  We measure graphene coplanar waveguides from direct current (DC) to 13.5GHz
and show that the apparent resistance (in the presence of parasitic impedances)
has an quadratic frequency dependence, but the intrinsic conductivity (without
the influence of parasitic impedances) is frequency-independent. Consequently,
in our devices the real part of the complex alternating current conductivity is
the same as the DC value and the imaginary part~0. The graphene channel is
modelled as a parallel resistive-capacitive network with a frequency dependence
identical to that of the Drude conductivity with momentum relaxation
time~2.1ps, highlighting the influence of alternating current (AC) electron
transport on the electromagnetic properties of graphene. This can lead to
optimized design of high-speed analogue field-effect transistors, mixers,
frequency doublers, low-noise amplifiers and radiation detectors.
