The invention concerns the field of reflectarray antennas, and more particularly the phase shifter modules that equip such antennas.
Reflectarray antennas are one of the two main array antenna families, the other family being phased array antennas. These array antennas are particularly advantageous as they can be reconfigured, for example to allow switching from one coverage area (or “spot”) to another.
A reflectarray antenna is made up of radiating elements designed to intercept, with minimum losses, waves consisting of signals to be transmitted, emitted by a primary source, in order to reflect them in a chosen direction, known as the pointing direction. To allow the reconfigurability of the antenna diagram, each radiating element is equipped with a phase control device with which it forms a passive or active phase shifter module.
“Phase shifter module” is understood to mean both radiating cavity and slot structures and radiating patch resonant planar structures.
The invention more particularly concerns linear polarization active phase shifter modules. These usually consist of a phase shifter module with a switch made up of diodes (usually the PIN type), MESFETs, varactors, or mechanical control devices (such as, for example, a motor designed to move a dielectric rod).
Switch-operated phase shifter modules consume a large amount of energy and are subject to significant losses and heating. Mechanical control phase shifter modules are complicated to implement, in particular in the case of large arrays, and consume a lot of energy. In both cases, the disadvantages entailed by the phase control techniques used limit the applications of phase shifter modules, particularly in the aerospace field, and more specifically in observation platforms, such as satellites, for example.
The object of the invention is therefore to improve the situation in the case of linear polarization active phase shifter module reflectarray antennas.
To this end, it proposes a phase shifter module with a characteristic resonant length that, in at least one selected place, has an MEMS (Micro ElectroMechnical System) device able to be placed in at least two different states respectively permitting and prohibiting the establishing of a short-circuit intended to vary the characteristic resonant length, in order to vary the phase shifting of the waves to be reflected that present at least one linear polarization.
Each MEMS device may, for example, consist of a flexible conducting bridge whose states are controlled by two control electrodes that are placed roughly on top of each other, one of which is comprised of the bridge. Alternatively, each MEMS device may consist of a suspended flexible conducting beam (or cantilever) whose states are controlled by a control electrode placed below its suspended section.
In one family of embodiments, the module may have a resonant planar structure consisting of at least one rectangular upper patch placed roughly parallel to a lower ground plane, at a selected distance, the lower ground plane defining at least one conducting “wafer”, that may be rectangular, for example, completely surrounded by a non-conducting zone, placed below the upper patch and of smaller dimensions. In this case, the module has at least one metallic bushing connecting the upper patch to the wafer and the MEMS device is placed in the non-conducting zone, in order to establish, in one of its states, a link between the wafer and the rest of the ground plane to control the resonant length of the upper patch.
The lower ground plane may possibly define at least two wafers (that may be rectangular, for example) completely surrounded by a non-conducting zone, placed below the upper patch and of smaller dimensions. In this case, the module has at least two metallic bushings respectively connecting the upper patch to one of the wafers, and at least two MEMS devices each placed in one of the non-conducting zones, in order to establish links between at least one of the wafers and the rest of the ground plane, allowing the defining of at least three upper patch resonant lengths that differ according to their states.
As a variant of this family of embodiments, the module may consist of an upper ground plane with at least one radiating slot, equipped with an MEMS device controlling its characteristic resonant length, a lower ground plane and metallic bushings connecting the lower ground plane to peripheral sections of the upper ground plane in order to define a resonant cavity. For example, the upper ground plane may have at least two radiating slots, each equipped with a single MEMS device controlling their characteristic resonant length. Each MEMS device may thus preferably be placed roughly in the middle of a radiating slot. Furthermore, the slots are preferably roughly parallel to each other and may have slightly different lengths. They may also be curved, however, so that together they form an annular slot short-circuited at two roughly opposite points.
Alternatively, the upper ground plane may have one radiating slot, equipped with at least two MEMS devices allowing the defining of at least three resonant lengths that differ according to their states.
Moreover, the upper ground plane may possibly have at least one rectangular radiating slot with large sides parallel to a first direction, and at least one other rectangular radiating slot with large sides parallel to a second direction perpendicular to the first, in order to allow a double linear polarization.
In another family of embodiments, the module may consist of a resonant planar structure comprising an upper patch placed roughly parallel to a lower ground plane, at a selected distance. In this case, the patch has at least one slot equipped with at least one MEMS device controlling its characteristic resonant length.
The module may thus have a single slot (of a half-wave length) equipped with at least two MEMS devices, allowing the defining of at least three resonant lengths that differ according to their states. As an alternative, the upper patch may be roughly square and the module may have at least a first and second rectangular slot (of a quarter-wave length) placed roughly opposite each other, coming out onto two non-radiating opposite sides of the square, each being equipped with at least two MEMS devices, allowing the defining of at least three resonant lengths that differ according to their states. In this last case, the module may also have at least a third and fourth rectangular slot (of a quarter-wave length) placed roughly opposite each other, coming out onto two non-radiating opposite sides of the square, each being equipped with at least two MEMS devices, allowing the defining of at least three resonant lengths that differ according to their states. Several upper patches may also be used, each with at least one quarter-wave half-slot, with pairs of half-slots opposite each other then forming half-wave slots.
In the presence of a bridge MEMS device and rectangular slots, the bridge is preferably placed roughly parallel to the large sides of the slot. However, in the presence of a beam MEMS device and rectangular slots, said beam is preferably placed roughly perpendicularly to the large sides of the slot.
Furthermore, the lower ground plane may define a lower patch placed below the upper patch and of smaller dimensions. In this case, the module has metallic bushings that connect the ground plane to peripheral sections of the upper patch, in order to define a resonant cavity. This patch and cavity structure defines a further family of phase shifter modules.
The invention also proposes a reflectarray antenna equipped with at least two phase shifter modules of the type presented above.
The invention is particularly suited, although not exclusively, to Ku-band geostationary telecommunication antennas (12 to 18 GHz) with reconfigurable coverage (changing of orbital position, adapting of traffic), and to band C (4 to 8 GHz) or band X (8 to 12 GHz) radar antennas, and SARs in particular.
Other features and advantages of the invention will appear on examination of the detailed description below, and of the drawings appended, in which:
The drawings appended may not only complete the invention, but also contribute to its definition, where applicable.
The invention concerns a linear polarization active phase shifter module for an active reflectarray antenna.
The reflectarray antenna may, for example, be dedicated to telecommunications, for example Ku-band (12 to 18 GHz) geostationary telecommunications with reconfigurable coverage (changing of orbital position or adapting of traffic), or band C (4 to 8 GHz) or band X (8 to 12 GHz) radars, SARs (synthetic aperture radars) in particular, or high-throughput ISL-RF type links, particularly within a small constellation of satellites flying in formation.
Generally speaking, a phase shifter module, according to the invention, consists of an MEMS (Micro ElectroMechanical System) device in one or several selected places. Each MEMS device may be placed, through electrical controls, in at least two different states respectively permitting and prohibiting the establishing of a short-circuit intended to vary one of the module's characteristic resonant lengths, in order to vary the phase shifting of the waves to be reflected (originating from the antenna's source) presenting at least one linear polarization.
Such a phase shifter module may belong to one of three major families depending on its radiating structure. A first family consists of radiating cavity and slot structures, a second family consists of patch resonant planar structures and a third family consists of cavity resonant planar structures.
FIGS. 1 to 9 are first of all referred to in describing embodiment examples of phase shifter modules belonging to the first family.
The substrate SB is made, for example, from Duroid or TMM, and has a thickness equal, for example, to λ/4, where λ is the vacuum wavelength of the waves to be reflected, originating from the antenna's source.
The lower ground plane GP1 and the upper ground plane GP2 are electrically connected together by means of metallic holes (or bushings) MH formed in the substrate SB. These planes are made, for example, from alumina, silicon or glass substrates which, owing to their small thicknesses (typically 500 μm), must be laid onto a Duroid or TMM substrate SB to achieve a thickness equal to λ/4. The metallic holes MH are preferably arranged around the outside of the lower ground plane GP1 and the upper ground plane GP2, in order to define a resonant cavity.
Two techniques may be envisaged for creating this assembly. A first technique consists of laying a Duroid (or Metclad) substrate, around 3 mm thick, for example, on top of an alumina substrate, around 0.254 mm thick, for example, then placing a lower ground plane GP1 on the lower face of the Duroid substrate and an upper ground plane GP2 on the upper face of the alumina substrate, said upper ground plane GP2 being locally interrupted by the slots. A second technique consists of only using a Duroid (or Metclad) substrate, around 2 or 3 mm thick, for example, then forming on its upper face portions of an intermediate ground plane in which are formed voltage control lines, then laying onto this upper face portions of alumina substrates, around 0.245 mm thick, for example, with on an upper face an upper ground plane GP2, each with one or several slots, then placing a lower ground plane GP1 on the lower face of the Duroid substrate, and finally connecting the lower, intermediate and upper ground planes through two levels of metallic holes (or bushings).
The upper ground plane GP2 also has a single radiating slot RS, preferably rectangular in shape, defined by two large (longitudinal) sides of length b, and two small (transverse) sides of width a.
This radiating slot RS is created, for example, by etching the upper ground plane GP2.
Furthermore, the radiating slot RS has a parallel LC resonance. The parameters of such a resonator (resonance frequency and bandwidth) depend mainly on the lengths b and the width a of the radiating slot RS, and on the permittivity εr of the substrate SB.
Several modes may be propagated in the cavity delimited by the metallic holes MH. Each of these modes has a specific propagation constant β and a specific characteristic impedance Z0. The cavity mode cut-off frequency depends mainly on the length mx and the width my of the lower ground plane GP1 and the upper ground plane GP2, and on the permittivity εr of the substrate SB. Remember also that a vertical resonance may occur in this type of cavity if its thickness d is equal to nλg/2, where n is an integer and λg is the wavelength of the guided mode(s) propagated in the cavity.
For example, a square mesh array may be chosen, in which mx=my=0.7λ=8 mm. In this case, and with a wavelength A corresponding to a working frequency of 26.4 GHz, the cavity has a cut-off frequency equal to 18.75 GHz and only functions in its fundamental mode, which corresponds to a guided wavelength λg equal to around 16.14 mm, in the case of an air cavity.
With a cavity of a thickness equal to λ/4 (which here is around λg/5.7), phase shifts of up to 360° may be obtained with widths a of slot RS of between around 0.25 mm and around 1 mm. For example, with a width equal to 0.5 mm, the phase shift's inflexion point is obtained at the resonance of the slot RS, which corresponds to a length b equal to around 5.5 mm, taking into account the other values previously stated.
In this embodiment, the radiating slot RS is preferably centered in the middle of the upper ground plane GP2. However, this may not be the case, in particular in the presence of an additional parasite slot. In this last case, the slots are preferably located symmetrically in relation to the centre of the module.
Moreover, in this embodiment example, the radiating slot RS is equipped with three MEMS devices SD each constituting a two-state switch. Of course, the radiating slot may have a different number of MEMS devices SD if this number is at least equal to one.
Each MEMS device SD here consists of a flexible conducting bridge BR whose ends are joined to retaining studs ST that are themselves joined to the upper face of the substrate SB. These studs ST are made, for example, from Gold or Aluminum and are slightly thicker than the upper ground plane GP2. The flexible bridge BR is made in the form of a blade made conductive, for example, through Gold or Aluminum plating, and installed in the slot RS roughly parallel to its longitudinal edges.
Furthermore, each MEMS device SD consists of two control electrodes placed roughly on top of each other, one of these comprising of the flexible bridge BR and the other being, for example, placed at a higher level above the flexible bridge BR (not shown), these two electrodes being connected to a power-supply circuit (not shown).
In addition, on the upper face of the substrate SB, inside the radiating slot RS and roughly in a central section of its longitudinal edges, two small access lines AL may be placed roughly opposite each other, perpendicularly to the flexible bridge BR, and electrically connected to the upper ground plane GP2.
In the presence of a control current chosen at control electrode level, the suspended section of the bridge BR is attracted to said access lines AL. The suspended section then bends until it comes into contact with the two access lines AL, which locally generates a short-circuit in the radiating slot RS and reduces its characteristic resonant length (b), which is its electrical length. This constitutes one of the two states of the MEMS device SD.
In the absence of a control current, the bridge BR is apart from the access lines AL, so that the length of the radiating slot RS is not altered. This constitutes the other state of the MEMS device SD.
By separately controlling the various MEMS devices SD, it is therefore possible, in this embodiment example, to define three short-circuits in three different positions, corresponding to at least four different resonant lengths, for the slot RS. Of course, the positions of the various MEMS devices SD are chosen to allow the regular quantification of the phase rule. This positional constraint favors the arranging of the MEMS devices on the edges of the slot. These different resonant lengths correspond to different phase shifts of the wave reflected by the phase shifter module PSM.
Here, each MEMS device SD consists of a conducting flexible beam (or cantilever) BE with an end joined to a conducting retaining stud ST′, formed in the radiating slot RS along one of the longitudinal edges and electrically connected to the upper ground plane GP2.
This stud ST′ is made, for example, from Gold or Aluminum and is slightly thicker than the upper ground plane GP2, so that the beam BE is suspended above the radiating slot RS and the level of the upper ground plane GP2. The flexible beam BE is made in the form of a blade made conductive, for example, through Gold or Aluminum plating, installed roughly perpendicularly to its longitudinal edges. The free end of the beam BE crosses the slot RS across its width and slightly juts out onto the upper ground plane GP2 at a place where an electrically conductive contact stud CST is preferably placed.
Moreover, each MEMS device SD′ consists of a control electrode CE′ placed below the central suspended section of the beam BE and connected to a power-supply circuit (not shown), another electrode being comprised of the conducting flexible beam BE. The control electrode CE′ is formed on the upper face of the substrate SB, inside the radiating slot RS.
In the presence of a control current chosen at control electrode CE′ level, the suspended section of the beam BE is attracted to said electrode. It therefore bends until its free end comes into contact with the contact stud CST, which locally generates a short-circuit in the radiating slot RS and reduces its characteristic resonant length (b), which is its electrical length. This constitutes one of the two states of the MEMS device SD′.
In the absence of a control current, the free end of the beam BE is apart from the contact stud CST, so that the length of the radiating slot RS is not altered. This constitutes the other state of the MEMS device SD.
By separately controlling the various MEMS devices SD′, it is therefore also possible, in this embodiment example, to define three short-circuits in three different positions, corresponding to at least four different resonant lengths, for the slot RS. Of course, the positions of the various MEMS devices SD′ are chosen to allow the regular quantification of the phase rule. These different resonant lengths correspond to different phase shifts of the wave reflected by the phase shifter module PSM.
In this embodiment example, the radiating slot RS is equipped with three MEMS devices SD′. However, the radiating slot RS may have a different number of MEMS devices SD′ if this number is at least equal to one.
Some radiating slots may have different lengths. More specifically, in the example illustrated, the upper ground plane GP2 has two end radiating slots RS1, with a first characteristic resonant length L1, two intermediate radiating slots RS2, with a second characteristic resonant length L2 greater than L1, and a central radiating slot RS3, with a third characteristic resonant length L3 greater than L2. In one variant, the five slots may have five different lengths.
Here, the five radiating slots RS1 to RS3 are roughly centered in relation to the middle of the upper ground plane GP2, and their MEMS device SD with a bridge BR is also installed in a centered position. However, other alternatives are possible.
Indeed, in the example described above, the undesirable slots are short-circuited, but the resonant length of some of them may also be modified in order to excite several resonances and effectively control the phase shifting between slots, with coupling.
The distance separating two neighboring slots may be fixed or variable. It varies according to need. It is typically between around 100 μm and 500 μm.
In this case, only one or several radiating slots are used, their respective MEMS devices SD being placed in their second state (not arrowed). The slots that are not required are short-circuited, by placing their MEMS devices SD in their first state (arrowed). The phase variation of the reflected wave is therefore obtained here by selecting one of the combinations of short-circuited and non-short-circuited slots. Indeed, a specific and discrete phase shift corresponds to each combination, mainly according to the ratio between the smallest characteristic resonant length and the largest characteristic resonant length.
Each slot short-circuited in its middle acts like a parasitic element for the neighboring non-short-circuited slot. Here it is a question of exciting several resonances in order to have an acceptable range of phase shifts, while preventing a highly resonant response leading to low band performances. The coupling between the various resonances, created through coupling between a slot and a patch, attenuates the resonant response.
More specifically, what differentiates the fourth embodiment example from the third is the embodiment of the MEMS devices. In this example, each MEMS device SD with a bridge BR is in fact replaced with an MEMS device SD′ with a beam BE, of the type described with reference to
This phase shifter module PSM operates in the same way as the phase shifter module described above with reference to
As illustrated in the fifth example in
This requires the use of at least one radiating slot VRS oriented in a first (“vertical”) direction, and at least one radiating slot HRS oriented in a second (“horizontal”) direction, perpendicular to the first. Of course, as illustrated in
It is possible to use radiating slots VRS and HRS equipped with only a single MEMS device with a bridge BR or a beam BE, however it is preferable to use radiating slots VRS and HRS that have at least two MEMS devices with a bridge BR or a beam BE (as illustrated).
FIGS. 10 to 18 are now referred to in describing embodiment examples of phase shifter modules belonging to the second family.
The substrate SB is made, for example, from Duroid or TMM and has a low thickness d′, typically of around λ/10 to λ/5, where λ is the vacuum wavelength of the waves to be reflected, originating from the antenna's source.
The upper patch UP is placed roughly parallel to the lower ground plane GP1 and has smaller dimensions. For example, and as illustrated, the upper patch UP is rectangular in shape, and preferably square.
Furthermore, the upper patch UP has a single slot IS, preferably rectangular in shape, defined by two large sides (longitudinal) of length b, and two small sides (transverse) of width a.
This slot IS is created, for example, by etching the ground plane constituting the upper patch UP.
In this embodiment example, the slot IS is equipped with three MEMS devices SD with a bridge BR, each constituting a two-state switch of the type described previously with reference to
The operating principle of this phase shifter module PSM, and more specifically of its MEMS devices SD, is identical to that described previously with reference to
It is important to note that the invention can only be applied if the upper patch UP is resonant at λ/2.
Here, each MEMS device SD′ is of the type with a beam BE, as in the embodiment example described above with reference to
As illustrated in
More specifically, the third example illustrated in
In the fourth example illustrated in
Furthermore, a metallic hole (or bushing) MH allows the electrical coupling of the upper patch UP and the lower ground plane GP1 in a central section located between the two small interference slots S1 and S2. This metallic holes MH is intended to supply the upper patch UP with a direct current in order to polarize the MEMS device. Two or more small quarter-wave interference slots may be created, coming out onto at least one of the non-radiating sides.
Of course, it may be envisaged for the upper patch UP (roughly square) to have only one rectangular slot coming out onto a non-radiating side of the square, equipped with at least two MEMS devices SD or SD′.
As illustrated in the fifth example in
To this end, at least two small interference slots S1 and S2 may be used, for example, oriented in a first direction, and at least two small interference slots S3 and S4 oriented in a second direction, perpendicular to the first. Here, “small slot” is understood to mean an interference slot IS of the type presented above with reference to
It is possible to use small interference slots S1 to S4, of a quarter-wave length, equipped with only a single MEMS device with a bridge BR or a beam BE, however it is preferable to use small interference slots S1 to S4 that have at least two MEMS devices with a bridge BR or a beam BE (as illustrated). The number of MEMS devices used in each slot depends on the number of phase states required.
As in the previous example, a metallic hole (or bushing) MH allows the electrical coupling of the upper patch UP and the lower ground plane GP1 in a central section located between the four small interference slots S1 to S4, of a quarter-wave length. This metallic hole MH is intended to supply the upper patch UP with a direct current in order to polarize the MEMS device.
In the last three embodiment examples (FIGS. 13 to 15), the upper patch UP is powered by at least one metallic hole MH. However, as an alternative, this power may be supplied by a high impedance quarter-wave line.
It is important to note that the length of the upper patch UP is chosen so that it is resonant at λ/4.
The substrate SB is made, for example, from Duroid or TMM and has a low thickness d′, typically of around λ/10 to λ/5, where λ is the vacuum wavelength of the waves to be reflected, originating from the antenna's source.
The upper patch UP′ is placed roughly parallel to the lower ground plane GP1 and has very much smaller dimensions in at least one direction.
As illustrated in
Each metallic hole MH is connected to the upper patch UP′ in a selected place, the various places being preferably roughly aligned along a line parallel to the longitudinal sides of said upper patch UP.
In addition, each small conducting wafer LW is equipped with an MEMS device with a bridge BR or a beam BE (as illustrated in
This structure is advantageous as, its devices being placed on the back face, they are more protected from radiation.
In the example illustrated in
Of course, the phase shifter module PSM may have a number of MEMS devices (SD or SD′) other than five, if this number is at least equal to one. The number of MEMS devices used depends on the number of phase states required.
It is important to note that in this embodiment example, at the resonance frequency, the sum of the “active” dipole length (in other words the length between the short-circuit and the other end of the dipole) and the length of the short-circuit must be equal to a quarter of the wavelength of the guided mode λg.
This embodiment example may allow the creating of a double linear polarization phase shifter module, of the type illustrated in
This embodiment example constitutes a type of intermediate structure between the embodiment examples illustrated in FIGS. 5 to 8 and the embodiment examples illustrated in FIGS. 10 to 12.
Here, the phase shifter module PSM consists of a substrate SB with a back (or lower) face, joined to a lower ground plane GP1, and a front (or upper) face, joined to an upper patch UP.
The substrate SB is made, for example, from Duroid or TMM and has a thickness d equal to λ/4, where λ is the vacuum wavelength of the waves to be reflected, originating from the antenna's source.
The substrate SB is crossed, on its periphery, by metallic holes (or bushings) MH connected to the lower ground plane GP1 and surrounding the upper patch UP in order to define a resonant cavity. For example, for operation in the Ku band, the upper patch UP is a square between around 15 mm and around 17 mm long.
Furthermore, the upper patch UP consists of at least two (here five) radiating slots, each with a single MEMS device (SD or SD′) with a bridge BR or a beam BE. Of course, the number N of radiating slots illustrated is not limitative. It may take any value greater than or equal to two. For example, the slots have a large side that is between around 5 mm and around 7 mm long, and a small side that is between around 0.3 mm and around 0.7 mm wide.
Some radiating slots may have different lengths. More specifically, in the example illustrated, the upper patch UP has two end radiating slots RS1, with a first characteristic resonant length L1, two intermediate radiating slots RS2, with a second characteristic resonant length L2 greater than L1, and a central radiating slot RS3, with a third characteristic resonant length L3 greater than L2. In one variant, the five slots may have five different lengths.
Here, the five radiating slots RS1 to RS3 are roughly centered in relation to the middle of the upper patch UP, and their MEMS devices SD with a bridge BR (or SD′ with a beam BE) are also installed in a centered position (for example).
In this case, only one or several radiating slots are used, their respective MEMS devices SD being placed in their second state (not arrowed). The slots that are not required are short-circuited, by placing their MEMS devices SD in their first state (arrowed). The phase variation of the reflected wave is therefore obtained here by selecting one of the combinations of short-circuited and non-short-circuited slots. Indeed, a specific and discrete phase shift corresponds to each combination, mainly according to the ratio between the smallest characteristic resonant length and the largest characteristic resonant length.
Each slot short-circuited in its middle acts like a parasitic element for the neighboring non-short-circuited slot. Consequently, it is likely to improve the wavelength of the non-short-circuited slot.
In the example described above, the undesirable slots are short-circuited, but this does not have to be the case. For example, the resonant length of certain slots may be modified to excite several resonances and effectively control the phase shifting between slots, with coupling. This modification may take place, for example, by placing one or several (for example two or three) MEMS devices, preferably of the cantilever type SD′, in the end sections opposite the slots, rather than in their central sections.
Of course, slots may be used that have roughly the same shapes and dimensions.
Some metallic holes (or bushings) MH, for example one in two, may be advantageously used to route voltage commands to the various MEMS devices SD or SD′.
The above describes modules that have single slots that are a quarter-wave or half-wave long. However, it is possible to create modules with composite slots, as illustrated in
More specifically, the modules in the embodiment examples illustrated in
In the example illustrated in
For example, the patches have a width equal to around 3.7 mm and are separated by a distance, forming a slot, equal to around 0.1 mm.
Such a dissymmetrical structure offers a stable frequency response owing to an effective coupling between the two resonances.
In the example illustrated in
Such a symmetrical structure also offers a stable frequency response owing to an effective coupling between the two resonances.
Many other combinations of upper patches may be envisaged. Thus, one option is a combination of several upper patches separated from each other by spaces creating slots of chosen widths with which they form what experts refer to as a “Jerusalem cross”. By reducing the width of the opposite slots with an MEMS device, it is possible to act on the resonance frequency of such a structure, and thus modify the phase of the reflected wave. A dual structure, consisting of metal lines in the form of a Jerusalem cross, is in particular described in the document by C. Simovski et al, “High-impedance surfaces with angular and polarization stability”, 27th ESA Antenna Technology Workshop on Innovative Periodic Antennas, pp 176-184. The resonance of such a structure is mainly provided by the inductive and capacitive sections of the Jerusalem cross, rather than by the resonance of the patches. This “metamaterial” structure thus operates with much lower frequency bands.
It is also possible to join to phase shifter modules that have at least one patch with at least one slot IS, described above, one or several auxiliary patches and at least one MEMS coupling device, in order to vary the dimensions of the patch 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 large side) of the slots IS. A phase shifter module PSM of this type is illustrated in
More specifically, the phase shifter module PSM illustrated in
The upper patches UP, AP1 and AP2 and the lower ground plane GP1 define a resonant planar structure.
The phase shifter module PSM also has at least one MEMS coupling device SD or SD′ installed between the patch UP and an auxiliary patch AP1, AP2, intended to establish or prevent contact between these patches according to the state in which it is placed.
In the example illustrated, the patch UP is able to be connected to each auxiliary patch AP1, AP2 by means of three MEMS devices SD′, consisting of one central and two end devices. The two end MEMS devices SD′ are preferably placed symmetrically in relation to the centre of the auxiliary patch AP1, AP2.
The various MEMS devices SD′ or SD that connect the patch UP to one of the auxiliary patches AP1, AP2 are preferably controlled by the same control current. In other words, they are preferably simultaneously placed in the same state, in order to ensure either an electrical link, or an absence of an electrical link, between the patch UP and the auxiliary patch AP1, AP2 concerned.
If a link is established between the patch UP and an auxiliary patch AP1, AP2, the physical length (along X) of the patch UP may therefore be increased. By simultaneously acting on the length of the patch UP and the length of the slot IS couple, it is therefore possible to simultaneously modify the phase shifting of the incident wave, over a range greater than 360°, and frequency dispersion of this phase shift couple. The possibility of controlling the frequency dispersion of this phase shift is particularly advantageous for compensating for the frequency dispersive illumination of a plane reflectarray by a primary source.
It is important to note that several (at least two) auxiliary patches, preferably of the same dimensions, may be placed parallel to each other on at least one of the two sides of the patch UP, the patches being connected two by two by one or several MEMS coupling devices SD′ or SD, and preferably three. This allows still further varying of the patch UP's physical length, according to need, by playing on the respective states of the MEMS devices SD′ or SD coupling the auxiliary patches.
Furthermore, the auxiliary patches that are located on either side of the two parallel sides of the patch UP do not need to have the same dimensions. This is notably the case in the example illustrated in
As in the examples previously described, the patch UP may have one or several MEMS devices SD or SD′. The number of MEMS devices used depends on the number of phase states required.
This type of phase shifter module PSM therefore allows the phase shifting and the frequency phase dispersion to be varied according to need, which is particularly advantageous for an active (or reconfigurable) antenna. The choice of phase shifting and phase shifting dispersion is in fact fixed by the physical length of the patch UP and by the electrical length of each slot IS of each patch UP, according to the respective states of the various MEMS devices used.
In order to create a passive phase shifter module PSM, for a non reconfigurable antenna, the use of MEMS devices at slot level may be avoided. More specifically, as illustrated in
Such a structure PSM therefore consists of a substrate SB with a back (or lower) face, joined to a lower ground plane GP1, and a front (or upper) face, joined to at least one upper patch UP with at least one slot IS. The upper patch UP and the lower ground plane GP1 define a resonant planar structure.
By carefully choosing the dimensions of the upper patch UP, and in particular its length x (along direction X), and of the slot IS, and in particular its length b (along direction Y), and the thickness d of the substrate SB, both a chosen phase shifting and a chosen frequency phase dispersion may be imposed.
The dimensions and thicknesses may be deduced from curves such as those illustrated in
If the upper patch UP has only a single slot IS, this is preferably placed roughly in its centre. However, the upper patch UP may have several slots IS, possibly of different dimensions.
Such a phase shifter module PSM allows the obtaining of any phase shift, and in particular phase shifts (very much) greater than 360°. It also allows the controlling of the frequency dispersion of this phase shift. Previous phase shifter modules PSM, which allow such characteristics to be obtained, have three patches placed parallely above each other and above a lower ground plane (they are in particular described in the article by J. A. Encinar et al, “Design of a three-layer printed reflectarray for dual polarization and dual coverage”, 27th ESA Antenna workshop, Santiago de Compostel, Spain, March 2004). The phase shifter modules PSM according to the invention have only a single level of plating (upper patch), in addition to the lower ground plane GP1, and are therefore a lot simpler to create than previous phase shifter modules.
The invention is not limited to the phase shifter module and reflectarray antenna embodiments described above, only by way of example, but covers all the variants that may be envisaged by experts within the framework of the claims above.
Number | Date | Country | Kind |
---|---|---|---|
04 50 575 | Mar 2004 | FR | national |