GB1336255A - Micro-wave intruder detector systems - Google Patents

Abstract

1336255 Radar SHORROCK DEVELOPMENTS Ltd 14 March 1972 [19 March 1971] 7357/71 Heading H4D [Also in Division G4] In an intruder alarm a micro-wave field is provided in a protected area PA by at least one transmitter T1, signals reflected from objects in the protected area being picked up by two receivers R1, R2 each producing a Doppler signal, a comparator C being included to provide an alarm-initiating output when the Doppler signals from the two receivers R1, R2 are substantially alike. As shown, two transmitters T1, T2 operate at 10,000 MHz and prevent false alarms due to transmitter noise. The receivers R1, R2 are synchronized by a reference signal from the respective transmitter. The comparator may be responsive to Doppler frequency, phase or amplitude, and may feed an AND gate D1, D2, D3 which only provides an output to the alarm B in the presence of Doppler signals from both receivers and a similarity signal from the comparator. The use of two receivers prevents false alarms due to movement of small objects. The two transmitters T1, T2 may operate on the same or slightly differing frequencies. In Fig. 1 (not shown) only one transmitter is employed and the AND gate is omitted.