EP2006954B1 - Communication device for a railway vehicle - Google Patents

Description

The present invention relates to a communication device between one or more rail vehicles and a control station in general, and relates, more particularly, to a continuous radiating waveguide communication device.

It is known from the document FR 2,608,119 of the Applicant a fundamental mode radiant waveguide communication device, also called TE ₀₁ mode, between a railway vehicle and a control station. This device comprises a hollow tube parallel to a transport path and deposited along this path in a continuous manner, forming a waveguide, of which a single emitting face is pierced with a network of geometrically asymmetrical openings for the passage of a electromagnetic radiation at microwave frequencies. This network of openings (called "slots" in the remainder of the description because of their narrow and elongated geometry) is itself then arranged to direct its emissive face at a small distance from the integral antenna of the vehicle, movable on along the radiating waveguide. The geometry, the dimensions of the slots as well as the spacing between these slots are dimensioned according to the frequency ranges used. The section of the guide is of the order of the wavelength and the large dimension of the slits is small in front of the wavelength. The frequency range that can be used varies by country. In France and in many parts of the world, it can advantageously be carried out in the range of 2.4 GHz where are the exploitable channels according to IEEE 802.11 b and g standards called Wi-Fi for Wireless Fidelity or in the 5.8 GHz band according to IEEE 802.11 a. The electromagnetic theory considers that for distances between antennas of the order of magnitude of the wavelength or of a small number of wavelengths, these antennas are said to operate in the near field and require a particular approach in order to study their coupling. For example, at 2.4 GHz, that is to say for a wavelength in air of 12.5 cm, the near field condition as conventionally expressed in electromagnetism is valid until at a distance of the order of magnitude of three to four wavelengths, or 40 to 50 centimeters. Beyond this distance, the antenna starts to operate in the far field.

Along the guide, and at distances of less than four wavelengths, the global signal radiated by the waveguide can be likened to the sum of each of the near field radiation of the few slots located upstream and downstream of the waveguide. current point where the antenna of the vehicle is. The energy is radiated perpendicular to the plane of the slots. It is not possible to demonstrate, for these short spans, a preferred direction of radiation such as would be obtained by considering the combination of far-field radiation of the slits when they have, between them, relations of appropriate phase and power. As a result, the vehicle is provided with an antenna for transmitting and / or receiving microwave waves, promoting this close-field coupling between the emitting portion of the waveguide and the antenna of the vehicle, without any particular favorable orientation.

The traffic control station is provided with a power supply member of the microwave waveguide and / or at least one microwave wave reception member from the waveguide. This device makes it possible to continuously maintain a high bandwidth link (> 100 MHz) between the ground control station and the vehicles. In the near field, the device also simultaneously authorizes the speed measurement of the vehicles without material contact with the ground and the location of the vehicles by reading a pseudo-random sequence etched in the structure of the waveguide. The device is operational whatever the environment of the track (tunnel, viaduct, trench ...). The use of high frequencies in the range of 2 - 6 GHz makes it possible to overcome most of the problems of electromagnetic compatibility that are binding in the railway environment.

The waveguide is made of metal. The choice of this metal is a compromise between cost constraints and inherent conductivity constraints of the metal, affecting the conduction performance of the wave in the waveguide. Thus, depending on the metal chosen, the longitudinal attenuation will be higher or lower and the number of transmitters / receivers per kilometer of waveguide required will be proportionally higher or lower. The total longitudinal loss is the sum of the Joule loss and the loss due to the removal of energy from the wave that is radiated by the waveguide slots. For example, in a particular 2.4 GHz embodiment, an aluminum waveguide exhibits a Joule linear loss of 15-16 dB / km and a linear loss by constraint limited by construction to 2-3 dB / km .

It is also known from the document US 3,648,172 a circular waveguide with two longitudinal networks of circular openings arranged in the upper part of the waveguide. At the very high frequencies mentioned (7.5-10 GHz), this waveguide exploits higher order propagation modes generally noted TE _mn (m, n> 1) to obtain a limited longitudinal attenuation in relation to its exploitation. along a transport network. In order to allow the propagation of these modes, the diameter of the waveguide is at least three times greater than the wavelength of the waves propagated in the guide. The circular openings pierced on the waveguide simultaneously emit several components of electromagnetic radiation. They emit electromagnetic energy in different directions of space. However, the antenna-train generally receives a single electric field component oriented in a privileged direction of the space and thus shows only a fraction of the energy emitted from the guide, the other part proves radiated without use. This in turn reduces the signal-to-noise ratio of the link, which in turn limits the effective throughput of the ground-to-train communication which must, however, be high in a modern ground-train communication system. Furthermore, the possible propagation in this waveguide of several simultaneous propagation modes generates between these different modes of propagation beats and local signal attenuations requiring the use of a sandwich guide structure acting as a filter. modes, complex to achieve with acceptable materials in the railway environment, in terms of mechanical strength or emission of toxic fumes in case of fire ...

When the rail network to be equipped with communication devices is dual-channel, waveguides are arranged parallel to each channel, with as many transmitters / receivers as necessary on each side. The traffic control station thus communicates with each train running on each of the channels by sending the microwave waves in the two communication devices.

The problem that the invention aims to solve is to reduce the number of transmitters / receivers installed on the ground and to limit the length of guides to be installed along the double rail tracks in order to limit the quantity of material and the quantity of components required. without generating any particular mechanical constraint, to limit the time of installation or maintenance of the device while allowing a control station to communicate at high speed of information with the trains running on the two parallel tracks with the same security and the same availability as the communication device of the prior art. These two parallel paths are spaced a significant distance, as expressed in wavelengths of the microwave communication signals used.

The continuous communication device according to the invention between at least one railway vehicle and a control station, comprises at least one waveguide disposed between two parallel tracks resting on a non-emissive face, comprising two emissive faces each pierced by a network of openings for the passage of electromagnetic radiation in microwaves of given wavelength constituted by slots, at least one vehicle provided with at least one microwave transmission and reception antenna, the control station being provided with at least one microwave waveguide supply member and at least one microwave wave receiving member from the waveguide, and is such that the waveguide is parallelepipedic shape, whose emitting faces are arranged vertically.

• la grande dimension des faces émissives du guide d'ondes est de l'ordre de grandeur de la longueur d'onde du rayonnement électromagnétique propagé dans le guide d'ondes,
• la grande dimension des fentes est inférieure à au moins cinq fois la longueur d'ondes du rayonnement électromagnétique propagé dans le guide d'ondes,
• l'espacement inter-fentes est inférieur à la demi-longueur d'onde des signaux émis dans l'air,
• les deux réseaux de fentes sont identiques,
• l'un des réseaux de fentes est de plus grande dimension que l'autre,
• les fentes sont disposées verticalement,
• la distance entre l'antenne disposée à bord d'un véhicule et le dispositif de communication est d'au moins quatre longueurs d'onde,
• l'antenne disposée à bord d'un véhicule présente une directivité de rayonnement identique à celle du dispositif de communication.

The communication device also includes one or more of the following features:

• the large dimension of the emitting faces of the waveguide is of the order of magnitude of the wavelength of the electromagnetic radiation propagated in the waveguide,
• the large dimension of the slots is less than at least five times the wavelength of the electromagnetic radiation propagated in the waveguide,
• inter-slot spacing is less than the half-wavelength of the signals emitted into the air,
• the two networks of slots are identical,
• one of the slot networks is larger than the other,
• the slots are arranged vertically,
• the distance between the antenna disposed on board a vehicle and the communication device is at least four wavelengths,
• the antenna disposed on board a vehicle has a radiation directivity identical to that of the communication device.

A first advantage of the double grating slotted waveguide communication device is thus to halve the amount of material required to make the waveguides while only slightly increasing the number of emitters / receivers.

A second advantage of the dual-slot grating waveguide communication device is to impose fewer installation constraints on the track by deporting the waveguide out of the way itself, thereby facilitating operations. maintenance of it.

A third advantage is that with this arrangement, the waveguide, although robust is less exposed to material damage related to falling objects or trailing vehicles including track maintenance.

A fourth advantage is that the vertical arrangement of the double network of slots makes it less sensitive to the accumulation of dirt, water, snow, ice ... on its emitting surfaces.

In addition, the dimensions of the waveguide are such that only the basic propagation mode TE ₀₁ is used, which leads to a mechanical simplification of the guide since the different propagation modes must no longer be filtered.

• La figure 1 est une vue schématique du dispositif de communication pour un réseau ferroviaire,
• la figure 2 représente une vue en coupe du guide d'ondes conforme à l'invention,
• la figure 3 représente une vue en coupe du guide d'ondes conforme à l'invention selon un second mode de réalisation,
• La figure 4 représente un mode de réalisation du dispositif de communication conforme à l'invention,
• la figure 5 représente le diagramme de rayonnement mesuré en azimut du dispositif de communication conforme à l'invention, associé à une représentation physique du guide d'ondes.

The invention will be better understood on reading the description which follows, with reference to the appended drawings in which:

• The figure 1 is a schematic view of the communication device for a railway network,
• the figure 2 represents a sectional view of the waveguide according to the invention,
• the figure 3 represents a sectional view of the waveguide according to the invention according to a second embodiment,
• The figure 4 represents an embodiment of the communication device according to the invention,
• the figure 5 represents the radiation pattern measured in azimuth of the communication device according to the invention, associated with a physical representation of the waveguide.

The figure 1 represents a communication device between a control station P and at least one vehicle A traveling on a track, comprising a plurality of fixed waveguides 1, 1 ', 1 ⁿ , etc., arranged continuously and end to end along the way. The length of the communication device depends on the type of network. A waveguide is several hundred meters long and the communication device comprises n waveguides covering the entire railway network.

All the guides being identical, only the waveguide 1 will be described. The waveguide 1 consists of two separate sections 1a and 1b, in which the waves are injected, for example by means of a coaxial transition towards a waveguide, at the ends 2a and 2b of the sections 1a and 1b. 1 b. The ends 3a and 3b of the waveguide 1 are charged in order to avoid the establishment of a standing wave regime in the waveguide, for example by means of a waveguide to coaxial transition and a charge. resistive adapted or by the provision of a microwave absorbent material disposed before a metal short circuit plane of the guide. The ends 3a, 3b do not transmit any wave to the adjacent waveguides 1 'and 1 ⁿ .

The waves are transmitted or received by a transmitter / receiver 4 which is connected to a communication network R connecting all the emitters / receivers 4, 4 ', 4 ⁿ ...; at the control point P. The information flows from checkpoint P to vehicle A -or conversely- by the communication network R, the transceivers 4, 4 ', 4 ⁿ and the waveguides 1, 1 1 ⁿ .

As the figure 2 indicates, in this particular embodiment, the waveguide 1 is of parallelepiped shape, the large faces 6a, 6b being pierced with slots 8a, 8b (here shown vertical) which radiate or receive the waves. The faces 6a, 6b are said to be "large" because their side b is larger than the side a of the "small" faces 7a, 7b. The large dimension b of the emissive faces 6a, 6b is of the order of magnitude of the wavelength. With this characteristic only the fundamental mode TE ₀₁ is operated, that is to say that only the first mode can propagate in the guide to the exclusion of any other mode.

Et $$\mathrm{D}\mathrm{\le }\mathrm{\lambda }\mathrm{/}\mathrm{5}$$

λ étant la longueur d'onde du rayonnement électromagnétique se propageant dans le guide.The large dimension D of the slots is much smaller than the length of the side b : it is at least five times smaller than the wavelength propagated in the guide. This makes it possible to limit the linear radiation losses to 2-3 dB / km while maintaining a power radiated by the guide sufficient to ensure high-speed communication with the vehicle.
In other words, $$\mathrm{b}\mathrm{\approx }\mathrm{\lambda }$$

And $$\mathrm{D}\mathrm{\le }\mathrm{\lambda }\mathrm{/}\mathrm{5}$$

λ being the wavelength of the electromagnetic radiation propagating in the guide.

Preferably, the large dimension D of the slots is arranged in the vertical direction perpendicular to the direction of the waveguide. This arrangement and the very dissymmetrical shape of the slots (D is at least 6 times greater than the small size of the slots) allow to radiate essentially a single electric field component, oriented in the direction of the guide. This electric field component is exploited by the antenna of the vehicle. This limits the energy taken from the guide and radiated outward to the minimum required for ground-vehicle communication.

In practice, a waveguide operating at a low frequency of 2.4 GHz in fundamental mode has a large face b of about 12.5 cm, the wavelength λ of the electromagnetic radiation propagating in the guide. The large dimension of the slots D is 19 mm, the small dimension of the slots is 3 mm and the inter-slot pitch is 61 mm.

Alternatively, as shown on the figure 3 , the large dimension D ₁ of all the slots 8a of an emissive face-for example the emitting face 6a- can be uniformly increased with respect to the large dimension D ₂ of the slots 8b of the other emissive face 6b. This arrangement makes it possible to reinforce the electromagnetic radiation towards one of the two paths. This allows, by way of example, to compensate for a lack of symmetry in laying the waveguide between the channels as related to the configuration imposed by the site, a channel that may be further distant from the waveguide 1 than the other.

Alternatively (not shown), the guide could be of circular or oval section and have a similar behavior of its electromagnetic radiation in the air.

The figure 4 is a view of the continuous communication device between the traffic control station P (not shown) and two trains A and B traveling in two opposite directions on two parallel tracks, 2 and 3. The following description is given when two trains are present on the channels 2 and 3 but it is understood that the operation of the device is exactly the same even when there is only one train running on a single lane.

The waveguide 1 is disposed between the two channels 2 and 3, its small face 7b being placed on the ground, or on a support at a distance from the ground, the large faces 6a, 6b, which are emissive, being at the vertical. Alternatively, this waveguide 1 could be suspended in a tunnel vault, between two channels (2, 3).

The traffic control station P communicates with the trains A and B by injecting into the waveguides 1, 1 ', 1 ⁿ of the signals S1, S2 in the form of a set of microwave waves, which propagate according to a mode of propagation "Go" inside the waveguide 1a, 1b and which are all radiated by the emitting faces of the waveguide 1a, 1b towards the antennas 5 of the trains A and B (the waves emitted are symbolized on the Fig. 4 by two-way double arrows). Each onboard antenna thus receives all the waves injected into the waveguide 1a, 1b ( Fig. 1 ), the receiver of each antenna processing in a known manner the received signals S1, S2 so as to identify which signal is addressed to it. One or more antennas may be provided on board, on the same side or on each side of the train.

Considering the energy loss due to the Joule loss and the losses due to the energy withdrawals of the slits 8a, 8b, the power of the waves is maximum near the ends 2a, 2b ( Fig. 2 ) on the other hand, at the ends 3a, 3b, the power of the waves is minimal since the wave has lost energy by propagating along the guide and radiating by slots 8a, 8b.

The embedded antennas 5 ( Fig. 4 ) are transmitters and receivers. Thus, the trains A and B communicate with the control station P by transmitting microwave signals via the on-board antennas 5 to the waveguide 1, these signals then being propagated from the slots 8a, 8b of the emitting faces 6a, 6b towards the ends 2a, 2b ( Fig. 1 ) of the waveguide 1 with a propagation mode "return" identical to that of the "go".

In this case, given the loss of energy, the power of the wave injected into the waveguide 1 decreases towards the ends 2a, 2b to reach the transmitter / receiver 4 (FIG. Fig. 1 ).

It is known that the radiation pattern of a waveguide of the prior art of great length and pierced with slots on a single surface, these slots being of much smaller dimensions than the wavelength, present in the near field directed radiation, in a plane perpendicular to that of the openings, towards the outside of the guide, without it being possible to obtain a focusing of the energy in a preferred direction of the space.

It is also known that antennas can be made from a waveguide type transmission line. So the "Antenna Engineering Handbook" by Richard C. Johnson and Henry Jasik publishes, in his second edition edited by McGraw-Hill Book Company (chapter 10 page 11 ), an antenna description called "Leaky wave antenna". This antenna is constructed from a waveguide of rectangular section of short length. It uses slots whose large size is of the order of magnitude of the half-wavelength. These antennas are developed in order to obtain on the one hand a significant efficiency, that is to say in particular having the ability to radiate by means of a reduced antenna (of the order of a few wavelengths) all the energy that is communicated to them and, on the other hand, to focus at a great distance the energy radiated in the preferred direction of the desired space. Such an antenna thus operates in far field and its radiation pattern is directional.

In the same chapter, the authors describe another antenna made using slots pierced on the four faces of the guide in order to obtain a circular polarization of the signals emitted in a privileged direction of space. In these cases, the radiations of the different apertures interfere strongly and are composed in order to produce the required directivity and polarization. A strong coupling between these openings and the field present in the guide is thus realized and exploited.

The object of the invention is on the contrary to strongly limit the radiation of the structure so as to take only very little energy from inside the guide. The waveguide 1 is therefore pierced with very small slots 8a, 8b which individually take only a very limited amount of energy from inside the guide, as previously described.

However, the applicant has demonstrated that each slot 8a, 8b of the waveguide 1 according to the invention radiates, unlike the waveguide antennas pierced with four previously described slot gratings, independently without significant interaction. with the energy propagated in the guide or with other slits 8a, 8b close. The radiation of different slot networks 8a, 8b disposed on opposite emissive faces 6a, 6b of the waveguide 1 are effected in substantially independent ways, without significant coupling between the two emissive faces 6a, 6b. This effect therefore makes it possible to transmit and receive signals continuously and over great distances by n waveguides 1 arranged in the channel, each waveguide 1 radiating through two networks of slots 8a, 8b whose radiation characteristics are independent of each other.

Indeed, in the case of very small slots made in a conductive plane, the theory of polarizabilities demonstrates that the radiation of a slot whose transverse dimensions are very small in front of the wavelength is, if it is practiced in a thin conductive plane, and under far-field condition, comparable to that of an elementary magnetic dipole oriented along the axis of the large dimension of this slot which radiates an electric field component oriented in the direction of the guide. This elementary magnetic dipole is born due to the interruption of current lines on the surface of the metal related to the presence of the opening. This magnetic dipole equivalent radiation is oriented perpendicular to the plane of the slot.

By calculating the overall radiation contribution of a large number of these correctly spaced and out-of-phase slots, the formation of a particular radiation pattern is obtained in the far field. The waveguide 1 according to the invention therefore operates in a far-field and its radiation pattern is directional. However, it does not function as a waveguide of the prior art since the waveguide 1 according to the invention operates in a far field and not in a near field. It also does not function as a waveguide antenna of the prior art since the waveguide 1 according to the invention radiates only a tiny portion of the signal energy which passes through it on a very high frequency. long guide distance, while an antenna of the prior art radiates all the energy of the signal which passes through it over a very short guide distance.

The calculation of the inter-slot spacing is effected in a known manner taking into account, on the one hand, the phase shift introduced by the propagation of the microwave signals in the waveguide 1, and on the other hand the phase shift of these signals introduced by the propagation of the signals in the air on either side of the waveguide 1, after passage of the energy through the slots 8a, 8b. A critical inter-slot spacing, that is to say allowing a constructive summation of radiation of different consecutive slots, the order of magnitude is a few centimeters in the 2.4 - 5.8 GHz - an order of magnitude a little less than the half-wavelength of the signals emitted in the air- thus provides a signal of constant amplitude above the guide, regardless of the position of the antenna: above a slot, between two slots, etc .... Beyond this critical spacing , the signal transmitted by the network of slots fluctuates strongly from one opening to another and is therefore not very exploitable to maintain the communication ground-trains.

The figure 5 represents the radiation pattern of the waveguide 1 according to the invention, the slots 8a, 8b of the two emissive faces being of identical dimensions. The axis of the waveguide 1 corresponds to an angle of 0 °. Due to the symmetrical realization of the two slot gratings, a radiation pattern symmetrical with respect to the axis of the waveguide 1 consisting of two main lobes 9 and 10 appears. These two main lobes 9 and 10, transposed to the transport environment of the figure 3 , allow the electromagnetic energy to be concentrated simultaneously towards the two transport paths 2 and 3, by means of a single radiating waveguide 1 disposed in a central position on the ground or in a tunnel vault.

This radiation pattern is obtained when a sufficient number of slot radiation is integrated. A hundred slits in practice make it possible to obtain a high limit beyond which the summation effect of the contributions of the slits tends towards an asymptote. As indicated above, the radiating waveguide 1 is installed continuously between stations, over distances of several hundred meters. It has several thousands of slots.

In a vertical plane, these radiation lobes 9 and 10 have maxima that depend on the height of the waveguide above the ground. The presence of the soil and its physical characteristics influence the radiation pattern in elevation of the radiating waveguide. Depending on its effective height above the ground, as defined by the on-site mechanical installation constraints, a compatible vehicle antenna height will be selected to locate the vehicle antenna in the main lobe of the vehicle. radiation 9 or 19 from the waveguide 1 to the track. In practice, the distance between the on-board antenna 5 and the waveguide 1 must be at least four wavelengths to operate in far-field conditions. Below four wavelengths, the antenna is placed in near field condition. However, in a near field condition, the radiation pattern is not formed and therefore does not allow the waveguide 1 to effectively focus the microwave energy to the antennas 5, and thus communicate between trains and ground with a optimized link budget.

Although the distance between the waveguide 1 and each antenna 5 of the vehicle A, B is in practice increased relative to the waveguide of the prior art, the gain brought by this summation and this energy concentration compensates. for a large part the additional attenuation of the signals which travel a greater distance in the air, from the waveguide 1 to the on-board antenna 5.

The antenna 5 of the vehicle A or B is arranged so as to be permanently close to a network of slots 8a or 8b having the radiation pattern of the figure 4 and progressively and continuously sweeps all the thousands of slots 8a or 8b of the waveguide 1 during the movement of the vehicle A or B ( Fig. 4 ). The radiation pattern continuously accompanies the movement of the vehicle and provides continuously to the two transport paths 2 and 3 a maximum of electromagnetic energy in a preferred direction of space.

An omnidirectional antenna, that is to say an antenna which highlights an electromagnetic field irrespective of the direction of arrival of a signal emitted or alternately which radiates in the same way an electromagnetic signal in all directions of the space may be suitable. This antenna will be able to capture the signals emitted by the waveguide 1 in its preferred directions of radiation and to emit signals in the direction of the waveguide, in the same way as the signals received or emitted in other directions of space .

However, such an antenna has no particular gain related to the focusing of energy in one or more preferred directions of space. As a result, the signals highlighted by this antenna will be weak or will not to inject a high power into the waveguide, through the slots. This means that such an antenna will not achieve significant communication rates except increase the power emitted by the train or ground transmitter.

A directional antenna having a radiation pattern having radiation directivities allows the best possible transfer of energy between the waveguide 1 to the channel and this antenna. In other words, the radiation pattern of the antenna must have at least one main lobe of radiation whose orientation is identical to that of one of the main lobes of the waveguide radiation pattern 1. orientation is defined by the angle α that forms the axis of the main lobe with the axis of the antenna or the waveguide. For example, as the waveguide 1 according to the present invention figure 4 a main lobe directed at approximately 30 ° with respect to the axis of the waveguide, a collinear antenna 5 to the train must also have a starting angle of 30 ° in order to receive and transmit signals efficiently in this preferred direction from space. Such an antenna makes it possible to obtain high communication rates.

The total linear attenuation in the waveguide 1 is only slightly increased since, via a double number of identical slots, only the energy sampling loss from the waveguide is doubled. In the particular embodiment presented at 2.4 GHz, the total linear loss thus goes from 18 dB to 21 dB in the case of an aluminum waveguide and the reduction in range would therefore be 3: 18 or about 17 %. This range reduction can be mitigated by slightly reducing the size of the slots, which would however have the effect of reducing the energy emitted and received via the waveguide.

In particular, due to the weak electromagnetic coupling between adjacent slot gratings, the behavior of the double slot network and its far-field radiation pattern are stable over a wide frequency band and in practice depends only on the proper propagation mode. inside the waveguide 1.

Claims (9)

1. A continuous communication device between at least one rail vehicle (A, B) and a control post (P), including at least one waveguide (1, 1', 1 n) positioned between two parallel tracks and resting on a non-emissive face (7b), comprising two emissive faces (6a, 6b) each pierced with an array of openings (8a, 8b) for the passage of hyperfrequency electromagnetic radiation with a given wavelength made up of slits, at least one vehicle (A, B) being provided with at least one antenna (5) emitting and receiving hyperfrequency waves, the control post (P) being provided with at least one unit for supplying the waveguide (1, 1', 1 n) with hyperfrequency waves and at least one unit for receiving hyperfrequency waves coming from the waveguide (1, 1', 1n), characterized in that the waveguide (1, 1', 1n) is parallelepiped and in that the emissive faces (6a, 6b) are vertical faces of said waveguide.
2. The device according to claim 1, characterized in that the large dimension of the emissive faces (6a, 6b) of the waveguide (1, 1', 1n) is of the approximate size of the wavelength of the electromagnet radiation propagated in the waveguide.
3. The device according to claim 1 or 2, characterized in that the large dimension (D) of the slits (8a, 8b) is smaller than at least five times the wavelength of the electromagnetic radiation propagated in the waveguide (1, 1', 1n).
4. The device according to one of claims 1 to 3, characterized in that the inter-slit spacing is smaller than the half-wavelength of the signals emitted in the air.
5. The device according to one of claims 1 to 4, characterized in that the two arrays of slits (8a, 8b) are identical.
6. The device according to one of claims 1 to 4, characterized in that one of the arrays of slits (8a, 8b) is larger than the other (8a, 8b).
7. The device according to one of claims 1 to 6, characterized in that the slits (8a, 8b) are positioned vertically.
8. The device according to claim 1 to 7, characterized in that the distance between the antenna (5) positioned onboard a vehicle (A, B) and the communication device is equal to at least four wavelengths.
9. The device according to claim 8, characterized in that the antenna (5) positioned onboard a vehicle (A, B) has a radiation directivity identical to that of the communication device.

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