EP0373028B1 - Passive band-pass filter - Google Patents

Passive band-pass filter Download PDF

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Publication number
EP0373028B1
EP0373028B1 EP89403257A EP89403257A EP0373028B1 EP 0373028 B1 EP0373028 B1 EP 0373028B1 EP 89403257 A EP89403257 A EP 89403257A EP 89403257 A EP89403257 A EP 89403257A EP 0373028 B1 EP0373028 B1 EP 0373028B1
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EP
European Patent Office
Prior art keywords
filter
impedance
microstrips
input
substrate
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EP89403257A
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German (de)
French (fr)
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EP0373028A1 (en
Inventor
Henri Budan
Patrick Algani
Alain Grosjean
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Thomson Hybrides
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Thomson Hybrides
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Priority claimed from FR8815664A external-priority patent/FR2639776B1/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
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/203—Strip line filters
    • H01P1/20327—Electromagnetic interstage coupling
    • H01P1/20336—Comb or interdigital filters

Definitions

  • the present invention relates to a passive bandpass filter, produced using hybrid circuit technology.
  • the structure of this passive filter makes it possible to adapt it, in the microwave domain, to the desired central frequency with a good rate of rejection of the lower frequencies. It is produced in the form of microstrips on a ceramic substrate.
  • FIG. 1 An example is given in FIG. 1, on which two combs of interdigitated microstrips 1 and 2 are deposited on a substrate 3.
  • the microstrips have a length ⁇ g / 4, ⁇ g being the wavelength guided in a microstrip, and their point common is joined to the ground plane which is on the rear face of the substrate 3.
  • the signal input E is applied to a free end of the first microstrip of a first comb, and the filtered output S is collected at one end free of the last microstrip of a second comb.
  • These known filters have two types of drawbacks. First, they occupy a relatively important place.
  • hybrid circuit techniques are influenced by the density of integrated circuits that are reported on a hybrid circuit substrate, especially VLSIs with very high integration density, and the components reported on a hybrid circuit must also be densified, especially if they operate at microwave frequencies.
  • the passive bandpass filter according to the invention eliminates these two drawbacks. It occupies only a small surface on a dielectric substrate, and its response curve is clear: outside the bandwidth, it virtually cuts outside frequencies, especially lower frequencies.
  • microstrip line It consists of a plurality of microstrip lines, mutually parallel, all the ends of which on the same side are joined to the ground plane carried by the opposite face of the dielectric substrate.
  • the signal input E is applied to the first microstrip and the output S of the filtered signal is collected on the last microstrip.
  • at least two non-neighboring microstrip lines therefore not coupled by electromagnetics, are coupled by an impedance, self or capacitance, reported on the substrate.
  • the distances from the ground points, to which the input, output and impedance connections are connected, are used to adjust the input and output impedances and to modify the shape of the filter response curve. .
  • This type of bandpass filter makes it possible to obtain a response curve for the passband whose flanks are relatively steep, because the coupling impedance cancels a term from the denominator of the equation of transfer through the filter.
  • a first improvement to this bandpass filter consists in providing it with an additional impedance, at its input, which cancels a second term in the transfer equation, and makes the sides of the response curve more abrupt.
  • a second improvement consists in folding the band-pass filter over itself, in the same way as one closes a book. This makes it a smaller component, the dimensions of which are in accordance with its environment of integrated circuits or miniaturized components.
  • the invention relates to a passive bandpass filter, produced by means of microstrips deposited on one face of a dielectric substrate, comprising at least three microstrips, parallel to each other, one end of which is joined by means appropriate to the ground plane carried by the second face of the substrate, at least two of said microstrips, not neighboring on the substrate, being coupled by a coupling impedance Z, which is a self or a capacitance, this filter being characterized in that, with a view to reducing its bulk, it is folded back on itself along a median line perpendicular to the microstrips, and jumpers allowing the passive filter to be fixed by its access and ground plane connections.
  • the passive filter according to the invention is supported by a substrate 4, one face of which is metallized at 5 to form a ground plane.
  • This substrate is made of ceramic, alumina or materials with a high dielectric constant (9 ⁇ ⁇ ⁇ 100), and its thickness is between 0.3 and 1 mm approximately.
  • microstrip lines On the non-metallized face of this substrate 4 are deposited a plurality of microstrip lines, parallel to each other. At least three microbands 6, 7, 8 are required so that at least two of them are not neighboring. By one of their ends, but on the same side for all the microstrip lines, these are joined to the ground plane 5: in the figure, this connection is made by means of metallized holes 9, but other known means are possible.
  • These lines microstrips are produced either by thick film technology, by screen printing, or by thin film technology, by vacuum evaporation.
  • the input E of the signal to be filtered is applied laterally to the first band 6 of the series by means of a metallization 10 which, generally, is oriented towards the edge of the substrate 4, or towards the signal generator if the latter is integrated on the same substrate.
  • the filtered output signal S is collected on a metallization 11, lateral on the last strip of the series.
  • the metallizations 10 and 11 are, respectively, at distances x1 and x2 from the ends to the mass of the two microstrip lines considered.
  • two non-neighboring microstrip lines are coupled by an impedance Z 12, joined by two wires or metallizations 13 and 14 at two points, respectively, of the first strip 6 and the second band 8 not neighboring.
  • the impedance Z is either a self or a capacitor, deposited on the substrate 4 in the form of a discrete component or in the form of thick layers.
  • the wires or metallizations 13 and 14 are fixed on the two non-neighboring microstrip lines at distances x3 and x4, respectively, from the ends to the mass of the two microstrip lines considered.
  • the displacement of the input metallization 10, by varying x1, makes it possible to adapt the impedance to 75 or 100 ohms, or to some other value.
  • the distance x2 makes it possible to adjust the output impedance of the passive filter.
  • the central frequency of the bandpass filter is adjusted by the length L of the microstrip lines.
  • the bandwidth of the filter is adjusted by the width "l" of the lines, and by the spacing "d” between lines.
  • the spacing "d” plays the same role as the width "l” but more important.
  • microstrips and / or narrow spacings give wide bandwidths and low TOS.
  • Narrow microstrips and / or wide spacings give narrow bandwidths and high TOS.
  • the distances x3 and x4 make it possible to optimize the coupling between two non-neighboring microstrips: they define the input impedance and the output impedance linked to the capacitance or self Z 12, and are calculated according to the specifications required for the filtered.
  • a filter according to the invention of one or more uncoupled microstrips improves the rejection of frequencies outside the central frequency, and makes the response curve more "square"".
  • a filter according to the invention can comprise more than three microstrips as shown in FIG. 2. Let us take the case of a filter with 4 microstrips, which will be called A, B, C, D. Different couplings can be carried out: A-D coupling or A-C and B-D coupling. The choice is made according to the specifications imposed on the filter.
  • FIG. 4 A first improvement to the filter according to the invention is shown in FIG. 4. They consist in adding to the input E of the filter a double impedance Z1 and Z2.
  • the impedance Z1 is provided by a microstrip 17, finer and of higher impedance than the microstrips 6,7,8 of the filter. Typically, it is about 200 micrometers wide, and a length equal to ⁇ / 4. Unlike other microstrips, it has no end joined to the ground plane 5.
  • this impedance Connected in parallel on the input circuit, this impedance resonates for the rejection frequency. It cancels a second term in the filter transfer equation, which completes the action of the impedance 12 of the filter, which cancels a first term.
  • Impedance 17 can also be achieved by a line and a capacity.
  • Impedance Z2 corrects the deterioration of the input impedance, brought by Z1. Placed in series between the input E of the filter, and the connection point on the first microstrip 6, it can be performed either by a line 18, or by a line and a capacitor.
  • the characteristic impedances of 17 and 18 are interactive, and calculated to obtain the desired slope and rejection level, on the response curve of the filter.
  • the second improvement makes it possible to produce a bandpass filter even smaller than that of the main invention.
  • a filter according to the invention only the substrate 4 is reported with its ground plane 5, and three microstrips 6,7,8 with an input E and an output S.
  • this filter could comprise more than three bands , and the impedances 17 and 18 of the first improvement.
  • the second improvement consists in cutting the filter along a line 19 which, perpendicular to the microstrips 6,7,8, separates it into two equal parts, in the direction of the length of the substrate 4. The two parts are then, as shown on the right of the figure, brazed one on the other, by their faces supporting the ground plane 5.
  • microstrips 6,7,8, the halves of which are now carried by the upper and lower faces of a sandwich including in its center a ground plane 5, are reformed by means of jumpers or metallizations 20, on the side of the sandwich: the electrical continuity of each microstrip is thus ensured.
  • microstrips must be slightly shorter in length than ⁇ g / 4: the length of the jumpers 20, equal to twice the thickness of the substrate 4, reduces this length to ⁇ g / 4.
  • jumpers 21, or other suitable external connections are fixed to the edges of the sandwich.
  • a minimum of three jumpers 21 is required, corresponding to the input E, the output S and the ground plane 5.
  • These jumpers are provided with means 22 for either implanting the component in the holes of a substrate, or mounting it in SMD (surface mountable components).
  • SMD surface mountable components
  • This type of passive filter is used in information processing systems, for example in radio telephones, in the range 0.5 to 10 GHz, with a bandwidth of 0.9 to 1 GHz.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)
  • Filters And Equalizers (AREA)
  • Networks Using Active Elements (AREA)

Abstract

The invention relates to a passive band-pass filter constructed by means of microstrips on a dielectric substrate (4). This filter is composed of at least three microstrips (6,7,8), which are parallel to one another and one end of which is grounded (5). At least two microstrips (6,8) which are not adjacent are coupled by a coupling impedance Z (12). The distances x1, x2, x3, x4 of fixings on the microstrips of the input (10), coupling impedance Z (12) and output (11) regulate the impedances and the characteristics of the filter. A first improvement permits the narrowing of the pass band, by means of a high impedance (17) in parallel on the input (E) of the filter. A second impedance (18), in series on the input, corrects the input impedance modification. A second improvement consists in folding the filter back on itself, in order to reduce its space requirement. Continuity of the microstrip lines (6,7,8) is ensured by metallised coatings (20) on the flanks of the substrate (4), and jumper links (21) provide the channels for access to the filter and its fixing means.

Description

La présente invention concerne un filtre passif passe-bande, réalisé selon la technologie des circuits hybrides. La structure de ce filtre passif permet de l'adapter, dans le domaine des hyperfréquences, à la fréquence centrale recherchée avec un bon taux de réjection des fréquences inférieures. Il est réalisé sous forme de microbandes sur un substrat céramique.The present invention relates to a passive bandpass filter, produced using hybrid circuit technology. The structure of this passive filter makes it possible to adapt it, in the microwave domain, to the desired central frequency with a good rate of rejection of the lower frequencies. It is produced in the form of microstrips on a ceramic substrate.

Différents types de filtres passe-bande sont connus, réalisés en microbandes sur un substrat céramique, selon les technologies couche épaisse ou couche mince. Un example en est donné en figure 1, sur laquelle deux peignes de microbandes interdigités 1 et 2 sont déposés sur un substrat 3. Les microbandes ont une longueur λg/4, λg étant la longueur d'onde guidée dans une microbande, et leur point commun est réuni au plan de masse qui se trouve sur la face arrière du substrat 3. L'entrée E du signal est appliquée à une extrémité libre de la première microbande d'un premier peigne, et la sortie S filtrée est recueillie à une extrémité libre de la dernière microbande d'un second peigne. Ces filtres connus ont deux types d'inconvénients. D'abord, ils occupent une place relativement importante. Actuellement, les techniques de circuits hybrides subissent l'influence de la densité des circuits intégrés qui sont rapportés sur un substrat de circuit hybride, surtout les VLSI à très haute densité d'intégration, et les composants rapportés sur un circuit hybride doivent eux aussi être densifiés, surtout s'ils fonctionnent en hyperfréquences.Different types of bandpass filters are known, produced in microstrips on a ceramic substrate, according to the thick layer or thin layer technologies. An example is given in FIG. 1, on which two combs of interdigitated microstrips 1 and 2 are deposited on a substrate 3. The microstrips have a length λg / 4, λg being the wavelength guided in a microstrip, and their point common is joined to the ground plane which is on the rear face of the substrate 3. The signal input E is applied to a free end of the first microstrip of a first comb, and the filtered output S is collected at one end free of the last microstrip of a second comb. These known filters have two types of drawbacks. First, they occupy a relatively important place. Currently, hybrid circuit techniques are influenced by the density of integrated circuits that are reported on a hybrid circuit substrate, especially VLSIs with very high integration density, and the components reported on a hybrid circuit must also be densified, especially if they operate at microwave frequencies.

Ensuite, ces filtres connus ont une courbe de réponse qui, pour une perte d'insertion donnée, n'est pas suffisamment carrée : c'est une courbe en cloche dont les flancs ne sont pas assez abrupts.Then, these known filters have a response curve which, for a given insertion loss, is not square enough: it is a bell curve whose flanks are not steep enough.

Le filtre passif passe-bande selon l'invention permet de supprimer ces deux inconvénients. Il n'occupe qu'une faible surface sur un substrat diélectrique, et sa courbe de réponse est franche : en dehors de la bande passante, elle coupe franchement les fréquences extérieures, surtout les fréquences plus faibles.The passive bandpass filter according to the invention eliminates these two drawbacks. It occupies only a small surface on a dielectric substrate, and its response curve is clear: outside the bandwidth, it frankly cuts outside frequencies, especially lower frequencies.

Il est constitué d'une pluralité de lignes microbandes, parallèles entre elles, dont toutes les extrémités d'un même côté sont réunies au plan de masse porté par la face opposée du substrat diélectrique. L'entrée E du signal est appliquée sur la première microbande et la sortie S du signal filtré est recueillie sur la dernière microbande. Dans cette série de microbandes, au moins deux lignes microbandes non voisines, donc non couplées par électromagnétique, sont couplées par une impédance, self ou capacité, rapportée sur le substrat. Les distances, par rapport aux points de masse, auxquelles sont connectées l'entrée, la sortie et les connexions de l'impédance, permettent de régler les impédances d'entrée, de sortie et de modifier la forme de la courbe de réponse du filtre.It consists of a plurality of microstrip lines, mutually parallel, all the ends of which on the same side are joined to the ground plane carried by the opposite face of the dielectric substrate. The signal input E is applied to the first microstrip and the output S of the filtered signal is collected on the last microstrip. In this series of microstrips, at least two non-neighboring microstrip lines, therefore not coupled by electromagnetics, are coupled by an impedance, self or capacitance, reported on the substrate. The distances from the ground points, to which the input, output and impedance connections are connected, are used to adjust the input and output impedances and to modify the shape of the filter response curve. .

Ce type de filtre passe-bande permet d'obtenir une courbe de réponse pour la bande passante dont les flancs sont relativement abrupts, car l'impédance de couplage annule un terme du dénominateur de l'équation de transfert à travers le filtre.This type of bandpass filter makes it possible to obtain a response curve for the passband whose flanks are relatively steep, because the coupling impedance cancels a term from the denominator of the equation of transfer through the filter.

Un premier perfectionnement à ce filtre passe-bande consiste à la munir d'une impédance supplémentaire, à son entrée, qui annule un second terme dans l'équation de transfert, et rend les flancs de la courbe de réponse plus abrupts.A first improvement to this bandpass filter consists in providing it with an additional impedance, at its input, which cancels a second term in the transfer equation, and makes the sides of the response curve more abrupt.

Un second perfectionnement consiste à replier le filtre passe-bande sur lui même, à la façon dont on referme un livre. Cela permet d'en faire un composant plus petit, dont les dimensions sont en accord avec son environnement de circuits intégrés ou de composants miniaturisés.A second improvement consists in folding the band-pass filter over itself, in the same way as one closes a book. This makes it a smaller component, the dimensions of which are in accordance with its environment of integrated circuits or miniaturized components.

De façon plus précise, l'invention concerne un filtre passif passe-bande, réalisé au moyen de microbandes déposées sur une face d'un substrat diélectrique, comprenant au moins trois microbandes, parallèles en elles, dont une extrémité est réunie par des moyens appropriés au plan de masse porté par la seconde face du substrat, au moins deux des dites microbandes, non voisines sur le substrat, étant couplées par une impédance Z de couplage, qui est une self ou une capacité, ce filtre étant caractérisé en ce que, en vue de diminuer son encombrement, il est replié sur lui-même selon une ligne médiane perpendiculaire aux microbandes , et des cavaliers permettant de fixer le filtre passif par ses connexions d'accès et de plan de masse.More specifically, the invention relates to a passive bandpass filter, produced by means of microstrips deposited on one face of a dielectric substrate, comprising at least three microstrips, parallel to each other, one end of which is joined by means appropriate to the ground plane carried by the second face of the substrate, at least two of said microstrips, not neighboring on the substrate, being coupled by a coupling impedance Z, which is a self or a capacitance, this filter being characterized in that, with a view to reducing its bulk, it is folded back on itself along a median line perpendicular to the microstrips, and jumpers allowing the passive filter to be fixed by its access and ground plane connections.

L'invention sera mieux comprise par la description d un exemple d'application, faite en s'appuyant sur les figures jointes en annexe, qui représentent :

  • fig. 1 : schéma d'un filtre passif passe-bande selon l'art connu, déjà exposé,
  • fig. 2 : schéma d'un filtre passif passe-bande selon l'invention,
  • fig. 3 : courbe de réponse, en fonction de la fréquence, d'un filtre selon l'invention, sans ou avec impédance de couplage,
  • fig. 4 : vue en plan du filtre passe-bande, constituant un premier perfectionnement à l'invention,
  • fig. 5 : vue de 3/4 dans l'espace du filtre, avant et après pliage, constituant un second perfectionnement à l'invention.
The invention will be better understood from the description of an example of application, made on the basis of the appended figures, which represent:
  • fig. 1: diagram of a passive bandpass filter according to the known art, already exposed,
  • fig. 2: diagram of a passive bandpass filter according to the invention,
  • fig. 3: response curve, as a function of frequency, of a filter according to the invention, with or without coupling impedance,
  • fig. 4: plan view of the bandpass filter, constituting a first improvement to the invention,
  • fig. 5: 3/4 view in the filter space, before and after folding, constituting a second improvement to the invention.

Le filtre passif selon l'invention, représenté en figure 2, est supporté par un substrat 4, dont une face est métallisée en 5 pour former un plan de masse. Ce substrat est en céramique, alumine ou matériaux à haute constante diélectrique (9 ≦ ε ≦100), et son épaisseur est comprise entre 0,3 et 1 mm environ.The passive filter according to the invention, shown in FIG. 2, is supported by a substrate 4, one face of which is metallized at 5 to form a ground plane. This substrate is made of ceramic, alumina or materials with a high dielectric constant (9 ≦ ε ≦ 100), and its thickness is between 0.3 and 1 mm approximately.

Sur la face non métallisée de ce substrat 4 sont déposées une pluralité de lignes microbandes, parallèles entre elles. Il faut au moins trois microbandes 6, 7, 8 pour que deux d'entre elles, au moins, ne soient pas voisines. Par l'une de leurs extrémités, mais du même côté pour toutes les lignes microbandes, celles-ci sont réunies au plan de masse 5 : sur la figure, cette liaison est opérée au moyen de trous métallisés 9, mais d'autres moyens connus sont envisageables. Ces lignes microbandes sont réalisées soit par la technologie en couche épaisse, par sérigraphie, soit par la technologie en couche mince, par évaporation sous vide.On the non-metallized face of this substrate 4 are deposited a plurality of microstrip lines, parallel to each other. At least three microbands 6, 7, 8 are required so that at least two of them are not neighboring. By one of their ends, but on the same side for all the microstrip lines, these are joined to the ground plane 5: in the figure, this connection is made by means of metallized holes 9, but other known means are possible. These lines microstrips are produced either by thick film technology, by screen printing, or by thin film technology, by vacuum evaporation.

Les lignes microbandes ont une longueur L = λg/4, λg étant la longueur d'onde guidée, et une largeur "l"; elles sont séparées d'une distance "d".The microstrip lines have a length L = λg / 4, λg being the guided wavelength, and a width "l"; they are separated by a distance "d".

L'entrée E du signal à filtrer est appliquée latéralement à la première bande 6 de la série au moyen d'une métallisation 10 qui, généralement, est orientée vers le bord du substrat 4, ou vers le générateur de signal si celui-ci est intégré sur le même substrat. De la même façon le signal de sortie S, filtré, est recueilli sur une métallisation 11, latérale sur la dernière bande de la série. Les métallisations 10 et 11 sont, respectivement, à des distances x₁ et x₂ des extémités à la masse des deux lignes microbandes considérées.The input E of the signal to be filtered is applied laterally to the first band 6 of the series by means of a metallization 10 which, generally, is oriented towards the edge of the substrate 4, or towards the signal generator if the latter is integrated on the same substrate. In the same way, the filtered output signal S is collected on a metallization 11, lateral on the last strip of the series. The metallizations 10 and 11 are, respectively, at distances x₁ and x₂ from the ends to the mass of the two microstrip lines considered.

Selon l'invention, deux lignes microbandes non voisines, telles que les lignes 6 et 8 sur la figure 2, sont couplées par une impédance Z 12, réunie par deux fils ou métallisations 13 et 14 à deux points, respectivement, de la première bande 6 et de la deuxième bande 8 non voisines. L'impédance Z est soit une self, soit une capacité, déposées sur le substrat 4 sous forme de composant discret ou sous forme de couches épaisses. Les fils ou métallisations 13 et 14 sont fixés sur les deux lignes microbandes non voisines à des distances x₃ et x₄ , respectivement, des extrémités à la masse des deux lignes microbandes considérées.According to the invention, two non-neighboring microstrip lines, such as lines 6 and 8 in FIG. 2, are coupled by an impedance Z 12, joined by two wires or metallizations 13 and 14 at two points, respectively, of the first strip 6 and the second band 8 not neighboring. The impedance Z is either a self or a capacitor, deposited on the substrate 4 in the form of a discrete component or in the form of thick layers. The wires or metallizations 13 and 14 are fixed on the two non-neighboring microstrip lines at distances x₃ and x₄, respectively, from the ends to the mass of the two microstrip lines considered.

La distance x₁ est choisie pour que le taux d'onde stationnaire à l'entrée TOS = 1, pour une impédance de 50 ohms. Le déplacement de la métallisation d'entrée 10, en faisant varier x₁, permet d'adapter l'impédance à 75 ou 100 ohms, ou à quelqu'autre valeur.The distance x₁ is chosen so that the standing wave rate at the input TOS = 1, for an impedance of 50 ohms. The displacement of the input metallization 10, by varying x₁, makes it possible to adapt the impedance to 75 or 100 ohms, or to some other value.

Pour raison de symétrie, et pour le même motif, la distance x₂ permet d'ajuster l'impédance de sortie du filtre passif.For reasons of symmetry, and for the same reason, the distance x₂ makes it possible to adjust the output impedance of the passive filter.

La fréquence centrale du filtre passe-bande est réglée par la longueur L des lignes microbandes.The central frequency of the bandpass filter is adjusted by the length L of the microstrip lines.

La bande passante du filtre est réglée par la largeur "l" des lignes, et par l'écartement "d" entre lignes. Plus une microbande est large, meilleur est le filtrage, mais moins bon est le rendement. L'écartement "d" joue le même rôle que la largeur "l" mais plus important.The bandwidth of the filter is adjusted by the width "l" of the lines, and by the spacing "d" between lines. The larger a microstrip, the better the filtering, but the worse is the yield. The spacing "d" plays the same role as the width "l" but more important.

Des microbandes larges et/ou des écartements étroits donnent des bandes passantes larges et des TOS faibles. Des microbandes étroites et/ou des écartements larges donnent des bandes passantes étroites et des TOS importants.Large microstrips and / or narrow spacings give wide bandwidths and low TOS. Narrow microstrips and / or wide spacings give narrow bandwidths and high TOS.

Les distances x₃ et x₄ permettent d'optimiser le couplage entre deux microbandes non voisines : elles définissent l'impédance d'entrée et l'impédance de sortie liées à la capacité ou self Z 12, et sont calculées en fonction des spécifications requises pour le filtre.The distances x₃ and x₄ make it possible to optimize the coupling between two non-neighboring microstrips: they define the input impedance and the output impedance linked to the capacitance or self Z 12, and are calculated according to the specifications required for the filtered.

En effet, un filtre dans lequel des microbandes 6 et 8 ne seraient pas couplées a une courbe de réponse en fréquence qui est une courbe de Gauss, bien symétrique, et dont les flancs sont aplatis : le filtrage n'est pas sélectif.Indeed, a filter in which microbands 6 and 8 would not be coupled to a frequency response curve which is a Gaussian curve, well symmetrical, and whose flanks are flattened: the filtering is not selective.

Au contraire, un filtre selon l'invention qui comporte une impédance de couplage Z 12 a une courbe de réponse (S 21) en fonction de la fréquence F :

  • qui se rapproche de la courbe 15 de la figure 3 lorsque la valeur de Z augmente : ce filtre coupe bien les fréquences supérieures à la fréquence centrale
  • qui au contraire se rapproche de la courbe 16 lorsque la valeur de Z diminue : ce filtre a une meilleure réjection des fréquences inférieures.
On the contrary, a filter according to the invention which includes a coupling impedance Z 12 has a response curve (S 21) as a function of the frequency F:
  • which gets closer to the curve 15 of figure 3 when the value of Z increases: this filter cuts well the frequencies higher than the central frequency
  • which, on the contrary, approaches curve 16 when the value of Z decreases: this filter has better rejection of the lower frequencies.

Par conséquent, le calcul et le choix des valeurs de x₃, x₄ et Z permet d'obtenir un filtre passif qui

  • soit a une forte réjection des fréquences supérieures,
  • soit a une forte réjection des fréquences inférieures
  • soit a une courbe de réponse symétrique avec de bonnes réjections hors de la fréquence centrale.
Consequently, the calculation and the choice of the values of x₃, x₄ and Z makes it possible to obtain a passive filter which
  • either a strong rejection of the higher frequencies,
  • either a strong rejection of lower frequencies
  • either has a symmetrical response curve with good rejection outside the center frequency.

Par ailleurs, on a constaté que la présence sur un filtre selon l'invention d'une ou plusieurs microbandes non couplées telle que la microbande 7 centrale améliore la réjection des fréquences extérieures à la fréquence centrale, et rend la courbe de réponse plus "carrée". Plus il y a de microbandes non couplées, plus la bande passante est étroite, mais plus est importante la perte d'insertion du filtre.Furthermore, it has been found that the presence on a filter according to the invention of one or more uncoupled microstrips such as the central microstrip 7 improves the rejection of frequencies outside the central frequency, and makes the response curve more "square"". The more microbands there are coupled, the narrower the bandwidth, the greater the loss of filter insertion.

De façon plus générale, un filtre selon l'invention peut comporter plus de trois microbandes telles que représentées en figure 2. Prenons le cas d'un filtre à 4 microbandes, qu'on appellera A,B,C,D. Différents couplages peuvent être effectués : couplage A-D ou couplage A-C et B-D. Le choix est effectué en fonction des spécifications imposées au filtre.More generally, a filter according to the invention can comprise more than three microstrips as shown in FIG. 2. Let us take the case of a filter with 4 microstrips, which will be called A, B, C, D. Different couplings can be carried out: A-D coupling or A-C and B-D coupling. The choice is made according to the specifications imposed on the filter.

Un premier perfectionnement au filtre selon l'invention est représenté en figure 4. Ils consiste à ajouter à l'entrée E du filtre une double impédance Z1 et Z2.A first improvement to the filter according to the invention is shown in FIG. 4. They consist in adding to the input E of the filter a double impedance Z1 and Z2.

L'impédance Z1 est apportée par une microbande 17, plus fine et d'impédance plus élevée que les microbandes 6,7,8 du filtre. Typiquement, elle a environ 200 micromètres de largeur, et une longueur égale à λ/4. Contrairement aux autres microbandes, elle n'a pas d'extrémité réunie au plan de masse 5.The impedance Z1 is provided by a microstrip 17, finer and of higher impedance than the microstrips 6,7,8 of the filter. Typically, it is about 200 micrometers wide, and a length equal to λ / 4. Unlike other microstrips, it has no end joined to the ground plane 5.

Connectée en parallèle sur le circuit d'entrée, cette impédance résonne pour la fréquence de réjection. Elle annule un second terme dans l'équation de transfert du filtre, ce qui vient compléter l'action de l'impédance 12 du filtre, qui annule un premier terme.Connected in parallel on the input circuit, this impedance resonates for the rejection frequency. It cancels a second term in the filter transfer equation, which completes the action of the impedance 12 of the filter, which cancels a first term.

L'impédance 17 peut aussi être réalisée par une ligne et une capacité.Impedance 17 can also be achieved by a line and a capacity.

L'impédance Z2 corrige la détérioration de l'impédance d'entrée, apportée par Z1. Placée en série entre l'entrée E du filtre, et le point de connexion sur la première microbande 6, elle peut être réalisée soit par une ligne 18, soit par une ligne et une capacité.Impedance Z2 corrects the deterioration of the input impedance, brought by Z1. Placed in series between the input E of the filter, and the connection point on the first microstrip 6, it can be performed either by a line 18, or by a line and a capacitor.

Les impédances caractéristiques de 17 et 18 sont inter-actives, et calculées pour obtenir la pente et le niveau de réjection souhaités, sur la courbe de réponse du filtre.The characteristic impedances of 17 and 18 are interactive, and calculated to obtain the desired slope and rejection level, on the response curve of the filter.

Le second perfectionnement permet de réaliser un filtre passe-bande encore plus petit que celui de l'invention principale.The second improvement makes it possible to produce a bandpass filter even smaller than that of the main invention.

Sur la partie gauche de la figure 5 est très sommairement représenté un filtre selon l'invention : ne sont rapportés que le substrat 4 avec son plan de masse 5, et trois microbandes 6,7,8 avec une entrée E et une sortie S. Bien entendu, ce filtre pourrait comporter plus de trois bandes, et les impédances 17 et 18 du premier perfectionnement.On the left side of Figure 5 is very briefly shown a filter according to the invention: only the substrate 4 is reported with its ground plane 5, and three microstrips 6,7,8 with an input E and an output S. Of course, this filter could comprise more than three bands , and the impedances 17 and 18 of the first improvement.

Bien qu'un tel filtre constitue un progrès en miniaturisation par rapport à l'art connu, il est encore encombrant si on le compare aux puces de circuits intégrés, ou aux puces de composants discrets montables en surface auxquelles il est associée sur un circuit hybride.Although such a filter constitutes a progress in miniaturization compared to the known art, it is still cumbersome if we compare it to integrated circuit chips, or to discrete surface-mountable component chips with which it is associated on a hybrid circuit. .

Le second perfectionnement consiste à couper le filtre selon une ligne 19 qui, perpendiculaire aux microbandes 6,7,8, le sépare en deux parties égales, dans le sens de la longueur du substrat 4. Les deux parties sont alors, comme montré sur la droite de la figure, brasées l'une sur l'autre, par leurs faces supportant le plan de masse 5.The second improvement consists in cutting the filter along a line 19 which, perpendicular to the microstrips 6,7,8, separates it into two equal parts, in the direction of the length of the substrate 4. The two parts are then, as shown on the right of the figure, brazed one on the other, by their faces supporting the ground plane 5.

Les microbandes 6,7,8 dont les moitiés sont désormais portées par les faces supérieure et inférieure d'un sandwich incluant en son centre un plan de masse 5, sont reformées au moyen de cavaliers ou de métallisations 20, sur le flanc du sandwich : la continuité électrique de chaque microbande est ainsi assurée.The microstrips 6,7,8, the halves of which are now carried by the upper and lower faces of a sandwich including in its center a ground plane 5, are reformed by means of jumpers or metallizations 20, on the side of the sandwich: the electrical continuity of each microstrip is thus ensured.

Les microbandes doivent être de longueur légèrement plus petite que λg/4 : la longueur des cavaliers 20, égale à deux fois l'épaisseur du substrat 4, ramène cette longueur à λg/4.The microstrips must be slightly shorter in length than λg / 4: the length of the jumpers 20, equal to twice the thickness of the substrate 4, reduces this length to λg / 4.

Pour monter ce composant miniaturisé sur un substrat, des cavaliers 21, ou autres connexions extérieures adéquates, sont fixés sur les bords du sandwich. Il faut un minimum de trois cavaliers 21, correspondant à l'entrée E, la sortie S et le plan de masse 5. Ces cavaliers sont munis de moyens 22 pour soit implanter le composant dans les trous d'un substrat, soit le monter en CMS (composants montables en surface). L'avantage d'un composant de type DIL, par rapport à un composant en plaquette, est manifeste : gain de place et facilité de fixation d'un filtre qui, replié sur lui-même, a des dimensions proches de celles d'un boîtier de circuit intégré.To mount this miniaturized component on a substrate, jumpers 21, or other suitable external connections, are fixed to the edges of the sandwich. A minimum of three jumpers 21 is required, corresponding to the input E, the output S and the ground plane 5. These jumpers are provided with means 22 for either implanting the component in the holes of a substrate, or mounting it in SMD (surface mountable components). The advantage of a DIL type component, compared to a plate component, is obvious: space saving and ease of attachment of a filter which, folded back on itself, has close dimensions those of an integrated circuit package.

Ce type de filtre passif est utilisé dans les systèmes de traitement de l'information, par exemple dans les radio-téléphones, dans la gamme 0,5 à 10 GHz, avec une bande passante de 0,9 à 1 GHz.This type of passive filter is used in information processing systems, for example in radio telephones, in the range 0.5 to 10 GHz, with a bandwidth of 0.9 to 1 GHz.

Claims (4)

  1. Passive bandpass filter, in hybrid technology, including, supported by one face of a dielectric substrate (4), at least three microstrips (6, 7, 8), mutually parallel, one end of which is joined by appropriate means (9) to the earth plane (5) carried by the second face of the substrate (4), at least two of the said microstrips (6, 8), not adjacent on the substrate (4) being coupled by a coupling impedance Z (12), which is a choke or a capacitor, this filter being characterized in that, with a view to reducing its size, it is folded on itself along a median line (19) perpendicular to the microstrips (6, 7, 8), and jumper leads (21) allowing the passive filter to be fixed by its access (I, O) and earth plane (5) connections.
  2. Passive filter according to Claim 1, characterized in that it further comprises a first impedance (17), of high value, in parallel on the input (I) of the filter, and a second impedance (18), for correcting the input impedance, in series on the input (I).
  3. Passive filter according to Claim 1, characterized in that the first impedance (17) consists of a microstrip, of length λg/4, λg being the wavelength at the working frequency of the filter, and of narrow width in order to increase the impedance.
  4. Passive filter according to Claim 1, characterized in that the second impedance (18) consists of a microstrip.
EP89403257A 1988-11-30 1989-11-24 Passive band-pass filter Expired - Lifetime EP0373028B1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
FR8815664 1988-11-30
FR8815664A FR2639776B1 (en) 1988-11-30 1988-11-30 PASSIVE BAND PASS FILTER
FR898908017A FR2648641B2 (en) 1988-11-30 1989-06-16 PASSIVE BAND PASS FILTER
FR8908017 1989-06-16

Publications (2)

Publication Number Publication Date
EP0373028A1 EP0373028A1 (en) 1990-06-13
EP0373028B1 true EP0373028B1 (en) 1994-05-18

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EP89403257A Expired - Lifetime EP0373028B1 (en) 1988-11-30 1989-11-24 Passive band-pass filter

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EP (1) EP0373028B1 (en)
AT (1) ATE105976T1 (en)
CA (1) CA2004184A1 (en)
DE (1) DE68915408T2 (en)
FI (1) FI895714A0 (en)
FR (1) FR2648641B2 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2669476A1 (en) * 1990-11-21 1992-05-22 Valtronic France PASSIVE BAND PASS FILTER.
DE19652799C2 (en) * 1996-12-18 1999-05-20 Siemens Ag Microwave filter
ES2143964B1 (en) * 1998-09-15 2000-12-01 Univ Catalunya Politecnica DUAL DIPLEXOR FOR CELL PHONE GSM AND DCS.
KR100392682B1 (en) * 2001-02-26 2003-07-28 삼성전자주식회사 Radio filter of combline structure with frequency cut off circuit and method
US10862185B2 (en) 2017-12-01 2020-12-08 Semiconductor Components Industries, Llc Integrated circuit with capacitor in different layer than transmission line

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1906059A1 (en) * 1969-02-07 1970-08-13 Licentia Gmbh Comb filter
JPS49119170A (en) * 1973-03-19 1974-11-14
DE2407313A1 (en) * 1974-02-15 1975-08-21 Kathrein Werke Kg Multi-module cavity resonator assembly - rectangular cavity resonators have one open wall and one matching wall held together by threaded rods
US4253073A (en) * 1978-08-17 1981-02-24 Communications Satellite Corporation Single ground plane interdigital band-pass filter apparatus and method
US4706050A (en) * 1984-09-22 1987-11-10 Smiths Industries Public Limited Company Microstrip devices
FR2578104B1 (en) * 1985-02-27 1987-03-20 Alcatel Thomson Faisceaux BAND PASS FILTER FOR MICROWAVE
US4740765A (en) * 1985-09-30 1988-04-26 Murata Manufacturing Co., Ltd. Dielectric filter
JPS62260401A (en) * 1986-05-02 1987-11-12 Murata Mfg Co Ltd Strip line filter
FR2613557A1 (en) * 1987-03-31 1988-10-07 Thomson Csf FILTER COMPRISING CONSTANT DISTRIBUTED ELEMENTS ASSOCIATING TWO TYPES OF COUPLING

Also Published As

Publication number Publication date
ATE105976T1 (en) 1994-06-15
EP0373028A1 (en) 1990-06-13
CA2004184A1 (en) 1990-05-31
DE68915408D1 (en) 1994-06-23
FI895714A0 (en) 1989-11-29
FR2648641A2 (en) 1990-12-21
DE68915408T2 (en) 1994-09-08
FR2648641B2 (en) 1994-09-09

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