EP2571098B1 - Reconfigurable radiating phase-shifter cell based on resonances, slots and complementary microstrips - Google Patents

Description

The field of the invention is that of reconfigurable radiative phase-shifting cells. It applies in particular to reflector networks for an antenna intended to be mounted on a spacecraft such as a telecommunications satellite or on a terrestrial terminal for telecommunication or satellite broadcasting systems.

A reflecting array antenna ("reflectarray antenna") comprises a set of radiant phase-shifter cells assembled in one or two-dimensional array and forming a reflective surface for increasing the directivity and gain of the antenna. The radiative phase-shifting cells of the reflector network, of the metal-pellets (also called "metal patches") and / or slot-type, are defined by parameters which can vary from one cell to another, these parameters being for example the geometric dimensions of the etched patterns (length and width of "patches" or slits) that are set to obtain a desired radiation pattern.

The radiative phase-shifting cells may consist of metal patches charged with radiating slots and separated from a metal mass plane of a typical distance between λg / 10 and λg / 6, where λg is the guided wavelength in the spacer medium. This spacer medium may be a dielectric material, but also a composite stack produced by a symmetrical arrangement of a honeycomb type separator and dielectric skins of thin thicknesses. For an antenna to be efficient, it is necessary that the elementary cell can precisely control the phase shift it produces on an incident wave, for the different frequencies of the bandwidth. It is also necessary that the manufacturing process of the reflector network is as simple as possible.

For this, the plaintiff filed in the past a first French patent application FR 0450575 entitled "phase-shifting cell to linear polarization and resonant variable length by means of "mems" switches. The figure 1 represents an embodiment of this type of CD phase shifter cell. Its operating principle consists in modifying the electrical length of the slot FP by placing one or more variable localized and controlled loads DC 'in several different states allowing and preventing the establishment of a short circuit. The variation of the characteristic resonant length of the cell makes it possible to modify the phase shift of the waves to be reflected. For an antenna, the waves come from the RF source. A cell according to the figure 1 comprises a substrate SB having a rear face secured to a ground plane.

This phase-shifting cell only works for a single linear polarization of the incident wave. In addition, the size of the cell is relatively large, of the order of 0.7 λ, where λ denotes the wavelength. The mesh of the reflective network, ie the spatial periodicity according to which the cells are arranged in a network, is therefore much greater than 0.5λ. This results in a non-optimal behavior for very oblique incidences of the wave, related to the possibility of excitation of a mode of Floquet higher order. This effect results in degradation of the secondary lobes of the radiation pattern, also designated by the person skilled in the art as the "image lobe".

The phase shifter cell functions primarily as a "patch" type resonance, modulated by the electrical length of the slot or slots. The realization of a phase cycle greater than 360 ° by the modulation of this single resonance is a critical point, and certain phase states are made by very resonant configurations of the phase-shifter cell. These highly resonant configurations are also characterized by higher losses, as well as higher sensitivities of electrical characteristics to manufacturing uncertainties of the cell and variable and controlled localized loads.

The Applicant filed a second French patent application entitled "Optimally Arranged Reflector Network and Antenna With Such Reflector Network". It presents a phase cycle carried out by phase-shifting cells having a progressively progressive internal structure from a phase-shifting cell to another phase-shifting cell. adjacent, and thus not introducing strong ruptures of periodicity on the reflecting surface. This type of cell thus makes it possible to avoid, in the radiation pattern, the disturbances induced by a parasitic diffraction phenomenon on areas with sudden rupture of periodicity. The figure 1 bis represents an example of a periodic pattern comprising a one-dimensional arrangement of a plurality of elementary radiating elements and making it possible to obtain a phase rotation of 360 °. It has the property of having the same extreme phasing cells of the phase cycle. A progressive phase cycle has also been proposed from a phase-shifting cell with variable and controlled localized loads.

The figure 2 presents the diagram of a radiant phase-shifting cell for such a reflector grating. This phase-shifting cell is, according to one embodiment, in the form of a cross with two perpendicular branches. The cross has three concentric annular slots 81, 82 and 83 made in a metal patch. Variable localized and controlled loads 85 are arranged in a chosen manner in the slots and make it possible to vary the electrical length of the slots and therefore the phase of a wave reflected by the phase-shifting cell. From several cells, it is possible to produce on the surface of a reflector a pattern with progressive phase variation and not having a sudden transition, by using several radiating elements having the same geometry, the same number of MEMS positioned at same place in the annular slots, but MEMS configured in different states. For example, with a pattern consisting of several cross-shaped or hexagonal radiating elements, provided with three concentric annular slots and MEMS in each slot, it is possible to progressively vary the phase up to 1000 ° in short. progressively circulating the different slots of the adjacent radiating elements to obtain a radiating element having all its MEMS in the closed state, then on several additional adjacent elements, to gradually put the MEMS in the open state until a radiating element is obtained having all his MEMS in the open state.

If it is possible to carry out a phase cycle greater than 360 °, and having the same initial and final phase-shifting cell of the cycle, it is very difficult to obtain these phase states with poorly resonant cells. A large number of resonant modes may be potentially excited, due to the presence of several resonators. The appearance of these resonant modes can lead to a sudden variation of the phase as a function of frequency. Rapid phase changes result in significant losses especially when ohmic MEMS are used and sensitivity to MEMS fabrication dispersions.

An object of the invention is to propose a variable phase and controlled localized phase shifter cell (microswitches) making it possible to cover a range of phase shift with a reduced frequency variation of the phase, in other words with a more linear, more stable behavior of the phase according to the frequency of the incident signal. In other words, an object of the invention is to minimize the resonant nature of the cell.

For this purpose, the subject of the invention is a radiant phase-shifting cell comprising a plurality of conductive elements formed on the surface of a substrate, above and away from a ground plane, said conductive elements being separated by slots , the arrangement of the slots forming an equivalent resonator whose electrical shape configures the phase shift applied on a wave to be reflected, characterized in that the cell comprises controlled variable loads able to vary the length and / or the electrical width of said slots, the conductive elements and the variable loads controlled are arranged so that, according to at least a first configuration of said charges, a conductive surface of microwave signals is formed in order to create an inductively dominant resonator, and so that, according to at least one second configuration, a slot is formed around at least one conductive element to create a resonator dominated said capacitive surface, said conductive surface formed in the first configuration surrounding said conductive element around which a slot is formed in the second configuration.

The management of the resonances of the slots and the resonators of the microstrip type is carried out so as to rather excite an equivalent resonance of the "slits" type in a first part of the phase cycle, and rather equivalent resonance of the "microstrip" type (also called "microstrip"). patch ") in a second part of the phase cycle. The first part of the cycle phase corresponds to a resonator whose predominant behavior is inductive, in other words, whose equivalent resonator is more that of a parallel LC resonator than that of a serial LC. The second part of the phase cycle corresponds to a resonator whose predominant behavior is capacitive, that is, whose equivalent resonator is more that of a series LC resonator than that of a parallel LC.

The equivalent resonators of the variable and controlled localized phase-shifting cell can describe a cycle similar to that presented in figure 1bis . This property makes it possible, for example, to perform a phase cycle greater than 360 °, and to have similar equivalent resonators for the extreme values of the phase cycle.

This property also makes it possible to optimize the bandwidth of the phase-shifting cells. The phase range of 360 °, for example, can indeed be segmented into two sub-ranges of about 180 °. This segmentation into two sub-ranges is made possible by the complementarity of the resonant modes of slot or patch type.

Minimizing the resonance results in lower losses. The more the phase varies in a linear fashion, the more this characteristic is obtained over a wide band (as opposed to a threshold type operation). Bandwidths of the order of 30% can be obtained thanks to the cell according to the invention.

The periodic arrangement of the radiant phase shifter cell according to the invention defines a reflector panel of an antenna assembly. The assembly may, in addition, comprise a plurality of reflector panels comprising phase-shifting cells according to the invention.

Advantageously, the conductive surface on the front face is separated from the ground plane by a distance equal to a quarter of the wavelength of the incident signal. In this way, the resonances in slot mode (first configuration) and in microstrip mode (second configuration) can be separated by 180 °.

According to one embodiment of the radiative phase-shifter cell according to the invention, the conductive element around which a slot is formed in the second configuration is located substantially in the center of the cell, the conductive elements forming the conductive surface being located at the periphery, said conductive surface being annular, each of said peripheral conductors being connected to the central conductor and neighboring peripheral conductors via controlled capacitive loads. By "annular" is meant a slot shaped closed loop. This is formed by the interconnection of different peripheral conductive elements. Its shape may be, for example, rectangular, circular, hexagonal or any other polygonal shape, or closed curve.

The conductive elements may take the form of a cross with four branches aligned in several rows, the crosses belonging to two successive rows being offset relative to each other, the crosses being connected via controlled variable capacitive loads. The shape of the conductive elements may be different, for example, square patches, disc-shaped areas. An advantage of the cross-shaped conductive elements is that they allow easier interconnections.

According to another embodiment of the radiative phase-shifting cell according to the invention, said annular conductive surface is formed by conducting ribbons framed by annular slots, said ribbons being connected by capacitive charges able to modify the length and / or the electrical width. interconnecting slots of said annular slots.

In other words, the cell may comprise a conductive surface in which at least two first substantially concentric slots are spaced apart from one another, the conductive surface being disposed above a ground plane, arrangement of the slots forming an equivalent resonator whose electrical shape configures the phase shift applied to an incident wave, the cell being characterized in that it comprises interconnection slots connecting said first slots to each other, and a plurality of variable charges controllers adapted to vary the length and / or the electrical width of said first slots and said interconnection slots, said charges being activatable to configure the cell according to a resonator substantially equivalent to a parallel LC circuit, said charges being also activatable according to at least another configuration to configure the cell according to a substantially equivalent resonator to a LC series circuit.

This same phase-shifting cell can also be considered as the arrangement of microstrip resonators, namely a metal frame, an intermediate metal ring cut at several points, and a metal central patch. The connections made by variable and controlled localized loads - also called micro-actuators, microswitches or short-circuiting means - make it possible to modify the length and / or the electrical width of the equivalent microstrip resonator.

According to another embodiment of the cell according to the invention, the cell comprises more than two concentric slots. It comprises for example three slots, with interconnection slots between each successive concentric slot.

According to one embodiment of the radiant phase shifter cell according to the invention, when the cell is in the first configuration, the charges connecting the peripheral conductive elements to each other are activated, the charges connecting the central conductive element to the peripheral conductive elements being deactivated. , so as to form a resonant slot whose main contribution is equivalent to that of a parallel LC circuit.

Advantageously, the charges connecting the peripheral conductive elements to each other are adapted to take multiple values between two extreme values in order to be able to vary the dimensions of the resonant slot according to said values progressively.

According to one embodiment of the radiative phase-shifter cell according to the invention, when the cell is in the second configuration, the charges connecting the peripheral conductive elements to each other are deactivated, the charges connecting the central conductive element to the peripheral conductive elements being activated. , so as to form a resonant microstrip whose main contribution is equivalent to that of a series LC circuit.

Advantageously, the charges connecting the central conductive element to the peripheral conductive elements are adapted to take multiple values between two extreme values in order to be able to vary the dimensions of the gradually equivalent resonant microstrip according to said values.

According to one embodiment of the radiative phase shifter cell according to the invention, the charges connecting the central conductive element to the peripheral conductive elements are adapted to vary independently of the value of the charges connecting the peripheral conductive elements to each other, so that the phase difference range applied to the incident wave is decomposed into two phase shift intervals, the phase shifts applied in the first interval being obtained with a resonant slot type configuration, the phase shifts applied in the second range being obtained with a microstrip type configuration resonant.

According to one embodiment of the radiant phase-shifter cell according to the invention, the variable charges and the dimensions of the conductive elements are determined so that the configuration of the cell making it possible to apply the phase shift corresponding to the first end of the phase-shift range is identical to the configuration of the cell for applying the phase shift corresponding to the second end of the range.

According to one embodiment of the radiative phase-shifting cell according to the invention, the phase-shift range is 360 °.

According to one embodiment of the radiative phase-shifting cell according to the invention, the conductive elements, the slots and the capacitive charges are arranged on the cell according to a center of symmetry placed at the center of the cell.

According to one embodiment of the radiative phase-shifter cell according to the invention, the capacitive charges are diodes, MEMS, or ferroelectric capacitors.

The subject of the invention is also a reflector array comprising a plurality of radiative phase-shifting cells as described above, said cells forming the reflecting surface of the grating.

The invention also relates to an antenna comprising a reflector network as described above.

• la figure 3, un exemple d'un schéma d'architecture mécanique et de positionnement de charges localisées variables et commandées d'une cellule déphaseuse rayonnante selon l'invention, en vue de face du plan de rayonnement de la cellule ;
• la figure 4, un exemple d'un cycle de cellules déphaseuses rayonnantes selon l'invention couvrant une plage de déphasage de 360°; la figure représente un exemple d'agencement de l'architecture mécanique et de la configuration des charges localisées variables et commandées pour chaque cellule déphaseuse du cycle ;
• la figure 5a, une représentation du résonateur équivalent lorsque la cellule déphaseuse selon l'invention est en mode de résonance « fente » ;
• la figure 5b, une représentation du résonateur équivalent lorsque la cellule déphaseuse selon l'invention est en mode de résonance « microruban » ;
• la figure 5c, un modèle électrique de la cellule déphaseuse selon l'invention ;
• les figures 6a et 6b, des cellules déphaseuses selon l'invention à MEMS capacitifs ;
• la figure 7, un autre mode de réalisation de la cellule déphaseuse selon l'invention ;
• la figure 8a, une illustration d'un premier type de dispositif de commande des charges variables utilisées pour reconfigurer la cellule déphaseuse selon l'invention ;
• la figure 8b, une illustration d'un deuxième type de dispositif de commande des charges variables utilisées pour reconfigurer la cellule déphaseuse selon l'invention ;
• la figure 9, un mode de réalisation de la cellule déphaseuse selon l'invention dans laquelle des vias sont disposés pour faire transiter les signaux de commandes vers les charges capacitives variables ;
• la figure 10, un autre mode de réalisation d'une cellule déphaseuse rayonnante selon l'invention ;
• la figure 11, une pluralité de configurations prises successivement par une même cellule déphaseuse telle que celle présentée en figure 10 ;
• la figure 12, un exemple de moyens d'acheminement des signaux de commande vers une cellule déphaseuse telle que celle de la figure 10.

The invention will be better understood and other advantages will appear on reading the description which follows, given by way of non-limiting example, and by virtue of the appended figures among which:

• the figure 3 an example of a mechanical architecture scheme and localized variable and controlled load positioning of a radiative phase shifter cell according to the invention, in front view of the radiation plane of the cell;
• the figure 4 an example of a cycle of radiative phase shifters according to the invention covering a range of 360 ° phase shift; the figure shows an example of arrangement of the mechanical architecture and the configuration of variable and controlled localized loads for each phase-shifting cell of the cycle;
• the figure 5a , a representation of the equivalent resonator when the phase-shifter cell according to the invention is in "slot" resonance mode;
• the figure 5b , a representation of the equivalent resonator when the phase-shifter cell according to the invention is in "microstrip" resonance mode;
• the figure 5c an electrical model of the phase-shifting cell according to the invention;
• the Figures 6a and 6b phase-shifting cells according to the invention with capacitive MEMS;
• the figure 7 another embodiment of the phase-shifter cell according to the invention;
• the figure 8a , an illustration of a first type of variable load control device used to reconfigure the phase shifter cell according to the invention;
• the figure 8b , an illustration of a second type of variable load control device used to reconfigure the phase shifter cell according to the invention;
• the figure 9 , an embodiment of the phase-shifter cell according to the invention in which vias are arranged for passing the control signals to the variable capacitive loads;
• the figure 10 another embodiment of a radiant phase-shifting cell according to the invention;
• the figure 11 , a plurality of configurations successively taken by the same phase-shifting cell as that presented in FIG. figure 10 ;
• the figure 12 , an example of means for routing the control signals to a phase-shifting cell such as that of the figure 10 .

The figure 3 presents an embodiment of a radiant phase shifter cell 200 according to the invention. The cell 200 comprises a planar structure as described in the phase-shifting cells of the state of the art and the figure 3 represents the front view of the planar structure. Typically a planar structure comprises a substrate having a rear face secured to a ground plane and a front face. The materials used to form the substrate, the dielectric layers and the conductive layers do not limit the scope of the invention. For example, mention may be made of the materials named in the documents of the state of the art described above.

The phase shifter cell 200 is preferably of rectangular shape. However, other embodiments are possible and may be mentioned by way of non-limiting example a hexagonal shaped surface or circular shape.

The cell comprises at least two first slots, a first slot 202 and a second slot 203 concentric. The first slot 202 is positioned at the outer periphery with respect to the second slot 203, that is to say at a greater distance from the center of the patch relative to the second slot 203. The phase-shifter cell 200 may comprise two slots 202 and 203 or more, as illustrated on the figure 3 . Preferably, the slots 202 and 203 have a shape extending longitudinally to the shape of the metal frame 201. Thus, the slots 202 positioned at the outer periphery of the patch surround the slots 203 at the inner periphery. If the phase-shifting cells are intended to operate for a single linear polarization, it is possible to short-circuit the concentric slots at a point where the electric field is zero, as shown in FIG. figure 7 . This possibility is not available when the cell is intended to operate in double linear polarization, because at the point where the electric field is zero in the concentric slot for a linear polarization, it is maximum for the other linear polarization orthogonally. The periphery 201 of the cell is separated from the outer concentric slot 202 by a conductive strip 208, also known as the "frame".

The slots 202 and 203 are connected by at least four interconnection slots 204. This slot arrangement defines metal strips 207 placed in interface between the concentric slots 201, 202. In addition, localized variable and controlled loads 206 are arranged at selected locations on the first slots 202 and 203, and on the interconnection slots 204. These are for example on / off switches for making short circuits, or variable capacitive loads. The purpose of the switches is to change the length and / or electrical width of the equivalent "slot" resonator or equivalent "microstrip" resonator.

According to the invention, the various variable and controlled localized loads 206 of the phase-shifting cell are controlled to configure the length and / or the electrical width of the first slots 202 and 203 so that the equivalent resonator of the phase-shifting cell acts as a phase-shifting cell. introducing a selected phase shift onto an incident wave. The variation of the electrical length of the interconnected slots 202, 203 and 204 modifies the electrical dimensions of the equivalent slot or patch resonator. Thus, thanks to the variable and controlled localized loads 206, it is possible to obtain a phase-shifting cell covering a phase shift range of at least 360 ° delimited by a first extreme value and by a second extreme value. It is also possible, advantageously, to obtain a cell whose electrical form of the equivalent resonator is identical for the first and for the second extreme value. Within the phase shift range, the phase shift values of the same cell can vary continuously or discontinuously. Electronic control means, described below with regard to figures 8a , 8b , and 9 are able to control variable localized loads and controlled so as to vary the phase shift continuously or discontinuously.

In particular, two methods can be distinguished for modifying the electrical parameters of the slots: the first is to dispose of the microswitches ON / OFF along the slot, and to vary the length of the section of the slot between two switches performing a short circuit (ON). Advantageously, when the ground plane is separated from the front surface of the antenna by a thickness equal to a quarter of the guided wavelength, then it is possible to cover the entire phase of 360 °.

According to the first method, the microswitches are activated according to a progression making it possible to approach the cycle of equivalent cells. An example is proposed: the first cell 401 of the cycle illustrated in figure 4 is where all the micro-switches are in the low state. The phase difference is 180 °, corresponding to the response of a metallized plate. Gradually, from the second cell illustration 402 to the fifth cell illustration 405, the microswitches are released in the center of the cell, to perform a function equivalent to an opening in the metallized plate, the size of which increases. . Then, starting from the sixth illustration of cell 406, the microswitches are progressively closed again from the center, to have an operation equivalent to that of a central patch which expands, until finding for the ninth illustration 409 a identical configuration to the first illustration of cell 401. With such a progression, the cycle travels a phase shift over a range of value delimited by a first extreme value and by a second extreme value, with a configuration of micro-switches identical for the first and for the second extreme value, without having to operate around a resonance frequency.

This first method of modifying the electric parameters of the slots requires a significant number of micro-switches. It is possible to reduce the number, and optimize the cycle to cover a range of sufficient phase shift. However, if the number of micro-actuators is significantly reduced, it will not be possible to avoid the excitation of higher modes inside this cell. These higher modes make it possible to carry out a phase shift, but are often associated with greater frequency variations of the phase. They can also induce cross polarization radiation. The micro-switches are reconfigurable localized loads, for example MEMS type (acronym for Micro Electro-Mechanical System), diodes, or variable ferroelectric capacitors.

Advantageously, a phase-shifting cell producing the same phase for the two linear polarizations is invariable by rotation. This property of symmetry avoids exciting higher modes contributing to the cross polarization, and also can alter the stability of the phase in the main polarization. A minimum of four MEMS per command must generally be used to respect this symmetry constraint.

Advantageously, a phase-shifting cell operating in linear double polarization and producing independent phases in each of the linear polarizations has two axial symmetries. This property avoids exciting higher modes contributing to the cross polarization, and also can alter the stability of the phase in the main polarization. Such a property requires the use of a minimum of two MEMS per command and bias.

Advantageously, a cell operating in simple linear polarization has two axial symmetries. This property avoids exciting higher modes contributing to cross polarization and may also alter the stability of the phase in the main polarization. Such a property requires the use of a minimum of two MEMS per command.

Degraded embodiments can also be realized, for example with the aim of reducing the number of MEMS, or of increasing the number of phase states for the same number of MEMS. Thus, it is possible to slightly vary the location of the MEMS around these symmetries, or to modulate slightly the value of the capacitances achieved by these MEMS arranged at the symmetrical locations.

The second method for managing the phase cycle by successively exciting a slot-like or patch-type equivalent resonator is to vary the capacitive loading of the slots. A slot is loaded by a capacity, for example at its center. This capacitive loading of the slot makes it possible to vary the speed of the phase in the slot, and thus to modify their resonance frequency. The capacity variation can be performed using several digital capabilities. The concept is derivative of distributed capacitive loading transmission lines DMTL (Distributed MEMS Transmission Line).

An example of progression is presented below in relation to Figures 6a and 6b . In a first part of the phase cycle, illustrated in figure 6a , the interconnect slots are not loaded. The capacitive loads of the concentric slots, on the other hand, are varied. The phase-shifting cell operates in the same way as a slot whose length and electrical width parameters are varied. In a second part of the cycle, illustrated in figure 6b , the concentric slits are non-resonant. The capacitive loads of the interconnection slots are varied, thus connecting the four pieces of tape 207 (cf. figure 2 ) of the intermediate microstrip ring. The phase-shifting cell operates in the same way as a microstrip resonator whose length and electrical width parameters are varied.

In the case where variable capacitive loads are used to short-circuit the slots, these charges can be realized by means of a micro-switch in series with a capacitance. The usual loading capacity values for changing slot resonances are between 20 and 200 fF for operation around 10 GHz. Nevertheless, it is not always easy to achieve varying capacities, and it is possible to vary the capacity in digital increments. In this case, the load consists of several parallel capabilities connected to a switch.

As illustrated in figure 4 , the 360 ° phase shift range begins and ends optionally with an identical equivalent resonator. The cell according to the invention can thus cover a range of 360 ° by a loopback of the equivalent resonator shape. Thus, a reflecting surface may consist of several periodic patterns, a pattern consisting of several adjacent phase shifters each configuring a near phase shift, to avoid a significant break in the shape of the equivalent resonator of two adjacent cells. This reduces the parasites formed in the beam reflected by the reflective surface. The electrical dimensions of the equivalent resonator depend on the length and / or the electrical width of the slots 202 and 203. Calculation and control means adapted to control the variable localized loads of the cells of the reflective surface allow to configure the desired phase shift. According to another embodiment, there is no loopback of the equivalent resonator shape; in other words, the 360 ° phase shift range can start and end with two different configurations.

In the first sub-range, a slot-like resonance is excited, of which an equivalent diagram is presented in figure 5a . In this first sub-range, the phase-shifting cell behaves with respect to the incident wave, as a parallel LC circuit 501.

In the second sub-range, a microstrip resonance is excited, the equivalent diagram is presented in figure 5b . In this second sub-range, the phase-shifting cell behaves with respect to the incident wave, like a series LC 502 circuit. The ground plane separated from the conductive surface on the front face can be represented by a transmission line 504. .

In summary, the double resonance phase shifter cell can be likened to two parallel LC circuits 503, 505 placed in series. Depending on the values of the inductive and capacitive parameters, the cell can be placed in a "slot" mode as illustrated in FIG. figures 5a and in the configurations 402, 403, 404, 405 of the figure 4 or in a "patch" mode, as illustrated in figure 5b and in the configurations 406, 407, 408, 409, 401.

The phase-shifting cell according to the invention provides a significant advantage over a phase-shifting cell of the prior art, based on a single resonance (slit or microstrip type). In fact, for a cell of the prior art, it is necessary to make a 360 ° excursion by modifying the only parameters of the electric length and width of the resonator. This constraint leads to very resonant behaviors. By using the fact that the cell is based on complementary slot and microstrip resonances operating on reduced ranges, the resonance stresses are significantly reduced, and it is thus possible to significantly widen the bandwidth of the phase-shifter cell.

The figure 5c represents an equivalent diagram of the phase-shifting cell according to the invention. Depending on the configuration of the reconfigurable charges of the cell, it can adopt a behavior close of the "slot" configuration illustrated in figure 5a , or a behavior close to the "microstrip" configuration illustrated in figure 5b .

The figure 6a and the figure 6b represent phase shifters according to the invention with capacitive MEMS. The figure 6a represents the case where the interconnection slots 640 are lightly charged and the capacitive loads of the slots 650 are varied. The cell in such a configuration is equivalent to a slot-type resonator whose length and electrical width would be varied. The figure 6b represents the case where the interconnection slots 640 are capacitively charged and the capacitive loads of the slots are varied. The cell in such a configuration is equivalent to a "microstrip" resonator whose length and electrical width would be varied.

According to the embodiment of the figure 7 , the radiant phase-shifter cell 700 is of rectangular shape with four first slots 702 and 703 and four second slots 704. Two first slots 702 and 703, interconnected by two second slots 704, are positioned in a first half of the conductive surface 708. The two other first slots 702 and 703, interconnected by the other two second slots 704, are positioned in the second half of the conductive surface of the patch. The first slots 702 and 703 have a physical width advantageously chosen to be of the same order as that of the intermediate metal strips 707. Nevertheless, according to other embodiments, the widths of the slots 702 and 703 and the intermediate metal strips 707 can be different.

The phase-shifter cell 700 of the figure 7 is particularly suitable for the reflection of linear polarized incident waves. A portion 705 of the conductive layer separates the first slots 702 and 703 from the upper half of the first slots 702 and 703 of the lower half of the patch.

The routing of the control signals to the microswitches arranged on a phase-shifting cell is also a problem. This routing must not disturb the radiation of the reflector network. Advantageously, the invention also proposes an answer to the resolution of this problem.

As illustrated in figure 8a to limit routing constraints, a distributed control architecture is proposed. The control information is transmitted for example digitally to a specialized integrated circuit (ASIC) 801 placed near the variable loads controlled on the rear face 810 of the antenna panel. This circuit transforms the information received into a control signal adapted for each controlled load. A difficulty therefore consists in routing these control signals from the rear face to each load located on the front face 820 of the reflector network, by not disturbing the electromagnetic operation of the radiating cells.

In a first embodiment, illustrated in figure 8a , the panel consists of a multilayer dielectric substrate on which is shown on the front face of the radio frequency (RF) chips, comprising the metallic pattern of the cell, and the MEMS. These RF chips are then called monolithic, and for example made of quartz, fused silica or alumina. The dielectric substrate, for example in RO 4003, carries out the spacer function between the RF chips 803 and the ground plane, and carries out the traverses of the control signals towards the DC chips reported on the rear face of the substrate. The routing of the control signals on the front panel is then performed within the RF chips. The microelectronic methods can be used to make the resistive lines, at least in sections, where these lines intersect slots.

In a second embodiment illustrated in figure 8b the panel consists of a multilayer dielectric substrate on which is engraved the metal pattern 851 of the cell, and on which are reported MEMS 853 components. This is a hybrid concept.

As illustrated in figure 9 it is possible to arrange the vias 901 commands at the periphery of the cell (in the frame 908), or in its center, without fundamentally altering its operation. Also, the periodic arrangement of peripheral metal bushings may have the same effect as a metallic peripheral wall connecting the frame 908 and the ground plane. Several of these vias can then be used to route control signals from the back to the front. It is also possible to connect the central patch of cell 903 to the ground plane via a metal bushing without modifying significantly its electrical behavior. A control via 902 can therefore also be implemented here. When this via is used for the control, it must be isolated from the pattern to avoid any risk of electrical short circuit.

A difficulty then consists in routing on the front face this control signal without altering the operation of the phase-shifting cell. If the technology makes it possible to produce very resistive lines (typically 10 kΩ /), the commands can be conveyed to the MEMS without particular precautions. The control tracks can for example pass through resonant slots without altering their behavior. However, it may also be advisable to use these resistive lines with moderation, so that the total impedance of the line is not too important. This is the case for example if a diagnostic device is used, to check if the micro-switch has been correctly activated. In this case, the command line may be resistive by section, these sections corresponding to the penetrations of the slots.

The figure 10 presents another embodiment of a radiant phase-shifting cell according to the invention. The cell comprises a plurality of conductive elements 1001, 1002 in the form of, for example, printed patterns on a dielectric substrate. The cell comprises a central conductive element 1001 and four peripheral conductive elements 1002 placed around this first conductive element 1001, the centers of the four peripheral conductive elements 1002 forming a square in the center of which the central conductive element 1001 is placed. interconnection 1004 are interposed between each of the conductive elements 1001, 1002.

The conductive elements 1001, 1002 are connected with the interconnecting conductive elements 1004 by variable and controlled capacitive loads 1006.

Due to its reduced dimensions, a conductive element 1001 does not, on its own, create a resonant mode. It is the interconnection of these conductive elements that can make it possible to establish such a mode.

In the example, each conductive element has a cross-shaped pattern with four orthogonal branches, so that for aligned conductive elements, the ends of the branches of the crosses belonging to two adjacent crosses are close and easily connectable by an interconnecting conductive element 1004.

Variable and controlled capacitive loads 1005 are arranged in interface between the interconnecting conductor elements 1004 and the ends of the branches of the crosses forming the conductive elements 1001, 1002.

The figure 11 illustrates a plurality of configurations taken successively by the same phase-shifting cell as that presented in FIG. figure 10 .

In a first configuration 1101, the cell behaves like a solid metal patch. All conductive elements are connected by capacitive loads. This first configuration 1101 may, for example, be used to effect a phase shift of the incident wave around 180 °.

In a second configuration 1102, the central capacitive charges 1110 - those which in the example are placed in interface between the central conductive element and the interconnecting conductive elements - are reduced, so that the cell behaves like an opening in the plane of mass, in other words, like an annular cleft 1150. The cell has an inductive behavior. This second configuration 1102 may correspond to a phase shift progressively moving away from 180 ° to reach, for example, about 80 ° when the central capacitors are totally discharged.

In a third configuration 1103, the peripheral capacitive loads 1120 - i.e. those which in the example are interfaced between the peripheral conductive elements and the interconnecting conductive elements - are decreased, so that the behavior inductive is attenuated in favor of a capacitive behavior of the radiating cell. This third configuration 1103 may correspond to a phase shift variation of between 80 ° (second configuration 1102) and -20 ° when the peripheral capacitors have totally discharged.

In a fourth configuration 1104, the central capacitive loads 1110 are increased, while the peripheral capacitive loads are still discharged. The cell has, in this fourth configuration 1104, a capacitive behavior. This fourth configuration 1104 may correspond to a phase shift variation of between -20 ° and -50 °.

In a fifth configuration 1105, the central capacitive loads are increased until the state of the first configuration 1101 is restored, this configuration being able to correspond, in the example, to a phase shift applied to the incident signal between -50 ° and -180. °. The cell returns to its initial state corresponding to a solid metal patch.

The figure 12 illustrates means for routing the control signals to a phase-shifting cell such as that of the figure 10 .

Vias 1210 are made at the centers of the crosses forming the conductive elements. The routing of commands can be done at a level below the surface of the cell.

The phase-shifting cell according to the invention has several advantages with regard to the solutions of the state of the art.

A first advantage is that the phase-shifting cell is able to have two complementary resonances, a first resonance with a slot-like equivalent resonator and a second resonance with a patch-type equivalent resonator. This makes it possible to avoid the presence of highly resonant modes, and thus to limit the sensitivity of the cells to frequency variations. The phase value thus evolves much more linearly as a function of the frequency of the source signal, thus avoiding sudden phase jumps. The phase-shifter cell according to the invention is usable over a wider frequency band (for example 30% band).

A second advantage is the reduction of parasitic effects of a reflector network as described in the patent application. FR 0450575 because there is no strong break between two adjacent cells constituting the reflector array. This is possible thanks to the possibility of covering a 360 ° phase shift range by a variable localized load control cycle making it possible to minimize the frequency variation of the phase.

Thanks to the invention, it is possible to design a reflector network for an antenna whose surface is covered with radiating phase-shifting cells according to the invention. These are controlled to introduce a selected phase shift on an incident wave, each of the adjacent cells is controlled so that the equivalent resonator is in a configuration close to that of an adjacent cell. The invention applies in particular to reflector array antennas on mobile equipment, such as for example a telecommunication satellite antenna.

The cell can be used in satellite panels for use in Ku-band or Ka-band both in transmission and reception. By way of example, the phase-shifter cells according to the invention can be used around 20 GHz for the emission and around 30 GHz for the reception.

Claims (15)

1. A radiating phase-shifting cell comprising a plurality of conducting elements (207, 209, 1001, 1002) formed on the surface of a substrate, above and spaced apart from a ground plane, said conducting elements being separated by slots (202, 203, 204), the arrangement of said slots (204) forming an equivalent resonator, the electrical form of which configures the phase-shifting applied to a wave to be reflected, said cell comprising controlled variable loads (206, 1005) that can vary the electrical length and/or width of said slots, said conducting elements (207, 209, 1001, 1002) and said controlled variable loads (206, 1005) being arranged so that, in at least one first configuration of said loads, an annular conducting surface of microwave signals is formed so as to create an inductive-dominant resonator and so that, in at least one second configuration, a slot is formed around at least one central conducting element (209, 1001) so as to create a capacitive-dominant resonator, characterised in that said conducting surface is formed by a plurality of conducting elements (207, 1002) surrounding said central conducting element (209, 1001) and separated from each other by said slots (204), which have a radial orientation relative to said central conducting element.
2. The radiating phase-shifting cell according to claim 1, wherein said conducting elements (207, 1002) forming said conducting surface are located on the periphery, each of said peripheral conductors (207, 1002) being connected to said central conductor (209, 1001) and to the neighbouring peripheral conductors by means of controlled capacitive loads (206, 1005).
3. The radiating phase-shifting cell according to claim 1 or 2, wherein said conducting elements (1001, 1002) are in the shape of a cross with four branches aligned along a plurality of rows, with the crosses belonging to two successive rows being offset relative to each other, said crosses being connected by means of controlled variable capacitive loads.
4. The radiating phase-shifting cell (200) according to claim 1 or 2, wherein said conducting surface is formed by conducting strips (207) encompassed by annular slots (202, 203), said strips being connected by capacitive loads (206) that can modify the electrical length and/or width of said slots (204), which have a radial orientation, forming slots for interconnecting said annular slots (202, 203).
5. The radiating phase-shifting cell according to any one of claims 2 to 4, wherein, when said cell is in said first configuration, the loads connecting together said peripheral conducting elements (207, 1002) are activated, with the loads connecting said central conducting element (209, 1001) to said peripheral conducting elements (207, 1002) being deactivated so as to form a resonating slot, the main contribution of which is equivalent to that of a parallel LC circuit.
6. The radiating phase-shifting cell according to claim 5, wherein the loads connecting together said peripheral conducting elements (207, 1002) are adapted to assume multiple values between two extreme values so as to be able to progressively vary the dimensions of the equivalent resonating slot as a function of said values.
7. The radiating phase-shifting cell according to any one of claims 2 to 6, wherein, when said cell is in said second configuration, the loads connecting together said peripheral conducting elements (207, 1002) are deactivated, with the loads connecting said central conducting element (209, 1001) to said peripheral conducting elements (207, 1002) being activated, so as to form a resonating microstrip, the main contribution of which is equivalent to that of a series LC circuit.
8. The radiating phase-shifting cell according to claim 7, wherein the loads connecting said central conducting element (209, 1001) to said peripheral conducting elements (207, 1002) are adapted to assume multiple values between two extreme values in order to be able to progressively vary the dimensions of said equivalent resonating microstrip as a function of said values.
9. The phase-shifting cell according to any one of the preceding claims, wherein the loads connecting said central conducting element (209, 1001) to said peripheral conducting elements (207, 1002) are adapted to vary independently of the value of the loads connecting together said peripheral conducting elements (207, 1002), so that the range of the phase-shift applied to the incident wave is broken down into two phase-shifting intervals, the phase-shifts applied in the first interval being obtained with a configuration of the resonating slot type, the phase-shifts applied in the second interval being obtained with a configuration of the resonating microstrip type.
10. The radiating phase-shifting cell according to any one of the preceding claims, wherein said variable loads and the dimensions of said conducting elements (207, 209, 1001, 1002) are determined so that the cell configuration that allows the corresponding phase-shift to be applied to the first end of the phase-shifting range is identical to the cell configuration that allows the corresponding phase-shift to be applied to the second end of the range.
11. The radiating phase-shifting cell according to any one of the preceding claims, wherein the phase-shifting range is 360°.
12. The radiating phase-shifting cell according to any one of the preceding claims, wherein said conducting elements, said slots and said capacitive loads are disposed on said cell along a centre of symmetry that is placed at the centre of said cell.
13. The radiating phase-shifting cell according to any one of the preceding claims, wherein said capacitive loads are diodes, MEMS or ferroelectric capacitors.
14. A reflector array comprising a plurality of radiating phase-shifting cells according to any one of the preceding claims, said cells forming the reflective surface of said array.
15. An antenna comprising a reflector array according to claim 14.

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