Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Patent
1974-09-26
1976-06-29
Wilbur, Maynard R.
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
343 5PD, 343 14, 343 172PC, 340258B, G01S 942
Patent
active
039672832
ABSTRACT:
An intrusion detector operating with electromagnetic sensors to detect intruder motion within large, defined areas is disclosed. The system provides an acceptably low false alarm rate by means of range discrimination whereby moving objects outside the protected area do not affect the system and by improving sensitivity to slow-moving targets even when located very close to the sensor location. The system incorporates a transmitter which is frequency modulated by a triangular or sawtooth wave and a receiver which produces an output signal that varies in accordance with the instantaneous difference between the transmitted and received frequencies. The frequency of this difference signal is the beat frequency, and is proportional to the range of the target. Storage means are provided to permit comparison of successively received signals over a predetermined period of time, and this comparison serves to reveal slowly varying changes in the return signal pattern. Alarm means are provided which respond to significant variations in successive measurements, and when a threshold level of difference is exceeded for a certain number of consecutive sweeps, an alarm is sounded.
REFERENCES:
patent: 3344423 (1967-09-01), Thue
patent: 3500399 (1970-03-01), Norris, Jr.
patent: 3562750 (1971-02-01), Fishbein et al.
patent: 3665443 (1972-05-01), Galvin
patent: 3741655 (1973-06-01), Ling et al.
patent: 3761946 (1973-09-01), Johannessen et al.
Clark Robert V.
Linder Francis X.
McCreary Terrance J.
Taylor William R.
Automation Industries, Inc.
Buczinski S. C.
Wilbur Maynard R.
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