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EP0995125A1 - Microwave reflectometer and method, and microwave oven equipped therewith - Google Patents

Microwave reflectometer and method, and microwave oven equipped therewith

Info

Publication number
EP0995125A1
EP0995125A1 EP98939673A EP98939673A EP0995125A1 EP 0995125 A1 EP0995125 A1 EP 0995125A1 EP 98939673 A EP98939673 A EP 98939673A EP 98939673 A EP98939673 A EP 98939673A EP 0995125 A1 EP0995125 A1 EP 0995125A1
Authority
EP
European Patent Office
Prior art keywords
power
magnetron
microwave
antennas
reflectometry
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP98939673A
Other languages
German (de)
French (fr)
Inventor
Michel Le Roy
Sylvain Cailleau
Jean-Paul Morizot
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Moulinex SA
Original Assignee
Moulinex SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Moulinex SA filed Critical Moulinex SA
Publication of EP0995125A1 publication Critical patent/EP0995125A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/70—Feed lines
    • H05B6/705—Feed lines using microwave tuning
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/04—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant in circuits having distributed constants, e.g. having very long conductors or involving high frequencies
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/28—Measuring attenuation, gain, phase shift or derived characteristics of electric four pole networks, i.e. two-port networks; Measuring transient response
    • G01R27/32—Measuring attenuation, gain, phase shift or derived characteristics of electric four pole networks, i.e. two-port networks; Measuring transient response in circuits having distributed constants, e.g. having very long conductors or involving high frequencies
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/6447—Method of operation or details of the microwave heating apparatus related to the use of detectors or sensors
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/70—Feed lines
    • H05B6/707—Feed lines using waveguides
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B40/00—Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Definitions

  • the present invention relates to a microwave reflectometric device. It also relates to a process implemented in this reflectometric device, as well as a microwave oven equipped with this device.
  • Optimal use of a microwave oven means being able to follow the evolution of the impedance of this oven during cooking.
  • a magnetron impedance diagram such as the Rieke diagram is usually used to study this evolution.
  • a directional power coupler used alone makes it possible to measure the power emitted by the magnetron of a microwave oven and the power reflected by this oven.
  • the present invention also relates to a microwave reflectometric device including in its shortened version a power coupler used alone.
  • a microwave reflectometric device including in its shortened version a power coupler used alone.
  • the ratio of these two voltages provides a complex reflection coefficient seen by the magnetron with a module p and a phase ⁇ .
  • the function of the "six-port" coupler is precisely to recover this phase information.
  • a reflectometry device for monitoring the evolution of the impedance of a microwave oven comprising a magnetron emitting an electromagnetic wave of predetermined wavelength and a waveguide to guide this wave from the magnetron to a heating or cooking chamber, comprising a directional power coupler comprising two antennas arranged in this waveguide and connected together by a conductive strip or stripline.
  • the distance between these two antennas is chosen to be less than a quarter of the emission wavelength of the magnetron.
  • the reflectometry device further comprises a multi-port junction circuit disposed downstream of the power directional coupler, this multi-port junction circuit cooperating with the power directional coupler to deliver , from signals delivered by said directional power circuit, information on the phase of the reflected wave coming from the enclosure with respect to the incident wave emitted by the magnetron.
  • the reflectometry device comprises two power-voltage converters each comprising an adaptation stage and a microwave detection stage, a first power-voltage converter cooperating with the directional power coupler for measuring the incident power and a second power-voltage converter cooperating with the directional power coupler to measure the reflected power.
  • the antennas are arranged on either side of a center line of the waveguide respectively in phase planes distant by less than a quarter of the length of emission wave of the magnetron.
  • the ribbon or stripline connecting the two antennas can then be designed to be substantially straight. This particular configuration has the effect of considerably reducing the radiation of the ribbon observed at the loops. With a straight ribbon, this radiation is minimum.
  • a method for carrying out reflectometry measurements in a microwave oven provided with a reflectometry device according to any one of the preceding claims, in which signals are taken from the respective terminals of two antennas arranged inside a waveguide, these signals are applied to a multi-port junction circuit to deliver signals allowing after processing to provide a information on the phase of the wave reflected by the cavity formed by the box of the microwave oven, with respect to the incident wave generated by the magnetron.
  • the microwave signals are taken from the waveguide at two points located in phase planes separated by a distance less than a quarter of the emission wavelength of the magnetron.
  • a microwave oven comprising at least one reflectometric device according to the invention.
  • FIG. 1 is a perspective view of a part of the reflectometric device according to the invention arranged on a waveguide;
  • FIG. 2 is a partial sectional view of a directional coupler implemented in a reflectometric device according to the invention
  • FIG. 3A and 3B illustrate two embodiments of a "six-port" junction circuit implemented in a reflectometric device according to the invention
  • - Figure 4 is a top view of a first embodiment of a directional coupler for a reflectometric device according to the invention
  • FIG. 5 is a top view of a second embodiment of a directional coupler for a reflectometric device according to the invention.
  • FIG. 6 shows schematically a microwave oven provided with a reflectometric device according to the invention
  • FIG. 7 schematically shows a microwave oven provided with two reflectometric devices according to the invention
  • - Figure 8 shows a power-voltage converter implementing a reflectometry device according to the invention
  • FIG. 9 represents an experimental configuration for measuring the incident and reflected powers using two power-voltage converters of the type shown in FIG. 8
  • FIG. 10 illustrates a reading of reflectometry measurement carried out with a device according to the invention, in the case of idling of a microwave oven;
  • FIG. 11 illustrates a reflectometry measurement reading, illustrating the detection of the boiling of a cup of water in a microwave oven.
  • a reflectometric device 1 comprises, with reference to FIGS. 1 and 2, a directional power coupler 10 fixed on the upper face 11 of a waveguide 100, and a "six-port" junction circuit 30 as described for example in the article “A Versatile Easy to do Six-Port Based High-Power Reflectometer” by M.Caron et al. published in the journal 3International Microwave Power Institute “Vol.30, No4, 1995.
  • the reflectometric device 1 is positioned on the top of the waveguide 100, and makes it possible to measure, on the one hand, the incident power, and on the other hand, the reflected power.
  • the waveguide 100 shown in Figure 1 typically corresponds to an application to a microwave oven 60 as shown in Figure 6. At one of its ends, this waveguide 100 communicates with a housing 13 provided to contain a transmitting antenna 62 of a magnetron 61, while its other end opens into a cavity or enclosure 63 intended for receive a load 64.
  • the upper wall of the housing 13 contiguous to the waveguide 100 may for example have a boss 5 shaped so as to optimize the operation and the arrangement of the transmitting antenna 62 located below.
  • the cavity 63 receives incident radiation 01 generated by the magnetron 61 and channeled by the waveguide 100, and returns reflected radiation OR in return.
  • the directional coupler 10 of the reflectometric device 1 is fixed on the upper part 11 of the waveguide and is connected to the "six-port" junction circuit 30 which delivers a set of four microwave signals which are filtered and processed in a processing and control module which controls the magnetron 61.
  • the power directional coupler 10 comprises two antennas 22, 23 penetrating inside the waveguide 100 and connected to two connectors 2, 3 accessible on the upper face of the directional coupler 10.
  • the two antennas 22, 23 are interconnected by a deposited conductive tape or stripline 13 disposed on an upper plate 6 of insulating material, for example epoxy resin, itself disposed on a lower plate 7 forming a plane massive.
  • the power directional coupler 10 is securely fixed to the waveguide 100 by means of a set of screws (not shown).
  • the antennas 23, 22, fixed to the connectors 3, 2 extend inside the waveguide 100 through two holes formed in the latter, and of larger diameter than that of the antennas so as to avoid short-circuiting. antenna-guide circuit.
  • the conductive tape 43 connecting the connectors 2, 3 of the coupler directive 40 is of substantially sinusoidal or more generally wavy shape and corresponds to an arrangement of the ports PI, P2 on the longitudinal and median line of the waveguide.
  • Such a configuration is described in particular in document US 4,211,911.
  • the connectors 3, 2 of the directional coupler 50 are offset on either side of the center line so that it becomes possible to provide a tensioned conductive tape 13.
  • the "six-port" junction circuit 30 includes, with reference to FIG. 3A, two directional couplers and a resonance loop.
  • the port PI constitutes a first input port and is connected for example, via the connector 3, to the antenna 23 of the directional coupler 10.
  • the port P2 constitutes a second input port and is connected, via the connector 2, to the antenna 22 of the directional coupler 10.
  • the port P3 constitutes a reference port providing a power level proportional to the input power level of the port PI.
  • a suitable load is connected to port P'3.
  • the performance of the "six-port" junction circuit 30 ′ can also be significantly improved by inserting microwave capacities C13, C13 ', C24, C26, of a fraction of picoFarad, at the points of coupling of this junction circuit.
  • the addition of these capacities has the effect of much better defining the coupling points and of improving the directivity.
  • the addition of a microwave capacity of 1 pF brings the coupling to 3dB instead of 30dB, with a satisfactory directivity of 25dB.
  • Port 2 (corresponding to antenna 22) e -j ⁇ g.L Port 3 l / 2 (Cl.e "jps - s + C2. E " j ⁇ g - L )
  • the coupling coefficients C1 and C2 are substantially equal.
  • V 1/2.
  • the power of the wave on port 4 is given by the expression:
  • VV * C 2/2. (1 - cos (2 ⁇ g.L)) If we choose for example a length L equal to ⁇ g / 8 (i.e. 2.167 cm), we obtain on port P4 a complex amplitude equal to l / 2C (l + j), this that corresponds to an amplitude of 0.707C phase-shifted by 45 ° with respect to port 1, and to a power equal to C 2/2, quite sufficient to track the evolution of the impedance. It is important that the contribution of the incident signal be zero or negligible on port 3, while the contribution of the reflected signal will be zero on port 4. As a practical example of embodiment, a directional coupler having an inter-antenna distance is produced. equal to 1/8 of the wavelength of the waveguide.
  • the length Ls of the ribbon depends on the dielectric constant of the support of this ribbon. The more this dielectric constant is increased, the shorter this length; and the thinner the thickness of the dielectric plates, the narrower the strip.
  • Compact reflectometric devices according to the invention can also be implemented in ovens provided with a magnetron and two injection slots, as illustrated diagrammatically in the figure 7.
  • a microwave oven 70 comprising a magnetron 71 and two injection slots 721, 72S respectively lower and upper, is equipped with two reflectometric devices II, IS respectively lower and upper arranged on waveguides 731 , 73S on either side of magnetron 71.
  • a reflectometry device comprising a power coupler used alone without a six-port coupler, but with two detectors. This coupler provides the amplitude of the reflection coefficient, which is sufficient in simple cases such as idling safety.
  • a power-voltage converter 80 composed of an adaptation stage 81 produced in micro-strip technology comprising at the input, for example, an SMA connector 811 or the end of a stripped coaxial cable, and a 50 ⁇ ribbon 812, a microwave detection stage 82 comprising a Schottky detection diode 822, a 50 ⁇ ribbon 821 and a radial ferrite 823, and a follower stage or equivalent 83 for computer processing of the voltage measurements obtained.
  • This type of detector can also be used in the case of the implementation of a six-port coupler in P3, P4, P5, P6.
  • two power converters 91, 92 are placed in a structure 90 illustrated in FIG. 9. These converters measure an incident power and a reflected power by recovering two proportional electrical signals Si, S2, picked up by the reflectometer R antennas inside the waveguide. By calibration, it is possible to determine the incident power emitted and the power reflected by the load and the cavity. We deduce the power consumed from the difference between the incident power and the reflected power.
  • the present invention can be implemented in any type of microwave oven, for any sector of activity, domestic or professional.
  • microwave ovens used in chemistry experiments can advantageously be provided with reflectometric devices according to the invention.
  • the reflectometry device it becomes possible to identify idle phases of a microwave oven as illustrated in FIG. 10, in which the continuous curve represents the time evolution of the coefficient of reflection for a cup of water, while the dotted curve represents the evolution of this reflection coefficient in the event of idling.
  • the continuous curve represents the time evolution of the coefficient of reflection for a cup of water
  • the dotted curve represents the evolution of this reflection coefficient in the event of idling.
  • the invention is not limited to the examples which have just been described and numerous modifications can be made to these examples without departing from the scope of the invention.
  • the dimensions and shapes of the waveguides and of the components of the reflectometric devices may vary depending on the type of oven equipped. It is the same for the frequencies and wavelengths considered in the present invention.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)
  • Constitution Of High-Frequency Heating (AREA)
  • Measurement Of Resistance Or Impedance (AREA)

Abstract

The invention concerns a microwave reflectometer for monitoring the evolution of a microwave oven impedance, comprising a power directive feed (10) including two antennae penetrating into the waveguide (100) and mutually connected by a stripline (13), and a multi-port coupler comprising several coupling lines. The multi-port coupler co-operates with the power directive feed (10) to deliver an information concerning the reflected wave phase coming from the chamber with respect to the incident wave emitted by the magnetron. The selected distance between these two antennae is less by a quarter than the magnetron emitting wavelength. The invention is useful in microwaves for domestic and industrial purposes.

Description

"DISPOSITIF ET PROCEDE DE REFLECTOMETRIE HYPERFREQUENCES, ET FOUR A MICRO-ONDES AINSI EQUIPE""DEVICE AND METHOD FOR MICROWAVE REFLECTOMETRY, AND MICROWAVE OVEN THUS EQUIPPED"
La présente invention concerne un dispositif réflectométrique hyperfréquences . Elle vise également un procédé mis en œuvre dans ce dispositif réflectométrique, ainsi qu'un four à micro-ondes équipé de ce dispositif.The present invention relates to a microwave reflectometric device. It also relates to a process implemented in this reflectometric device, as well as a microwave oven equipped with this device.
Une utilisation optimale d'un four à micro-ondes, qu'il soit à usage domestique ou professionnel, suppose de pouvoir suivre l'évolution de l'impédance de ce four pendant la cuisson. Un diagramme d'impédance du magnétron tel que le diagramme de Rieke est habituellement utilisé pour étudier cette évolution. On peut utiliser pour cela un dispositif réflectométrique composé d'un coupleur directif de puissance fixé sur le guide d'onde du four à micro-ondes et tel que divulgué dans le document US 4 211 911, et d'un coupleur "six ports" tel que divulgué dans l'article intitulé "A versatile easy to do six-ports based high power reflectometer" de M. Caron et al., Journal of microwave Vol.30, No4 1995. Un coupleur directif de puissance utilisé seul permet de mesurer la puissance émise par le magnétron d'un four à micro-ondes et la puissance réfléchie par ce four. Il est à noter à ce sujet que la présente invention concerne également un dispositif réflectométrique hyperfréquence incluant dans sa version raccourcie un coupleur de puissance utilisé seul. On dispose en fait de deux tensions complexes proportionnelles aux champs électriques hyperfréquences respectivement incident et réfléchi. Le rapport de ces deux tensions fournit un coefficient de réflexion complexe vu par le magnétron avec un module p et une phase φ. Le coupleur "six-ports" a précisément pour fonction de récupérer cette information de phase.Optimal use of a microwave oven, whether for domestic or professional use, means being able to follow the evolution of the impedance of this oven during cooking. A magnetron impedance diagram such as the Rieke diagram is usually used to study this evolution. One can use for this a reflectometric device composed of a directional power coupler fixed on the waveguide of the microwave oven and as disclosed in document US 4 211 911, and of a "six port" coupler as disclosed in the article entitled "A versatile easy to do six-ports based high power reflectometer" by M. Caron et al., Journal of microwave Vol.30, No4 1995. A directional power coupler used alone makes it possible to measure the power emitted by the magnetron of a microwave oven and the power reflected by this oven. It should be noted in this regard that the present invention also relates to a microwave reflectometric device including in its shortened version a power coupler used alone. There are in fact two complex voltages proportional to the microwave electric fields, incident and reflected respectively. The ratio of these two voltages provides a complex reflection coefficient seen by the magnetron with a module p and a phase φ. The function of the "six-port" coupler is precisely to recover this phase information.
Le document US 4 211 911 enseigne que la distance entre les deux antennes d'un coupleur directif de puissance doit être égale à un quart de la longueur d'onde. Or, dans la gamme de fréquence où opèrent normalement les fours à micro-ondes, cette contrainte de distance entre antennes ne permet pas en pratique l'installation d'un tel coupleur sur un guide d'un four à micro-ondes pour des raisons d'encombrement. Le but de la présente invention est de remédier à cet inconvénient en proposant un dispositif réflectométrique présentant un encombrement moindre que les dispositifs actuels tout en procurant des mesures de précision suffisante pour permettre un suivi de l'évolution de l'impédance du four.Document US 4,211,911 teaches that the distance between the two antennas of a directional power coupler must be equal to a quarter of the wavelength. Now in the frequency range where operate normally microwave ovens, this distance constraint between antennas does not in practice allow the installation of such a coupler on a guide of a microwave oven for reasons of space. The object of the present invention is to remedy this drawback by proposing a reflectometric device having a smaller footprint than current devices while providing measurements of sufficient precision to allow monitoring of the evolution of the impedance of the furnace.
Cet objectif est atteint avec un dispositif de réflectométrie pour suivre l'évolution de l'impédance d'un four à micro-ondes comprenant un magnétron émettant une onde électromagnétique de longueur d'onde prédéterminée et un guide d'onde pour guider cette onde depuis le magnétron vers une enceinte de chauffage ou de cuisson, comprenant un coupleur directif de puissance comportant deux antennes disposées dans ce guide d'onde et reliées entre elles par un ruban conducteur ou stripline.This objective is achieved with a reflectometry device for monitoring the evolution of the impedance of a microwave oven comprising a magnetron emitting an electromagnetic wave of predetermined wavelength and a waveguide to guide this wave from the magnetron to a heating or cooking chamber, comprising a directional power coupler comprising two antennas arranged in this waveguide and connected together by a conductive strip or stripline.
Suivant l'invention, la distance entre ces deux antennes est choisie inférieure au quart de la longueur d'onde d'émission du magnétron.According to the invention, the distance between these two antennas is chosen to be less than a quarter of the emission wavelength of the magnetron.
Ainsi, il devient maintenant possible de placer des dispositifs reflectometriques compacts sur les guides d'onde équipant actuellement la majorité des fours à micro-ondes, là où des réflectomètres classiques ne pouvaient être implantés .Thus, it now becomes possible to place compact reflectometric devices on the waveguides currently fitted to the majority of microwave ovens, where conventional reflectometers could not be installed.
Dans une première forme de réalisation, le dispositif de réflectométrie selon l'invention comprend en outre un circuit de jonction multi-ports disposé en aval du coupleur directif de puissance, ce circuit de jonction multi-ports coopérant avec le coupleur directif de puissance pour délivrer, à partir de signaux délivrés par ledit circuit directif de puissance, une information sur la phase de l'onde réfléchie en provenance de l'enceinte par rapport à l'onde incidente émise par le magnétron.In a first embodiment, the reflectometry device according to the invention further comprises a multi-port junction circuit disposed downstream of the power directional coupler, this multi-port junction circuit cooperating with the power directional coupler to deliver , from signals delivered by said directional power circuit, information on the phase of the reflected wave coming from the enclosure with respect to the incident wave emitted by the magnetron.
Dans une autre forme de réalisation, le dispositif de réflectométrie selon l'invention comporte deux convertisseurs puissance-tension comprenant chacun un étage d'adaptation et un étage de détection hyperfréquences, un premier convertisseur puissance- tension coopérant avec le coupleur directif de puissance pour mesurer la puissance incidente et un second convertisseur puissance-tension coopérant avec le coupleur directif de puissance pour mesurer la puissance réfléchie .In another embodiment, the reflectometry device according to the invention comprises two power-voltage converters each comprising an adaptation stage and a microwave detection stage, a first power-voltage converter cooperating with the directional power coupler for measuring the incident power and a second power-voltage converter cooperating with the directional power coupler to measure the reflected power.
Suivant une version préférée du dispositif réflectométrique selon l'invention, les antennes sont disposées de part et d'autre d'une ligne médiane du guide d'onde respectivement dans des plans de phase distants de moins d'un quart de la longueur d'onde d'émission du magnétron. Le ruban ou stripline reliant les deux antennes peut alors être conçu sensiblement rectiligne. Cette configuration particulière a pour effet de diminuer considérablement le rayonnement du ruban observé au niveau des boucles. Avec un ruban rectiligne, ce rayonnement est minimum.According to a preferred version of the reflectometric device according to the invention, the antennas are arranged on either side of a center line of the waveguide respectively in phase planes distant by less than a quarter of the length of emission wave of the magnetron. The ribbon or stripline connecting the two antennas can then be designed to be substantially straight. This particular configuration has the effect of considerably reducing the radiation of the ribbon observed at the loops. With a straight ribbon, this radiation is minimum.
Par ailleurs, il est possible de réduire l'atténuation induite habituellement par le circuit de jonction multi-ports en fixant au niveau des points de couplage de ce circuit de jonction des capacités CMS hyperfréquences de l'ordre du picoFarad.Furthermore, it is possible to reduce the attenuation usually induced by the multi-port junction circuit by fixing at the coupling points of this junction circuit microwave SMD capacities of the order of picoFarad.
Suivant un autre aspect de l'invention, il est proposé un procédé pour réaliser des mesures de réflectométrie dans un four à micro-ondes pourvu d'un dispositif de réflectométrie selon l'une quelconque des revendications précédentes, dans lequel on prélève des signaux aux bornes respectives de deux antennes disposées à l'intérieur d'un guide d'onde, on applique ces signaux à un circuit de jonction multi-ports pour délivrer des signaux permettant après traitement de fournir une information sur la phase de l'onde réfléchie par la cavité formée par le caisson du four à micro-ondes, par rapport à l'onde incidente générée par le magnétron.According to another aspect of the invention, a method is proposed for carrying out reflectometry measurements in a microwave oven provided with a reflectometry device according to any one of the preceding claims, in which signals are taken from the respective terminals of two antennas arranged inside a waveguide, these signals are applied to a multi-port junction circuit to deliver signals allowing after processing to provide a information on the phase of the wave reflected by the cavity formed by the box of the microwave oven, with respect to the incident wave generated by the magnetron.
Suivant l'invention, on prélève les signaux hyperfréquences dans le guide d'onde en deux points situés dans des plans de phase séparés d'une distance inférieure à un quart de la longueur d'onde d'émission du magnétron .According to the invention, the microwave signals are taken from the waveguide at two points located in phase planes separated by a distance less than a quarter of the emission wavelength of the magnetron.
Suivant encore un autre aspect de l'invention, il est proposé un four à micro-ondes comprenant au moins un dispositif réflectométrique selon l'invention.According to yet another aspect of the invention, there is provided a microwave oven comprising at least one reflectometric device according to the invention.
D'autres particularités et avantages de l'invention apparaîtront encore dans la description ci-après. Aux dessins annexés donnés à titre d'exemples non limitatifs: - la figure 1 est une vue en perspective d'une partie du dispositif réflectométrique selon l'invention disposé sur un guide d'onde;Other features and advantages of the invention will appear in the description below. In the accompanying drawings given by way of nonlimiting examples: - Figure 1 is a perspective view of a part of the reflectometric device according to the invention arranged on a waveguide;
- la figure 2 est une vue en coupe partielle d'un coupleur directif mis en œuvre dans un dispositif réflectométrique selon l'invention;- Figure 2 is a partial sectional view of a directional coupler implemented in a reflectometric device according to the invention;
- les figures 3A et 3B illustrent deux modes de réalisation d'un circuit de jonction "six-ports" mis en œuvre dans un dispositif réflectométrique selon 1 ' invention; - la figure 4 est une vue de dessus d'un premier mode de réalisation d'un coupleur directif pour un dispositif réflectométrique selon l'invention;- Figures 3A and 3B illustrate two embodiments of a "six-port" junction circuit implemented in a reflectometric device according to the invention; - Figure 4 is a top view of a first embodiment of a directional coupler for a reflectometric device according to the invention;
- la figure 5 est une vue de dessus d'un second mode de réalisation d'un coupleur directif pour un dispositif réflectométrique selon l'invention;- Figure 5 is a top view of a second embodiment of a directional coupler for a reflectometric device according to the invention;
- la figure 6 représente schématiquement un four à micro-ondes pourvu d'un dispositif réflectométrique selon l'invention;- Figure 6 shows schematically a microwave oven provided with a reflectometric device according to the invention;
- la figure 7 représente schématiquement un four à micro-ondes pourvu de deux dispositifs reflectometriques selon l'invention; - la figure 8 représente un convertisseur puissance- tension mettant en œuvre un dispositif de réflectométrie selon l'invention; la figure 9 représente une configuration expérimentale de mesure des puissances incidentes et réfléchies mettant en œuvre deux convertisseurs puissance-tension du type représenté en figure 8; la figure 10 illustre un relevé de mesure de réflectométrie effectué avec un dispositif selon l'invention, dans le cas de la marche à vide d'un four à micro-ondes; et- Figure 7 schematically shows a microwave oven provided with two reflectometric devices according to the invention; - Figure 8 shows a power-voltage converter implementing a reflectometry device according to the invention; FIG. 9 represents an experimental configuration for measuring the incident and reflected powers using two power-voltage converters of the type shown in FIG. 8; FIG. 10 illustrates a reading of reflectometry measurement carried out with a device according to the invention, in the case of idling of a microwave oven; and
- la figure 11 illustre un relevé de mesure de réflectométrie, illustrant la détection de l'ébullition d'une tasse d'eau dans un four à micro- ondes.- Figure 11 illustrates a reflectometry measurement reading, illustrating the detection of the boiling of a cup of water in a microwave oven.
On va maintenant décrire plusieurs exemples de réalisation d'un dispositif réflectométrique selon l'invention, en référence aux figures précitées.We will now describe several embodiments of a reflectometric device according to the invention, with reference to the aforementioned figures.
Un dispositif réflectométrique 1 selon l'invention comprend, en référence aux figures 1 et 2, un coupleur directif de puissance 10 fixé sur la face supérieure 11 d'un guide d'onde 100, et un circuit de jonction "six- ports" 30 tel que décrit par exemple dans l'article "A Versatile Easy to do Six-Port Based High-Power Reflectometer" de M.Caron et al. paru dans la revue 3International Microwave Power Institute" Vol.30, No4, 1995. Le dispositif réflectométrique 1 est positionné sur le haut du guide d'onde 100, et permet de mesurer, d'une part, la puissance incidente, et d'autre part, la puissance réfléchie.A reflectometric device 1 according to the invention comprises, with reference to FIGS. 1 and 2, a directional power coupler 10 fixed on the upper face 11 of a waveguide 100, and a "six-port" junction circuit 30 as described for example in the article "A Versatile Easy to do Six-Port Based High-Power Reflectometer" by M.Caron et al. published in the journal 3International Microwave Power Institute "Vol.30, No4, 1995. The reflectometric device 1 is positioned on the top of the waveguide 100, and makes it possible to measure, on the one hand, the incident power, and on the other hand, the reflected power.
Le guide d'onde 100 représenté en figure 1 correspond typiquement à une application à un four à micro-ondes 60 tel que représenté en figure 6. A l'une de ses extrémités, ce guide d'ondes 100 communique avec un logement 13 prévu pour contenir une antenne emettrice 62 d'un magnétron 61, tandis que son autre extrémité débouche dans une cavité ou enceinte 63 destinée à recevoir une charge 64. La paroi supérieure du logement 13 contiguë au guide d'onde 100 peut par exemple présenter un bossage 5 conformé de façon à optimiser le fonctionnement et la disposition de l'antenne emettrice 62 située en dessous. La cavité 63 reçoit un rayonnement incident 01 généré par le magnétron 61 et canalisé par le guide d'onde 100, et renvoie en retour un rayonnement réfléchi OR. Le coupleur directif 10 du dispositif réflectométrique 1 selon l'invention est fixé sur la partie supérieure 11 du guide d'onde et est relié au circuit de jonction "six-ports" 30 qui délivre un ensemble de quatre signaux hyperfréquence qui sont filtrés et traités dans un module de traitement et de commande qui pilote le magnétron 61. Le coupleur directif de puissance 10 comprend deux antennes 22, 23 pénétrant à l'intérieur du guide d'onde 100 et reliées à deux connecteurs 2, 3 accessibles sur la face supérieure du coupleur directif 10. Les deux antennes 22, 23 sont reliées entre elles par un ruban conducteur déposé ou stripline 13 disposé sur une plaque supérieure 6 en matériau isolant, par exemple en résine époxy, elle-même disposée sur une plaque inférieure 7 faisant plan de masse. Une feuille métallique 8, par exemple en aluminium, est avantageusement disposée entre la plaque inférieure 7 et la partie supérieure 11 du guide d'onde 100. Le coupleur directif de puissance 10 est solidement fixé au guide d'onde 100 au moyen d'un ensemble de vis (non représentées). Les antennes 23, 22, fixées aux connecteurs 3, 2 s'étendent à l'intérieur du guide d'onde 100 à travers deux trous ménagés dans ce dernier, et de diamètre plus grand que celui des antennes de façon à éviter le court-circuit antenne-guide.The waveguide 100 shown in Figure 1 typically corresponds to an application to a microwave oven 60 as shown in Figure 6. At one of its ends, this waveguide 100 communicates with a housing 13 provided to contain a transmitting antenna 62 of a magnetron 61, while its other end opens into a cavity or enclosure 63 intended for receive a load 64. The upper wall of the housing 13 contiguous to the waveguide 100 may for example have a boss 5 shaped so as to optimize the operation and the arrangement of the transmitting antenna 62 located below. The cavity 63 receives incident radiation 01 generated by the magnetron 61 and channeled by the waveguide 100, and returns reflected radiation OR in return. The directional coupler 10 of the reflectometric device 1 according to the invention is fixed on the upper part 11 of the waveguide and is connected to the "six-port" junction circuit 30 which delivers a set of four microwave signals which are filtered and processed in a processing and control module which controls the magnetron 61. The power directional coupler 10 comprises two antennas 22, 23 penetrating inside the waveguide 100 and connected to two connectors 2, 3 accessible on the upper face of the directional coupler 10. The two antennas 22, 23 are interconnected by a deposited conductive tape or stripline 13 disposed on an upper plate 6 of insulating material, for example epoxy resin, itself disposed on a lower plate 7 forming a plane massive. A metal sheet 8, for example made of aluminum, is advantageously disposed between the lower plate 7 and the upper part 11 of the waveguide 100. The power directional coupler 10 is securely fixed to the waveguide 100 by means of a set of screws (not shown). The antennas 23, 22, fixed to the connectors 3, 2 extend inside the waveguide 100 through two holes formed in the latter, and of larger diameter than that of the antennas so as to avoid short-circuiting. antenna-guide circuit.
On peut envisager diverses configurations du ruban ou stripline inter-antenne au sein du coupleur directif, comme le représentent les figures 4 et 5. Dans un premier exemple de réalisation illustré par la figure 4, le ruban conducteur 43 reliant les connecteurs 2, 3 du coupleur directif 40 est de forme sensiblement sinusoïdale ou plus généralement ondulée et correspond à une disposition des ports PI, P2 sur la ligne longitudinale et médiane du guide d'ondes. Une telle configuration est notamment décrite dans le document US 4 211 911.We can consider various configurations of the ribbon or stripline inter-antenna within the directional coupler, as shown in Figures 4 and 5. In a first embodiment illustrated by Figure 4, the conductive tape 43 connecting the connectors 2, 3 of the coupler directive 40 is of substantially sinusoidal or more generally wavy shape and corresponds to an arrangement of the ports PI, P2 on the longitudinal and median line of the waveguide. Such a configuration is described in particular in document US 4,211,911.
Dans un second exemple de réalisation représenté en figure 5, les connecteurs 3, 2 du coupleur directif 50 sont décalés de part et d'autre de la ligne médiane de telle sorte qu'il devient possible de prévoir un ruban conducteur tendu 13.In a second exemplary embodiment shown in FIG. 5, the connectors 3, 2 of the directional coupler 50 are offset on either side of the center line so that it becomes possible to provide a tensioned conductive tape 13.
Le circuit de jonction "six-ports" 30 comprend, en référence à la figure 3A, deux coupleurs directifs et une boucle de résonance. Le port PI constitue un premier port d'entrée et est relié par exemple, via le connecteur 3, à l'antenne 23 du coupleur directif 10. Le port P2 constitue un second port d'entrée et est relié, via le connecteur 2, à l'antenne 22 du coupleur directif 10. Le port P3 constitue un port de référence procurant un niveau de puissance proportionnel au niveau de puissance d'entrée du port PI. Une charge adaptée est reliée au port P'3.The "six-port" junction circuit 30 includes, with reference to FIG. 3A, two directional couplers and a resonance loop. The port PI constitutes a first input port and is connected for example, via the connector 3, to the antenna 23 of the directional coupler 10. The port P2 constitutes a second input port and is connected, via the connector 2, to the antenna 22 of the directional coupler 10. The port P3 constitutes a reference port providing a power level proportional to the input power level of the port PI. A suitable load is connected to port P'3.
Comme l'illustre la figure 3B, On peut aussi améliorer significativement les performances du circuit de jonction "six-ports" 30' en insérant des capacités hyperfréquences C13, C13', C24, C26, d'une fraction de picoFarad, aux points de couplage de ce circuit de jonction. Outre la réduction significative de l'atténuation du circuit six-ports ainsi obtenue, l'ajout de ces capacités a pour effet de beaucoup mieux définir les points de couplage et d'améliorer la directivité. Ainsi, l'ajout d'une capacité hyperfréquence de 1 pF ramène le couplage à 3dB au lieu de 30dB, avec une directivité satisfaisante de 25dB.As illustrated in FIG. 3B, the performance of the "six-port" junction circuit 30 ′ can also be significantly improved by inserting microwave capacities C13, C13 ', C24, C26, of a fraction of picoFarad, at the points of coupling of this junction circuit. In addition to the significant reduction in the attenuation of the six-port circuit thus obtained, the addition of these capacities has the effect of much better defining the coupling points and of improving the directivity. Thus, the addition of a microwave capacity of 1 pF brings the coupling to 3dB instead of 30dB, with a satisfactory directivity of 25dB.
On va maintenant montrer pourquoi la distance entre les deux antennes peut être choisie quelconque inférieure au quart d'onde. Soient : L, la distance inter-antenne (à déterminer) Ls, la longueur du ruban ou stripline inter-antenne, λs, la longueur d'onde dans le ruban, λg, la longueur d'onde dans le guide, βs=2π/λs βg=2π/λgWe will now show why the distance between the two antennas can be chosen to be less than a quarter wave. Let: L, the inter-antenna distance (to be determined) Ls, the length of the inter-antenna ribbon or stripline, λs, the wavelength in the ribbon, λg, the wavelength in the guide, βs = 2π / λs βg = 2π / λg
Cl, C2, des coefficients de couplage au sein du coupleur directif.Cl, C2, coupling coefficients within the directional coupler.
La longueur électrique du ruban ou stripline doit respecter la condition de phase suivante: βs.Ls = βg.L + πThe electrical length of the strip or stripline must respect the following phase condition: βs.Ls = βg.L + π
On considère maintenant les amplitudes complexes aux différents ports du coupleur directif de puissance, en référence à la figure 2, en prenant comme référence la tension incidente normalisée à 1:We now consider the complex amplitudes at the different ports of the directional power coupler, with reference to FIG. 2, taking as reference the incident voltage normalized to 1:
Port 1 (correspondant à l'antenne 23) 1Port 1 (corresponding to antenna 23) 1
Port 2 (correspondant à l'antenne 22) e-jβg.L Port 3 l/2(Cl.e"jps- s + C2. e"jβg-L)Port 2 (corresponding to antenna 22) e -jβg.L Port 3 l / 2 (Cl.e "jps - s + C2. E " jβg - L )
port 4 l/2(Cl+C2.e-jβs-Ls * e~jPg-L)port 4 l / 2 (Cl + C2.e- jβs - Ls * e ~ jPg - L )
En pratique, on peut considérer que les coefficients de couplage Cl et C2 sont sensiblement égaux. En prenant en compte cette égalité et la condition précitée sur la longueur électrique, on montre aisément que l'amplitude complexe du signal sur le port 3 du coupleur directif est nulle. Par ailleurs, l'amplitude complexe du signal sur le port 4 peut être exprimée de la façon suivante: V = 1/2. C. (1-cos (2. βg.L) + j sin(2.βg.L) De même, la puissance de l'onde sur le port 4 est donnée par l'expression:In practice, it can be considered that the coupling coefficients C1 and C2 are substantially equal. By taking into account this equality and the aforementioned condition on the electrical length, it is easily shown that the complex amplitude of the signal on port 3 of the directional coupler is zero. Furthermore, the complex amplitude of the signal on port 4 can be expressed as follows: V = 1/2. C. (1-cos (2. βg.L) + j sin (2.βg.L) Similarly, the power of the wave on port 4 is given by the expression:
V.V* = C2/2 . (1 - cos(2βg.L)) Si on choisit par exemple une longueur L égale à λg/8 (soit 2.167 cm), on obtient sur le port P4 une amplitude complexe égale à l/2C(l+j), ce qui correspond à une amplitude de 0.707C déphasée de 45° par rapport au port 1, et à une puissance égale à C2/2, tout à fait suffisante pour effectuer un suivi de l'évolution de l'impédance. II importe que la contribution du signal incident soit nulle ou négligeable sur le port3, tandis que la contribution du signal réfléchi sera nulle sur le port 4. A titre d'exemple pratique de réalisation, on réalise un coupleur directif présentant une distance inter- antenne égale à 1/8 de la longueur d'onde du guide d'onde. Par exemple, on considère un guide d'onde présentant une hauteur égale à 36.6 mm et une largeur égale à 92 mm. Si la longueur d'onde du magnétron est λ=122,36 mm, la longueur d'onde du guide d'onde est alors λg=163,84 mm et la distance entre plans de phase est par exemple choisie égale à λg/8, à savoir 20,48 mm.VV * = C 2/2. (1 - cos (2βg.L)) If we choose for example a length L equal to λg / 8 (i.e. 2.167 cm), we obtain on port P4 a complex amplitude equal to l / 2C (l + j), this that corresponds to an amplitude of 0.707C phase-shifted by 45 ° with respect to port 1, and to a power equal to C 2/2, quite sufficient to track the evolution of the impedance. It is important that the contribution of the incident signal be zero or negligible on port 3, while the contribution of the reflected signal will be zero on port 4. As a practical example of embodiment, a directional coupler having an inter-antenna distance is produced. equal to 1/8 of the wavelength of the waveguide. For example, consider a waveguide having a height of 36.6 mm and a width of 92 mm. If the wavelength of the magnetron is λ = 122.36 mm, the wavelength of the waveguide is then λg = 163.84 mm and the distance between phase planes is for example chosen to be equal to λg / 8 , namely 20.48 mm.
Les caractéristiques du ruban ou stripline disposé sur le coupleur directif de puissance sont par exemple les suivantes: permittivité relative εr=4.3 (époxy) longueur d'onde dans la structure triplaque The characteristics of the strip or stripline placed on the power directional coupler are for example the following: relative permittivity εr = 4.3 (epoxy) wavelength in the triplate structure
La longueur du ruban est par exemple choisie égale à 5.λt/8= 36.88 mm. Plus généralement, la longueur du ruban Ls peut être déterminée par la relation suivante: Ls = L/λg .λs + k. λs/2 avec k=l, 3, 5 etc..The length of the ribbon is for example chosen to be 5.λt / 8 = 36.88 mm. More generally, the length of the ribbon Ls can be determined by the following relation: Ls = L / λg .λs + k. λs / 2 with k = l, 3, 5 etc.
La longueur Ls du ruban dépend de la constante diélectrique du support de ce ruban. Plus on augmente cette constante diélectrique, plus cette longueur est courte; et plus l'épaisseur des plaques diélectriques est faible, moins le ruban est large.The length Ls of the ribbon depends on the dielectric constant of the support of this ribbon. The more this dielectric constant is increased, the shorter this length; and the thinner the thickness of the dielectric plates, the narrower the strip.
Des dispositifs reflectometriques compacts selon l'invention peuvent aussi être mis en œuvre dans des fours pourvus d'un magnétron et de deux fentes d'injection, comme l'illustre schématiquement la figure 7. Ainsi, un four à micro-ondes 70 comprenant un magnétron 71 et deux fentes d'injection 721, 72S respectivement inférieure et supérieure, est équipé de deux dispositifs reflectometriques II, IS respectivement inférieur et supérieur disposés sur des guides d'ondes 731, 73S de part et d'autre du magnétron 71. Dans cette configuration, il est possible de mesurer des coefficients de réflexion supérieurs à 1 car une onde peut sortir par une fente et rentrer par l'autre. II est à noter qu'on peut envisager dans le cadre de la présente invention un dispositif de réflectométrie comportant un coupleur de puissance utilisé seul sans coupleur six-ports, mais avec deux détecteurs. Ce coupleur fournit l'amplitude du coefficient de réflexion, ce qui suffit dans des cas simples comme la sécurité de marche à vide.Compact reflectometric devices according to the invention can also be implemented in ovens provided with a magnetron and two injection slots, as illustrated diagrammatically in the figure 7. Thus, a microwave oven 70 comprising a magnetron 71 and two injection slots 721, 72S respectively lower and upper, is equipped with two reflectometric devices II, IS respectively lower and upper arranged on waveguides 731 , 73S on either side of magnetron 71. In this configuration, it is possible to measure reflection coefficients greater than 1 because one wave can exit through a slot and enter through the other. It should be noted that, within the framework of the present invention, it is possible to envisage a reflectometry device comprising a power coupler used alone without a six-port coupler, but with two detectors. This coupler provides the amplitude of the reflection coefficient, which is sufficient in simple cases such as idling safety.
Ainsi, en référence à la figure 8, on peut concevoir un convertisseur puissance-tension 80 composé d'un étage d'adaptation 81 réalisé en technologie micro-strip comportant en entrée, par exemple, un connecteur SMA 811 ou l'extrémité d'un câble coaxial dénudé, et un ruban 50Ω 812, un étage de détection hyperfréquence 82 comprenant une diode de détection Schottky 822, un ruban 50Ω 821 et une ferrite radiale 823, et un étage suiveur ou équivalent 83 en vue d'un traitement informatique des mesures de tension obtenues . Ce type de détecteur peut d'ailleurs être également utilisé dans de cas de la mise en œuvre d'un coupleur six-ports en P3, P4, P5, P6.Thus, with reference to FIG. 8, it is possible to design a power-voltage converter 80 composed of an adaptation stage 81 produced in micro-strip technology comprising at the input, for example, an SMA connector 811 or the end of a stripped coaxial cable, and a 50Ω ribbon 812, a microwave detection stage 82 comprising a Schottky detection diode 822, a 50Ω ribbon 821 and a radial ferrite 823, and a follower stage or equivalent 83 for computer processing of the voltage measurements obtained. This type of detector can also be used in the case of the implementation of a six-port coupler in P3, P4, P5, P6.
Afin de mesurer les puissances incidente et réfléchie, on place deux convertisseurs de puissance 91, 92 dans une structure 90 illustrée en figure 9. Ces convertisseurs mesurent une puissance incidente et une puissance réfléchie en récupérant deux signaux électriques Si, S2 proportionnels, capté par les antennes du réflectomètre R à l'intérieur du guide d'onde. Par étalonnage, on peut déterminer la puissance incidente émise et la puissance réfléchie par la charge et la cavité. On en déduit la puissance consommée à partir de la différence entre la puissance incidente et la puissance réfléchie.In order to measure the incident and reflected powers, two power converters 91, 92 are placed in a structure 90 illustrated in FIG. 9. These converters measure an incident power and a reflected power by recovering two proportional electrical signals Si, S2, picked up by the reflectometer R antennas inside the waveguide. By calibration, it is possible to determine the incident power emitted and the power reflected by the load and the cavity. We deduce the power consumed from the difference between the incident power and the reflected power.
La présente invention peut être mise en œuvre dans tout type de four à micro-ondes, pour tout secteur d'activité, domestique ou professionnel. En particulier, des fours à micro-ondes utilisés dans des expérimentations de chimie peuvent avantageusement être pourvus de dispositifs reflectometriques selon l'invention.The present invention can be implemented in any type of microwave oven, for any sector of activity, domestic or professional. In particular, microwave ovens used in chemistry experiments can advantageously be provided with reflectometric devices according to the invention.
Grâce au dispositif de réflectométrie selon l'invention, il devient possible d'identifier des phases de marche à vide d'un four à micro-ondes comme l'illustre la figure 10, dans laquelle la courbe continue représente l'évolution temporelle du coefficient de réflexion pour une tasse d'eau, tandis que la courbe en pointillés représente l'évolution de ce coefficient de réflexion en cas de marche à vide. On peut également détecter des situations d'ébullition d'une tasse, comme représenté en figure 11.Thanks to the reflectometry device according to the invention, it becomes possible to identify idle phases of a microwave oven as illustrated in FIG. 10, in which the continuous curve represents the time evolution of the coefficient of reflection for a cup of water, while the dotted curve represents the evolution of this reflection coefficient in the event of idling. We can also detect situations when a cup is boiling, as shown in Figure 11.
Bien sûr, l'invention n'est pas limitée aux exemples qui viennent d'être décrits et de nombreux aménagements peuvent être apportés à ces exemples sans sortir du cadre de l'invention. Ainsi, les dimensions et les formes des guides d'onde et des composants des dispositifs reflectometriques peuvent varier en fonction du type de four équipé. Il en est de même pour les fréquences et longueurs d'onde considérées dans la présente invention. Of course, the invention is not limited to the examples which have just been described and numerous modifications can be made to these examples without departing from the scope of the invention. Thus, the dimensions and shapes of the waveguides and of the components of the reflectometric devices may vary depending on the type of oven equipped. It is the same for the frequencies and wavelengths considered in the present invention.

Claims

REVENDICATIONS
1. Dispositif de réflectométrie hyperfréquences (1) pour suivre l'évolution de l'impédance d'un four à micro- ondes (60) comprenant un magnétron (61) émettant une onde électromagnétique de longueur d'onde prédéterminée (λ) et un guide d'onde (100) pour guider cette onde depuis le magnétron (61) vers une enceinte de chauffage ou de cuisson (63), comprenant un coupleur directif de puissance (10) comportant deux antennes (23, 22) disposées dans ledit guide d'onde (100) et reliées par un ruban conducteur ou stripline (13, 43) , caractérisé en ce que la distance (L) entre ces deux antennes (23, 22) est choisie inférieure au quart de la longueur d'onde (λ) d'émission du magnétron (61) .1. Microwave reflectometry device (1) for monitoring the evolution of the impedance of a microwave oven (60) comprising a magnetron (61) emitting an electromagnetic wave of predetermined wavelength (λ) and a waveguide (100) for guiding this wave from the magnetron (61) to a heating or cooking chamber (63), comprising a power directional coupler (10) comprising two antennas (23, 22) arranged in said guide wave (100) and connected by a conductive strip or stripline (13, 43), characterized in that the distance (L) between these two antennas (23, 22) is chosen to be less than a quarter of the wavelength ( λ) emission of the magnetron (61).
2. Dispositif de réflectométrie selon la revendication 1, caractérisé en ce qu'il comprend en outre un circuit de jonction multi-ports (30, 30') disposé en aval du coupleur directif de puissance (10) , ce circuit de jonction multi-ports (30, 30') coopérant avec le coupleur directif de puissance (10) pour délivrer, à partir de signaux délivrés par ledit circuit directif de puissance (10) , une information sur la phase d-e l'onde réfléchie (OR) en provenance de l'enceinte (63) par rapport à l'onde incidente (01) émise par le magnétron (61) .2. A reflectometry device according to claim 1, characterized in that it further comprises a multi-port junction circuit (30, 30 ') disposed downstream of the directional power coupler (10), this multi-junction circuit ports (30, 30 ') cooperating with the power directional coupler (10) to deliver, from signals delivered by said power directional circuit (10), information on the phase of the reflected wave (OR) coming from of the enclosure (63) with respect to the incident wave (01) emitted by the magnetron (61).
3. Dispositif de réflectométrie (90) selon la revendication 1, caractérisé en ce qu'il comporte deux convertisseurs puissance-tension (91, 92; 80) comprenant chacun un étage d'adaptation (81) et un étage de détection hyperfréquences (82), un premier convertisseur puissance-tension (91) coopérant avec le coupleur directif de puissance (R) pour mesurer la puissance incidente et un second convertisseur puissance-tension (92) coopérant avec le coupleur directif de puissance (R) pour mesurer la puissance réfléchie.3. Reflectometry device (90) according to claim 1, characterized in that it comprises two power-voltage converters (91, 92; 80) each comprising an adaptation stage (81) and a microwave detection stage (82 ), a first power-voltage converter (91) cooperating with the directional power coupler (R) to measure the incident power and a second power-voltage converter (92) cooperating with the directional power coupler (R) to measure the reflected power.
4. Dispositif de réflectométrie selon l'une des 5 revendications précédentes, caractérisé en ce que les antennes (23, 22) sont disposées de part et d'autre d'une ligne longitudinale et médiane du guide d'onde (100) respectivement dans des plans de phase distants de moins d'un quart de la longueur d'onde (λ) d'émission du 0 magnétron (61) .4. Reflectometry device according to one of the 5 preceding claims, characterized in that the antennas (23, 22) are arranged on either side of a longitudinal and median line of the waveguide (100) respectively phase planes distant by less than a quarter of the emission wavelength (λ) of the 0 magnetron (61).
5. Dispositif de réflectométrie selon l'une des revendications 1 à 3, caractérisé en ce que les antennes sont sensiblement alignées sur une ligne longitudinale et 5 médiane du guide d'onde.5. A reflectometry device according to one of claims 1 to 3, characterized in that the antennas are substantially aligned on a longitudinal and median line of the waveguide.
6. Dispositif de réflectométrie selon l'une des revendications 4 ou 5, caractérisé en ce que le ruban ou stripline (13) reliant les deux antennes (23, 22) est 0 sensiblement rectiligne.6. A reflectometry device according to one of claims 4 or 5, characterized in that the strip or stripline (13) connecting the two antennas (23, 22) is 0 substantially rectilinear.
7. Dispositif de réflectométrie selon la revendication 6, caractérisé en ce que la longueur Ls du ruban stripline (13) est déterminée par la relation 5 suivante:7. A reflectometry device according to claim 6, characterized in that the length Ls of the stripline strip (13) is determined by the following relation:
Ls=L/λg . λs + k. λs/2 avec k=l, 3, 5 etc.. où 1 représente l'écart entre les deux antennes, λs représente la longueur d'onde associée au 0 coupleur directif de la structure triplaque.Ls = L / λg. λs + k. λs / 2 with k = 1, 3, 5 etc. where 1 represents the difference between the two antennas, λs represents the wavelength associated with the directional coupler of the three-plate structure.
8. Dispositif de réflectométrie selon la revendication 7, caractérisé en ce que k est choisi égal à 1 et 1 est choisi égal à λg/8. 8. A reflectometry device according to claim 7, characterized in that k is chosen equal to 1 and 1 is chosen equal to λg / 8.
9. Dispositif de réflectométrie selon l'une quelconque des revendications précédentes, caractérisé en ce que le circuit de jonction multi-ports (30') comprend en chaque point de couplage une capacité hyperfréquence9. A reflectometry device according to any one of the preceding claims, characterized in that the multi-port junction circuit (30 ') comprises at each coupling point a microwave capacity
(C13, C13' , C24, C26) .(C13, C13 ', C24, C26).
10. Dispositif de réflectométrie selon la revendication 9, caractérisé en ce que ces capacités hyperfréquences sont de l'ordre du picofarad.10. A reflectometry device according to claim 9, characterized in that these microwave capacities are of the order of picofarad.
11. Dispositif de réflectométrie selon l'une quelconque des revendications précédentes, caractérisé en ce que le coupleur directif de puissance est réalisé sous la forme d'un circuit triplaque.11. A reflectometry device according to any one of the preceding claims, characterized in that the directional power coupler is produced in the form of a three-plate circuit.
12. Dispositif de réflectométrie selon la revendication 11, caractérisé en ce qu'il comprend en outre une feuille métallique ou une plaque conductrice (8) insérée entre le plan de masse inférieur du coupleur directif de puissance (10) et la partie supérieure (11) du guide d'onde (100).12. A reflectometry device according to claim 11, characterized in that it further comprises a metal foil or a conductive plate (8) inserted between the lower ground plane of the directional power coupler (10) and the upper part (11 ) of the waveguide (100).
13. Procédé pour réaliser des mesures de réflectométrie dans un four à micro-ondes (60) pourvu d'un dispositif de réflectométrie (1) selon l'une quelconque des revendications précédentes et la revendication 2, dans lequel on prélève des signaux sur deux antennes (23, 22) pénétrant à l'intérieur d'un guide d'onde (100), on applique ces signaux à un circuit de jonction multi-ports (30) pour délivrer des signaux permettant après traitement de fournir une information sur la phase et le module de l'onde réfléchie (OR) par l'enceinte ou la cavité par rapport à l'onde incidente13. Method for carrying out reflectometry measurements in a microwave oven (60) provided with a reflectometry device (1) according to any one of the preceding claims and claim 2, in which two signals are sampled antennas (23, 22) penetrating inside a waveguide (100), these signals are applied to a multi-port junction circuit (30) to deliver signals allowing after processing to provide information on the phase and modulus of the reflected wave (OR) by the enclosure or the cavity with respect to the incident wave
(01) générée par le magnétron (61), caractérisé en que les antennes (23, 22) sont distantes d'une distance inférieure à un quart de la longueur d'onde d'émission du magnétron ( 61) . (01) generated by the magnetron (61), characterized in that the antennas (23, 22) are distant by a distance less than a quarter of the emission wavelength of the magnetron (61).
14. Four à micro-ondes (60) comprenant un dispositif de réf lectométrie (1) selon l'une quelconque des revendications 1 à 12.14. Microwave oven (60) comprising a ref lectometry device (1) according to any one of claims 1 to 12.
15. Four à micro-ondes (70) comprenant au moins deux dispositifs de réflectométrie (IS, II) selon l'une quelconque des revendications 1 à 12 disposés sur des guides d'onde (73S, 731) de part et d'autre d'un magnétron (71) . 15. Microwave oven (70) comprising at least two reflectometry devices (IS, II) according to any one of claims 1 to 12 arranged on waveguides (73S, 731) on either side of a magnetron (71).
EP98939673A 1997-07-15 1998-07-13 Microwave reflectometer and method, and microwave oven equipped therewith Withdrawn EP0995125A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
FR9708928A FR2766272B1 (en) 1997-07-15 1997-07-15 DEVICE AND METHOD FOR MICROWAVE REFLECTOMETRY, AND MICROWAVE OVEN THUS EQUIPPED
FR9708928 1997-07-15
PCT/FR1998/001529 WO1999004275A1 (en) 1997-07-15 1998-07-13 Microwave reflectometer and method, and microwave oven equipped therewith

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FR2766272A1 (en) 1999-01-22
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CN1135394C (en) 2004-01-21
WO1999004275A1 (en) 1999-01-28
KR20010021942A (en) 2001-03-15

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