Sealed microwave movement detector - comprises oscillator with cavities and antenna on printed circuit board, and analysis circuits to sense variation of frequency

摘要

The microwave movement detector operates on the Doppler principal and has the antenna, cavities and oscillator mounted on a printed circuit board with the processing circuits. This allows sealing of the system with an epoxy resin. A microwave oscillator circuit on a printed circuit board comprises a transistor and three cavities, the emitting cavity of which eliminates the parasitic harmonics of the waveform. This emitting cavity is open to allow transmission of the wave via an antenna. The other two cavities are closed to operate in an absorption mode to isolate the oscillator frequency from the analysis circuits. The analysis circuits sence variation of oscillator frequency due to presence of objects.