Abstract: 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.

Abstract: A microwave movement detector which is capable of discriminating between progressive or unidirectional movement such as that by an unauthorized intruder and reciprocating movement such as by a curtain. The detector includes a pair of receiver/mixer diodes into which a transmitted signal is mixed with a surveying signal causing a phase difference so that the resultant signals have a different phase relationship amplifying the resultant signals feeding the signal into an integrating circuit in similar counter so that an alarm is sounded when the counter reaches a high or low threshold level.