EP0047203B1 - Microwave filter with a dielectric resonator tunable over a large bandwidth - Google Patents

Microwave filter with a dielectric resonator tunable over a large bandwidth Download PDF

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Publication number
EP0047203B1
EP0047203B1 EP81401319A EP81401319A EP0047203B1 EP 0047203 B1 EP0047203 B1 EP 0047203B1 EP 81401319 A EP81401319 A EP 81401319A EP 81401319 A EP81401319 A EP 81401319A EP 0047203 B1 EP0047203 B1 EP 0047203B1
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EP
European Patent Office
Prior art keywords
dielectric
filter
resonator
cylinder
filter according
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EP81401319A
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German (de)
French (fr)
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EP0047203A1 (en
Inventor
Jacques Delaballe
Jean Fouillet
Yves Le Nohaic
Alexandre Osias
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Thales SA
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Thomson CSF SA
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Priority to AT81401319T priority Critical patent/ATE16659T1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/207—Hollow waveguide filters
    • H01P1/208—Cascaded cavities; Cascaded resonators inside a hollow waveguide structure
    • H01P1/2084—Cascaded cavities; Cascaded resonators inside a hollow waveguide structure with dielectric resonators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P7/00—Resonators of the waveguide type
    • H01P7/10—Dielectric resonators

Definitions

  • the invention relates to microwave filters and more particularly to a microwave filter, with dielectric resonator, tunable over a large bandwidth.
  • microwave transmission equipment for military equipment for example, increasingly has to work successively on several tuning frequencies.
  • civilian fixed frequency transmission equipment can also be produced from standard tunable elements, tuning to the fixed working frequency being determined on site by adjusting these standard tunable elements.
  • the technical problem solved by the invention is the production of such tunable elements, in particular microwave filters, so that they keep determined characteristics in a tuning bandwidth as large as possible to cover with a given standard element. , a wide frequency band, without the characteristics of the element being degraded in this tuning band, in particular the response curve of the filter, the overvoltage coefficient, the coupling etc ...
  • the subject of the invention is a microwave filter with dielectric resonator, tunable over a large bandwidth, which satisfies these conditions.
  • a microwave filter with a dielectric resonator comprising a waveguide and at least one dielectric resonator coupled to the guide, is mainly characterized in that each resonator is double and comprises a first cylinder, made of dielectric material, fixed relative to the guide and having a planar end, and a second cylinder, of dielectric material, of dimensions equal to or close to those of the first cylinder, movable relative to the guide and having a planar end facing that of the first, the dielectric materials constituting the cylinders having dielectric constants of the order of 15 to 40, the distance between the two facing planar ends being variable and allowing the tuning of the filter in a bandwidth of the order of 5 to 15% of the central frequency d tuning of the filter according to the dielectric constants of the chosen materials.
  • Figures 1 and 2 show a tunable notch filter according to the invention respectively in top view, cover removed, and in section, cover closed.
  • FIG. 3 represents a tunable bandpass filter according to the invention.
  • a microwave filter is calculated as a function of a certain number of parameters including the working frequency, the width of the transmission or cut-off band, depending on whether they are band-pass filters or tape cutter.
  • the bandwidth determines the number of poles of the filter, and this number determines the number of resonators arranged along the direction of propagation as well as their spacing.
  • the resonators can be made of a dielectric material with a high dielectric constant but whose dimensions are stable as a function of the temperature. If this were not the case, the characteristics would be highly dependent on the temperature; what to avoid as much as possible.
  • the material must be of high dielectric constant for the effect of the resonator to be sufficient while keeping the dimensions fairly small, which makes it possible to limit the bulk of the materials.
  • the tuning frequency is adjusted for each resonator by a dielectric element, of dimensions close to those of the fixed element facing it, arranged at a variable distance from the first, the assembly forming the resonator.
  • the displacement of this second element modifies the tuning frequency and makes it possible to cover a wide band.
  • Figures 1 and 2 show an embodiment of a notch filter according to the invention; respectively in top view, cover removed, and in section, cover closed.
  • the housing 1 contains a coaxial line 2.
  • An input plug 3 and an output plug, 4, are fixed to the housing, the coaxial line 2 being connected to these two plugs.
  • Each resonator comprises a fixed element 5, consisting of a dielectric patch, placed at a certain distance from the coaxial line (these fixed elements being the only ones visible on the first view) glued to the bottom of the housing on a patch or a support washer such that 6.
  • mobile dielectric elements 8 roughly similar to the first come opposite the fixed dielectric elements such as 5.
  • Adjustment supports such as 9, associated with nuts 10, accessible on the outside of the cover 7, make it possible to vary the depression of these mobile dielectric elements, and therefore the distance d between the fixed element 5, and the mobile element, 8 forming the resonator.
  • the adjustment supports can be of any kind, metallic, dielectric, since they do not influence the propagation in the line from which they are quite far apart.
  • the line length s between resonators is a function of the wavelength: where n is an integer.
  • Such a filter works in the following manner.
  • the input plug is directly connected to the coaxial line 2, and excites the line following the coaxial TEM mode.
  • the housing is only used to position relative to this line the resonators which disturb the field lines by the effect of the plug circuits brought in series on the transmission line: the coupling of the resonator to this coaxial line of characteristic impedance, Z , brings back to the frequency.
  • the cross section of the dielectric patch d may be equal to, less than or greater than that of the fixed patch, the elements remaining roughly similar and of similar dimensions, as indicated above, the penetration necessary for a given variation of the tuning frequency can be adjusted.
  • the relative dimensions of these two elements are therefore not always critical. Similarly, the axial alignment of these two elements does not have to be achieved with great precision.
  • the movable tuning element made of a dielectric material like the fixed element, has a great influence on the characteristics of the resonator thus produced with the fixed element and the mobile element.
  • the frequency variation that can be obtained is of the order of 10% of the central frequency of the strip for a small stroke, of the same order as the stroke of the metal screws in agreement with the prior devices for which the frequency variation could only be of the order of 1% of the central frequency.
  • FIG. 3 represents a bandpass microwave filter, tunable over a large bandwidth, according to the invention.
  • the filter is made with dielectric resonators, the number of which determines the number of poles of the filter before a strong dielectric constant.
  • the propagation mode is a TM 11 mode, guided in the microwave circuit formed by a box provided with its cover.
  • the filter comprises a housing 10, an input dipole 30 and an output dipole 40. It also includes resonators, four in the figure, consisting of a fixed dielectric element, and a movable dielectric element.
  • the mobile elements are carried by rods also made of dielectric material, a5; accessible outside the housing by adjustment screws 90, blocked by nuts 100.
  • the input signal excites the magnetic dipole mode of the dielectric resonator closest to the input line. Transmission is carried out step by step by coupling the magnetic field lines from a dielectric resonator to the next resonator by evanescent waves, up to the output line.
  • the coupling coefficient between two consecutive resonators is a function of the distance S which separates you.
  • each resonator is in practice made up of the fixed dielectric element 5, of the mobile dielectric element which faces it, 8, and of the dielectric support rod to which the latter is linked.
  • the tuning frequency of this resonator depends on the distance d which separates the facing elements.
  • D the diameter of the cylinders and h their height
  • the variation in the tuning frequency will be all the greater the lower the height of the movable cylinder.
  • the variation in tuning frequency with respect to the center frequency of the tuning band can be of the order of 10% to 15%.
  • the dimensions of the dielectric material elements and the spacing of the resonators are chosen so that the overvoltage coefficient remains high. This is how D / s should, if possible, vary between 0.3 and 1.
  • the dielectric material chosen to constitute the resonators has as large a dielectric constant as possible, the limitation being generally imposed by the temperature resistance, so that the resonators can have as small a volume as possible taking into account the required performance (high working frequencies in the frequency bands 3.8 to 4.2 GHz and 6.4 to 7.1 GHz).
  • the variation in tuning frequency with respect to the central frequency of the band does not always need to be of the order of 10%.
  • this variation of the tuning frequency does not have to exceed 5%, it is possible to very significantly reduce the bandwidth variations due to modifications of the tuning frequency, for this the dielectric constant of the mobile elements is chosen between 15 and 20 and no longer of the order of 40, on the other hand the dielectric constant of the fixed elements remains of the order of 40; thus the disturbance brought into the electromagnetic field around the fixed elements of the resonators by the approach of the mobile elements is reduced.
  • each resonator then comprises a fixed dielectric element and a mobile dielectric element separated by a variable distance to modify the tuning frequency.

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Abstract

A dielectric resonator ultra-high frequency filter tunable in a large band width in which each dielectric resonator is constituted by a dielectric component with a high dielectric constant, which is fixed relative to an enclosure and a component made from the same dielectric material which is movable relative to the first component, in such a way that the distance d between facing surfaces of these two dielectric components varies, leading to a variation in the tuning frequency of the filter by modifying the coupling conditions.

Description

L'invention se rapporte aux filtres hyperfréquence et plus particulièrement à un filtre hyperfréquence, à résonateur diélectrique, accordable dans une grande largeur de bande.The invention relates to microwave filters and more particularly to a microwave filter, with dielectric resonator, tunable over a large bandwidth.

Dans les filtres hyperfréquence à résonateur diélectrique connus, l'accord fin de la fréquence d'accord du filtre est réalisé à l'aide d'une vis métallique dont l'enfoncement est variable. Le réglage de cette vis métallique permet alors d'ajuster la fréquence d'accord du filtre à la fréquence nominale. Cette vis métallique peut être prolongée par un doigt diélectrique destiné à rentrer dans le résonateur diélectrique, creux, comme dans le filtre décrit dans la demande de brevet japonais JP-A-54-154960. La plage de réglage ainsi obtenue est faible et ne permet pas de réaliser des filtres hyperfréquence à grande largeur de bande d'accord.In known microwave filters with a dielectric resonator, fine tuning of the tuning frequency of the filter is carried out using a metal screw whose depression is variable. The adjustment of this metal screw then makes it possible to adjust the tuning frequency of the filter to the nominal frequency. This metal screw can be extended by a dielectric finger intended to enter the hollow dielectric resonator, as in the filter described in Japanese patent application JP-A-54-154960. The adjustment range thus obtained is small and does not allow microwave filters with large tuning bandwidth to be produced.

Or, les équipements de transmission en hyperfréquence, pour les matériels militaires par exemple, ont de plus en plus à travailler successivement sur plusieurs fréquences d'accord. Par ailleurs, les équipements civils de transmission à fréquence fixe peuvent aussi être réalisés à partir d'éléments standard accordables, l'accord à la fréquence fixe de travail étant déterminé sur le site par le réglage de ces éléments standard accordables.However, microwave transmission equipment, for military equipment for example, increasingly has to work successively on several tuning frequencies. Furthermore, civilian fixed frequency transmission equipment can also be produced from standard tunable elements, tuning to the fixed working frequency being determined on site by adjusting these standard tunable elements.

Le problème technique résolu par l'invention est la réalisation de tels éléments accordables, en particulier les filtres hyperfréquence, de façon qu'ils gardent des caractéristiques déterminées dans une largeur de bande d'accord aussi grande que possible pour couvrir avec un élément standard donné, une large bande de fréquences, sans que les caractéristiques de l'élément soient dégradées dans cette bande d'accord, en particulier la courbe de réponse du filtre, le coefficient de surtension, le couplage etc...The technical problem solved by the invention is the production of such tunable elements, in particular microwave filters, so that they keep determined characteristics in a tuning bandwidth as large as possible to cover with a given standard element. , a wide frequency band, without the characteristics of the element being degraded in this tuning band, in particular the response curve of the filter, the overvoltage coefficient, the coupling etc ...

L'invention a pour objet un filtre hyperfréquence à résonateur diélectrique, accordable dans une grande largeur de bande, qui satisfasse à ces conditions.The subject of the invention is a microwave filter with dielectric resonator, tunable over a large bandwidth, which satisfies these conditions.

Suivant l'invention un filtre hyperfréquence à résonateur diélectrique comportant un guide d'onde et au moins un résonateur diélectrique couplé au guide, est principalement caractérisé en ce que chaque résonateur est double et comporte un premier cylindre, en matériau diélectrique, fixe par rapport au guide et ayant une extrémité plane, et un second cylindre, en matériau diélectrique, de dimensions égales ou voisines de celles du premier cylindre, mobile par rapport au guide et ayant une extrémité plane faisant face à celle du premier, les matériaux diélectriques constituant les cylindres ayuant des constantes diélectriques de l'ordre de 15 à 40, la distance entre les deux extrémités planes en regard étant variable et permettant l'accord du filtre dans une largeur de bande de l'ordre de 5 à 15 % de la fréquence centrale d'accord du filtre selon les constantes diélectriques des matériaux choisis.According to the invention a microwave filter with a dielectric resonator comprising a waveguide and at least one dielectric resonator coupled to the guide, is mainly characterized in that each resonator is double and comprises a first cylinder, made of dielectric material, fixed relative to the guide and having a planar end, and a second cylinder, of dielectric material, of dimensions equal to or close to those of the first cylinder, movable relative to the guide and having a planar end facing that of the first, the dielectric materials constituting the cylinders having dielectric constants of the order of 15 to 40, the distance between the two facing planar ends being variable and allowing the tuning of the filter in a bandwidth of the order of 5 to 15% of the central frequency d tuning of the filter according to the dielectric constants of the chosen materials.

L'invention sera mieux comprise et d'autres caractéristiques apparaîtront à l'aide de la description qui suit en référence aux figures annexées.The invention will be better understood and other characteristics will appear from the following description with reference to the appended figures.

Les figures 1 et 2 représentent un filtre coupe-bande accordable suivant l'invention respectivement en vue de dessus, couvercle enlevé, et en coupe, couvercle fermé.Figures 1 and 2 show a tunable notch filter according to the invention respectively in top view, cover removed, and in section, cover closed.

La figure 3 représente un filtre passe-bande accordable suivant l'invention.FIG. 3 represents a tunable bandpass filter according to the invention.

D'une manière générale, un filtre hyperfréquence est calculé en fonction d'un certain nombre de paramètres dont la fréquence de travail, la largeur de la bande de transmission ou de coupure, suivant qu'il s'agit de filtres passe-bande ou coupe-bande. La largeur de bande détermine le nombre de pôles du filtre, et ce nombre détermine le nombre de résonateurs disposés le long de la direction de propagation ainsi que leur espacement. Les résonateurs peuvent être réalisés dans un matériau diélectrique de forte constante diélectrique mais dont les dimensions sont stables en fonction de la température. Si ce n'était pas le cas, les caractéristiques seraient fortement dépendantes de la température ; ce qu'il faut, autant que possible, éviter. Le matériau doit être de constante diélectrique élevée pour que l'effet du résonateur soit suffisant tout en gardant des dimensions assez faibles, ce qui permet de limiter l'encombrement des matériels.In general, a microwave filter is calculated as a function of a certain number of parameters including the working frequency, the width of the transmission or cut-off band, depending on whether they are band-pass filters or tape cutter. The bandwidth determines the number of poles of the filter, and this number determines the number of resonators arranged along the direction of propagation as well as their spacing. The resonators can be made of a dielectric material with a high dielectric constant but whose dimensions are stable as a function of the temperature. If this were not the case, the characteristics would be highly dependent on the temperature; what to avoid as much as possible. The material must be of high dielectric constant for the effect of the resonator to be sufficient while keeping the dimensions fairly small, which makes it possible to limit the bulk of the materials.

Dans les filtres hyperfréquence suivant l'invention, le réglage de la fréquence d'accord est réalisé pour chaque résonateur par un élément en diélectrique, de dimensions voisines de celles de l'élément fixe lui faisant face, disposé à une distance variable du premier, l'ensemble formant le résonateur. Le déplacement de ce second élément modifie la fréquence d'accord et permet de couvrir une large bande.In the microwave filters according to the invention, the tuning frequency is adjusted for each resonator by a dielectric element, of dimensions close to those of the fixed element facing it, arranged at a variable distance from the first, the assembly forming the resonator. The displacement of this second element modifies the tuning frequency and makes it possible to cover a wide band.

Les figures 1 et 2 représentent un mode de réalisation d'un filtre coupe-bande suivant l'invention ; respectivement en vue de dessus, couvercle enlevé, et en coupe, couvercle fermé.Figures 1 and 2 show an embodiment of a notch filter according to the invention; respectively in top view, cover removed, and in section, cover closed.

Les mêmes références sur ces deux figures désignent les mêmes éléments.The same references in these two figures designate the same elements.

Sur la première vue, le boîtier 1 renferme une ligne coaxiale 2. Une fiche d'entrée 3 et une fiche de sortie, 4, sont fixées au boîtier, la ligne coaxiale 2 étant connectée à ces deux fiches.In the first view, the housing 1 contains a coaxial line 2. An input plug 3 and an output plug, 4, are fixed to the housing, the coaxial line 2 being connected to these two plugs.

L'exemple de réalisation représenté est un filtre à trois résonateurs. Chaque résonateur comporte un élément fixe 5, constitué d'une pastille en diélectrique, placé à une certaine distance de ligne coaxiale (ces éléments fixes étant les seuls visibles sur la première vue) collé au fond du boîtier sur une pastille ou une rondelle support telle que 6. Lorsque le couvercle 7 vient refermer l'ensemble, des éléments diélectriques mobiles 8, à peu près semblables aux premiers viennent en face des éléments diélectriques fixes tels que 5. Des supports de réglage tels que 9, associés à des écrous 10, accessibles sur la face extérieure du couvercle 7, permettent de faire varier l'enfoncement de ces éléments diélectriques mobiles, et donc la distance d entre l'élément fixe 5, et l'élément mobile, 8 formant le résonateur. Les supports de réglage peuvent être de nature quelconque, métalliques, diélectriques, car ils n'influent pas sur la propagation dans la ligne de laquelle ils sont assez éloignés. La longueur de ligne s entre résonateurs est fonction de la longueur d'onde :

Figure imgb0001
où n est entier. Un tel filtre fonctionne de la manière suivante. La fiche d'entrée est directement connectée à la ligne coaxiale 2, et excite la ligne suviant le mode TEM, coaxial. Le boîtier sert seulement à positionner par rapport à cette ligne les résonateurs qui viennent perturber les lignes de champ par l'effet des circuits bouchon ramenés en série sur la ligne de transmission : le couplage du résonateur à cette ligne coaxiale d'impédance caractéristique, Z,, ramène à la fréquence. d'accord fa un circuit bouchon et le circuit se comporte alors comme un circuit ouvert et amène une atténuation d'amplitude A à cette fréquence fa. La section de la pastille diélectrique d:accord peut être égale, inférieure ou supérieure à celle de la pastille fixe, les éléments restant à peu près semblables et de dimensions voisines, comme indiqué ci-dessus l'enfoncement nécessaire pour une variation donnée de la fréquence d'accord pouvant être ajusté. Les dimensions relatives de ces deux éléments ne sont donc pas toujours critiques. De même l'alignement axial de ces deux éléments n'a pas à être réalisé avec une grande précision.The embodiment shown is a filter with three resonators. Each resonator comprises a fixed element 5, consisting of a dielectric patch, placed at a certain distance from the coaxial line (these fixed elements being the only ones visible on the first view) glued to the bottom of the housing on a patch or a support washer such that 6. When the cover 7 closes the assembly, mobile dielectric elements 8, roughly similar to the first come opposite the fixed dielectric elements such as 5. Adjustment supports such as 9, associated with nuts 10, accessible on the outside of the cover 7, make it possible to vary the depression of these mobile dielectric elements, and therefore the distance d between the fixed element 5, and the mobile element, 8 forming the resonator. The adjustment supports can be of any kind, metallic, dielectric, since they do not influence the propagation in the line from which they are quite far apart. The line length s between resonators is a function of the wavelength:
Figure imgb0001
 where n is an integer. Such a filter works in the following manner. The input plug is directly connected to the coaxial line 2, and excites the line following the coaxial TEM mode. The housing is only used to position relative to this line the resonators which disturb the field lines by the effect of the plug circuits brought in series on the transmission line: the coupling of the resonator to this coaxial line of characteristic impedance, Z ,, brings back to the frequency. agree f has a plug circuit and the circuit then behaves like an open circuit and brings an attenuation of amplitude A at this frequency f a . The cross section of the dielectric patch d: accord may be equal to, less than or greater than that of the fixed patch, the elements remaining roughly similar and of similar dimensions, as indicated above, the penetration necessary for a given variation of the tuning frequency can be adjusted. The relative dimensions of these two elements are therefore not always critical. Similarly, the axial alignment of these two elements does not have to be achieved with great precision.

L'élément d'accord mobile, réalisé dans un matériau diélectrique comme l'élément fixe, a une grande influence sur les caractéristiques du résonateur ainsi réalisé avec l'élément fixe et l'élément mobile. Dans le cas où ces deux éléments sont réalisés dans un même matériau ayant une constante diélectrique s de l'ordre de 40, la variation de fréquence susceptible d'être obtenue est de l'ordre de 10 % de la fréquence centrale de la bande pour une course faible, du même ordre que la course des vis métalliques d'accord des dispositifs antérieurs pour lesquels la variation de fréquence ne pouvait être que de l'ordre de 1 % de la fréquence centrale.The movable tuning element, made of a dielectric material like the fixed element, has a great influence on the characteristics of the resonator thus produced with the fixed element and the mobile element. In the case where these two elements are made of the same material having a dielectric constant s of the order of 40, the frequency variation that can be obtained is of the order of 10% of the central frequency of the strip for a small stroke, of the same order as the stroke of the metal screws in agreement with the prior devices for which the frequency variation could only be of the order of 1% of the central frequency.

Le matériau diélectrique peut être, à titre d'exemple non limitatif, du titanate de zirconium dont la constante diélectrique est ε = 36 et qui est suffisamment stable en température.The dielectric material can be, by way of nonlimiting example, zirconium titanate whose dielectric constant is ε = 36 and which is sufficiently stable in temperature.

La figure 3 représente un filtre hyperfréquence passe-bande, accordable dans une grande largeur de bande, suivant l'invention.FIG. 3 represents a bandpass microwave filter, tunable over a large bandwidth, according to the invention.

Comme dans le cas précédent, le filtre est réalisé avec des résonateurs diélectriques, dont le nombre détermine le nombre de pôles du filtre avant une forte constante diélectrique. Mais dans un tel filtre, le mode de propagation est un mode TM11, guidé dans le circuit micro-onde formé par un boîtier muni de son couvercle.As in the previous case, the filter is made with dielectric resonators, the number of which determines the number of poles of the filter before a strong dielectric constant. But in such a filter, the propagation mode is a TM 11 mode, guided in the microwave circuit formed by a box provided with its cover.

Le filtre comporte un boîtier 10, un dipôle d'entrée 30 et un dipôle de sortie 40. Il comporte également des résonateurs, quatre sur la figure, constitués d'un élément diélectrique fixe, et d'un élément mobile diélectrique. Les éléments mobiles sont portés par des tiges également en matériau diélectrique, a5; accessibles à l'extérieur du boîtier par des vis de réglage 90, bloquées par des écrous 100. Le signal d'entrée excite le mode dipolaire magnétique du résonateur diélectrique le plus proche de la ligne d'entrée. La transmission est réalisée de proche en proche par le couplage des lignes de champ magnétique d'un résonateur diélectrique au résonateur suivant par des ondes évanescentes, jusqu'à la ligne de sortie. Le coefficient de couplage entre deux résonateurs consécutifs est fonction de la distance S qui tes sépare. Dans ce filtre chaque résonateur est en pratique constitué de l'élément diélectrique fixe 5, de l'élément diélectrique mobile qui lui fait face, 8, et de la tige diélectrique support à laquelle ce dernier est lié. La fréquence d'accord de ce résonateur dépend de la distance d qui sépare les éléments en vis-à-vis. Le champ électrique existant dans l'intervalle entre les deux cylindres en matériau diélectrique est d'autant plus grand que le rapport D/h (D étant le diamètre des cylindres et h leur hauteur) est grand. A diamètre constant, la variation de la fréquence d'accord sera d'autant plus importante que la hauteur du cylindre mobile est faible. Comme dans le cas précédent, la variation de fréquence d'accord par rapport à la fréquence centrale de la bande d'accord peut être de l'ordre de 10 %à 15 %. Par exemple, le mode de réalisation représenté sur la figure 2 a permis de réaliser, autour de 7 GHz, une variation de la fréquence d'accord dans une bande de 500 MHz avec des pastilles diélectriques en titanate de zirconium (s = 36).The filter comprises a housing 10, an input dipole 30 and an output dipole 40. It also includes resonators, four in the figure, consisting of a fixed dielectric element, and a movable dielectric element. The mobile elements are carried by rods also made of dielectric material, a5; accessible outside the housing by adjustment screws 90, blocked by nuts 100. The input signal excites the magnetic dipole mode of the dielectric resonator closest to the input line. Transmission is carried out step by step by coupling the magnetic field lines from a dielectric resonator to the next resonator by evanescent waves, up to the output line. The coupling coefficient between two consecutive resonators is a function of the distance S which separates you. In this filter each resonator is in practice made up of the fixed dielectric element 5, of the mobile dielectric element which faces it, 8, and of the dielectric support rod to which the latter is linked. The tuning frequency of this resonator depends on the distance d which separates the facing elements. The greater the electric field existing in the interval between the two cylinders of dielectric material, the greater the ratio D / h (D being the diameter of the cylinders and h their height). At constant diameter, the variation in the tuning frequency will be all the greater the lower the height of the movable cylinder. As in the previous case, the variation in tuning frequency with respect to the center frequency of the tuning band can be of the order of 10% to 15%. For example, the embodiment represented in FIG. 2 made it possible to achieve, around 7 GHz, a variation of the tuning frequency in a band of 500 MHz with dielectric pellets made of zirconium titanate (s = 36).

Les dimensions des éléments en matériau diélectrique et l'espacement des résonateurs sont choisis pour que le coefficient de surtension reste élevé. C'est ainsi que D/s doit, si possible, varier entre 0,3 et 1.The dimensions of the dielectric material elements and the spacing of the resonators are chosen so that the overvoltage coefficient remains high. This is how D / s should, if possible, vary between 0.3 and 1.

Du fait que le volume des résonateurs n'est pas sensiblement modifié dans la gamme d'accord, les conditions de couplage entre résonateurs restent à peu près inchangées dans toute la gamme d'accord et il n'y a donc que peu de perturbations introduites du fait de cet accord.Since the volume of the resonators is not appreciably modified in the tuning range, the coupling conditions between resonators remain almost unchanged throughout the tuning range and there is therefore only a few disturbances introduced because of this agreement.

Comme dans le premier mode de réalisation, le matériau diélectrique choisi pour constituer les résonateurs a une constante diélectrique aussi grande que possible, la limitation étant en général imposée par la tenue en température, de sorte que les résonateurs puissent avoir un volume aussi faible que possible compte tenu des performances requises (fréquences de travail élevées dans les bandes de fréquence 3,8 à 4,2 GHz et 6,4 à 7,1 GHz).As in the first embodiment, the dielectric material chosen to constitute the resonators has as large a dielectric constant as possible, the limitation being generally imposed by the temperature resistance, so that the resonators can have as small a volume as possible taking into account the required performance (high working frequencies in the frequency bands 3.8 to 4.2 GHz and 6.4 to 7.1 GHz).

Il est à noter que la variation de fréquence d'accord par rapport à la fréquence centrale de la bande n'a pas toujours besoin d'être de l'ordre de 10%. Pour de telles applications il est possible de concevoir le filtre selon l'invention de manière à améliorer la stabilité de ses caractéristiques, en particulier de sa largeur de bande. Dans le cas, par exemple, où cette variation de la fréquence d'accord n'a pas à dépasser 5 %, il est possible de réduire très sensiblement les variations de bande passante dues aux modifications de la fréquence d'accord, pour cela la constante diélectrique des éléments mobiles est choisie entre 15 et 20 et non plus de l'ordre de 40, par contre la constante diélectrique des éléments fixes reste de l'ordre de 40 ; ainsi la perturbation amenée dans le champ électromagnétique autour des éléments fixes des résonateurs par l'approche des éléments mobiles est réduite. Des expériences ont montré que, dans les conditions précitées, c'est-à-dire pour une variation de la fréquence d'accord n'ayant pas à dépasser 5 %, et des éléments mobiles, à constante diélectrique comprise entre 15 et 20, les variations de la largeur de bande du filtre étaient réduites dans un rapport de l'ordre de 2 à 3 par rapport aux mêmes filtres mais avec des éléments mobiles à constante diélectrique de l'ordre de 40.It should be noted that the variation in tuning frequency with respect to the central frequency of the band does not always need to be of the order of 10%. For such applications it is possible to design the filter according to the invention so as to improve the stability of its characteristics, in particular of its bandwidth. In the case, for example, where this variation of the tuning frequency does not have to exceed 5%, it is possible to very significantly reduce the bandwidth variations due to modifications of the tuning frequency, for this the dielectric constant of the mobile elements is chosen between 15 and 20 and no longer of the order of 40, on the other hand the dielectric constant of the fixed elements remains of the order of 40; thus the disturbance brought into the electromagnetic field around the fixed elements of the resonators by the approach of the mobile elements is reduced. Experiments have shown that, under the aforementioned conditions, that is to say for a variation of the tuning frequency not having to exceed 5%, and mobile elements, with dielectric constant between 15 and 20, the variations in the bandwidth of the filter were reduced in a ratio of the order of 2 to 3 compared to the same filters but with mobile elements with dielectric constant of the order of 40.

L'invention n'est pas limitée aux modes de réalisation décrits. Elle peut être mise en oeuvre dans tout filtre hyperfréquence accordable dans lequel la fonction de filtrage est réalisée par des résonateurs diélectriques ; chaque résonateur comporte alors un élément diélectrique fixe et un élément diélectrique mobile séparés d'une distance variable pour modifier la fréquence d'accord.The invention is not limited to the embodiments described. It can be implemented in any tunable microwave filter in which the filtering function is performed by dielectric resonators; each resonator then comprises a fixed dielectric element and a mobile dielectric element separated by a variable distance to modify the tuning frequency.

Claims (6)

1. A dielectric resonator microwave frequency filter, comprising a waveguide and at least one dielectric resonator coupled to the guide, characterized in that each resonator is a twin resonator and comprises a first cylinder (5) made from a dielectric material, fixed relative to the guide and having a plane end, and a second cylinder (8) made from a dielectric material of dimensions equal to or near those of the first cylinder, this cylinder being movable relative to the guide and having a plane end facing that of the first cylinder, the dielectric materials constituting the cylinders having dielectric constants from about 15 to 40, the distance between the two facing plane ends being variable and permitting the filter to be tuned in a band width of 5 to 15 % of the central tuning frequency of the filter according to the dielectric constants of the chosen materials.
2. A filter according to claim 1, characterized in that the two cylinders (5 and 8) are constituted by the same dielectric material with a dielectric constant of about 40, having a thermal behaviour such that the dimensions of the elements are not significantly modified when the temperature varies.
3. A filter according to claim 2, characterized in that the dielectric material from which the resonator is made is zirconium titanate.
4. A filter according to claim 1, characterized in that the dielectric constant of the mobile cylinder is approximately twice lower than that, near 40, of the fixed cylinder.
5. A filter according to claim 1, characterized in that in the case of a band pass filter the waveguide is the box (10) of the actual filter, the resonators thus being placed within the guide modifying by their movable elements (8) the coupling conditions within the guide and the corresponding tuning frequency.
6. A filter according to claim 1, characterized in that in the case of a band stop filter the waveguide is a coaxial line (2) located within the box (1, 7), the box also supporting the fixed (5) and movable elements (8) of the resonators, and the axis of each resonator being placed at a given distance from said line, the resonators thus placed in the vicinity of the line bringing on to that line band stop circuits with a frequency variable with the position of the movable element (8) compared with that of the fixed element (5).
EP81401319A 1980-08-29 1981-08-19 Microwave filter with a dielectric resonator tunable over a large bandwidth Expired EP0047203B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT81401319T ATE16659T1 (en) 1980-08-29 1981-08-19 WIDE BANDWIDTH TUNABLE MICROWAVE FILTER WITH A DIELECTRIC RESONATOR.

Applications Claiming Priority (2)

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FR8018771 1980-08-29
FR8018771A FR2489605A1 (en) 1980-08-29 1980-08-29 DIELECTRIC RESONATOR HYPERFREQUENCE FILTER, TUNABLE IN A BIG BANDWIDTH, AND CIRCUIT COMPRISING SUCH A FILTER

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EP0047203A1 EP0047203A1 (en) 1982-03-10
EP0047203B1 true EP0047203B1 (en) 1985-11-21

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US (1) US4459570A (en)
EP (1) EP0047203B1 (en)
JP (1) JPS5776901A (en)
AT (1) ATE16659T1 (en)
DE (1) DE3172989D1 (en)
FR (1) FR2489605A1 (en)

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Also Published As

Publication number Publication date
DE3172989D1 (en) 1986-01-02
EP0047203A1 (en) 1982-03-10
ATE16659T1 (en) 1985-12-15
FR2489605B1 (en) 1984-05-04
FR2489605A1 (en) 1982-03-05
JPS5776901A (en) 1982-05-14
US4459570A (en) 1984-07-10

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