Generic BFIC front-end antenna tile set

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. Figure for the summary: Figure 6

Description

Title of the invention: Generic BFIC tile assembly for the front end of an antenna

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

[0002] The antenna front-end is understood to be the part of an antenna receiving or transmitting system that processes signals before amplification.

[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 context of developing an active antenna front-end, several functional elements must be interconnected, as illustrated in [Fig. 1]: - an antenna panel 1 (radiating elements: horns, patches, slots...); - 2-power or low-noise amplifier cards; - 3 cards incorporating components used for training beams called BFIC, an acronym for "Beam Former Integrated Components" in English; - a digital card 4 allowing real-time management of beam formation called ACU for acronym of "antenna control unit" in English; - a frequency transposition card 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 in [Fig.1] schematically illustrates a concept of RF front-end implementing the elements listed above.

[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 on which 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] In order to limit costs and optimize losses, designers seek to minimize the number of parts and try to share 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 another application, it is desired to change the type of radiating element to achieve different performance levels, the BFIC tile must be specifically redesigned, which is very costly.

[0008] Tiles with integrated patch antennas are known. Patch antennas require the use of thick substrate layers, which does not allow for symmetrical stacking of printed circuit board layers, thus violating printed circuit board design rules and impairing their large-scale manufacturability and reliability.

[0009] This type of assembly presents significant risks because the different nature of the materials composing the circuit board and the antenna leads to differential expansion, which compromises the reliability of the assembly. 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 of the BFIC cards separable, the latter can be equipped with connectors on the side opposite the side containing the BFICs. In this case, it is necessary to have space to integrate a very 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 proves feasible, this approach is extremely expensive because these connectors are very costly.

[0011] In known examples, aligning the 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 particularly 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 front-end antenna tile assembly 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 in a coaxial pad, and opening at its other end onto the outer face of the printed circuit board in 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 side 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 between layers; and - the inner layer of the printed circuit board comprising elementary groups of one or two coaxial pads arranged in a regular grid.

[0014] In one embodiment, the elementary groups 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 provided 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 pellets 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 distance between two groups is equal to half the wavelength of the highest frequency of 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] According to another aspect of the invention, an active antenna comprising: - at least one radiating element; - at least one tile set; - at least one interposer placed 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:

[0025] [Fig-1] schematically illustrates a concept of RF front-end, according to the state of the technique;

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

[0027] [Fig.3] and [Fig.4] schematically illustrate a coaxial connection in a circuit multi-layer printing, according to the state of the art;

[0028] [Fig.5] schematically illustrates a generic BFIC tile assembly for the front part of an antenna, according to one aspect of the invention;

[0029] [Fig.6] schematically illustrates an active antenna equipped with at least one generic BFIC tile assembly of antenna front part, according to one aspect of the invention;

[0030] [Fig.7] and [Fig.8] schematically illustrate the two inner and outer faces of a generic BFIC front antenna tile assembly, with elementary groupings of one or two coaxial pads arranged according to a regular trigonal mesh, according to one aspect of the invention;

[0031] [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.

[0032] Across all figures, elements with identical references are similar.

[0033] [Fig.2] schematically illustrates a coaxial link, according to the prior art.

[0034] A coaxial link consists of a central conductor 8 of radius a, an external conductor 9 located 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 εr and the relative permeability Pr. Such a coaxial link of length z allows the propagation of an electromagnetic wave between the two ends of the The connections are called 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 ZO depends on the aforementioned physical quantities according to the following law: fËT* 1^) X 2n

[0035] The normalized characteristic impedance for a coaxial conductor is generally 50 Q. The dimensions a and b are chosen to obtain an impedance of 50 Q for a given material for which r and are known.

[0036] A coaxial link can be formed by a cable (e.g., copper wire coated with Teflon, the whole coated with metal) or by two pads on a printed circuit board connected by a via.

[0037] As illustrated in [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 constitutes 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.

[0038] 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 Q if the geometries (a and b) are correctly chosen.

[0039] The multi-layer printed circuit board structure 1 allows for the interconnection of signals that are not directly opposite each other. To achieve this, each layer 15, 16 of the printed circuit board 1, the example illustrated in [Fig. 3] and [Fig. 4] having only two layers 15, 16, incorporates a coaxial link. The two coaxial links are interconnected via the microband line 13 with impedance 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.

[0040] 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 X / 10, form an external conductor of the [Fig.2].

[0041] Also, it is possible to connect the inputs or outputs of electronic components to an external interconnection system whose accesses are not opposite each other.

[0042] In other words, as illustrated in [Fig. 5], the invention relates to a generic BFIC antenna front-end tile assembly, comprising: - a multilayer printed circuit board 1; - at least one BFIC 18 component; - 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 track 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 track 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; - the RF tracks 13 and ground tracks 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 of impedance 50 Q to connect two coaxial pads of a track in interlayers; and - the internal layer 23 of the printed circuit board comprising elementary groups of one or two coaxial pads arranged in a regular mesh.

[0043] 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 1 provided with coaxial pads can be square in shape.

[0044] The elementary groups of one or two coaxial pellets are arranged according to a regular trigonal mesh, and the internal layer 23 provided with coaxial pellets is substantially square in shape, the opposite sides of which have complementary shapes so that two contiguous tile sets can fit together and the arrangement of the pellet groups on the two tiles forms a regular trigonal mesh.

[0045] 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 comprising a diffuse contact 26.

[0046] BFIC components integrate several inputs and / or outputs whose main 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 called spatial combination. By controlling the In the phase of the BFIC components, it is also possible to perform a sweep of the combination point: this is called electronic scanning.

[0047] 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 access points being directly opposite each other (offset). This feature is important because, for the spatial combination device to function, the radiating elements must form a mesh in which each unit element is spaced at most half a wavelength X apart (this is called an antenna array). The wavelength X is inversely proportional to the operating frequency according to the formula X = c / f, where c represents the speed of light and f represents the maximum operating frequency.

[0048] 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.

[0049] A printed circuit board in which the spacing between pads of the coaxial links located on the antenna side respects the mesh relative to half the wavelength (7 / 2) of the highest frequency of the instantaneous band of the transmitted signal allows for spatial combination at the board level. The mesh can be trigonal or square.

[0050] Such a map is called an elementary map or generic beam formation tile.

[0051] A complete antenna array comprises several beamforming elementary maps arranged contiguously such that the spacing between pads located on either side of two adjacent maps remains constant. When this condition is met, the beamforming elementary map is more precisely called a generic BFIC tile.

[0052] As illustrated in [Fig.7], in the case of a trigonal mesh, the inner layer 23 of the generic tile provided with coaxial pellets 22 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 pellet groups on the two tiles forms a regular trigonal mesh.

[0053] The complementary shapes of the opposite sides can take any shape provided that the pellets remain equidistant card to card so as to respect a uniform pattern.

[0054] Fig. 8 schematically represents the other side of a generic BFIC tile set.

[0055] Fig. 9 schematically represents a plurality of generic BFIC tile sets mounted contiguously on the radiating panel or element 25.

[0056] The present invention enables: - to ensure repair or replacement of the card because the tile is detachable from the radiating element; - to produce large quantities of parts at a target cost because these tiles do not incorporate RF connectors; - to have a unique design capable of being associated with any type of antenna or radiating element (patch, slot, 3D additive... This makes it possible to achieve different antenna performances from the same generic brick (BFIC tile) without costly and time-consuming new design; - to present a symmetrical PCB structure to avoid circuit bending or buckling during reflow soldering. It is also possible to process 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).

[0057] 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 symmetrical circuit layer stacking structure, tiles usable for multiple applications without costly specific design efforts; and - to produce a low-cost tile because RF connectors are excluded from the tile

[0058] to produce a repairable tile when assembled with a flexible interposition device thanks to the compatible interconnection range of the flexible interposition device.

Claims

Demands

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 such 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 spacing between two groupings is equal to half the wavelength of the highest frequency in 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).

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