Radio waves are a type of electromagnetic radiation, artificially generated radio waves are used for fixed and mobile communication, broadcasting, radar, computer networks and navigation. These artificially generated radio waves are created from antennas, antennas convert the electric current of a signal into a radio wave, so it can travel through space to a receiving antenna, which then converts it back into an electric current to be used by a receiver. Objects between the transmitter and receiver may reflect and block the signal, this means waves have to have a line of sight between the two for the signal to be received.
There are three different types of waves, each with different characteristics, they are:
1- Ground waves
which are lower frequency waves that travel close to the surface of the earth and will in fact follow the curvature of the earth. The lower the frequency of a wave the further the signal will be able to travel. These ground waves travel reliably and predictably along the same route day after day, not being influenced by outside factors.
2- Sky waves
which are higher frequency waves they can also travel for long distances but instead of following the curvature of the earth, the waves are refracted or bent by the ionosphere and sent back down to earth. Using sky waves high frequency radios can send messages across oceans using only 50 to 100 watts of power.
3- Space waves
consist of very high frequency waves, or higher that neither bend nor refract, these waves travel in a straight line passing through the ionosphere and allow navigation from space. Most major navigation systems these days operate with signals broadcasting space waves.