Low-profile antenna with two-dimensional electronic scanning

Abstract

The invention relates to a two-dimensional beam scanning antenna comprising: a folded parallel-plate waveguide (240) that emits a quasi-planar wave in a first direction (Ox); a linear array of stubs (230) extending in a second direction (Oy) perpendicular to the first; a first and a second phase-shifting surface which comprise elementary phase-shifting cells (221) and elementary phase-shifting bands (221), respectively, each band being associated with a stub; and a first and a second set of control lines, controlling the phase shifts of the elementary phase-shifting cells and bands, respectively, so as to control the orientation of the beam in a plane orthogonal to the first and the second direction, respectively. The first phase-shifting surface is a reflective phase-shifting surface, which receives the planar wave propagating in the first direction and reflects it in the opposite direction after phase-shifting.

Description

[0001] DESCRIPTION

[0002] Title: LOW-PROFILE TWO-DIMENSIONAL ELECTRONICALLY SCANNING ANTENNA

[0003] TECHNICAL FIELD

[0004] The present invention relates generally to the field of phased array antennas allowing two-dimensional control of beam orientation. It finds particular application in terrestrial terminals in the K / Ka band for satellite communications, on-board communication systems on trains or aircraft, 5G base stations, near-field microwave focusing systems.

[0005] STATE OF THE PRIOR ART

[0006] Two-dimensional scanning antennas are well known in the state of the art, particularly for satellite communication terminals or communication systems on board moving vehicles. These make it possible to dynamically control the direction of the beam (in transmission and / or reception) along two orthogonal axes and are therefore capable of scanning a predetermined solid angle.

[0007] The first generation of two-dimensional scanning antennas uses mechanical scanning. These generally include a directional antenna (e.g., parabolic) mounted on a gimbal joint allowing it to be oriented along two axes. In addition to the fact that they do not allow rapid angular scanning, these antennas are bulky and heavy. They are difficult to integrate into vehicles and often degrade their aerodynamic behavior. Finally, the servomotors that equip them require fairly heavy maintenance and consume energy.

[0008] To overcome these drawbacks, a second generation of antennas uses phased array antennas and beamforming techniques that allow electronic scanning. These second-generation antennas are compact and can fit the shape of a vehicle (conformal antennas on an aircraft, for example). They allow rapid angular scanning, in the absence of any mechanical inertia. On the other hand, the large number of elementary antennas forming the array makes their electronics particularly complex and their manufacture expensive.

[0009] Hybrid mechanical / electronic scanning antennas are also available on the market, using for example a mechanical azimuth positioner and an electronic elevation scan. However, their performance is not optimal, mechanical pointing remains slow and their size is too large for many applications.

[0010] Recently, an antenna suitable for one-dimensional electronic scanning using a continuous transverse stub array (CTS) was described in the article by M. Ettore et al. entitled "Continuous transverse stub array for Ka-band applications" published in IEEE Trans. Antennas Propag., vol. 63, no. 11, pp. 4792-4800, Nov. 2015.

[0011] Such an antenna has been shown schematically in Fig. 1A. This comprises an array of continuous stubs, the stubs in question extending in a transverse direction (Oy) to a waveguide to a parallel plate waveguide or PPW (Parallel Plate Waveguide), 140. As illustrated in Fig. 1B, the feeding of the CTS array from the waveguide is obtained by means of a tree of T-junctions whose different branches feed the stubs.

[0012] For the sake of simplification, the stubs have been represented here with zero height and are therefore reduced to transverse radiative slits 111, parallel to the axis (Oy).

[0013] By "stub", in a manner known per se, we mean here a part, a section of guide open in the direction orthogonal to that of propagation of the wave, allowing impedance transformations to be made.

[0014] Figures 1C and 1D respectively represent a section of the PPW waveguide along a plane (xy) and a plane (xz). A microwave source in the Ka band, 130, here an H-plane sectorial horn, injects a wave into the PPW waveguide, 140. The sectorial horn is flared in the H plane of the PPW waveguide, in other words in the plane (xy). The PPW waveguide has a “pillbox” or “U” type transition section, 160, such that it is folded back on itself, said transition section ensuring the connection between a first rectilinear section 141 and a second rectilinear section 142, substantially parallel to each other. The sector horn 130 opens directly into the first straight section of the PPW waveguide and the second straight section of the PPW waveguide opens into the parallel feed network 120 of the CTS network.

[0015] The transition section has a parabolic reflector 150 in the (xy) plane as seen in Fig. 1C. The focal point of the parabolic reflector is located at the center of the sector horn aperture, which allows for a quasi-plane wave in the second section of the PPW waveguide.

[0016] A change in the position of the sector horn along the (y) axis, at the input of the PPW waveguide, modifies the phase distribution along this axis and ensures a beam scan in the H plane at the output of the CTS network, in other words a scan in the (yz) plane. Thus, by mechanically moving the horn antenna in front of the waveguide input or by switching the power supply of several sector horns arranged along the (y) axis in front of this same input, a one-dimensional scan of the beam in the (yz) plane is obtained. In the majority of implementations, however, this architecture only allows switching between a discrete set of beams and does not offer fine angular depointing of the antenna beam in the (yz) scanning plane.

[0017] A two-dimensional electronically scanned antenna using a CTS array has been disclosed in US-B-6677899. The CTS array feeds in the near field an array of MEMS-reconfigurable radiating elements located above it. Each element comprises at its input a wideband receiving element, at its output a wideband receiving element and a MEMS-controlled phase shift module between the input and output elements.

[0018] However, such an antenna is very complex to produce and is subject to malfunctions of MEMS devices, which are generally unreliable over time. In addition, the alignment between the lens array and the CTS feed network must be precise, otherwise insertion losses can be significant. The two arrays cannot be integrated into a single monolithic structure since the reconfigurable array is produced in the form of a plurality of printed circuits or PCBs (Printed Circuit Boards) mounted vertically in parallel above the CTS feed network. Finally, beam scanning requires the ability to individually control each MEMS device and therefore to have a control network comprising as many lines as there are MEMS devices.

[0019] Transmit array antennas offer a compact solution when two-dimensional electronic scanning (2-degree-of-freedom scanning, in half-space) is required. An example of such a transmit array can be found in the article by AR Vilenskiy et al. entitled "Reconfigurable transmitarray with near-field coupling to gap waveguide array antenna for efficient 2-D beam steering" published in IEEE Trans. Antennas Propag. Vol. 68, no. 12, pp. 7854-7865. More precisely, the two-dimensional scanning antenna here comprises a first 2D array of slot antennas illuminating in the near field a transmit array in the form of a phase shifting surface or PSS (Phase Shifting Surface).The phase shift surface is formed by a two-dimensional array of elementary cells, each elementary cell comprising a first elementary antenna for reception and being connected to a second elementary antenna for transmission via a phase shift module. Each phase shift module is individually controllable so as to be able to control the orientation and perform a two-dimensional scanning of the beam. However, such an antenna requires a complex control network, the number of layers and power dividers increasing as a function of the size of the antenna. In addition, the near-field coupling between the slot antenna array and the transmitter array necessarily induces insertion losses which are higher as the size of the array increases.

[0020] An object of the present invention is therefore to provide a two-dimensional electronic scanning antenna (with 2 degrees of freedom) which does not have the aforementioned drawbacks, in particular which is simple, has low power consumption and is compact, is easy to integrate and does not require a large number of control lines, even for large antennas.

[0021] STATEMENT OF THE INVENTION

[0022] The present invention is defined by a two-dimensional beam scanning antenna comprising a waveguide intended to be fed by a microwave source and to provide a quasi-plane wave propagating in a first direction, a linear array of transverse stubs, extended in a second direction perpendicular to the first, said stubs being arranged periodically in the first direction with a pitch substantially equal to the wavelength guided in the waveguide, said antenna being original in that it comprises:

[0023] - a first electronically reconfigurable phase shift surface comprising a first plurality, M, of elementary phase shift cells arranged periodically in the second direction with a pitch less than or equal to half the wavelength in free space of the microwave source;

[0024] - a second phase shift surface, electronically reconfigurable, comprising a second plurality, N, of elementary phase shift bands, each elementary phase shift band being extended in the second direction and being associated with a transverse stub of said network, said elementary phase shift band being arranged directly on the output of the transverse stub with which it is associated;

[0025] - a first set of control lines intended to control the respective phase shifts of the elementary phase shift cells so as to control the orientation of the beam in a plane orthogonal to the first direction;

[0026] - a second set of control lines intended to control the respective phase shifts of the elementary phase shift bands so as to control the orientation of the beam in a plane orthogonal to the second direction; and in that the first phase shift surface is a reflection phase shift surface, adapted to receive the wave provided by the microwave source propagating in a direction opposite to the first direction and to reflect it in the first direction after the elementary phase shift cells have applied first phase shift values ​​to it along the second direction.

[0027] Preferably, each of the elementary cells of the first phase shift surface is a reflective cell, configured to receive the plane wave propagating in the first direction and reflect it in the opposite direction.

[0028] In some embodiments, each elementary cell of the first surface and / or each elementary strip of the second surface is controlled using a single control line.

[0029] In this case, it is considered that each of the M cells of the first surface and each cell of the N phase shift bands of the second surface can introduce, respectively, Ki and K2 different phase shift values; the total number of diode control lines of the diodes is M log2K + N log2K2. The number of control lines therefore increases less rapidly with the radiating surface compared to an equivalent 2-D scanning antenna of the transmitter array or phased array type with NM radiating elements, which would require NM Iog2 Ki Iog2 K2 control lines or NM RF chains, respectively.

[0030] In some embodiments, at least one of the controllable systems comprises (is based on) PIN diodes. An exemplary embodiment of an electronically reconfigurable phase shift cell, using PIN diodes, in transmission, adapted to the second phase shift surface, is described in US patent 10,680,329 B2 by A. Clemente, L. Dussopt, L. Di Palma, entitled "Unit cell of a transmission network for a reconfigurable antenna".

[0031] The waveguide is preferably a parallel plate waveguide.

[0032] It advantageously comprises a first rectilinear section in which the wave emitted by the microwave source propagates in a direction opposite to the first direction, a second rectilinear section, parallel to the first rectilinear section, in which the plane wave propagates in the first direction after having been phase-shifted by the first phase-shifting surface and a U-shaped transition section, ensuring the 180° folding and connecting the first rectilinear section to the second rectilinear section.

[0033] According to some variants, the first phase shift surface is arranged on a cylindro-parabolic structure.

[0034] Alternatively, the waveguide is fed by the microwave source through a sector horn.

[0035] The waveguide can thus include in its transition section a cylindro-parabolic structure allowing the first phase shift surface to reflect the wave provided by the microwave source through the sector horn in the form of a quasi-plane wave.

[0036] Each elementary phase shift band may advantageously consist of a plurality P of second elementary cells, said second elementary cells of an elementary phase shift band being arranged periodically along the second direction with a pitch less than or equal to half a wavelength in free space, the same phase shift value being applied to said plurality of second elementary cells belonging to the same elementary phase shift band. Each first elementary cell, resp. each second elementary cell, may comprise a plurality of metal layers alternating with dielectric layers as well as a plurality of PIN diodes interconnecting at least some of said different metal layers, controlled by a plurality k of control lines of the first, resp. of the second set.

[0037] Each first elementary cell, resp. each second elementary cell, may comprise a plurality of varactor diodes, controlled by at least one control line of the first, resp. second set.

[0038] In some embodiments, each elementary cell of the second phase shift surface (in transmission, on the stubs) is configured to radiate a field having a fixed circular polarization (i.e. either right circular or left circular).

[0039] This reconfigurable cell therefore receives and transforms the linearly polarized field emitted by each stub, into a fixed circularly polarized field and, at the same time, introduces on this field an electronically variable phase shift between a set of K2 different values. An example of the realization of such a reconfigurable cell in transmission using PIN diodes is described for example in the document by L.Di Palma, A.CIemente, L.Dussopt, R.Sauleau, P. Potier, and Ph.Pouliguen, “Experimental Characterization of a Circularly Polarized 1 Bit Unit Cell for Beam Steerable Transmitarrays at Ka-Band”, IEEE Trans. Antennas Propag., vol. 67, no. 2, Feb. 2019.

[0040] In some embodiments, each elementary cell of the second phase shift surface (in transmission, on the stubs) is configured to radiate a field having a circular polarization with an electronically reconfigurable direction (right or left).

[0041] Such a cell can be realized by using PIN diodes according to the design described in the document by F. Foglia Manzillo et al., Transmitarray antenna cell (US patent 2022 / 0359982 A1). In another embodiment, this reconfigurable cell (elementary cell of the second phase shift surface) can consist of a first section which receives the linearly polarized field emitted by each stub and transmits it by introducing on this field an electronically variable phase shift between a set of K2 different values, and a second section which functions as an electronically reconfigurable polarization converter (from linear to circular). This second section receives the linearly polarized field transmitted by the first section and emits a linearly polarized field with an electronically reconfigurable direction (right / left).A possible implementation of such a cell using PIN diodes provides for the stacking of: (i) (first section), the reconfigurable phase-shift transmission cell described in the patent of A. Clemente, L. Dussopt, L.Di Palma, entitled "Unit cell of a transmission network for a reconfigurable antenna" (US 10680329 B2); (ii) (second section), the cell of the reconfigurable polarization converter described in the patent of A. Clemente entitled "Transmitarray antenna cell" (US 2023 0010547 A1).

[0042] In some embodiments, the two-dimensional beam scanning antenna is configured to emit two beams, of orthogonal and independently controllable polarizations, and such that each band of the second phase shift surface (in transmission, on the stubs) comprises two sets of reconfigurable phase shift cells capable of radiating fields having orthogonal polarizations. For example, the cells of the first set can be configured to radiate a field in horizontal linear polarization and those of the second set to radiate a field in vertical linear polarization, respectively. Two beams in orthogonal polarizations can thus be formed. The depointing directions of these two beams can be reconfigured independently by controlling with two sets of control lines the two sets of cells of each band.An example of realization of the cells of the two sets, using PIN diodes, capable of receiving a vertical linear polarization and radiating either a horizontal linear polarization field or a vertical linear polarization field is described in the document by F. Foglia Manzillo et al., “A Ka-band Beam-Steering Transmitarray Achieving Dual-Circular Polarization”, 15th Eur. Conf. Antennas Propag. (EuCAP), Dusseldorf, Germany, 2021.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Other characteristics and advantages of the invention will appear on reading a preferred embodiment of the invention, made with reference to the attached figures among which:

[0045] Figs. 1A to 1D, already described, represent different views of a one-dimensional electronic scanning antenna known from the state of the art;

[0046] Fig. 2 schematically represents a two-dimensional electronic scanning antenna according to an embodiment presented to aid understanding of the invention;

[0047] Fig. 3 schematically represents the control lines of the first and second phase shift surfaces used in the antenna of Fig. 2;

[0048] Fig. 4 schematically represents a two-dimensional electronic scanning antenna according to one embodiment of the invention;

[0049] Fig. 5 illustrates a PPW waveguide comprising a slow wave structure, used in a variation of the first or second embodiment of the invention; and

[0050] Figs. 6A and 6B schematically represent, respectively in perspective and in section, a reflective cell which can be used in an antenna according to the present invention. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0051] In the following, we consider a two-dimensional electronic scanning antenna, that is, an antenna whose beam can be oriented according to two degrees of freedom. For example, the beam can be oriented around two orthogonal axes, in azimuth and in elevation.

[0052] The antenna according to the present invention is intended to operate with a microwave source typically operating in the millimeter and centimeter bands, from 3 to 300 GHz. It is particularly suitable for operation in the frequency range from 10 GHz to 60 GHz and can be used in particular in satellite terminals (in the K / Ka bands) or 5G terminals / base stations.

[0053] The antenna in question uses a waveguide acting as a quasi-optical beamformer. This waveguide provides a plane or quasi-plane wave, preferably in quasi-TEM (Transverse Electro-Magnetic) mode propagating in a first direction (Ox), to an array of radiating transverse stubs, or slots, extended in a second direction (Oy), perpendicular to the first direction.

[0054] The idea behind the present invention is to provide a first phase shift surface comprising a first plurality, M, of elementary phase shift cells arranged periodically along the second direction and a second phase shift surface, comprising a second plurality, N, of elementary phase shift strips, each elementary phase shift strip being extended along the second direction and being associated with a stub, or a slot, continuous transverse to the network and arranged directly above it.

[0055] The first phase shift surface scans the beam in the (xy) plane. The second phase shift surface scans the beam around the second direction in the (xz) plane. For example, the first phase shift surface can scan the beam in azimuth and the second phase shift surface can scan the beam in elevation. The waveguide is advantageously produced in the form of a parallel plate waveguide or PPW (Parallel Plate Waveguide), folded back on itself for reasons of compactness. It comprises a first straight section in a direction opposite to the first direction, a second straight section, parallel to the first straight section, and a U-shaped transition section, ensuring the 180° folding by connecting the first straight section to the second straight section.The transition section may include a reflector for reversing the direction of propagation between the first straight section and the second straight section of the waveguide.

[0056] The waveguide, and more precisely its first rectilinear section, is fed by a primary source, for example by means of a horn antenna, more precisely a sector horn, the wide edges of the sector horn joining the upper and lower plates of the guide and the narrow edges joining the side walls of the guide, so as to minimize insertion losses.

[0057] Fig. 2 schematically represents a two-dimensional electronically scanned antenna in a first embodiment which does not correspond to the present invention but is useful for understanding it.

[0058] Unless otherwise indicated, technical features of this embodiment which are technically compatible with the present invention may be applied thereto.

[0059] The waveguide 240 represented here is a parallel plate waveguide comprising a first rectilinear section 241 in which the wave injected by the sector horn (not shown) propagates in the direction opposite to the Ox direction, a rectilinear section 243 in which the wave propagates in the Ox direction after being reflected on the reflector 250 placed in the transition section, 242, of the guide.

[0060] The reflector 250 preferably has a cylindrical-parabolic reflecting surface whose focal line is vertical, so that the wave injected into the first part of the guide, with a cylindrical wavefront, is reflected in the form of a plane wave propagating in the second rectilinear section of the waveguide. According to a variant, the primary source is an array of antennas, for example horn antennas fed in parallel, which radiates a quasi-plane wave in the first part of the guide. In this case, the reflecting surface of the U-shaped transition is preferably planar.

[0061] The reflected plane wave propagates in the first direction and is phase-shifted by crossing a first phase-shifting surface 210. This first phase-shifting surface comprises a first plurality, M, of elementary phase-shifting cells, 211, arranged periodically in the second direction (y) with a pitch less than or equal to half the wavelength, Âo / 2, where  o is the propagation wavelength in vacuum.

[0062] The elementary phase shift cells of the first phase shift surface apply a phase shift law to orient the direction of the beam in the (yz) plane.

[0063] The plane wave thus phase-shifted then propagates in the direction (Ox) in the second rectilinear section, 243, of the waveguide 240. It is distributed, via a network of stubs, to a second phase-shifting surface 220. The second phase-shifting surface comprises a second plurality, N, of elementary phase-shifting strips, each elementary phase-shifting strip being associated with a continuous transverse stub 230 and arranged directly on the latter. The stubs at least partially protrude from the upper plane of the PPW guide, their open ends being turned in the direction Oz. The continuous transverse stubs extend in the second direction (Oy), also called the transverse direction.According to a variant, the stubs may have a zero height (the height being the height of the part of the stub which protrudes relative to the surrounding surface; in this variant, the radiating elements are therefore comparable to radiating slots (the term "stub" in fact including the particular case of a radiating slot). In all cases, the stubs are arranged periodically in the first direction with, preferably, a pitch substantially equal to the wavelength guided in the waveguide, i.e. X. g .

[0064] Where appropriate, each elementary band may be made up of a third plurality P of second elementary phase shift cells, 231, all the second elementary phase shift cells of the same elementary band then applying the same phase shift to the wave emitted by the stub associated with said band.

[0065] Advantageously, the third plurality will be chosen equal to the second plurality, in other words P = M.

[0066] The elementary phase shift bands of the second phase shift surface apply a phase shift law allowing the beam to be oriented in the (xz) plane.

[0067] If we note 60 and <p Q respectively the elevation and the azimuth corresponding to the desired orientation of the beam, it can be shown that the application of the phase shifts ip^, m = 1, . . , M by the elementary cells of the first phase shift surface and the phase shifts ip , n = by the elementary bands of the second phase shift surface, allows the beam to be oriented in the direction (0 O , <p0) souhaitée. Les valeurs des déphasages ip , n = ip = —mk Q d y sin 60sin <p Q

[0068] 2.7T where k Q = — is the wave number in vacuum of the wave emitted by the microwave source, kgx is the propagation constant along the x axis of the fundamental mode guided by the waveguide, d x is the step between the elementary phase shift bands of the second surface and d y is the step between the elementary phase shift cells of the first surface. As indicated above, we will advantageously choose d y = Â o / 2 and d x = X g .

[0069] According to a first variant, each (first or second) elementary cell, or even elementary phase shift strip, can be made from a succession of metal layers alternating with dielectric layers. One or more metal layers comprise(s) one or more electronic switches, for example PIN diodes, making it possible to vary the frequency response, in particular the phase of the transmission and / or reflection coefficient of the elementary cell among a set of discrete values.

[0070] Alternatively, according to a second variant, each (first or second) elementary cell, or even each elementary phase shift band, can be produced by means of a variable capacitance of the varactor type. This second variant has the advantage of being able to carry out a continuous variation of the phase shift, whereas the first variant only allows switching between discrete values.

[0071] An important advantage of the present invention is that it requires only a small number of phase shift control lines and therefore simplifies the control electronics.

[0072] Indeed, 2D electronically scanned antennas of the transmitting array type require at least as many control lines as cells, i.e. N x M for a matrix of M rows and N columns. Conversely, in the present case, assuming that an elementary phase shift cell / band can be controlled by means of a single control line, the number of control lines required for the same orientation precision is no more than N + M.

[0073] Fig. 3 schematically represents the control lines of the different elementary cells / strips of the first surface and of the second phase shift surface. In this embodiment, each elementary cell of the first surface and / or each elementary strip of the second surface is controlled using a single control line. For example, the elementary cells / strips are made from varactors and each control line analogically controls the capacitance of the associated varactor.

[0074] When the phase shifts can only take a plurality K of discrete values, as in the case of a PIN diode cell, the number of control lines per elementary cell / strip may be equal to log2K . The elementary cells / strips may apply an attenuation in addition to a phase shift, so as to be able to apodize the beam and reduce its secondary lobes. When these attenuation coefficients can take L discrete values, the number of control lines per elementary cell / strip then increases to log2K + log2L , which leads to a total number of control lines equal to (log2K + log2L) N + M). According to an alternative embodiment, the attenuation coefficients can be chosen to be fixed (fixed apodization) and in this case the number of control lines is no more than (N + M) log2L .

[0075] Fig. 4 schematically represents a two-dimensional electronic scanning antenna according to the invention.

[0076] This embodiment differs from the first in that the first phase shift surface, 410, no longer operates in transmission but in reflection. This configuration makes it possible to separate by a ground plane the RF elements of each cell of the surface and the structures necessary for the polarization of the reconfigurable electronic devices. Indeed, these structures can be arranged outside the guide, which facilitates the interconnection of the reflective surface (the first phase shift surface) with its control circuits. The elements bearing the reference signs 420-442 are functionally similar to the elements 220-242. The reference 441 designates the lower PPW waveguide 441 and the reference 442 the upper PPW waveguide. In this configuration, the first phase shift surface operates as an electronically reconfigurable reflector, and can be produced either on a concave or convex surface, or on a planar surface parallel to the zy plane.Therefore, in this embodiment it is no longer necessary to provide a first parabolic-shaped phase shift surface.

[0077] The first reconfigurable phase shift surface (or reflective surface) can be advantageously placed at a distance d r ~ 3A g / 4 + / A g / 2, of the upper surface of the lower PPW waveguide 441 and the lower surface of the upper PPW waveguide 442, where / is a natural number (zero or not), and A g is the wavelength in the two guides at the working frequency.

[0078] The wave from the microwave source, after being guided by the first rectilinear section of the guide, is reflected by the first phase shift surface 410 before propagating in the second rectilinear section of the guide. The first reflecting phase shift surface here applies, on the one hand, if necessary, for example when the surface is planar, a first phase shift law aimed at converting the cylindrical wave into a plane wave and, on the other hand, a second phase shift law along the y direction, aimed at orienting the beam in the (yz) plane. This optimal phase shift law in practice is approximated and achieved by opportunely choosing the electrical polarization state of the reconfigurable electronic devices in each cell (for example, PIN diodes) and therefore the phase of the reflection coefficient of each cell between a discrete number Ki of possible values.To ensure efficient operation of the reflector, the Ki values ​​are preferably uniformly spaced over the entire phase range [0-2n) in the working frequency band. In this case, we speak of a Iog2 Ki bit cell, which means that the reflection phase shift values ​​perform a Iog2 Ki bit quantization of the range [0-2n). For example, a reconfigurable cell capable of introducing the two (four) reflection phase values ​​0 and n (or respectively 0, n / 2, n, 3n / 2), is called 1 bit (or respectively 2 bit). As before, the first elementary cells 411 can further perform a beam apodization (here orthogonally to the axis (Ox) by applying appropriate attenuation values ​​(for example approximating a cardinal sine).

[0079] The 1-bit and 2-bit reconfigurable reflective cells using PIN diodes can be produced according to known embodiments, such as those proposed for example by the documents:

[0080] • S. Gharbieh, R. D'Errico, A. Clemente, “Reconfigurable intelligent surface design using PIN diodes via rotation technique - Proof of concept”, in Proc. Eur. Conf. Antennas Propag., EuCAP 2023, Florence, Italy.

[0081] • F. Liu et al., “A 2-Bit Reconfigurable Reflectarray Unit Design Using Only 2 PIN Diodes,” IEEE MTT-S Int. Microwave Workshop Series on Advanced Materials and Processes for RF and THz Appl., Guangzhou, China, 2022.

[0082] • H. Luyen, J. Booske, N. Behdad, “2-Bit Phase Quantization Using Mixed Polarization-Rotation / Non-PolarizationRotation Reflection Modes for Beam-Steerable Reflectarrays,” IEEE Trans. Antennas Propag., vol. 68, no. 12, Dec. 2020.

[0083] As an example, an example of an embodiment for producing a 1-bit reflective cell (2 values ​​of phase shifts in reflection, with a difference of n) is illustrated in Fig.6. In this embodiment, the reflective cell has a structure similar to that presented in the document by S. Gharbieh et al. cited above.

[0084] In this embodiment, the reflector cell comprises a patch antenna with an opening in the middle on which two PIN diodes, DI and D2, are assembled. The two diodes are in antiparallel configuration: the cathode of DI and the anode of D2 are in DC at the same potential, since they are physically connected to a metal pad in the middle of the opening. This pad is connected through a shorting via (SV) to a ground plane (PM), located under the antenna. The DI diode can activate and deactivate a 90° phase delay line (RPh), connected by V vias to the patch antenna and realized by using an intermediate metal layer between the patch antenna and the ground plane. The DC bias signal of the diodes is applied to a layer below the ground plane. A bias tee (BT) structure to decouple the DC signal and the RF signals is also realized. The DC signal is connected to the patch by through-hole vias.In this configuration (unlike what is described in the document by S.Gharbieh et al. cited above), the control lines and the patch antenna are made on opposite sides with respect to the ground plane and therefore do not influence each other significantly: the control lines do not significantly disturb the RF behavior of the patch antenna and the cell. In addition, the position of the control lines under the ground plane facilitates their interconnection with the electronic boards that generate and control the control signals.

[0085] In both operating states, only one of the diodes is forward biased (ON), while the other is reverse biased (OFF). When diode DI is OFF and diode D2 is ON, the delay line is disabled. The reflected wave is phase shifted by a value of 2xA <p par rapport à l'onde incidente, ou A<p est le déphasage acquis par l'onde en se propageant entre le patch et le plan de masse. Dans l'autre état de fonctionnement, la diode DI est ON et la diode D2 est OFF, et la ligne de retard de phase de 90° est active. Dans ce cas, le déphasage entre l'onde réfléchie et l'onde incidente est 2xA<p + 2x90° = 2xA<p + 180°. La différence de phase entre les phases des coefficients de réflexion dans les deux états de fonctionnement est donc 180°.

[0086] Finally, the PPW 240 or 440 waveguide can be produced in different variants. According to a first variant, the space between its parallel plates is simply filled with air. According to a second variant, this space is occupied by a dielectric. According to a third variant, shown schematically in Fig. 5, a slow-wave structure is provided by crenellating the lower plate of the second straight section of the waveguide, and by tilting it relative to the upper metal plate in which the stubs are formed. It is noted here that the gap between the upper plate M1 and the lower plate M2 is reduced in the propagation direction (Ox) and that the lower plate M2 has undulations on its upper face, in the direction (Oz). The presence of a dielectric and a fortiori of a slow-wave structure in the waveguide makes it possible to lower the phase velocity and reduce the guided wavelength.As a result, the pitch of the continuous stub array can be chosen smaller, which helps to avoid the appearance of side lobes and to extend the scanning angular range.

Claims

DEMANDS 1. Two-dimensional beam-scanning antenna comprising a waveguide intended to be fed by a microwave source and to provide a quasi-plane wave propagating in a first direction, a linear array of transverse stubs, extended in a second direction perpendicular to the first, said stubs being arranged periodically in the first direction with a step substantially equal to the wavelength guided in the waveguide, characterized in that it comprises: a first electronically reconfigurable phase-shifting surface comprising a first plurality, M, of elementary phase-shifting cells arranged periodically in the second direction with a step less than or equal to half the free-space wavelength of the microwave source;a second phase-shifting surface, electronically reconfigurable, comprising a second plurality, N, of elementary phase-shifting bands, each elementary phase-shifting band being extended along the second direction and being associated with a transverse stub of said array, said elementary phase-shifting band being disposed directly on the output of the transverse stub to which it is associated; a first set of control lines intended to control the respective phase shifts of the elementary phase-shifting cells so as to control the orientation of the beam in a plane orthogonal to the first direction; a second set of control lines intended to control the respective phase shifts of the elementary phase-shifting bands so as to control the orientation of the beam in a plane orthogonal to the second direction; and in that the first phase-shifting surface is a reflecting phase-shifting surface, adapted to receive the wave supplied by the microwave source; propagating in a direction opposite to the first direction and reflecting it back in the first direction after the elementary phase-shifting cells have applied initial phase-shift values ​​along the second direction.

2. Two-dimensional beam scanning antenna according to claim 1, characterized in that each elementary cell of the first surface and / or each elementary band of the second surface is controlled using a single control line.

3. Two-dimensional beam scanning antenna according to claim 1 or 2, characterized in that at least one of the controllable systems comprises PIN diodes.

4. Two-dimensional beam scanning antenna according to claim 2 or 3, characterized in that the waveguide is a parallel plate waveguide.

5. Two-dimensional beam scanning antenna according to claim 4, characterized in that the waveguide comprises a first straight section in which the wave emitted by the microwave source propagates in a direction opposite to the first direction, a second straight section, parallel to the first straight section, in which the plane wave propagates in the first direction after being phase-shifted by the first phase-shifting surface and a U-shaped transition section, ensuring 180° folding and connecting the first straight section to the second straight section.

6. Two-dimensional beam scanning antenna according to claim 5, characterized in that the waveguide is fed by the microwave source through a sector horn.

7. Two-dimensional beam scanning antenna according to any one of claims 1 to 6, characterized in that the first phase-shifting surface is arranged on a parabolic cylindro structure.

8. Two-dimensional beam scanning antenna according to any one of the preceding claims, characterized in that each elementary phase band consists of a plurality P of second elementary cells, said second elementary cells of an elementary phase band being arranged periodically along the second direction with a step less than or equal to half the free-space wavelength, the same phase shift value being applied to said plurality of second elementary cells belonging to the same elementary phase band.

9. Two-dimensional beam scanning antenna according to claim 8, characterized in that each first elementary cell, resp. each second elementary cell, comprises a plurality of metallic layers alternating with dielectric layers and a plurality of PIN diodes interconnecting at least some of said different metallic layers, controlled by a plurality k of control lines of the first, resp. of the second set.

10. Two-dimensional beam scanning antenna according to claim 8, characterized in that each first elementary cell, resp. each second elementary cell, comprises a plurality of varactor diodes, controlled by at least one control line of the first, resp. second set.

11. Two-dimensional beam-scanning antenna according to any one of claims 1 to 10, characterized in that each cell elementary of the second phase-shifting surface (420) is configured to radiate a field exhibiting a fixed circular polarization.

12. A two-dimensional beam-scanning antenna according to any one of claims 1 to 11, characterized in that each elementary cell of the second phase-shifting surface (420) is configured to radiate a circularly polarized field with an electronically reconfigurable direction.

13. A two-dimensional beam-scanning antenna according to any one of claims 1 to 12, configured to emit two independently controllable, orthogonally polarized beams, such that each band of the second phase-shifting surface (420) comprises two sets of reconfigurable phase-shifting cells capable of radiating fields with orthogonal polarizations.

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