DUAL-MODE INTERCONNECT ASSEMBLY BETWEEN RADIO-FREQUENCY INTEGRATED CIRCUITS AND A PLASTIC WAVEGUIDE

Abstract

 A dual-mode interconnect assembly (1) comprising at least one plastic waveguide (4), and at least two integrated circuits (8, 9/8', 9') mounted on a printed circuit board (7), each one of these two integrated circuits (8, 9/8', 9') being connected to a respective transmission line (10).
This assembly (1) comprises at least one orthomode transducer portion and one twist converter portion, each one of these portions being respectively connected to a respective transmission line (10) and comprising at least one multilayer printed circuit board extending in a plane which is parallel to the respective printed circuit (7) supporting the transmission lines (10).

Description

Technical domain

[0001] The disclosure generally relates to communication systems wherein data are transferred through plastic waveguides. More particularly, this disclosure relates to a dual-mode interconnect assembly between radio-frequency integrated circuits and at least one plastic waveguide. For example, this disclosure finds applications in the field of connectors for automotive vehicles.

State of the art

[0002] Automotive vehicles are more and more equipped with sensors, calculators and various electronic devices. Generally, it is important that the information signals transmitted through the information network comprising such sensors, calculators and electronic devices be reliable and not disturbed by electromagnetic interferences (EMI). This becomes of paramount importance when the information and the corresponding signals are used for controlling the safety, as this is the case for example for autonomous vehicles. Further, with the increasing quantity of information to be collected and managed in automotive vehicles, it is also important to keep the weight of interconnecting harnesses as low as possible.

[0003] Plastic waveguide communication links appear as a potential solution for automotive in the future. Plastic waveguides are relatively cheap compared to copper wires or optical fibres. They have many other advantages. For example, they provide a large bandwidth, they may be less sensitive than metallic conductors to EMI issues, they allow less severe alignment requirements than optical fibres (therefore they allow for a relatively easy assembly), they are compatible with CMOS circuits and they allow for coherent detection.

[0004] Plastic waveguide communication links can be used in full-duplex two-way communication systems wherein data are transferred simultaneously in two opposite ways (see for example "Polymer Microwave Fibres: A New Approach That Blends Wireline, Optical, and Wireless Communication", to De WIT MAXIME et AL, IEEE Microwave magazine, IEEESERVICE CENTER, Piscataway, NJ, US, vol. 21, no 1,1 January 2020, pages 51-66, XP011758664, ISSN: 1527-3342, DOI: 10.1109/MMM.2019.2945158). It is known that full-duplex bi-directional transmissions can be achieved in a single plastic waveguide with polarized electromagnetic waves. Polarized electromagnetic waves can be obtained for example with an orthomode transducer (OMT) or an orthomode junction (OMJ). An OMT and an OMJ both serve either to separate or to combine two orthogonally polarized microwaves of the same frequency. Classical OMTs are made of metal and have a relatively complex structure.

Summary of the invention

[0005] The present disclosure provides a dual-mode interconnect assembly comprising an OMT and a twist converter component, both made using substrate integrated waveguide (SIW) technology.

[0006] More particularly, the present disclosure provides a dual-mode interconnect assembly according to claim 1.

[0007] The dual-mode interconnect assembly of claim 1 has an improved mechanical robustness, in particular because it does not require a connection configuration with a plastic waveguide perpendicular to the plane of the printed circuit. Contrary to the claimed interconnect assembly, such a perpendicular configuration is relatively unstable and not compatible with automotive applications. Further, there is no need to attach a relatively heavy metallic component to a PCB. It also presents a good performance because there are less losses between the plastic waveguide and the transmission lines connected to the integrated circuits. Further, this is compatible dual-mode interconnect assembly with classical RF components (e.g. connectors).

[0008] This dual-mode interconnect assembly may also optionally include one and / or the other of the features of any one of claims 2 to 10.

[0009] The disclosure also relates to a printed circuit board according to claim 11.

[0010] The disclosure also relates to a connector according to claim 12.

Brief description of the drawings

[0011] Other features, objects and advantages of the invention will become apparent from reading the detailed description that follows, and the attached drawings, given as non-limiting examples and in which:

FIG. 1 is a schematic diagram illustrating an example of interconnect assembly.

FIG. 2 is a schematic perspective view of the coupling, according to a first embodiment, between a printed circuit board and a plastic waveguide for a connector assembly compatible with a full-duplex bi-directional transmission.

FIG. 3 is a schematic perspective view of the coupling, according to a second embodiment, between a printed circuit board and a plastic waveguide for a connector assembly compatible with a full-duplex bi-directional transmission.

FIG. 4 is a schematic perspective view of the OMT portion of the coupling shown in FIG. 2 or FIG. 3.

FIG. 5 is a schematic cross-section of the OMT portion shown in FIG. 4.

FIG. 6 shows the various copper layers stacked in the OMT portion shown in FIG. 4 and 5.

FIG. 7 is a schematic perspective view of the twist converter portion of the coupling shown in FIG. 2 or FIG. 3.

FIG. 8 is a schematic cross-section of the twist converter portion shown in FIG. 7.

FIG. 9 shows the various copper layers stacked in the twist converter portion shown in FIGs. 7 and 8.

FIGs. 10A and 10B schematically illustrate the connection of the OMT and twist converter portions shown in FIGs 4, 5, 7 and 8 with the PCBs of respectively shown in FIG. 2 and FIG. 3.

Detailed description

[0012] As schematically shown in FIG. 1, an example of an interconnect assembly 1 comprises a first connector assembly 2, a second connector assembly 3 and a plastic waveguide 4 interconnecting the first and second connector assemblies 2, 3. For example, the interconnect assembly 1 is designed to transmit millimetre-waves between the first and second connector assemblies 2, 3 along the plastic waveguide 4. Advantageously the plastic waveguide 4 has a symmetrical cross-section (circle, square, etc.).

[0013] Both the first and second connector assemblies 2, 3 respectively comprises a connector and a counter-connector. For example, the connector and counter-connector are the same in the first connector assembly 2 as in the second connector assembly 3. For example, the connector is a plug connector 5 and the counter-connector is a header 6. For example, the plug connector 5 is a cable connector and the header 6 is an edge connector. Each edge connector is mounted on a respective printed circuit board 7. Further, at least two RFICs 8, 9, respectively 8', 9' (where RFIC stands for Radio-Frequency Integrated Circuit) are mounted on each printed circuit board 7. These two RFICs 8, 9 (8', 9') are respectively a TX chip (for transmission) and a RX chip (for reception). For example, each RFIC 8 or 9 (8' or 9') may be a CMOS chip in the form of a millimetric-wave integrated circuit. Each one of these two RFICs 8, 9 (8', 9') is connected to a respective transmission line 10. The transmission lines 10 connected to these two RFICs extend respectively along a longitudinal direction LD. In the embodiment illustrated in FIG 2, the longitudinal directions LD of the transmission lines 10 are parallel. In the embodiment illustrated in FIG 3, the longitudinal directions LD of the transmission lines are perpendicular. For example, each transmission line 10 comprises a GCPW portion 11 (where GCPW stands for Grounded Co-Planar Waveguide). Each GCPW portion 11 is in continuity with a funnel shaped portion 12 which serves as a transition portion from the GCPW portion 11 to a SIW portion 21 (where SIW stands for Substrate Integrated Waveguide). The respective structures of the GCPW portion 11 and the funnel shaped portion 12 are disclosed in the European patent application # 21156713 which is incorporated by reference (the GCPW portion 11 of the present disclosure corresponds to the transmission line disclosed - with the reference number 8 - in the European patent application # 21156713, and the funnel shaped portion 12 of the present disclosure corresponds to the third multilayer section disclosed - with the reference 31 - in the European patent application # 21156713).

[0014] The interconnect assembly 1 further comprises, at each end of the plastic waveguide 4, an OMT portion 13 and a twist converter portion 14. The OMT portion 13 and twist converter portion 14 are connected to a respective RFIC 8 or 9 (8' or 9') via a transmission line 10.

[0015] In the illustrated embodiments, the OMT portion 13 and the twist converter portion 14 are made from different PCBs, which are themselves different from the PCB 7 supporting the RFICs 8, 9 (8', 9') and the transmission lines 10. The OMT portion 13 is aligned with the longitudinal direction of the plastic waveguide 4 (in the illustrated embodiments the longitudinal direction of the plastic waveguide 4 corresponds to the mating direction of the plug connector 5).

[0016] As shown on FIG. 4, the OMT portion 13 comprises a multilayer PCB. The total thickness of the multilayer PCB may be for example 2.06mm. In the embodiment illustrated in FIGs 4 to 6, the OMT portion 13 comprises six copper layers 15. For example, each copper layer 15 may be 17.5 micrometres thick. The OMT portion 13 may also comprise five dielectric layers 16, each respectively interposed between two adjacent copper layers 15. Each dielectric layer 16 is comprised, for example, of a laminate substrate 17 (e.g. Roger RT/duroid 5880 from Rogers Corporation, having a dielectric constant ε_r =2.2, and a dissipation factor tanδ=0.0009 at 10 GHz). For example, the thicknesses of the dielectric layers are respectively, from one main face of the PCB to the other face, 0.504mm, 0.127mm, 0.381mm. 0.127mm and 0.504mm. The laminate substrates 17 in the dielectric layers 16 have various thicknesses. The multilayer stack-up is assembled using prepreg layers 18 (e.g. fastRise^™ from taconic, 76 micrometres thick, having a dielectric constant ε_r =2.7, and a dissipation factor tanδ=0.0017 at 10 GHz).

[0017] As shown on FIG. 5, the OMT portion 13 has conductive vias connecting various copper layers 15. Each via extends essentially perpendicular to the copper layers 15 and dielectric layers 16. For example, vias V_61 connect the copper layer #1 to the copper layer #6, vias V_65 connect the copper layer #6 to the copper layer #5 and vias V_12 the copper layer #1 to the copper layer #2. Vias V_65 and vias V_12 prevent leakages. For example, vias V_61, V_65 and V_12 are cylindrical with a diameter of 0.4mm, and a centre-to-centre distance between two vias that are side by side of 0.8mm for vias V_61 and 0.7mm for vias V_65 and V12.

[0018] Vias V_61 are roughly aligned in respective rows so as to continue the alignments of the vias of the respective SIW portion 21. There are four vias V_61 in each row. These two rows of four vias V_61 delimit a first input channel 22 of the OMT portion. For example, the waves transmitted through the first input channel 22 are polarized according to the

propagation mode (where TE stands for Transverse Electric). Two longitudinal trenches 19 extend respectively essentially aligned with a row of Vias V_61. Two transversal trenches 23 extend perpendicular to a row of Vias V_61. One end of one of these transversal trenches 23 is close to one of the rows of four vias V_61. These two transversal trenches 23 delimit a second input channel 32 of the OMT portion. For example, the waves transmitted through the second input channel 32 are polarized according to the

propagation mode, which is orthogonal to the

propagation mode. On the one hand, Vias V_65 and V_12 control the direction of the

mode from the second input channel 32 so as to transform it into a horizontal mode at the output 33 of the OMT portion 13. On the other hand, the mode

is excited from the first input channel 22 between layer #5 and layer #2. Then, thanks to the etched part of layers #5 and #2, the

mode spreads out in all dielectric layers 16 between layer #1 and layer #6 to create the vertical mode at the output 33 of the OMT portion 13. Vias V_65 and V_12 prevent leakages of

during this transformation.

[0019] The longitudinal and transversal trenches 19, 23 are formed through the entire thickness of the multilayer stack-up of copper layers 15 and dielectric layers 16 with a minimum width of 0.4mm. The width of the trenches 19, 23 does not impact the performances of the OMT portion 13. The width can be increased to adapt to the PCB fabrication. The surface of these longitudinal and transversal trenches 19, 23 are metallized so as to form metallized walls 20. The centre-to-centre distance between the longitudinal trenches 19 is about 2.4mm for an OMT portion 13 working in the V band (50 to 75 GHz) The distance between the transversal trenches 23 is about 1.4mm for an OMT portion 13 working in the V band.

[0020] Vias V_65 are aligned in a row of six vias V_65. This row extends essentially from the end of a transversal trench which is close to one of the rows of four vias V_61, to the longitudinal trench 19 continuing the other rows of four vias V_61. The angle between the row of vias V_65 and the longitudinal trench is about 28 degrees for an OMT portion 13 working in the V band.

[0021] Openings are cut or etched through the various copper layers 15 (See FIG. 6).

[0022] The openings made through the copper layers #1 and #6 are the same and correspond to the longitudinal trenches 19, the transversal trenches 23, as well as the vias V_61 and V_12.

[0023] The openings made through the copper layers #2 and #5 are the same and correspond to the longitudinal trenches 19, the transversal trenches 23, as well as the vias V_61 and V_12. Further, the copper layer is removed between the transversal trenches 23, as well as in a first coupling region 24 essentially delimited by portions of the longitudinal trenches 19 and the row of vias V_65.

[0024] The openings made through the copper layers #3 and #4 are the same and correspond to the longitudinal trenches 19, the transversal trenches 23, as well as the vias V_61. Further, the copper layer is removed between the transversal trenches 23, as well as in a second coupling region 25 essentially delimited by the longitudinal trenches 19, the transversal trenches 23 and the row of vias V_61.

[0025] As shown on FIG. 7, the twist converter portion 14 also comprises a multilayer PCB.

[0026] In the embodiment illustrated in FIGs 7 to 9, the twist converter portion 14 comprises six copper layers 15, five dielectric layers 16 and prepreg layers 18 which are identical or similar to those already described in relation to the OMT portion 13.

[0027] The twist converter portion 14 has also conductive vias connecting various copper layers 15. Each via extends essentially perpendicular to the copper layers 15 and dielectric layers 16. For example, vias V_61 connect the copper layer #1 to the copper layer #6, vias V_65 connect the copper layer #6 to the copper layer #5 and vias V_12 the copper layer #1 to the copper layer #2. Vias V_65 and vias V_12 prevent leakages. Vias V_61, V_65 and V_12 are cylindrical with a diameter of 0.4mm and a centre-to-centre distance of 0.8mm (for an OMT portion 13 working in the V band). Further there are vias V_13 and V_64 which are rectangular (for example, 1mmx0.7mm). Vias V_13 and V_64 rotate the TE₁₀ mode of 90 degrees.

[0028] Vias V_61 are roughly aligned in respective rows so as to continue the alignments of the vias of the respective SIW portion 21. There are five vias V_61 in each row (of course as it is a portion of transmission line, it can be longer and the rows may comprise more vias, for example). These two rows of five vias V_61 delimit an input channel 26 of the twist converter portion. For example, the waves transmitted through the input 26 are polarized according to the

propagation mode. Two longitudinal trenches 27 extend respectively essentially aligned with a row of Vias V_61. The distance between the two closest edges of the longitudinal trenches 27 is about 1mm (for an OMT portion 13 working in the V band). They have a minimum width of 0.4 mm (for an OMT portion 13 working in the V band). The surface of these longitudinal trenches 27 are metallized so as to form walls 20 which prevent leakages.

[0029] There are two vias V_12 (the number and shape of these vias may vary). The vias V_12 (respectively V_65) are aligned perpendicular to the longitudinal trenches 27. The vias V_12 (respectively V_65) are located close to the end of a longitudinal trench 27. This end of this longitudinal trench 27 is close to the row of vias V_61. The via V_13 (respectively V_64) extends from the other longitudinal trench 27. The row of vias V_12 through the layers #1 and #2 extends from a longitudinal trench 27 (lefthand side in FIG. 9), whereas the row of vias V_65 through the layers #6 and #5 extends from the other longitudinal trench 27 (right-hand side in FIG. 9). The respective positions of the vias V_12 and V_13 are staggered. Similarly, the respective positions of the vias V_65 and V_64 are staggered.

[0030] Openings are cut or etched through the various copper layers 15 (See FIG. 9).

[0031] The openings made through the copper layers #1 and 6 are the same and correspond essentially to the longitudinal trenches 27, the vias V_61, as well as vias V_12 and V_13 (respectively V_65 and V64).

[0032] The openings made through the copper layer #2 and 5 are the same and correspond to the longitudinal trenches 27, the vias V_61, as well as vias V_12 and V_13 (respectively V_65 and V64). Further, the copper layer is removed in a region between the longitudinal trenches 27.

[0033] The openings made through the copper layer #3 and 4 are the same and correspond to the longitudinal trenches 27. Further, the copper layer is removed in a region between the longitudinal trenches 27 and between the two rows of vias V_61.

[0034] The plug connector 5 comprises a housing for accommodating the OMT portion 13 and the twist converter portion 14, as well as a coupler 28 such as one of the couplers disclosed for example in the European patent application # 21156713. The coupler 28 is made of a metallic piece with a tubular portion 29 having a shape and dimensions adapted for receiving, along an insertion direction ID, the end of a plastic waveguide 5 therein. The coupler 28 may also comprise a horn antenna 30. For example, the horn antenna 30 is conical shaped with a vertex connected to the free end of the tubular potion 29.

[0035] When the edge and plug connectors are mated the OMT portion and the twist converter portion face and contact the edge of the PCB 7 (in this document, the edge corresponds to the thickness face of the PCB).

[0036] In the embodiment shown in FIGs 2 and 10A, the transmission lines 10 are parallel. Therefore, a curved SIW portion 31 is necessary for connecting one of the SIW portion 21 of the parallel transmission lines 10, the other SIW portion 21 being in parallel alignment with the OMT portion.

[0037] In the embodiment shown in FIGs 3 and 10B, the transmission lines 10 are perpendicular so that the OMT portion 13 and twist converter portion 14 directly face a respective transmission line 10.

[0038] In the example of the interconnect assembly shown in FIG. 1, the RFIC 8 (TX) sends data to RFIC 8' (RX) using the fundamental mode

(where HE stands for Hybrid Electromagnetic) of the plastic waveguide 4 and at the same time the RFIC 9' (TX) sends data to RFIC 9 (RX) using the

mode of the plastic waveguide. Because,

and

modes of the symmetric plastic waveguide 4 are orthogonal they can provide two independent channels covering a bandwidth of interest.

[0039] The OMT portion 13 can be excited by two modes

and

respectively at the first 22 and second 32 input channels. The OMT portion 13 then enable to mix these modes and transform them into dual- polarized modes,

and

, at its output 33. These dual- polarized modes

and

are respectively converted into

and

modes at the tubular portion 29. Then, the horn antenna 30 respectively transforms

and

modes of the tubular portion 29 into the

and

modes of the plastic waveguide 4.

[0040] The simulated results of the transition from the OMT portion 13 to the plastic waveguide 4 presents over about 30.7 percent of the bandwidth, 1.22 dB of maximum insertion loss and about 50 dB of isolation between two

and

modes.

[0041] It is possible to manufacture both the OMT portion 13 and the twist converter portion 14 on the same PCB stack-up.

[0042] It is also possible to manufacture the OMT portion 13 and the twist converter portion 14 on the same PCB stack-up as the PCB supporting the RFICs 8, 9 (8', 9') so that the plug connector 5 accommodates only the metallic coupler 28.

[0043] The various vias mentioned above are not necessarily cylindrical. They may have a rectangular cross-section.

Claims

1. A dual-mode interconnect assembly (1) for interconnecting, with at least one plastic waveguide (4), at least two integrated circuits (8, 9/8', 9') mounted on a printed circuit board (7), each one of these two integrated circuits (8, 9/8', 9') being connected to a respective transmission line (10), characterized in that it further comprises at least one orthomode transducer portion (13) and one twist converter portion (14), each one of these portions (13, 14) being respectively connected to a respective transmission line (10) and comprising at least one multilayer printed circuit board extending in a plane which is parallel to the respective printed circuit (7) supporting the transmission lines (10).

2. A dual-mode interconnect assembly (1) according to claim 1, wherein said at least one plastic waveguide (4) has two orthogonal fundamental modes of propagation for electromagnetic waves, these two fundamental modes being transmitted through the thickness of a multilayer printed circuit board.

3. A dual-mode interconnect assembly (1) according to claim 1 or 2, comprising at least one connector assembly (2 or 3) comprising a connector housing accommodating at least one of the multilayer printed circuit boards in which at least one of said one orthomode transducer portion (13) and said one twist converter portion (14) is formed.

4. A dual-mode interconnect assembly (1) according to any one of the preceding claims, comprising at least one connector assembly (2 or 3) comprising a connector housing accommodating a metallic coupler (28).

5. A dual-mode interconnect assembly (1) according to claim 4, comprising at least one connector assembly (2 or 3) comprising another connector housing accommodating the at least one of the multilayer printed circuit boards in which at least one of said one orthomode transducer portion (13) and said one twist converter portion (14) is formed.

6. A dual-mode interconnect assembly (1) according to any one of the preceding claims, wherein the printed circuit (7) supporting the transmission lines (10) comprises at least two parallel transmission lines (10), one of these transmission lines (10) being connected to said one orthomode transducer portion (13) and the other of these transmission lines (10) being connected to said one twist converter portion (14).

7. A dual-mode interconnect assembly (1) according to any one of claims 1 to 5, wherein the printed circuit (7) supporting the transmission lines (10), comprises at least two perpendicular transmission lines (10), one of these transmission lines (10) being connected to said one orthomode transducer portion (13) and the other of these transmission lines (10) being connected to said one twist converter portion (14).

8. A dual-mode interconnect assembly (1) according to any one of the preceding claims, wherein each one of said one orthomode transducer portion (13) and said one twist converter portion (14) comprises a distinct multilayer printed circuit board, these multilayer printed circuit boards being accommodated in a single connector housing.

9. A dual-mode interconnect assembly (1) according to any one of claims 1 to 7, wherein said one orthomode transducer portion (13) and said one twist converter portion (14) are formed in a same multilayer printed circuit board, which is accommodated in a single connector housing.

10. A dual-mode interconnect assembly (1) according to any one of the preceding claims, wherein the multilayer printed circuit board in which the orthomode transducer portion (13) and said one twist converter portion (14) are respectively formed, comprises four, six or eight conductive layers (15).

11. A printed circuit board (7) specifically configured for the dual-mode interconnect assembly (1) according to any one of claims 1 to 9, the printed circuit board (7) supporting at least one transmission chip and one reception chip, said at least one transmission chip and said one reception chip being respectively connected to a transmission line (10) comprising a Grounded Co-Planar Waveguide, GCPW, portion (11) and a funnel shaped portion (12).

12. A connector specifically configured for the dual-mode interconnect assembly (1) according to any one of claims 1 to 9, the connector accommodating a metallic coupler (28) and at least one multilayer printed circuit board in which at least one of said one orthomode transducer portion (13) and said one twist converter portion (14) is formed.

Drawing