RF energy harvesting is the process by which ambient electromagnetic energy from different sources in the environment is captured, converted and stored. It can provide an alternative energy capable of replacing, totally or partially, the batteries of a number of micro-systems and devices that have low energy requirements. In particular, solar energy harvesting has been commonly used to overcome this barrier. However, it should be noted that wireless sensor networks (WSN) operating on solar power suffer form energy shortage during nighttimes. Therefore, to solve this problem, we exploit the use of 3G broadcasts airwaves as energy sources to power wireless sensor nodes. This paper focuses on the design, optimization and experiments of 3G-band rectenna, based on a modified double slot coplanar waveguide (CPW) antenna. It contains also an RF-to-dc conversion circuit based on a zero bias Schottky diode SMS 7630. The reported rectenna have been fabricated and measured for 2100 MHz band. It achieves 400 mV voltage over an optimum load of 1700 Ω and about 50 % efficiency when the incident RF power is -7 dBm. The developed antenna is able to harvest the electromagnetic energy in several communication standards: GSM 900 and 1800, Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE) and Wi-Fi. Numerical results and experiments are presented and discussed in this paper