Do you want to make a DC generator with no input and have it work by perpetual motion? You have an oscillator and rectify its output that is used to power the oscillator and maybe power a load? Impossible.
It must have an external power supply to make up for losses. It wastes energy by making heat and it feeds energy to a load.
i would like to design an AC-DC rectifier by applying this concept, where the charge will be store in a component before entering to the mosfet. Thus, the mosfet can function although the ambient RF is lower than Vth.