US3754254A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Target detection by doppler shift
Assignee: Microwave and Electronic Systems Ltd
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Filing: 1971-03-22
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Granted: 1973-08-21
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Expires: 1991-03-22
Abstract
Abstract Detection of moving targets by detection of the doppler shift of radiation scattered or reflected by the target when illuminated by such radiation, is liable to give a false target indication if an interfering signal is received which has a frequency difference from the transmitted radiation lying in the range of the expected doppler shift. The problem is found in intruder alarm systems which use doppler shift detection. To mitigate the problem, the transmitted radiation is frequency modulated, by noise or by an audio tone, so that the scattered or reflected radiation has a coherence with the transmitted radiation but the interfering signal does not. The principle is applicable to both electromagnetic and pressure-wave radiation. In one intruder alarm system two separately operating, doppler shift detector units are coupled together to give a warning signal only when both indicate an intruder. Application of the above principle to one or both units prevents them giving false alarms due to mutual interference.
Inventors
- 👤 M Jinman
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-23 07:51
CPC Classifications
G; G01; G01S; G01S13/00; G01S13/02; G01S13/50; G01S13/52; G01S13/56
Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
182 words
Apparatus for detection of a moving target comprising: a transmitter for producing output signals, and a receiver for receiving target echo signals and interfering signals, said receiver including a mixer responsive to a portion of the transmitter output signals and target echo signals for deriving therefrom Doppler shift signals resulting from the motion of the target illuminated by radiated transmitter output signals, means for blocking mixer output signals outside a prescribed frequency passband, and time duration detector means responsive to mixer output signals within said passband for producing a target indicative signal upon receipt of a plurality of cycles of said mixer output signals within a predetermined time interval, wherein said transmitter includes means for frequency modulating said transmitter output frequency at an average frequency sweep rate sufficiently high that, upon reception of an interfering signal having a frequency range within the frequency deviation range of said transmitter output signal, the time for which the difference frequency therebetween lies within said prescribed passband is too short to allow a significant mixer output signal to be derived in response to the interfering signal.
Claim 2
Dependent Claim
182 words
Apparatus for detection of a moving target comprising: a transmitter for producing output signals, and a receiver for receiving target echo signals and interfering signals, said receiver including a mixer responsive to a portion of the transmitter output signals and target echo signals for deriving therefrom Doppler shift signals resulting from the motion of the target illuminated by radiated transmitter output signals, means for blocking mixer output signals outside a prescribed frequency passband, and time duration detector means responsive to mixer output signals within said passband for producing a target indicative signal upon receipt of a plurality of cycles of said mixer output signals within a predetermined time interval, wherein said transmitter includes means for frequency modulating said transmitter output frequency at an average frequency sweep rate sufficiently high that, upon reception of an interfering signal having a frequency range within the frequency deviation range of said transmitter output signal, the time for which the difference frequency therebetween lies within said prescribed passband is too short to allow a significant mixer output signal to be derived in response to the interfering signal.
Claim 3
Dependent Claim
15 words
Apparatus as claimed in claim 1 wherein said frequency modulating means comprises a noise source.
Claim 4
Dependent Claim
22 words
Apparatus as claimed in claim 2 wherein said frequency modulating means includes means for limiting the frequency deviation of the transmitted frequency.
Claim 5
Dependent Claim
23 words
Apparatus as claimed in claim 1 wherein said frequency modulating means comprises a source of a repetitive waveform in the audio frequency range.
Claim 6
Dependent Claim
15 words
Apparatus as claimed in claim 1 wherein said transmitter operates in the microwave frequency region.
Claim 7
Dependent Claim
14 words
Apparatus as claimed in claim 5 wherein said transmitter comprises a Gunn diode oscillator.
Claim 8
Dependent Claim
31 words
Apparatus as claimed in claim 6 wherein said frequency modulator means is arranged to provide an amplitude modulated operating current for said Gunn diode oscillator whereby the latter is frequency modulated.
Claim 9
Dependent Claim
33 words
Apparatus as claimed in claim 1 wherein said receiver further includes an amplitude gate means for allowing only Doppler shift signals above a predetermined level to cause a target-indicative signal to be produced.
Claim 10
Dependent Claim
27 words
Apparatus as claimed in claim 1 wherein said time duration detector includes a circuit means for averaging the mixer output signals over a preselected period of time.
Claim 11
Dependent Claim
142 words
A system for detecting a moving target comprising a first moving target detection apparatus as claimed in claim 1, and a second moving target detection apparatus which comprises a transmitter, producing an output signal and a receiver having a mixer responsive to a portion of the transmitter output signal and to target echo signals to derive therefrom Doppler shift signals resulting from the motion of a target illuminated by the radiated output signal from the transmitter, and means coupled to said receiver mixer and responsive to Doppler shift signals lying within a prescribed frequency band to produce a target indicative signal upon detection of a plurality of cycles of said prescribed Doppler shift signal, wherein said first and second target detection apparatus are disposed relative to one another such that, in operation, each receives some radiated transmitter output signal from the other.
Claim 12
Dependent Claim
47 words
A target detection system as claimed in claim 10, wherein each apparatus comprises a respective aerial system for radiating said transmitter output signal and for reCeiving radiation to be coupled to the associated receiver mixer, said aerial systems being arranged to survey a common volume of space.
Claim 13
Dependent Claim
48 words
A target detection system as claimed in claim 11, further comprising means coupled to the respective Doppler shift signal responsive means of said first and second apparatus and responsive to said target-indicative signals therefrom to produce a warning signal only if said target indicative signals are generated simultaneously.
Claim 14
Dependent Claim
118 words
A target detection system as claimed in claim 10, wherein said second apparatus further includes means operable to frequency modulate said transmitter output signal thereof at an average frequency sweep rate sufficiently high that, upon reception of an interfering signal having a frequency within the frequency deviation range of said transmitter output signal, the time for which the difference frequency between the interfering signal frequency and the instantaneous transmitter output signal frequency lies within said prescribed frequency band is too short to allow an apparent Doppler shift signal to be derived from said receiver mixer of said second apparatus, and wherein the respective frequency modulation means of said first and second apparatus are operable at different modulating frequencies.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1976-08-20 | 1977-02-19 | 1977-08-21 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1980-08-20 | 1981-02-19 | 1981-08-21 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1984-08-20 | 1985-02-19 | 1985-08-21 | $7700.00 | Window Closed / Lapsed |