Radio wave propagation

There exist two ways of radio wave propagation. They are ground wave propagation and ionospheric propagation. If the electromagnetic waves are propagating near the surface of the earth, it is called ground wave propagation. This includes propagation of radio waves through troposphere too. Electromagnetic waves can travel in different ways (multiple paths) between transmitter and receiver antenna. A direct path can be established by fixing transmitter and receiver antenna in the line of sight of each other.  A wave which propagates along this path is called direct wave. The different mechanisms for electromagnetic energy transfer are direct, reflection, scattering and diffraction. The direct, reflected, scattered and diffracted waves are collectively known as space wave. When an electromagnetic wave reaches an interface between two dissimilar media, a part of the energy flows along the interface. This is known as surface wave. For a vertically polarized electromagnetic radiation, surface wave is predominant at low and medium frequencies.