Communications: directive radio wave systems and devices (e.g. – Presence detection only – By motion detection
Reexamination Certificate
1999-10-29
2001-05-29
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Presence detection only
By motion detection
C342S110000, C342S115000, C342S114000, C340S554000
Reexamination Certificate
active
06239736
ABSTRACT:
TECHNICAL FIELD
This invention relates to intrusion monitoring security systems and more particularly to a range-gated radar motion detector.
BACKGROUND OF THE INVENTION
There are previously known apparatus and methods for detecting intrusion into a space. Common detectors include door and window contacts, glass break detectors, and motion sensors. Motion detectors typically employ ultrasound, passive infrared (“PIR”), or radar detection techniques. Ultrasonic motion detectors are commonly used for automatic door openers and security alarms. They are inexpensive and can operate with narrow beamwidths. However, installation options are limited because ultrasonic beams are easily blocked by thin materials, including paper. Another disadvantage is false triggering caused by reflections from blowing curtains, pets, and flying insects.
PIR motion detectors are perhaps the most frequently used home security device. They employ a special Fresnel lens to generate multiple thermal images of a warm object, such as a person. As the person traverses the PIR field of view, the thermal images produce periodic fluctuations that are detectable by inexpensive electronics. As with ultrasound detectors, PIR detectors are disadvantageous because they can be blocked by a sheet of paper. Moreover, PIR detectors have no range adjustment and may be false-triggered by pets or rodents.
Radar-based motion detectors may emit a continuous-wave (“CW”) microwave signal and compare the emitted and echo frequencies to produce a beat frequency that is proportional to range. Such detectors employ microwave oscillators, detector diodes, and audio frequency processing electronics to detect objects. Nonranging radar detectors emit a CW microwave carrier and detect a Doppler shifted echo from a sensed moving object. Such swept and Doppler radar-based motion detectors are disadvantageous because of limited materials penetration, microphonics, frequency crowding, poor short-range operation, and difficulty meeting Federal Communications Commission (“FCC”) testing and certification requirements.
Some of the disadvantages of swept and Doppler radar-based motion detectors have been circumvented by another radar-based motion sensing technique. U.S. Pat. No. 5,361,070 for ULTRA-WIDEBAND RADAR MOTION SENSOR describes ultra-wideband (“UWB”) radar motion sensing in which a UWB radar operates as a pulse-echo system that clocks the two-way time of flight of a very short electrical pulse. Rather than employing a carrier frequency, a fast electrical voltage impulse is applied directly to an antenna. The resulting spread spectrum emissions resemble the Fourier transform of the emitted pulse and generally span hundreds of megaHertz to several gigaHertz. Because most materials exhibit rapidly increasing attenuation with frequency, UWB radar is advantageous for materials penetration, allowing installation of UWB radar detectors behind walls and appliance panels, above ceilings, and below floors. UWB radar motion detectors are also advantageous for detecting close objects and may have an adjustable sensing range. The patent asserts that “a frequency allocation by the FCC is not relevant” because of the UWB emissions. However, UWB radar-based motion detectors have not attained market acceptance because they have not readily met FCC regulatory limits as an intentional radiator, a fact that is well documented in “The Development and Commercialization of Micropower Impulse Radar at Lawrence Livermore National Laboratory”, a report by the Democratic Staff Committee on Science, U.S. House of Representatives, Apr. 12, 1999.
SUMMARY OF THE INVENTION
An object of this invention is, therefore, to provide an apparatus and a method for sensing moving objects that overcomes the disadvantages of prior motion detectors.
Another object of this invention is to provide a radar-based motion detector that is FCC approved as an intentional radiator.
A further object of this invention is to provide a combined PIR and radar-based motion detector.
Still another object of this invention is to provide a motion detector having predetermined ranges and object size discrimination.
A motion detector of this invention employs an FCC approved homodyne pulsed range-gated radar (“RGR”) detector that may also be combined with a PIR detector to improve detection flexibility and reduce false-alarm conditions. Narrow microwave pulses are transmitted at a predetermined pulse repetition frequency (“PRF”), and the pulses are reflected by a moving target. The RGR detector senses the presence of moving human sized objects within predetermined ranges. Moving objects beyond the ranges are not sensed. Stationary objects are not sensed because the RGR detector is AC coupled, although DC-coupled applications are possible and exist.
The RGR detector employs a pulsed 5.8 GHz microwave oscillator that is triggered by a system clock and immediately retriggered after a 10 to 70 nanosecond delay. The duration of each triggered pulse is 3 to 20 nanoseconds of carrier having a half-sine envelope shape. The PRF of the transmitted pulses is about 312.5 to 400 kHz. The average power of the transmitted pulses is designed to stay within FCC regulatory limits set forth in 47 CFR Parts 15.209 and 249 (1999).
The RGR employs homodyne detection and shares the same antenna as the transmitter. The receiver range is determined by imposing a predetermined delay between transmitting a pulse and enabling the receiver. Each received 5.8 GHz pulse is mixed down to a baseband by a homodyne peak detector. The detected baseband signal is amplified, processed, and filtered to frequencies below 500 Hz. If the output exceeds a predetermined threshold, an alarm condition is indicated. The threshold is adjustable as a function of range and may be set to discriminate object sizes.
The PIR detector operates conventionally, but its output may be logically combined with the RGR detector output to further reduce false-alarm indications, or it may be disabled to operate in microwave mode only.
Additional objects and advantages of this invention will be apparent from the following detailed description of a preferred embodiment thereof that proceeds with reference to the accompanying drawings.
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“SafeGate™ Series RGR Detector Installation Instructions,” Copyright 1998 (Nov. 1998), Sentrol, Tualatin, OR.
Barrows Charles R.
Bigelow Stephen K.
McCoy Steven J.
McDonald Kevin B.
Interlogix, Inc.
Rives LLP Stoel
Sotomayor John B.
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