# 1.3 Physical Phenomena in the High Frequency Domain

We will now take a deeper look at RF engineering through two examples that introduce wave propagation on transmission lines and electromagnetic radiation from antennas.

*1.3.1 Electrically Short Transmission Line*

As a *first example* we consider a simple circuit (Figure 1.3a) with a sinusoidal (monofrequent) voltage source (internal resistance *R*_{I}), which is connected to a load resistor *R*_{A} = *R*_{I} by an *electrically short* transmission line. *Electrically short* means that the transmission length of the line is much shorter than the wavelength λ, that is λ. In vacuum–or approximately air–electromagnetic waves propagate with the speed of light *c*_{0}.

1.1

Therefore, the free space wavelength λ_{0} for a frequency *f* yields:

1.2

In media other than vacuum the speed of light *c* is lower and given by

1.3

where ε_{r} is the relative permittivity and μ_{r} is the ...