A wide-band 900 MHz to 2.45 GHz rectenna has been developed for Radio Frequency (RF) energy harvesting in the context of outdoors Wireless Sensor Nodes (WSN). Based on simulations of different rectifying circuits, the most appropriate one for low incident power levels has been manufactured and tested with a wide-band antenna. The theoretical analysis, confirmed by measurements, shows that the proposed method yields a 20% increase in average in the DC output voltage compared to a single frequency system.