Intrusion detection system and method

Details Intrusion detection system and method Intrusion detection system and method

1982-12-29

1985-08-20

Rowland, James L.

Communications: electrical

Condition responsive indicating system

Specific condition

343 5PD, G08B 1318

Patent

active

045367523

ABSTRACT:
An intrusion detection system includes a transmitter coupled to one end of a coaxial cable, a plurality of antennas spaced along and loosely coupled to the cable, and a receiver circuit coupled to the opposite end of the cable, the antennas being aimed at a protected region. The transmitter transmits microwave energy along the cable. A portion of the energy is transmitted by each antenna into the protected region and is reflected by a moving intruder or target back to one of the antennas. The receiver circuit imposes a low frequency square wave signal on the center conductor of the cable. A diode is attached across the two radiating elements of each antenna. The square wave on the center conductor forward biases the diode and thereby shorts each antenna for half of each low frequency cycle, resulting in chopping of the received signals from each antenna. Noise signals on the cable and the chopped received energy signals are filtered and mixed to produce a low frequency chopped doppler signal superimposed on the noise low frequency chopped doppler signal. The signal is amplified to a predetermined level, and adjacent maximums and minimums thereof are synchronously sampled by a doppler amplifier to produce a signal representative of the amplitude of the doppler signal.

REFERENCES:
patent: 4328487 (1982-05-01), Cheal
patent: 4358764 (1982-11-01), Cheal et al.
"A Volumetric Terrain Following Sensor", by James Cheal from the Proceedings of the 1981 Carnahan Conference on Crime Countermeasures, Lexington, KY, May 13-15, pp. 125-128.

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