This paper summarizes theoretical work that was performed at MPB Technologies Inc. to explain the behaviour of a certain type of non-linear detector. A theoretical model of the rectifying mechanism taking place at the Schottky junction of a quasioptical Schottky diode detector has been developed and compared to various experiments of FIR and microwave detection. An excellent fit has been obtained between this model and the experimental results for both video and heterodyne detection. This study has resulted in a good understanding of the detector behaviour. The existence of an optimum diode biasing current has been shown. A generalized theoretical curve of the saturation power has been calculated for the complete SMM wavelength range. This curve defines the linear dynamic range of any type of Schottky diode detector device. The theory has been also extended to higher order terms to describe the non-linear effects observed at high biasing currents and for strong incident radiation.