Intrusion detection radar system

• US 20020060639A1
• Filed: 10/04/2001
• Published: 05/23/2002
• Est. Priority Date: 10/11/2000
• Status: Active Grant

• Current Assignee: Southwest Microwave, Inc.
• Original Assignee: Southwest Microwave, Inc.
• Inventors: Harman, Robert Keith
• Granted Patent: US 6,677,887 B2
• Time in Patent Office: Days
• 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 13/582 adapted for simultaneous range and velocity measurements
• CPC Class Codes: G01S 13/62 Sense-of-movement determination G01S13/589 takes precedence

Abstract

An outdoor microwave transceiver intrusion detector that alternately transmits pulses of RF energy at two different frequencies and uses range and direction of travel information derived from the phase of the two Doppler responses to optimize the signal processing and apply range dependent thresholds. The time delay between the onset of the transmitted pulse and the sample of the Doppler response is controlled to provide an accurate range cutoff. The two frequencies are selected so that the difference in phase of the Doppler response at the two frequencies increases from zero to ninety degrees as the target goes from the Transceiver to the maximum range. Digital signal processing is used to measure the difference in phase of the two Doppler responses and translate this information into location of the target. The location information is used to create a number of range bins. The response integration time and the threshold level are optimized for each of the range bins thereby minimizing the number of nuisance alarms.

Claims

1. The method of intrusion detection wherein first and second signals of different frequency are transmitted into a detection zone, said method comprising the following steps:

a) establishing the range limit of the detection zone;

b) alternately transmitting the first and second frequency signals in the detection zone;

c) detecting Doppler response signals from a target in the zone;

d) determining the phase difference between the Doppler response signals, and

e) deriving range information from said phase difference.

2. The method of intrusion detection in accordance with claim 1 wherein the step of alternately transmitting the first and second frequency signals includes transmitting first and second signals having a frequency difference so that the signals are in quadrature phase at the range limit of the detection zone.

3. The method of intrusion detection in accordance with claim 2 wherein the step of alternately transmitting the first and second frequency signals includes transmitting pulses of length greater than the time delay in receiving a Doppler response signal from a target at the range limit of the detection zone, the pulse length establishing a range cutoff for deriving range information.

4. The method of intrusion detection in accordance with claim 3 wherein the step of determining the phase difference between the Doppler response signals is conducted for Doppler response signals received during the transmitting of the corresponding pulse.

5. The method of intrusion detection in accordance with claim 4 further comprising the step of compressing the detected Doppler response signals.

6. The method of intrusion detection in accordance with claim 5 further comprising the steps of sampling the compressed Doppler response signals and determining the phase difference between the samples of the Doppler response signals.

7. The method of intrusion detection in accordance with claim 6 further comprising the steps of converting the sampled Doppler responses to a target to digital form, summing the digital signals according to the direction of movement of a target providing the Doppler responses and deriving range information therefrom.

8. The method of intrusion detection in accordance with claim 7 wherein the step of deriving range information includes the step of determining the ratio of the sum of positive digital signals to the sum of negative digital signals to indicate target range.

9. The method of intrusion detection in accordance with claim 8 wherein the step of deriving range information includes the step of determining the statistical distribution of the positive and negative digital signals to indicate target range.

10. The method of intrusion detection in accordance with claim 9 wherein the detection zone is divided into a number of range bins and further comprising the steps of assigning thresholds for the range bins and comparing the data from the Doppler response signals to a threshold.

11. The method of intrusion detection in accordance with claim 10 wherein the data from the Doppler response signals is integrated over an interval which increases with the distance of the range bin from the transmitter.

12. The method of intrusion detection in accordance with claim 11 wherein the step of deriving range information includes the step of detecting and counting sign change in succeeding samples to indicate the net motion of a target.

13. The method of intrusion detection in accordance with claim 12 wherein thresholds of net motion are assigned for the range bins and further comprising the step of comparing the accumulated sign change to the threshold of the range bin.

14. The method of intrusion detection in accordance with claim 5 wherein the step of compressing the detected Doppler response signals includes logarithmic amplification of said signals.

15. The method of intrusion detection in accordance with claim 14 further comprising the steps of sampling the compressed Doppler response signals and determining the phase difference between the samples of the Doppler response signals.

16. The method of intrusion detection in accordance with claim 15 further comprising the steps of converting the sampled Doppler responses to a target to digital form, summing the digital signals according to the direction of movement of a target providing the Doppler responses and deriving range information therefrom.

17. The method of intrusion detection in accordance with claim 16 wherein the step of summing the digital signals includes the step of unequal weighting of the sampled Doppler responses to improve the linearity of the response throughout the range of the detection zone.

18. The method of intrusion detection in accordance with claim 7 wherein the steps of sampling the compressed Doppler response signals includes processing at two rates to provide data signals for high speed and low speed targets moving in the detection zone.

19. The method of intrusion detection in accordance with claim 18 further comprising the step of integrating the data signals for high speed and low speed targets over different intervals.

20. An intrusion detection system for determining the presence and location of a target in a detection zone, said system comprising:

a) an antenna for transmitting RF energy in the detection zone and receiving Doppler response signals from a target;

b) a transmitter for supplying the antenna with RF signals at first and second signal frequencies, said RF signals having a phase angle of ninety degrees at the terminus of the detection zone;

e) a control logic circuit coupled to the transmitter for controlling the timing and duration of the RF pulses;

f) a detector coupled to the antenna for receiving Doppler response signals said detector providing first and second frequency response signals;

g) an analog to digital converter coupled to the detector for providing first and second response signals in digital form, and

h) a microprocessor coupled to the converter for determining the phase difference between the first and second frequency response signals and generating a signal indicative of an intruder.

21. The intrusion detection system in accordance with claim 20 further comprising an amplifier coupled to the detector, said amplifier compressing the amplitude of Doppler responses from targets near the antenna more than from more distant targets.

22. The intrusion detection system in accordance with claim 21 wherein said amplifier is a logarithmic amplifier.

23. The intrusion detection system in accordance with claim 21 further comprising first and second switch means coupled between the amplifier and first and second converters respectively, said first and second switches being controlled by the control logic circuit, said control logic circuit actuating said switches to sample the Doppler responses from targets.

24. The intrusion detection system in accordance with claim 23 wherein said control logic circuit actuates said switches alternately following the transmission of an RF pulse generating the Doppler response.

25. The intrusion detection system in accordance with claim 24 wherein said microprocessor sums the signals from the converter according to the direction of movement of a target and derives ranges information therefrom.

26. The intrusion detection system in accordance with claim 25 wherein said microprocessor determines the ratio of the sum of positive digital signals to the sum of negative digital signals to indicate target range.

27. The intrusion detection system in accordance with claim 26 wherein said microprocessor determines the statistical distribution of the positive and negative digital signals to indicate target range.

28. The intrusion detection system in accordance with claim 27 wherein said microprocessor detects and counts sign change in succeeding samples to indicate the velocity of target motion.