MOTION DETECTION SYSTEM WITH SPLIT-RING MONOSTATIC DOPPLER DETECTION

• US 3,703,722 A
• Filed: 06/02/1971
• Issued: 11/21/1972
• Est. Priority Date: 06/02/1971
• Status: Expired due to Term

• Current Assignee: Alex Y. Lee, David N. Gershberg
• Original Assignee: Alex Y. Lee, David N. Gershberg
• Inventors: Lee, Alex Y., Gershberg, David N.
• Primary Examiner(s): Tubbesing, T. H.
• Application Number:
  US05/149,151
• Time in Patent Office: 538 Days
• Field of Search: 340/258A 343/5PD,7.7,8
• US Class Current: 342/28
• CPC Class Codes: G01S 13/56 for presence detection presence detection using near field arrangements G01V3/00, e.g. G01V3/08, G01V3/12; burglar, theft or intruder alarms with electrical actuation G08B13/22 - G08B13/26

Abstract

A motion detection system wherein an RF transmitter is connected through a split-ring doppler detector to a transmit/receive antenna. Both the RF transmitter and the antenna are connected to nodes on the split-ring detector to provide a matched and balanced system. Diode detectors are connected, in opposite directions, to the ring detector at points between the transmitter load and the antenna to insure desired transmitter injection to the diodes for sensitive receiver operation. The diode detectors connect through individual low-pass filters to the inputs of an AC coupled, active filter, amplifier, which amplifies the doppler return signal that has been conducted by the diode detectors, while rejecting unwanted doppler frequencies to reduce false alarms. A microwave band-pass filter is so positioned in the antenna line to further reduce false alarms by defining a specific radio frequency bandwidth. A self-test feature is provided in that the DC level at one or both detector diodes can be monitored. To further reduce false alarms a correlating detection system provides a back-up signal for the doppler detector.

Claims

1. In a doppler frequency motion detector system having a transmitter generating electromagnetic energy at a radio frequency for an antenna radiating the generated energy throughout a given surveillance area and receiving energy reflected by objects within the area, and wherein movement within the surveyed area produces an alarm from an indicator responsive to the output of a doppler frequency amplifier connected to a detector mixer that receives energy from said antenna, the detector mixer comprising:

a first transmission line having a length related to the wavelength of the generated electromagnetic energy, said first transmission line connected between said transmitter and said antenna, a second transmission line with a length on the order of onethird of the length of said first transmission line and joined thereto at said transmitter in parallel therewith, a third transmission line with a length on the order of twothirds the length of said first transmission line and joined thereto at said antenna and to said second transmission line, and a pair of detector elements coupled to said third transmission line at points symmetrically placed about a transmit frequency voltage wave distribution zero-crossing, wherein signals from said detector elements are differentially combined and interconnect to the doppler frequency amplifier.

2. In a doppLer frequency motion detector system as set forth in claim 1 wherein the length of said first transmission line equals three-quarters wavelength of the generated electromagnetic energy.

3. In a doppler frequency motion detector system as set forth in claim 1 including a reference load coupled to said second transmission line at the point of joining with said third transmission line.

4. In a doppler frequency motion detector system as set forth in claim 1 wherein the characteristic impedance of each of said three transmission lines equals Square Root 2 Zo, where Zo equals the characteristic impedance of said transmitter.

5. In a doppler frequency motion detector system as set forth in claim 1 including a pair of low-pass filters, one connected to each of said detector elements.

6. In a doppler frequency motion detector system as set forth in claim 1 wherein said detector elements comprise a pair of reverse connected diodes.

7. In a doppler frequency motion detector system wherein movement within a given surveillance area produces an alarm from an indicator responsive to a doppler frequency signal, comprising:

a transmitter for generating electromagnetic energy at a radio frequency, an antenna for radiating said energy throughout said area and for receiving radiated energy as reflected by objects within said area, a detector mixer including;

a. a first transmission line having a a length related to the wavelength of the generated energy and connected between said transmitter and said antenna, b. a second transmission line with a length on the order of one-third the length of said first transmission line and joined thereto at said transmitter in parallel therewith, c. a third transmission line with a length on the order of two-thirds the length of said first transmission line and joined thereto at said antenna and to said second transmission line, a pair of detector elements coupled to said third transmission line at points symmetrically placed about a transmit frequency voltage wave distribution zero-crossing to generate doppler frequency signals from energy reflected to said antenna, doppler frequency responsive means including a differential comparator with one input responsive to the doppler frequency signals differentially combined from said detector elements, means for generating a correlation signal to the second input of said differential comparator to provide improved motion detector reliability, and circuit means responsive to the output means of said differential comparator for generating a correlation signal to generate a motion signal to said indicator.

8. In a doppler frequency motion detector system as set forth in claim 7 wherein the length of said first transmission line equals three-quarters wavelength of the generated energy and the characteristic impedance of each of said three transmission lines equals Square Root 2 Zo, where Zo equals the characteristic impedance of said transmitter.

9. In a doppler frequency motion detector system as set forth in claim 8 wherein said detector mixer includes a pair of low-pass filters, one connected to each of said detectors.

10. In a doppler frequency motion detector system as set forth in claim 9 wherein said detector mixer further includes a reference load coupled to said second transmission line at the point of joining with said third transmission line.

11. In a doppler frequency motion detector system as set forth in claim 7 including a second antenna for radiating said energy throughout a second surveillance area and for receiving radiated energy as reflected by objects within said second area, said second antenna coupled to said second transmission line at the point of joining with said third transmission line.

12. A detector circuit for producing at the output thereof a doppler frequency signal from oppositely travelling waves at an antenna connected thereto, said detector comprising:

phase Inverting, power-divider means coupled to said antenna element, a reference load coupled to said divider means at a point to split the power of an input signal applied to said divider means equally between said reference load and the antenna element, a pair of detector elements coupled to said divider means at points symmetrically displaced about a transmit frequency voltage wave distribution zero-crossing, and circuit means for differentially combining the detector element signals to produce a detector output doppler frequency signal.

13. In a detector circuit as set forth in claim 12 including circuit means for coupling a D.C. current through said detector elements to ground.

14. A detector circuit as set forth in claim 12 wherein said divider means includes three interconnected transmission line segments each with a characteristic impedance equal to Square Root 2 Zo, where Zo equals the characteristic impedance of a transmitter supplying input power.

15. A detector circuit as set forth in claim 13 wherein a first of said transmission lines has a length equal to three-quarter wavelengths of an input frequency signal applied to said detector, a second of said transmission lines has a length equal to one-third that of said first transmission line and the third of said transmission lines has a length equal to two-thirds of said first transmission line.