In this paper a single and a dual band rectifier based on an Enhancement-mode Pseudomorphic High Electron Mobility Transistor (E-pHEMT) are proposed. Both rectifiers were designed with E-pHEMT devices with unbiased gates. This circuits were optimized to have high efficiencies at high power values, and are suited for high power wireless power transmitter approaches, due to its higher robustness when compared with diode based solutions. On top of this the use of special designed waveforms, specially multisine type signals will be evaluated to increase the efficiency range at lower powers.