Planar Y-junction microwave circulator

Abstract

Planar Y-junction microwave circulator The invention relates to a planar Y-junction microwave circulator comprising: - a substrate having an upper face and a lower face; - a resonator having a shape having a symmetry by rotation of 120° with respect to the center of the shape, the resonator being disposed on the upper face; - three input / output lines each comprising a connection zone making a connection with the resonator, the input / output lines being separated from each other by 120°;- a ground plane consisting of a metallic layer covering the lower face, having a point opposite the center, the metallic layer comprising a recess comprising three elementary parts located opposite said connection zones and having a surface area at least equivalent to a surface area of ​​said associated connection zone, said elementary parts having an identical surface area and a symmetry by rotation of 120° with respect to the point. Figure for the abbreviation: Fig. 1a;

Description

Title of the invention: Planar Y-junction microwave circulator

[0001] The invention relates to microwave wave components and more particularly, planar Y-junction microwave circulators.

[0002] In the context of satellite telecommunications systems, designers are facing an increase in the number of users and the data rate demanded per user, due to the massive increase in usage (video streaming, etc.). To address this, new frequency bands in the millimeter wave range have been allocated: 71-76 GHz and 81-86 GHz. These frequency bands (W-band) impose significant constraints on the manufacturing of microwave components related to wavelength, for example, the fineness of metallization etching and the thinning of substrates. Furthermore, the development of new telecommunications systems based on active electronically scanned antennas requires the design of microwave components to prevent parasitic mutual coupling between radiating elements: these are the insulators.

[0003] Ferrite microwave circulators / isolators are used in the transmit / receive modules of modern microwave systems (telecommunications and radar). They are used for systems operating at frequencies from the hundreds of megahertz to the hundreds of gigahertz (0.1–100 GHz). They can be used to perform microwave signal routing functions in these modules. For example, they can be used to transmit and receive simultaneously, on the same frequency band, with the same antenna. The system thus implemented is called a "Full-Duplex" system, as illustrated in [Fig. 1a]. The system comprises a transmitting chain Tx including an isolator Iso and a receiving chain Rx, and between the two, a circulator Cire connected to an antenna Ant. The Cire circulator selectively sends the signal received by the antenna to the receiving chain and the transmitting signal emitted by the Tx chain to the antenna.

[0004] As illustrated in Figures 1b and 1a, when the circulators are connected to a matched load on one of their ports, they become isolators. They serve to protect the amplifier chains against parasitic reflections (by isolating the amplifiers from each other) or against parasitic coupling of the microwave signal from one radiating element (an Ant antenna) to another radiating element (another Ant antenna) in the context of active antennas.

[0005] For all these reasons, it is important to have planar insulators on a hexaferrite substrate, making it possible to perform the insulator function without resorting to to bulky magnets, as used in the state of the art. Indeed, hexaferrite materials have the property of retaining a high remanent magnetization once they have been magnetized. A planar insulator is based on a Y-junction circulator, to which a suitable resistive load is attached. For example, hexaferrite substrates exhibit such dielectric properties (high permittivity > 20) that edge effects ("fringing fields") impose a maximum thickness of 100 µm.

[0006] An example of a planar Y-junction CircO circulator according to the prior art is illustrated [Fig. 2]. The CircO circulator comprises a resonator R0, metal input or output lines L0, L02, L03, a hexaferrite substrate S0, and a metal ground plate PM0. The input or output lines are arranged with 120° symmetry about the center of the resonator R0. A circulator is a three-port component (port 1, port 2, port 3) whose role is to direct signals from one port to a second port within a telecommunications chain, isolating the third. The arrow in the CircO circulator represents its direction of rotation. Each port corresponds to a transmission line or the equivalent of a transmission line of a waveguide propagation mode. The S parameters relate the incident waves with the waves reflected by the ports of the CircO circulator.The S parameters can be defined in matrix form. The S parameter matrix defining the CircO circulator can be given in the following form, for the case of a component rotating in the counterclockwise direction: .

[0007] 511 521 531 512 513' 522 523 532 533.

[0008] The parameters S1, S22, and S33 correspond to the reflection at each respective port. The parameters S21, S13, and S32 represent the transmission coefficient to the coupled port (i.e., from port 1 to port 2, from port 2 to port 3, and from port 3 to port 1). In other words, these parameters S21, S13, and S32 represent the insertion losses. Finally, the parameters S31, S12, and S23 represent the isolation coefficient between ports 1 and 3, ports 1 and 2, and ports 2 and 3, respectively. In other words, in a circulator, the aim is to obtain the highest possible level of isolation (for example, the minimum absolute value S311) and the lowest possible insertion losses (for example, the maximum absolute value S211).

[0009] In the context of designing Y-junction circulators using planar technology on a substrate made exclusively of hexaferrite to simplify production, the substrate thickness is a critical characteristic. Indeed, an increase in substrate thickness results in a significant degradation of the circulator's electromagnetic performance: the insulation level is degraded, as illustrated in Figure 3a. Consequently, this also impacts the coefficient of reflection and insertion losses which are higher. Indeed, Figure 3a compares two input or output lines having the same thickness and the same line width w_a, but arranged on a substrate of different thickness, hl and h2, with h2 > h{.

[0010] Due to the high relative permittivity of hexaferrite substrates, which can exceed 20, the electric field does not remain confined below the metallization. It is observed that, for the same line width M'«, we aw«eff > w“ef f, ' Waeff{ Waefj\ being the effective widths for the thinnest substrate (thickness hl) and the thickest (thickness h2), respectively.

[0011] This is also illustrated in [Fig. 3b] concerning examples of magnetic performance for substrates with thicknesses ranging from 50 µm to 200 µm. Indeed, in [Fig. 3b], the curves represent the isolation coefficient S31 between ports 3 and 1 as a function of frequency. Here, the frequency band of the CircO circulator is between 81 and 86 GHz. The curves in [Fig. 3b] demonstrate that, as the substrate thickness S0 increases, the isolation coefficient S31 decreases in absolute value. These examples therefore show that as the substrate thickness increases, the electromagnetic performance degrades.

[0012] This decrease in electromagnetic performance is due to the spreading of electromagnetic fields in the structure.

[0013] To maintain sufficient electromagnetic performance, edge effects necessitate a very thin substrate, on the order of 100 pm in the Q band (~40 GHz) and on the order of 50 pm in the spatial W band (71-76 GHz and 81-86 GHz). These hexaferrite substrate thicknesses are difficult to achieve by machining; a lengthy polishing step is required. The components thus produced are extremely fragile and can break during handling and during integration into microwave modules and systems.

[0014] Furthermore, due to the high permittivity of these substrates, the design of planar microwave circulators on hexaferrite requires very thin input and output lines, which become increasingly thin as the substrate thickness increases. Indeed, to achieve circulation for a planar circulator in the 81-86 GHz band on a substituted strontium hexaferrite substrate 200 µm thick, it is theoretically necessary to reduce the width of the matching lines to a value well below the minimum values ​​required for etching this type of metallization by an industrial process, in order to ensure optimal coupling.

[0015] Two solutions exist to allow the increase in the thickness of the substrates in the circulators: the use of higher order resonance modes and the assembly of a ferrite disk in a dielectric.

[0016] The use of higher order resonance modes implies a larger component which will offer higher insertion losses.

[0017] Assembling a ferrite disc within a dielectric changes the circulation conditions and also allows for an additional degree of freedom in the design of planar circulators. However, this solution proves to be complicated to implement because it requires complex machining steps, and bonding the ferrite disc to the dielectric is impossible to do simply and systematically.

[0018] One object of the present invention is to remedy the aforementioned drawbacks by proposing a planar microwave circulator with a Y-junction whose ground plane has a recess.

[0019] The invention presented here consists of a planar Y-junction microwave circulator whose ground plane has a recess.

[0020] This structuring of the ground plane allows for increased substrate thickness, particularly in hexaferrites, which simplifies their fabrication by improving their mechanical strength. Furthermore, since the width of the input and output lines is proportional to the substrate thickness for a given impedance value, it becomes possible to produce high-impedance lines that were previously too thin for the metallization and etching process. The resulting increase in thickness also improves the power handling of these components. The invention therefore optimizes the electromagnetic performance of planar circulators while simplifying their fabrication.

[0021] The object of the invention therefore relates to:

[0022] A planar Y-junction microwave circulator comprising:

[0023] - a substrate having a top face in the foreground and a bottom face in a second plan;

[0024] - a resonator having a shape having a rotational symmetry of 120° by relative to the center of the shape, the resonator being positioned on the upper face of the substrate;

[0025] - three input or output lines, each comprising a so-called connection zone associated making a connection with the resonator, the input or output lines being separated from each other by 120°;

[0026] - a ground plane consisting of a metallic layer covering at least a part of the underside of the substrate, the ground plane presenting a point opposite the center and in which a so-called resonator zone is defined opposite the resonator and having a shape identical to the shape of the resonator; and

[0027] characterized in that the metallic layer comprises a recess comprising at least three elementary parts located respectively opposite said zones of connection of input or output lines, each elementary part having a surface at least equivalent to a surface of said associated connection zone and said elementary parts having an identical surface and a symmetry by rotation of 120° with respect to the point, the elementary parts being further disposed outside the resonator zone.

[0028] Optionally, the area of ​​each elementary part is equal to the area of ​​said associated connection zone.

[0029] Optionally, the surface area of ​​each elementary part is greater than the surface area of ​​said associated connection zone.

[0030] Optionally, the recess also has complementary parts connecting the elementary parts together so as to achieve a continuous recess exhibiting a symmetry by rotation of 120° with respect to said point of the ground plane.

[0031] Optionally, the continuous recess has a band shape arranged around the resonator area.

[0032] Optionally, the shape of the resonator is hexagonal, circular or triangular.

[0033] Optionally, the substrate is made of a ferrite material.

[0034] Optionally, the substrate has a thickness greater than or equal to 100 pm.

[0035] Optionally, the input or output lines are microstrip type lines.

[0036] The structuring of the ground plane of planar Y-junction microwave circulators, i.e. the hollowing of the ground plane, makes it possible to limit the spreading of microwave fields outside the resonator and to ensure optimal coupling between the resonator and the input or output lines.

[0037] The following description presents several embodiments of the device of the invention: these examples are not limiting to the scope of the invention. These embodiments present both the essential features of the invention and additional features related to the embodiments considered.

[0038] The invention will be better understood and other advantages will become apparent upon reading the following description, given by way of non-limiting example, and through the figures, among which:

[0039] [Fig.la] [Fig.la] illustrates a so-called "full-duplex" system;

[0040] [Fig.lb] the [Fig.lb] illustrates an amplification chain;

[0041] [Fig. le] the [Fig. le] illustrates a coupling between the radiating elements;

[0042] [Fig.2] [Fig.2] illustrates an example of a planar microwave circulator Y-junction according to the state of the art;

[0043] [Fig. 3a] [Fig. 3a] illustrates two input or output lines having a thickness of different substrate, cross-sectional views;

[0044] [Fig. 3b] [Fig. 3b] illustrates the performance of a microwave circulator Y-junction planar when the substrate thickness is increased

[0045] [Fig.4a] [Fig.4a] illustrates an example of a planar microwave circulator Y-junction according to the invention seen in perspective;

[0046] [Fig.4b] [Fig.4b] illustrates an example of a planar microwave circulator Y-junction seen in the second plane P2 according to the invention;

[0047] [Fig. 5a] [Fig. 5a] illustrates an example of a planar Y-junction microwave circulator seen in the first PI plane according to the invention;

[0048] [Fig. 5b] [Fig. 5b] illustrates an example of a planar Y-junction microwave circulator seen in the first PI plane;

[0049] [Fig. 5c] [Fig. 5c] illustrates an example of a planar Y-junction microwave circulator seen in the first PI plane;

[0050] [Fig. 6a] [Fig. 6a] illustrates an example of a planar microwave circulator Y-junction seen in the second plane P2;

[0051] [Fig. 6b] [Fig. 6b] illustrates an example of a planar microwave circulator Y-junction seen in the second plane P2;

[0052] [Fig. 6c] [Fig. 6c] illustrates an example of a planar microwave circulator Y-junction seen in the second plane P2;

[0053] [Fig. 6d] [Fig. 6d] illustrates an example of a planar Y-junction microwave circulator seen in the second plane P2; and

[0054] [Fig.7] [Fig.7] illustrates the performance of a planar microwave circulator at Y-junction with and without recess in the ground plane.

[0055] The invention relates to a planar microwave circulator with a Y-junction, the ground plane of which includes a recess. Figures 4a and 4b illustrate an example of a planar microwave circulator with a Y-junction according to the invention, one being viewed in perspective and the other in a plane P2.

[0056] The planar Y-junction microwave circulator Cire comprises a substrate S having an upper face Fsup in a first plane PI and a lower face Finf in a second plane P2;

[0057] In one embodiment, the substrate S is made of a hexaferrite material. Hexaferrites are hard ferrites with strong saturation magnetization (up to 5000 G). When in the form of polycrystalline ceramics made of oriented particles, once magnetized, they have the characteristic of retaining a strong remanent magnetization and allow operation without a magnet. For this reason, they are also called self-polarizing ferrites. Advantageously, they exhibit a higher saturation magnetization than garnets as well as a strong coercive field ensuring the stability of their magnetic characteristics. Their anisotropic fields are also between 100 and 1000 times stronger than those found in soft ferrites. These ferrites are therefore advantageous for higher frequency applications (up to 100 GHz).

[0058] In another example, the material is a barium and / or strontium hexaferrite in which a portion of the barium ions and / or a portion of the strontium ions has been substituted by lanthanum ions and a portion of the iron ions has been substituted by cobalt ions, the general chemical formula of the barium-strontium hexaferrite being BaxSryLazFei2w CowOi9+Y, the indices x, y, z and y being defined by :0 <x<l;0<y<l;0<z< 0.3 ; 0 < w < 0.3 et -0.3 < y < 0.3.

[0059] In one example, the material is a hexaferrite in which part of the ions have been replaced by aluminium, the general chemical formula being BaxSryFei2wAlwOi9 with x+y=l and 0 < w < 0.3.

[0060] The microwave circulator Cire also includes a resonator R having a shape with 120° rotational symmetry about the center O of the shape, the resonator R being disposed on the upper face Fsup of the substrate S. Several examples of resonators R are illustrated in [Fig. 5a], [Fig. 5b], and [Fig. 5c], in which the resonators are viewed in the plane of the upper face P2. As illustrated in these figures, in one example, the shape of the resonator R is hexagonal ([Fig. 5c]), circular ([Fig. 5b]), or triangular ([Fig. 5a]). It is noted that for hexagonal or triangular resonators, the input or output lines can arrive either at the edges or at the vertices. Advantageously, the shape of the resonator provides an additional degree of freedom for the component designer to achieve the electrical performance objectives. The resonator R includes a metal, such as gold or silver.

[0061] The microwave circulator Cire also includes three input or output lines L1, L2, L3, each comprising an associated connection zone Z1, Z2, Z3, which makes a connection with the resonator. The input or output lines L1, L2, L3 are separated from each other by 120°. The input or output lines L1, L2, L3 are in the plane P2 of the upper face Fsup of the substrate S. The three connection zones Z1, Z2, Z3 are of identical dimensions, having a surface area Sz.

[0062] The connection zones are zones of the input or output lines L1, L2, L3, but are not part of the resonator R. In particular, they are located on the periphery of the resonator R.

[0063] In one embodiment, the input or output lines L1, L2, L3 comprise a metal, such as gold or silver. For example, the input or output lines L1, L2, L3 may be made of the same material as the resonator R.

[0064] In one embodiment, the input or output lines (L1, L2, L3) are microstrip type lines.

[0065] The microwave circulator Cire also includes a ground plane (PM) consisting of a metallic layer C covering at least a portion of the lower face Finf of the substrate S, the ground plane PM having a point O' opposite the center O and in which a zone called resonator Zr is defined opposite the resonator and having a shape identical to that of resonator R. In other words, the resonator zone Zr and the resonator R have identical surfaces. Thus, like resonator R, the resonator zone Zr of the PM ground plane can be circular, triangular, or hexagonal.

[0066] The metallic layer comprises a recess E consisting of at least three elementary parts PE1, PE2, PE3 located respectively opposite the connection zones Z1, Z2, Z3 of the input or output lines L1, L2, L3, each elementary part PE1, PE2, PE3 having a surface area at least equivalent to the surface area Sz of the associated connection zone Z1, Z2, Z3. The term "recess" refers to a material defect extending through the entire thickness of the metallic layer. The elementary parts PE1, PE2, PE3 have identical surface areas Sp and are symmetrical by a rotation of 120° about point O'. Furthermore, the elementary parts are located outside the resonator zone Zr.

[0067] The recess E has a length le. The length le of the recess E depends on the properties of the materials involved, the geometry of the resonator, and the transmission lines and technological limitations. The length le is defined by the interval:

[0068] 0 <l gap <x,

[0069] where is the wavelength of the microwave wave at the minimum operating frequency.

[0070] The presence of a recess E in the ground plane PM of the Cire circulator according to the invention creates a physical boundary that concentrates the electromagnetic fields inside the resonator R: it reduces the edge effects inherent in the use of substrates with high permittivity. It allows the use of thicker substrates S for the same electrical performance or improves performance at the same thickness. Thus, the constraints on the mechanical strength and shaping of the substrates are relaxed.

[0071] Furthermore, the presence of the recess E allows for an increase in the thickness of the substrate S, without using a substrate S consisting of a ferrite disc within a dielectric. Indeed, the use of a homogeneous substrate comprising, for example, only a ferrite material is made possible, thus simplifying the manufacture of the Cire circulator.

[0072] Furthermore, since the width of the input or output lines L1, L2, L3 is proportional to the substrate thickness S for a given impedance value, it becomes possible to produce high-impedance lines that were previously too thin for the metallization and etching process. The resulting increase in thickness also improves the power handling of these components. The invention therefore makes it possible to optimize the electromagnetic performance of planar circulators while simplifying their manufacture.

[0073] In one embodiment, the PM ground plane comprises a metal, such as gold or silver. For example, the PM ground plane may be made of the same material as the resonator R and / or the input or output lines.

[0074] Figures 6a-6d illustrate examples of planar microwave circulators with a Y-junction seen in the second plane P2. In particular, these figures illustrate examples of PM ground plane.

[0075] In [Fig. 6a], three examples of PM ground planes are illustrated, in which the area Sp of each elementary part PE1, PE2, PE3 is equal to the area Sz of the associated connection zone Z1, Z2, Z3. Thus, in these examples, the width WPE of each elementary part PE1, PE2, PE3 of the recess E is equal to the width W of the associated inlet or outlet line L1, L2, L3.

[0076] In [Fig. 6b], three examples of PM ground planes are illustrated, in which the surface area Sp of each elementary part is greater than the surface area Sz of the associated connection zone Z1, Z2, Z3. Thus, in these examples, the width WPE of each elementary part PE1, PE2, PE3 of the recess E is greater than the width W of the associated input or output line L1, L2, L3. Advantageously, the wider the recess, the greater its impact on electrical performance.

[0077] In [Fig. 6c], three examples of PM ground planes of the Cire circulator according to the invention are illustrated in which the recess E further has complementary parts PC connecting the elementary parts PE1, PE2, PE3 together so as to create a continuous recess exhibiting symmetry by rotation of 120° with respect to point O' of the PM ground plane. Moreover, in these examples, the continuous recess has a band-like shape arranged around the resonator zone Zr. In this configuration, the recess E has a length le that is the same length as the length Iz of zones Z1, Z2, and Z3. In another embodiment, the recess E has a length le that is greater than the length Iz of zones Z1, Z2, and Z3. Advantageously, the greater the length of the recess le, the greater the impact on performance.

[0078] In [Fig. 6d], three examples of PM ground planes of the Cire circulator according to the invention are illustrated in which the recess E further has complementary parts PC connecting the elementary parts PE1, PE2, PE3 together so as to create a continuous recess exhibiting symmetry by rotation of 120° with respect to point O' of the PM ground plane. In this configuration, the recess is not a band of identical thickness but of any shape as long as the 120° symmetry is maintained.

[0079] Thus, in these examples, the hollowing is formed all around the resonator zone Zr, following the shape of the resonator zone Zr ([Fig.6c]) or by forming additional parts having a symmetry by rotation of 120° with respect to point O'.

[0080] For example, as illustrated in [Fig. 6c], when the resonator R is circular, the recess E forms a ring around the resonator area Zr. In another example, when the resonator R is triangular, the recess E forms a triangular band around the resonator area Zr. In yet another example, when the resonator R is hexagonal, the recess E forms a hexagonal band around the resonator area Zr.

[0081] In one embodiment, the substrate S has a thickness greater than or equal to 100 µm. In particular, the substrate S may have a thickness greater than or equal to 200 µm. Advantageously, the recess in the ground plane allows the substrate thickness to be increased, thus enabling the production of high-impedance lines that were previously too thin for the metallization and etching process. The resulting increase in substrate thickness also improves the power handling of these components. The invention therefore optimizes the electromagnetic performance of planar circulators while simplifying their fabrication.

[0082] Figure 7 illustrates the magnetic performance of a planar Y-junction microwave circulator without a recess in the ground plane and the performance of an example of a planar Y-junction microwave circulator according to the invention, respectively. The microwave circulators of the examples illustrated in these figures have a hexaferrite substrate with a thickness of 200 µm, in microstrip lines, for the 81-86 GHz frequency band.

[0083] Fig. 7 shows the curves of the coefficients S21 (i.e. the insertion losses between ports 3 and 1), SI1 (the reflection at port 1) and S31 (the isolation between ports 2 and 1) as a function of frequency, with and without hollowing.

[0084] Figure 7 shows that, without structuring of the ground plane, the circulator offers degraded performance. Indeed, the maximum isolation level achieved in this case is 18 dB at 83 GHz (see S31) and the minimum insertion loss level achieved is 1.76 dB at 83.5 GHz (see S21).

[0085] Figure 7 shows that, for the case of the ground plane circulator with a recess E, the maximum isolation level is 41.6 dB (see S31) and the minimum insertion losses are 0.75 dB (see S21). Furthermore, the SU curve, showing the wave reflection at the component's input, is lower compared to that of the case without a ground plane structure. Indeed, the lower the SI1 parameter, the better, since it is desirable to transmit as much energy as possible from port 1 to port 2. In fact, the reflection at the component's input must be minimal.

[0086] Thus, for an identical substrate, the level of isolation is significantly increased when the ground plane has a recess. Similarly, for an identical substrate, the level of insertion loss and wave reflection at the component input is significantly reduced when the ground plane has a recess. The ground plane structuring circulator therefore makes it possible to guarantee a good level of performance over the entire frequency band studied (here, 81-86 GHz), with a minimum isolation level of 15.6 dB and a maximum insertion loss level of less than 1.02 dB.

[0087] The figures therefore illustrate that the magnetic performance is improved when the substrate has a recess E.

[0088] The circulators according to the invention can then be integrated into microwave telecommunications systems or radar systems. More particularly, the industrial applications immediately targeted by this invention are W-band satellite telecommunications systems (71-76 GHz and 81-86 GHz).

[0089] The industrial applications envisaged at a later stage are lower frequency satellite telecommunications systems such as in low Ka band (17.3 GHz - 20.2 GHz), in high Ka band (~30 GHz), in Q band (~40 GHz), or even radar systems in Ku band (12 - 18 GHz).

[0090] It is also possible to use the circulators according to the invention for radar systems in automobiles (~77 GHz). Furthermore, it is also possible to use the circulators according to the invention in mobile telephony (3G / 4G / 5G / 6G), particularly for systems in the millimeter wave bands of 5G (~60 GHz) and the future 6G, whether at the mobile device level or at the base station level.

[0091] The invention presented here creates a physical boundary that concentrates the electromagnetic fields inside the resonator: it reduces the edge effects inherent in the use of substrates with high permittivity. It allows the use of thicker ferrite substrates for the same electrical performance or improves performance at the same thickness. Thus, the constraints of mechanical strength and shaping of the ferrite substrates are relaxed.

[0092] Adding a recess as claimed significantly increases the impedance of the matching line and allows compliance with the flow requirements for lines with greater widths. Therefore, the design constraint related to impedance matching and the technological constraint related to the fineness of etching thin-film metallizations in industrial processes are relieved.

[0093] Also, increasing the thickness makes it possible to decrease the intensity of the maximum electric field in the component, which makes it possible to postpone the appearance Non-linear spin wave effects occur at higher applied microwave power levels, resulting in improved power handling.

[0094] Although the invention has been illustrated and described in detail using a preferred embodiment, the invention is not limited to the disclosed examples. Other variations can be deduced by a person skilled in the art without departing from the scope of protection of the claimed invention.

Claims

Demands

1. Planar microwave circulator with Y-junction (Cire) comprising: - a substrate (S) having a top face (Fsup) in a first plane (PI) and a bottom face (Finf) in a second plane (P2); - a resonator (R) having a shape having a symmetry by rotation of 120° with respect to the center (O) of the shape, the resonator (R) being disposed on the top face (Fsup) of the substrate (S); - three input or output lines (L1, L2, L3) each comprising an associated connection zone (Z1, Z2, Z3) making a connection with the resonator, the input or output lines (L1, L2, L3) being separated from each other by 120°;- a ground plane (PM) consisting of a metallic layer (C) covering at least part of the lower face (Finf) of the substrate (S), the ground plane (PM) having a point (0') opposite the center (0) and in which a so-called resonator zone (Zr) is defined opposite the resonator and having a shape identical to the shape of the resonator; and characterized in that the metallic layer comprises a recess (E) comprising at least three elementary parts (PE1, PE2, PE3) located respectively opposite said connection zones (Z1, Z2, Z3) of the input or output lines (L1, L2, L3), each elementary part having a surface at least equivalent to a surface (Sz) of said associated connection zone (Z1, Z2, Z3) and said elementary parts having an identical surface (Sp) and a rotational symmetry of 120° with respect to point (0'), the elementary parts being further disposed outside the resonator zone (Zr).;

2. Circulator (Wax) according to claim 1, wherein the surface area (Sp) of each elementary part is equal to the surface area (Sz) of said associated connection zone (Z1, Z2, Z3).

3. Circulator (Wax) according to claim 1, wherein the surface area (Sp) of each elementary part (PE1, PE2, PE3) is greater than the surface area (Sz) of said associated connection zone (Z1, Z2, Z3).

4. Circulator (Wax) according to claim 1, wherein the recess further comprises complementary parts connecting the elementary parts (PE1, PE2, PE3) together so as to achieve a

5.

6.

7.

8.

9. obviously continuous exhibiting a symmetry by rotation of 120° with respect to said point (O') of the ground plane (PM). Circulator (Wax) according to the preceding claim, wherein the continuous recess has a band shape arranged around the resonator zone (Zr). Circulator (Wax) according to any one of the preceding claims, wherein the shape of the resonator is hexagonal, circular or triangular. Circulator (Wax) according to any one of the preceding claims, wherein the substrate is made of a ferrite material. Circulator (Wax) according to any one of the preceding claims, wherein the substrate has a thickness greater than or equal to 100 pm. Circulator (Wax) according to any one of the preceding claims, wherein the inlet or outlet lines (L1, L2, L3) are microstrip type lines.

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