MICROWAVE DOPPLER SENSOR

PROBLEM TO BE SOLVED: To provide a microwave Doppler sensor capable of detecting a moving body with high accuracy, without being affected by noise which the sensor itself has and by the noise due to the influence of a fluorescent lamp etc. SOLUTION: An output signal from a local oscillator 11 is emitted from a transmitting antenna 13, and a reflected wave from an object 20 is received by a receiving antenna 14. The output signal is fed directly into a first mixer 12 and is fed into a second mixer 18 via a second phase shifter 17. The reflected wave is input into the first mixer via a first phase shifter 16, and is input directly into the second mixer. Each of the phase shifters has the phase delayed by 90°. Since the reflected wave from the moving body is thereby frequency-modulated by the Doppler effect, a phase difference of 180° is generated in the Doppler signal output as a mixed signal from each mixer. By using a negative feedback amplifier 19 and applying negative feedback of a mixed signal generated by the second mixer, a signal generated in the local oscillator 11 is amplitude-modulated. Unwanted amplitude noise components, such as noises, are reduced, since phase differences are not produced. COPYRIGHT: (C)2007,JPO&INPIT