The energy harvesting is the process by which energy from different sources of radiation is captured and stored. The harvesting of this energy would be an alternative energy capable of replacing, totally or partially, the battery of certain micro systems that require a low amount of energy. This paper firstly presents the quantification of the radiated power available in the ambient environment with respect to frequency through various measurements. This quantification of the RF power according to the considered environment is necessary since, it allows to choose frequency bands with the highest power density, and then to estimate the recoverable maximal DC power. Secondly, we present various simulation results under HFSS software to analyze the performance of antenna candidates for this study and which are the first elements constituting the rectennas.