Power management and charging of batteries for wireless sensors become a problem when using them in the field applications. In this paper, we present RF energy harvesting circuit with three different approaches resonator, number of multiplier stages and low pass filter (LPF). Resonator provide 30 times improvement in amplitude of input (100 mV) ac signal. In proposed circuit L type network, between input power source and rectifier, works as resonator as well as matching network at resonant frequency. It results in maximum efficiency 79% with 50Kohm load at -10 dBm input power. We also presents the effect of multiplier stages on output voltage and RF to dc conversion efficiency. Optimum efficiency of approximately 80% is achieved with Dickson topology in input power region 0 to 10dBm for 3rd, 5th and 7th stages, respectively. Application of LPF is also introduced with an existing circuit. It provides 140 mV improvement in output voltage with input power -10dBm. It also shows that maximum efficiency 75% and 64% is possible with dielectric constant (Er=9) and substrate height (H=0.0004m), for microstrip line of matching circuit at
-10 dBm input power with 10 Kohm load.