propagation covers the area between the earth’s surface and the ionosphere for signal transmission. It follows the earth’s contours and can transmit signals to considerable distances. Ground wave propagation utilizes the low frequency and medium frequency portion of the radio spectrum. It is the ideal radio wave propagation for short-distance communication, especially during the daytime, and is applied in local radio broadcasting, radar, amateur radio communications, and radio navigation.

In ground wave propagation, the transmitting as well as receiving antennas are on the earth’s surface, offering multiple paths for communication. When the transmitting antenna and receiving antenna are in the line of sight, then a direct path exists between them. A wave that propagates between antennas at the line of sight is called a direct wave. The direct wave is a component of a ground wave.

Ground waves are divided into three components:

1. Surface wave - The component of a ground wave that uses the earth’s surface as the wave conductor.

2. Direct wave - The component of a ground wave that propagates through the shortest distance between two points on the earth’s surface.

3. Earth reflected wave - The component of a ground wave that gets reflected from the earth’s surface and then travels towards the receiving antenna. 

Factors Affecting Ground Wave Propagation

This section briefly addresses the factors that affect ground wave propagation. 

Nature of Ground

Ground waves, especially surface waves, are influenced by the nature of the ground above which the signal propagates. The signal attenuation in ground wave propagation is dependent on factors such as ground conductivity, topography, and dielectric constant.

The ground penetration and surface conductivity are very important when it comes to low-frequency ground wave propagation. At the lower frequency range of ground wave propagation, ground strata down to a distance up to 100m have a certain effect on signal transmission. The ground penetration of low-frequency ground waves is high and affects surface conductivity as well.

Terrain with good conductivity is best suited for ground wave propagation. The soil type and its moisture content boost the conductivity of the ground and are influential in ground wave propagation.

Polarization

The antenna polarization is of great importance in ground wave propagation. Vertical polarization is better suited for ground wave propagation than horizontally polarized antennas. Because of the vertical polarization requirement, medium and long-wave radio stations generally employ self-radiating vertical transmitting antennas. 

Weather

The weather plays an important role in the losses incurred in ground wave propagation. Dry and sandy signal propagation paths are not suitable for ground wave propagation. The moisture content in the atmosphere can be helpful to ground wave propagation.  

Signal Frequency

The signal attenuation in ground wave propagation is dependent on the signal frequency. As the frequency increases, the losses in the wave propagation increase, and this phenomenon limits the ground wave propagation above 3MHz. The signal frequency also influences the maximum range of ground wave propagation.

Other factors affecting the ground wave propagation maximum range are the density of the ionization of the layer and the angle of incidence at which the wave enters the surface. Cadence’s suite of design and analysis tools can assist you in developing ground wave propagation systems and can help you analyze how various factors influence signal attenuation.

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