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

TECHNICAL FIELD

[0001] The present invention relates generally to the field of phased array antennas enabling two-dimensional control of beam orientation. It finds particular application in terrestrial terminals in the K / Ka band for satellite communications, communication systems on board trains or aircraft, 5G base stations, and near-field microwave focusing systems. PREVIOUS STATE OF THE ART

[0002] Two-dimensional scanning antennas are well-known in the prior art, particularly for satellite communication terminals or communication systems installed on moving vehicles. These antennas allow dynamic control of the beam direction (during transmission and / or reception) along two orthogonal axes and are therefore capable of scanning a predetermined solid angle.

[0003] The first generation of two-dimensional scanning antennas uses mechanical scanning. These generally consist of a directional antenna (for example, parabolic) mounted on a gimbal joint, allowing it to be oriented along two axes. Besides not allowing for rapid angular scanning, these antennas are bulky and heavy. They are difficult to integrate into vehicles and often degrade their aerodynamic performance. Finally, the servomotors that power them require significant maintenance and consume considerable energy.

[0004] To overcome these drawbacks, a second generation of antennas uses phased array antennas (phased array)and beamforming techniques enabling electronic scanning. These second-generation antennas are compact and can conform to the shape of a vehicle (conformal antennas on an aircraft, for example). They allow for rapid angular scanning, with no mechanical inertia. However, the large number of individual antennas forming the array makes their electronics particularly complex and their manufacture expensive.

[0005] Hybrid mechanical / electronic scanning antennas are also available on the market, using, for example, a mechanical positioner for azimuth and electronic scanning for elevation. However, their performance is not optimal, mechanical pointing remains slow, and their size is too large for many applications.

[0006] Recently, an antenna adapted for one-dimensional electronic scanning using a continuous transverse stub array or CTS array ( Continuous Transverse Stubs ) 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.

[0007] Such an antenna has been schematically represented in Fig. 1A This comprises a network of continuous stubs, the stubs in question extending in a transverse direction (Oy) to a parallel-plate waveguide or PPW waveguide ( Parallel Plate Waveguide ), 140. As illustrated in Fig. 1B The CTS network is supplied from the waveguide by means of a tree of T-junctions whose different branches supply the stubs.

[0008] 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 (Oy) axis.

[0009] By "stub", in a way known in itself, we designate here a part, a section of open guide in the direction orthogonal to that of wave propagation, allowing impedance transformations to be made.

[0010] THE Figures 1C And 1D represent respectively a cross-section of the PPW waveguide along a (xy) plane and an (xz) plane.

[0011] 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, that is, in the (xy) plane. The PPW waveguide has a pillbox or U-shaped transition section, 160, so that it is folded back on itself. This transition section provides the link between a first straight section 141 and a second straight section 142, which are substantially parallel to each other. The sectorial 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 array.

[0012] The transition section presents a parabolic reflector 150 in the (xy) plane as can be seen in Fig. 1CThe focal point of the parabolic reflector is located at the center of the sector horn opening, which allows for a quasi-plane wave in the second section of the PPW waveguide.

[0013] Changing the position of the sector horn along the y-axis at the PPW waveguide inlet modifies the phase distribution along this axis and ensures beam scanning in the H-plane at the CTS output, in other words, scanning in the yz-plane. Thus, by mechanically moving the horn antenna in front of the waveguide inlet or by switching the feed of several sector horns arranged along the y-axis in front of this same inlet, one-dimensional beam scanning in the yz-plane is achieved. In most implementations, however, this architecture only allows switching between a discrete set of beams and does not offer fine angular beam offsetting in the yz-scan plane.

[0014] A two-dimensional electronically scanned antenna using a CTS array was disclosed in US patent B-6677899. The CTS array feeds a near-field array of MEMS-reconfigurable radiating elements located above it. Each element comprises a broadband receiving element at its input, a broadband receiving element at its output, and a MEMS-controlled phase-shifting module between the input and output elements.

[0015] However, such an antenna is very complex to manufacture and is prone to malfunctions in MEMS devices, which are generally unreliable over time. Furthermore, 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 implemented as a plurality of printed circuit boards or PCBs ( Printed Circuit Board ) mounted vertically in parallel above the CTS power supply network. Finally, beam scanning requires the ability to individually control each MEMS device and therefore to have a control network with as many lines as there are MEMS devices.

[0016] Transmitting array antennas ( transmitarray antennas) offer a compact solution when two-dimensional electronic scanning is desired (scanning with 2 degrees of freedom, in a half-space). An example of such a transmit array can be found in the article by A.R. 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 SurfaceThe phase-shifting surface is formed by a two-dimensional array of elementary cells, each elementary cell comprising a first elementary antenna for reception and connected to a second elementary antenna for transmission via a phase-shifting module. Each phase-shifting module is individually controllable, allowing for control of its orientation and two-dimensional beam scanning. Such an antenna, however, requires a complex control network, with the number of layers and power dividers increasing with the antenna size. Furthermore, the near-field coupling between the slot antenna array and the transmitting array inevitably induces insertion losses, which are higher with larger array sizes.

[0017] Other electronically scanned antenna technologies are disclosed in the documents: US 2006 / 132369 A1 (Robertson Ralston S et al.) (2006-06-22) US 5,579,021 A (Lee Jar J et al.) (1996-11-26) Yang Xuexia et al. : "A compact beam steering planar array with broadband and high gain", 2015 International symposium on antennas and propagation (ISAP), The Institute of Electronics, Information and Comm, (2015-11-9), pages 1-3, XP032888863, US 2004 / 257288 A1 (Robertson Ralston et al.) (2004 -12-23) US 6 064 349 A (Robertson Ralston) (2000-05-16)

[0018] An object of the present invention is therefore to provide a two-dimensional (2-degree-of-freedom) electronically scanned antenna that does not have the aforementioned disadvantages, in particular that is simple, has low power consumption and small footprint, is easily integrable and does not require a large number of control lines, even for large antennas. DESCRIPTION OF THE INVENTION

[0019] 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: a first electronically reconfigurable phase-shifting surface comprising a first plurality, M, of elementary phase-shifting cells arranged periodically along the second direction with a step less than or equal to half the free-space wavelength of the microwave source; a second electronically reconfigurable phase-shifting surface 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 to reflect it in the first direction after the elementary phase-shifting cells have applied first phase-shift values ​​to it along the second direction.

[0020] Preferably, each of the elementary cells of the first phase-shifting surface is a reflective cell, configured to receive the plane wave propagating in the first direction and reflect it in the opposite direction.

[0021] 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.

[0022] In this case, we consider 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, K 1 And K 1 different phase shift values; the total number of diode control lines is M log 2 K 1 + N log 2 K2. The number of control lines therefore grows less rapidly with the radiating surface compared to an equivalent 2-D scanning antenna of the transmitting array or phased array type with NM radiating elements, which would require NM log 2 K 1 log 2 K 2 command lines or NM RF channels, respectively.

[0023] In some embodiments, at least one of the controllable systems includes (is based on) PIN diodes.

[0024] An example of the realization of an electronically reconfigurable phase-shifting cell, using PIN diodes, in transmission, adapted to the second phase-shifting 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".

[0025] The waveguide is preferably a parallel plate waveguide.

[0026] It advantageously 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.

[0027] According to some variants, the first phase-shifting surface is arranged on a cylindro-parabolic structure.

[0028] According to one variant, the waveguide is fed by the microwave source through a sector horn.

[0029] The waveguide can thus include in its transition section a cylindro-parabolic structure allowing the first phase-shifting surface to reflect the wave supplied by the microwave source through the sector horn in the form of a quasi-plane wave.

[0030] Each elementary phase-shift band can advantageously be made up 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 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-shift band.

[0031] Each first elementary cell, resp each second elementary cell, may comprise 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 the second set.

[0032] Each first elementary cell, or each second elementary cell, can comprise a plurality of varactor diodes, controlled by at least one control line from the first, or second set.

[0033] In some embodiments, each elementary cell of the second phase-shifting surface (in transmission, on the stubs) is configured to radiate a field with a fixed circular polarization (i.e. either right-hand circular or left-hand circular).

[0034] This reconfigurable cell receives and transforms the linearly polarized field emitted by each stub into a fixed circularly polarized field and, at the same time, introduces an electronically variable phase shift between a set of K2 different values ​​onto this field. An example of the implementation of such a reconfigurable cell in transmission using PIN diodes is described, for example, in the document by L. Di Palma, A. Clemente, 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.

[0035] In some embodiments, each elementary cell of the second phase-shifting surface (in transmission, on the stubs) is configured to radiate a field exhibiting circular polarization with a direction (right or left) that can be reconfigured electronically.

[0036] Such a cell can be made 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).

[0037] In another embodiment, this reconfigurable cell (elementary cell of the second phase-shifting surface) can consist of a first section that receives the linearly biased field emitted by each stub and transmits it by introducing an electronically variable phase shift between a set of K2 different values, and a second section that functions as an electronically reconfigurable polarization converter (from linear to circular). This second section receives the linearly biased field transmitted by the first section and emits a linearly biased field with an electronically reconfigurable direction (right / left). A possible implementation of such a cell using PIN diodes involves stacking: (i) (first section), the reconfigurable phase-shifting 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 reconfigurable polarization converter cell described in A. Clemente's patent entitled "Transmitarray antenna cell" (US 2023 0010547 A1).

[0038] In some embodiments, the two-dimensional beam-scanning antenna is configured to emit two independently controllable, orthogonally polarized beams, such that each band of the second phase-shifting surface (in transmission, on the stubs) comprises two sets of reconfigurable phase-shifting cells capable of radiating fields with orthogonal polarizations. For example, the cells of the first set can be configured to radiate a horizontally polarized field, and those of the second set to radiate a vertically polarized field, respectively. Two orthogonally polarized beams can thus be formed. The pointing directions of these two beams can be independently reconfigured by controlling the two sets of cells in each band with two sets of control lines.

[0039] An example of the realization of the cells of the two sets, using PIN diodes, capable of receiving a vertical linear bias and radiating either a horizontal linear bias field or a vertical linear bias 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features and advantages of the invention will become apparent upon reading a preferred embodiment of the invention, made with reference to the accompanying figures, among which: THE Figs. 1A to 1D The diagrams already described represent different views of a one-dimensional electronically scanned antenna known from the prior art; Fig. 2schematically represents a two-dimensional electronically scanned antenna according to an embodiment presented to aid in understanding the invention; The Fig. 3 schematically represents the control lines of the first and second phase-shifting surfaces used in the antenna of the Fig. 2 ; There Fig. 4 schematically represents a two-dimensional electronically scanned antenna according to an embodiment of the invention; The Fig. 5 illustrates a PPW waveguide comprising a slow-wave structure, used in a variant of the first or second embodiment of the invention; and The Figs. 6A and 6B schematically represent, respectively in perspective and in section, a reflective cell that can be used in an antenna according to the present invention. DETAILED DESCRIPTION OF SPECIFIC METHODS OF IMPLEMENTATION

[0041] We will now consider a two-dimensional electronically scanned antenna, that is, an antenna whose beam can be oriented along two degrees of freedom. For example, the beam can be oriented around two orthogonal axes, in azimuth and elevation.

[0042] The antenna described herein is designed to operate with a microwave source typically operating in the millimeter and centimeter bands, from 3 to 300 GHz. It is particularly suited for operation in the frequency range from 10 GHz to 60 GHz and can be used in satellite terminals (in the K / Ka bands) or 5G terminals / base stations.

[0043] 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.

[0044] The idea behind the present invention is to provide a first phase-shifting surface comprising a first plurality, M, of elementary phase-shifting cells arranged periodically along the second direction and a second phase-shifting surface, comprising a second plurality, N, of elementary phase-shifting strips, each elementary phase-shifting strip being extended along the second direction and being associated with a continuous transverse stub, or slot, of the array and disposed directly above it.

[0045] The first phase-shifting surface ensures the beam is scanned in the (xy) plane. The second phase-shifting surface ensures the beam is scanned around the second direction in the (xz) plane. For example, the first phase-shifting surface could ensure the beam is scanned in azimuth and the second phase-shifting surface could ensure the beam is scanned in elevation.

[0046] The waveguide is advantageously implemented in the form of a parallel plate waveguide or PPW ( Parallel Plate Waveguide),Folded back on itself for compactness, it comprises a first straight section in the opposite direction to the first, a second straight section parallel to the first, and a U-shaped transition section that provides a 180° fold by connecting the first and second straight sections. The transition section may include a reflector to reverse the direction of propagation between the first and second straight sections of the waveguide.

[0047] The waveguide, and more specifically its first straight section, is fed by a primary source, for example by means of a horn antenna, more specifically a sector horn, the wide edges of the sector horn joining the top and bottom plates of the guide and the narrow edges joining the side walls of the guide, so as to minimize insertion losses.

[0048] There 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 the latter.

[0049] Unless otherwise indicated, the technical features of this embodiment which are technically compatible with the present invention may be applied to it.

[0050] The waveguide 240 shown here is a parallel plate waveguide comprising a first straight section 241 in which the wave injected by the sector horn (not shown) propagates in the opposite direction to the Ox direction, a straight 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.

[0051] The reflector 250 preferably has a parabolic cylindrical reflecting surface with a vertical focal line, so that the wave injected into the first part of the waveguide, with its cylindrical wavefront, is reflected as a plane wave propagating in the second, straight section of the waveguide. In a variant, the primary source is an antenna array, for example, horn antennas fed in parallel, which radiates a quasi-planar wave into the first part of the waveguide. In this case, the reflecting surface of the U-transition is preferably planar.

[0052] The reflected plane wave propagates in the first direction and is phase-shifted upon crossing a first phase-shift surface 210. This first phase-shift surface comprises a first plurality, M, of elementary phase-shift cells, 211, arranged periodically along the second direction (y) with a step less than or equal to half the wavelength, λ0 / 2, where λ 0 is the propagation wavelength in a vacuum.

[0053] The elementary phase-shifting cells of the first phase-shifting surface apply a phase-shifting law allowing the beam direction to be oriented in the (yz) plane.

[0054] The phase-shifted plane wave then propagates along the (Ox) direction in the second straight section, 243, of the waveguide 240. It is distributed, via a network of stubs, to a second phase-shifting surface 220. This second phase-shifting surface comprises a second plurality, N, of elementary phase-shifting bands, each elementary phase-shifting band being associated with a continuous transverse stub 230 and arranged directly on it. The stubs protrude at least partially from the upper plane of the PPW waveguide, their open ends facing in the Oz direction. The continuous transverse stubs extend in the second (Oy) direction, also called the transverse direction.According to one variant, the stubs may have a height of zero (the height being the height of the part of the stub that protrudes from the surrounding surface; in this variant, the radiating elements are therefore comparable to radiating slits (The term "stub" indeed includes the special case of a radiating slit).

[0055] In all cases, the stubs are arranged periodically along the first direction with, preferably, a step approximately equal to the wavelength guided in the waveguide, i.e. λ g .

[0056] Where appropriate, each elementary band can 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.

[0057] Advantageously, the third plurality will be chosen to be equal to the second plurality, in other words P = M.

[0058] The elementary phase-shift bands of the second phase-shifting surface apply a phase-shifting law which allows the beam to be oriented in the (xz) plane.

[0059] If we note θ 0 and φ Given the elevation and azimuth corresponding to the desired beam orientation, it can be shown that the application of phase shifts ψ m y , m = 1,.., M by the elementary cells of the first phase-shifting surface and the phase shifts ψ n x , n = 1,.., N by the elementary bands of the second phase-shifting surface, allows the beam to be oriented in the direction ( θ 0, φ 0) desired. The phase shift values ψ n x , n = 1,..,N and ψ m y , m = 1,.., M are defined by: ψ n x = − nk 0 d x sin θ 0 cos φ 0 − n − 1 k gx d x ψ m y = − mk 0 d y sin θ 0 sin φ 0 Or k 0 = 2 π λ 0 is the wavenumber in a vacuum of the wave emitted by the microwave source. k gx is the propagation constant along the x-axis of the fundamental mode guided by the waveguide, dx is the step between the elementary phase-shift bands of the second surface and dy is the step between the elementary cellular phase shifts of the first surface. As indicated above, it will be advantageous to choose dy = λ 0 / 2 and dx = λ g .

[0060] According to a first variant, each (first or second) elementary cell, or even elementary phase-shift band, can be made from a succession of metallic layers alternating with dielectric layers. One or more metallic layers include one or more electronic switches, for example PIN diodes, allowing the frequency response, in particular the phase of the transmission and / or reflection coefficient of the elementary cell, to be varied among a set of discrete values.

[0061] Alternatively, according to a second variant, each (first or second) elementary cell, or even each elementary phase-shift band, can be implemented using a variable varactor-type capacitor. This second variant has the advantage of allowing continuous variation of the phase shift, whereas the first variant only allows switching between discrete values.

[0062] 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.

[0063] Indeed, 2D electronically scanned antennas of the transmit array type require at least as many control lines as cells, i.e. N × M for a matrix of M rows and N columns. Conversely, In this case, assuming that a single phase-shift cell / band can be controlled by means of a single control line, the number of control lines required for the same orientation accuracy is now only N + M.

[0064] There Fig. 3 schematically represents the control lines of the different elementary cells / bands of the first surface and the second phase-shifting surface.

[0065] 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.

[0066] When 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 can be equal to log 2 K. The elementary cells / bands can apply attenuation in addition to phase shifting, in order to apodize the beam and reduce its side lobes. When these attenuation coefficients can take L discrete values, the number of control lines per elementary cell / band then changes to log 2 K + log 2 L , which leads to a total number of control lines equal to ( log 2 K + log 2 L)(N + M ). According to one embodiment, the attenuation coefficients can be chosen to be fixed (fixed apodization) and in this case the number of control lines is only (N + M) log 2 L .

[0067] There Fig. 4 schematically represents a two-dimensional electronically scanned antenna according to the invention.

[0068] This embodiment differs from the first in that the first phase-shifting surface, 410, no longer operates in transmission but in reflection. This configuration allows the RF elements of each cell of the surface and the structures necessary for the biasing of the reconfigurable electronic devices to be separated by a ground plane. These structures can be located outside the waveguide, which facilitates the interconnection of the reflecting surface (the first phase-shifting surface) with its control circuits. The elements bearing the reference designations 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.

[0069] In this configuration, the first phase-shifting surface operates as an electronically reconfigurable reflector, and can be implemented either on a concave or convex surface, or on a planar surface parallel to the plane zy. Therefore, in this embodiment it is no longer necessary to provide a first phase-shifting surface of parabolic shape.

[0070] The first reconfigurable phase-shifting surface (or reflective surface) can advantageously be placed at a distance dr ≈ 3 λ g / 4 + I λ g / 2, of the upper surface of the lower PPW waveguide 441 and the lower surface of the upper PPW waveguide 442, where I is a natural number (zero or not), and λ g is the wavelength in both guides at the working frequency.

[0071] The wave from the microwave source, after being guided by the first straight section of the waveguide, is reflected by the first phase-shifting surface 410 before propagating in the second straight section of the waveguide. The first reflective phase-shifting surface applies, on the one hand, if necessary (for example, when the surface is planar), a first phase-shifting law to convert the cylindrical wave into a plane wave, and on the other hand, a second phase-shifting law along the y-direction to orient the beam in the (yz) plane. This optimal phase-shifting law is approximated and achieved by appropriately choosing the electrical polarization state of the reconfigurable electronic devices in each cell (for example, PIN diodes) and thus the phase of the reflection coefficient of each cell from a discrete number of values. K 1 of possible values. To ensure efficient operation of the reflector, the K 1 values ​​are preferably uniformly spaced over the entire phase range [0-2π) in the operating frequency band. In this case, we speak of a cell with log 2 K 1 bits, which means that the phase shift values ​​in reflection achieve a quantization at log 2 K 1 bits from the range [0-2π). For example, a reconfigurable cell capable of inputting the two (four) reflection phase values ​​0 and π (or respectively 0, π / 2, π, 3π / 2), is named at 1 bit (or respectively at 2 bits).

[0072] As before, the first elementary cells 411 can further perform apodization of the beam (here orthogonally to the (Ox) axis) by applying appropriate attenuation values ​​(e.g. approximating a cardinal sine).

[0073] Reconfigurable 1-bit and 2-bit reflector cells using PIN diodes can be implemented using known methods, such as those proposed, for example, by the following documents: 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. 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. 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.

[0074] As an example, a possible implementation for a 1-bit reflector cell (2 phase shift values ​​in reflection, with a difference of π) is illustrated by the 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.

[0075] In this embodiment, the reflector cell comprises a patch antenna with a central aperture on which two PIN diodes, D1 and D2, are mounted. The two diodes are in an antiparallel configuration: the cathode of D1 and the anode of D2 are DC at the same potential, as they are physically connected to a metal pad in the center of the aperture. This pad is connected via a shorting via (SV) to a ground plane (PM) located below the antenna. Diode D1 can activate and deactivate a 90° phase-delay line (RPh), connected via V-vias to the patch antenna and implemented using an intermediate metal layer between the patch antenna and the ground plane. The DC bias signal from the diodes is applied to a layer below the ground plane. A bias tee (BT) structure is also implemented to decouple the DC signal from the RF signals. The DC signal is connected to the patch via through-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 located on opposite sides of the ground plane and therefore do not significantly influence each other: the control lines do not substantially disrupt the RF behavior of the patch antenna and the cell. Furthermore, the position of the control lines below the ground plane facilitates their interconnection with the electronic boards that generate and control the control signals.

[0076] In both operating states, only one diode is forward biased (ON), while the other is reverse biased (OFF). When diode D1 is OFF and diode D2 is ON, the delay line is deactivated. The reflected wave is phase-shifted by a value of 2 × Δϕ relative to the incident wave, where Δϕ is the phase shift acquired by the wave propagating between the patch and the ground plane. In the other operating state, diode D1 is ON and diode D2 is OFF, and the 90° phase-delay line is active. In this case, the phase shift between the reflected and incident waves is 2 × Δϕ + 2 × 90° = 2 × Δϕ + 180°. The phase difference between the phases of the reflection coefficients in the two operating states is therefore 180°.

[0077] Finally, the PPW 240 or 440 waveguide can be manufactured in different configurations. In one configuration, the space between its parallel plates is simply filled with air. In a second configuration, this space is filled with a dielectric. In a third configuration, schematically represented in Fig. 5 A slow-wave structure is achieved by crenellating the lower plate of the second straight section of the waveguide and 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 decreases in the (Ox) propagation direction, and that the lower plate M2 exhibits undulations on its upper surface in the (Oz) direction. The presence of a dielectric and a fortioriUsing a slow-wave structure in the waveguide allows for a lower phase velocity and a reduction in the guided wavelength. As a result, the pitch of the continuous stub array can be chosen to be smaller, thus preventing the formation of sidelobes and extending the scanning angular range.

Claims

1. A two-dimensional beam scanning antenna comprising a waveguide (440) intended to be fed by a microwave source (130) and to provide a quasi-planar wave propagating in a first direction (Ox), a linear array of transverse stubs, extended along a second direction (Oy) perpendicular to the first one, said stubs being arranged periodically along the first direction with a pitch substantially equal to the wavelength guided in the waveguide, said antenna further comprising: - a first electronically reconfigurable phase shift surface (410) comprising a first plurality (M) of phase shift elementary cells (411) periodically arranged along the second direction with a pitch less than or equal to the half wavelength (λ0 / 2) in free space of the microwave source; - a second electronically reconfigurable phase shift surface (420), comprising a second plurality (N) of phase shift elementary bands, each phase shift elementary band being extended along the second direction and being associated with a transverse stub of said array, said phase shift elementary band being disposed directly on the output of the transverse stub with which it is associated; - a first set of control lines to control the respective phase shifts of the phase shift elementary cells so as to control orientation of the beam in a plane orthogonal to the first direction; - a second set of control lines to control the respective phase shifts of the phase shift elementary bands so as to control orientation of the beam in a plane orthogonal to the second direction; said antenna being characterised in that the first phase shift surface is a reflective phase shift surface (420), 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 along the second direction thereto.

2. The two-dimensional beam scanning antenna according to claim 1, characterised 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. The two-dimensional beam scanning antenna according to claim 1 or 2, characterised in that at least one of the controllable systems comprises PIN diodes (D1, D2).

4. The two-dimensional beam scanning antenna according to claim 2 or 3, characterised in that the waveguide is a parallel-plate waveguide (440).

5. The two-dimensional beam scanning antenna according to claim 4, characterised in that the waveguide comprises a first rectilinear section in which the wave emitted by the microwave source propagates in a direction opposite to the first direction (Ox), a second rectilinear section, parallel to the first rectilinear section, in which the plane wave propagates in the first direction (Ox) after being phase shifted by the first phase shift surface and an U-shaped transition section, ensuring 180° folding and connecting the first rectilinear section to the second rectilinear section.

6. The two-dimensional beam scanning antenna according to claim 5, characterised in that the waveguide (440) is fed by the microwave source (130) through a sectoral horn.

7. The two-dimensional beam scanning antenna according to any one of claims 1 to 6, characterised in that the first phase shift surface (410) is disposed on a cylindrical parabolic structure.

8. The two-dimensional beam scanning antenna according to one of the preceding claims, characterised in that each phase shift elementary band consists of a plurality (P) of second elementary cells, said second elementary cells of a phase shift elementary band being periodically arranged along the second direction with a pitch less than or equal to the half wavelength (λ0 / 2) in free space, a same phase shift value being applied to said plurality of second elementary cells belonging to the same phase shift elementary band.

9. The two-dimensional beam scanning antenna according to claim 8, characterised in that each first elementary cell, resp. each second elementary cell, comprises 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. second set.

10. The two-dimensional beam scanning antenna according to claim 8, characterised 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. The two-dimensional beam scanning antenna according to any one of claims 1 to 10, characterised in that each elementary cell of the second phase shift surface (420) is configured so as to radiate a field having a fixed circular polarisation.

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

13. The two-dimensional beam scanning antenna according to any one of claims 1 to 12, and configured to emit two beams, of orthogonal and independently controllable polarisations, such that each band of the second phase shift surface (420) comprises two sets of reconfigurable phase shift cells capable of radiating fields having orthogonal polarisations.

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