MILLIMETRIC WAVEGUIDE AND TRANSMISSION SYSTEM INCLUDING SUCH A WAVEGUIDE

Abstract

MILLIMETRIC WAVEGUIDE AND TRANSMISSION SYSTEM COMPRISING SUCH A WAVEGUIDE This description relates to a millimeter waveguide (50) comprising a first portion (51) connected to a second portion (52), the first portion (51) comprising first waveguides (541, 542, 543), each configured to receive a first millimeter wave, and the second portion corresponding to a second waveguide, each first waveguide (541, 542, 543) comprising a first free end (551, 552, 553) and a second end joined with the second waveguide (52), each first and second waveguide being made of a dielectric material. Figure for the abstract: Fig. 2

Description

Title of the invention: MILLIMETER WAVEGUIDE AND TRANSMISSION SYSTEM COMPRISING SUCH A WAVEGUIDE Technical field

[0001] The present application relates to a millimeter waveguide made of a dielectric material and a millimeter wave transmission system comprising such a waveguide. Prior art

[0002] It is known to transmit millimeter waves by a waveguide made of dielectric plastic material. For certain applications, it is desirable to be able to transmit millimeter waves corresponding to the aggregation of several millimeter waves in different frequency bands, each corresponding to a signal to be transmitted.

[0003] [Fig.l] is a diagram showing an example of a millimeter wave transmission system 5. The millimeter wave transmission system 5 comprises a millimeter wave transmission device 10, a millimeter wave reception device 30, and a waveguide 20 made of dielectric plastic material transmitting the millimeter electromagnetic waves between the transmission device 10 and the reception device 30.

[0004] The millimeter wave transmission device 10 comprises N transmission blocks 111 to 11N, N being an integer between 2 and 8 typically, but possibly being a higher integer, N being equal to 3 as an example in [Fig.l]. Each transmission block 11;, i varying from 1 to N, comprises a modulation circuit 12; receiving at least one digital signal SBT; and providing an analog signal ST; in a frequency band which may depend on the block 11;. The transmission device 10 further comprises a combination circuit 14 receiving the analog signals STi to STN provided by the transmission blocks 111 to 11N and providing a global analog signal STG in a transmission frequency band AB corresponding substantially to the sum of the signals STi to STN to control an antenna 15 for transmitting millimeter electromagnetic waves. The combination circuit 14 can be implemented by conductive tracks of a printed circuit.The millimeter electromagnetic waves provided by the antenna 15 are guided by the waveguide 20 to the receiving device 30.

[0005] The millimeter wave receiving device 30 comprises an antenna 31 millimeter wave reception capturing electromagnetic waves millimeters provided by the waveguide 20 and providing a reception signal SRG in the transmission band AB. The reception device 30 further comprises a distribution circuit 32 receiving the analog reception signal SRG and providing M analog reception signals SRi to SRM to M reception blocks 33i to 33m, M being an integer between 1 and 8 typically, but possibly being a higher integer, M being equal to 3 as an example in [Fig.l]. Each reception block 33j, j varying from 1 to M, comprises a demodulation circuit 34j receiving the reception signal SRj and providing a signal SBRj in the final frequency band.

[0006] A disadvantage of the millimeter wave transmission system 5 of [Fig.l] is that the generation of the overall analog signal STG can present significant losses. A disadvantage of the millimeter wave transmission system 5 of [Fig.l] is that good coupling between the waveguide 20 and each antenna 31 and 35 can be difficult to implement over the entire transmission frequency band AB which can be greater than several tens of GHz. Summary of the invention

[0007] One embodiment overcomes all or part of the drawbacks of millimeter waveguides made of a dielectric material and of millimeter wave transmission systems comprising such a known waveguide.

[0008] One embodiment provides a millimeter waveguide comprising a first portion connected to a second portion, the first portion comprising first waveguides, each configured to receive a first millimeter wave, and the second portion corresponding to a second waveguide, each first waveguide comprising a first free end and a second end joined to the second waveguide, each first and second waveguide being made of a dielectric material.

[0009] According to one embodiment, the millimeter waveguide further comprises a third part comprising third waveguides, each third waveguide comprising a first free end and a second end joined to the second waveguide.

[0010] According to one embodiment, the first and second waveguides each comprise a tube delimiting an internal volume filled with a gas, a mixture of gases, a fluid or a solid whose dielectric constant is lower than that of the dielectric material.

[0011] According to one embodiment, the dimensions of the cross sections of the first waveguides are different.

[0012] According to one embodiment, the cross section of the tube of at least one of the first waveguides is rectangular and the cross section of the tube of the second waveguide is circular.

[0013] According to one embodiment, the first and second waveguides are each made of a plastic material, in particular polytetrafluoroethylene, polypropylene or polystyrene.

[0014] An embodiment also provides a system for transmitting first millimeter waves comprising a millimeter wave guide as defined previously, a millimeter wave transmission device and a millimeter wave reception device, the millimeter wave transmission device comprising, for each first wave guide, an antenna configured for the transmission of millimeter waves and coupled with said first wave guide.

[0015] According to one embodiment, each first millimeter wave has a frequency band between 30 GHz and 300 GHz.

[0016] According to one embodiment, the frequency bands of the first millimeter waves are distinct. Brief description of the drawings

[0017] These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments given without limitation in relation to the attached figures among which:

[0018] [Fig.l], described above, is a diagram showing an example of a millimeter wave transmission system;

[0019] [Fig.2] is a diagram showing one embodiment of a millimeter wave transmission system;

[0020] [Fig.3] is a diagram showing another embodiment of a millimeter wave transmission system;

[0021] [Fig.4] is a partial, schematic, cross-sectional view of an embodiment of a branch of a waveguide of the millimeter wave transmission system of [Fig.2];

[0022] [Fig.5] is a partial, schematic perspective view of an embodiment of the waveguide of the millimeter wave transmission system of [Fig.2];

[0023] [Fig.6] is a partial, schematic perspective view of another embodiment of the waveguide of the millimeter wave transmission system of [Fig.2];

[0024] [Fig.7] and [Fig.8] are respectively a top view and a side view, partial and schematic, of an embodiment of assembly between the guide waves and a transmitting device of the millimeter wave transmission system of [Fig.2];

[0025] [Fig.9] and [Fig.10] are respectively a top view and a side view, partial and schematic, of another embodiment of assembly between the waveguide and the transmission device of the millimeter wave transmission system of [Fig.2];

[0026] [Fig.l 1] is a block diagram of an embodiment of a transmission block of the millimeter wave transmission system of [Fig.2];

[0027] [Fig. 12] is a block diagram of another embodiment of the transmission block of the millimeter wave transmission system of [Fig. 2]; and

[0028] [Fig. 13] is a partial and schematic perspective view of the internal volume of an embodiment of the waveguide of the millimeter wave transmission system of [Fig.2] integrating a filtering function. Description of the embodiments

[0029] The same elements have been designated by the same references in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same references and may have identical structural, dimensional and material properties.

[0030] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, the millimeter wave transmission and reception circuits are well known to those skilled in the art and are not described in detail.

[0031] Unless otherwise specified, when referring to two elements connected to each other, this means directly connected without intermediate elements other than conductors, and when referring to two elements connected (in English "coupled") to each other, this means that these two elements can be connected or be connected by means of one or more other elements.

[0032] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made unless otherwise specified to the orientation of the figures.

[0033] Unless otherwise specified, the expressions "about", "approximately", "substantially", and "of the order of" mean to within 10%, preferably to within 5%. In the remainder of the description, a millimeter wave is an electromagnetic wave whose wavelength can vary between 1 mm and 10 mm, which corresponds to a frequency that can vary between 30 GHz and 300 GHz.

[0034] [Fig.2] is a diagram showing one embodiment of a system 40 millimeter wave transmission. The millimeter wave transmission system 40 comprises all the elements of the millimeter wave transmission system 5 shown in [Fig.l] with the difference that the combination circuit 14, the antenna 15, the antenna 31, and the distribution circuit 32 are not present, that the transmission device 10 comprises an antenna 42; for each transmission block 1 h, i varying from 1 to N, that the reception device 30 comprises an antenna 44j for each reception block 33j, j varying from 1 to M, and that the waveguide 20 is replaced by a waveguide 50. Each transmission block 1 h, i varying from 1 to N, and the corresponding antenna 42; then forms a transmission circuit 45; of millimeter waves in a transmission frequency band AB;.

[0035] According to one embodiment, the waveguide 50 comprises a first part also called the collection part 51, a second part 52, and a third part also called the distribution part 53. The central waveguide 52 connects the collection part 51 to the distribution part 53.

[0036] The collection part 51 comprises N branches 54; to 54N (three branches 54b 542, and 543 being shown as an example in [Fig.2]). Each branch 54;, i varying from 1 to N, corresponds to a first waveguide. The second part 52 corresponds to a second waveguide and called central waveguide thereafter. Each branch 54;, i varying from 1 to N, comprises a free end 55; and is connected, on the side opposite the free end 55;, to the central waveguide 52. The distribution part 53 comprises M branches 56; to 56M (three branches 56;, 562, and 563 being shown in [Fig.2]). Depending on the application envisaged, the number M may be equal to N or different from N. Each branch 56j, j varying from 1 to M, corresponds to a third waveguide which comprises a free end 57j and which is connected, on the side opposite the free end 57j, to the central waveguide 52.

[0037] Each antenna 42;, i varying from 1 to N, is arranged in proximity, preferably in contact with the axial end 55; of the branch 54;. Each antenna 42; is for example adapted to emit millimeter waves which propagate in the corresponding branch 54;. Each antenna 42; is adapted to emit a millimeter wave in the transmission frequency band AB;. By coupling between the antenna 42; and the corresponding branch 54;, millimeter waves in the transmission frequency band AB; propagate in the branch 54; to the central waveguide 52. The millimeter waves add up at the junction between each branch 54; and the central waveguide 52 to form a millimeter wave in the transmission frequency band AB. Each antenna 44j, j varying from 1 to M, is arranged in proximity, preferably in contact with the axial end 57j of the branch 56j. Each antenna 44 j is for example adapted to capture millimeter waves which propagate in the corresponding 56j branch.

[0038] For the system 40 of [Fig. 2], the aggregation of millimeter waves in the transmission frequency bands AB; is carried out by the waveguide 50 while for the system 5 of [Fig. 2], this aggregation is carried out on the ST signals; by the combining circuit 14 of the transmitting device 10. The aggregation of millimeter waves in the transmission frequency bands AB; can, advantageously, be carried out with fewer losses, especially insertion losses, by the waveguide 50 than when it is carried out by the combining circuit 14. Similarly, for the system 40 of [Fig. 2], the distribution of millimeter waves in the transmission frequency bands AB; is carried out by the waveguide 50 while for the system 5 of [Fig. 2], this distribution is carried out on the ST signals; by the distribution circuit 32 of the receiving device 30.The distribution of millimeter waves in the transmission frequency bands AB; can, advantageously, be carried out with less losses, in particular insertion losses, by the waveguide 50 than when it is carried out by the distribution circuit 32.

[0039] According to one application, the signals ST;, i varying from 1 to N, correspond to different signals. The transmission frequency bands AB; can then be distinct and the transmission frequency band AB can correspond to the sum of the transmission frequency bands AB;. The width of the transmission frequency band AB is then greater than the width of each transmission frequency band AB;. According to one embodiment, the width of each transmission frequency band AB; can be less than 10 GHz. For example, the transmission device 10 can provide signals STi, ST2, ST3, and ST4, the signal STi being in the frequency band AB! from 122 GHz to 131 GHz, the ST2 signal being in the AB2 frequency band from 131 GHz to 140 GHz, the ST3 signal being in the AB3 frequency band from 140 GHz to 149 GHz, and the ST4 signal being in the AB4 frequency band from 149 GHz to 157 GHz.The width of each frequency band ABi, AB2, AB3, and AB4 is equal to 9 GHz. The millimeter waves transported in the central waveguide 52 are then in the frequency band AB from 122 GHz to 157 GHz. The width of the frequency band AB is equal to 35 GHz. The efficiency of the coupling between a millimeter waveguide and an antenna depends in particular on the width of the frequency band of millimeter waves to be transmitted to the waveguide. Therefore, the coupling between each antenna 42; and the branch 54; for the system 40 of [Fig.2], which is to be carried out on the frequency band AB;, can, advantageously, be more efficient than the coupling between the antenna 15 and the guide. of waves 20 for system 5 of [Fig.2] which is to be carried out on the wider AB frequency band.

[0040] In one application, the ST; signals are identical. The transmission frequency bands AB; can then be substantially identical and the transmission frequency band AB can be substantially equal to the transmission frequency band AB;. Such an application allows to generate a high-power millimeter wave transmitted by the central waveguide 52 from low-power millimeter waves emitted by each antenna 42;, i varying from 1 to N.

[0041] [Fig. 3] is a diagram showing an embodiment of a millimeter wave transmission system 60. The millimeter wave transmission system 60 comprises all of the elements of the millimeter wave transmission system 40 shown in [Fig. 2] with the difference that the reception device 30 comprises a single reception block 331, and that the waveguide 50 does not comprise the distribution part 53, the central guide 52 comprising an end 58 located opposite the antenna 44i of the reception block 33b. This embodiment can in particular be implemented in the case where the transmission frequency bands AB; are substantially identical and the transmission frequency band AB.

[0042] [Fig. 4] is a cross-sectional view of an embodiment of the branch 54i of the waveguide 50 of the millimeter wave transmission system 40 of [Fig. 2]. The branch 54i comprises a tube 62 made of a dielectric plastic material delimiting an internal volume 64. The internal volume 64 may be filled with a gas or a gas mixture, for example air, or with a liquid or solid dielectric material whose dielectric constant may be lower than that of the dielectric material making up the tube 62. Preferably, the internal volume 64 is filled with air. According to one embodiment, the tube 62 is surrounded by a sheath, not shown in [Fig. 4], made of a dielectric material whose dielectric constant is lower than that of the dielectric material making up the tube 62. According to another embodiment, the branch 54i comprises a solid rod of the dielectric plastic material.

[0043] According to one embodiment, the tube 62 or the solid rod has a substantially rectangular or circular cross-section, other cross-section shapes nevertheless being conceivable (for example, an elliptical cross-section). Preferably, the tube 62 or the solid rod has a substantially rectangular cross-section which promotes the propagation of millimeter waves in the TE10 mode. In the embodiment illustrated in [Fig. 4], the tube 62 or the rod has a substantially rectangular cross-section having a width L and a height H. According to one embodiment, the width L is between 0.5 mm and 10 mm. According to one embodiment, the height H is between 0.25 mm and 5 mm. According to one embodiment, the thickness E of the wall of the tube 62 is between 0.5 mm and 10 mm.

[0044] The dielectric constant of the dielectric material forming the tube 62 or the rod of the branch 54; is for example between 1 and 4, preferably between 2 and 4. The loss angle or delta tangent of the dielectric material forming the tube 62 or the rod of the branch 54i is for example less than 103 to ensure minimal signal losses in the branch 54;. This material may be a dielectric plastic material such as for example polytetrafluoroethylene, polypropylene or polystyrene. By way of example, for a material with a dielectric constant equal to 2 and for a frequency between 30 GHz and 300 GHz, the wavelength of the electromagnetic waves propagating in the branch 54i is between 7 mm and 0.7 mm. For example, waves at a frequency of around 60 GHz can be used, for which, for a material with a dielectric constant of 2, the wavelength is 3.5 mm.

[0045] Each branch 542 to 54N may have the same characteristics as those previously described for branch 54;. Each branch 56; to 56M may have the same characteristics as those previously described for branch 54p. The central waveguide 52 may have the same characteristics as those previously described for branch 54;.

[0046] According to one embodiment, the dimensions of the straight sections of the branches 54i to 54n are different. In particular, the dimensions of the straight section of the branch 54i are adapted to the frequency band AB; of the millimeter waves transported by the branch 54;. According to another embodiment, the dimensions of the straight sections of the branches 54; to 54N are identical. According to one embodiment, the dimensions of the straight sections of the branches 56; to 56M are different. In particular, the dimensions of the straight sections of the branch 56j are adapted to the frequency band of the millimeter waves to be processed by the reception block 33j associated with the branch 56j. According to another embodiment, the dimensions of the straight sections of the branches 56; to 56M are identical.

[0047] According to an embodiment, the shape (e.g., circular shape, rectangular shape, etc.) of the cross-section of the central waveguide 52 is different from the shape of the cross-section of the branches 54; to 54N.

[0048] [Fig.5] is a partial and schematic perspective view of an embodiment of the waveguide 50 in which the collecting part 51 includes two branches 54; and 542, although the number of branches 54; can be greater than 2, each having a rectangular cross-sectional shape and in which the central waveguide 52 has a circular cross-sectional shape.

[0049] This can be advantageous insofar as the waveguide 52 can have a length greater than the length of each branch 54i and 542 and the manufacture on an industrial scale of a waveguide having a circular cross-section is simpler than the manufacture of a waveguide having a rectangular cross-section. Each branch 54b 542 having a rectangular cross-section which receives a millimeter wave provided by the associated antenna 42b 422 makes it possible to reduce losses during the capture by the branch 54b 542 of millimeter wave emitted by the associated antenna 42b 422.

[0050] This can further allow the transmission on the central waveguide 52 of circular section of a first millimeter wave coming from the branch 54i and of a second millimeter wave coming from the branch 542, the first and second millimeter waves being polarized orthogonally, the frequency bands ABi and AB2 possibly being identical. This advantageously makes it possible to double the data transmission rate on the frequency band ABb.

[0051] The waveguide 50 may correspond to a single piece or be obtained by assembling several pieces.

[0052] [Fig.6] is a partial and schematic perspective view of an embodiment of the waveguide 50 whose collection part 51 comprises two branches 54i and 542, the number of branches 54; however being able to be greater than 2, and which corresponds to a separate part from the central waveguide 52. The manufacturing methods of the central waveguide 52 and the collection part 51 can then be different. For example, the central waveguide 52 can be manufactured by extrusion and the collection part 51 can be manufactured by molding.

[0053] [Fig.7] and [Fig.8] are respectively a top view and a side view, partial and schematic, illustrating the connection between the waveguide 50 and the transmission device 10 according to one embodiment. [Fig.9] and [Fig. 10] are figures similar respectively to [Fig.7] and [Fig.8] illustrating the connection between the waveguide 50 and the transmission device 10 according to another embodiment.

[0054] In Figures 7 to 10, the collection part 51 of the waveguide 50 comprises two branches 54i and 542, the number of branches 54; however being able to be greater than 2. In Figures 7 to 10, the transmission device 10 comprises, by way of example, a printed circuit 70 and at least one microprocessor 72 mounted on the printed circuit 70. The antennas 42i and 422 are formed by conductive tracks 74 of the printed circuit 70, the antennas 42i and 422 being represented in dotted lines in [Fig.9].

[0055] In Figures 7 and 8, the waveguide 50 is mounted according to a so-called edge coupling. The antennas 42i and 422 are formed along an edge 76 of the printed circuit 70 and the branches 54i and 542 of the waveguide 50 are arranged along the edge 76 so that the axis of each branch 54b 542 at the end 55b 552 is substantially parallel to the plane of the printed circuit 70. Each antenna 42b 422 may be in contact with the end 55b 552 of the corresponding branch 54b 542.

[0056] In Figures 9 and 10, the waveguide 50 is mounted according to a so-called vertical coupling. The branches 54i and 542 of the waveguide 50 are arranged so that the axis of each branch 54b 542 at the end 55b 552 is substantially perpendicular to the plane of the printed circuit 70. Each antenna 42b 422 can be covered by the corresponding branch 54i, 542.

[0057] [Fig. 11] is a block diagram of an embodiment of a transmission block 1 h , i varying from 1 to N, in which the transmission block 11; receives a single digital signal SBTi, and performs modulation to provide the SMT signal in the transmission frequency band AB;.

[0058] Block 11; of emission comprises: - a digital-to-analog converter 80 (DAC) receiving the SBT signal; and providing an analog signal in a basic frequency band; - an adjustable gain amplifier 81 (VGA) receiving the analog signal supplied by the digital / analog converter 80 and providing an amplified analog signal; - a filter 82 receiving the amplified analog signal supplied by the adjustable gain amplifier 81 and providing a filtered signal; - a mixer 83 receiving the filtered signal supplied by the filter 82 and further receiving an oscillating signal LO; and supplying a signal in the transmission frequency band AB; corresponding to the filtered signal supplied by the filter 82 mixed with the oscillating signal LO; ; - an amplifier 84 (IFA) receiving the signal supplied by the mixer 83 and supplying the signal ST; which corresponds to the signal supplied by the mixer 83 which is amplified.

[0059] [Fig. 12] is a block diagram of another embodiment of a transmission block 1 li, i varying from 1 to N. In this embodiment, the transmission block 1 li receives several digital signals SBTi and performs a first modulation to provide an analog signal STIi in an intermediate frequency band. The transmission block 1 li then provides an analog signal STGIi equal to the sum of the analog signals STIi and then performs a second modulation from the signal STGi to provide the signal STi in the transmission frequency band ABi.

[0060] According to one embodiment, the 1 h transmission block comprises: - for each digital signal SBT; received, a sub-block 85; which comprises all of the elements described previously in relation to [Fig.l 1] and which provides the analog signal STI; in an intermediate frequency band; - a combination circuit 86 receiving the STI signals; provided by the sub-blocks 85; and providing the global signal STG; corresponding substantially to the sum of the ST signals; ; - a mixer 87 receiving the global signal STG; and further receiving an oscillating signal LO2; and providing a signal in the transmission frequency band AB; , corresponding to the global signal STG; mixed by the oscillating signal LO2; ; and - an amplifier 88 (PA) receiving the signal provided by the mixer 87 and providing the signal ST; which corresponds to the signal provided by the mixer 87 which is amplified.

[0061] For certain applications, it may be desirable to filter the signal ST;, i varying from 1 to N, and / or to filter the signal SRj, j varying from 1 to M. According to one embodiment, this is achieved by adding, for each transmission block 11;, a filter receiving the signal ST; and providing a filtered signal to the antenna 42; and / or by adding, for each reception block 33j, a filter receiving the signal SRj from the antenna 44j and providing a filtered signal to the reception block 33j.

[0062] According to another embodiment, this filtering function is performed directly by the waveguide 50. According to one embodiment, the filtering function can be implemented on each branch 54;, on the central waveguide 52, and / or on each branch 56j. According to one embodiment, the filtering function is implemented by providing the branch 54;, the central waveguide 52, and / or the branch 56j with a cross-section that varies along the branch 54;, the central waveguide 52, and / or the branch 56j.

[0063] [Fig. 13] is a perspective, partial and schematic view of the internal volume 64 of the branch 54; illustrating the performance of a filtering function by the branch 54;. By way of example, the cross-section of the branch 54; comprises abrupt variations, for example one or more constriction zones 90 in which the cross-section of the branch 54; is reduced, one or more expansion zones 92 in which the cross-section of the branch 54; is increased, and / or one or more obstacles 94 on the path of the millimeter waves.

[0064] Various embodiments and variations have been described. Those skilled in the art will understand that certain features of these various embodiments and variations could be combined, and other variations will occur to those skilled in the art. The system 40 of [Fig. 2] may be used in full duplex mode, with the transmitting device 10 further comprising a millimeter wave receiving device, for example analogous to the receiving device 30, and the receiving device 30 further comprising a millimeter wave transmitting device, for example analogous to the receiving device 10, such that millimeter waves may be carried by the waveguide 50 in both directions.

[0065] Finally, the practical implementation of the embodiments and variants described is within the reach of those skilled in the art from the functional indications given above.

Claims

Claims

1. A millimeter waveguide (50) comprising a first portion (51) connected to a second portion (52), the first portion (51) comprising first waveguides (54b 542, 543), each configured to receive a first millimeter wave, and the second portion corresponding to a second waveguide, each first waveguide (54b 542, 543) comprising a first free end (55b 552, 553) and a second end joined to the second waveguide (52), each first and second waveguide being made of a dielectric material.

2. A millimeter waveguide according to claim 1, further comprising a third portion (53) comprising third waveguides (56b 562, 563), each third waveguide (56b 562, 563) comprising a first free end (57b 572, 573) and a second end joined to the second waveguide (52).

3. A millimeter waveguide according to claim 1 or 2, wherein the first and second waveguides each comprise a tube (62) delimiting an internal volume (64) filled with a gas, a mixture of gases, a fluid or a solid whose dielectric constant is lower than that of the dielectric material.

4. A millimeter waveguide according to claim 3, wherein the dimensions of the cross sections of the first waveguides (54b 542, 543) are different.

5. A millimeter waveguide according to claim 3 or 4, wherein the cross-section of the tube (62) of at least one of the first waveguides (54b 542, 543) is rectangular and wherein the cross-section of the tube (62) of the second waveguide (52) is circular.

6. A millimeter waveguide according to any one of claims 1 to 5, wherein the first and second waveguides are each made of a plastic material, in particular polytetrafluoroethylene, polypropylene or polystyrene.

7. A system (40; 60) for transmitting first millimeter waves comprising a millimeter waveguide (50) according to any one of claims 1 to 6, a millimeter wave transmission device (10) and a millimeter wave reception device (30), the millimeter wave transmission device (10) 14 comprising, for each first waveguide (54b 542, 543), an antenna (42b 422, 423) configured for the emission of millimeter waves and coupled with said first waveguide.

8. The system of claim 7, wherein each first millimeter wave has a frequency band between 30 GHz and 300 GHz.

9. The system of claim 8, wherein the frequency bands of the first millimeter waves are distinct.