A SYSTEM FOR THE DETECTION OF MOVING OBJECTS WITHIN A SURVEY AREA BY MICROWAVE DIFFRACTION

摘要

1491578 Intruder alarms B SCHLOER O T JENSEN E LANDERT H B HANSEN and N O WRIST 7 Nov 1975 [7 Nov 1974] 46235/75 Heading G4N A system for the detection of moving objects within an area comprises a transmitter 1 having a microwave oscillator 5, a pulse modulator 4 and an antenna 6, a receiver 7 having an antenna 8, a detector 9, an amplifier 10 and a filter 11, an alarm unit 12, and a modulation generator 2, the filter 11 being a commutative filter having a plurality of capacitors C which are cyclically connectable as filter shunt capacitors in a cycle controlled by a modulation signal from the generator 2, the cycling period being equal to the modulation period. As shown, in Fig. 3, the filter comprises a pulse generator 17 which receives the modulation signal over cable 3 and provides a signal at eight times the modulation frequency to a binary (3 bit) counter 18. The digital signal delivered by the counter is decoded by decoders 19 to apply a signal successively to the bases of transistors T1-T8 to make each of these transistors conductive for a period of # of the modulation period. Thus the receiver will always be accurately tuned to the transmitter. The alarm unit 12, Fig. 4 (not shown), comprises a detector unit having zero point displacement connected to the output of the filter 11, the detector output being applied to an alarm relay circuit and to a low-pass filter which connects the output of the detector unit to the amplifier 10 or a stage thereof for automatic gain control purposes. The alarm relay circuit operates an alarm device which may be a bell or siren and/or a warning light.