GB2048601A - Movement detection apparatus - Google Patents

Abstract

Movement detection apparatus having means for comparing the frequency of transmitted microwave signals with return doppler-shifted echo signals to determine the velocity of a target and/or its direction of movement relative to said apparatus. A first channel V1 is arranged to derive an echo return signal V1 from the 'self-detect' action of a signal transmitting source 5, and a second channel V2 is arranged to derive an echo return signal V2 from a mixer-detector diode 3, the relative positions of the signal transmitting source and the mixer-detector diode being such that output signals produced by said channels are in quadrature. The source 5 may be a Gurm diode. <IMAGE>

Description

SPECIFICATION Movement detection apparatus This invention relates to movement detection apparatus and more particularly to movement detection apparatus incorporating radar systems in which the Doppler effect is adapted to determine the speed and/or direction of a moving target. Such movement detection apparatus may be used, for example, to determine the speed of movement of a vehicle along a public highway, to detect the presence of intruders in a prohibited area, to actuate a door in response to the approach of a person orto sense and control the movement of machinery or articles for industrial purposes.

The effectiveness of such movement detection apparatus may be diminished because reflected signals may be received from an irradiated area which are produced by objects other than those whose presence or movement is being detected, for example, in an intruder alarm system spurious reflected signals may be produced by swinging lamp fittings or rattling doors. In order to reduce the adverse effects of such spurious reflected signals, it has been proposed to employ two receiving mixerdetector diodes arranged to produce target generated output signals having a phase relationship of 90 degrees or 270 degrees.However, in mass produced movement detection apparatus difficulty may be experienced in obtaining sufficiently accurate phase relationships, and variations in the sensitivities of the two mixer-detector diodes or in the physical dimensions of the apparatus can result in high production cost due to difficulty in calibrating the apparatus.

An object of the present invention is to provide movement detection apparatus which employs only one mixer-detector diode and therefore avoids the problems associated with the variations in the sensitivities of mixer diodes.

According to the present invention movement detection apparatus having means for comparing the frequency of transmitted signals with return doppler-shifted echo signals to determine the velocity of a target and/or its direction of movement relative to said apparatus, comprises a first channel arranged to derive an echo return signal from the 'self-detect' action of a signal transmitting source, and a second channel arranged to derive an echo return signal from a mixer-detector diode, the relative positions of the signal transmitting source and the mixer-detector diode being such that output signals produced by said channels are in quadrature.

Preferably the movement detection apparatus comprises a microwave transmission antenna coupled to a source of microwave energy, the first channel having a reception antenna arranged to receive microwave energy directly from said source and from the self-detect action of said source, the second channel having a reception antenna arranged to receive microwave energy directly from said source and an echo return signal from the mixer-detector diode.

The transmission and reception antennae may be constituted by a common antenna and may com prise a horn antenna coupled to a waveguide in which the signal transmitting source is mounted to form the first channel and a further waveguide in which the mixer-detector diode is mounted to form the second channel.

Alternatively, the transmission and reception antennae may be constituted by separate transmission and reception antenna. The transmission and reception antenna may be located at spaced positions on the perimeter of an area under surveillance, and the output signals from the two channels may be arranged to provide an indication of the move ment of an intruder in said area.

Embodiments of the invention will now be described, by way of example, with reference to the accdmpanying drawings.

Figure lisa schematic diagram of a movement detection apparatus in accordance with the invention; and Figure 2 shows certain waveforms which will be used to explain the operation of the apparatus shown in Figure 1.

Referring in the first instance to Figure 1, the movement detection apparatus comprises a horn antenna 1 of a kind suitable for both transmitting and receiving radar signals, for example, signals in the frequency band 9 to 11 GHz. The horn antenna 1 is coupled pled to a first section of waveguide 2 having a mixer-detector diode 3 mounted therein. A further section ofwaveguide 4, coupled to the first section of waveguide 2 at the end away frdm the horn antenna 1, has a gun diode oscillator 5 mounted therein.

The cathode of the mixer-detector diode 3 is con nected by way of a resistor 6 to the wall 7 of the first section of waveguide 2 which serves as an earth connection. The anode of the mixer detector 3 is connected to an output lead 8. The gun diode oscil lator 5 is connected to a supply terminal 9 by way of a load resistor 10 and is provided with an output lead 11.

Microwave energy generated by the gun diode oscillator5 is radiated from the antenna 1 and is reflected from objects passing in front of the antenna 1. The reflected signals from such objects are received by the antenna 1 and passed by the sec tions of waveguide 2 and 4to the gun diode oscil lator 5 which is arranged to act in the 'self-detect' mode. The gun diode oscillator 5 therefore produces doppler effect current fluctuations frdm the transmit ted and received signals and these current fluctua tions passing through the load resistor 10 provided an output voltage V1 on output lead 11.

The reflective signals from objects received by the antenna 1 are also passed to the mixer-detector diode 3 by the section of waveguide 2. The mixer detector diode 5 is also arranged to produce doppler effect current fluctuation from the signals transmit ted and received by the antenna 1. These current fluctuations provide an output voltage V2 on the output lead 8. The relative positions of the mixer detector diode 3 and the gun diode oscillator in their respective waveguide sections 2 and 4 are chosen so that the voltages V1 and V2 provided on output leads 11 and 8 are in quadrature, i.e. differ in phase by 90 degrees. It will be appreciated that voltage V1 may be arranged to lead or lag voltage V2 by 90 degrees.

Referring now to Figure 2, when the voltage V1 leads the voltage V2 by 90 degrees, as shown in the upper part of the Figure, the target is approaching the antenna 1. When the voltage V1 lags the voltage V2 by 90 degrees, as shown in the lower part of the Figure, the target is receding from the antenna 1.

Preferably the voltage V1 is used as a reference signal and the voltage V2 is compared with it in a phase discriminator (not shown).

In another embodiment of the invention (not illus trated) separate transmitting and receiving antennae may be used. In such an embodiment operating as an intruder alarm system, the transmitting and receiving antennae may be located at suitably spaced positions on the perimeter of an area which is under surveillance, and the apparatus may include circuits arranged to provide an indication of the movements of an intruder in the area from the voltages V1 and V2 on the output leads 8 and 11. On the other hand, when the direction of a moving target is known, for example, a vehicle travelling along a public highway, the voltages V1 and V2 may be arranged to determine the speed of the vehicle and provide a visual indication thereof.

In a modification of the apparatus illustrated in Figure 1 the load resistor 10may be replaced by an electronic circuit arranged to provide an electrical output indicative of the voltage V1 and arranged to vary the amplitude of this electrical output to match the output voltage V2 from the mixer detector diode 3.

While the frequency band referred to in the embodiments of the invention described above is 9 to 11 GHz, it will be appreciated that other frequency bands may be employed depending on the purpose for which the apparatus is intended. Moreover, while the mixer-detector diode 3 and the gun diode oscil lator are mounted in two sections of waveguide 2 and 4 coupled to the antenna 1, it will be appreciated that they could be equally well be located in a single section of waveguide or in another form of resonant cavity.

Without necessarily limiting the scope of the invention claimed, preferred embodiments of the invention may be summarized as follows.

1 ) Apparatus for comparing the frequencyof transmitted signals with return doppler-shifted echo signals to determine the velocity of a target and its movement relative to the said apparatus, comprising a two channel receiving system wherein one channel derives the said echo return signal from the 'self detect' action of the transmitting source and the other channel derives the echo signal from a mixer/detector diode, such apparatus being arranged to produce signals in one of said channels out of phase with signals in the other of said chan nels in such a manner that leading signals in one channel indicate a higher echo return frequency and leading signals in the other channel indicate a lower echo return frequency than the frequency of said transmitted signals.

2) Apparatus as in Summary 1, wherein the signal from the transmitting-element is produced by an electronic circuit associated with said transmitting element.

3) Apparatus as in Summary 1 or Summary 2, wherein signals having a suitable phase relationship are suitably processed by electronic means to determine the presence, relative speed and relative direction of a target.

4) Apparatus as in any preceding Summary, wherein the transmitter element and the mixer/detector diode are associated with a single antenna system used for both transmit and receive functions.

5) Apparatus as in any one of Summaries 1 to 3, wherein the transmitter element and the mixer/detector diode are associated with two antenna systems used separately for transmit and receive functions within the apparatus.

6) Apparatus as in Summary 5, wherein the two antennas are located separately as in a perimeter intruder alarm system and use doppler related sign als from both the transmit unit and the receive unit for the purpose of determining the relative motion of an intruder.

7) Apparatus as in any preceding Summary hav ing an integrated circuit module such as may be built on to a substrate material wherein the two channels are derived from the receiver and the tranSmitter element.

Claims (10)

1. Movement detection apparatus having means for comparing the frequency of transmitted signals with return doppler-shifted echo signals to deter mine the velocity of a target and/or its direction of movement relative to said apparatus, comprising a first channel arranged to derive an echo return signal from the 'self-detect' action of a signal transmitting source, and a second channel arranged to derive an echo return signal from a mixer-detector diode, the relative positions ofthe signal transmitting source and the mixer-detector diode being such that output signals produced by said channels are in quadrature.

2. Apparatus as claimed in Claim 1, comprising a microwave transmission antenna coupled to a source of microwave energy, the first channel hav ing a reception antenna arranged to receive mic rowave energy directly from said source and from the self-detect action of said source, the second channel having a reception antenna arranged to receive microwave energy directly from said source and an echo return signal from the mixer-detector diode.

3. Apparatus as claimed in Claim 2, wherein the transmission and reception antennae are constituted by a common antenna.

4. Apparatus as claimed in Claim 2 or Claim 3, wherein the transmission and reception antennae are constituted by a common antenna coupled to a waveguide in which the signal transmitting source is mounted to form the first channel, and to a further waveguide in which the mixer-detector diode is mounted to form the second channel.

5. Apparatus as claimed in Claim 2, wherein the transmission and reception antennae are constituted by separate transmission and reception antennae.

6. Apparatus as claimed in Claim 4, wherein the transmission and reception antennae are located at spaced positions on the perimeter of an area under surveillance, and output signals from the two channels are arranged to provide an indication of the movement of an intruder in the said area.

7. Apparatus as claimed in any preceding claim, wherein the echo return signal from the signal transmitting source is provided by an electronic circuit arrangement.

8. Apparatus as claimed in any preceding claim, wherein output signals from the two channels are arranged to provide an indication of the speed and relative movement of an object.

9. Apparatus as claimed in any preceding claim, wherein the two channels are constituted by an integrated circuit module.

10. Movement detection apparatus substantially as hereinbefore described with reference to the accompanying drawing.