NON-RECIPROCAL MICROWAVE COMPONENT

Description

TECHNICAL FIELD

[0001] The present invention relates to a non-reciprocal microwave component comprising at least three waveguides and a central resonator. The invention applies to the field of microwave components, in particular based on microwave transmission lines. STATE OF THE PRIOR ART

[0002] Among microwave components, non-reciprocal components provide essential functions such as a circulator function or an isolator function, in order to ensure the routing of radiofrequency signals.

[0003] Typically, such non-reciprocal components include a magnetized ferromagnetic ceramic element allowing such switching.

[0004] For example, it is known to produce a circulator comprising three waveguides extending at 120° from each other and connected to a single central ferrite resonator which gives the circulator its non-reciprocity. Such a resonator is, classically, an Okada resonator comprising two ferrite elements stacked in a direction orthogonal to a plane in which the waveguides extend. More precisely, each ferrite element is bonded to a respective wall among two electrically conductive walls of the resonator facing each other, the two ferrite elements being spaced apart by a dielectric, generally an air gap (or vacuum for space applications). Such a circulator topology provides broadband operation.

[0005] However, such a circulator does not give complete satisfaction.

[0006] Indeed, in the context of aerospace applications, and due to the presence of said air gap between the two ferrite elements, such a component generally undergoes two destructive effects, namely the corona effect and the so-called "corona" effect. multipactor ", which have detrimental consequences on the power performance of said component.

[0007] The corona effect occurs naturally because air is not a perfect insulator. On the contrary, under normal conditions, it contains many free electrons and ions. Therefore, when an electric field is established in the air between two conductors, the free ions and electrons in the air experience a force that moves and accelerates them. Charged particles collide with each other as they move, as well as with slow-moving uncharged molecules. Thus, the number of charged particles increases rapidly. If the electric field is strong enough, a dielectric breakdown occurs and an arc forms between the conductors.

[0008] This phenomenon is common in microwave devices operating during satellite launches, when the pressure is too low, transforming the air into plasma.

[0009] The effect multipactoris an electronic resonance effect that occurs when radiofrequency fields accelerate electrons in a vacuum and cause them to collide with a surface, which, depending on their kinetic energy, releases one or more electrons into the vacuum. These electrons may in turn be accelerated by the radiofrequency fields and collide with the same or another surface. When the impact energies, the number of electrons released, and the timing of the impacts are such that there is a sustained multiplication of the number of electrons, the phenomenon increases exponentially and is likely to cause operational problems.

[0010] In radio frequency space systems, the effect multipactorcauses loss and / or distortion of the radio frequency signal (increase in noise figure or bit error rate) and may damage radio frequency components or subsystems due to excess radio frequency power being reflected or dissipated by the system.

[0011] An aim of the invention is therefore to propose a non-reciprocal microwave component which is less sensitive to corona effects and multi-actor, while providing satisfactory bandwidth.

[0012] JP 2010 283774 A and US 4 672 333 A disclose Y-junction circulators with ferrite layers. STATEMENT OF THE INVENTION

[0013] To this end, the invention relates to a non-reciprocal microwave component comprising at least three waveguides and a central resonator, characterized in that the central resonator comprises an upper substrate and a lower substrate extending on either side of a resonance volume for the propagation of electromagnetic waves, each of the upper substrate and the lower substrate comprising a dielectric layer having an outer face and an inner face opposite each other, the outer face being covered by an outer conductive layer and the inner face being covered by an inner conductive layer, the inner face of the dielectric layer of the lower substrate being oriented towards the inner face of the dielectric layer of the upper substrate, the upper substrate further comprising a plurality of vias extending, through the associated dielectric layer, between the corresponding outer conductive layer and inner conductive layer,and being in electrical contact with said outer conductive layer and inner conductive layer at connection points, the connection points of the inner conductive layer surrounding a free surface of the inner face of the dielectric layer, the free surface not being covered by the inner conductive layer, a single magnetized ferromagnetic ceramic element being arranged between the free surface of the upper substrate and the lower substrate, each waveguide extending along a respective propagation axis, each waveguide comprising a propagation zone for the propagation of electromagnetic waves, the central resonator and each waveguide being arranged so that electromagnetic waves can circulate between the resonance volume of the central resonator and the propagation zone of each waveguide.

[0014] Thanks to the invention, a non-reciprocal microwave component is obtained which is less sensitive to corona effects and multipactor than other known components, while presenting a satisfactory bandwidth.

[0015] According to other advantageous aspects of the invention, the non-reciprocal microwave component comprises one or more of the following characteristics, taken in isolation or in all technically possible combinations: According to a preferred feature, the lower substrate also comprises a plurality of vias extending, through the associated dielectric layer, between the corresponding outer conductive layer and inner conductive layer, and being in electrical contact with said outer conductive layer and inner conductive layer at connection points, the connection points of the inner conductive layer surrounding a free surface of the inner face of the dielectric layer, the free surface not being covered by the inner conductive layer, the free surface of the lower substrate being opposite the free surface of the upper substrate, the magnetized ferromagnetic ceramic element being arranged between the free surface of the lower substrate and the free surface of the upper substrate.

[0016] According to a preferred characteristic, the vias of the upper substrate, respectively of the lower substrate, surround an upper cavity, respectively a lower cavity, at the level of the corresponding dielectric layer, the upper cavity and the lower cavity having different shapes and / or receiving different dielectric materials.

[0017] According to a preferred feature, the magnetized ferromagnetic ceramic element extends from the free surface of the dielectric layer of the upper substrate to the lower substrate.

[0018] According to a preferred characteristic, the magnetized ferromagnetic ceramic element is surrounded radially, with respect to an axis orthogonal to the free surface of the upper substrate, by at least one annular impedance matching coating made of a dielectric or ferromagnetic material.

[0019] According to a preferred feature, the magnetized ferromagnetic ceramic element is made of ferrite, and is magnetized by an external polarizing magnet.

[0020] According to a preferred feature, the magnetized ferromagnetic ceramic element is made of an anisotropic material, preferably a hexagonal ferrite.

[0021] According to a preferred characteristic, the thermal variation of the permittivity of the dielectric material forming the upper cavity and / or the lower cavity acts in an opposite manner to the thermal variation of the non-reciprocal microwave component.

[0022] According to a preferred feature, the non-reciprocal microwave component further comprises an additional substrate extending parallel to the upper substrate, the additional substrate comprising a dielectric layer having an inner face in contact with the outer conductive layer of the upper substrate, and an outer face, opposite the inner face, and covered by an outer conductive layer, the vias of the upper substrate extending, through the dielectric layer of the additional substrate, to the outer conductive layer of said additional substrate, being in electrical contact with said outer conductive layer of the additional substrate, and surrounding a transition surface at the interface between the upper substrate and the additional substrate, the transition surface not being covered by the outer conductive layer of the upper substrate.

[0023] According to a preferred characteristic, the dielectric layer of the upper substrate and the dielectric layer of the additional substrate are made of different dielectric materials.

[0024] Furthermore, the invention relates to an on-board radiofrequency system comprising at least one non-reciprocal microwave component as previously presented. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention will be better understood with the aid of the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which: [ Fig. 1 ] is an exploded and perspective view of a first embodiment of a non-reciprocal microwave component according to the invention; [ Fig. 2 ] is a sectional view of the microwave component of the figure 1 , according to a section plane orthogonal to a plane in which waveguides of said microwave component extend; [ Fig. 3 ] is a sectional view, similar to that of the figure 2 , of a second embodiment of a non-reciprocal microwave component according to the invention; [ Fig. 4 ] is a sectional view, similar to that of the figure 2 , of a third embodiment of a non-reciprocal microwave component according to the invention; [ Fig. 5 ] is a graph illustrating the frequency evolution of the reflection coefficient S 11 of a non-reciprocal microwave component of the state of the art, at three different temperatures; and the figure 6 is a graph illustrating the frequency evolution of the reflection coefficient S 11 of the non-reciprocal microwave component of the figure 4 , at the same temperatures as those of the Figure 5 . DETAILED DESCRIPTION

[0026] A non-reciprocal microwave component 2 (hereinafter referred to as “component 2”) according to the invention is schematically illustrated by the Figures 1 and 2 .

[0027] Such a component 2 is, in particular, intended to provide a circulator function, or even an isolator function.

[0028] Component 2 is intended to be integrated into an on-board radiofrequency system, in particular one carried on board a spacecraft (not shown).

[0029] Component 2 comprises at least three waveguides 4 and a central resonator 6.

[0030] Each waveguide 4 extends along a respective propagation axis XX, and comprises a respective propagation zone 8 for the propagation of electromagnetic waves.

[0031] As it appears on the figure 1 , the waveguides 4 are arranged around the central resonator 6, their respective propagation axes XX extending radially from the central resonator 6, for example at 120° from each other.

[0032] The central resonator 6 and the waveguides 4 are arranged so that electromagnetic waves can circulate between a resonance volume 10 of the central resonator 6 and the propagation zone 8 of each waveguide.

[0033] The central resonator 6 comprises an upper substrate 12, a lower substrate 14 and a magnetized ferromagnetic ceramic element 15 arranged between the upper substrate 12 and the lower substrate 14.

[0034] The upper substrate 12 and the lower substrate 14 have a role of impedance matching between the resonator and the waveguides 4. In addition, the magnetized ferromagnetic ceramic element 15 gives the component 2 its non-reciprocity.

[0035] The upper substrate 12 and the lower substrate 14 extend on either side of the resonance volume 10 intended for the propagation of electromagnetic waves.

[0036] Each of the upper substrate 12 and the lower substrate 14 comprises a dielectric layer 16 having an outer face 18 and an inner face 20 opposite each other. Furthermore, the inner face 20 of the dielectric layer 16 of the upper substrate 12 is oriented towards the inner face 20 of the dielectric layer 16 of the lower substrate 14.

[0037] The dielectric layer 16 is made of a single dielectric material. Alternatively, the dielectric layer 16 comprises a stack of at least two layers made of different dielectric materials.

[0038] The outer face 18 is covered by an outer conductive layer 22. In addition, the inner face 20 is covered by an inner conductive layer 24.

[0039] The inner conductive layer 24 of the upper substrate 12 and the inner conductive layer 24 of the lower substrate 14 are at a distance from each other, in particular separated by a dielectric insulating layer 25, for example air or vacuum.

[0040] Each of the upper substrate 12 and the lower substrate 14 further comprises a plurality of vias 26. Such vias are electrically conductive.

[0041] For each of the upper substrate 12 and the lower substrate 14, the respective vias 26 extend, through the associated dielectric layer 16, between the corresponding outer conductive layer 22 and inner conductive layer 24. Furthermore, for each substrate 12, 14, the associated vias 26 are in electrical contact with the corresponding outer conductive layer 22 and inner conductive layer 24 at connection points 28.

[0042] At the level of the inner conductive layer 24 of each upper 12 and lower 14 substrate, the corresponding connection points 28 surround a free surface 30 of the inner face 20 of the associated dielectric layer 16, this free surface 30 not being covered by the inner conductive layer 24.

[0043] Preferably, the free surface 30 of the lower substrate 14 is opposite the free surface 30 of the upper substrate 12.

[0044] Furthermore, at the level of the dielectric layer 16 of the upper substrate 12, respectively of the lower substrate 14, the corresponding vias 26 surround an upper cavity 32, respectively a lower cavity 34. The cavities 32 and 34 and the magnetized ferromagnetic ceramic element 15 are coupled because the free surfaces 30 are not covered by the inner conductive layer 24.

[0045] Depending on the desired characteristics of the component 2, the shapes of the upper cavity 32 and the lower cavity 34 are likely to be different. Furthermore, the upper cavity 32 and the lower cavity 34 are likely to receive different dielectric materials, in order to give the component 2 the desired characteristics. In particular, these shapes and materials are chosen to achieve satisfactory impedance matching between the waveguides 4 and the central resonator 6.

[0046] As previously indicated, the magnetized ferromagnetic ceramic element 15 gives component 2 its non-reciprocity.

[0047] This magnetized ferromagnetic ceramic element 15 is capable of having any shape leading to desired performances of the component 2, in particular a satisfactory impedance matching between the central resonator 6 and the waveguides 4, or even reflection and / or transmission coefficients whose respective values ​​belong to desired working ranges. For example, the magnetized ferromagnetic ceramic element 15 has a shape of cylinder, prism, sphere, etc.

[0048] As already described, the magnetized ferromagnetic ceramic element 15 is arranged between the upper substrate 12 and the lower substrate 14, and more precisely between the free surface 30 of the upper substrate 12 and the lower substrate 14, in particular between the free surface 30 of the upper substrate 12 and the free surface 30 of the lower substrate 14.

[0049] This magnetized ferromagnetic ceramic element 15 is unique, that is to say that there is only one ferromagnetic ceramic element in the central resonator 6, arranged between the upper substrate 12 and the lower substrate 14.

[0050] The magnetized ferromagnetic ceramic element 15 is made of a soft magnetic material, preferably soft ferrite, magnetized with an external permanent magnet. Preferably, the magnetized ferromagnetic ceramic element 15 is made of highly anisotropic ferrite, for example a hexagonal ferrite, commonly called "hexaferrite". The use of such a material is advantageous insofar as it makes the application, during operation of the component 2, of an external magnetic field intended to polarize the magnetized ferromagnetic ceramic element 15 superfluous. Indeed, a highly anisotropic ferromagnetic ceramic element, in particular hexaferrite, has the property of retaining its magnetization once subjected to a magnetic field.

[0051] It should be noted that element 15 may be an assembly of several stages of ferromagnetic ceramic elements.

[0052] Advantageously, the magnetized ferromagnetic ceramic element 15 extends from the free surface 30 of the inner face 20 of the upper substrate 12 to the free surface 30 of the inner face 20 of the lower substrate 14, being in contact with each of these two free surfaces 30. This eliminates any air gap between the free surface 30 of the inner face 20 of the upper substrate 12 and the free surface 30 of the inner face 20 of the lower substrate 14. Thus, the resistance to corona effects and multipactor are increased because there is no air or void in the junction composed of the cavities 32 and 34 and the magnetized ferromagnetic ceramic element 15.

[0053] Advantageously, the magnetized ferromagnetic ceramic element 15 is surrounded radially, relative to an axis ZZ orthogonal to the free surface 30 of the upper substrate 12, by at least one annular impedance matching coating 36 made of a dielectric or ferromagnetic material.

[0054] An alternative 102 of a non-reciprocal microwave component according to the invention is illustrated by the figure 3 .

[0055] Component 102 of the figure 3 differs from component 2 of the Figures 1 and 2 only in that it further comprises at least one additional substrate. For example, the component 102 comprises an upper additional substrate 112.

[0056] The upper additional substrate 112 extends parallel to the upper substrate 12. This upper additional substrate 112 comprises a dielectric layer 116 having an outer face 118 and an inner face 120 opposite each other.

[0057] The inner face 120 of the upper additional substrate 112 is in contact with the outer conductive layer 22 of the upper substrate 12. Furthermore, the outer face 118 of the upper additional substrate 112 is covered by an outer conductive layer 124.

[0058] In this case, the vias 26 of the upper substrate 12 extend, through the dielectric layer 116 of the upper additional substrate 112, to the outer conductive layer 124 of said upper additional substrate 112, and are in electrical contact with the outer conductive layer 124 of the upper additional substrate 112.

[0059] As it appears on the figure 3, the vias 26 surround a transition surface 130 at the interface between the upper substrate 12 and the upper additional substrate 112. This transition surface 130 is not covered by the outer conductive layer 22 of the upper substrate 12. In this way, the volume radially delimited by the vias 26 extending from the free surface 30 of the upper substrate 12 to the outer conductive layer 124 of the upper additional substrate 112 forms a dielectric cavity 132.

[0060] As before, the magnetized ferromagnetic ceramic element 15 is arranged between the upper substrate 12 and the lower substrate 14.

[0061] Preferably, the dielectric layer 16 of the upper substrate 12 and the dielectric layer 116 of the upper additional substrate 112 are made of different dielectric materials.

[0062] This configuration allows for more complex geometric shapes to be created on the ZZ axis, adding an additional degree of freedom for impedance matching.

[0063] The lower substrate 14 is also capable of receiving a respective lower additional substrate. In this case, the arrangement of the lower additional substrate relative to the lower substrate 14 is similar to what has been described relative to the upper additional substrate 112 and the upper substrate 12.

[0064] An alternative 202 of non-reciprocal microwave component according to the invention is illustrated by the figure 4 .

[0065] Component 202 of the figure 4 differs from component 2 of the Figures 1 and 2only in that the lower substrate 14 has no free surface. In other words, opposite the free surface 30 of the upper substrate 12 is a conductive portion of the inner conductive layer 24 of the lower substrate 14.

[0066] Advantageously, in this case, the magnetized ferromagnetic ceramic element 15 arranged in the central resonator 6 is directly in contact with the inner conductive layer 24 of the lower substrate 14.

[0067] This is advantageous, insofar as, in this configuration, the lower substrate 14 acts as a heat sink, the inner conductive layer 24 of the lower substrate 14 being capable of being optimized to achieve heat transfer to a heat sink.

[0068] Such an effect is advantageous because the saturation magnetization of the magnetized ferromagnetic ceramic element 15 changes with its heating, which is potentially detrimental to the performance of the non-reciprocal microwave component.

[0069] There Figure 5 illustrates the frequency evolution of the reflection coefficient S 11 of a non-reciprocal microwave component of the state of the art, at three different temperatures: 100°C; 20°C and -50°C.

[0070] It is observed that a temperature variation results in a frequency shift. This is due to the thermal variation of the effective permeability of the magnetized ferromagnetic ceramic element.

[0071] There figure 6 illustrates the frequency evolution of the reflection coefficient S 11 of the non-reciprocal microwave component according to the present invention, at the same temperatures as those of the Figure 5 .

[0072] A thermal stabilization of the non-reciprocal microwave component is observed. This thermal stabilization is obtained by selecting a dielectric material or an assembly of dielectric materials forming the cavity 32 above and / or the cavity 34 below the magnetized ferromagnetic ceramic element 15, such that the thermal variation of the permittivity of the material of the cavity 32 and / or 34 acts in a manner opposite to the thermal variation of the non-reciprocal microwave component.

Claims

1. A non-reciprocal microwave component (2) comprising at least three waveguides (4) and a central resonator (6), characterized in that the central resonator comprises an upper substrate (12) and a lower substrate (14) extending on either side of a resonance volume (10) for propagating electromagnetic waves, each of the upper substrate and the lower substrate comprising a dielectric layer (16) having an outer face (18) and an inner face (20) opposite one another, the outer face being covered by an outer conductive layer (22) and the inner face being covered by an inner conductive layer (24), the inner face of the dielectric layer of the lower substrate (14) being oriented toward the inner face of the dielectric layer of the upper substrate (12), the upper substrate (14) further comprising a plurality of vias (26) extending, through the associated dielectric layer, between the corresponding outer conductive layer and inner conductive layer, and being in electrical contact with said outer conductive layer and inner conductive layer at connection points (28), the connection points of the inner conductive layer enclosing a free surface (30) of the inner face of the dielectric layer, the free surface not being covered by the inner conductive layer, a single magnetized ferromagnetic ceramic element (15) being arranged between the free surface of the upper substrate and the lower substrate, each waveguide extending along a respective propagation axis (X-X), each waveguide comprising a propagation zone (8) for propagating electromagnetic waves, the central resonator and each waveguide being arranged so that electromagnetic waves can circulate between the resonance volume of the central resonator and the propagation zone of each waveguide.

2. The non-reciprocal microwave component according to claim 1, wherein the lower substrate (14) also comprises a plurality of vias (26) extending, through the associated dielectric layer, between the corresponding outer conductive layer and inner conductive layer, and being in electrical contact with said outer conductive layer and inner conductive layer at connection points, the connection points of the inner conductive layer enclosing a free surface of the inner face of the dielectric layer, the free surface not being covered by the inner conductive layer, the free surface of the lower substrate facing the free surface of the upper substrate, the magnetized ferromagnetic ceramic element (15) being arranged between the free surface of the lower substrate and the free surface of the upper substrate.

3. The non-reciprocal microwave component according to claim 2, wherein the vias (26) of the upper substrate, respectively the lower substrate, enclose an upper cavity (32), respectively a lower cavity (34), at the corresponding dielectric layer, the upper cavity and the lower cavity having different shapes and / or receiving different dielectric materials.

4. The non-reciprocal microwave component according to any one of claims 1 to 3, wherein the magnetized ferromagnetic ceramic element (15) extends from the free surface of the dielectric layer of the upper substrate to the lower substrate.

5. The non-reciprocal microwave component according to any one of claims 1 to 4, wherein the magnetized ferromagnetic ceramic element (15) is radially surrounded, relative to an orthogonal axis to the free surface of the upper substrate, by at least one annular impedance matching coating (36) made of a dielectric or ferromagnetic material.

6. The non-reciprocal microwave component according to any one of claims 1 to 5, wherein the magnetized ferromagnetic ceramic element (15) is made of ferrite, and is magnetized by an external polarization magnet.

7. The non-reciprocal microwave component according to any one of claims 1 to 6, wherein the magnetized ferromagnetic ceramic element (15) is made of an anisotropic material, preferably a hexagonal ferrite.

8. The non-reciprocal microwave component according to claim 3, wherein the thermal variation of the permittivity of the dielectric material forming the upper cavity (32) and / or the lower cavity (34) acts in an opposite manner to the thermal variation of the non-reciprocal microwave component.

9. The non-reciprocal microwave component (102) according to any one of claims 1 to 8, further including an additional substrate (112) extending parallel to the upper substrate, the additional substrate comprising a dielectric layer (116) having an inner face (120) in contact with the outer conductive layer of the upper substrate, and an outer face (118), opposite the inner face, and covered by an outer conductive layer (124), the vias (26) of the upper substrate extending, through the dielectric layer of the additional substrate, to the outer conductive layer of said additional substrate, while being in electrical contact with said outer conductive layer of the additional substrate, and enclosing a transition surface (130) at the interface between the upper substrate and the additional substrate, the transition surface not being covered by the outer conductive layer of the upper substrate.

10. The non-reciprocal microwave component according to claim 9, wherein the dielectric layer of the upper substrate and the dielectric layer of the additional substrate are made of different dielectric materials.

11. An on-board radiofrequency system comprising at least one non-reciprocal microwave component according to any one of claims 1 to 10.