This paper presents a dual band rectenna for RF energy harvesting applications. The receiving slot antenna has a single feed configuration with a coplanar waveguide (CPW) structure. A grounded-L strip is employed for circular polarized (CP) radiation. A stepped impedance matching stub is used to enhance the coupling between the feed line, inverted L-strip, and the slot. An asymmetric U-shaped strip is embedded near the upper right corner of the slot as a perturbed element. This asymmetric U-shaped strip is a key component to excite the required phase perturbation to produce a CP radiation. The antenna operates in the WiFi frequency bands of 2.45 GHz (IEEE 802.11 b&g) and 5 GHz (IEEE 802.11 a/h/j/n/ac/ax WLAN system). A dual band voltage doubler rectifier has been designed and implemented for RF to DC conversion. The impedance matching network for this rectifier is based on a П-model dual band impedance transformer that is optimized to match two unequal complex loads at two operational frequencies.