EP0520851B1 - Antenna combination for reception of signals from satellites and groundstations, particularly for the reception of digital audio broadcasting signals - Google Patents

Antenna combination for reception of signals from satellites and groundstations, particularly for the reception of digital audio broadcasting signals Download PDF

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Publication number
EP0520851B1
EP0520851B1 EP92401560A EP92401560A EP0520851B1 EP 0520851 B1 EP0520851 B1 EP 0520851B1 EP 92401560 A EP92401560 A EP 92401560A EP 92401560 A EP92401560 A EP 92401560A EP 0520851 B1 EP0520851 B1 EP 0520851B1
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EP
European Patent Office
Prior art keywords
antenna
skirt
reception
signals
radioelectric
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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EP92401560A
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German (de)
French (fr)
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EP0520851A1 (en
Inventor
Philippe Piolé
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Telediffusion de France ets Public de Diffusion
Orange SA
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Telediffusion de France ets Public de Diffusion
France Telecom SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00—Antenna arrays or systems
    • H01Q21/29—Combinations of different interacting antenna units for giving a desired directional characteristic
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q21/00—Antenna arrays or systems
    • H01Q21/24—Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
    • H01Q9/04—Resonant antennas
    • H01Q9/30—Resonant antennas with feed to end of elongated active element, e.g. unipole
    • H01Q9/40—Element having extended radiating surface

Definitions

  • the invention relates to an antenna for receiving signals transmitted simultaneously by land and satellite.
  • DAB Digital Audio Broad-casting
  • DAB Digital Audio Broad-casting
  • the broadcasting of high quality sound is however a particularly critical application in terms of performance and quality that the user is entitled to demand, in particular in the case of reception on board vehicles moving in urban environment, and it will be seen that, by its various characteristics, the antenna of the invention is particularly well suited to such use.
  • One of the aims of the present invention is to propose a mixed antenna, allowing the simultaneous reception of these two types of signals despite their very different reception conditions, and which is of simple and compact construction, in particular to allow its mounting on the roof of a vehicle, and which exhibits high radio performance.
  • the starting point of the invention is an antenna of the so-called “quarter-wave skirt” type, that is to say an antenna, to be placed above a radioelectric counterweight, comprising a closed vertical cylindrical tube in the upper part and a feed coaxial arranged inside the tube, the radiation diagram of this skirt antenna being an essentially omnidirectional diagram at low elevation angle.
  • Such an antenna is for example described in US-A-2,531,476. Given its diagram with a low elevation angle, such an antenna, which is moreover provided for land mobile radiocommunications in vertical polarization, does not allow to receive signals from satellites.
  • the basic idea of the invention is to associate with such a skirted antenna an antenna of the so-called “spiral” type, for example described in DE-B-1 056 673. But, taken as such, this antenna only allows reception in one mode, the axial mode.
  • the invention therefore proposes, in particular for the reception of digital sound broadcasting signals, to combine the skirt antenna (of the type described by the aforementioned US-A-2,531,476) according to the preamble of claim 1, which is suitable on reception of signals transmitted by earth stations, with: a helical antenna, arranged vertically above the skirt antenna and coaxially with respect thereto, the surface closing the upper part of the antenna tube at skirt constituting for the helical antenna a reflective plane whose distance from the helical antenna is defined to favor a hybrid mode of its own hybrid, partially axial and partially radial, by lowering the lobe of reception of the radiation diagram towards a angle of elevation conducive to reception of signals from satellites; and with coupling means connected to a point of attack of the cylindrical tube of the skirt antenna and to the base of the helical antenna, to combine the signals received by each of the two antennas and direct them towards the common coaxial line .
  • preamplifier means can also be provided, disposed between the output of the helical antenna and the input of the coupling means, and means forming a multi-pole filter with phase inversion on a narrow band, arranged between the output of the preamplifier means and the input of the coupling means.
  • the height of the skirt-propeller assembly above said radioelectric counterweight is adjustable.
  • the coaxial line is formed of a rigid or semi-rigid conductor, the assembly formed by the skirt, the spiral, the coupling means and the coaxial line being a self-supporting assembly supported by said conductor above said radioelectric counterweight, and this self-supporting assembly is surrounded by a radome connecting, at the bottom, to said radioelectric counterweight with interposition of sealing means.
  • the reference 1 designates a helical antenna, made up of a spiral conductive wire, which is combined with a skirted antenna 2 made up, in turn, of a conductive cylindrical tube, open at the bottom 3 and closed in the upper part 4 by a flat disc shorting the cylindrical tube at this location.
  • the skirt-propeller assembly is supported by a semi-rigid coaxial cable 5, self-supporting, on which is inserted an amplifier 6 and a phase shift filter 7.
  • the amplifier 6 and the filter 7 act on the signal picked up by the helical antenna 1, while the signal received by the skirt antenna 2 is picked up at an attack point 8 to be combined in a coupler 9 with the signal received by the helical antenna, previously amplified and filtered.
  • the output of the coupler is applied to a coaxial section 10 leading to a socket 11 intended to be connected to the receiver.
  • the assembly is for example mounted on the roof 12 of a vehicle, with a screw-nut system 13 making it possible to adjust the height of the skirt above this roof.
  • the assembly can advantageously be mounted inside a radome 14, for example made of polyester, bearing on the roof 12 of the vehicle with the interposition of a seal 15.
  • a radome 14 for example made of polyester
  • the assembly thus appears, above the vehicle, in the form of a cylinder having a height H of the order of 10 cm and a diameter D of the order of 3 cm (dimensions corresponding to a reception around 1.5 GHz).
  • Such an antenna consisting of a metallic conductor wound in a spiral excited at its base, is in itself well known.
  • the antenna can radiate in two essentially different modes: in the first mode, which corresponds to most of the known applications of helical antennas, the antenna essentially radiates with the diagram illustrated in dashed lines in Figure 2, that is to say with an axially directed radiation lobe ( ⁇ o being the axis of the helix) and with a circular polarization; on the other hand, in particular for very shortened antennas (that is to say whose pitch is very small compared to the diameter, a case in practice quite rare), the radiation diagram is an essentially radial diagram and with a polarization vertical rectilinear, as illustrated in solid line in FIG. 2 (in all cases, the diagram is omnidirectional in azimuth).
  • the lower end of the conductor that is to say the part of the conductor connecting the spiral proper to the outlet of the coaxial, is configured so as to act, in cooperation with the metal disc 4 of the skirt 2, in impedance adapter element, which avoids the need for any additional impedance adaptation component for this purpose.
  • One of the original features of the present invention consists in making the helical antenna radiate not on one or the other of these two typical modes, but according to an intermediate, hybrid mode, obtained by deforming the axial radiation diagram of so as to dig it in the axis and thus lower the main reception lobe towards a site angle suitable for reception of a signal emitted by a satellite.
  • FIG. 3 This deformed diagram corresponding to the proper hybrid mode is illustrated in FIG. 3 in solid lines (the dashed diagram corresponds to the pure axial mode): it can be seen that one can thus orient the axis A i of the main lobe towards a site angle a corresponding to the general direction of the satellites transmitting the signals that one wishes to receive, and this while preserving the circular polarization, typical of these emissions by satellite (of course, this distortion of the diagram leave it omnidirectional in azimuth).
  • Digging the diagram in the vertical axis A o corresponding to a direction in which there is no transmission to be received, provides additional gain in the direction A i of pointing to the satellite, of the order of 2 dB per compared to the isotropic.
  • the parameters which contribute to distort the diagram and make the mode of radiation hybrid are essentially: the size of the reflective disc 4, the position (distance) of the latter relative to the propeller, and the dimensions, diameter and pitch, of the turns of the propeller. It will also be noted that the presence of the reflective disc 4 advantageously makes it possible, by re-diffusion effect, to slightly increase the gain of the propeller.
  • skirt antenna 2 which is intended for the reception of the signals emitted by the earth stations.
  • Such an antenna is a section close to the quarter wave (in size and in radiation, a frequency of 1.5 GHz, typical of the diffusion of DAB signals, corresponding to a quarter-wave of 5 cm), supplied from the inside by an output of the coupler 9 at a point of attack 8 which corresponds to an impedance close to that of the coupler and of the complete antenna ( typically an impedance of 50 Q).
  • the point of attack is determined so that the real part of the admittance is equal to 50 Q, the reactive admittance being eliminated by the section of skirt located below the point of attack, which behaves like a stub correction.
  • the skirt is supported by the semi-rigid coaxial 5, which passes through the upper part 4 to supply the helical antenna.
  • the diameter of the skirt, the diameter of the coaxial 5 and the total height of the skirt are optimized to meet various mechanical and electrical constraints (the diameter of the skirt influencing in particular the bandwidth).
  • FIG. 4 illustrates the radiation diagram of the skirt, which has a gain of the order of 4 dB in a direction A 2 relative to the isotrope, for a low site angle ⁇ , typically of the order of 5 at 20 °.
  • the skirt antenna radiates in a vertical rectilinear polarization, unlike the circular polarization of the propeller.
  • skirt antenna it is necessary for the skirt antenna to be arranged above a metal surface, such as the metal roof of a vehicle. Otherwise, another configuration or non-metallic roof, there must be provided under the skirt a metal disc with a diameter of about 20 cm or other radioelectric counterweight playing a similar role.
  • FIG. 5 shows the overall diagram of the antenna according to the invention, which results from the combination of the two diagrams of FIGS. 3 (helix) and 4 (skirt): it can be seen that this resulting diagram has two preferred directions, one ⁇ 1 suitable for reception of signals transmitted by a satellite, with an angle of elevation a of the order of 60 ° and a circular polarization, the other A 2 adapted for the reception of signals transmitted by earth stations, with a very low ⁇ site angle (5 to 20 °) and vertical rectilinear polarization.
  • the diagram is of course omnidirectional in azimuth.
  • the signals received by the skirt 2 and by the propeller 1 are combined in a coupler 9 with low losses, ensuring sufficient insulation between its two input channels.
  • the adaptation is made to a typical value of 50 ohms.
  • the coupler 9 can be a commercially available 3 dB coupler or miniature “combiner” placed inside the skirt 2, this configuration allowing (as for the amplifier 6 and the filter 7) a noticeable gain in space while being neutral. from the radio point of view.
  • an amplifier 6 is provided upstream of the coupler, on the path of the helical antenna; the isolation provided by the coupler 9 makes it possible to put an amplifier stage on one of the input channels of the coupler, avoiding any feedback on the amplifier 6 which could generate parasitic modes.
  • the filter 7 is a component imposing a phase shift on a small frequency variation (typically, over a range of 3 MHz around a central frequency of 1.5 GHz), in order to implement the so-called COFDM reception technique ( Coded Orthogonal Frequency Division Multiplex: coded orthogonal frequency division multiplex), which is a spectral modulation and organization process proposed as an alternative to spread spectrum techniques: in fact, in the absence of any specific processing, the resource bandwidth for broadcasting a digital audio program would be prohibitive.
  • This COFDM method is based on the principle of dividing the initial frequency band into a large number of narrow-band subchannels, with respect to which the transmission does not introduce distortion.
  • the elementary signals are orthogonal to each other, which allows spectral overlap of subchannels providing high spectral efficiency by distributing the signal energy uniformly in the frequency band.
  • the delays introduced by the two different propagation paths mean that, overall, the transmission channel presents the characteristics of a Rayleigh channel, that is to say that its response to a pulse consists of a series of pseudo-pulses whose amplifier tude follows a Rayleigh law, which, in the absence of any particular measure, would create numerous errors in digital data transmission by signal weakening and distortion.
  • the COFDM process makes it possible, precisely, to overcome this drawback.
  • the filter 7 can be, instead of a long phase shift line, consisting of a multi-pole filter (typically, with 8 to 10 poles) or a surface wave filter. , whose effects will be similar.

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  • Variable-Direction Aerials And Aerial Arrays (AREA)
  • Radio Relay Systems (AREA)
  • Waveguide Aerials (AREA)

Description

L'invention concerne une antenne pour la réception de signaux émis simultanément par voie terrestre et par satellite.The invention relates to an antenna for receiving signals transmitted simultaneously by land and satellite.

Elle s'applique tout particulièrement à la réception des signaux de radiodiffusion sonore numérique ou DAB (Digital Audio Broad-casting)quoique, bien entendu, elle ne soit pas limitée à cette application et puisse être utilisée pour la réception d'autres types de signaux (radiodiffusion numérique d'informations autres que des programmes sonores, radiotéléphonie, etc.), ou même, par application du principe de réciprocité, pour l'émission de signaux radio.It is particularly applicable to the reception of digital sound broadcasting signals or DAB (Digital Audio Broad-casting) although, of course, it is not limited to this application and can be used for the reception of other types of signals. (digital broadcasting of information other than sound programs, radiotelephony, etc.), or even, by application of the principle of reciprocity, for the emission of radio signals.

La diffusion d'un son de haute qualité constitue cependant une application particulièrement critique sur le plan des performances et de la qualité que l'utilisateur est en droit d'exiger, notamment dans le cas d'une réception à bord de véhicules se déplaçant en milieu urbain, et l'on verra que, de par ses diverses caractéristiques, l'antenne de l'invention est particulièrement bien adaptée à un tel usage.The broadcasting of high quality sound is however a particularly critical application in terms of performance and quality that the user is entitled to demand, in particular in the case of reception on board vehicles moving in urban environment, and it will be seen that, by its various characteristics, the antenna of the invention is particularly well suited to such use.

Pour pallier la présence des obstacles naturels venant occulter la réception, notamment en milieu urbain, on est en effet amené à prévoir, pour un même programme, une diffusion simultanée à la fois par un satellite et par une pluralité de stations terrestres.To overcome the presence of natural obstacles obscuring reception, especially in urban areas, it is indeed necessary to provide, for the same program, simultaneous broadcasting both by a satellite and by a plurality of earth stations.

Or, les conditions de réception des signaux émis selon ces deux modes sont tout à fait différentes, tant en ce qui concerne le diagramme de rayonnement nécessaire, que la largeur de bande et le type de polarisation.However, the conditions of reception of the signals transmitted according to these two modes are quite different, as regards the necessary radiation diagram, as the bandwidth and the type of polarization.

Plus précisément, dans le cas des signaux émis par les stations terrestres, il est nécessaire de disposer d'un diagramme de rayonnement présentant un gain maximal (direction du lobe principal) pour à un angle de site faible, de l'ordre de 5 à 20°, avec une large bande passante et sous une polarisation verticale, tandis que, dans le cas des signaux émis par le satellite, l'angle de site doit être beaucoup plus élevé (de l'ordre de 60°, typiquement), et la polarisation correspondante doit être une polarisation circulaire ; dans l'un et l'autre cas, le diagramme doit être omnidirectionnel en azimut.More precisely, in the case of signals transmitted by earth stations, it is necessary to have a radiation diagram having a maximum gain (direction of the main lobe) for at a low elevation angle, of the order of 5 to 20 °, with a wide passband and with vertical polarization, while, in the case of signals transmitted by the satellite, the elevation angle must be much higher (of the order of 60 °, typically), and the corresponding polarization must be a circular polarization; in both cases, the diagram must be omnidirectional in azimuth.

L'un des buts de la présente invention est de proposer une antenne mixte, permettant la réception simultanée de ces deux types de signaux malgré leurs conditions de réception très différentes, et qui soit de construction simple et compacte, notamment pour permettre son montage sur le toit d'un véhicule, et qui présente des performances radioélectriques élevées.One of the aims of the present invention is to propose a mixed antenna, allowing the simultaneous reception of these two types of signals despite their very different reception conditions, and which is of simple and compact construction, in particular to allow its mounting on the roof of a vehicle, and which exhibits high radio performance.

Le point de départ de l'invention est une antenne du type dit « à jupe quart d'onde », c'est-à-dire une antenne, à disposer au-dessus d'un contrepoids radioélectrique, comportant un tube cylindrique vertical fermé en partie supérieure et un coaxial d'alimentation disposé à l'intérieur du tube, le diagramme de rayonnement de cette antenne à jupe étant un diagramme essentiellement omnidirectionnel à faible angle de site.The starting point of the invention is an antenna of the so-called “quarter-wave skirt” type, that is to say an antenna, to be placed above a radioelectric counterweight, comprising a closed vertical cylindrical tube in the upper part and a feed coaxial arranged inside the tube, the radiation diagram of this skirt antenna being an essentially omnidirectional diagram at low elevation angle.

Une telle antenne est par exemple décrite dans le US-A-2 531 476. Compte tenu de son diagramme à faible angle de site, une telle antenne, qui est d'ailleurs prévue pour des radiocommunications mobiles terrestres en polarisation verticale, ne permet pas de recevoir des signaux en provenance de satellites.Such an antenna is for example described in US-A-2,531,476. Given its diagram with a low elevation angle, such an antenna, which is moreover provided for land mobile radiocommunications in vertical polarization, does not allow to receive signals from satellites.

L'idée de base de l'invention est d'associer à une telle antenne à jupe une antenne du type dit « spirale », par exemple décrite dans le DE-B-1 056 673. Mais, prise en tant que telle, cette antenne ne permet la réception que dans un seul mode, le mode axial.The basic idea of the invention is to associate with such a skirted antenna an antenna of the so-called “spiral” type, for example described in DE-B-1 056 673. But, taken as such, this antenna only allows reception in one mode, the axial mode.

L'invention propose donc, notamment pour la réception de signaux de radiodiffusion sonore numérique, de combiner l'antenne à jupe (du type décrit par le US-A-2 531 476 précité) selon le préambule de la revendication 1, qui est propice à une réception de signaux émis par des stations terrestres, avec : une antenne hélicoïdale, disposée verticalement au-dessus de l'antenne à jupe et coaxialement par rapport à celle-ci, la surface fermant la partie supérieure du tube de l'antenne à jupe constituant pour l'antenne hélicoïdale un plan réflecteur dont la distance à l'antenne hélicoïdale est définie pour privilégier un mode de rayonnement hybride propre de cette dernière, partiellement axial et partiellement radial, en abaissant le lobe de réception du diagramme de rayonnement vers un angle de site propice à une réception de signaux émis par des satellites ; et avec des moyens de couplage reliés à un point d'attaque du tube cylindrique de l'antenne à jupe et à la base de l'antenne hélicoïdale, pour combiner les signaux reçus par chacune des deux antennes et les diriger vers la ligne coaxiale commune.The invention therefore proposes, in particular for the reception of digital sound broadcasting signals, to combine the skirt antenna (of the type described by the aforementioned US-A-2,531,476) according to the preamble of claim 1, which is suitable on reception of signals transmitted by earth stations, with: a helical antenna, arranged vertically above the skirt antenna and coaxially with respect thereto, the surface closing the upper part of the antenna tube at skirt constituting for the helical antenna a reflective plane whose distance from the helical antenna is defined to favor a hybrid mode of its own hybrid, partially axial and partially radial, by lowering the lobe of reception of the radiation diagram towards a angle of elevation conducive to reception of signals from satellites; and with coupling means connected to a point of attack of the cylindrical tube of the skirt antenna and to the base of the helical antenna, to combine the signals received by each of the two antennas and direct them towards the common coaxial line .

Il peut en outre être avantageusement prévu des moyens préamplificateurs, disposés entre la sortie de l'antenne hélicoïdale et l'entrée des moyens de couplage, et des moyens formant filtre multi-pôles à inversion de phase sur bande étroite, disposés entre la sortie des moyens préamplificateurs et l'entrée des moyens de couplage.Advantageously, preamplifier means can also be provided, disposed between the output of the helical antenna and the input of the coupling means, and means forming a multi-pole filter with phase inversion on a narrow band, arranged between the output of the preamplifier means and the input of the coupling means.

De préférence, la hauteur de l'ensemble jupe-hélice au-dessus dudit contrepoids radioélectrique est réglable.Preferably, the height of the skirt-propeller assembly above said radioelectric counterweight is adjustable.

De préférence également, la ligne coaxiale est formée d'un conducteur rigide ou semi-rigide, l'ensemble formé par la jupe, la spirale, les moyens de couplage et la ligne coaxiale étant un ensemble autoporteur soutenu par ledit conducteur au-dessus dudit contrepoids radioélectrique, et cet ensemble autoporteur est entouré par un radôme se raccordant, en partie inférieure, audit contrepoids radioélectrique avec interposition de moyens d'étanchéité.Also preferably, the coaxial line is formed of a rigid or semi-rigid conductor, the assembly formed by the skirt, the spiral, the coupling means and the coaxial line being a self-supporting assembly supported by said conductor above said radioelectric counterweight, and this self-supporting assembly is surrounded by a radome connecting, at the bottom, to said radioelectric counterweight with interposition of sealing means.

On va maintenant décrire un exemple de réalisation de l'invention, en référence aux dessins annexés.

  • La figure 1 est une vue schématique, en perspective cavalière, de l'antenne de l'invention.
  • Les figures 2 et 3 illustrent la manière dont est modifié le diagramme propre de l'antenne hélicoïdale, destinée à la réception du signal émis par le satellite.
  • La figure 4 illustre le diagramme propre de l'antenne à jupe, destinée à la réception du signal émis par les stations terrestres.
  • La figure 5 illustre le diagramme global de l'antenne.
We will now describe an embodiment of the invention, with reference to the accompanying drawings.
  • Figure 1 is a schematic view, in perspec rider, of the antenna of the invention.
  • Figures 2 and 3 illustrate how the proper diagram of the helical antenna is modified, intended for the reception of the signal transmitted by the satellite.
  • FIG. 4 illustrates the proper diagram of the skirt antenna, intended for the reception of the signal transmitted by the earth stations.
  • Figure 5 illustrates the overall antenna diagram.

Sur la figure 1, la référence 1 désigne une antenne hélicoïdale, constituée d'un fil conducteur spiralé, que l'on combine à une antenne à jupe 2 constituée, quant à elle, d'un tube cylindrique conducteur, ouvert en partie inférieure 3 et fermé en partie supérieure 4 par un disque plan venant court-circuiter le tube cylindrique en cet endroit.In FIG. 1, the reference 1 designates a helical antenna, made up of a spiral conductive wire, which is combined with a skirted antenna 2 made up, in turn, of a conductive cylindrical tube, open at the bottom 3 and closed in the upper part 4 by a flat disc shorting the cylindrical tube at this location.

L'ensemble jupe-hélice est supporté par un câble coaxial semi-rigide 5, autoporteur, sur lequel est inséré un amplificateur 6 et un filtre déphaseur 7. L'amplificateur 6 et le filtre 7 agissent sur le signal capté par l'antenne hélicoïdale 1, tandis que le signal reçu par l'antenne à jupe 2 est capté en un point d'attaque 8 pour être combiné dans un coupleur9 au signal reçu par l'antenne hélicoïdale, préalablement amplifié et filtré. La sortie du coupleur est appliquée à une section de coaxial 10 débouchant sur une prise 11 destinée à être raccordée au récepteur. L'ensemble est par exemple monté sur le toit 12 d'un véhicule, avec un système à vis-écrou 13 permettant de régler la hauteur de la jupe au-dessus de ce toit.The skirt-propeller assembly is supported by a semi-rigid coaxial cable 5, self-supporting, on which is inserted an amplifier 6 and a phase shift filter 7. The amplifier 6 and the filter 7 act on the signal picked up by the helical antenna 1, while the signal received by the skirt antenna 2 is picked up at an attack point 8 to be combined in a coupler 9 with the signal received by the helical antenna, previously amplified and filtered. The output of the coupler is applied to a coaxial section 10 leading to a socket 11 intended to be connected to the receiver. The assembly is for example mounted on the roof 12 of a vehicle, with a screw-nut system 13 making it possible to adjust the height of the skirt above this roof.

L'ensemble peut être avantageusement monté à l'intérieur d'un radôme 14, par exemple en polyester, venant en appui sur le toit 12 du véhicule avec interposition d'un joint d'étanchéité 15.The assembly can advantageously be mounted inside a radome 14, for example made of polyester, bearing on the roof 12 of the vehicle with the interposition of a seal 15.

L'ensemble se présente ainsi, au-dessus du véhicule, sous la forme d'un cylindre ayant une hauteur H de l'ordre de 10 cm et un diamètre D de l'ordre de 3 cm (dimensions correspondant à une réception autour de 1,5 GHz).The assembly thus appears, above the vehicle, in the form of a cylinder having a height H of the order of 10 cm and a diameter D of the order of 3 cm (dimensions corresponding to a reception around 1.5 GHz).

On va maintenant expliciter les divers composants de cette antenne.We will now explain the various components of this antenna.

On va tout d'abord décrire l'antenne hélicoïdale 1, qui est destinée à la réception des signaux émis par satellite.We will first describe the helical antenna 1, which is intended for the reception of signals transmitted by satellite.

Une telle antenne, constituée d'un conducteur métallique enroulé en spirale excité à sa base, est en elle-même bien connue. Cependant, selon le pas et le diamètre de l'hélice, l'antenne peut rayonner selon deux modes essentiellement différents: dans le premier mode, qui correspond à la majeure partie des applications connues des antennes hélicoïdales, l'antenne rayonne essentiellement avec le diagramme illustré en tiretés figure 2, c'est-à-dire avec un lobe de rayonnement dirigé axialement (Δo étant l'axe de l'hélice) et avec une polarisation circulaire ; en revanche, notamment pour des antennes très raccourcies (c'est-à-dire dont le pas est très faible en regard du diamètre, cas de figure en pratique assez rare), le diagramme de rayonnement est un diagramme essentiellement radial et avec une polarisation rectiligne verticale, comme illustré en trait plein sur la figure 2 (dans tous les cas, le diagramme est omnidirectionnel en azimut).Such an antenna, consisting of a metallic conductor wound in a spiral excited at its base, is in itself well known. However, depending on the pitch and the diameter of the helix, the antenna can radiate in two essentially different modes: in the first mode, which corresponds to most of the known applications of helical antennas, the antenna essentially radiates with the diagram illustrated in dashed lines in Figure 2, that is to say with an axially directed radiation lobe (Δ o being the axis of the helix) and with a circular polarization; on the other hand, in particular for very shortened antennas (that is to say whose pitch is very small compared to the diameter, a case in practice quite rare), the radiation diagram is an essentially radial diagram and with a polarization vertical rectilinear, as illustrated in solid line in FIG. 2 (in all cases, the diagram is omnidirectional in azimuth).

Par ailleurs, l'extrémité inférieure du conducteur, c'est-à-dire la partie de conducteur reliant la spirale proprement dite au débouché du coaxial, est configurée de manière à agir, en coopération avec le disque métallique 4 de lajupe 2, en élément adaptateurd'impédance, ce qui évite le recours à tout composant additionnel d'adaptation d'impédance à cette fin.Furthermore, the lower end of the conductor, that is to say the part of the conductor connecting the spiral proper to the outlet of the coaxial, is configured so as to act, in cooperation with the metal disc 4 of the skirt 2, in impedance adapter element, which avoids the need for any additional impedance adaptation component for this purpose.

L'une des originalités de la présente invention consiste à faire rayonner l'antenne hélicoïdale non pas sur l'un ou l'autre de ces deux modes typiques, mais selon un mode intermédiaire, hybride, obtenu en déformant le diagramme de rayonnement axial de manière à le creuser dans l'axe et abaisser ainsi le lobe principal de réception vers un angle de site propice à une réception d'un signal émis par un satellite.One of the original features of the present invention consists in making the helical antenna radiate not on one or the other of these two typical modes, but according to an intermediate, hybrid mode, obtained by deforming the axial radiation diagram of so as to dig it in the axis and thus lower the main reception lobe towards a site angle suitable for reception of a signal emitted by a satellite.

Ce diagramme déformé correspondant au mode hybride propre est illustré figure 3 en trait plein (le diagramme en tiretés correspond au mode axial pur): on voit que l'on peut ainsi orienter l'axe Ai du lobe principal vers un angle de site a correspondant à la direction générale des satellites émettant les signaux que l'on souhaite recevoir, et ceci tout en conservant la polarisation circulaire, typique de ces émissions par satellite (bien entendu, cette déformation du diagramme laisser celui-ci omnidirectionnel en azimut). Le creusement du diagramme dans l'axe vertical Ao, correspondant à une direction dans laquelle on ne trouve aucune émission à recevoir, procure un surcroît de gain dans la direction Ai de pointage vers le satellite, de l'ordre de 2 dB par rapport à l'isotrope.This deformed diagram corresponding to the proper hybrid mode is illustrated in FIG. 3 in solid lines (the dashed diagram corresponds to the pure axial mode): it can be seen that one can thus orient the axis A i of the main lobe towards a site angle a corresponding to the general direction of the satellites transmitting the signals that one wishes to receive, and this while preserving the circular polarization, typical of these emissions by satellite (of course, this distortion of the diagram leave it omnidirectional in azimuth). Digging the diagram in the vertical axis A o , corresponding to a direction in which there is no transmission to be received, provides additional gain in the direction A i of pointing to the satellite, of the order of 2 dB per compared to the isotropic.

De façon caractéristique de l'invention, cette déformation du diagramme pour faire rayonner l'antenne en mode hybride est obtenue grâce à la présence du disque plat4 court-circuitant la jupe 2 en partie supérieure et qui, dans la configuration proposée par l'invention, constitue pour l'hélice un plan réflecteur permettant la modification du diagramme dans le sens souhaité. On notera ici incidemment que le toit métallique 12, disposé relativement loin en arrière de l'hélice, est pratiquement sans effet sur le diagramme de cette dernière.Characteristically of the invention, this deformation of the diagram for radiating the antenna in hybrid mode is obtained thanks to the presence of the flat disc 4 shorting the skirt 2 in the upper part and which, in the configuration proposed by the invention , constitutes for the propeller a reflective plane allowing the modification of the diagram in the desired direction. It will be noted here incidentally that the metal roof 12, disposed relatively far behind the propeller, has practically no effect on the diagram of the latter.

Les paramètres qui contribuent à déformer le diagramme et rendre hybride le mode de rayonnement sont essentiellement : la dimension du disque réflecteur 4, la position (éloignement) de ce dernier rapport à l'hélice, et les dimensions, diamètre et pas, des spires de l'hélice. On notera en outre que la présence du disque réflecteur 4 permet avantageusement, par effet de rediffusion, d'augmenter légèrement le gain de l'hélice.The parameters which contribute to distort the diagram and make the mode of radiation hybrid are essentially: the size of the reflective disc 4, the position (distance) of the latter relative to the propeller, and the dimensions, diameter and pitch, of the turns of the propeller. It will also be noted that the presence of the reflective disc 4 advantageously makes it possible, by re-diffusion effect, to slightly increase the gain of the propeller.

On va maintenant décrire l'antenne à jupe 2, qui est destinée à la réception des signaux émis par les stations terrestres.We will now describe the skirt antenna 2, which is intended for the reception of the signals emitted by the earth stations.

Le fonctionnement d'une telle antenne, en tant que telle, est connu : il s'agit d'un tronçon proche du quart d'onde (en dimension et en rayonnement, une fréquence de 1,5 GHz, typique de la diffusion de signaux DAB, correspondant à un quart d'onde de 5 cm), alimenté de l'intérieur par une sortie du coupleur 9 en un point d'attaque 8 qui correspond à une impédance proche de celle du coupleur et de l'antenne complète (typiquement, une impédance de 50 Q). Le point d'attaque est déterminé de manière que la partie réelle de l'admittance soit égale à 50 Q, l'admittance réactive étant éliminée par le tronçon de jupe situé au-dessous du point d'attaque, qui se comporte comme un stub de correction.The operation of such an antenna, as such, is known: it is a section close to the quarter wave (in size and in radiation, a frequency of 1.5 GHz, typical of the diffusion of DAB signals, corresponding to a quarter-wave of 5 cm), supplied from the inside by an output of the coupler 9 at a point of attack 8 which corresponds to an impedance close to that of the coupler and of the complete antenna ( typically an impedance of 50 Q). The point of attack is determined so that the real part of the admittance is equal to 50 Q, the reactive admittance being eliminated by the section of skirt located below the point of attack, which behaves like a stub correction.

La jupe est supportée par le coaxial semi-rigide 5, qui traverse la partie supérieure 4 pour alimenter l'antenne hélicoïdale. Le diamètre de la jupe, le diamètre du coaxial 5 et la hauteur totale de la jupe sont optimisés pour répondre aux diverses contraintes mécaniques et électriques (le diamètre de la jupe influant notamment sur la bande passante).The skirt is supported by the semi-rigid coaxial 5, which passes through the upper part 4 to supply the helical antenna. The diameter of the skirt, the diameter of the coaxial 5 and the total height of the skirt are optimized to meet various mechanical and electrical constraints (the diameter of the skirt influencing in particular the bandwidth).

L'influence de l'antenne hélicoïdale sur l'antenne à jupe est faible (mais le contraire n'est pas vrai, comme on l'a vu plus haut), car l'hélice et la jupe ne sont pas reliées électriquement entre elles (le coupleur 9 est un coupleur isolant). Un léger effet de capacité terminale est cependant possible, ce qui implique que l'ajustement de la jupe soit fait en présence de l'hélice.The influence of the helical antenna on the skirt antenna is low (but the opposite is not true, as we saw above), because the propeller and the skirt are not electrically connected to each other (the coupler 9 is an insulating coupler). A slight effect of terminal capacity is however possible, which implies that the adjustment of the skirt is made in the presence of the propeller.

La figure 4 illustre le diagramme de rayonnement de la jupe, qui présente un gain de l'ordre de 4 dB dans une direction A2 par rapport à l'isotrope, pour un angle de site β faible, typiquement de l'ordre de 5 à 20°. L'antenne à jupe rayonne selon une polarisation rectiligne verticale, à la différence de la polarisation circulaire de l'hélice.FIG. 4 illustrates the radiation diagram of the skirt, which has a gain of the order of 4 dB in a direction A 2 relative to the isotrope, for a low site angle β, typically of the order of 5 at 20 °. The skirt antenna radiates in a vertical rectilinear polarization, unlike the circular polarization of the propeller.

On notera que, pour obtenir un tel diagramme, il est nécessaire que l'antenne à jupe soit disposée au-dessus d'une surface métallique, telle que le toit métallique d'un véhicule. Dans le cas contraire, autre configuration ou toit non métallique, il doit être prévu sous la jupe un disque métallique avec un diamètre de l'ordre de 20 cm ou autre contrepoids radioélectrique jouant un rôle semblable.It will be noted that, to obtain such a diagram, it is necessary for the skirt antenna to be arranged above a metal surface, such as the metal roof of a vehicle. Otherwise, another configuration or non-metallic roof, there must be provided under the skirt a metal disc with a diameter of about 20 cm or other radioelectric counterweight playing a similar role.

La figure 5 montre le diagramme global de l'antenne selon l'invention, qui résulte de la combinaison des deux diagrammes des figures 3 (hélice) et 4 (jupe) : on voit que ce diagramme résultant présente deux directions privilégiées, l'une Δ1 adaptée à une réception de signaux émis par un satellite, avec un angle de site a de l'ordre de 60° et une polarisation circulaire, l'autre A2 adaptée à la réception de signaux émis par des stations terrestres, avec un très faible angle de site β (5 à 20°) et une polarisation rectiligne verticale. Le diagramme est bien entendu omnidirectionnel en azimut.FIG. 5 shows the overall diagram of the antenna according to the invention, which results from the combination of the two diagrams of FIGS. 3 (helix) and 4 (skirt): it can be seen that this resulting diagram has two preferred directions, one Δ 1 suitable for reception of signals transmitted by a satellite, with an angle of elevation a of the order of 60 ° and a circular polarization, the other A 2 adapted for the reception of signals transmitted by earth stations, with a very low β site angle (5 to 20 °) and vertical rectilinear polarization. The diagram is of course omnidirectional in azimuth.

On va maintenant décrire les circuits proprement électriques de l'antenne.We will now describe the properly electrical circuits of the antenna.

Les signaux reçus par la jupe 2 et par l'hélice 1 sont combinés dans un coupleur 9 à faibles pertes, assurant une isolation suffisante entre ses deux voies d'entrée. L'adaptation est faite sur une valeur typique de 50 ohms. Le coupleur 9 peut être un coupleur 3 dB ou « combineur » miniature du commerce disposé à l'intérieur de la jupe 2, cette configuration permettant (comme pour l'amplificateur 6 et le filtre 7) un gain de place notable tout en étant neutre du point de vue radioélectrique.The signals received by the skirt 2 and by the propeller 1 are combined in a coupler 9 with low losses, ensuring sufficient insulation between its two input channels. The adaptation is made to a typical value of 50 ohms. The coupler 9 can be a commercially available 3 dB coupler or miniature “combiner” placed inside the skirt 2, this configuration allowing (as for the amplifier 6 and the filter 7) a noticeable gain in space while being neutral. from the radio point of view.

On peut avantageusement prévoir, également à l'intérieur de la jupe, un amplificateur miniature (non représenté) en sortie du coupleur 9, amplificateur dont l'alimentation serait assurée par le câble coaxial et qui permettrait de remonter le niveau du signal haute fréquence de 10 à 20 dB environ, améliorant ainsi de façon notable le rapport signal/bruit par une amplification au niveau de l'antenne, en amont du câble de liaison au récepteur (antenne « active »).One can advantageously provide, also inside the skirt, a miniature amplifier (not shown) at the output of the coupler 9, amplifier whose power would be provided by the coaxial cable and which would raise the level of the high frequency signal of 10 to 20 dB approximately, thus significantly improving the signal / noise ratio by amplification at the antenna, upstream of the connection cable to the receiver (“active” antenna).

De préférence également, pour relever le niveau du signal satellite et compenser la perte d'insertion due au filtre 7, il est prévu en amont du coupleur, sur la voie de l'antenne hélicoïdale, un amplificateur 6 ; l'isolement procuré par le coupleur 9 permet en effet de mettre un étage amplificateur sur l'une des voies d'entrée du coupleur, en évitant toute rétroaction sur l'amplificateur 6 qui pourrait engendrer des modes parasites.Preferably also, to raise the level of the satellite signal and compensate for the insertion loss due to the filter 7, an amplifier 6 is provided upstream of the coupler, on the path of the helical antenna; the isolation provided by the coupler 9 makes it possible to put an amplifier stage on one of the input channels of the coupler, avoiding any feedback on the amplifier 6 which could generate parasitic modes.

Le filtre 7 est un composant imposant un déphasage de sur une variation de fréquence faible (typiquement, sur une plage de 3 MHz autour d'une fréquence centrale de 1,5 GHz), afin de mettre en oeuvre la technique de réception dite COFDM (Coded Orthogonal Frequency Division Multiplex : multiplex orthogonal codé à division de fréquence), qui est un procédé de modulation et d'organisation spectrale proposé comme alternative aux techniques d'étalement de spectre: en effet, en l'absence de traitement particulier, la ressource en largeur de bande pour la diffusion d'un programme audionumérique serait prohibitive. Cette méthode COFDM repose sur le principe d'une division de la bande de fréquence initiale en un grand nombre de sous-canaux à bande étroite, vis-à-vis desquels la transmission n'introduit pas de distorsion. Les signaux élémentaires sont orthogonaux entre eux, ce qui autorise un inter-recouvrement spectral de sous-canaux procurant une grande efficacité spectrale en répartissant de façon uniforme l'énergie du signal dans la bande de fréquences.The filter 7 is a component imposing a phase shift on a small frequency variation (typically, over a range of 3 MHz around a central frequency of 1.5 GHz), in order to implement the so-called COFDM reception technique ( Coded Orthogonal Frequency Division Multiplex: coded orthogonal frequency division multiplex), which is a spectral modulation and organization process proposed as an alternative to spread spectrum techniques: in fact, in the absence of any specific processing, the resource bandwidth for broadcasting a digital audio program would be prohibitive. This COFDM method is based on the principle of dividing the initial frequency band into a large number of narrow-band subchannels, with respect to which the transmission does not introduce distortion. The elementary signals are orthogonal to each other, which allows spectral overlap of subchannels providing high spectral efficiency by distributing the signal energy uniformly in the frequency band.

En cas de réception simultanée des signaux par les deux antennes (hélice et jupe), les retards introduits par les deux trajets différents de propagation (depuis la station terrestre et depuis le satellite) font en sorte que, globalement, le canal de transmission présente les caractéristiques d'un canal de Rayleigh, c'est-à-dire que sa réponse à une impulsion est constituée d'une suite de pseudo-impulsions dont l'amplitude suit une loi de Rayleigh, ce qui, en l'absence de toute mesure particulière, créerait de nombreuses erreurs de transmission de données numériques par affaiblissement et distorsion du signal. Le procédé COFDM permet, précisément, de pallier cet inconvénient.In the event of simultaneous reception of signals by the two antennas (propeller and skirt), the delays introduced by the two different propagation paths (from the earth station and from the satellite) mean that, overall, the transmission channel presents the characteristics of a Rayleigh channel, that is to say that its response to a pulse consists of a series of pseudo-pulses whose amplifier tude follows a Rayleigh law, which, in the absence of any particular measure, would create numerous errors in digital data transmission by signal weakening and distortion. The COFDM process makes it possible, precisely, to overcome this drawback.

Pour conserver la compacité d'ensemble du système, le filtre 7 peut être, au lieu d'une ligne de déphasage longue, constitué d'un filtre multipôle (typiquement, à 8 à 10 pôles) ou d'un filtre à ondes de surface, dont les effets seront semblables.To maintain the overall compactness of the system, the filter 7 can be, instead of a long phase shift line, consisting of a multi-pole filter (typically, with 8 to 10 poles) or a surface wave filter. , whose effects will be similar.

Claims (6)

1. An antenna, comprising:
- a quarter-wave skirt antenna arranged above a radioelectric counterpoise (12), the said skirt antenna comprising a vertical cylindrical tube (2), closed by a metal surface at the upper end, and a co-axial feed line (10) arranged inside the tube, the radiation pattern of the said skirt antenna being a substantially omnidirectional pattern having a small angle of elevation in accordance with vertical polarisation,

characterised in that, in particular for the reception of digital audio broadcasting signals, the said skirt antenna, which favours the receptions of signals transmitted by ground stations, is combined with:
- a helical antenna (1) arranged vertically above the skirt antenna and co-axially therewith, the surface (4) closing the upper portion of the tube of the skirt antenna constituting a reflective plane for the helical antenna, the distance between the said reflective plane and the helical antenna being determined so as to favour a mode of hybrid radiation, partly axial and partly radial, peculiar to the latter by lowering the reception lobe of the radiation pattern towards an angle of elevation favouring reception of signals transmitted by satellites, and
- coupling means (9), connected to a drive point of the cylindrical tube of the skirt antenna and to the base of the helical antenna, for combining the signals received by each of the two antennae and directing them towards the common co-axial line.
2. The antenna accoraing to claim 1, wherein pre- amplification means (6) are also provided which are arranged between the output of the helical antenna and the input of the coupling means.
3. The antenna according to claim 2, wherein means are also provided which form a multipole fitter for phase reversal on a narrow band (7) and are arranged between the output of the preampli- fication means and the input of the coupling means.
4. The antenna according to claim 1, wherein means (13) are also provided for adjusting the height of the skirt-helix assembly above the said radioelectric counterpoise (12).
5. The antenna according to claim 1, wherein the co-axial line (5) is formed by a rigid or semi-rigid conductor, the assembly formed by the skirt, the helix, the coupling means and the co-axial line being a self-supporting assembly carried by the said conductor above the said radioelectric counterpoise (12).
6. The antenna according to claim 5, wherein the said self-supporting assembly is surrounded by a radome ( 14), the lower end of which is connected to the said radioelectric counterpoise with interposition of sealing means (15).
EP92401560A 1991-06-28 1992-06-05 Antenna combination for reception of signals from satellites and groundstations, particularly for the reception of digital audio broadcasting signals Expired - Lifetime EP0520851B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR9108089A FR2678437B1 (en) 1991-06-28 1991-06-28 MIXED ANTENNA FOR RECEIVING SIGNALS TRANSMITTED SIMULTANEOUSLY BY SATELLITE AND EARTH STATIONS, PARTICULARLY FOR RECEIVING DIGITAL SOUND BROADCASTING SIGNALS.
FR9108089 1991-06-28

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EP0520851B1 true EP0520851B1 (en) 1995-11-29

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DE69206333D1 (en) 1996-01-11
US5317327A (en) 1994-05-31
FR2678437B1 (en) 1994-01-28
EP0520851A1 (en) 1992-12-30
ES2084303T3 (en) 1996-05-01
DE69206333T2 (en) 1996-05-23
FR2678437A1 (en) 1992-12-31

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