In the wireless communication era, radio frequencies (RF) are always present in the surrounding environment. This availability of abundant RF energy ignites the idea of the RF energy harvesting concept. This concept coins the eco-friendly self-sustainable wireless communication links between two nodes. In this paper, RF energy harvesting components required to scavenge RF energy from ambient energy sources are reviewed and cost-effective, environment eco-friendly with high RF to DC conversion efficiency rectenna design challenges are also presented.