Modulated pulse doppler sensor

• US 6,426,716 B1
• Filed: 02/27/2001
• Issued: 07/30/2002
• Est. Priority Date: 02/27/2001
• Status: Active Grant

• Current Assignee: Mcewan Technologies LLC
• Original Assignee: Mcewan Technologies LLC
• Inventors: McEwan, Thomas E.
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US09/794,268
• Time in Patent Office: 518 Days
• Field of Search: 375/239, 342/27, 342/28, 342/118, 342/134-144, 342/192-197, 342/89-103, 342/82-88, 455/46, 455/47, 329/311, 329/313, 329/347, 329/356, 329/357
• US Class Current: 342/28
• CPC Class Codes: G01S 13/04 Systems determining presence of a target based on relative movement of target G01S13/56
• CPC Class Codes: G01S 13/18 wherein range gates are used
• 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 range gated microwave motion sensor having adjustable minimum and maximum detection ranges with little response to close-in false alarm nuisances such as insects or vibrating panels. The sensor resolves direction of motion and can respond to target displacement in a selected direction and through a selected distance, in contrast to conventional hair-trigger motion sensors. A constant false alarm rate (CFAR) detector prevents false triggers from fluttering leaves, vibrating machinery, and RF interference. The sensor transmits an RF pulse and, after a modulated delay, mixes echo pulses with a mixer pulse. Thus, the echo pulses are modulated at the mixer output while transmit and mixer pulse artifacts remain unmodulated and easily filtered from the output. Accordingly, the sensor only responds to echoes that fall within its minimum and maximum range-gated region, and not to close-in or far-out objects. Applications for the low-cost system include indoor and outdoor burglar alarms, automotive security alarms, home and industrial automation, robotics, vehicle proximity sensors, cardiac motion detection, and a universal radar “bubble” detector.

Claims

1. A radar Doppler transceiver apparatus comprising:

a PRF generator for producing a sequence of clock cycles;

a modulated delay element connected to the PRF generator for producing a modulated delay;

a transmit pulse generator connected to the modulated delay element for generating a transmit pulse having a modulated delay;

an adjustable delay element connected to the PRF generator for producing an adjustable fixed delay;

a mixer pulse generator connected to the adjustable delay element for generating a mixer pulse, the mixer pulse having an adjustable plus modulated delay relative to the transmit pulse;

a summation circuit connected to the transmit and mixer pulse generators;

an RF oscillator connected to the summation circuit for producing a pair of RF bursts from each clock cycle, a transmit burst and a mixer burst, the mixer burst being delayed from the transmit burst by an adjustable plus modulated delay;

an antenna connected to the RF oscillator for transmitting the transmit burst towards a target;

a mixer connected to the antenna for mixing reflected bursts produced by the transmit burst with the mixer burst to produce a modulated mixer signal;

an IF filter/amplifier for rejecting unmodulated mixer outputs and amplifying modulated mixer outputs;

an envelope detector for demodulating the modulated and amplified mixer outputs and producing a Doppler signal;

a baseband filter/amplifier for conditioning the Doppler signal and providing a range gated Doppler signal output.

2. The apparatus of claim 1 wherein the modulated range delay is modulated periodically at a sub-multiple of the PRF.

3. The apparatus of claim 2 wherein the modulated range delay is modulated by an arbitrary waveshape.

4. The apparatus of claim 1 wherein the antenna is a single antenna employed for both transmitting and receiving, or a pair of antennas, one for transmitting and the other for receiving.

5. The apparatus of claim 1 wherein the mixer is an RF peak envelope detector, which detects and averages RF pulses from multiple clock cycles.

6. The apparatus of claim 5 wherein the RF peak envelope detector is a peak-to-peak detector.

7. The apparatus of claim 1 further comprising quadrature receivers formed of a delay line or a lumped-element phasing network having I and Q RF outputs, each connected to a receiver to produce respective I and Q baseband outputs.

8. The apparatus of claim 7 further comprising an SSB demodulator to produce USB and LSB outputs.

9. The apparatus of claim 8 further comprising a CFAR detector responsive to envelope detected USB or LSB signals, with the CFAR threshold being increased by the envelope detected LSB or LSB signals.

10. The apparatus of claim 9 further comprising a jam threshold detector responsive to the simultaneous presence of above-threshold LSB and USB signals.

11. The apparatus of claim 1 further comprising a processor connected to the range gated Doppler signal output for actuating an alarm, controlling devices, or displaying signals.

12. A short pulse radar Doppler sensor comprising:

a pulsed RF oscillator for providing a set of first and second RF bursts, each set repeating at a PRF and having a modulated delay between the first and second bursts;

an antenna system for transmitting RF bursts and receiving echoes of the RF bursts;

an RF receiver responsive to modulated echoes of the first burst mixed with the second burst.

13. The sensor of claim 12 further comprising a quadrature receiver having I and Q outputs and responsive to the echoes of the first burst mixed with the second burst.

14. The sensor of claim 13 further comprising a SSB demodulator.

15. A method of radar sensing, comprising:

generating a set of first and second RF bursts, each set repeating at a PRF and having a modulated delay between the first and second bursts;

transmitting the first burst and receiving echoes from the transmitted burst;

mixing the received echoes with the second burst to provide a modulated signal;

filtering the modulated signal;

detecting the filtered signal to provide a Doppler output from the echoes.

16. The method of claim 15 further comprising controlling the maximum sensing range by selecting the widths of the first and second bursts and the delay between the bursts.

17. The method of claim 16 further comprising quadrature mixing the received echoes with the second burst to provide I and Q modulated signals.

18. The method of claim 17 further comprising filtering the I and Q modulated signals to provide filtered I and Q signals.

19. The method of claim 18 further comprising detecting the filtered I and Q signals to provided detected I and Q signals.

20. The method of claim 19 further comprising SSB demodulating the detected I and Q signals to provide LSB and USB signals.

21. The method of claim 20 further comprising triggering a jam detector when LSB and USB signals are simultaneously present.

22. The method of claim 20 further comprising threshold triggering an alarm comparator with an integrated USB or LSB signal.

23. The method of claim 22 further comprising referencing the alarm comparator with an integrated LSB or USB signal.

24. A method of sensing SSB Doppler signals, comprising:

generating a set of first and second RF bursts, each set repeating at a PRF and having a modulated delay between the first and second bursts;

transmitting the first burst and receiving echoes from the transmitted burst;

shifting the phase between the transmitted and received bursts;

mixing the received echoes with the second burst to provide modulated signal I and Q signals;

filtering the modulated I and Q signals to provide filtered I and Q signals;

detecting the filtered I and Q signals to provide detected I and Q signals;

phase shifting the detected I and Q signals to provide phase shifted I and Q baseband signals;

algebraically summing the phase shifted baseband I and Q signals to form LSB and USB signals.

25. The method of claim 24 wherein the mixed signals from mixing the received echoes with the second burst are integrated over multiple repetitions at the PRF.

26. The method of claim 25 further comprising threshold triggering a jam signal when LSB and USB signals are simultaneously present.

27. A method of sensing radar target displacement, comprising:

transmitting a set of first and second RF bursts, each set repeating at a PRF and having a modulated delay between the first and second bursts;

mixing echoes from the first burst with the second burst to form modulated I and Q signals;

processing the modulated I and Q signals to form USB and LSB signals that represent respective inbound and outbound motion;

envelope detecting the USB and LSB signals to form envelope detected USB and LSB signals;

weighting the envelope detected LSB signal relative to the envelope detected USB signal to provide weighted USB and LSB signals;

threshold detecting the weighted USB or LSB signal relative to the weighted LSB or USB signal to provide a detection signal for a defined amount of target movement in a given direction.

28. The method of claim 27 further comprising triggering a jam signal when LSB and USB signals are simultaneously present.