Communications: directive radio wave systems and devices (e.g. – Presence detection only – By motion detection
Patent
1992-07-29
1993-11-16
Tubbesing, T. H.
Communications: directive radio wave systems and devices (e.g.,
Presence detection only
By motion detection
342114, 455327, G01S 1356, G01S 1362
Patent
active
052627837
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a motion detector unit for detecting a moving person or object by means of doppler frequency shift.
2. Description of Related Art
The use of the doppler effect for detecting such motion is well-known. Typical applications include intruder alarms and automatic door openers, for which a unit of conventional construction comprises a gunn diode oscillator mounted in a cavity resonator such as a simple waveguide tube. A diode mixer also mounted in the tube provides an output at the doppler frequency. This construction has a number of drawbacks: its relative complexity for mass-production, the power consumption of the oscillator, and, especially, difficulties in meeting the stringent harmonic radiation suppression requirements imposed by the regulatory authorities in most countries.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a motion detector unit which can be more cheaply and conveniently fabricated and which to a considerable extent overcomes the aforementioned shortcomings.
According to one aspect of the invention a motion detector unit for detecting motion by means of doppler frequency shift comprises a microwave circuit board, an antenna circuit board, and a ground plane layer, the two boards being superimposed with the ground plane layer intervening, the microwave circuit board comprising an oscillator and a mixer, and the antenna circuit board comprising transmit and receive antennas, each antenna having a respective feed stripline which substantially overlies an associated stripline on the microwave circuit board, the ground plane layer having, for each antenna, a respective slot to provide coupling between the microwave circuit and the antenna, the slot being resonant at the fundamental frequency of the oscillator, with said feed stripline and said associated stripline lying orthogonal to the resonant dimension of the slot and extending beyond the slot.
Preferably at least one of the feed stripline and the associated stripline terminates in a T-section comprising a cross-bar strip parallel with the slot.
If the stripline on the microwave circuit board terminates in such a T-section, it preferably includes a further cross-bar strip parallel with the slot but on the opposite side of the slot to the T-secton.
In one embodiment of the invention, the mixer comprises a pair of diodes connected in series, the common connection point of the diodes constituting a first input of the mixer, and a stripline section which connects the other ends of the diodes via high-pass capacitance means, a second input of the mixer being at such a point on the stripline section as to introduce a quadrature phase difference between signals applied to the two diodes via the second input, the two mixer inputs being coupled respectively to the oscillator and the receive antenna, the mixer producing, in operation, two doppler outputs at the terminals of the capacitance means of identical frequency but differing phase, the phase relationship of the two outputs being indicative of the sense of the detected motion.
The first input of the mixer may be coupled to the oscillator and the second input of the mixer coupled to the stripline on the microwave circuit board which is associated with the receive antenna.
Each antenna preferably comprises an array of patch elements connected to a said feed stripline on the antenna circuit board.
Said ground plane layer is preferably carried by the microwave circuit board.
According to another aspect of the invention a microwave mixer, for use in detecting target motion by means of doppler frequency shift, comprises a pair of diodes connected in series, the common connection point of the diodes constituting a first input of the mixer, and a stripline section which connects the other ends of the diodes via high-pass capacitance means, the stripline section having a length which is such as to introduce a quadrature phase difference between signals applied to the two diodes via a second
REFERENCES:
patent: 3845461 (1974-10-01), Foreman
patent: 3955194 (1976-05-01), Chua
patent: 4195296 (1980-03-01), Williams
patent: 4249263 (1981-02-01), Shinkawa et al.
patent: 4286260 (1981-08-01), Gershberg et al.
patent: 4499467 (1985-02-01), Rittenbach
patent: 4731611 (1988-03-01), Muller et al.
patent: 5153536 (1992-10-01), Muller
Aldred Ian R.
Dodd Robert T. J.
Humphryes Reginald F.
Philpott Andrew G.
GEC--Marconi Limited
Tubbesing T. H.
LandOfFree
Motion detector unit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Motion detector unit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Motion detector unit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-24697