Study On RF Front-end Of Doppler Detect System

Doppler effect can be used in non-destructive testing, and it has outstanding advantages. According to practical demand from microwave non-destructive testing, this thesis applied Doppler effect to non-destructive testing system and discussed emphatically the related problems of Doppler RF front-end, designed and developed Doppler RF front-end in 1GHz frequency band.The Doppler RF front-end mainly consists of transistor oscillator and diode mixer. Based on the basic principles of three-point oscillator, the complexity of RF oscillator was analyzed. Considering the distributed parameters of transistor, the amplitude and phase relations between feedback and input signals, in addition to the oscillation mechanism of circuit were discussed in detail. For the mixer part, the role and the principle of mixer were introduced, and the detailed analysis on the mixing process and its circuit performance was shown.The Doppler RF front-end circuit was tested by using of PC-based virtual oscilloscope and spectrum analyzer. Such test scheme is simple and can obtain correct measurement results with low hardware requirement; and the measured data are easy to store for further analysis, evaluation and processing.