EP1580844B1 - Phase shifter with linear polarization and a resonating length which can be varied using mem switches. - Google Patents

Abstract

The phase shifter has a slot radiator (FR) provided with micro electromechanical systems (DC). The systems are to be placed in two different states permitting and prohibiting respectively creation of a short circuit intended to vary a characteristic resonating length of the slot radiator, in order to shift a phase of wave reflected by the phase shifter. An independent claim is also included for a reflectarray antenna comprising a phase shifter.

Description

The invention relates to the field of reflector array antennas (or "reflectarray antennas"), and more particularly the phase-shifting cells that equip such antennas.

The reflector network antennas constitute one of the two main families of network antennas, the other family consisting of phased array antennas (or "Phased Array Antennas"). These network antennas are particularly interesting because they can be reconfigured, for example to allow the passage of a coverage area (or "spot") to another.

A reflective array antenna is constituted by radiating elements charged with intercepting with minimal losses of the waves, comprising signals to be transmitted, delivered by a primary source, in order to reflect them in a chosen direction, called the pointing direction. In order to allow the reconfigurability of the antenna pattern, each radiating element is equipped with a phase control device with which it constitutes a passive or active phase-shifting cell.

By "phase-shifting cell" is meant here both the cavity and radiating slot structures and planar resonant structures radiating pad (or "patch").

The invention is more particularly directed to active phase shifting cells with linear polarization. These generally comprise a phase-shifter cell provided either with a switch (or switch) consisting of diodes (generally PIN type), or MESFETs, or alternatively varactors, or mechanical control means (such as for example a loaded motor). to move a dielectric bar).

The phase switch cells consume a large amount of energy and are subject to significant losses and overheating. Mechanically controlled phase shifters are complex to put particularly in the case of large networks, and energy consumers. In either case, the disadvantages induced by the phase control techniques used limit the applications of phase-shifting cells, especially in the space domain and more specifically in observation platforms such as satellites.

The object of the invention is therefore to improve the situation in the case of linear polarized active phase-shifter cell reflector array antennas.

It proposes for this purpose a phase-shifted cell having a characteristic resonant length and comprising in at least one selected location a micron electromechanical device, MEMS type (for "Micro ElectroMechanical System"), which can be placed in at least two different states allowing and prohibiting respectively establishing a short circuit for varying the characteristic resonant length, to vary the phase shift of the waves to reflect which have at least one linear polarization.

Each MEMS device may for example comprise a flexible conductor bridge whose states are controlled by two substantially superimposed control electrodes and one of which is constituted by the bridge. Alternatively, each MEMS device may comprise a suspended conductive flexible beam (or "cantilever") whose states are controlled by a control electrode placed below its suspended part.

The cell according to the invention comprises a resonant planar structure comprising at least one rectangular upper block placed substantially parallel to a lower ground plane, at a selected distance, the lower ground plane defining at least one conductive "pad", for example rectangular , entirely surrounded by a non-conductive zone, placed below the upper pavement and of smaller dimensions than its own. In this case, the cell comprises at least one metallized bushing connecting the upper pad to the pad, and the MEMS device is placed at the level of the non-conductive zone in order to establish in one of its states a connection between the pellet and the rest of the mass plan to control the resonant length of the upper pad.

The lower ground plane may optionally define at least two pellets (for example rectangular) completely surrounded by a non-conductive area, placed below the upper pad and of smaller dimensions than hers. In this case, the cell comprises at least two metallized bushings respectively connecting the upper block to one of the pads, and at least two MEMS devices each placed at one of the non-conductive areas to establish links between the at least one of the pellets and the rest of the ground plane, thus making it possible to define at least three resonant lengths of different upper pavement according to their states.

In a variant of this family of embodiments, the cell may comprise a higher ground plane comprising at least one radiating slot, provided with a MEMS device controlling its characteristic resonant length, a lower ground plane, and metallized vias connecting the plane. of lower mass to peripheral portions of the upper ground plane to define a resonant cavity. For example, the upper ground plane may comprise at least two radiating slots each provided with a single MEMS device controlling their characteristic resonant length. Each MEMS device can then be preferentially placed substantially in the middle of a radiating slot. Furthermore, the slots are preferably substantially parallel to each other and may have slightly different lengths. But, they may also have a curved shape, so as to achieve together a short annular slot circuited at two substantially opposite points.

Alternatively, the upper ground plane may comprise a radiating slot, provided with at least two MEMS devices for defining at least three different resonant lengths according to their states.

On the other hand, the upper ground plane may optionally comprise at least one rectangular radiating slot having long sides parallel to a first direction, and at least one other rectangular radiating slot having long sides parallel to a second direction perpendicular to the first, so to allow a double linear polarization.

In another family of embodiments, the cell may comprise a resonant planar structure comprising an upper block placed substantially parallel to a lower ground plane at a selected distance. In this case, the block comprises at least one slot provided with at least one MEMS device controlling its characteristic resonant length.

The cell may then comprise a single slot (of half-wave length) provided with at least two MEMS devices, making it possible to define at least three different resonant lengths according to their states. Alternatively, the upper block may be substantially square, and the cell may comprise at least a first and a second rectangular slot (quarter-wavelength) placed substantially opposite one another, opening on two opposite sides non-radiating square, and each having at least two MEMS devices for defining at least three different resonant lengths according to their states. In the latter case, the cell may also comprise at least third and fourth rectangular slots (quarter-wave length) placed substantially opposite one another, opening on two other opposite non-radiating sides of the square, and each comprising at least two MEMS devices, making it possible to define at least three other different resonant lengths according to their states, in order to allow a linear double polarization. It is also possible to provide several upper blocks each provided with at least a half quarter wave slot, pairs of half slots facing then forming half-wave slots.

In the presence of a MEMS bridge device and slot (s) rectangular (s), the bridge is preferably placed substantially parallel to the long sides of the slot. On the other hand, in the presence of a beam MEMS device and of rectangular slot (s), said beam is preferably placed substantially perpendicular to the long sides of the slot.

Moreover, the lower ground plane can define a lower block placed below the upper block and of smaller dimensions than its own. In this case, the cell comprises metallized vias which connect the plane. of mass to peripheral parts of the upper block to define a resonant cavity. This pavement and cavity structure defines yet another family of phase-shifting cells.

The invention also proposes a reflector array antenna equipped with at least two phase-shifting cells of the type of those presented above.

The invention is particularly well suited, although not exclusively, to Ku-band (12 to 18 GHz) geostationary telecommunication antennas, with reconfigurable coverage (orbital position change, traffic adaptation), and band radar antennas. C (4 to 8 GHz) or in the X band (8 to 12 GHz), in particular for radars of SAR type (radars with synthetic aperture).

• la figure 1 illustre de façon schématique, dans une vue du dessus, un premier exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 2 est une vue en coupe transversale selon l'axe II-II de la cellule déphaseuse de la figure 1,
• la figure 3 illustre de façon schématique, dans une vue du dessus, un deuxième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 4 est une vue en coupe transversale selon l'axe IV-IV de la cellule déphaseuse de la figure 3,
• la figure 5 illustre de façon schématique, dans une vue du dessus, un troisième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 6 est une vue en coupe transversale selon l'axe VI-VI de la cellule déphaseuse de la figure 5,
• la figure 7 illustre de façon schématique, dans une vue du dessus, un quatrième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 8 est une vue en coupe transversale selon l'axe VIII-VIII de la cellule déphaseuse de la figure 7,
• la figure 9 illustre de façon schématique, dans une vue du dessus, un cinquième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 10 illustre de façon schématique, dans une vue du dessus, un sixième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 11 est une vue en coupe transversale selon l'axe XI-XI des cellules déphaseuses des figures 10 et 12,
• la figure 12 illustre de façon schématique, dans une vue du dessus, un septième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 13 illustre de façon schématique, dans une vue du dessus, un huitième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 14 illustre de façon schématique, dans une vue du dessus, un neuvième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 15 illustre de façon schématique, dans une vue du dessus, un dixième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 16 illustre de façon schématique, dans une vue du dessus, un onzième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 17 est une vue en coupe transversale selon l'axe XVII-XVII de la cellule déphaseuse de la figure 16,
• la figure 18 est une vue en perspective détaillant une partie de la cellule déphaseuse de la figure 16,
• la figure 19 illustre de façon schématique, dans une vue du dessus, un douzième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 20 est une vue en coupe transversale selon l'axe XX-XX de la cellule déphaseuse de la figure 19,
• la figure 21 illustre de façon schématique, dans une vue du dessus, un treizième exemple de réalisation d'une cellule déphaseuse selon l'invention, sans ses dispositifs MEMS,
• la figure 22 illustre de façon schématique, dans une vue du dessus, un quatorzième exemple de réalisation d'une cellule déphaseuse selon l'invention, sans ses dispositifs MEMS,
• la figure 23 illustre de façon schématique, dans une vue du dessus, un quinzième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 24 illustre de façon schématique, dans une vue du dessus, un seizième exemple de réalisation d'une cellule déphaseuse selon l'invention,
• la figure 25 est une vue en coupe transversale selon l'axe XXV-XXV de la cellule déphaseuse de la figure 24, et
• la figure 26 est un diagramme illustrant l'évolution du déphasage (Δφ en degrés) en fonction de la longueur d'une fente (b en mm), pour plusieurs valeurs différentes de longueur de pavé supérieur (x = 3, 4, 5, 7,5 et 8 mm respectivement en allant du haut vers le bas) et pour une épaisseur de substrat (d').

Other features and advantages of the invention will appear on examining the detailed description below, and the attached drawings, in which:

• the figure 1 schematically illustrates, in a view from above, a first embodiment of a phase-shifter cell according to the invention,
• the figure 2 is a cross-sectional view along the axis II-II of the phase shifter cell of the figure 1 ,
• the figure 3 schematically illustrates, in a view from above, a second embodiment of a phase-shifting cell according to the invention,
• the figure 4 is a cross-sectional view along the axis IV-IV of the phase-shifting cell of the figure 3 ,
• the figure 5 schematically illustrates, in a view from above, a third embodiment of a phase-shifting cell according to the invention,
• the figure 6 is a cross-sectional view along the axis VI-VI of the phase-shifter cell of the figure 5 ,
• the figure 7 schematically illustrates, in a view from above, a fourth embodiment of a phase-shifting cell according to the invention,
• the figure 8 is a cross-sectional view along the axis VIII-VIII of the phase-shifter cell of the figure 7 ,
• the figure 9 schematically illustrates, in a view from above, a fifth embodiment of a phase-shifting cell according to the invention,
• the figure 10 schematically illustrates, in a view from above, a sixth exemplary embodiment of a phase-shifting cell according to the invention,
• the figure 11 is a cross-sectional view along the axis XI-XI of the phase-shifter cells of figures 10 and 12 ,
• the figure 12 schematically illustrates, in a view from above, a seventh embodiment of a phase-shifting cell according to the invention,
• the figure 13 schematically illustrates, in a view from above, an eighth embodiment of a phase-shifting cell according to the invention,
• the figure 14 schematically illustrates, in a view from above, a ninth embodiment of a phase-shifting cell according to the invention,
• the figure 15 schematically illustrates, in a view from above, a tenth embodiment of a phase-shifting cell according to the invention,
• the figure 16 schematically illustrates, in a view from above, an eleventh embodiment of a phase-shifting cell according to the invention,
• the figure 17 is a cross-sectional view along the axis XVII-XVII of the phase-shifter cell of the figure 16 ,
• the figure 18 is a perspective view detailing a portion of the phase shifter cell of the figure 16 ,
• the figure 19 illustrates diagrammatically, in a view from above, a twelfth embodiment of a phase-shifting cell according to the invention,
• the figure 20 is a cross-sectional view along the axis XX-XX of the phase-shifting cell of the figure 19 ,
• the figure 21 schematically illustrates, in a view from above, a thirteenth embodiment of a phase-shifting cell according to the invention, without its MEMS devices,
• the figure 22 schematically illustrates, in a view from above, a fourteenth embodiment of a phase-shifting cell according to the invention, without its MEMS devices,
• the figure 23 schematically illustrates, in a view from above, a fifteenth embodiment of a phase-shifting cell according to the invention,
• the figure 24 schematically illustrates, in a view from above, a sixteenth embodiment of a phase-shifting cell according to the invention,
• the figure 25 is a cross-sectional view along the XXV-XXV axis of the phase shifter cell of the figure 24 , and
• the figure 26 is a diagram illustrating the evolution of the phase shift (Δφ in degrees) as a function of the length of a slot (b in mm), for several different values of higher paver length (x = 3, 4, 5, 7.5 and 8 mm respectively from top to bottom) and for a substrate thickness (d ').

The attached drawings may not only serve to complete the invention, but also contribute to its definition, if any.

The invention relates to a linear polarization active phase shifter cell for an active reflector array antenna.

The reflector array antenna may for example be dedicated to telecommunications, for example of the Ku-band geostationary type (12 to 18 GHz), with reconfigurable coverage (orbital position change or traffic adaptation), or to C-band radars ( 4 to 8 GHz) or in the X band (8 to 12 GHz), in particular for radars of SAR type (synthetic aperture radars), or high-speed ISL-RF type links, particularly inside a small constellation of satellites flying in formation.

In its greater generality, a phase-shifting cell, according to the invention, comprises in one or more selected locations a micron electromechanical device, MEMS type (for "Micro ElectroMechanical System"). Each MEMS device can be placed, using electrical controls, in at least two different states enabling and prohibiting respectively the establishment of a short circuit intended to vary a characteristic resonant length of the cell, in order to vary the phase shift of the waves to be reflected (coming from the source of the antenna) having at least one polarization linear.

Such a phase-shifting cell can be broken down into three large families according to its radiating structure. A first family groups the cavity and slit (s) radiating structures, a second family groups planar resonant structures (or "patches") and a third family groups planar resonant cavity structures.

We first refer to Figures 1 to 9 to describe embodiments of phase-shifting cells belonging to the first family.

On the Figures 1 and 2 is illustrated a first example of a phase shifter cell CD comprising a substrate SB having a "rear" (or "lower") face, secured to a ground plane "lower" PM1, and a face "before" (or "upper") , secured to an "upper" mass plane PM2.

The substrate SB is for example made of Duroid or TMM and has a thickness d equal, for example, to λ / 4, where λ is the wavelength in the vacuum of the waves to be reflected, coming from the source of the antenna .

The lower ground planes PM1 and upper PM2 are electrically connected to each other via metallized holes (or vias) TM formed in the substrate SB. These planes are for example made from substrates of alumina, silicon or glass which, because of their small thicknesses (typically 500 microns) must be reported on a substrate SB Duroid or TMM so as to allow obtaining a thickness equal to λ / 4. The metallized holes TM are preferably implanted at the periphery of the lower mass planes PM1 and PM2 higher so as to define a resonant cavity.

Two techniques can be envisaged to achieve this assembly. A first technique consists in superimposing a Duroid (or Metclad) substrate, for example with a thickness of about 3 mm, on an alumina substrate, for example with a thickness of about 0.254 mm, and then depositing a lower ground plane PM1 on the underside of the Duroid substrate and an upper ground plane PM2, on the upper face of the alumina substrate, said upper ground plane PM2 being locally interrupted by the slots. A second technique consists in using only a Duroid (or Metclad) substrate, for example of thickness equal to approximately 2 or 3 mm, and then forming on its upper face portions of an intermediate ground plane in which are formed voltage control lines, then to report on this upper surface portions of alumina substrates, for example of thickness equal to about 0.254 mm, having on an upper face a ground plane PM2 each comprising one or more slots, then to deposit a lower ground plane PM1 on the underside of the Duroid substrate, and finally to connect the lower ground plane, intermediate and upper by two levels of holes (or traverses) metallized.

Furthermore, the upper ground plane PM2 comprises a single radiating slot FR, preferably of rectangular shape defined by two long sides (longitudinal), of length b, and two small sides (transverse), of width a.

This radiating slot FR is for example made by etching the upper ground plane PM2.

Moreover, the radiating slot FR has a resonance of parallel LC type. The parameters of such a resonator (resonant frequency and bandwidth) depend mainly on the length b and width a of the radiating gap FR, as well as the permittivity ε _r of the substrate SB.

Several modes can propagate in the cavity delimited by the metallized holes TM. Each of these modes has a clean propagation constant β and a characteristic impedance Z _{0 of its} own. The cut-off frequency of the modes in the cavity depends mainly on the length m _x and width m _y of the lower mass planes PM1 and higher PM2, as well as the permittivity ε _r of the substrate SB. It is also recalled that a vertical resonance can occur in this type of cavity when its thickness d is equal to nλ _g / 2, where n is an integer and λ _g is the wavelength of the mode (s) ) guided (s) propagating in the cavity.

For example, one can choose a square mesh network in which m _x = m _y = 0.7λ = 8 mm. In this case, and in the presence of a wavelength λ corresponding to a working frequency of 26.4 GHz, the cavity has a cutoff frequency equal to 18.75 GHz and operates only in its fundamental mode, this which corresponds to a guided wavelength λ _g equal to approximately 16.14 mm, in the case of an air cavity.

In the presence of a cavity with a thickness d equal to λ / 4 (in this case approximately λ _g / 5.7), phase shifts of up to 360 ° can be obtained for slot widths FR of between approximately 0.25 mm. and about 1 mm. For example, in the presence of a width equal to 0.5 mm, the point of inflection of the phase shift is obtained at the resonance of the slot FR, which corresponds to a length b equal to about 5.5 mm, taking into account other values mentioned above.

In this exemplary embodiment, the radiating slot FR is preferably centered in the middle of the upper ground plane PM2. But, it could be otherwise, especially in the presence of a possible complementary parasitic slot. In the latter case, the slots are located preferentially symmetrically with respect to the center of the cell.

Furthermore, in this embodiment, the radiating slot FR is provided with three MEMS devices DC each constituting a two-state switch. Of course, the radiating slot could comprise a different number of MEMS DC devices as long as it is at least one.

Each MEMS DC device here consists of a flexible PT conductive bridge whose two ends are secured to the holding pads PL themselves secured to the upper face of the substrate SB. These PL pads are for example made of gold or aluminum and have a thickness slightly greater than that of the upper ground plane PM2. The flexible bridge PT is made in the form of a blade made conductive, for example by a metallization in gold or aluminum, and installed in the slot FR substantially parallel to its longitudinal edges.

Moreover, each MEMS DC device comprises two substantially superimposed control electrodes, one of them being constituted by the flexible bridge PT, and the other being, for example, placed at a level of above the flexible bridge PT (not shown), these two electrodes being connected to a supply circuit (not shown).

It is also provided on the upper face of the substrate SB, inside the radiating slot FR and substantially at a central portion of its longitudinal edges, two small access lines LA placed substantially opposite one of the the other, perpendicular to the flexible bridge PT, and electrically connected to the upper ground plane PM2.

In the presence of a control current selected at the control electrodes, the suspended portion of the bridge PT is attracted to said LA access lines. The suspended portion then flexes to come into contact with the two access lines LA, which locally generates a short circuit in the radiating slot FR and reduces its characteristic resonant length (b), which is its electrical length. This is one of the two states of the MEMS DC device.

In the absence of control current, the bridge PT is remote from the access lines LA, so that the length of the radiating gap FR is not disturbed. This is the other state of the MEMS DC device.

By controlling separately the different MEMS devices DC, it is therefore possible, in this embodiment, to define in three different positions three short circuits corresponding to at least four different resonant lengths for the slot FR. Of course, the positions of the different MEMS DC devices are chosen so as to perform a regular quantization of the phase law. This positional constraint favors the implementation of MEMS devices at the edge of the slot. These different resonant lengths correspond to different phase shifts of the wave reflected by the phase-shifter cell CD.

On the Figures 3 and 4 a second example of a phase-shifter cell CD of the first family is illustrated. This is a variant of the phase-shifting cell CD described above with reference to the Figures 1 and 2 . More specifically, what differentiates the first embodiment of the second is the embodiment of the MEMS devices.

Here, each MEMS device DC 'comprises a flexible beam (or "cantilever") conducting PE having an end secured to a stud conductor support PL 'formed in the radiating gap FR along one of the longitudinal edges and electrically connected to the upper ground plane PM2.

This pad PL 'is for example made of gold or aluminum and has a thickness slightly greater than that of the upper ground plane PM2, so that the beam PE is suspended above the radiating slot FR and the level of the ground plane higher PM2. The flexible beam PE is made in the form of a made conductive blade, for example by means of a metallization in gold or aluminum, installed substantially perpendicular to its longitudinal edges. The free end of the beam PE crosses the slot FR in its width and overflows slightly on the upper ground plane PM2 at a location where is preferably placed an electrically conductive contact pad PLC.

Moreover, each MEMS device DC 'comprises a control electrode EC' placed below the suspended central part of the beam PE, and connected to a supply circuit (not shown), another electrode being constituted by the flexible beam PE conductor. The control electrode EC 'is formed on the upper face of the substrate SB, inside the radiating slot FR.

In the presence of a control current selected at the control electrode EC ', the suspended portion of the beam PE is drawn toward said electrode. It then flexes until its free end comes into contact with the PLC contact pad, which locally generates a short circuit in the radiating slot FR and reduces its characteristic resonant length (b), which is its electrical length. This constitutes one of the two states of the MEMS device DC '.

In the absence of control current, the free end of the beam PE is remote from the contact pad PLC, so that the length of the radiating slot FR is not disturbed. This is the other state of the MEMS DC device.

By separately controlling the different MEMS devices DC ', it is therefore also possible, in this embodiment, to define in three different positions three short circuits corresponding to the minus four different resonant lengths for the FR slot. Of course, the positions of the different MEMS devices DC 'are chosen so as to perform a regular quantization of the phase law. These different resonant lengths correspond to different phase shifts of the wave reflected by the phase-shifter cell CD.

In this embodiment, the radiating slot FR is provided with three MEMS devices DC '. But, the radiating slot FR could comprise a different number of devices MEMS DC 'when it is at least equal to one.

On the Figures 5 and 6 a third example of a phase shifter cell CD of the first family is illustrated. In this example, the phase-shifting cell CD takes up the structure of the first example described above with reference to the Figures 1 and 2 , but instead of a single radiating slot it has several (N = 5), and each slot has a single device MEMS DC bridge PT. Of course, the number N of radiating slots illustrated is not limiting. It can take any value greater than or equal to two. Furthermore, it can be envisaged that at least one of the slots is not equipped with a MEMS device.

The radiating slots have, for some, different lengths. More precisely, in the example illustrated, the upper ground plane PM2 comprises two end radiating slots FR1, having a first characteristic resonant length L1, two intermediate radiating slots FR2, having a second characteristic resonant length L2 greater than L1, and a central radiating slot FR3 having a third characteristic resonant length L3 greater than L2. In one variant, the five slots could have five different lengths.

Here, the five radiating slots FR1 to FR3 are substantially centered with respect to the middle of the upper ground plane PM2, and their MEMS DC bridge PT device is also installed in a centered position. But, we could do differently. Indeed, in the example described above we run the undesirable slots, but we could also change the resonant length of some of them to excite several resonances and well control the phase shift between slots, with the coupling.

The distance separating two adjacent slits may be fixed or variable. It varies according to the needs. It is typically between about 100 μm and 500 μm.

This is to use one or more radiating slots by placing their respective MEMS devices DC in their second state (not bent). The slot or slots that one does not wish to use are short-circuited by placing their MEMS DC devices in their first state (bent). The phase variation of the reflected wave is here obtained by selecting one of the combinations of short-circuited and non-short-circuited slots. Each combination corresponds in fact to a particular and discrete phase shift mainly function of the ratio between the smallest characteristic resonant length and the greatest characteristic resonant length.

Each slot short-circuited in the middle acts as a parasitic element for the neighboring non-shorted slot. This is to excite several resonances to have a range of acceptable phase shifts, while avoiding a very resonant response leading to low band performance. The coupling between the different resonances, made by coupling between a slot and a patch (or patch), makes it possible to attenuate the resonant response.

On the figures 7 and 8 a fourth example of a phase-shifter cell CD of the first family is illustrated. This is a variant of the phase-shifting cell CD described above with reference to the Figures 5 and 6 .

More specifically, what differentiates the fourth embodiment of the third is the MEMS device embodiment. In this example, each MEMS DC device with a PT bridge is indeed replaced by a MEMS DC 'PE beam device, of the type of those described with reference to FIGS. Figures 3 and 4 .

The operation of this phase-shifting cell CD is identical to that of the phase-shifting cell described above with reference to the Figures 5 and 6 .

As illustrated on the fifth example of the figure 9 , it is possible to constitute a phase-shifting cell CD belonging to the first family and adapted to a linear double polarization.

To do this, at least one FRV radiating slot is oriented in a first direction ("vertical"), and at least one FRH radiating slot oriented in a second direction ("horizontal"), perpendicular to the first. Of course, as illustrated on the figure 9 , the phase-shifter cell CD may comprise one or more FRV radiating slots and one or more FRH radiating slots, as required. The cell is then preferably rectangular and has a width substantially equal to half of its length.

It is possible to use FRV and FRH radiating slots with only one PT bridge or PE beam MEMS device, but it is preferable to use FRV and FRH radiating slots with at least two bridge MEMS devices. PT or PE beam (as shown).

We now refer to Figures 10 to 18 to describe embodiments of phase-shifting cells belonging to the second family.

On the figures 10 and 11 is illustrated a first example of a phase shifter cell CD comprising a substrate SB having a rear face (or lower), secured to a lower ground plane PM1 defining a lower pad (or "patch"), and a front face (or upper) , secured to a higher ground plane defining an upper patch (or "patch") PS. The upper PS and lower PM1 blocks define a resonant planar structure.

The substrate SB is for example made of Duroid or TMM and has a thickness of weak, typically of the order of λ / 10 to λ / 5, where λ is the wavelength in the vacuum of the waves to be reflected, from the source of the antenna.

The upper block PS is placed substantially parallel to the lower ground plane PM1 and has dimensions smaller than its own. For example, and as illustrated, the upper block PS is of rectangular shape, and preferably square.

In addition, the upper block PS has a single slot FP, preferably of rectangular shape defined by two long sides (longitudinal), of length b, and two small sides (transverse), of width a.

This slot FP is for example made by etching the ground plane constituting the upper pad PS.

In this embodiment, the slot FP is provided with three MEMS devices DC bridge PT each constituting a two-state switch, of the type of those described above with reference to the Figures 1 and 2 . Of course, the slot FP could comprise a different number of MEMS devices DC when it is at least equal to one.

The operating principle of this phase-shifting cell CD, and more precisely of its MEMS DC devices, is identical to that described above with reference to the Figures 1 and 2 . Only the physical effect involved differs. The slot FP is here intended to disrupt the path of currents flowing in the upper pad PS. By varying the length of the disturbing slot FP, by setting short-circuit (s) selected (s) by means of at least one of the MEMS devices DC placed in its first state (skewed), the current path disturbances are varied, which varies the characteristic resonant length (or electrical length) of the upper pad PS and thus the phase shift of the reflected wave.

It is important to note that the invention can only be applied here if the upper block PS is resonant at λ / 2.

On the figure 12 is illustrated a second example of phase shifter cell CD of the second family. This is a variant of the phase-shifting cell CD described above with reference to the figures 10 and 11 . More specifically, what differentiates the first embodiment of the second is the embodiment of the MEMS devices.

Here, each MEMS device DC 'is of PE beam type, as in the embodiment described above with reference to FIGS. Figures 3 and 4 . Moreover, in this exemplary embodiment, the disturbing slot FP is provided with three MEMS devices DC '. But, the disturbing slot FP could comprise a different number of devices MEMS DC 'since this one is at least equal to one.

As illustrated on the Figures 13 and 14 , it is possible to envisage at least third and fourth exemplary embodiments, variants of the first and second embodiments described above with reference to FIGS. Figures 10 to 12 .

More specifically, the third example illustrated on the figure 13 comprises two metallized holes (or traverses) TM for electrically coupling the upper pad PS and the lower ground plane PM1 on either side of the two opposite ends of the disturbing slot FP. These metallized holes MT are intended to supply DC power to the upper pad PS so as to bias the MEMS device.

In the fourth example shown on the figure 14 the upper block PS comprises two small disturbing slots F1 and F2, whose resonance corresponds approximately to a length equal to a quarter of the wavelength, placed substantially opposite one another and opening on opposite edges, non-radiating. Each small slot F1, F2 is provided with at least one (here two) MEMS device PT bridge (but it could be a PE beam). In addition, a metallized hole (or traverse) TM makes it possible to electrically couple the upper pad PS and the lower ground plane PM1 in a central portion located between the two small disturbing slots F1 and F2. This metallized hole MT is intended to supply DC power to the upper pad PS so as to bias the MEMS device. It is conceivable to produce two small quarter-wave disruptive slots, or more, opening on at least one of the non-radiating sides.

Of course, it is also conceivable that the upper block PS (substantially square) comprises only a rectangular slot opening on a non-radiating side of the square and having at least two MEMS devices DC or DC '.

As illustrated on the fifth example of the figure 15 it is possible to constitute a phase-shifting cell CD belonging to the second family and adapted to a linear double polarization.

To do this, it is possible for example to use at least two small disturbing slots F1 and F2 oriented in a first direction, and at least two small disturbing slots F3 and F4 oriented in a direction. second direction, perpendicular to the first. Here, the term "small slot" denotes a disturbing slot FP of the type presented above with reference to the figure 14 .

It is possible to use small quarter-wave length F1 to F4 disruptive slots having only a single PT bridge or PE beam MEMS device, but it is nevertheless preferable to use small F1 disruptive slots. at F4 having at least two PT bridge or PE beam MEMS devices (as shown). The number of MEMS devices used in each slot depends on the number of phase states that it is desired to obtain.

As in the preceding example, a metallized hole (e) TM (electromagnetic) makes it possible to electrically couple the upper pad PS and the lower ground plane PM1 in a central portion located between the four small disturbing slots F1 to F4, of length quarter wave. This metallized hole MT is intended to supply DC power to the upper pad PS so as to bias the MEMS device.

In the last three examples of realization ( figure 13 to 15 ), the power supply of the upper block PS is carried out by means of at least one metallized hole TM. But, alternatively this power can be performed by means of a quarter-wave line with high impedance.

On the Figures 16 to 18 is illustrated a sixth example of phase shifter cell CD comprising a substrate SB having a rear face (or lower), secured to a lower ground plane PM1, and a front face (or upper), secured to a higher ground plane defining a patch (or patch) upper PS 'rectangular shape. The upper pavement PS 'and the lower ground plane PM1 constitute a short-circuited cobblestone structure which defines a resonant planar structure. It is important to note that the length of the upper PS block is chosen so that it is resonant at λ / 4.

The substrate SB is for example made of Duroid or TMM and has a thickness of weak, typically of the order of λ / 10 to λ / 5, where λ is the wavelength in the vacuum of the waves to be reflected, from the source of the antenna.

The upper pavement PS 'is placed substantially parallel to the lower mass plane PM1 and has dimensions much smaller than its own at least in one direction.

As illustrated on the figure 18 , the lower ground plane PM1 comprises at least one small conductive "pellet" PI, isolated from its own conductive part by a non-conductive zone Z, made for example by etching. Each small conductive pad P1 is electrically connected to the upper pad PS 'via a metallized hole (or traverse) TM. Moreover, each small conductive pad P1 is preferably of rectangular shape, and more preferably square.

Each metallized hole TM is connected to the upper pavement PS 'in a chosen location, the various locations being preferably substantially aligned along a line parallel to the longitudinal sides of said upper pavement PS.

Moreover, each small conductive pad PI is provided with a MEMS device with a PT bridge or with a PE beam (as illustrated on FIG. figure 18 ), of the type described above. Each MEMS device DC '(or DC) is intended to establish an electrical connection between its small lower block P1 and the conductive part of the lower ground plane PM1, when it is placed in its first state (bent). Thus, when one of the MEMS devices DC '(or DC) is placed in its first state (bent), the metallized hole TM, which is connected to its small conductive pad P1, bypasses the upper pad PS' substantially to the place where it is connected, which has the effect of varying its characteristic resonant length (or electrical length) and thus the phase shift of the reflected wave.

This structure is advantageous because its devices being placed on the rear face they are more protected from radiation.

In the example shown on the Figures 16 and 17 , five metallized holes TM can define five short circuits corresponding to at least six different resonant lengths for the upper pad PS '. Consequently, by separately controlling the different MEMS devices DC '(or DC), it is possible to obtain several different phase shifts of the wave reflected by the phase-shifter cell CD.

Of course, the phase-shifting cell CD may comprise a number of MEMS devices (DC or DC ') different from five, since this is at least one. The number of MEMS devices used depends on the number of phase states that one wishes to obtain.

It is important to note that in this exemplary embodiment, at the resonant frequency, the sum of the length of the "active" dipole (that is to say between the short circuit and the other end of the dipole) and the length of the short-circuit must be equal to one quarter of the wavelength of the guided mode λ _g .

This exemplary embodiment can allow the constitution of a linear double polarization phase shifter cell, of the type of that illustrated on FIG. figure 9 . To do this, it is necessary to combine "horizontal" dipoles and "vertical" dipoles of the type described above with reference to the Figures 16 to 18 .

We now refer to Figures 19 and 20 to describe an example of a phase-shifting cell belonging to the third family.

This exemplary embodiment constitutes, as it were, an intermediate structure between the exemplary embodiments illustrated on the Figures 5 to 8 and the exemplary embodiments illustrated on the Figures 10 to 12 .

Here, the phase-shifter cell CD comprises a substrate SB having a rear face (or bottom), secured to a lower ground plane PM1, and a front face (or upper), secured to an upper pad PS.

The substrate SB is for example made of Duroid or TMM and has a thickness d equal to λ / 4, where λ is the wavelength in the vacuum of the waves to be reflected from the antenna source.

The substrate SB is traversed, on its periphery, by holes (or traverses) metallized (e) TM connected to the lower ground plane PM1 and surrounding the upper pad PS to define a resonant cavity. For example, for operation in the Ku band, the upper pad PS is a square of length between about 15 mm and about 17 mm.

Furthermore, the upper block PS comprises at least two (here five) radiating slots each comprising a single MEMS device (DC or DC ') PT bridge or PE beam. Of course, the number N of slots radiating illustrated is not limiting. It can take any value greater than or equal to two. For example, the slits have a long side length of about 5 mm to about 7 mm, and a small side of width of about 0.3 mm to about 0.7 mm.

The radiating slots have, for some, different lengths. More precisely, in the example illustrated, the upper block PS comprises two end radiating slots FR1, having a first characteristic resonant length L1, two intermediate radiating slots FR2, having a second characteristic resonant length L2 greater than L1, and a slot radiating central FR3, having a third characteristic resonant length L3 greater than L2. In one variant, the five slots could have five different lengths.

Here, the five radiating slots FR1 to FR3 are substantially centered with respect to the middle of the upper pad PS, and their MEMS DC devices with PT bridge (or DC 'with PE beam) are also installed in a centered position (for example).

This is to use one or more radiating slots by placing their respective MEMS devices DC in their second state (not bent). The slot or slots that one does not wish to use are short-circuited by placing their MEMS DC devices in their first state (bent). The phase variation of the reflected wave is here obtained by selecting one of the combinations of short-circuited and non-short-circuited slots. Each combination corresponds in fact to a particular and discrete phase shift mainly function of the ratio between the smallest characteristic resonant length and the greatest characteristic resonant length.

Each slot short-circuited in the middle acts as a parasitic element for the neighboring non-shorted slot. Therefore, it is likely to improve the bandwidth of the non-shorted slot.

In the example described above we run the undesirable slots, but we could proceed differently. For example, we can modify the resonant length of some slots to excite several resonances and well control the phase shift between slots, with the coupling. This can for example be done by placing one or more (for example two or three) MEMS devices, preferably cantilever type DC ', in the opposite end portions of the slots, and not in their central part.

Of course, slots of substantially identical shapes and sizes can be used.

Some holes (or crossings) metallized (e) TM, for example one out of two, can be advantageously used to route the voltage commands at different MEMS devices DC or DC '.

In the foregoing, cells having single slits of quarter-wave or half-wave length have been described. But, it is possible to make cells with composite slots, as shown in the Figures 21 and 22 .

More precisely, the cells of the exemplary embodiments illustrated on the Figures 21 and 22 substantially reflect the structure of the cells illustrated on the Figures 10 to 12 . Here, each slot of half-wave length is constituted by two half-slots of quarter-wave length. MEMS devices DC or DC 'were deliberately omitted so as not to overload the drawings.

In the example shown on the figure 21 two upper blocks PS1 and PS2 are placed substantially parallel to the lower ground plane PM1 and at a distance therefrom. These two upper blocks PS1 and PS2 are spaced from each other by a distance chosen so as to define between them a capacitive area. They have different shapes and each have a half quarter wave slot FR1, FR2. These two half slots FR1 and FR2 together constitute a half-wave slot and an inductive zone whose effect is advantageously compensated (at least partially) by the capacitive inter-pad area.

For example, the blocks have a width equal to about 3.7 mm and are separated by a distance, forming a slot, equal to about 0.1 mm.

Such an asymmetrical structure provides a good stability frequency response due to an effective coupling between the two resonances.

In the example shown on the figure 22 , three upper blocks PS1, PS2 and PS3 are placed substantially parallel to the lower ground plane PM1 and at a distance therefrom. The two upper blocks PS1 and PS3 are substantially identical and surround the PS2 pad. Furthermore, the two upper blocks PS1 and PS3 each have a half quarter wave slot FR1, FR4, while the upper block PS2 has two half quarter wave slots FR2 and FR3 opening on two opposite sides, one placed next to the half slot FR1 of the upper block PS1 and defining with it a first half wave slot, and the other placed next to the half slot FR4 of the upper pad PS3 and defining with it a second half wave slot.

Such a symmetrical structure also offers a frequency response of good stability due to an effective coupling between the resonances.

Many other combinations of upper pavers can be envisaged. Thus, it is possible to envisage a combination of several upper pavers separated from one another by spaces constituting slits of selected widths with which they constitute what the person skilled in the art calls a "Jerusalem cross". By reducing, with a MEMS device, the width of the slots opposite, one can act on the resonance frequency of such a structure, and thus modify the phase of the reflected wave. A dual structure, including metallic lines in the shape of a Jerusalem cross, is described in the document C. Simovski et al, "High-impedance surfaces with angular and polarization stability", 27th ESA Antenna Technology Workshop on Innovative Periodic Antennae, pp. 176-184 . The resonance of such a structure is mainly ensured by the inductive and capacitive parts of the Jerusalem cross, and not by the resonance of the pavement. This structure, called "metamaterial" type, then operates in much lower frequency bands.

It is also possible to add to the phase-shifting cells, which comprise at least one block provided with at least one slot FP, described above, one or more auxiliary blocks and at least one MEMS device. coupling, so as to vary the size of the tile in at least one of its two directions (X and Y), and preferably along its length X which is parallel to the direction defining the length b (or long side) of FP slots. A CD phase shifter cell of this type is illustrated on the figure 23 .

More precisely, the phase-shifting cell CD illustrated on the figure 23 part of a structure of the type illustrated in the Figures 10 to 12 . It therefore comprises a substrate SB having a rear face (or lower), secured to a lower ground plane PM1, and a front face (or upper), secured to at least one PS pad and at least one auxiliary block PA1, PA2. Here, there is shown two auxiliary blocks PA1 and PA2, placed on both sides of two parallel sides of the PS pad (themselves parallel to the long sides (Y) of the slot FP). But, we could consider providing only one auxiliary pad PA. Moreover, it is also possible, alternatively or in addition, to place an auxiliary block along at least one of the two non-radiating sides of the PS block (parallel to the small side (X) of the slot FP).

The upper blocks PS, PA1 and PA2 and the lower ground plane PM1 define a resonant planar structure.

The phase-shifter cell CD also comprises at least one DC or DC coupling device MEMS installed between the pad PS and an auxiliary pad PA1, PA2 and responsible for establishing or not a contact between these blocks according to the state in which it is placed.

In the example shown, the PS block may be connected to each auxiliary pad PA1, PA2 via three MEMS devices DC ', a central and two end. The two end MEMS devices DC 'are preferably placed symmetrically with respect to the center of the auxiliary pad PA1, PA2.

The different DC or DC MEMS devices which connect the PS block to one of the auxiliary blocks PA1, PA2 are preferably controlled by the same control current. In other words, they are preferably placed simultaneously in the same state so as to ensure either an electrical connection or an absence of electrical connection, between the PS block and the auxiliary block PA1, PA2 concerned.

When a link is established between the PS pad and an auxiliary pad PA1, PA2, the physical length (following X) of the PS pad can be increased. By simultaneously acting on the pair length of the PS pad and length of the slot FP, it is then possible to simultaneously modify the phase shift torque of the incident wave, over a range greater than 360 °, and dispersion of this phase shift in frequency. The possibility of controlling the dispersion of this phase shift in frequency is particularly interesting to compensate for the dispersive illumination in frequency of a planar reflector grating by a primary source.

It is important to note that several (at least two) auxiliary blocks, preferably of the same dimensions, may be placed parallel to each other, on at least one of the two sides of the PS pad, the blocks being connected in pairs by one or more coupling devices MEMS DC 'or DC, and preferably three. This makes it possible to further vary the physical length of the PS block, as needed, by playing on the respective states of the MEMS devices DC 'or DC coupling the auxiliary blocks.

Furthermore, the auxiliary blocks which are located on either side of the two parallel sides of the PS pad do not necessarily have the same dimensions. This is particularly the case in the example illustrated on the figure 23 , where the auxiliary pad PA1 has a length (in the X direction) greater than that of the auxiliary pad PA2, but a width (in the Y direction) substantially identical to that of the auxiliary pad PA2. For example, if the length of the keypad PS is equal to L, the lengths of the auxiliary keypads PA1 and PA2 can be respectively equal to L / 2 and L / 3.

As in the previously described examples, the PS block may comprise one or more MEMS devices DC or DC '. The number of MEMS devices used depends on the number of phase shift states that it is desired to obtain.

This type of phase-shifting cell CD therefore makes it possible to dynamically vary, as needed, the phase shift and the phase-to-frequency dispersion, which is particularly advantageous for an active (or reconfigurable) antenna. The choice of phase shift and dispersion the phase shift is in fact fixed by the physical length of the PS pad and by the electrical length of each slot FP of each pad PS, according to the respective states of the different MEMS devices used.

In order to form a passive phase-shift CD cell for a non-reconfigurable antenna, MEMS devices can be omitted at the slots. More specifically, as illustrated in Figures 24 and 25 , one can use a structure of the type of that illustrated on the Figures 10 to 12 , but without MEMS device.

Such a structure CD therefore comprises a substrate SB having a rear (or lower) face, secured to a lower ground plane PM1, and a front face (or upper), secured to at least one upper patch (or patch) PS comprising at least one least one FP slot. The upper block PS and the lower ground plane PM1 define a resonant planar structure.

By judiciously choosing the dimensions of the upper block PS, and in particular its length x (in the X direction), and the slot FP, and in particular its length b (in the Y direction), as well as the thickness d of the substrate SB, it is possible to impose both a chosen phase shift and a phase dispersion in frequency chosen.

The dimensions and thicknesses can be deduced from curves of the type illustrated in the figure 26 , giving the evolution of the phase shift ΔΦ as a function of the length b of the slot FP, for several different values x of upper paver length PS and for a thickness of substrate SB (for example equal to about 2 mm).

When the upper block PS has only one slot FP, it is preferably placed substantially at its center. But, the upper block PS could have several FP slots, possibly of different dimensions.

Such a phase-shifting cell CD makes it possible to obtain any phase shift, and in particular phase shifts (very) greater than 360 °. It also makes it possible to control the dispersion of this phase shift in frequency. The phase-shifting cells of the prior art, which make it possible to obtain such characteristics, comprise three blocks placed parallel to one another above and above a lower ground plane (they are particular described in the article of JA Encinar et al., 27th ESA Antenna Workshop, Santiago de Compostela, Spain, March 2004, "Design of a three-layer printed reflectarray for dual polarization and dual coverage" ). The phase-shifter cells CD according to the invention comprise only one level of metallization (upper block), in addition to the lower ground plane PM1, and are therefore much simpler to achieve than the phase-shifting cells of the prior art.

Claims (25)

1. Phase shifter cell (CD), for a reflecting array antenna, defined by a characteristic resonant length, characterized in that it comprises a resonant planar structure comprising an upper patch (PS) placed substantially parallel to a lower ground plane (PM1), a chosen distance away, and in that it comprises, at at least one chosen spot, at least one micro electromechanical device of MEMS type (DC, DC') controlling the characteristic resonant length of the said upper patch (PS), the MEMS device being suitable for being placed in at least two different states allowing and prohibiting respectively the establishment of a short-circuit intended to vary the said resonant length, so as to vary the phase shift of a wave to be reflected exhibiting at least one linear polarization.
2. Cell according to Claim 1, characterized in that the said MEMS device (DC) comprises a conducting flexible bridge (PT) whose states are controlled by two substantially superimposed control electrodes, one of which consists of the said bridge (PT).
3. Cell according to Claim 1, characterized in that the said MEMS device (DC') comprises a suspended conducting flexible beam (PE) whose states are controlled by a control electrode (EC') placed below a suspended part of the said beam (PE), which constitutes another electrode.
4. Cell according to one of Claims 1 to 3,
   characterized in that the MEMS device (DC, DC') is placed in a slot (FP) located in the said upper patch (PS) .
5. Cell according to Claim 4, characterized in that it comprises a single slot (FP) furnished with at least two MEMS devices (DC, DC'), making it possible to define at least three different resonant lengths (FP) according to the states in which they are respectively placed.
6. Cell according to one of Claims 4 and 5, characterized in that it comprises at least one auxiliary patch (PA1, PA2) placed along one at least of the sides of the said upper patch (PS), at a chosen distance from the latter, and at least one MEMS coupling device (DC', DC), placed between the said auxiliary patch (PA1, PA2) and the said upper patch (PS) and making it possible to establish, or not, an electrical link between the said auxiliary and upper patches according to the state in which it is placed.
7. Cell according to Claim 6, characterized in that it comprises at least two mutually parallel neighbouring auxiliary patches, of substantially identical dimensions and placed along one at least of the sides of the said upper patch (PS), and at least one MEMS coupling device (DC', DC) placed between the said neighbouring auxiliary patches and making it possible to establish, or not, an electrical link between them according to the state in which it is placed.
8. Cell according to Claim 4, characterized in that the said upper patch (PS) is substantially square, and in that it comprises at least one rectangular slot emerging on a non-radiating side of the said square and comprising at least two MEMS devices (DC, DC'), making it possible to define at least three different resonant lengths according to the states in which they are respectively placed.
9. Cell according to Claim 4, characterized in that the said upper patch (PS) is substantially square, and in that it comprises at least first (F1) and second (F2) rectangular slots placed substantially facing one another and emerging on two opposite, non-radiating, sides of the said square, each slot (F1, F2) comprising at least two MEMS devices (DC, DC'), making it possible to define at least three different resonant lengths according to the states in which they are respectively placed.
10. Cell according to Claim 9, characterized in that it comprises at least third (F3) and fourth (F4) rectangular slots placed substantially facing one another and emerging on two other opposite sides of the said square, each slot (F3, F4) comprising at least two MEMS devices (DC, DC'), making it possible to define at least three other different resonant lengths according to the states in which they are respectively placed, so as to allow a double linear polarization.
11. Cell according to one of Claims 4 to 10 in combination with Claim 2, characterized in that each slot (FP, F1-F4) is rectangular, and in that each MEMS device (DC) bridge (PT) is placed substantially parallel to large sides of the said slot.
12. Cell according to one of Claims 4 to 10 in combination with Claim 3, characterized in that each slot (FP, F1-F4) is rectangular, and in that each MEMS device (DC') beam (PE) is placed substantially perpendicular to large sides of the said slot.
13. Cell according to one of Claims 4, 5, 11 and 12, characterized in that the said upper patch (PS) exhibits smaller dimensions than the dimensions of the lower ground plane (PM1), and in that it comprises metallized bushings (TM) connected to the said lower ground plane (PM1) and surrounding the said upper patch (PS) so as to define a resonant cavity.
14. Cell according to one of Claims 4 to 13, characterized in that the said resonant planar structure comprises at least two upper patches (PS1, PS2) separated from one another by a chosen distance, each patch comprising at least one half slot (FR1, FR2, FR3, FR4) emerging on one of its sides and two facing half slots constituting a slot.
15. Cell according to one of Claims 4 to 13, characterized in that the said resonant planar structure comprises several upper patches separated from one another by spaces constituting slots of chosen widths, the said patches and the said slots constituting a "Jerusalem cross".
16. Cell according to one of Claims 1 to 3, characterized in that it comprises, on the one hand, a resonant planar structure comprising a rectangular upper patch (PS) placed substantially parallel to a lower ground plane (PM1), a chosen distance away, the said lower ground plane (PM1) defining at least one wafer (P1) wholly surrounded by a non-conducting zone (Z), placed below the said upper patch (PS) and of smaller dimensions than the dimensions of the latter, and on the other hand, at least one metallized bushing (TM) linking the said upper patch (PS) to the said wafer (P1) , and in that the said MEMS device (DC, DC') is placed at the level of the said zone (Z) so as to establish in one of its states a link between the said wafer (P1) and the remainder of the said ground plane (PM1) so as to control the resonant length of the said upper patch (PS) .
17. Cell according to Claim 16, characterized in that the said lower ground plane (PM1) defines at least two wafers (P1) wholly surrounded by a non-conducting zone (Z), placed below the said upper patch (PS) and of smaller dimensions than the dimensions of the latter, and in that it comprises, on the one hand, at least two metallized bushings (TM) linking respectively the upper patch (PS) to one of the said wafers (P1), and on the other hand, at least two MEMS devices (DC, DC') each placed at the level of one of the zones (ZI) so as to establish links between one at least of the said wafers (P1) and the remainder of the said ground plane (PM1), thus making it possible to define at least three different resonant lengths of the upper patch (PS) according to the states in which they are respectively placed.
18. Cell according to one of Claims 1 to 3, characterized in that it comprises an upper ground plane (PM2) comprising at least one radiating slot (FR), provided with a MEMS device (DC, DC') controlling its characteristic resonant length, a lower ground plane (PM1), and metallized bushings (TM) linking the said lower ground plane (PM1) to peripheral parts of the said upper ground plane (PM2) so as to define a resonant cavity.
19. Cell according to Claim 18, characterized in that the said upper ground plane (PM2) comprises at least two radiating slots (FR1, FR2, FR3) each provided with a single MEMS device (DC, DC') controlling their characteristic resonant length.
20. Cell according to Claim 19, characterized in that each MEMS device (DC, DC') is placed substantially in the middle of a radiating slot (FR1, FR2, FR3).
21. Cell according to one of Claims 19 and 20, characterized in that the said slots (FR1, FR2, FR3) are substantially mutually parallel and exhibit different lengths.
22. Cell according to Claim 18, characterized in that the said upper ground plane (PM2) comprises a radiating slot (FR), provided with at least two MEMS devices (DC, DC') making it possible to define at least three different resonant slot lengths according to the states in which they are respectively placed.
23. Cell according to one of Claims 18 to 22, characterized in that the said upper ground plane (PM2) comprises at least one rectangular radiating slot (FRV) exhibiting large sides parallel to a first direction, and at least one other rectangular radiating slot (FRV) exhibiting large sides parallel to a second direction perpendicular to the first, so as to allow a double linear polarization.
24. Phase shifter cell (CD), for a reflecting array antenna, characterized in that it comprises a resonant planar structure comprising an upper patch (PS) placed substantially parallel to a lower ground plane (PM1), a chosen distance away, and comprising at least one slot (FP), the dimensions of the patch (PS) and of the slot (FP) and the said distance being chosen so as to impose a chosen phase shift and a chosen frequency-phase dispersion on a wave to be reflected exhibiting at least one linear polarization.
25. Reflecting array antenna, characterized in that it comprises at least two phase shifter cells (CD) according to one of the preceding claims.

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