EP2042402A1 - Radio communication device in a guided transport means - Google Patents

Abstract

The device has a continuous radiating structure (10) formed by waveguides of a rectangular section presenting three sections (a, b, c) pierced with a series of slots (12, 14, 16) respectively. A microwave signal is injected into the slots. An energy transition unit transmits energy between the structure and a Yagi type directive antenna, where the sections are adjacent and consecutive to each other. Large dimension of the slots (14) progressively extends on length of the section (b).

Description

The invention relates to a radio communication device comprising a continuous radiating structure, a directional antenna and an energy transition means between the continuous radiating structure and the directional antenna.

Such a continuous radiating structure - described for example in the document FR 2,608,119 - is used on certain urban guided transport sites to maintain continuous radio coverage between a ground control station and trains, as much as possible from the specific propagation conditions related to the track environment (in tunnels in particular). Its operation is very different from that of a traditional antenna since it allows, via a continuous network of slots made in a waveguide, to bring a small part of the radiofrequency energy propagated inside the structure. radiating outwards in the immediate vicinity (a few tens of cm) of the antenna of the moving train along the track, almost completely free of local propagation conditions. This type of structure is called "continuous" because it typically extends over several hundred meters long.

The known continuous radiating structure thus effectively covers an area that can be described as "one-dimensional" concentrating radiofrequency energy in the immediate vicinity of the track, along it. This structure is however not able to effectively cover a large volume such as that presented by a stop station, a garage or workshop area. In this case it would be necessary to arrange the waveguide in the form of a network of parallel guides, regularly spaced, which proves to be economically unrealistic. The radio coverage of the station, garage or workshop, however, has a necessary and even vital character.

These zones, however, are less constrained from the point of view of radio propagation and are effectively covered by free radio propagation, that is to say using discrete, directive antennas arranged at intervals, every few hundred from meters to the track. A mixed solution exploiting in complex radio coverage areas a continuous radiating support freeing itself from these constraints of propagation environment and, in Areas of easier radio coverage of discrete antennas thus proves to be an efficient configuration.

In order to meet these constraints, the current technical solution represented on the figure 1 is implemented: at the end 3 of the continuous radiating structure 1 (here a waveguide), a significant radiofrequency energy remains, since the attenuation related to the propagation and to the radiation from the waveguide amounts to a value less than 20 dB per kilometer and that waveguide lengths generally used are limited to a few hundred meters, the inter-station distance generally encountered in urban guided transport. This energy is taken up by a "guide / coaxial" transition 4, is transported by a coaxial cable 5, then feeds a directional antenna 6 - for example of the Yagi type - providing radio coverage in free propagation in the volume of the zone to be cover and relayed, if necessary, by other similar antennas arranged judiciously further and far and away.

However, such a solution has several disadvantages: it is relatively expensive because of the transitions 4 "guide / coaxial", cable 5 and the directive antenna 6 to be added to each volume to cover, it is complicated to implement and the microwave signal available at the end of the waveguide is rapidly attenuated by passing through the transitions and the coaxial cable 5 towards the directional antenna 6. In addition, sudden variations of the transmitted signals are recorded at the passage between the guide and the directional antenna.

It is not currently known optimal solution for joining Yagi type antenna technology to the continuous radiating structure technology to reduce the problem of signal attenuation.

Prior art is known from slit waveguide directional antennas. This type of traditional antenna is generally arranged on towers high in order to have a good radio clearance and, in particular, to clear the first Fresnel communication area to mobiles. This type of antenna is intended to radiate in a directive manner with a minimum footprint all the energy communicated by a transmitter. Typically, according to the expected gain of such an antenna, its large dimension, developed along the axis of propagation, does not exceed a few wavelengths, a large dimension less than 1 meter at 2.5 GHz. Beyond a size of a few wavelengths, the gain of such an antenna and its directivity no longer grow significantly and therefore no longer practical use.

It is not possible, however, to directly attach such a waveguide directive antenna to a continuous radiating waveguide structure - using, for example, guides of identical section - because the antenna of the train passing suddenly to right of the radiation zone of the directive antenna section would be "dazzled" by the very brutal transition of a signal of reduced power, that radiated by the radiating structure continues, towards an identical signal but of much greater power (typically 60 decibels moreover), due to intense local radiation from this directional antenna. Since the transition takes place at a very small distance, less than one meter (length of the directional antenna) and traveled at the speed of the train, the train or ground radio equipment could therefore lose their synchronization and would thus not be more temporarily able to communicate effectively with each other.

The communication device of the present invention aims to solve the problems of the radio coverage devices of several zones whose propagation conditions are different from each other by proposing an economical solution, effective, simple to manufacture and flexible to implement.

According to the invention, the communication device comprises a continuous radiating waveguide structure pierced by a first series of slots forming a first section of radiating structure, inside which a microwave signal is injected, an antenna directive and an energy transition means between the radiating continuous structure and the directional antenna and such that the transition means and the directional antenna are constituted respectively of a second and a third section of radiating structure respectively pierced by a second and third series of slots, the first, second and third sections of radiating structure being adjacent and consecutive.

• la grande dimension de la première série de fentes est très inférieure à la longueur d'onde du signal hyperfréquence se propageant dans la structure rayonnante,
• la grande dimension de la deuxième série de fentes s'étend progressivement sur la longueur du deuxième tronçon, depuis la grande dimension de la première série de fentes jusqu'à une dimension qui reste inférieure à celle de la troisième série de fentes,
• la grande dimension de la troisième série de fentes est identique sur la longueur du troisième tronçon et proche mais inférieure à la demi longueur d'onde du signal propagé dans la structure rayonnante;
• le pas entre deux fentes consécutives est constant et identique le long des trois tronçons de structure rayonnante ;
• les fentes sont disposées transversalement à la direction longitudinale de la structure rayonnante,
• la longueur du deuxième tronçon est comprise entre 1 et 20 mètres.
• la troisième série de fentes comprend jusque dix fentes ;
• la troisième série de fentes est formée par la jonction de la deuxième série de fentes avec la même série de fentes inversée en ce que la grande dimension diminue progressivement de la demi-longueur d'onde du signal propagé à une dimension très inférieure à la longueur d'onde du signal propagé,

The communication device of the invention also satisfies one of the following characteristics:

• the large dimension of the first series of slots is much smaller than the wavelength of the microwave signal propagating in the radiating structure,
• the large dimension of the second series of slots progressively extends over the length of the second section, from the large dimension of the first series of slots to a dimension which remains smaller than that of the third series of slots,
• the large dimension of the third series of slots is identical over the length of the third section and close to but less than half the wavelength of the signal propagated in the radiating structure;
• the pitch between two consecutive slots is constant and identical along the three sections of radiating structure;
• the slots are arranged transversely to the longitudinal direction of the radiating structure,
• the length of the second section is between 1 and 20 meters.
• the third series of slits comprises up to ten slits;
• the third series of slots is formed by the junction of the second series of slots with the same series of inverted slots in that the large dimension decreases progressively from the half-wavelength of the propagated signal to a dimension much smaller than the length waveform of the propagated signal,

• la figure 1 est une vue schématique du dispositif de communication radioélectrique par support rayonnant continu le long de la voie puis en propagation libre par antenne directive de l'art antérieur,
• la figure 2 représente schématiquement un dispositif de communication radioélectrique par support rayonnant le long de la voie puis en propagation libre conforme à un premier mode de réalisation,
• la figure 3 représente schématiquement un dispositif de communication radioélectrique par support rayonnant le long de la voie permettant localement d'augmenter la portée de la liaison sol-train conforme à un second mode de réalisation.

Other objects, features and advantages of the invention will appear on reading the description of the embodiments of the communication device, a description given in connection with the drawings in which:

• the figure 1 is a schematic view of the radio communication device continuous radiating support along the path and free propagation by directive antenna of the prior art,
• the figure 2 schematically represents a radio communication device by support radiating along the path and then in free propagation according to a first embodiment,
• the figure 3 schematically represents a radio communication device by support radiating along the path allowing locally to increase the range of the ground-train link according to a second embodiment.

The figure 1 is a schematic view of the radio communication device continuous radiating support along the path and free propagation by directional antenna, and has been described above.

The figure 2 schematically shows a radio communication device 10 according to a first embodiment. The communication device 10 is composed of a radiating structure formed by a waveguide of rectangular section having three radiating structure sections a, b, c respectively pierced with slots 12, 14 and 16. The communication device 10 is arranged in elevation above the ground or, where appropriate, installed in a tunnel vault. The first radiating section extends into a traffic zone of a train over a distance of up to several hundred meters. The second and third sections b and c extend in an area allowing a gradual rise in the radiated power, over a distance of several meters in length compatible with the characteristics of resistance to sudden variations of the signals incident of train and ground radio equipment, and also making it possible to construct a marked directivity of the signals towards the zone to be covered in free propagation, after the mechanical end of the structure 10 (station, workshop, garage or mixed radio coverage by continuous radiating structure then discrete antennas). The section c makes it particularly possible to exploit and radiate all the residual energy at the end of the structure towards the volume to be covered.

The communication device 10 performs two functions: the first function, maintained by the first section a of continuous radiating structure, makes it possible to communicate in a space dimension with an antenna of a train traveling above and close to the structure. The second function, maintained by the third section c of the directional antenna, makes it possible to communicate in free propagation in a volume with an antenna arranged at a distance from the end of the communication device 10, for example on a train leaving the section c. The intermediate radiating structure b makes it possible to progressively and efficiently switch from one mode of operation to another by allowing the transition of radiofrequency energy between the continuous radiating structure a and the directional antenna c.

The slots 12 of the first section a are arranged transversely to the longitudinal direction of the waveguide and their large size is much smaller than the wavelength of the microwave signal propagating in the waveguide. The large dimension is understood to be the dimension of the slot in the transverse direction (also called "major axis"), this dimension being significantly larger than the dimension of the slot in the longitudinal direction (also called "minor axis"). This characteristic allows to take very little energy along the guide and thus to obtain a radiating structure with a very low linear attenuation. The radiated signal is weak but continuous along the structure and of sufficient power to ensure radio communication via the antenna train moving in the immediate vicinity. This stretch is called "continuous radiating". Depending on the configuration of the transport network, it can extend over several hundred meters.
The slots 14 of the second section b (which corresponds to the energy transition means) are arranged transversely to the longitudinal direction of the waveguide. Their large size varies from the large dimension of the slots 12 of the first section a (large dimension much smaller than the wavelength) to a dimension which remains smaller than that of the slots 16 of the third section c (which corresponds to the directional antenna). The slots 16 of the third section c are all identical and also transverse to the longitudinal direction of the waveguide, and their large dimension is close to the half-wavelength of the signal propagated in the guide. For the sake of simplicity, only a few slots 12, 14 and 16 are shown on the figure 2 . The energy taken, and therefore the power radiated from each slot 14 increases rapidly when the size thereof increases, the size of each slot 14 remains less than half the wavelength. This energy is transferred from inside the waveguide to the outside. A directivity, in the axis of the guide towards its end and therefore in the direction of the volume to be covered after the end of the guide is born from the composition of the radiation of the different slots 12, 14, 16 successive regularly spaced and out of phase according to the calculation principle inter-slot distance explained below.

, expression ou « e » est l'excentricité de l'ouverture en forme d'ellipse, « K(e) » et « E(e) » sont respectivement les intégrales elliptiques complètes de première et de seconde espèce. La polarisabilité magnétique d'une fente de géométrie rectangulaire 12 s'avère correctement approchée par celle d'une fente de géométrie elliptique de même grand et petit axe. Dès lors, le long du tronçon rayonnant continu a, on dispose des fentes 12 de grand axe calculées telles que la polarisabilité de ces fentes permette un couplage réduit d'environ 60 décibels entre la puissance propagée à l'intérieur du guide et celle rayonnée à l'extérieur, permettant le passage d'une puissance suffisante à entretenir la communication sol-train. L'expression précédente de la polarisabilité magnétique de l'ouverture montre également que α _m croit en fonction de l ³.In section a, the radiation theory of small apertures due to HA Bethe, "Theory of diffraction by small holes, Phys. Rev., vol. 66, pp. 1263, 1944 » apply. Therefore, the radiation of a small aperture, here an elementary slit 12, can be expressed in the form of the radiation of equivalent magnetic dipoles noted m and in the form of a relationship between the magnetic field propagated within the waveguide, noted H ₀ , and a coefficient called "magnetic polarizability of the opening", noted α _m . At a sufficient distance from the opening, the magnetic moment of the magnetic dipole equivalent to the radiation of this opening is written in the form of the dyad m = α _m : H ₀ . The magnetic polarizability of a very elongated ellipse-shaped slot has an analytical solution. It is written along the large axis of dimension "2 l " of the opening in the form ${\alpha }_m=\frac{2\pi }{3}\frac{l^3{e}^2}{E\left(e\right)-K\left(e\right)}$

, expression or "e" is the eccentricity of the elliptical opening, "K (e)" and "E (e)" are respectively the complete elliptic integrals of first and second kinds. The magnetic polarizability of a slot of rectangular geometry 12 is correctly approximated by that of a slot of elliptical geometry of the same large and small axis. Therefore, along the continuous radiating section a, there are slots of calculated long axis such that the polarizability of these slots allows a reduced coupling of about 60 decibels between the power propagated inside the guide and that radiated at the outside, allowing the passage of a sufficient power to maintain the ground-train communication. The previous expression of the magnetic polarizability of the aperture also shows that α _m increases as a function of l ³ .

Along the transition section b, the polarizability of the openings is increased very progressively by regularly modifying this parameter 1 of the slots 14 so that, from the initial -60 dB, the level of radiated power extracted from the guide and received by the antenna of the train in translation nearby. The evolution of this dimension l is calculated so that the evolution of the power transmitted by each slot, which varies in l ³ , produces the linear variation ramp up required along this section b, as long as Bethe's assumption of small openings remains valid. At the end of section b, the power of the radiated signal has increased strongly.

, de la puissance transmise en interne au guide et au rayonnement efficace de toute l'énergie résiduelle, sans pertes additionnelles (transitions, connecteurs, câble) et dans la direction de propagation commune aux trois tronçons a, b et c. L'extrémité du guide ne transportant plus d'énergie radiofréquence pourra être laissée ouverte, simplement protégée par un capuchon diélectrique assurant l'étanchéité mécanique.In the directional antenna formed by the section c, starting from this already important level of radiation obtained progressively along the second section b, the objective is to make the best use of all the residual energy in order to radiate rapidly and efficiently the entire residual energy at the end of the guide. A half-wave resonant slot in the air, properly powered, has a high radiation efficiency and has the property of radiating virtually all the energy that is communicated to it. Therefore, if we have in this third section c a resonant slot 16 half wave at the working frequency, it radiates on both sides of its plane most of the incident energy. This energy is radiated for half in the half-center of the waveguide (it is reinjected into it) and radiated halfway outwards. In practice, there remains therefore in the waveguide, in the section c, after a first half-wave resonant slot 16, about half of the initial power. There is therefore a reduced number n of successive half-wave resonant slots 16 (n <10) in this c-terminal part so that it can be considered that all the residual energy is effectively radiated, slot 16 after slot 16. This process leads to a rapid attenuation, close to $(\frac{1}{2}{)}^{\mathrm{not}}$

, the power transmitted internally to the guide and the effective radiation of all the residual energy, without additional losses (transitions, connectors, cable) and in the direction of propagation common to the three sections a, b and c. The end of the guide no longer carrying radiofrequency energy can be left open, simply protected by a dielectric cap ensuring the mechanical seal.

The pitch between two consecutive slots 12, 14 and 16 is a function of the section of the waveguide and the wavelength of the signals used. It is calculated so as to obtain a signal of constant amplitude all along the communication device in the vicinity of the continuous radiating structure, in particular above a slot, or between two slots. It is obtained by taking into account the phase shift of the signals feeding the slots of the waveguide, from the guided wavelength - itself a function of the internal geometrical dimensions of the guide and its propagation mode - as well as the phase shift experienced in the air, outside of the waveguide, by all the radiation of the slots contributing to the total field received at all points of reception near the guide. This inter-slot distance is constant and identical along sections a, b and c to ensure a continuously increasing level of signal above the waveguide.

The radiating waveguide is installed along the transport path in the form of unitary sections electrically and mechanically connected to each other. In order to ensure the transport and easy assembly / disassembly of these sections, the length of each of these unitary sections is limited in practice to a value not exceeding 20 m. A terminal section is formed of sections b and c represented in figure 2 . The directional antenna formed by the third section c has a short length, limited to less than ten slots, of length well below one meter. The second transition section b may advantageously have a dimension at most equal to the length of a unit section less the length of the section c. The first continuous radiating section is very long and is produced by all the other unitary sections situated upstream, but may alternatively be part of the terminal section, depending on the signal variation dynamics tolerable by the radio equipment and therefore the effective transition distance necessary to ensure sections b and c.

Beyond the directional antenna formed by the third section c, the downstream radio coverage is carried out in free propagation, that is to say with characteristics depending on the radio environment specific to the propagation environment. station, workshop, garage or, track in the case of mixed solution operating by continuous radiating structure and discrete antennas.

The above explanation was given by considering a train moving above the communication device and leaving this radio coverage area. The radiating terminal section formed of the second and third sections b and c ensures the gradual increase in power of the signals received by the train. The problem is reversible when a train approaches from a non-equipped area by the communication device according to the invention to an equipped area, ensuring a continuous decay of the power of the signals received since this time the directional antenna (third section c) to the continuous radiating structure (first section a). This reversible arrangement is particularly useful in the scenario where two sections of complex radio coverage track require the use of a radiating waveguide and frame a simpler environment whose radio coverage is provided by one or more antenna (s) discrete (s) consecutive. At the end of the first waveguide zone equipped with a transition terminal section in accordance with the invention, the power of the transmitted signals will gradually increase, in accordance with the dynamic tolerable by the radio equipment used. The free propagation conditions then apply in the intermediate free propagation environment for which a maximum of radiofrequency energy has however been communicated by the very low loss transition terminal section, thus making it possible to ensure efficient free propagation. Near the second installation zone of the waveguide again covered by a radiating waveguide according to the invention, the signal will increase because of the proximity of the radiation source and then past the beginning of the third section. c and along the second section b, the signal will gradually decrease over a few meters, until it returns to the basic level received all along the first section a.

In this first embodiment, the first, second and third sections of the communication device are adjacent and consecutive, the second section b making it possible to progressively change from a continuous low-radiation mode of operation to a local mode of intense radiation operation. .
The invention thus makes it possible to realize very simply and economically a radio communication device which provides two types of communication in two different propagation environments.
This device allows a continuous rise in power, over an adjustable length, up to several meters and allowing the radio equipment on board the train to "follow" this rise in power gradually, without risk of loss of signal synchronization.

Alternatively, it is possible to reinforce the radiation locally by practicing larger slots size over a few meters, for example in the case where the waveguide is physically and locally remote from the antenna of the train to bypass a device of way. The additional energy radiated locally over these few meters makes it possible to mitigate the additional attenuation related to this distance gap increased locally. Such a variant is represented by the figure 3 .

On a region of the radiating structure 20 where it is desired to locally increase the signal radiation, it is practiced between two radiating sections continuous to a first series of slots 14 (intermediate radiating zone b) whose large dimension grows from a very long length. less than the wavelength of the signal propagated in the guide to a length less than half the wavelength. A second series of slots 14 '(intermediate radiating zone b') is then produced, the large dimension of which decreases from a length less than half the wavelength to a length much shorter than the wavelength of the signal propagated in guide. The evolution profile of the length of the major axes of the slots in these intermediate sections b and b 'is theoretically determined as previously described for the second section b. The series of slots of the section b, followed by the series of slots of the section b 'locally creates a more intense section c' radiating. In order to obtain the reinforcement of the necessary signal over the desired length, the section c 'can be developed to the desired length by adding slots whose large dimensions are all equal to that of the last slot 14 of the section b or to the first slot 14 'of the section b'. This dimension, the upper limit of the major axis of the slots of the sections b, c ', b' is calculated from the previous expression of the magnetic polarizability α _m of the slot in order to obtain the radiated power necessary to compensate the attenuation further related to the distance gap increased locally then allow a return to a type of operation after this local enhancement zone c 'signal, via the section b'. Of course, the energy of the signal propagated after this type of zone is attenuated with respect to a waveguide structure which does not include the sections b, c 'and b', which implies that it is necessary, with equal length of waveguide, to provide repeaters in greater numbers.

The operation of such a device has been described by considering the case of a ground-to-train communication, where the radiofrequency energy is communicated to the radiating structure for trains. The general principle of reversibility transmitting-receiving antennas applies to the invention, that is to say in the case of a train-to-ground communication for which radiofrequency energy is emitted by the train antenna, captured by the radiating structure and propagated internally to this structure to a remote receiving equipment.

Claims (9)

Radio communication device (10, 20) comprising a continuous radiating structure (a) with a waveguide pierced by a first series of slots (12) forming a first section of radiating structure, inside which a microwave signal is injected, a directional antenna (c) and a transition means (b) of energy between the continuous radiating structure (a) and the directional antenna (c) characterized in that said transition means (b) and said antenna (c) are constituted respectively of a second and a third section of radiating structure respectively drilled with a second and third series of slots (14, 16), said first, second and third sections of radiating structure (a, b, c) being adjacent and consecutive. Radio communication device (10, 20) according to claim 1 characterized in that the large dimension of the first series of slots (12) is much smaller than the wavelength of the microwave signal propagating in the radiating structure. Radio communication device (10, 20) according to claim 1 characterized in that the large dimension of the third series of slots (16) is identical over the length of the third section (c) and close to but less than half the length of signal wave propagated in the radiating structure. Radio communication device (10, 20) according to any one of the preceding claims, characterized in that the large dimension of the second series of slots (14) progressively extends over the length of the second section (b), from the large dimension of the first series of slots (12) to a dimension which remains smaller than that of the third series of slots (16). Radio communication device (10, 20) according to one of the preceding claims, characterized in that the pitch between two consecutive slots (12, 14, 16) is constant and identical along the three sections of radiating structure (a, b, c). Radio communication device (10, 20) according to any one of the preceding claims, characterized in that the slots (12, 14, 16) are arranged transversely to the longitudinal direction of the radiating structure. Radio communication device (10, 20) according to any one of the preceding claims, characterized in that the length of the second section (b) is between 1 and 20 meters. Radio communication device (10, 20) according to one of the preceding claims, characterized in that the third series of slots (16) comprises up to ten slots. Radio communication device (10, 20) according to one of the preceding claims, characterized in that the third series of slots (16) is formed by the junction of the second series of slots (14) with the same series of slots ( 14 ') in that the large dimension decreases progressively from the half-wavelength of the propagated signal to a dimension much smaller than the wavelength of the propagated signal.

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