  Graphene supports surface plasmon polaritons with comparatively slow
propagation velocities in the THz region, which becomes increasingly
interesting for future communication technologies. This ability can be used to
realize compact antennas, which are up to two orders of magnitude smaller than
their metallic counterparts. For a proper functionality of these antennas some
minimum material requirements have to be fulfilled, which are presently
difficult to achieve, since the fabrication and transfer technologies for
graphene are still evolving. In this work we analyze available graphene
materials experimentally and extract intrinsic characteristics at THz
frequencies, in order to predict the dependency of the THz signal emission
threshold as a function of the graphene relaxation time tau_r and the chemical
potential mu_c.
