DETECTION OF MOVEMENT IN CONFINED SPACES

• US 3,691,556 A
• Filed: 01/19/1971
• Issued: 09/12/1972
• Est. Priority Date: 06/03/1970
• Status: Expired due to Term

• Current Assignee: John Anthony Bloice
• Original Assignee: John Anthony Bloice
• Inventors: Bloice, John Anthony
• Primary Examiner(s): Hubler, Malcolm F.
• Application Number:
  US05/107,808
• Time in Patent Office: 602 Days
• Field of Search: 343/5PD,7.7 340/258A,258B
• US Class Current: 342/27
• 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: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005

Abstract

A radar unit comprises a single microwave launching and receiving antenna, and a microwave oscillator feeding microwave energy to the antenna. A second oscillator is arranged to oscillate at a frequency much lower than that of the microwave energy, and includes an element common to the microwave oscillator. This common element is adapted to respond to load changes on the microwave oscillator, caused by changes in the standing wave pattern of the antenna, by varying at least one oscillation characteristic of the signal provided by the second oscillator. These changes are monitored to provide an indication of the presence and movement of objects in front of the antenna. The microwave oscillator includes a Gunn diode mounted within a resonant cavity and tuned to oscillate at the microwave frequency. An inductance connected in series with the cavity provides a series-tuned circuit of the second oscillator, the cavity providing the common element. The lower frequency oscillations are limited to lie within a predetermined range to improve the sensitivity of the arrangement. This may be done with a feedback circuit. Three such units may be mounted on a common support so as to lie in respective vertical planes at 120* to one another, their combined responses overlapping to provide unbroken coverage in horizontal plane surrounding the common support. The aerials may be shaped to have lobes such that the unbroken coverage extends to a range of some 30 feet from the support.

Claims

1. A radar unit comprising:

a microwave launching and receiving antenna;

a microwave first oscillator tuned to oscillate at a microwave first frequency and arranged to feed microwave energy to said antenna, said first oscillator including means defining a resonant cavity and a Gunn diode disposed within said cavity;

a second oscillator arranged to oscillate at a second frequency different to said first frequency, said second oscillator including a series-tuned circuit comprising an inductance connected in series with said resonant cavity, said means constituting an inter-oscillator coupling element common to said first and second oscillators and adapted to respond to impedance load changes on said first oscillator by varying at least one oscillation characteristic of the oscillatory signal of said second oscillator; and

circuitry of monitoring the oscillatory signal of said second oscillator, whereby changes in the standing wave pattern of said antenna caused by objects in front of said antenna are detected by monitoring the variations in the oscillatory signal of said second oscillator.

2. A radar unit as set forth in claim 1, wherein said inductance comprises an auto-transformer connected to change the voltage of the oscillatory signal of said second oscillator and to supply the changed voltage signal to said circuitry for monitoring the oscillatory signal of said second oscillator.

3. A radar unit as set forth in claim 1, including circuitry for liMiting the amplitude of the oscillatory signal of said second oscillator.

4. A radar unit as set forth in claim 3, wherein said circuitry comprises a feedback circuit including a rectifier circuit connected to receive a portion of the oscillatory signal of said second oscillator, an amplifier connected to receive the rectifier circuit output, and current control means connected between said first oscillator and its power supply to receive the amplifier output and to control the microwave oscillation in accordance therewith.

5. Radar apparatus comprising three radar units each including:

a microwave launching and receiving antenna;

a microwave first oscillator tuned to oscillate at a microwave first frequency and arranged to feed microwave energy to said antenna, said first oscillator including means defining a resonant cavity and a Gunn diode disposed within said cavity;

a second oscillator arranged to oscillate at a second frequency different to said first frequency, said second oscillator including a series-tuned circuit comprising an inductance connected in series with said resonant cavity, said means constituting an inter-oscillator coupling element common to said first and second oscillators and adapted to respond to impedance load changes on said first oscillator by varying at least one oscillation characteristic of the oscillatory signal of said second oscillator; and

circuitry for monitoring the oscillatory signal of said second oscillator;

said radar units being outwardly directed and mounted on a common support, being so arranged in use as to lie in respective vertical planes at substantially 120* to one another, each unit having a radiation pattern which is of flattened lens shaped in the vertical plane and of substantially circular shape in the horizontal plane, so that the three horizontal circles overlap one another to provide unbroken coverage in a horizontal plane surrounding the position of mounting of the apparatus.

6. Radar apparatus as set forth in claim 5, wherein the antennae of said radar units are shaped to define radiation patterns intersecting to provide substantially unbroken coverage extending to a radius of some 30 feet from said support.