FR2916908A1 - WAVEGUIDE ANTENNA TRAINED ON A RAILWAY VEHICLE - Google Patents

Abstract

The antenna (4) has a fixed direction communication device arranged along channels of desired wavelength microwave signal. A rectangular section waveguide is provided with a large face that is drilled by a set of rectangular slits (5), whose large dimension (D) is lower than half-length of waves of the microwave signal, where spacing (E) between center of successive slits is near to the half-length of waves of the microwave signal propagated in the waveguide.

Description

The invention relates to a directional transmission / reception device for

  waveguide in general, and more particularly a bidirectional and symmetrical waveguide antenna.

  A transmitting / receiving antenna having a bi-directional radiation pattern makes it possible to communicate with transmitters / receivers in two preferred directions of space.

  Such an antenna finds its application for example along a road transport axis, railway, etc. Conventionally, the radio coverage is ensured by a network of transmitters disposed on the ground from time to time and raised by the use of pylons. A mobile moves between these transmitters on the ground.

  During its movement along the transport axis, this mobile is in communication with the transmitter which is immediately upstream. By moving away from this upstream transmitter, the signal received from this transmitter gradually decreases until it becomes unusable. However, simultaneously, the signal received from the downstream transmitter increases since its distance to the mobile decreases. A transfer of communication must be established so that the mobile transfers its communication, become inoperative, from the downstream transmitter to the upstream transmitter. This step is called a handover in a cellular communication network.

  In order to ensure this communication with the upstream station and at the same time this monitoring of the reception level of the signal transmitted by the downstream transmitter, the receiver must use two antennas pointing respectively towards the front and the rear pointing above the horizon towards antennas on pylons.

  In the case of a rail communication system, the fixed communication device is disposed on the ground or in a tunnel vault along this path.

  The fixed communication device may be omnidirectional, that is, which radiates or receives an electromagnetic signal in all directions of space. The communication device may also be directional, i.e., the signals have a high gain in one direction of space: the radiation pattern shows a given main lobe. A directional antenna having the same radiation pattern greatly optimizes communication with the latter device.

  In open propagation medium, the ground communication device will for example consist of directional transmitters / receivers. In closed propagation medium, for example in a metropolitan network, the ground communication device will for example be a waveguide.

  A ground waveguide device must operate at very high frequencies, higher than gigahertz (GHz), in order to lead to a mechanical construction of space compatible with its use at the track. The use of these microwaves makes it possible to ensure all the envisaged ground-train communications. These high frequencies correspond to wavelengths in the air of the order of 5 to 20 cm (1.5 GHz to 6 GHz and beyond). As a result, the waveguide at the track is often far-in terms of the number of wavelengths-of this antenna embarked on the train. This leads to far-field electromagnetic radiation for which radiation patterns can be calculated theoretically and measured experimentally.

  As the vehicle moves in two opposite directions along the transport axis (at 0 and 180, assuming that the track axis is set to 0), the transmitting / receiving antenna shall be able to communicate with the communication device to the lane in both directions.

  It is known from US 6,091,372 a communication system between a transmission line to the track and a transmission line on board a railway vehicle, type radiating cables. The principle developed in this document is similar to a coupling between radiating propagation lines, the transmission line embedded on the vehicle acting as an antenna being several meters long. At the frequencies operated by the radiating cables (generally around 500 MHz) and for the on-board radiated cable-cable radiating on the ground (or tunnel vault) of the order of one meter, the communication is essentially effected in the near electromagnetic field, or at a low number of wavelengths.

  A coupling between transmission lines favorably oriented relative to each other is clearly more important than coupling in opposite orientation. To receive a maximum signal and according to the orientation of the train relative to the track, it is therefore necessary to reverse by a manual switch the relative terminal positions of the generator / receiver and loads on the radiating cable embedded on the train.

  A disadvantage of this device is the length of the propagation lines necessary for this type of coupling, ie a train antenna a few meters long. Another disadvantage is the need to switch the orientation of the transmission lines according to the direction of traffic of the vehicles to increase the coupling and improve the communication between the vehicle and the device to the track.

  The device of the present invention relates to a receiving antenna and / or directional transmission on board a vehicle that can communicate reliably and stably with a fixed directional communication device disposed to the track, this antenna being simple design, compact and independent of the direction of traffic of the vehicle.

  According to the invention, the reception and / or transmission antenna mounted on a vehicle traveling along at least one path and communicating with a fixed communication device arranged along at least one pathway by means of of microwave signals of given wavelength, consists of a waveguide of rectangular cross section, a large face of which is pierced with rectangular slots, the large dimension of which is less than half the wavelength of said microwave signal, and in that the spacing between the center of two successive slits is close to half a wavelength of the microwave signal propagated in the waveguide.

  The receiving and / or transmitting antenna may also have one or more of the following characteristics, considered individually or in any technically possible combination: the number of slots is between five and ten, the emitting face of the waveguide of said antenna is vertical and is disposed parallel to an emitting face of the fixed communication device disposed along the path, -the axis of the waveguide of the antenna is parallel to the axis of the device of fixed communication, - the antenna is distant from the fixed continuous communication device of at least four wavelengths of said microwave signal propagated in the air, - the antenna is arranged on one side of the vehicle, - antenna is arranged on each side of the vehicle, the antenna is covered with a radome.

  Thanks to the invention, each slot of the antenna radiates a signal having two main lobes in two directions symmetrical with respect to a plane perpendicular to the plane of this slot. The waveguide is easy to manufacture, simple to use and reliable, and the dual directivity makes it possible to overcome the direction of traffic of the vehicle without special intervention. The propagation environment of the ground-train communication being characterized by intense reflections on the various surrounding obstacles (trains, walls, etc.), a directional antenna, focusing its radiation towards the waveguide at the track, limits the the impact of these multiple reflections on the quality of the link and thus makes it possible to increase the antenna distance embedded on the train-waveguide to the track exploitable in practice.

  In addition, from the waveguide to the track and to the antenna according to the invention, the amplitude of the signals is remarkably constant and does not require special smoothing of the signals. A particular focus, symmetrical in two particular orientations of the space, and only in these directions corresponding to the maximum radiation of the waveguide to the track is particularly favorable in order to optimize the ground-train transmission balances.

  Other objects, features and advantages of the invention will appear on reading the description which follows, description given in connection with the drawings in which: FIG. 1 is a schematic view of the communication device of a railway network, the FIG. 2 represents the radiation pattern measured in azimuth of the communication device, associated with a physical representation of the waveguide; FIG. 3 represents a perspective view of the waveguide antenna according to the invention; FIG. 4 represents a specific radiation pattern of the antenna according to the invention, FIG. 5 represents a vehicle equipped with an antenna according to the invention, changing direction and path by means of a loop between two lanes, Figure 6 shows a vehicle equipped with two antennas according to the invention, changing direction and lane by means of a siding. FIG. 1 is a schematic view of the communication device of a railway network, for example a metropolitan line. A directional communication device 1 allowing the control station of the line to communicate with the vehicles A, B traveling on the tracks 2, 3 (and vice versa, allowing the vehicle to communicate with the control station) is arranged by example between the two channels 2, 3. This information can be for example automatic control information of vehicles, information concerning the signaling of the line or video or audio information from the vehicle to the control station. They are contained in microwave signals symbolized by the solid arrows S1 and S2. Alternatively, the directional communication device may be disposed on each side of the track.

  The microwave signals are injected into the communication device 30 1, consisting of at least one waveguide. The waveguide is in the form of a hollow tube of rectangular section with four faces. It is arranged on the ground or tunnel vault on a non-emissive side.

  Each waveguide has two vertical and opposite emitting faces 1a and 1b, each face being pierced with a network of slots perpendicular to the axis of the guide, arranged on the large faces of the guide, the large dimension of which is much larger. small as the wavelength of the signals propagating in the waveguide. This characteristic makes it possible to take at each slot only a very small part of the energy of the propagated signal. Consequently, since the signal is only slightly attenuated by the emissions towards the outside of the guide through the slots, the waveguide at the track can have a length of several hundred meters.

  The communication device is bi-directional in the sense that the slots of the two faces can also receive the microwave signals from the antennas 4 mounted on board vehicles A, B.

  FIG. 2 shows the radiation pattern measured in azimuth of the waveguide 1 of the communication device, placed on the ground on a small non-emissive surface. The double grating waveguide 1 has a far-field directional radiation pattern which has two main lobes LI and L2 symmetrical about the axis of the guide (axis 0). The orientation of each lobe is at an angle alpha with the waveguide axis of about 30.

  The transmitting / receiving antenna on board the vehicle must, in order to communicate with such a waveguide, also be directional. It must thus have a radiation pattern having a directivity allowing the best possible transfer of energy between the waveguide to the track 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.

  For example, to effectively communicate with the waveguide having a main lobe directed at the waveguide axis, the antenna on the vehicle must also have a starting angle of 30 in order to receive and to effectively emit signals in this privileged direction of space.

  To overcome the direction of vehicle traffic on either of the two channels flanking the waveguide 1 to the track, the on-board antenna 4 must be symmetrical, that is to say that each emitting slot must radiate symmetrically with respect to a plane passing in its center and perpendicular to the longitudinal axis of the guide. In other words, and to use the example above, each slot must have a lobe with an orientation of 30 and a lobe with an orientation of 150 (180 minus 30).

  An antenna comprising these two characteristics (directional and symmetrical) is the transmitting and / or receiving antenna 4 according to the invention shown in FIG. 3. It consists of a rectangular section waveguide of which the one of the large faces of length b is pierced by seven slots 5 disposed perpendicularly to the longitudinal axis of the guide. The waveguide is closed at one end by a 50 ohm coaxial impedance load 7, and its other end is connected via a coaxial link 6 to a receiver (not shown). The large dimension D of the slots 5 is close to the half-wavelength of the microwave signal propagated in the waveguide but lower, so as not to take too much energy from the signal that propagates in the guide.

  The distance E separating the center from two successive slots 5 is close to half a wavelength of the signal propagated in the guide. In a waveguide of rectangular section, the relationship connecting the wavelength of the signal propagated in this guide denoted by g, the wavelength of the signal propagated in air denoted by λ and the cut-off wavelength of the waveguide (above which the waveguide no longer propagates energy) written at c is: (1 \ 2/1 '\ 2 + \ 2 In this section waveguide rectangular, the cut-off wavelength λ is equal to twice the large internal transverse dimension of the guide As an example, for a guide 10 cm long on the inner side, we obtain λ = 20 cm. a low cut-off frequency of 1.5 GHz Under this frequency, no signal propagates in the guide: we obtain with the preceding formula that g tends towards infinity, above this frequency the signals start at spread in the guide with low attenuation.

  Under the same conditions, at 2 GHz, ie a wavelength in the air λ of 15 cm, the wavelength λ g of the signals propagated in the guide, calculated from the preceding formula, will be 22.6 cm. Consider a network of a few regularly spaced slots and fed at one end. The energy communicated at this end propagates from one slot to another with a phase shift proportional to this guided wavelength λ. Part of this energy is radiated outside the guide and is propagated this time in the air with a wavelength λ. The combination of the radiation in the air of these powered and out-of-phase slots by the propagation of the signals in the metallic waveguide provides a radiation pattern having the required radiation departure angle. Lg the phase shift of one half Guided wavelength 2 provides the necessary double lobe of radiation and having identical starting angles for orientations 0 and 180. This phase shift is physically achieved by a spacing E between two successive slots 5 adjacent to the guided half-wavelength. For a smaller gap spacing E between slots, only one radiation lobe is present, similar to that obtained on waveguide 1 at the channel used. The polarization of the electromagnetic field obtained is linear, the radiated electric field has a main component oriented along the longitudinal axis of the antenna or the support guide.

  Each slot 5 formed in the waveguide has a small side sufficiently large so that the metal thickness of the waveguide is small vis-à-vis this dimension (if we consider a thickness of the guide metal 1 mm, we will take slits of 3-4 mm short side in order to neglect another waveguide effect introduced by the propagation of signals through a very thin slot, in the thickness of metal ).

  The antenna gain increases with the number of slots that combine the radiation. Under a minimum of five slots the gain is suboptimal but may be sufficient if there is a problem of severe antenna-train congestion. Above ten slots gain still slightly increases but the radiation lobe becomes narrow, concentrates the energy into a thin beam and there is a risk of getting out of the appropriate coverage area in case of vehicle suspension travel too much important (pitch, roll).

  Figure 4 shows the proper diagram of the antenna according to the invention. The longitudinal axis of the waveguide of the antenna is the axis at 0. Two lobes LA and LB appear clearly at about 30 and about 150, indicating that the wave is emitted with equivalent gain in these two favored directions.

  The emitting face of the waveguide of the antenna is disposed vertically and is arranged parallel to an emitting face of the fixed continuous communication device arranged along the path. Indeed, the waveguide of the communication device is arranged on a non-emissive face, the emitting faces being arranged vertically. The polarization of the radiation from the waveguide to the channel is identical to that of the receiving / transmitting antenna.

  The antenna is thus disposed on the vehicle so that the longitudinal axis of the waveguide of the antenna is parallel to the longitudinal axis of the waveguide at the track so that a lobe of the Antenna radiation and a lobe of the radiation pattern from the waveguide 1 to the channel should have an identical orientation.

  The antenna is mounted either under the vehicle body if the communication device 1 is placed on the ground between the two tracks 2, 3, or on the roof of the vehicle if the communication device 1 is arranged in a tunnel vault between the two channels 2, 3. The distance between the receiving and / or transmitting antenna and the communication device 1 is at least four wavelengths of the microwave signal propagated in the air because the radiation of the communication device to the antenna-and vice versa-is in the far field. The antenna train can be installed laterally, its waveguide volume integrated into the body, the plane of the slots covered with a radome flush with the surface of the body.

  The antenna is arranged on one side of the vehicle or on both sides of the vehicle. Indeed, when the vehicle arrives at one of the terminals of the one-way line, it moves on the parallel return line either by a wide-radius loop which links the ends of the two lanes, or by making a round-trip on a siding located upstream of the return lane.

  FIG. 5 illustrates the first case in point: the vehicle A is on the return lane 3 in the same configuration as on the outbound lane 2, that is to say the head-to-head cabin. The arrow on the vehicle symbolizes the path of the vehicle on the track. The waveguide 1 disposed at the channel transmits the signals along two directions represented by triangles LI and L2. For simplicity, a signal provided by the energy radiated from a few slits of the waveguide 1 only is shown in FIG. 5 but physically, this signal exists all along the waveguide 1. The antenna 4 mounted on the The vehicle has two LA and LB lobes.

  On the forward path 2, the antenna 4 communicates with the waveguide 1 to the channel because the signal transmitted (or received) by the waveguide 1 in the zone of the lobe LI has the same orientation as the zone of the lobe LB receiving (or transmitting) the antenna 4. On the return path 3, the antenna 4 communicates with the waveguide 1 to the channel because the signal transmitted (or received) by the guide of 1 in the L2 lobe area has the same orientation as the receiving lobe LA (or emission) area of the antenna 4. In this end-of-line configuration, only one antenna 4 is required on the side of the antenna. vehicle nearest the waveguide 1 to the track.

  FIG. 6 illustrates the second case in point: the vehicle A passes from the outbound lane 2 to the return lane 3 via a siding 20. It therefore presents itself in the configuration opposite to that of the outbound lane 2, it is to say the cab from head to tail of the vehicle (in this case, the vehicle usually has a cabin at each end which is not pictured here). Two antennas must be mounted on both sides of the vehicle, because the antenna 4, mounted on the vehicle so as to be closest to the waveguide 1 at the track when moving the vehicle on the outbound lane 2, then ends up on the furthest side of the waveguide 1 at the track when the vehicle is traveling on the return lane 3 by making a return trip on the siding 20.5

Claims (6)

claims   Receiving and / or transmitting antenna (4) mounted on a vehicle (A, B) traveling along at least one track (2, 3) and communicating with a fixed communication device (1) arranged on along at least one channel (2, 3) by means of microwave signals of a given wavelength, characterized in that it consists of a waveguide of rectangular section, a large face of which is pierced with slots (5) rectangular whose large dimension is less than half the wavelength of said microwave signal, and in that the spacing between the center of two successive slots (5) is close to half a wavelength the microwave signal (λg) propagated in the waveguide.   2. Antenna according to claim 1 characterized in that the number of slots (5) is between five and ten.   3. Antenna according to claim 1 characterized in that the emitting face of the waveguide (1) of said antenna (4) is vertical and is arranged parallel to an emitting face of the communication device (1) fixed arranged along the the way (2, 3).   4. Antenna according to claim 1 characterized in that the axis of the waveguide of the antenna (4) is parallel to the axis of the communication device (1) fixed.   5. Antenna according to claim 1 characterized in that the antenna (4) is spaced from the communication device (1) fixed at least four wavelengths of said microwave signal propagated in the air.   6. Antenna according to claim 1 characterized in that it is arranged on one side of the vehicle (A, B) .7 Antenna according to claim 1 characterized in that it is arranged on each side of the vehicle (A, B). 8. Antenna according to claim 1 characterized in that it is covered with a radome.