Generic bef tile assembly of front part of an antenna of the said front-end

Abstract

Generic BFIC front-end antenna tile assembly comprising: - a multilayer printed circuit board (1); - a BFIC component (18); - the multilayer printed circuit board (1) comprising: - at least one RF track (13) and at least one ground track (20), each terminating at one end on the inner face of the printed circuit board (1) in a connection 21, and terminating at its other end in a connection 22 on the outer face of the printed circuit board; - the RF track(s) (13) and ground track(s) (20) comprising coaxial links in each layer of the printed circuit board, a coaxial link terminating on each face in a coaxial pad, and microstrip lines for connecting two coaxial pads of a track in interlayers; and the inner layer (23) of the printed circuit board comprising elementary groupings of one or two coaxial pads arranged in a regular grid.

Description

[0001] The present invention relates to a generic BFIC tile assembly integrating the front part of the antenna called the front-end.

[0002] An antenna front-end is the part of an antenna receiving or transmitting system that processes signals before they are amplified.

[0003] The invention is intended for active antennas ranging from the Ku band starting at 10 GHz up to microwave frequencies (40 GHz and above). It is applicable to all types of analog beamforming components. It is particularly useful for active antennas when combined with amplification or radiation functions where density and integration constraints are stringent.

[0004] In the development of an active antenna front-end, several functional elements must be interconnected, as illustrated in the [ Fig.1 ] : an antenna panel 1 (radiating elements: horns, patches, slots...); power or low-noise amplifier boards 2; boards 3 integrating components used for beamforming called BFICs for "Beam Former Integrated Components"; a digital board 4 allowing real-time management of beamforming called ACU for "antenna control unit"; a frequency transposition board 5 allowing conversion of RF signals to baseband or vice versa; a metallic structure 6 for shielding and heat dissipation; the various interconnection and interfacing elements 7 (electrical, mechanical and thermal).

[0005] The representation of the [ Fig.1 ] schematically illustrates a front-end RF concept implementing the elements listed previously.

[0006] For this assembly to function correctly, it is necessary to be able to connect the BFIC boards to the radiating elements. A simple solution is to print the antennas directly onto the side of the printed circuit board opposite the side where the BFICs are wired. It is also possible to permanently bond these elements together by gluing or soldering, or to interconnect them using RF connectors. Each of these solutions requires the design of a specific tile depending on the application.

[0007] To limit costs and minimize losses, designers strive to reduce the number of parts and combine as many functions as possible. It is therefore very common to see BFIC tiles that integrate the BFICs on one side and the patch antennas on the other. The functions are then inseparable. If, for a different application, a different type of radiating element is needed to achieve different performance levels, the BFIC tile must be specifically redesigned, which is very expensive.

[0008] It is known that tiles with integrated patch antennas are used. Patch antennas require the use of thick substrate layers, which prevents the stacking of symmetrical printed circuit board layers. This violates printed circuit board design rules and negatively impacts their large-scale manufacturability and reliability.

[0009] This type of assembly presents significant risks because the different nature of the materials used in the circuit board and the antenna leads to differential expansion, which compromises the overall reliability. The two components, the circuit board and the antenna panel, are then non-removable, posing a major repairability problem.

[0010] To make the radiating elements separate from the BFIC boards, the latter can be equipped with connectors on the opposite side from the side containing the BFICs. In this case, it is necessary to have enough space to integrate a large number of connectors on both the BFIC tiles and the radiating elements. This proves potentially impossible in cases where the density of interconnect signals is high (high frequency). Even if it is feasible, this approach is extremely expensive because these connectors are very costly.

[0011] In known examples, aligning components during assembly is generally complex. Furthermore, this type of design is prohibitively expensive. Transmission losses in the connectors at high frequencies are also very significant.

[0012] The aim of the invention is to overcome the aforementioned disadvantages, and more specifically to offer a generic BFIC tile for the front end of a front-end antenna.

[0013] According to one aspect of the invention, a generic BFIC tile assembly for the front end of an antenna, referred to as the front-end, is proposed, comprising: a multilayer printed circuit board; at least one BFIC component; solder balls between the BFIC component and the outer face of the printed circuit board; the multilayer printed circuit board comprising: at least one RF trace in the printed circuit board opening at one end onto the inner face of the printed circuit board as a coaxial pad, and opening at its other end as a coaxial pad on the outer face of the printed circuit board; at least one ground trace in the printed circuit board opening at one end onto the inner face of the printed circuit board as a coaxial pad, and opening at its other end onto the outer face of the printed circuit board as a coaxial pad;the RF track(s) and ground track(s) comprising coaxial links in each layer of the printed circuit board, a coaxial link terminating on each face in a coaxial pad, and microstrip lines (or "microstrips" in English), for example with an impedance of 50 Ω, to connect two coaxial pads of a track in interlayers; and the inner layer of the printed circuit board comprising elementary groupings of one or two coaxial pads arranged in a regular grid.

[0014] In one embodiment, the elementary groupings of one or two coaxial pellets are arranged according to a regular square grid.

[0015] According to one embodiment, the inner layer of the multilayer printed circuit board equipped with coaxial pads is square in shape.

[0016] In one embodiment, the elementary groupings of one or two coaxial pellets are arranged according to a regular trigonal mesh.

[0017] A trigonal mesh is understood to be a mesh in which the elementary groups of one or two coaxial dots form a triangle, for example isosceles or even equilateral, such a trigonal mesh being denser than a rectangular or even square mesh.

[0018] According to one embodiment, the inner layer provided with coaxial pellets is substantially square in shape, the opposite sides of which have complementary shapes so that two contiguous sets of tiles can fit together and the arrangement of the pellets on the two tiles remains a regular trigonal mesh.

[0019] In one embodiment, the center-to-center distance between two groups is equal to half the wavelength of the highest frequency in the instantaneous band of the transmitted signal.

[0020] According to one embodiment, the printed circuit board includes on its inner face, for each coaxial pad, at least one solder ball disposed in the central part of the coaxial pad, and at least two solder balls disposed on the outer periphery of the coaxial pad, to ensure a ground contact.

[0021] Another aspect of the invention also proposes an active antenna comprising: at least one radiating element; at least one tile assembly; at least one interposer arranged between the radiating element and the tile assembly.

[0022] In one embodiment, the interposer is a coaxial microwave interposer.

[0023] According to one embodiment, the coaxial microwave interposer includes a diffuse contact.

[0024] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which: [ Fig.1 ] schematically illustrates a concept of RF front-end, according to the state of the art; Fig.2 ] schematically illustrates a coaxial connection, according to the state of the art; Fig.3 ] And [ Fig.4 ] schematically illustrate a coaxial connection in a multilayer printed circuit board, according to the prior art; [ Fig.5 ] schematically illustrates a generic BFIC tile assembly for the front part of an antenna, according to one aspect of the invention; [ Fig.6 ] schematically illustrates an active antenna equipped with at least one generic BFIC tile assembly for the antenna front section, according to one aspect of the invention; [ Fig.7 ] And [ Fig.8 ] schematically illustrate the two inner and outer faces of a generic BFIC front-end antenna tile assembly, with elementary groupings of one or two coaxial pads arranged in a regular trigonal grid, according to one aspect of the invention; [ Fig.9 ] schematically illustrates a plurality of generic BFIC tile assemblies mounted contiguously on a radiating panel or element, according to one aspect of the invention.

[0025] Across all figures, elements with identical references are similar.

[0026] [ Fig.2 ] schematically illustrates a coaxial link, according to the state of the art.

[0027] A coaxial link consists of a central conductor 8 of radius a, an external conductor 9 positioned at a distance or radius b from the central axis of the central conductor 8, and an insulator 10 separating them, called the propagation medium. The propagation medium 10 is characterized by two physical quantities: the relative permittivity ε r and the relative permeability µ r Such a coaxial link of length z allows the propagation of an electromagnetic wave between the two ends of the link, called the input and output. For optimal signal transmission in a coaxial link, it must have a characteristic impedance compatible with that of the external elements at its connections (antenna, amplifier, transmitter, receiver, etc.). This normalized characteristic impedance Z0 depends on the aforementioned physical quantities according to the following law: Z 0 = ε r μ r × ln b a 2 π

[0028] The standardized characteristic impedance for a coaxial conductor is usually 50 Ω. Dimensions a and b are chosen to obtain an impedance of 50 Ω for a given material for which ε r and µ r are known.

[0029] A coaxial link can be formed by a cable (e.g., copper wire coated with Teflon, the whole thing coated with metal) or by two pads on a printed circuit board connected by a via.

[0030] As illustrated on the [ Fig.3 ] And [ Fig.4 A pad 11, 12 is a copper island isolated from the rest of the copper plane 27, 28, 29 on the surface of a multilayer printed circuit board 1, also called the ground plane. Such a pad 11, 12 provides a contacting area for an element external to the printed circuit board, such as the center conductor of a connector. Two pads 11, 12 placed on either side of the multilayer printed circuit board 1, connected by a via 13, form a center conductor.

[0031] The substrate or material that makes up the printed circuit board constitutes the propagation medium. The three elements described above 11, 12, 13 form a coaxial link whose characteristic impedance can reach 50 Ω if the geometries (a and b) are correctly chosen.

[0032] The multi-layer printed circuit board structure 1 allows the interconnection of signals that are not directly opposite each other. To do this, each layer 15, 16 of printed circuit board 1, the example illustrated in the [ Fig.3 ] And [ Fig.4 Having only two layers 15, 16, without limitation, it incorporates a coaxial link. The two coaxial links are interconnected via the microband line 13 with an impedance of 50 Ω (5). It is then possible to connect the pads on one side of the printed circuit board 11 to electronic components, for example by soldering. It is also possible to connect the pads 12 on the opposite side to a connector or an interconnect system such as an interposer, which can be connected to an antenna, for example a flexible interposer.

[0033] Two ground planes among the ground planes 27, 28 and 29, located around a pellet 11, 12 and on either side of the layers 15, 16 connected by rings of conducting vias 14 whose spacing is less than λ / 10, form an external conductor of the [ Fig.2 ].

[0034] It is also possible to connect the inputs or outputs of electronic components to an external interconnection system whose access points are not directly opposite each other.

[0035] In other words, as illustrated on the [ Fig.5 The invention relates to a generic BFIC tile assembly for the front end of an antenna, comprising: a multilayer printed circuit board 1; at least one BFIC component 18; solder balls 19 between the BFIC component 18 and the outer face of the printed circuit board 1; the multilayer printed circuit board 1 comprising: at least one RF trace 13 in the printed circuit board 1 opening at one end onto the inner face of the printed circuit board 1 in a coaxial pad 11, and opening at its other end into a coaxial pad 12 on the outer face of the printed circuit board 1; at least one ground trace 20 in the printed circuit board 1 opening at one end onto the inner face of the printed circuit board 1 in a coaxial pad 21, and opening at its other end onto the outer face of the printed circuit board 1 in a coaxial pad 22;RF tracks 13 and ground tracks 20 comprising coaxial links in each layer of the printed circuit board, a coaxial link terminating on each face in a coaxial pad, and microstrip lines of impedance 50 Ω to connect two coaxial pads of a track in interlayers; and the inner layer 23 of the printed circuit board comprising elementary groupings of one or two coaxial pads arranged in a regular grid.

[0036] The elementary groups of one or two coaxial pads can be arranged in a regular square grid, and the inner layer of the multilayer printed circuit board 1 equipped with coaxial pads can be square in shape.

[0037] The elementary groups of one or two coaxial pellets are arranged according to a regular trigonal grid, and the inner layer 23 equipped with coaxial pellets is substantially square in shape, whose opposite sides have complementary shapes so that two contiguous sets of tiles can fit together and the arrangement of the pellet groups on the two tiles forms a regular trigonal grid.

[0038] There [ Fig.6 ] represents an example of use in an active antenna with an interposer 24, and a radiating element 25. The interposer 24 can be a coaxial microwave interposer, for example including a diffuse contact 26.

[0039] BFIC components incorporate multiple inputs and / or outputs whose primary function is to amplify an incoming or outgoing signal while varying its phase and amplitude so that the signals, when radiated through an antenna, can combine in space: this is known as spatial combination. By controlling the phase of the BFIC components, it is also possible to perform a sweep of the combination point: this is known as electronic sweep.

[0040] It is possible to interconnect several BFIC components wired on the same outer face of the printed circuit board 1 to several pads on the opposite inner face without the connections being directly opposite each other (offset). This characteristic is important because, for the spatial combination device to function, the radiating elements must form a mesh in which each unit element is spaced no more than half a wavelength λ apart (this is called an antenna array). The wavelength λ is inversely proportional to the operating frequency according to the formula λ = c / f, where c represents the speed of light and f represents the maximum operating frequency.

[0041] Since the various inputs and / or outputs of a BFIC component are not spaced at the same pitch as the antenna array, it is usually necessary to use offset coaxial connectors thanks to the multi-layer circuit.

[0042] A printed circuit board where the spacing between the coaxial connection pads on the antenna side conforms to the mesh relative to half the wavelength (λ / 2) of the highest frequency in the instantaneous band of the transmitted signal allows for spatial arrangement at the board level. The mesh can be trigonal or square.

[0043] Such a map is called an elementary map or generic beamforming tile.

[0044] A complete antenna array comprises several beamforming element maps arranged contiguously such that the spacing between dots on either side of two adjacent maps remains constant. When this condition is met, the beamforming element map is more precisely called a generic BFIC tile.

[0045] As illustrated on the [ Fig.7 ], in the case of a trigonal mesh, the internal layer 23 of the generic tile equipped with coaxial pellets 22 is substantially square in shape, whose opposite sides have complementary shapes so that two contiguous sets of tiles can fit together and the arrangement of the pellet groups on the two tiles forms a regular trigonal mesh.

[0046] The complementary shapes on opposite sides can take any form provided that the dots remain equidistant card to card so as to respect a uniform pattern.

[0047] There [ Fig.8 ] schematically represents the other side of a generic BFIC tile set.

[0048] There [ Fig.9 ] schematically represents a plurality of generic BFIC tile sets mounted contiguously on the panel or radiating element 25.

[0049] The present invention enables: This allows for easy repair or replacement of the board because the tile is detachable from the radiating element; for the production of large quantities of parts at a target cost because these tiles do not incorporate RF connectors; and for a unique design compatible with any type of antenna or radiating element (patch, slot, 3D additive, etc.). This enables different antenna performance levels from the same generic building block (BFIC tile) without costly and time-consuming redesign; and for a symmetrical PCB structure that prevents circuit bending or buckling during reflow soldering. It also allows for the processing of larger, and therefore more economical, board formats.Indeed, if the board incorporates patch antennas, the PCB structure will necessarily be asymmetrical; and to automatically test each RF channel in series in a conventional manner without resorting to radiation testing methods in an anechoic chamber (a simple vector network analyzer is sufficient).

[0050] The present invention enables: to assemble several types of radiant panels of different technologies with a single version of tile: several antenna performances achievable from the same tile allowing valuable time to be saved in design; to produce in large quantities thanks to its stacking structure of symmetrical circuit layers tiles usable for several applications without costly specific design efforts; and to produce a low cost tile because RF connectors are excluded from the tile to produce a repairable tile when assembled with a flexible interposition device thanks to the compatible interconnection range of the flexible interposition device.

Claims

1. Generic antenna front-end BFIC tile assembly, comprising: - a multilayer printed circuit board (1); - at least one BFIC component (18); - solder balls (19) between the BFIC component (18) and the outer face of the printed circuit board (1); - the multilayer printed circuit board (1) comprising: - at least one RF trace (13) in the printed circuit board (1) opening at one end onto the inner face of the printed circuit board (1) in a connection (11), and opening at its other end into a connection (12) on the outer face of the printed circuit board 1; - at least one ground trace (20) in the printed circuit board (1) opening at one end onto the inner face of the printed circuit board (1) in a connection (21), and opening at its other end onto the outer face of the printed circuit board (1) in a connection (22);- the RF track(s) (13) and ground track(s) (20) comprising coaxial links in each layer of the printed circuit board, a coaxial link opening onto each face in a coaxial pad, and microstrip lines to connect two coaxial pads of a track in interlayers; and - the inner layer (23) of the printed circuit board comprising elementary groupings of one or two coaxial pads arranged in a regular grid.

2. Generic BFIC tile assembly according to claim 1, wherein the elementary groupings of one or two coaxial pellets are arranged in a regular square grid.

3. Generic BFIC tile assembly according to claim 2, wherein the inner layer of the multilayer printed circuit board (1) provided with coaxial pads (11, 21) is square in shape.

4. Generic BFIC tile assembly according to claim 1, wherein the elementary groupings of one or two coaxial pads are arranged in a regular trigonal mesh.

5. Generic BFIC tile assembly according to claim 4, wherein the inner layer provided with coaxial pellets is substantially square in shape, the opposite sides of which have complementary shapes so that two contiguous tile assemblies can interlock and the arrangement of the pellet groupings on the two tiles forms a regular trigonal mesh.

6. Generic BFIC tile assembly according to any one of the preceding claims, wherein a center-to-center distance between two groupings is equal to half the wavelength of the highest frequency of the instantaneous band of the transmitted signal.

7. Generic BFIC tile assembly according to any one of the preceding claims, wherein the printed circuit board (1) comprises on its inner face, for each coaxial pad, at least one solder ball disposed in the central part of the coaxial pad, and at least two solder balls disposed on the outer periphery of the coaxial pad.

8. Active antenna comprising: - at least one radiating element (25); - at least one tile assembly according to one of the preceding claims; - at least one interposer (24) disposed between the radiating element (25) and the tile assembly.

9. Active antenna according to claim 8, wherein the interposer (24) is a coaxial microwave interposer.

10. Active antenna according to claim 9, wherein the coaxial microwave interposer (24) comprises a diffuse contact (26).

Images