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What is Radio



Radio Propagation Modes

Ground Reflection


Ground Reflection

In LOS model, the assumption is that there is only one path for propagation of EM Wave from transmit antenna to receive antenna. The two antennas are kept in free space with no other objects intersecting radiation from transmitter antenna. If two antennas are situated close the ground due to discontinuity in the electrical properties at the air ground interface any wave that falls on the ground is reflected. The amount of reflection depending on factors like angle of incidence, Polarization of wave, Electrical Properties of the Ground i.e conductivity and dielectric constant, the frequency of the propagating wave. Thus, the field at any point above the ground is a vector sum of the fields due to the direct and the reflected waves.

Direct Wave:-

It is limited to “line-of sight” transmission distances .The limiting factors are antenna height and curvature of earth. The Radio horizon is about 80% greater than line of sight because of diffraction effects. A Part of the signal from the transmitter is bounced off the ground and reflected back to the receiving antenna. If the phase between the direct wave and the reflected wave are not in phase can cause problems Detune the antenna so that the reflected wave is too weak to receive

To compute the fields of a transmit antenna above an imperfect ground.
Used to design of communication links. To select the locations of the transmit and receive antennas and their patterns. Consider a transmit antenna located at point P at a height ht. Receive antenna located at point Q
at a height hr from the surface of the ground. Let the horizontal distance between the two antenna be d.
The electromagnetic wave from transmit antenna can reach the receive antenna by two possible paths (a) direct path (b) ground reflected path.
The total electric field at the field point Q is given by the vector sum of the electric field due to the direct wave and ground reflected wave.
1. The transmit antenna and the field points are located in the y-z plane.
2. The transmit antenna is an infinitesimal dipole oriented along the x-axis.

The electric field is of infinitesimal dipole oriented along the x-axis is given by