  We analyze the behavior of a non-Hermitian opened one-dimensional quantum
system with $\mathcal{PT}$ symmetry. This system is built by a dimer, with
balanced gains and losses described by a parameter $\gamma$. By varying
$\gamma$ the system resonances, which are naturally separated, coalesce at the
exceptional point (EP). The transmission spectrum is obtained by means of the
scattering matrix ($S$ matrix) formalism and we examine the wave functions
corresponding to the resonances as a function of $\gamma$. Specifically, we
look for the behavior and distribution of the phases of the $S$ matrix before,
at and after the EP.
