This paper presents a guideline to design and optimize a RF energy harvester operating in ISM Band at902 MHz. The circuit is implemented on a standard FR4 board with commercially available off-the-shelf devices. The topology of the impedance transformation block is selected to reduce the losses which improves the overall performances of the system.The characterization of the harvesting module shows sensitivityof -22.5 dBm for a dc output voltage of 200 mV up to -11 dBm for 1.08 V. A wireless power transmission in an indoor environment is measured with a radiated source power of 16.8 dBm. The harvester exhibits a DC rectified voltage of1.25 V at 0.5 meter and still 500 mV at 1.5 meter.