The goal of this study is to investigate the impact of waveforms on the RF-DC power conversion efficiency for several designs of energy harvesting circuits, as the RF-DC conversion is a crucial part of the RF wireless power transfer (WPT). The efficiency of two simplest and most commonly used energy harvesting circuit topologies, namely, a voltage doubler and single diode rectifier is analyzed. Both considered topologies include matching networks designed for the sub gigahertz frequency band 863-865 MHz. The impact of different powering signal waveforms including a sine wave, and multi-tone signals with different values of peak-to-average power ratio (PAPR) on the circuit is examined. The analysis of the single diode rectifier is performed by means of a fast theoretical model exploiting a two dimensional version of the well-established Harmonic Balance method. The results obtained using the model are verified experimentally. Additionally, the PCE obtained for the single diode rectifier is compared with the measured one of the voltage doubler circuit, to find the most optimal signal and circuit combinations.