EP3224897B1 - Filtering device and filtering array having an electrically conductive strip structure - Google Patents

Description

The present invention relates to a filtering device with an electrically conductive strip structure. It also relates to a filter assembly comprising a plurality of filtering devices of this type.

• une ligne de transmission formée par une bande électriquement conductrice imprimée sur une face d'un substrat électriquement isolant, cette bande conductrice présentant deux extrémités formant respectivement les deux seuls ports de connexion d'entrée et sortie du dispositif de filtrage, et
• une pluralité de résonateurs, chaque résonateur comportant une bande électriquement conductrice imprimée sur ladite face du substrat.

The invention applies more particularly to a filtering device with an electrically conductive strip structure, comprising:

• a transmission line formed by an electrically conductive strip printed on one side of an electrically insulating substrate, this conductive strip having two ends respectively forming the only two input and output connection ports of the filtering device, and
• a plurality of resonators, each resonator having an electrically conductive strip printed on said face of the substrate.

Many different configurations of electromagnetic filtering devices are feasible microstrip technology, especially to design high-frequency radiofrequency filters. According to this technology, a filtering device is produced using electrically conductive strips printed by simple etching on one side of an electrically insulating substrate. One or more ground planes can also be made on the same face of the substrate, on another face of the substrate, or by stacking substrates.

Most filtering devices printed in micro-ribbon technology use a technique called "distributed constant" filtering whereby discrete component assemblies are replaced by assemblies of elementary patterns of electrically conductive strips printed, each elementary pattern realizing a predetermined function R, L and / or C. According to this technique, the elementary patterns are far enough apart from each other not to interfere with each other. Moreover, to obtain high order filtering devices, it is necessary to multiply the number of filtering devices connected in series. This results in filters which have a congestion sometimes penalizing, the latter increasing with the order of the filter, given the frequencies targeted (those of the radio frequency spectrum up to 300 GHz) and applications envisaged.

In addition, in the field of transmission line filtering devices in micro-ribbon technology as can be illustrated by the work of Jia Sheng Hong, entitled "Microstrip Filters for RF Microwave Applications - Second Edition", published by Wiley in 2011 at a given working frequency, the person skilled in the art is generally guided by the objective of obtaining a line of impedance delay and thus of significant phase shift and with discrete values, that is to say π or π / 2, which implies deviations between neighboring resonators equal to or greater than λ / 2 or λ / 4. Unusually, the patent document US 3,875,538 presents an approach of trying to obtain a delay line having a phase shift of π / 4, which implies deviations between neighboring resonators of approximately λ / 8. But below this unusual value of phase shift, the delay line has a low impedance that is never sought.

It may thus be desired to design a filtering device with an electrically conductive strip structure that makes it possible to overcome at least some of the aforementioned problems and constraints.

• la bande conductrice de chaque résonateur présente une première extrémité couplée à la ligne de transmission entre les deux ports de connexion et au moins une deuxième extrémité libre ou raccordée à une masse de manière à engendrer une longueur d'onde de résonance fondamentale effective propre à chaque résonateur sur ladite face du substrat, et
• pour chaque paire de résonateurs voisins de la pluralité de résonateurs, la distance entre les premières extrémités des deux résonateurs voisins de cette paire est inférieure au dixième de la plus petite longueur d'onde de résonance fondamentale effective de la pluralité de résonateurs sur ladite face du substrat.

It is therefore proposed a filtering device with an electrically conductive strip structure of the aforementioned type in which:

• the conductive strip of each resonator has a first end coupled to the transmission line between the two connection ports and at least one second free end or connected to a ground so as to generate an effective fundamental resonance wavelength specific to each resonator on said face of the substrate, and
• for each pair of neighboring resonators of the plurality of resonators, the distance between the first ends of the two neighboring resonators of this pair is less than one-tenth of the smallest effective fundamental resonance wavelength of the plurality of resonators on said face of the substrate.

By "effective fundamental resonance wavelength" of a resonator, is meant, of course, the wavelength effectively generated on said face of the substrate by fundamental resonance of the resonator considered, this wavelength being different from that which would correspond in the air because of the index of refraction of the substrate which is not equal to that of the air.

By "first end coupled to the transmission line" is meant either a connection of said first end to the transmission line, or possibly a capacitive coupling by approaching said first end and the transmission line.

It results from the topology thus proposed a metamaterial structure obtained by micro-ribbon technology which has particularly surprising and advantageous properties. First, by bringing the resonators closer to one another so that the distances between the first ends of neighboring resonators are less than one tenth of the smallest effective fundamental resonance wavelength of the plurality of resonators, one obtains a very compact filtering device and minimal space for a given operating frequency band. Then, the compact filtering device obtained has a high order band-stop transfer function, thanks in particular to the bandgap hybridization property of metamaterials acting in the radiofrequency spectrum. Finally, there is also a decrease in the group speed of any electrical signal passing through the filtering device, which makes it possible to envisage such a device as an alternative to slow speed transmission lines which are generally very complex in micro-ribbon technology. . Finally, it will be noted that contrary to the teaching of the state of the art mentioned above, the object of the invention is not envisaged as comprising a delay line whose impedance or phase shift is considered. The main aim is to obtain a metamaterial effect from resonators coupled to a transmission line that is as short as possible, regardless of its impedance which then becomes negligible and not taken into consideration.

Optionally, the conductive strips forming the transmission line and the resonators are rectilinear, the resonators being otherwise parallel to each other so as to form a comb of resonators.

Optionally also, the resonators are perpendicular to the transmission line.

Optionally also, the resonators are all of the same nominal length, so as to generate the same nominal effective fundamental resonance wavelength, except at least one short resonator, each short resonator being surrounded by two neighboring resonators length nominal and being shorter than the nominal length so as to generate at least one resonant cavity in said plurality of resonators.

For example, the resonators are all of nominal length except for a single short resonator so as to generate a single resonant cavity in said plurality of resonators.

For example also, the resonators are all of nominal length except N short resonators, with N≥2, arranged in a periodic pattern so as to generate N resonant cavities periodically distributed in said plurality of resonators.

Optionally also, at least one resonator is provided with an electronic component for adjusting its equivalent electrical fundamental resonance frequency.

Also optionally, the electronic control component comprises one of the elements of the assembly consisting of a PIN diode, a varicap diode, a varistor and a transistor.

• les bandes électriquement conductrices formant les lignes de transmission et les résonateurs des dispositifs de filtrage sont imprimées sur une même face d'un même substrat,
• les dispositifs de filtrage sont couplés entre eux en série et/ou en parallèle.

There is also provided a filter assembly with at least one input connection port and at least one output connection port, comprising a plurality of filtering devices according to the invention, wherein:

• the electrically conductive strips forming the transmission lines and the resonators of the filtering devices are printed on the same face of the same substrate,
• the filtering devices are coupled together in series and / or in parallel.

Optionally, a filter assembly according to the invention can comprise a single input connection port and a single output connection port, the filtering devices being coupled together in series so that the input connection port the first filter device of the series forms the input connection port of the filter assembly and the output connection port of the last filter device of the series forms the output connection port of the filter assembly.

• la figure 1 représente schématiquement la structure générale d'un dispositif de filtrage selon un premier mode de réalisation préféré de l'invention,
• la figure 2 est un diagramme illustrant la fonction de transfert du dispositif de filtrage de la figure 1,
• la figure 3 représente schématiquement la structure générale d'un dispositif de filtrage selon un deuxième mode de réalisation préféré de l'invention,
• la figure 4 est un diagramme illustrant la fonction de transfert du dispositif de filtrage de la figure 3,
• la figure 5 représente schématiquement la structure générale d'un dispositif de filtrage selon un troisième mode de réalisation préféré de l'invention,
• la figure 6 représente schématiquement la structure générale d'un dispositif de filtrage selon un quatrième mode de réalisation préféré de l'invention,
• la figure 7 représente schématiquement la structure générale d'un dispositif de filtrage selon un cinquième mode de réalisation préféré de l'invention,
• la figure 8 est un diagramme illustrant la fonction de transfert du dispositif de filtrage de la figure 7,
• la figure 9 représente schématiquement la structure générale d'un ensemble filtrant selon un premier mode de réalisation préféré de l'invention,
• la figure 10 est un diagramme illustrant la fonction de transfert de l'ensemble filtrant de la figure 9,
• la figure 11 représente schématiquement la structure générale d'un ensemble filtrant selon un deuxième mode de réalisation préféré de l'invention,
• la figure 12 est un diagramme illustrant la fonction de transfert de l'ensemble filtrant de la figure 11,
• la figure 13 représente schématiquement la structure générale d'un ensemble filtrant selon un troisième mode de réalisation préféré de l'invention,
• la figure 14 est un diagramme illustrant la fonction de transfert de l'ensemble filtrant de la figure 13, et
• la figure 15 représente schématiquement la structure générale d'un ensemble filtrant selon un quatrième mode de réalisation préféré de l'invention.

The invention will be better understood with the aid of the description which follows, given solely by way of example and with reference to the appended drawings in which:

• the figure 1 schematically represents the general structure of a filtering device according to a first preferred embodiment of the invention,
• the figure 2 is a diagram illustrating the transfer function of the filtering device of the figure 1 ,
• the figure 3 schematically represents the general structure of a filtering device according to a second preferred embodiment of the invention,
• the figure 4 is a diagram illustrating the transfer function of the filtering device of the figure 3 ,
• the figure 5 schematically represents the general structure of a filtering device according to a third preferred embodiment of the invention,
• the figure 6 schematically represents the general structure of a filtering device according to a fourth preferred embodiment of the invention,
• the figure 7 schematically represents the general structure of a filtering device according to a fifth preferred embodiment of the invention,
• the figure 8 is a diagram illustrating the transfer function of the filtering device of the figure 7 ,
• the figure 9 schematically represents the general structure of a filter assembly according to a first preferred embodiment of the invention,
• the figure 10 is a diagram illustrating the transfer function of the filter assembly of the figure 9 ,
• the figure 11 schematically represents the general structure of a filter assembly according to a second preferred embodiment of the invention,
• the figure 12 is a diagram illustrating the transfer function of the filter assembly of the figure 11 ,
• the figure 13 schematically represents the general structure of a filter assembly according to a third preferred embodiment of the invention,
• the figure 14 is a diagram illustrating the transfer function of the filter assembly of the figure 13 , and
• the figure 15 schematically represents the general structure of a filter assembly according to a fourth preferred embodiment of the invention.

The filtering device 100 shown schematically on the figure 1 comprises a transmission line 102, for example a line 50 Ω formed by an electrically conductive strip printed on one side of an electrically insulating substrate 104. This conductive strip 102 has two ends 102 _IN and 102 _OUT respectively forming the two only ports of input and output connection of the filter device 100. In the embodiment illustrated in FIG. figure 1 the conductive strip 102 is rectilinear.

The filtering device 100 further comprises a plurality of resonators 106 ₁ ,..., 106 _M , each resonator 106 _i (1 _{i i M M} ) comprising a band electrically conductive printed on the same side of the substrate 104 as the conductive strip of the transmission line 102. The conductive strip of each resonator 106 _i has a first end 108 _i connected to the transmission line 102 between the two connection ports 102 _IN , _OUT 102 and a second end 110 _i free or connected to a ground so as to generate an effective fundamental resonance wavelength specific to each resonator 106 _i on said face of the substrate 104. In the embodiment illustrated in FIG. figure 1 , the conductive strips of the resonators 106 ₁ ,..., 106 _M are straight, all of the same length L and parallel to each other so as to form a comb of resonators. The resonators 106 ₁ ,..., 106 _M are further perpendicular to the transmission line 102 and their second ends 110 ₁ ,..., 110 _M are illustrated free.

Given the fact that the second ends 110 ₁ ,..., 110 _M are free, the resonators 106 ₁ ,..., 106 _M all have the same effective fundamental resonance wavelength λ equal to four times their length. Alternatively, if the second ends 110 ₁ ,..., 110 _M were connected to ground, the resonators 106 ₁ ,..., 106 _M would all have the same effective fundamental resonance wavelength λ equal to twice their length L.

According to the invention, for each pair (106 _i , 106 _{i + 1} ), with 1≤i≤M-1, resonators neighboring the plurality of resonators 106 ₁ , ..., 106 _M , the distance noted e _i between the first ends 108 _i and 108 _{i + 1} of the two neighboring resonators 106 _i and 106 _{i + 1} of this pair is less than one tenth of the smallest effective fundamental resonance wavelength of the plurality of resonators which is, in this example where all the resonators are all of the same length L, the effective wavelength λ mentioned above. These distances e ₁ ,..., E _M-1 may even advantageously be less than one tenth, or even one hundredth, of the smallest effective fundamental resonance wavelength of the plurality of resonators 106 ₁ ,. _M. In the particular embodiment of the figure 1 all these distances e ₁ , ..., e _M-1 are equal and of the same order of magnitude as the width of each resonator.

This gives a metamaterial structure in micro-ribbon technology which has advantageous properties as indicated above. In particular, the hybridization bandgap property is due to the phenomena of interference between the resonators 106 ₁ ,..., 106 _M which are very close together and respond in phase opposition to any incident electromagnetic field beyond their resonance frequency. Thus, by destructive interferences beyond this frequency, any incident electromagnetic field is reflected, and the metamaterial structure is a notch filter with interesting properties.

By way of example, for a transmission line 102 at 50 Ω, with a common length L of the resonators equal to 40 mm, a total width W of M = 9 resonators equal to 20 mm, a distance e = e ₁ =. .. = e _{M + 1} between adjacent resonators of a little more than 1 mm and a refractive index of the substrate 104 close to 1.45, we obtain the transfer function illustrated in FIG. figure 2 . This transfer function shows that it has thus been conceived a notch-filtering device 100, in other words, with a band-gap at -30 dB, having good performance, the forbidden band of transmission starting just after, in the frequency domain, the resonance frequency (about 1.3 GHz) corresponding to the effective wavelength λ mentioned above and extending to about 1.6 GHz. These good performances are furthermore obtained for a filtering device 100 which remains very compact and of minimal bulk.

Note that the filter structure illustrated on the figure 1 is only a particular example of filtering device according to the invention. More generally, the conductive strips forming the transmission line 102 and the resonators 106 ₁ ,..., 106 _M are not necessarily rectilinear, the resonators are not necessarily parallel to each other or perpendicular to the transmission line. and are not necessarily of the same length L. The distances e ₁ , ..., e _M-1 are not necessarily equal either. On the other hand, it is necessary that for each pair of resonators neighboring the plurality of resonators, the distance between the first ends of the two neighboring resonators of this pair is less than a quarter, or even advantageously to a tenth, of the shortest length of the pair. effective fundamental resonant wave of the plurality of resonators, this smaller effective fundamental resonance wavelength being that of the resonator of the smallest length. This condition is necessary to obtain a metamaterial structure with advantageous properties. By playing on all the other structural parameters mentioned above, it is then possible to adapt the transfer function of the filtering device to the different applications concerned.

The filtering device 200, shown schematically on the figure 3 according to a second preferred embodiment of the invention, comprises a transmission line 202 with two ends 202 _IN and 202 _OUT printed on a substrate 204 and resonators 206 ₁ , ..., 206 _M comprising first 208 ₁ ,. .., 208 _M and second 210 ₁ , ..., 210 _M ends. It is identical to the filter device 100 to except that one 206 _i of its resonators 206 ₁ , ..., 206 _M is shorter than the others. More specifically, the resonators 206 ₁ ,..., 206 _M are all of the same nominal length L, so as to generate the same nominal effective fundamental resonance wavelength λ, except the short resonator 206 _i , disposed somewhere in the metamaterial structure between the first resonator 206 ₁ and the last resonator 206 _M so as to generate a singular resonant cavity of very small size in the plurality of resonators 206 ₁ , ..., 206 _M.

It should be noted that the distances e ₁ ,..., E _M-1 must remain less than one quarter, or even advantageously one tenth, of the smallest effective fundamental resonance wavelength of the plurality of resonators which is, in this example, the effective fundamental resonance wavelength of the short resonator 206 _i .

Far from interfering with the metamaterial structure, the presence of the resonant cavity generated by the short resonator 206 _i makes it possible to trap certain waves so as to create a resonance peak, this resonance peak being adjustable in position in the forbidden band transmitting the filter device 200 by varying the position and size of the short resonator 206 _i in the plurality of resonators 206 ₁ , ..., 206 _M. Experience shows that the resonance peak thus obtained is very narrow, so that it has a large quality factor.

By way of example, for a transmission line 202 to 50 Ω, with a nominal length L equal to 40 mm, a total width W of M = 9 resonators equal to 20 mm, a distance e = e ₁ = ... = e _{M + 1} between neighboring resonators of a little more than 1 mm, a short resonator of 30 mm arranged at the center of the plurality of resonators and a refractive index of the substrate 204 close to 1.45, we obtain the function of illustrated transfer on the figure 4 . This transfer function shows that it has thus been conceived a filter device 200 notch-band or in other words, a bandgap of transmission at -30 dB, presenting not only good performance but also a resonance with a high quality factor. in its forbidden band. The -30 dB band gap, which ranges from about 1.3 GHz to 1.7 GHz, has a resonant peak at just under 1.6 GHz, the rejection being very steep around this resonance, 30 dB in a few tens of MHz. These good performances are also obtained for a filtering device 200 which remains very compact and compact.

It is also possible to widen the resonance peak inside the forbidden band of transmission by increasing the number of resonant cavities so to couple these cavities together. This effect is obtained for example by means of the filtering device 300 of the figure 5 .

The filtering device 300 comprises a transmission line 302 with two ends 302 _IN and 302 _OUT printed on a substrate 304 and resonators 306 ₁ , ..., 306 _M comprising first 308 ₁ , ..., 308 _M and second 310 ₁ , ..., 310 _M ends. It is similar to the filter devices 100 and 200 except that several 306 _{i, 1} , ..., 306 _{i, N} of its resonators 306 ₁ ,..., 306 _M are shorter than the others. More specifically, the resonators 306 ₁ ,..., 306 _M are all of the same nominal length L, so as to generate the same nominal effective fundamental resonance wavelength λ, except the N short resonators 306 _{i, 1} , ..., 306 _{i, N} , arranged in the metamaterial structure between the first resonator 306 ₁ and the last resonator 306 _M so as to generate N very small coupled resonant singular cavities in the plurality of resonators 306 ₁ , .. ., 306 _M. Each short resonator is surrounded by two neighboring resonators of nominal length.

Preferably, the N short resonators 306 _{i, 1} , ..., 306 _{i, N} are arranged in a periodic pattern so as to generate N resonant cavities periodically distributed in said plurality of resonators. In the example of the figure 5 a short resonator is arranged every three resonators. Each resulting resonant cavity is then separated from its neighbors by two resonators of nominal length and is therefore coupled directly only with its closest neighbors. This results in a filtering device that does not let any frequency pass in the forbidden band as mentioned for the device of the figure 1 , except on a frequency band centered on the resonant frequency of the cavities. The width of this frequency band can be modified by modifying the structural parameters of the filtering device 300. This makes it possible to produce a filter type with even more abrupt frequency transitions (ie increasing the order of the filter) and easier to adjust.

Another effect resulting from the increase in the number of cavities in the metamaterial structure of the figure 5 is to considerably slow the group speed of electrical signals passing through the filter device, because a band of slow speed propagation modes is thus created.

Finally, it should be noted that the distances e ₁ ,..., E _M-1 must remain less than one quarter, or even advantageously one tenth, of the smallest effective fundamental resonance wavelength of the plurality of resonators. which is, in this example, the effective fundamental resonance wavelength of the N short resonators 306 _{i, 1} , ..., 306 _{i, N.}

A variant of the embodiment of the figure 3 is illustrated on the figure 6 . The filtering device 400 according to this variant comprises a transmission line 402 with two ends 402 _IN and 402 _OUT printed on a substrate 404 and resonators 406 ₁ ,..., 406 _M comprising first 408 ₁ , ..., 408 _M and second 410 ₁ , ..., 410 _M ends. It is similar to the filtering device 200 except that the short resonator 206 _i is replaced by a resonator 406 _i of the same length as the others but provided with an electronic component 412 for adjusting its resonance equivalent electric frequency fundamental. Thanks to this component, it is possible to modulate this frequency, in particular to increase it, without modifying the length of the resonator. It is then possible to obtain the same effects as with the filtering device 200, in particular the same transfer function illustrated on FIG. figure 4 , with a structure of resonators all the same length as in the filter device 100. The electronic component 412 is for example a PIN diode, a varicap diode, a varistor or a transistor.

Finally, it should be noted that the distances e ₁ ,..., E _M-1 must remain less than one fourth, or even advantageously one tenth, of the smallest effective fundamental resonance wavelength of the plurality of resonators which is in this example, the effective fundamental resonance wavelength corresponding to the equivalent electrical resonance frequency of the resonator 406 _i .

• la première extrémité 458₁, ou ..., ou 458_M de chaque résonateur 456₁, ou ..., ou 456_M n'est pas directement raccordée à la ligne de transmission 452, mais couplée capacitivement avec elle par rapprochement sans contact, et
• chaque résonateur 456₁, ou ..., ou 456_M comporte deux deuxièmes extrémités libres 460₁, ou ..., ou 460_M en étant constitué d'une bande conductrice dédoublée en partie médiane selon une forme générale de diapason.

Another variant of the embodiment of the figure 3 is illustrated on the figure 7 . The filtering device 450 according to this other variant comprises a transmission line 452 with two ends 452 _IN and 452 _OUT printed on a substrate 454 and resonators 456 ₁ , ..., 456 _M comprising first 458 ₁ , ... , 458 _M and second 460 ₁ , ..., 460 _M ends. It is similar to the filtering device 200 except that:

• the first end 458 ₁ , or ..., or 458 _M of each resonator 456 ₁ , or ..., or 456 _M is not directly connected to the transmission line 452, but capacitively coupled with it by contact-less contact , and
• each resonator 456 ₁ , or ..., or 456 _M has two second free ends 460 ₁ , or ..., or 460 _M consisting of a band conductor split in the middle part according to a general form of tuning fork.

The resonator runs 456 _i remains shorter than the others. This split form of the so-called fractal resonators can be generalized into a multi-second tree shape for each resonator. It makes it possible to shorten the length of each resonator for the same effective resonance wavelength, at the cost of greater lateral bulk.

Finally, it should be noted that the distances e ₁ ,..., E _M-1 must remain less than one fourth, or even advantageously one tenth, of the smallest effective fundamental resonance wavelength of the plurality of resonators which is in this example, the effective fundamental resonance wavelength corresponding to the fundamental resonator equivalent electrical frequency of the short resonator 456 _i .

For example, for a transmission line 452 to 50 Ω, with a nominal length L equal to 40 mm, a total width W of M = 5 resonators equal to 20 mm, a distance e = e ₁ = ... = e _{M + 1} between adjacent resonators of about 3 mm, a short resonator of 20 to 30 mm disposed at the center of the plurality of resonators and a refractive index of the substrate 454 close to 1.45, the transfer function is obtained illustrated on the figure 8 . This transfer function shows that it has thus been conceived a band-stop filtering device 450, in other words, a bandgap band at -30 dB, which not only has good performance but also broadband resonance in its range. forbidden band. The -30 dB band gap, which ranges from about 1.45 GHz to 2.55 GHz, has a peak resonant at 1.9 GHz in a bandwidth of -30 dB which extends about 1, 8 GHz to 2.4 GHz. These good performances are also obtained for a filtering device 450 which remains very compact and compact.

From one or other of the filtering devices 100, 200, 300, 400, 450 previously described, or from other possible embodiments, a filter assembly with at least one input connection port and at least one output connection port, having a plurality of filtering devices according to the invention, can be designed. All the electrically conductive strips forming the transmission lines and the resonators of the filtering devices of such a filter assembly are printed on the same face of the same substrate. Furthermore, the filtering devices are coupled together in series and / or in parallel according to topologies that can be very diverse. It is thus possible to conceive a filtering unit that achieves ambitious objectives in terms of bandwidth, bandwidth loss and rejection level around this bandwidth.

According to a first family of possible topologies, the filtering devices are coupled together in series, so that the filter assembly comprises only one input connection port and one output connection port, the port of the first filtering device of the series forming the input connection port of the filter assembly and the output connection port of the last filtering device of the series forming the output connection port of the filter assembly.

A first embodiment of a filter assembly according to the invention and according to this first family of topologies is illustrated in FIG. figure 9 .

The filter assembly 500 with two connection ports 502 _IN and 502 _OUT illustrated in this figure comprises two filtering devices 504, 506 of the same type as the filtering device 200, that is to say resonators all of the same length. except one. The input connection port 502 _IN corresponds to the input connection port of the first filter device 504 and the output connection port 502 _OUT corresponds to the output connection port of the second and last filter device 506.

The two transmission lines of the two filtering devices 504 and 506 are in the extension of each other and the output connection port of the transmission line of the first filtering device 504 is coupled to the connection port of input of the transmission line of the second filter device 506 with a printed capacitive element 508. The latter is formed of two electrically conductive strips perpendicular to the transmission lines of the two filtering devices 504 and 506 coupled. It makes it possible to maintain the two filtering devices 504 and 506 at a distance from one another while coupling them.

By way of example, with structural experimental parameters similar to those of the filtering device 200, the transfer function illustrated on FIG. figure 10 . This transfer function shows that a filter set 500 has thus been designed whose band-gap and resonant band-band properties are improved. In particular, a bandwidth at -30 dB of around 100 MHz between 1.5 and 1.6 GHz in the forbidden band and a rejection of 40 dB in a few tens of MHz around this bandwidth are reached, losses at resonance peak being less than 3 dB.

A second embodiment of a filter assembly according to the invention and according to the first family of topologies is illustrated on the figure 11 .

The filter assembly 600 with two connection ports 602 _IN and 602 _OUT illustrated in this figure comprises two filtering devices 604, 606 of the same type as the filtering device 200, that is to say resonators all of the same length. except for one (the resonant cavity is not arranged at the center of the plurality of resonators). These two filtering devices 604 and 606 are arranged in axial symmetry with respect to each other along an axis perpendicular to the transmission lines. The input connection port 602 _IN corresponds to the input connection port of the first filter device 604 and the output connection port 602 _OUT corresponds to the output connection port of the second and last filter device 606.

The two transmission lines of the two filtering devices 604 and 606 are in the extension of each other and the output connection port of the transmission line of the first filter device 604 is electromagnetically coupled to the connection port of input of the transmission line of the second filtering device 606. For this purpose, the two coupled ports are brought closer to one another and the coupling is done directly without any particular element. This coupling varies as a function of the separation distance of the two filtering devices 604 and 606.

By way of example, with structural experimental parameters similar to those of the filtering device 200, the transfer function illustrated on FIG. figure 12 . This transfer function shows that a filter set 600 has thus been designed whose properties of band-cutter and resonant band in the forbidden band are improved. In particular, a bandwidth at -30 dB of around 50 MHz in the forbidden band and a rejection of 40 dB in a few tens of MHz around this bandwidth are reached, the losses at the resonant peak being less than 3 dB .

A third embodiment of a filter assembly according to the invention and according to the first family of topologies is illustrated in FIG. figure 13 .

The filter assembly 700 with two connection ports 702 _IN and 702 _OUT illustrated in this figure comprises two filtering devices 704, 706 of the same type as the filtering device 200, that is to say with resonators all of the same length. except for one (the resonant cavity is not arranged at the center of the plurality of resonators). These two filtering devices 704 and 706 are arranged in central symmetry with respect to one another on a point of the substrate on which they are printed. The input connection port 702 _IN corresponds to the input connection port of the first filter device 704 and the output connection port 702 _OUT corresponds to the output connection port of the second and last filter device 706.

Given the central symmetry arrangement, the two transmission lines of the two filtering devices 704 and 706 are parallel without being in the extension of one another. The electromagnetic coupling of the two filtering devices 704 and 706 is along two of their close resonators vis-à-vis, one connected to the output connection port of the first filtering device 704, the other connected to the input connection port of the second filter device 706. The coupling is done directly without any particular element. This coupling varies according to the separation distance of the two resonators vis-à-vis.

By way of example, with structural experimental parameters similar to those of the filtering device 200, the transfer function illustrated on FIG. figure 14 . This transfer function, very similar to that of the figure 10 , shows that a filter set 700 has thus been designed whose band-gap and resonant band-band properties are improved.

In accordance with a second family of possible topologies, the previously described filtering devices 100, 200, 300, 400, 450 may be coupled together in parallel so that the filter assembly has a plurality of input connection ports or a plurality of ports. output connection.

A fourth embodiment of a filter assembly according to the invention and according to this second family of topologies is illustrated in FIG. figure 15 .

The filter assembly 800 with n input connection ports 802 _IN1 , ..., 802 _INn and an output connection port 802 _OUT illustrated in this figure has n filters 804 ₁ ,..., 804 _n which can each be of the same type as any of the filtering devices 100, 200, 300, 400, 450 or others. The input connection port 802 _IN1 corresponds to the input connection port of the first filter 804 ₁ , ..., the input connection port 802 _INn corresponds to the input connection port of the last filter 804 _n and the output connection port 802 _OUT corresponds to the parallel interconnection of the n output connection ports of the n filters 804 ₁ ,..., 804 _n .

In particular, when the n filters 804 ₁ ,..., 804 _n have resonance peaks or bandwidths in their forbidden bands, it is thus possible to design a multiplexer (a duplexer if n = 2). For example, when a signal, whose spectrum is included in the forbidden band of each filter 804 ₁ , ..., 804 _n , is provided at the inputs 802 _IN1 , ..., 802 _INn of the filter assembly 800, only the part of the spectrum corresponding to the resonant peak or the bandwidth of the first filter 804 ₁ is transmitted by this first filter 804 ₁ at the output 802 _OUT , ..., only the part of the spectrum corresponding to the resonant peak or the bandwidth of the last filter 804 ₁ is transmitted by the latter 804 ₁ filter 802 _OUT output, so that we obtain at the output a signal multiplexed according to the different resonant peaks or bandwidths of the n filters 804 ₁ , ..., 804 _n .

It will be noted that the filter assembly 800 is passive and therefore reversible. It can then be seen and used as a filter assembly at an input connection port 802 _OUT and n output connection ports 802 _IN1 , ..., 802 _INn . By injecting therein a spectrum signal included in the forbidden band of each filter 804 ₁ ,..., 804 _n , there are at the outputs 802 _IN1 ,..., 802 _INn the n parts of the signal corresponding respectively to the n resonant peaks or bandwidths of n filters 804 ₁ , ..., 804 _n .

It is also possible to generalize the topology of the filter assembly 800 whereas the filter assemblies filtering devices coupled in series, such as filter assemblies 500, 600, 700, can also constitute all or part of the filters 804 ₁ , ..., 804 _n coupled in parallel.

Conversely, a filter assembly may be designed by serially coupling filter assemblies of parallel coupled filter devices.

It clearly appears that a filtering device or filter assembly such as one of those described above makes it possible to provide a high-performance filter for a minimum space requirement, thanks to a metamaterial structure obtained by bringing together a plurality of resonators so that the distances between neighboring resonators are always less than a quarter, or even advantageously one tenth, of the smallest effective fundamental resonance wavelength of the plurality of resonators.

Note also that the invention is not limited to the embodiments described above.

In particular, with regard to the filter assemblies presented in reference to figures 9 , 11 and 13 It should be noted that it is possible to increase the number of serially coupled filter devices as needed.

More generally, all the topologies of coupled filtering devices can be envisaged, in particular topologies in cascades, stars or others.

It will be apparent to those skilled in the art that various modifications can be made to the embodiments described above, in light of the teaching just disclosed. In the following claims, the terms used are not to be construed as limiting the claims to the embodiments set forth in this specification, but should be interpreted to include all the equivalents that the claims are intended to cover because of their formulation and whose prediction is within the reach of the person skilled in the art by applying his general knowledge to the implementation of the teaching which has just been disclosed to him.

Claims (10)

1. Filter device (100; 200; 300; 400; 450) with an electrically conducting strip structure, comprising:

   - a transmission line (102; 202; 302; 402; 452) formed by an electrically conducting strip printed on a surface of an electrically insulating substrate (104; 204; 304; 404; 454), said conducting strip having two ends (102_IN, 102_OUT; 202_IN, 202_OUT; 302_IN, 302_OUT; 402_IN, 402_OUT; 452_IN, 452_OUT) respectively forming the two sole input and output connection ports of the filter device (100; 200; 300; 400; 450),

   - a plurality of resonators (106₁, ..., 106_M; 206₁, ..., 206_M; 306₁, ..., 306_M; 406₁, ..., 406_M; 456₁, ..., 456_M), each resonator comprising an electrically conducting strip printed on said surface of the substrate (104; 204; 304; 404; 454),

   - the conducting strip of each resonator (106₁, ..., 106_M; 206₁, ..., 206_M; 306₁, ..., 306_M; 406₁, ..., 406_M; 456₁, ..., 456_M) has a first end (108₁, ..., 108_M; 208₁, ..., 208_M; 308₁, ..., 308_M; 408₁, ..., 408_M; 458₁, ..., 458_M) coupled to the transmission line between the two connection ports and at least one second end (110₁, ..., 110_M; 210₁, ..., 210_M; 310₁, ..., 310_M; 410₁, ..., 410_M; 460₁, ..., 460_M) that is free or connected to a ground so as to create an effective fundamental resonant wavelength specific to each resonator on said surface of the substrate, the filtering device being characterized in that:

   - for each pair of neighbouring resonators of the plurality of resonators, the distance (e₁, ..., e_M-1) between the first ends of two neighbouring resonators of this pair is less than one tenth of the smallest effective fundamental resonant wavelength of the plurality of resonators (106₁, ..., 106_M; 206₁, ..., 206_M; 306₁, ..., 306_M; 406₁, ..., 406_M; 456₁, ..., 456_M) on said surface of the substrate.
2. Filter device (100; 200; 300; 400) with an electrically conducting strip structure according to claim 1, wherein the conducting strips forming the transmission line (102; 202; 302; 402) and the resonators (106₁, ..., 106_M; 206₁, ..., 206_M; 306₁, ..., 306_M; 406₁, ..., 406_M) are rectilinear, the resonators also being parallel to each other so as to form a resonator comb.
3. Filter device (100; 200; 300; 400) with an electrically conducting strip structure according to claim 2, wherein the resonators (106₁, ..., 106_M; 206₁, ..., 206_M; 306₁, ..., 306_M; 406₁, ..., 406_M) are perpendicular to the transmission line (102; 202; 302; 402).
4. Filter device (200; 300; 450) with an electrically conducting strip structure according to any one of claims 1 to 3, wherein the resonators (206₁, ..., 206_M; 306₁, ..., 306_M; 456₁, ..., 456_M) all have the same nominal length (L), so as to produce the same nominal effective fundamental resonant wavelength, with the exception of at least one short resonator (206_i; 306_i,1, ..., 306_i,N; 456_i), each short resonator being surrounded by two neighbouring resonators of nominal length and having a length that is less than the nominal length so as to produce at least one resonant cavity in said plurality of resonators (206₁, ..., 206_M; 306₁, ..., 306_M; 456₁, ..., 456_M).
5. Filter device (200; 450) with an electrically conducting strip structure according to claim 4, wherein the resonators (206₁, ..., 206_M; 456₁, ..., 456_M) all have a nominal length (L) except for a single short resonator (206_i; 456_i) so as to produce a single resonant cavity in said plurality of resonators (206₁, ..., 206_M; 456₁, ..., 456_M).
6. Filter device (300) with an electrically conducting strip structure according to claim 4, wherein the resonators (306₁, ..., 306_M) all have a nominal length (L) except for N short resonators (306_i,1, ..., 306_i,N), where N≥2, positioned according to a periodic pattern so as to produce N resonant cavities periodically distributed in said plurality of resonators (306₁, ..., 306_M).
7. Filter device (400) with an electrically conducting strip structure according to any one of claims 1 to 6, wherein at least one resonator (406_i) is equipped with an electronic component (412) for adjusting its fundamental resonance equivalent electrical frequency.
8. Filter device (400) with an electrically conducting strip structure according to claim 7, wherein the electronic adjustment component (412) comprises one of the elements of the set consisting of a PIN diode, a varicap diode, a varistor and a transistor.
9. Filtering assembly (500; 600; 700; 800) with at least one input connection port (502_IN; 602_IN; 702_IN; 802_IN1, ..., 802_INn) and at least one output connection port (502_OUT; 602_OUT; 702_OUT; 802_OUT), comprising a plurality of filter devices (504, 506; 604, 606; 704, 706; 804₁, ..., 804_n) according to any one of claims 1 to 8, wherein:

   - the electrically conducting strips forming the transmission lines and the resonators of the filter devices (504, 506; 604, 606; 704, 706; 804₁, ..., 804_n) are printed on the same surface of the same substrate,

   - the filter devices (504, 506; 604, 606; 704, 706; 804₁, ..., 804_n) are coupled to each other in series and/or in parallel.
10. Filtering assembly (500; 600; 700) according to claim 9, comprising a single input connection port (502_IN; 602_IN; 702_IN) and a single output connection port (502_OUT; 602_OUT; 702_OUT), wherein the filter devices (504, 506; 604, 606; 704, 706) are coupled to each other via a series connection such that the input connection port of the first filter device (504; 604; 704) of the series forms the input connection port (502_IN; 602_IN; 702_IN) of the filtering assembly (500; 600; 700) and the output connection port of the last filter device (506; 606; 706) of the series forms the output connection port (502_OUT; 602_OUT; 702_OUT) of the filtering assembly (500; 600; 700).

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