초록 ▼

The reflected signal of a microwave or ultrasonic Doppler intrusion detector is split into two different channels, each containing a mixer for hetrodyning the received signal with a reference signal. The reference signal for one mixer is the transmitted signal, while the reference signal for the oth

The reflected signal of a microwave or ultrasonic Doppler intrusion detector is split into two different channels, each containing a mixer for hetrodyning the received signal with a reference signal. The reference signal for one mixer is the transmitted signal, while the reference signal for the other mixer is the transmitted signal with a phase shift. Thus the outputs of the mixers are of the same frequency but different phase. A phase comparator produces two mutually exclusive pulse trains as a function of the outputs of the two mixers, one said output representing motion toward the detector and the other representing motion away from the detector. These pulse trains are applied through a bidirectional counter to upper and lower limit sensors. An alarm circuit is activated if either limit is exceeded, thus providing an alarm in response to sufficient motion in either direction.

대표청구항 ▼

In an intrusion detector in which a signal generated by a microwave or ultrasonic generator is radiated into an area under surveillance and reflected from every object in the area; a receiver to receive said reflected signal and to present said reflected signal to a pair of mixers, each said mixer m

In an intrusion detector in which a signal generated by a microwave or ultrasonic generator is radiated into an area under surveillance and reflected from every object in the area; a receiver to receive said reflected signal and to present said reflected signal to a pair of mixers, each said mixer mixing said reflected signal with a portion of the transmitter signal, the improvement comprising (a) splitting of said portion of said transmitter signal into two paths, and (b) introducing a relative phase difference between said two paths, the resultant signals being fed into said mixers to produce Doppler signals of equal frequency and amplitude but differing phase, said Doppler signals being presented to phase detecting means having two output channels controlled such that only one such channel may produce an output pulse at any instant, the channel outputs representing incremental and decremental movement of said objects in said area respectively.