System and method for reducing interference in microwave motion sensors

• US 7,872,604 B2
• Filed: 12/20/2007
• Issued: 01/18/2011
• Est. Priority Date: 12/20/2007
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Wu, Xiaodong
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): BYTHROW, PETER M
• Application Number:
  US11/961,387
• Publication Number:
  US 20090160697A1
• Time in Patent Office: 1,125 Days
• Field of Search: 342/27, 342/28, 342 70- 72
• 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
• CPC Class Codes: G01S 7/025 involving the transmission of linearly polarised waves

Abstract

A microwave sensor comprises an oscillator configured to generate a microwave signal at a pre-determined frequency, and an antenna configured to transmit the microwave signal and/or to receive reflected signals. The antenna is linear polarized at 45 degrees and the transmitted microwave signal has an electric field at 45 degrees to the plane of the horizontal. The microwave sensor further includes a signal processor coupled to the antenna and configured to process the reflected signals to determine a presence of a moving object.

Claims

1. A security system comprising:

a first microwave sensor having a linearly polarized antenna with an electric field oriented at 45 degrees with respect to the horizon the linear polarized antenna transmits a microwave signal parallel to the plane of the horizon and receives reflected signals, wherein the transmitted microwave signal has an electric field at 45 degrees to the plane of the horizontal; and

a second microwave sensor, the second microwave sensor further comprising

an oscillator configured to generate a microwave signal at a pre-determined frequency;

a linearly polarized antenna having an electric field oriented at 45 degrees with respect to the horizon configured to transmit the microwave signal parallel to the plane of the horizon and to receive reflected signals, wherein the transmitted microwave signal has an electric field at 45 degrees to the plane of the horizontal;

a signal processor coupled to the antenna and configured to process the reflected signals to determine a presence of a moving object; and

a mixer coupled to the antenna and the oscillator and configured to mix the reflected signal with a portion the transmitted microwave signal to generate a corresponding inteimediate frequency wherein the linear polarized antenna of the first and second microwave sensors face each other and wherein the electric fields of the linear polarized antenna of the first and second microwave sensors are perpendicular to each other.

2. The microwave sensor of claim 1, wherein the antenna comprises one of a single patch antenna, patch array, a single slot antenna, a slot array, a horn antenna, and a combination thereof.

3. The microwave sensor of claim 1, wherein the antenna comprises sensors in one of a 1×

2 array, 2×

2 array or N×

M array.

4. The microwave sensor of claim 1, wherein the processor is further configured to generate an alarm based on the presence of a moving object.

5. The microwave sensor of claim 1, wherein the antenna further comprises a separate transmitting antenna and a separate receiving antenna.

6. The microwave sensor of claim 5, wherein the transmitting antenna and the receiving antenna are both linear polarized at 45 degrees.

7. The microwave sensor of claim 5, farther comprising a pulse generator configured to synchronized the transmitter and the sample/hold circuit in a signal conditioning circuitry by providing a gating signal to the signal conditioning circuitry.

8. The microwave sensor of claim 1, further comprising a signal conditioning circuitry coupled to the mixer and the signal processor and configured to condition the reflected signals, by sampling and holding, filtering and amplifying the signals.

9. A method for detecting a presence of a moving object, the method comprising:

generating a plurality of microwave signals at a corresponding pre-deteimined frequency;

a first linearly polarized antenna with an electric field oriented at 45 degrees with respect to the horizon transmitting the plurality of microwave signals parallel to the horizon;

a second linearly polarized antenna with an electric field oriented at 45 degrees with respect to the horizon transmitting the plurality of microwave signals parallel to the horizon;

receiving a plurality of reflected signals from the first and second linearly polarized antenna; and

processing the reflected signals from the first and second linearly polarized antenna to determine a presence of a moving object wherein processing the reflected signals includes mixing the reflected signals from each of the first and second linear polarized antenna with a portion of the transmitted microwave signal of the linear polarized antenna to generate a corresponding intermediate frequency mixed signal wherein the first and second linear polarized antenna face each other and wherein the electric fields of the first and second linear polarized antenna are perpendicular to each other.

10. The method of claim 9, further comprising conditioning the mixed signal prior to the processing step.

11. The method of claim 9, further comprising generating an alarm based on the presence of the moving object.

12. A security system comprising:

at least two microwave sensors located in the detection area facing each other, each microwave sensor comprising;

an oscillator configured to generate a microwave signal at a pre-determined frequency;

a linearly polarized antenna configured to transmit the microwave signal parallel to the horizon and/or to receive reflected signals, wherein an electric field of the antenna is linear polarized at 45 degrees with respect to the horizon;

a signal processor coupled to the antenna and configured to process the reflected signals to deteimine a presence of a moving object; and

a mixer coupled to the antenna and the oscillator and configured to mix the reflected signals with a portion of the transmitted microwave signal to generate a corresponding intermediate frequency mixed signal wherein the linear polarized antenna of the first and second microwave sensors face each other and wherein the electric fields of the linearly polarized antenna of the at least two microwave sensors are perpendicular to each other.

13. The security system of claim 12, wherein the microwave sensor further comprises a signal conditioning circuitry configured to condition the mixed signal prior to being processed.

14. The security system of claim 12, wherein the antenna comprises one of a patch array, a slot array, a single patch, a single slot, a horn antenna, and a combination thereof.

15. The security system of claim 12, wherein for each of the at least two microwave sensors, the microwave signal has an electric field at 45 degrees to the horizontal and parallel to the plane of the corresponding microwave sensor.

16. The security system of claim 12, further. comprising an alarm coupled to each microwave sensor, wherein the microwave sensor is configured to trigger the alarm based on the presence of a moving object.

17. The security system of claim 12, wherein electric fields of the at least two microwave sensors are perpendicular to each other.

18. The security system of claim 12, wherein the at least two microwave sensors achieve a cross polarized operation.

19. A security system comprising:

a first microwave sensor having a linear polarized antenna that transmits the microwave signal parallel to the plane of the horizon and receives reflected signals, wherein the linear polarized antenna exhibits a selected amount of linear polarization, and wherein the transmitted microwave signal has an electric field oriented at 45 degrees relative to the plane of the horizontal; and

a second microwave sensor further comprising;

an oscillator configured to generate a microwave signal at a pre-determined frequency;

a linearly polarized antenna configured to transmit the microwave signal parallel to the plane of the horizon and to receive reflected signals, wherein the antenna exhibits a selected amount of linear polarization, and wherein the transmitted microwave signal has an electric field oriented at 45 degrees relative to the plane of the horizontal;

a signal processor coupled to the antenna and configured to process the reflected signals to determine a presence of a moving object and generate an alarm based on the presence of a moving object; and

a mixer coupled to the antenna and the oscillator and configured to mix the reflected signal with a portion of the transmitted microwave signal to generate a corresponding intermediate frequency signal wherein the linear polarized antenna of the first and second microwave sensors face each other and wherein the electric fields of the linear polarized antenna of the first and second microwave sensors are perpendicular to each other.

20. The microwave sensor of claim 19, further comprising signal conditioning circuitry coupled to the mixer and the signal processor and configured to condition the reflected signals, by sampling and holding, filtering and amplifying the signals.

21. The microwave sensor of claim 19, wherein the antenna comprises one of a single patch antenna, patch array, a single slot antenna, a slot array, a horn antenna, and a combination thereof.

22. The microwave sensor of claim 19, wherein the antenna comprises one of a 1×

2 array, 2×

2 array or N×

M array.

23. The microwave sensor of claim 19 wherein the antenna further comprises a separate transmitting antenna and a separate receiving antenna and where the transmitting antenna and the receiving antenna are both linearly polarized at 45 degrees.

24. The microwave sensor of claim 23, further comprising a pulse generator configured to synchronize the transmitter and the sample/hold. circuit in signal conditioning circuitry by providing ‘

a gating signal to the signal conditioning circuitry.

25. A method for detecting a presence of a moving object, the method comprising:

providing first and second linearly polarized antenna that face each other;

generating a plurality of microwave signals at a corresponding pre-determined frequency;

transmitting at least some of the plurality of microwave signals from each of the first and second linearly polarized antenna parallel to the horizon with an electric field of the linearly polarized antenna oriented at 45 degrees with respect to the horizon and wherein the electric fields of the first and second linearly polarized antenna are perpendicular to each other;

receiving a plurality of reflected signals;

processing the reflected signals to determine a presence of a moving object; and

generating an indicium indicative of the presence of the moving object, wherein processing the reflected signals includes mixing the reflected signals with a portion of the transmitted microwave signal to generate a corresponding intermediate frequency mixed signal.

26. A security system comprising:

at least two microwave sensors located in the detection area facing each other, each microwave sensor comprising;

an oscillator configured to generate a microwave signal at a pre-determined frequency;

at least one linearly polarized antenna configured to transmit the microwave signal parallel to the horizon and/or to receive reflected signals, wherein the antenna is linearly polarized with an electric field at 45 degrees with respect to the horizon;

a signal processor coupled to the antenna and configured to process the reflected signals to deteimine a presence of a moving object; and

a mixer coupled to the antenna and the oscillator and configured to mix the reflected signals with a portion of the transmitted microwave signal to generate a corresponding intermediate frequency mixed signal and wherein the electric fields of the at least two linearly polarized antenna are perpendicular to each other.

27. The security system of claim 26, wherein the microwave sensor further comprises a signal conditioning circuitry configured to condition the mixed signal prior to being processed.

28. The security system of claim 27, wherein for each of the at least two microwave sensors, the microwave signal has an electric field at 45 degrees to the horizontal and parallel to the plane of the corresponding microwave sensor.

29. The security system of claim 26, wherein electric fields of the at least two microwave sensors are perpendicular to each other.

30. The security system of claim 26, wherein the at least two microwave sensors achieve a cross polarized operation.