The rectenna is a basic and fundamental element for RF energy harvesting. The development of efficient rectennas requires the implementation of some impedance matching technique between the rectifying circuit and the antenna element. An impedance matching technique inspired on the inset feeding of microstrip patches is proposed in this work. The technique keeps the size of the rectenna unchanged and does not require any additional component. An application example operating at 5.8 GHz and using a cheap FR4 substrate is presented.