A 2-18 GHz MMIC power amplifier has been simulated in GaAs technology, based on a non-uniform distributed transmission line topology. The resulting circuit is a non-uniform distributed power amplifier (NDPA), which uses the power pHEMT process available at WIN semiconductor. The NDPA has been optimized for maximum power and efficiency, and it exhibits 1W (CW) output power, 27% medium drain efficiency and 23% medium PAE in the whole operating bandwidth. The resulting small signal gain is 10 dB. Stability analysis has been performed for internal loops also, resulting in an unconditionally stable amplifier. Considering the available results in literature for similar design, the proposed NDPA gives the highest performances in terms of efficiency and output power in the 2-18 GHz operating bandwidth.