Radio Frequency (RF) propagation is defined as the travel of electromagnetic waves through or along a medium.
For RF propagation between approximately 100 MHz and 10 GHz, radio waves travel very much as they do in free space
and travel in a direct line of sight. There is a very slight difference in the dielectric constants of space and air. The dielectric
constant of space is one. The dielectric constant of air at sea level is 1.000536. In all but the highest precision calculations,
the slight difference is neglected.