In low frequencies, the diode rectifies the input signal depending of the bias polarity. This is because (the simples case) the diode is consider either an open or closed circuit.
In high frequencies (> 300MHz) the diode is consider as a equivalent circuit (Fig.1) but I do not understand how the rectifying process occurs.
My assumption is that, when talking about RF, the source must be adapted to the input impedance of the diode. When the impedances are adapted the signal is rectified.