Ground Wave Propagation
The wave which travel directly from the transmitting to the receiving antenna through the surface of the earth is called ground wave or surface wave and the phenomenon is known as ground wave or surface wave propagation.
|Ground or surface waves propagation|
This type of propagation is used when transmitted and receiving antennas are closed to the surface of the Earth. The ground wave propagation (also known as the surface wave propagation) is a mode of propagation of electromagnetic waves of longer wavelengths in which the ground has a strong influence on the propagation of waves from the transmitting antenna to the receiving antenna and the wave guides over the surface of the Earth.
It is found that to radiate signals with high efficiency, the transmitter antennas should have a size compared to the wavelength λ of the signal wave. The size of antenna should be at least equal to λ/4. At longer wavelengths the size of the antenna is large and tha antenna is located on or very near to the ground. In ground wave propagation, usually adopted for standard amplitude modulated micro wave broadcast, ground based vertical towers are used as transmitting antennas.
As it is clear that ground wave pass over the surface of the Earth. They becomes weaker and weaker as a result of energy absorbed by the earth as due to energy loss the ground wave cannot be used for long distance communication. The losses are dependent upon frequency of the wave. In case of high frequency the losses are also high. So the Ground wave propagation can be used for low frequency (500 kHz to 1500 kHz) or for radio broadcast.
Advantages of Ground Wave Propagation
- Ground waves are relatively unaffected by changing the atmospheric conditions.
- Ground waves can be used to communicate between any two location by giving enough power to them.
- Ground waves are vertically polarized in order to prevent short circuit of the electric field components.
Disadvantages of Ground Wave Propagation
- Ground waves are limited to very low frequency signal. Hence, these require large antenna.
- Ground waves losse power with surface material and composition.
- Ground waves are used to cover short ranges and also involve attenuation of waves.