We present dc and microwave experiments on a graphene-based top-gate field effect transistor. The transistor is acting as an active device far from the Dirac point, and turns into a passive device at the Dirac point, the transistor amplification being suppressed due to lack of carriers. In this way, microwave switches can be implemented based on the specific charge carrier transport in graphene. The maximum stable gain of the transistor is maintained up to 9 GHz, and the mobility of graphene FET is greater than 8000 cm2/Vs far from the Dirac point.