TWO-DIPOLE ANTENNA NETWORK AND ASSOCIATED COMMUNICATION SYSTEM

Abstract

An antenna device (102) comprising a low-frequency array (104) of low-frequency dipoles (112) having respective centers (112c) aligned on a vertical axis (A1); a high-frequency array (106) of high-frequency dipoles (114) having respective centers (114c) arranged vertically; and a support (115) for the low-frequency dipoles (112) and the high-frequency dipoles (114). The device is characterized in that the high-frequency dipoles (114) are arranged such that the center (112c) of each low-frequency dipole (112) is positioned vertically between the centers (114c) of a pair (P1; P2) of two high-frequency dipoles (114). Figure for the abbreviation: Fig. 1

Description

Title of the invention: ANTENNA DEVICE WITH TWO DIPOLE ARRAYS AND COMMUNICATION SYSTEM PARTNER Technical field of the invention

[0001] The invention relates to an antenna device with two dipole arrays and an associated communication system.

[0002] The invention finds a preferred application for pooling, on the same radio infrastructure, two distinct services operating in different frequency bands, such as for example an FM (Frequency Modulation) radio broadcasting service and a digital terrestrial radio service, also designated by the acronym RNT. Technological background

[0003] Patent GB1247629 describes a high azimuthal aperture antenna device for broadcasting UHF (Ultra High Frequency) signals. This antenna device comprises an array of low-frequency dipoles aligned vertically and an array of high-frequency dipoles also aligned vertically. The antenna device further comprises a support for the dipoles, in the form of a vertical mast.

[0004] To limit couplings between the networks, patent GB 1247629 proposes placing, along the mast, one network above the other. Because of this, the mast can reach a very high height, which can impose strong mechanical constraints to ensure stable and robust maintenance of the mast.

[0005] Adding low-frequency services to an existing pylon already hosting high-frequency services is particularly restrictive insofar as the low-frequency network must be positioned at the top of the pylon to preserve quasi-symmetrical radiation around the mast, while limiting interference with the networks already present on the mast.

[0006] Thus, the addition of a low frequency network intended to, for example, provide an FM radio broadcasting service operating between 87.5 MHz and 108 MHz, has the disadvantage of condemning the top of the pylon exclusively for this service, thus preventing the addition of a new service at a higher frequency, such as a digital terrestrial radio service operating for example between 174 MHz and 240 MHz.

[0007] Thus, it may be desirable to provide an antenna device which makes it possible to overcome at least some of the aforementioned problems and constraints. Summary of the invention

[0008] There is therefore proposed an antenna device comprising: a low-frequency array of low-frequency dipoles having respective centers aligned on a so-called vertical axis; a high-frequency array of high-frequency dipoles having respective centers succeeding each other vertically; and a support for the low-frequency dipoles and the high-frequency dipoles, in which the high-frequency dipoles are arranged so that the center of each low-frequency dipole is positioned vertically between the centers of a pair of two high-frequency dipoles.

[0009] Thus, the high-frequency dipoles are nested vertically with the low-frequency dipoles, so as to limit the coupling between the high-frequency dipoles and the low-frequency dipoles, while reducing the height of the support.

[0010] The invention may further comprise one or more of the optional features which will be described below, in any technically possible combination.

[0011] The support comprises a main support, along which the low-frequency dipoles are arranged vertically. The support further comprises an auxiliary support, along which the high-frequency dipoles are arranged vertically. Preferably, the auxiliary support is fixed to the main support.

[0012] The main support is a hollow and electrically conductive main mast. The antenna device further comprises a coaxial line comprising at least one inner conductor electrically connecting the low-frequency dipoles to the same input / output connector of the low-frequency network, so that the main mast constitutes a return line to a common electrical ground.

[0013] The antenna device further comprises on the main mast a device for decoupling the low-frequency dipoles from the high-frequency dipoles. The decoupling device is fixed to the main mast and connected to the inner conductor of the coaxial line of the low-frequency network.

[0014] The decoupling device is a coaxial low-pass filter arranged at the input of the low-frequency network. The filter comprises an alternation of high and low impedance coaxial sections.

[0015] The center of each low frequency dipole is arranged vertically in the middle of the centers of the pair of high frequency dipoles.

[0016] The centers of the high-frequency dipoles of each pair are aligned vertically.

[0017] The centers of the high-frequency dipoles of at least one pair of high-frequency dipoles frequency are horizontally offset to one side of the centers of the low-frequency dipoles, while the centers of at least one other pair of high-frequency dipoles are horizontally offset to the other side of the low-frequency dipoles.

[0018] The pairs of high frequency dipoles are arranged alternately on either side of the low frequency dipoles.

[0019] The two pairs of high-frequency dipoles associated with two consecutive low-frequency dipoles are horizontally offset on the same side of the low-frequency dipoles.

[0020] The low frequency dipoles and the high frequency dipoles are inclined relative to each other.

[0021] At least one high frequency dipole is arranged in the center of a low frequency dipole.

[0022] The low-frequency dipoles and / or the high-frequency dipoles comprise two collinear arms of the same length, preferably equal to a quarter of the wavelength associated with an operating frequency of said respective network.

[0023] The auxiliary support comprises at least one hollow and electrically conductive auxiliary mast. The antenna device further comprises a coaxial line comprising at least one internal conductor running inside said at least one auxiliary mast and electrically connecting the high-frequency dipoles to the same input / output connector of the high-frequency network, so that said at least one mast constitutes a return line to a common electrical ground.

[0024] The antenna device further comprises a device for decoupling the high-frequency dipoles from the low-frequency dipoles, said decoupling device being connected to the inner conductor of the coaxial line of the low-frequency network.

[0025] The decoupling device comprises one or more frequency rejection filters.

[0026] The antenna device further comprises, for each low-frequency dipole, at least one quarter-wave trap arranged around a foot of the low-frequency dipole.

[0027] The base of the low-frequency dipole comprises two fixing tubes parallel to each other, the quarter-wave trap comprising two hollow cylindrical bodies truncated longitudinally, so as to each have a flat surface. The two cylindrical bodies are arranged respectively around each of the two fixing tubes, so that the flat surfaces of the two cylindrical bodies are opposite each other.

[0028] Another object of the invention is a communication system configured to transmit and / or receive radiofrequency signals, in at least two distinct frequency bands. The communication system is characterized in that it comprises an antenna device according to the invention, as described above. Brief description of the figures

[0029] The invention will be better understood with the aid of the following description, given solely by way of example and with reference to the appended drawings, in which: [Fig.l] is a perspective view of a communication system including an antenna device according to a first embodiment of the invention; [Fig.2] is a schematic top view of the antenna device according to [Fig.l]; [Fig.3] schematically illustrates a front view of the arrangement of the high frequency dipoles relative to the low frequency dipoles of the antenna device according to [Fig.l]; [Fig.4] is a side sectional view of the low frequency network of the antenna device according to [Fig.l]; [Fig.5] is a schematic perspective view of the high-frequency network of the antenna device according to [Fig.l]; [Fig.6] schematically illustrates in perspective two variants of the arrangement of the support of the high-frequency network of the antenna device according to [Fig.1]; [Fig.7] is a side sectional view of the high frequency network of the antenna device according to [Fig.l]; [Fig.8] is a sectional view of a decoupling connecting part of the high-frequency network of the antenna device according to [Fig.l]; [Fig.9] illustrates azimuthal radiation patterns of the low frequency array of the antenna device according to [Fig.l]; [Fig. 10] illustrates elevation radiation patterns of the low frequency array of the antenna device according to [Fig.l]; [Fig. 11] illustrates azimuthal radiation patterns of the high frequency array of the antenna device according to [Fig.l]; [Fig. 12] illustrates elevation radiation patterns of the high frequency array of the antenna device according to [Fig.l]; [Fig. 13] illustrates the transmission parameter S12 of the antenna device according to [Fig.l] with and without decoupling devices; [Fig. 14] is a longitudinal sectional view of the low-frequency network of the antenna device according to [Fig. 1] illustrating an alternative embodiment of the decoupling device; [Fig. 15] is a longitudinal sectional view of the high-frequency network of the antenna device according to [Fig. 1] illustrating an alternative embodiment for the connection of the dipoles; [Fig. 16] is a cross-sectional view of the high-frequency network of [Fig. 15]; [Fig. 17] is a perspective view of an alternative embodiment of the antenna device according to [Fig.l] illustrating quarter-wave traps on the low frequency network; - [Fig. 18] illustrates azimuthal radiation patterns of the high-frequency array of the antenna device according to [Fig. 17], with and without quarter-wave traps; - [Fig. 19] illustrates in perspective an antenna device according to a second embodiment of the invention; - [Fig.20] illustrates in perspective an antenna device according to a third embodiment of the invention; - [Fig.21] schematically illustrates an arrangement of the dipoles according to a first variant embodiment of the antenna device according to [Fig.l]; - [Fig.22] schematically illustrates an arrangement of the dipoles according to a second variant embodiment of the antenna device according to [Fig.l]; - [Fig.23] schematically illustrates an arrangement of the dipoles according to a third variant embodiment of the antenna device according to [Fig.l]; - [Fig.24] schematically illustrates an arrangement of the dipoles according to a fourth variant embodiment of the antenna device according to [Fig.1]; and - [Fig.25] schematically illustrates an arrangement of the dipoles according to an alternative embodiment of the antenna device according to [Fig. 19]. Detailed description of the invention

[0030] In the description which follows, as well as in the claims, the terms of relative position of the elements described will be taken with respect to an orthogonal reference frame (X,Y,Z) comprising a so-called vertical direction Z, a so-called right / left direction Y and a so-called front / back direction X. In particular, the terms vertical(s), vertical, vertically will refer to the vertical direction Z as shown in the figures. Furthermore, the vertical direction Z is in particular intended to correspond to the usual vertical.

[0031] With reference to [Fig.l], an example of a communication system 100 implementing the invention will now be described.

[0032] This communication system 100 is configured to transmit and / or receive at the same time two radio frequency signals of two respective distinct services. For example, one of the services is an FM broadcasting service (“Frequency Modulation” in English) and the other is a digital terrestrial radio service (also designated by the acronym RNT, corresponding to the English “Digital Audio Broadcasting (DAB)”).

[0033] The two services operate respectively in a first frequency band and a second frequency band, higher than the first frequency band. Thus, the first frequency band is called the low frequency band, while that the second frequency band is called the high frequency band. The low frequency band is, for example, included in the metric frequency range, i.e., between 30 and 300 MHz. Furthermore, the high frequency band is, for example, included in the decimetric frequency range, i.e., between 300 and 3000 MHz.

[0034] Generally speaking, low frequency and high frequency do not necessarily belong to distinct frequency domains (i.e. metric, decimetric, etc.). For example, low frequency is an FM frequency (e.g. 88, 98 or 108 MHz) and high frequency is a DAB frequency (e.g. 174, 200 or 225 MHz), in which case both low and high frequencies belong to the same metric frequency domain.

[0035] The communication system 100 thus comprises an antenna device 102 grouping: - for the first service, a low-frequency network 104 of low-frequency dipoles 112 and a transmitter / receiver 108, and - for the second service, a high frequency network 106 of high frequency dipoles 114 and a transmitter / receiver 110.

[0036] Each dipole array is designed to transmit and / or receive in a frequency band centered around a so-called central frequency. Hereinafter, this central frequency will be considered to be the operating frequency of the dipole array, in transmission or reception.

[0037] In transmission mode, each transmitter / receiver 108, 110 is designed to convert data to be transmitted from the associated service into a radio frequency signal supplied to the dipoles 112, 114 of the associated network 104, 106. These dipoles 112, 114 are then designed to transmit the radio frequency signal in free space.

[0038] In reception mode, the dipoles 112, 114 of each network 104, 106 are designed to pick up a free-space radiofrequency signal received from the service in question for the associated transmitter / receiver 108, 110. The latter is then designed to convert this received radiofrequency signal into data received for the service in question.

[0039] Each dipole 112, 114 is an elementary antenna designed, when isolated, to emit and / or receive electromagnetic waves according to an omnidirectional radiation pattern, that is to say having a quasi-constant gain (i.e. to within 3 dB) in a horizontal plane (i.e. in all directions perpendicular to the Z axis) called azimuthal.

[0040] Structurally, each dipole 112, 114 comprises two electrically conductive arms 112a, 114a. Preferably, the arms 112a, 114a of the same dipole 112, 114 are identical, in particular of the same length and collinear. Thus, the two arms of each dipole has the same current density to limit the instabilities of electromagnetic radiation from the dipole.

[0041] The arms 112a, 114a of the dipoles 112, 114 thus have two respective ends facing each other, called central ends, separated by a gap having a midpoint. This midpoint constitutes a center 112c, 114c of the dipole 112, 114. The arms 112a, 114a of the dipoles 112, 114 have a length between X / 8 and X / 2, where X designates the reference wavelength associated with the central frequency of the frequency band used for the service concerned.

[0042] Preferably, the arms 112a of the low-frequency dipoles 112 are longer than the arms 114a of the high-frequency dipoles 114. In known manner, the longer the length of the arms of the dipole, the more the dipole is adapted to radiate at low frequency.

[0043] In the example of [Fig. 1], the arms 112a, 114a of the low-frequency 112 and high-frequency 114 dipoles are all vertical. This orientation allows the two networks 104, 106 to transmit and receive vertically polarized waves.

[0044] Each dipole 112, 114 further comprises a foot 112b, 114b for fixing the two arms 112a, 114a. The foot 112b, 114b is for example attached to the central ends of the two arms 112a, 114a. The foot 112b, 114b may be single or double in that it is made up of one or two hollow tubes respectively. The tubes may be of any cross-section, for example square, rectangular, circular or oval. In the case of a double foot, the two tubes are respectively fixed to the central ends of the arms 112a, 114a.

[0045] In all the embodiments described in the present application, each dipole 112, 114 has a double foot. However, according to other embodiments not described, each dipole may have a single foot, in particular the low-frequency dipoles and / or the high-frequency dipoles.

[0046] The length of the arms 112a, 114a and, more generally, the overall dimensions of the dipoles 112, 114 such as the thickness of the tubes of the foot, the length of the foot, may be adapted to achieve the desired radiation and impedance matching, taking into account the mutual couplings between the different constituent elements of the antenna device 102. Furthermore, all the dipoles of the same network will not necessarily be identical.

[0047] In the example of [Fig.l], the low-frequency network 104 comprises two low-frequency dipoles 112. In other embodiments, there could be more of them.

[0048] The centers 112c of the low-frequency dipoles 112 are aligned along the same vertical axis Al. By “aligned”, it is meant that the low-frequency dipoles 112 are substantially aligned along a vertical straight line, that is to say that their centers 112c can be offset horizontally relative to the vertical axis Al, for example less than one fifteenth of the reference wavelength associated with the low frequency network 104 as previously defined.

[0049] For example, in the case where the low-frequency network 104 operates at a frequency fi equal to 100 MHz in an FM band, the associated reference wavelength Xi is equal to 3 m (X1=c / f1, where c=3.108 m / s). In this case, it is considered that the low-frequency dipoles 112 are vertically aligned if they do not deviate by more than X / l5= 0.2 m perpendicular to the axis Al.

[0050] Still in the example of [Fig.l], the high-frequency network 106 comprises four high-frequency dipoles 114. In other embodiments, the number of high-frequency dipoles may be adjusted in particular as a function of the number of low-frequency dipoles, so that each low-frequency dipole is positioned vertically between the centers of a pair of two high-frequency dipoles.

[0051] A first pair of high-frequency dipoles 114 (called the upper pair) is fixed on an upper part of an auxiliary mast 118a, while a second pair of high-frequency dipoles 114 (called the lower pair) is fixed on a lower part of another auxiliary mast 118b.

[0052] According to a feature of the invention, the centers 114c of the dipoles of the lower pair are offset horizontally to the left of the centers 112c of the low-frequency dipoles 112, while the centers 114c of the lower pair of high-frequency dipoles 114 are offset horizontally to the right of the low-frequency dipoles 112.

[0053] As illustrated in [Fig.l], the high-frequency dipoles 114 located at the ends of the respective masts (called extreme dipoles) have dimensions greater than those of the other high-frequency dipoles (called central dipoles). In particular, each extreme dipole has a foot of length greater than that of the central dipole, so that for each of the two pairs, the arms of the extreme and central dipoles are not collinear, i.e. all the arms are not aligned along the same straight line, but are included in the same vertical plane.

[0054] According to a feature of the invention, the centers 114c of the high-frequency dipoles 114 of each pair are aligned vertically, so that all the pairs of centers are aligned in the same direction, parallel to the vertical axis Z.

[0055] Thus, the dipoles of the upper pair have a so-called upper vertical plane of symmetry, while the dipoles of the lower pair have a so-called lower vertical plane of symmetry. The dipoles of the upper pair are therefore aligned along the upper vertical plane (not shown), while the dipoles of the lower pair are aligned along the lower vertical plane jt. As illustrated, the feet of the dipoles of the lower pair are included in the lower vertical plane jt. In order not to make [Fig.l] cumbersome, only the lower vertical plane ir has been shown for the high-frequency dipoles 114 of the lower pair.

[0056] This configuration makes it possible to correct the edge effects at the ends of the high-frequency network, which has the effect of improving the radiation pattern of the network (e.g. symmetrization in the azimuthal plane, and / or reductions in radiation attenuation) as well as the overall impedance matching of the network by acting on the mutual impedances.

[0057] In other embodiments, the extreme dipoles may be collinear with the central dipoles, so as to significantly simplify the manufacture of the network from a mechanical point of view in particular.

[0058] In other embodiments, the high frequency dipoles 114 could of course be more numerous, for example depending on the number of low frequency dipoles 112.

[0059] In all cases, the high-frequency dipoles 114 are nested vertically with the low-frequency dipoles 112, in order to limit the height of the antenna device 102 while ensuring decoupling between the two networks.

[0060] To carry the dipoles 112, 114, the antenna device 102 further comprises a support 115 to which the dipoles 112, 114 are fixed by their respective feet 112b, 114b.

[0061] The support 115 comprises, for example, a vertical main mast 116 carrying the low-frequency dipoles 112 and at least one vertical auxiliary mast 118a, 118b carrying the high-frequency dipoles 114. In the example of [Fig.l], two auxiliary masts 118a, 118b are provided to carry all of the high-frequency dipoles 114 on either side of the main mast 116.

[0062] Preferably, the auxiliary mast(s) 118a, 118b are attached to the main mast 116. Thus, to deploy an additional service, the high frequency network 106 can be easily added to the previously deployed low frequency network 104. Conversely, the main mast 116 could be attached to the auxiliary mast(s) to add the low frequency network 104 to the previously deployed high frequency network 106.

[0063] For example, in the case of two auxiliary masts 118a, 118b, the support comprises at least one crosspiece 1180 interposed between the two auxiliary masts 118a, 118b, each crosspiece being attached and fixed to the main mast 116. In the example illustrated in [Fig.l], three crosspieces 1180 connect horizontally along the Y axis the two auxiliary masts 118a, 118b at their ends. A third central crosspiece (not visible in [Fig.l]) is preferably arranged equidistant from the other two crosspieces 1180 so as to reinforce the support of the two auxiliary masts 118a, 118b.

[0064] The support 115 is, for example, of hollow tubular structure and circular section, as illustrated in [Fig.l]. However, in other embodiments, this section could obviously take other shapes, such as a square, rectangular, triangular, oval or elliptical shape.

[0065] Generally, the support 115 is of multi-tubular structure in the sense that it comprises at least two tubular longitudinal pieces (i.e. masts) of any section, preferably rounded, such as circular or oval.

[0066] Thus, the support 115 is not a planar reflector, unlike the case of sector antennas typically used in mobile radio networks whose azimuthal aperture at -3 dB is generally limited to 120° precisely because of the presence of a reflector plane.

[0067] In the context of the present invention, each dipole array is defined as a set of interconnected dipoles contributing to the same radiation pattern. For example, the dipoles of the same array are all driven jointly to form a radiation pattern of the array. This definition naturally excludes any sub-array, i.e. any part of the same array grouping a subset of dipoles of this array.

[0068] Consequently, the support 115 is designed so that, on the one hand, all the low-frequency dipoles of the low-frequency network and, on the other hand, all the high-frequency dipoles of the high-frequency network respectively contribute to forming a radiation pattern in their respective frequency band having an azimuthal opening at -3 dB of at least 180°, in particular with radiation towards the rear of the support 115 in the direction X.

[0069] The main mast 116 is designed to be fixed vertically relative to the ground, directly or indirectly, for example by being fixed to a building or preferably to a pylon (standard use case). The main mast 116 is sized to withstand mechanical constraints imposed by the structure of the communication system.

[0070] [Fig.2] schematically illustrates the antenna device 102 seen from above, i.e. in the (X,Y) plane so as to visualize in particular the size of the support 115 which comprises the main mast 116 and the two auxiliary masts 118a, 118b.

[0071] The support 115 is dimensioned so as to limit deformations of the radiation of the high-frequency dipoles 114 and of the radiation of the low-frequency dipoles 112. Thus, the low-frequency radiation and the high-frequency radiation can remain almost constant around the axis AL

[0072] For example, the support 115 has a horizontal angular size E around the axis A1 of less than 20°, preferably equal to 15°. In other words, the support 115 obscures the low-frequency dipoles 112 by at most 20° horizontally.

[0073] This angular size E has a bisector A2. The front-rear direction X is taken along this bisector A2. Thus, the support 115 is located, along the direction X, at the rear of the low-frequency dipoles 112, as well as at the rear of the high-frequency dipoles 114.

[0074] Generally, the support 115 has a sufficiently small footprint to allow each of the networks to have a radiation pattern having an azimuthal opening at -3 dB of at least 180°.

[0075] In particular, the support 115 has a width that is sufficiently small to limit the masking of the radiation from the dipoles. Preferably, the main mast 116 has a diameter DI less than 10%, preferably 5%, of the central operating wavelength of the low-frequency network 104. Similarly, the auxiliary masts 118a, 118b have a diameter D2 less than 10% of the central operating wavelength of the high-frequency network 106.

[0076] For example, in the case of an RNT service, the central operating wavelength of the high-frequency network (i.e. corresponding to a central frequency of 200 MHz) is less than 1.5 m, so that the diameter of each of the auxiliary masts 118a, 118b is less than 15 cm. In the case of an FM service, the operating wavelength of the low-frequency network (i.e. corresponding to a central frequency of 100 MHz) is less than 3 m, so that the diameter of the main mast 116 is less than 30 cm. Thus, the support 115 has a width L defining the size of the support in the direction Y approximately equal to the sum of the diameter DI of the main mast 116 and the diameters D2 of the auxiliary masts 118a, 118b, i.e. Dl+2xD2=30+2*15*=60 cm, assuming that the auxiliary masts have the same diameter D2.

[0077] In the example of [Fig.2], the three masts are arranged so that the width L of the support 115 corresponds to the sum of the diameters of the three masts. According to an alternative embodiment not illustrated, the two auxiliary masts 118a, 118b are brought closer to each other in the Y direction, so that the distance separating them is less than the diameter DI of the main mast. In this case, the size of the support is less than the sum of the diameters of the three masts. Such an arrangement makes it possible to increase the azimuthal aperture of each of the dipole arrays by promoting in particular radiation at the rear of the support, which is not the case with planar reflector antennas of the prior art.

[0078] With reference to [Fig.3], the relative positioning of the dipoles 112, 114 of the two networks 104, 106 of the antenna device 102 will now be described in more detail.

[0079] In this figure, the centers 112c of the low-frequency dipoles 112 are represented by stars *, while the centers 114c of the high-frequency dipoles 114 are represented by crosses +. This nomenclature also applies to figures 21 to 25 which will be described later.

[0080] As explained previously, the low-frequency dipoles 112 are aligned vertically along the vertical axis A1. These are spaced regularly by a distance dl corresponding to the pitch of the low-frequency network. The value of this distance dl may be adjusted so as to limit or eliminate the presence of secondary lobes in a vertical plane of the radiation pattern of the low-frequency network. For example, in the case where the low frequency is equal to 100 MHz, the distance dl is adjusted so that d 1 = 0.72.X, where X denotes the wavelength associated with the operating frequency of the low-frequency network. Generally speaking and without other constraints, the pitch dl of the low-frequency network is between 0.7.X and 0.8.X so as to maximize the radiation in all directions contained in a horizontal plane, and more generally between 0.5.X and X.

[0081] For their part, the high-frequency dipoles 114 are arranged on the auxiliary masts 118a, 118b, so that each low-frequency dipole 112 is positioned vertically between a respective pair PI, P2 of high-frequency dipoles 114.

[0082] For example, the high-frequency dipoles 114 are divided into distinct pairs PI, P2 respectively associated with the low-frequency dipoles 112. The expression “distinct pairs” means that the same high-frequency dipole 114 belongs to only one pair PI, P2.

[0083] The two high-frequency dipoles 114 of each pair PI, P2 vertically frame the associated low-frequency dipole 112. For example, each low-frequency dipole 112 is positioned vertically in the middle of the high-frequency dipoles 114 of the associated pair PI, P2. This means that, along the axis A1, each low-frequency dipole 112 is vertically equidistant by the same height h from the two high-frequency dipoles 114 of the associated pair PI, P2.

[0084] Preferably, the high frequency dipoles 114 of each pair PI, P2 are aligned vertically.

[0085] In the example illustrated in [Fig. 3], for each pair PI, P2, the high-frequency dipoles 114 are spaced apart by the same pitch d2. The lower dipole of the pair PI is spaced apart from the upper dipole of the pair P2 by an inter-pair distance dl2. The inter-pair distance dl2 may be adjusted so as to modify the shape of the radiation pattern of the high-frequency network. In particular, the inter-pair distance dl2 may be equal to the pitch d2 of the high-frequency network, so that dl2=d2, so as to simplify the manufacture of the network.

[0086] Furthermore, preferably, at least one pair of high-frequency dipoles 114 is horizontally offset (i.e., relative to the Y direction) to the right of the plane (A1, A2) comprising the low-frequency dipoles 112 and at least one pair is horizontally offset to the left of the plane (A1, A2). In this way, the high-frequency dipoles 114 are distributed on either side of the low-frequency dipoles 112.

[0087] This right and left shift simplifies the addition of the high frequency dipoles 114, since it is possible to fix each left-shifted PI pair of high frequency dipoles 114 on the auxiliary mast 118a, and each right-shifted P2 pair is fixed on the other auxiliary mast 118b.

[0088] Furthermore, thanks to this shift to the right and to the left, the deformation of the radiation pattern of the low-frequency dipoles 112 introduced by the pair(s) of high-frequency dipoles 114 on the right is compensated at least in part by the pair(s) of high-frequency dipoles 114 on the left, and vice versa.

[0089] Preferably, the pairs of high-frequency dipoles 114 are distributed in a balanced manner to the right and to the left, so that each of the auxiliary masts 118a, 118b has the same number of pairs of dipoles. In other words, there are as many high-frequency dipoles to the right as to the left of the low-frequency dipoles (within one pair when the number of low-frequency dipoles 112 is odd). This improves the compensation for the distortion of the radiation pattern of the low-frequency dipoles 112.

[0090] More preferably, the pairs PI, P2 of high frequency dipoles 114 are alternately shifted to the right and left. This also improves the compensation for the distortion of the radiation pattern of the low frequency dipoles 112.

[0091] Still to improve this compensation, the right and left offset is preferably the same and noted by the reference “e” in [Fig.3]. More precisely, the first pair PI is offset horizontally (i.e. along the Y axis), by a distance e to the left of the low-frequency dipoles 112, while the second pair P2 is offset horizontally, along the Y axis, by the same distance e but to the right of the low-frequency dipoles 112.

[0092] In other embodiments (not shown), the offset of the pairs may be different on the right and left of the low-frequency dipoles 112.

[0093] With reference to [Fig.4] illustrating a cross-sectional view along the plane (A1, A2) of the low-frequency network 104, the antenna device 102 comprises an electrical connection 119, called low frequency, from the transmitter / receiver 108 to the low-frequency dipoles 112.

[0094] This low-frequency electrical connection 119 comprises, for example, an external electrical connection 121 connecting the transmitter / receiver 108 to the support 115. This external electrical connection 121 is, for example, a coaxial cable.

[0095] The low-frequency electrical connection 119 further comprises, carried by the support 115, an input / output connector 120, called low frequency, to which the external electrical connection 121 is designed to be connected. In particular, the low-frequency connector 120 is carried by the main mast 116. Preferably, the low-frequency connector 120 is a coaxial connector.

[0096] The low-frequency electrical connection 119 further comprises, in the support 115, for each low-frequency dipole 112, an internal electrical conductor 122a, 122b electrically connecting the low-frequency connector 120 to the low-frequency dipole 112 in question. Each internal electrical conductor is connected to the low frequency connector 120 at a bifurcation point C. In particular, the inner conductor 122a, 122b runs, from the low frequency connector 120, inside the main mast 116 then inside the foot 112b of the low frequency dipole 112 considered, to reach one of its arms 112a. In the case where the foot 112b is double, the inner conductor 120 runs in one of its tubes.

[0097] The arm 112a reached by the inner conductor 122a, 122b is the one pointing downwards in the example of [Fig.4].

[0098] The other arm 112a may be connected to the inner electrical conductor 122a, 122b by a conductive section 124 passing through the gap between the arms 112a.

[0099] Alternatively, the conductive section 124 is not electrically connected to the downwardly pointing arm 112a but capacitively coupled to the latter through the gap between the two arms 112a of the low-frequency dipole 112.

[0100] The inner electrical conductor 122a may comprise several electrical junctions placed end to end as illustrated in [Fig.4].

[0101] Each inner conductor 122a, 122b may have a variable section along its length, as illustrated in [Fig.4]. Thus, the dimension of this section can be adjusted locally to carry out appropriate impedance transformations, so as to best adapt the impedance of the low-frequency network 104 to that of the connector 120 and thus avoid losses due to impedance mismatch.

[0102] Furthermore, the main mast 116 and the foot 112b of each low-frequency dipole 112 are in electrical contact with each other and thus serve as a return line to connect all the low-frequency dipoles 112 to the same reference potential, for example a common ground or earth. The main mast 116 and the foot 112b surrounding the inner conductor 122a, 122b thus form a coaxial connection.

[0103] The use of the main mast 116 and each foot 112b as a return line has several advantages.

[0104] On the one hand, it contributes to making the antenna device 102 symmetrical from an electrical point of view, so that it generates little imbalance of the electric currents circulating inside the main mast 116 and on the arms 112a of the low-frequency dipoles 112 (in transmission or reception). In particular, the use of the main mast 116 as a return line makes it possible to avoid using coaxial cables outside the mast which would have the effect of increasing the equivalent section of the conductors thus obstructing the radiation at the rear of the mast.

[0105] On the other hand, it facilitates the adaptation of the impedance of the low-frequency network 104 in accordance with the characteristic impedance of the coaxial line 121 (generally of the order of 50 Q) when the latter is connected to the low-frequency connector 120.

[0106] Furthermore, the support 115 comprises, for example, a plurality of decoupling devices 126 configured to limit disturbances produced by the high-voltage network. frequency 106, for example by intermodulation phenomena, on the low frequency network 104.

[0107] These decoupling devices 126 are fixed to the support 115, for example to the main mast 116. Each decoupling device is, for example, associated with one of the low-frequency dipoles 112 and electrically connected to the internal conductor 122a, 122b of this low-frequency dipole 112. In the example illustrated, two decoupling devices 126 are associated with each low-frequency dipole 112. However, the number of decoupling devices 126 associated with each low-frequency dipole could be different, for example between 1 and 4.

[0108] Preferably, the decoupling devices 126 are rejection filters comprising, for example, an open bent coaxial line. The bent coaxial line 126 comprises an outer conductor 126b and an inner conductor 126a extending inside the outer conductor 126b and electrically insulated from the latter. In the present example, the electrical insulation is provided by air. However, in other embodiments, the air may be replaced by any other dielectric material having low dielectric losses, i.e. a dielectric tangent tan(e” / e') less than or equal to 0.001, where e” and e' represent respectively the imaginary part and the real part of the electrical permittivity.

[0109] The inner conductor 126a is in contact with the inner conductive line 122a, 122b. As illustrated, the bent open coaxial line is L-shaped and has a longitudinal portion of length Llz which extends parallel to the main mast 116 along the Z axis and a transverse portion of length Llx which extends perpendicular to the main mast 116 along the X direction. Thus, each bent open coaxial line has a developed length L1 equal to the sum of the lengths of the longitudinal and transverse portions, i.e. L1 = Llz + Llx.

[0110] Preferably, the developed length L1 of each open bent line is between Xg / 6 and Xg / 3, where Xg is the guided wavelength corresponding to the central operating frequency of the high frequency network 106. By central frequency, it will be understood that this is the median frequency of the frequency band of the radio service provided by the high frequency network, as defined previously.

[0111] In other embodiments (not described), other decoupling devices may be considered, such as an open coaxial line without conductor or any other equivalent device.

[0112] In the example of [Fig.4], four rejector filters 126 are distributed along the main mast 116 so as to form two pairs, each pair being located at a respective dipole. The rejector filters 126 are mounted two by two head-to-tail (or back-to-back). Other orientations of the elbows of the rejector filters may also be envisaged knowing that the relative orientation of the elbows of the filters re- injectors has no significant influence on decoupling performance.

[0113] For example, the filters of a pair of rejector filters 126 are vertically spaced apart from each other by a separation distance L4 between two filters of the same pair called intra-pair, the latter being less than three times the guided wavelength Xg, i.e. L4 < 3xXg.

[0114] The positioning of the rejection filters 126 relative to the low-frequency dipoles 112 may be adjusted so as to limit as much as possible their interaction with the low-frequency dipoles 112. For this purpose, the rejection filters 126 are arranged, for example, two by two at the foot of the respective dipoles, that is to say opposite the arms of the low-frequency dipoles 112. In general, the position of the decoupling devices 126 may be optimized so that they disturb the low-frequency network as little as possible, in other words so that they distort the radiation pattern of the low-frequency network as little as possible.

[0115] According to an alternative embodiment (not shown), the rejection filters located at the ends of the main mast 116 could be inserted inside the mast 116.

[0116] The developed length L1 and the intra-pair separation length L4 may be adjusted so as to take into account the inter-network frequency spacing and their respective bandwidth, by rejecting as best as possible the frequency band associated with the other network, by facilitating or at least not degrading the impedance matching of the network on which they are installed and by making it possible to achieve the average and peak power capacities required according to the use considered.

[0117] Preferably, the outer conductor 126b is slightly longer in the Z direction than the inner conductor 126a. This difference in length L4 makes it possible to limit radiation from the inner conductor 126a at the end of the open line. It can also make it possible to reduce possible interaction with a metal plug located at the end.

[0118] The inner 126a and outer 126b conductors have respective diameters which can be adjusted so as to obtain an impedance of the open angled coaxial line 126 of between 10 and 200 Q and to support average and maximum (peak) electrical powers required for reception and / or transmission.

[0119] Preferably, the decoupling devices 126 are all identical and positioned along the main mast 116, so that they form a symmetrical assembly with respect to the center C of the coaxial line 122, this center C corresponding to the place where the internal conductive lines 122a, 122b meet so as to be connected to the connector 120. Preferably, the center C of the coaxial line 122 is located at the connector 120. In practice, it will be considered that the decoupling devices 126 are identical insofar as they have the same structure with dimensions, such as the length, which are almost equal, that is to say varying by approximately + / - 10% around a median value.

[0120] With reference to [Fig.5] illustrating a three-dimensional schematic view of the high-frequency network 106, the antenna device 102 comprises an electrical connection 127, called high frequency, from the transmitter / receiver 110 to the high-frequency dipoles 114.

[0121] This high-frequency electrical connection 127 shown in simple dotted lines, comprises for example an external electrical connection 125 connecting the transmitter / receiver 110 to the support 115. This external electrical connection 125 is for example a coaxial cable.

[0122] The high-frequency electrical connection 127 further comprises, carried by the support 115, an input / output connector 128, called high frequency, to which the external electrical connection 125 is designed to be connected. In particular, the high-frequency connector 128 is carried by one of the auxiliary masts 118a, 118b. Preferably, the high-frequency connector 128 is a coaxial connector.

[0123] The high-frequency network 106 further comprises a coaxial line 130 configured to preferentially connect in parallel all of the high-frequency dipoles 114 of the network to the high-frequency connector 128. Thus, from the high-frequency connector 128, the coaxial line 130 separates into two distinct branches 103c, 130'c which themselves separate into two sub-branches {130a, 130b], {130'a, 130'b) respectively, as illustrated in [Fig. 5]. A parallel connection gives the network an extended bandwidth compared to a series connection according to which all the dipoles are conventionally connected in series one after the other without branching along the line.

[0124] In alternative embodiments (not illustrated), the coaxial connection may be serial or mixed, in the sense that it combines a serial architecture and a parallel architecture, depending on the intended application.

[0125] As with the coaxial line of the low frequency network, the coaxial line 130 of the high frequency network 106 comprises an inner conductive portion and an outer conductive portion surrounding the inner conductive portion. The inner and outer conductive portions are electrically conductive but electrically insulated from each other by air or any other dielectric material.

[0126] The inner conductive portion of the coaxial line is a filiform electrical conductor running inside the auxiliary masts 118a, 118b and inside the feet of the respective dipoles to connect one of the arms 114a of each of the dipoles to the high-frequency connector 128. The filiform electrical conductor comprises one or more sections 130a, 130b, 130c, 130'a, 130'b, 130'c. Each section may itself have subsections of different impedances.

[0127] In the example illustrated, the two dipoles fixed on an upper part of the mast auxiliary mast 118a are connected to connector 128 via sections 130a, 130b, 130c. The two dipoles fixed on a lower part of the other auxiliary mast 118b are connected to connector 128 via sections 130'a, 130'b, 130'c. Section 130'c includes a portion running inside a hollow crosspiece 132 connecting the two auxiliary masts 118a, 118b.

[0128] Considering that the section 130'c running inside the crosspiece 132 has a length hy, the high-frequency connector 128 is positioned vertically at a distance hzi from one pair of high-frequency dipoles and at a distance hz2 from the other pair of high-frequency dipoles, so that each of the high-frequency dipoles is connected to the high-frequency connector 128 along an electrical path of the same length, i.e. hzi- hz2+ hy, so that the currents flowing inside the lines are balanced between the high-frequency dipoles 114.

[0129] The outer conductive part of the coaxial line comprises the auxiliary masts 118a, 118b and the feet 114b of the high-frequency dipoles 114. The outer conductive part thus formed serves as a return line for the currents of the coaxial line, so that all the dipoles of the high-frequency network 114 are connected to the same reference potential. The reference potential can be obtained by connecting each auxiliary mast 118a, 118b to a common ground element or to earth. By bringing all the low-frequency 112 and high-frequency 114 dipoles to the same reference potential, the radiation patterns of the low-frequency 104 and high-frequency 106 networks are stabilized.

[0130] Preferably, the foot of each dipole has a length approximately equal to a quarter of the wavelength associated with the operating frequency of the network to which it belongs. This particular length has several advantages.

[0131] On the one hand, it contributes to making the antenna system more symmetrical in terms of the distribution of electric currents through the coaxial line connecting each of the dipoles of the same network, in particular by ensuring a homogeneous interface between the coaxial line which may be more or less asymmetrical and the symmetrical structure of the dipole.

[0132] On the other hand, it makes it possible to avoid excessive deformation of the azimuthal radiation pattern of the dipole array which could result from an interaction of the dipoles with their support mast. For example, a foot length which is too long will have the effect of crushing the azimuthal radiation pattern to the point of making the pattern bidirectional.

[0133] As illustrated in [Fig.6], the high-frequency network comprises a connecting device 129 configured to connect the two auxiliary masts 118a, 118b carrying the high-frequency dipoles 116. This connecting device 129 comprises a longitudinal hollow tubular part 129a extending vertically, in particular along a part of one 118 of the two masts. The connecting device 129 further comprises at least one hollow crosspiece 129b, transversely connecting the two masts 118a, 118b to each other.

[0134] Preferably, the tubular part 129a is fixed to the mast 118a as illustrated in the diagram on the right noted b). According to an alternative embodiment as illustrated in the diagram on the left noted a), an additional crosspiece 129b is arranged on the tubular part 129a so that the latter is further fixed to the other mast by means of this additional crosspiece.

[0135] As a whole, the connecting device 129 is hollow so as to provide a passage path for the coaxial lines to connect the high frequency dipoles 114 to the connector 128.

[0136] The high frequency network 106 will now be described with reference to [Fig.7] which illustrates a side sectional view along the plane (X,Z) of [Fig.5], more precisely along the section line identified by “A”.

[0137] On the left part of [Fig.7] is shown in enlarged form the upper pair of high frequency dipoles 114 carried by the auxiliary mast 118a.

[0138] As previously described with reference to [Fig.5], the high frequency dipoles of the upper pair are electrically connected to the high frequency connector 128 via the coaxial line 130.

[0139] As illustrated in [Fig.7], the inner part of the coaxial line 130 comprises several sections 130a, 130b. These sections are of different sizes (i.e. diameter, length) and have different impedances.

[0140] The dipoles of the upper pair belong to the same vertical plane denoted ir 1 comprising the auxiliary mast 118a, while the dipoles of the lower pair belong to the same other vertical plane ir2 comprising the auxiliary mast 118b hidden behind the auxiliary mast 118a according to the plane of [Fig.7]. Thus, the high-frequency dipoles of each pair are aligned vertically.

[0141] In the case where the high-frequency network comprises several upper pairs (instead of a single pair as shown in [Fig.7]), all the dipoles of these pairs belong to the same vertical plane jtl, so that the dipoles arranged on the auxiliary mast 118a are all aligned vertically.

[0142] Similarly, if the high-frequency network comprises several lower pairs (instead of a single pair as shown in [Fig.7]), these belong to the same vertical plane ir2, so that the dipoles arranged on the auxiliary mast 118b are all aligned vertically.

[0143] Generally speaking, dipoles will be considered to be aligned vertically if they belong to the same vertical plane (i.e. including the Z direction).

[0144] As described above, for each of the two pairs of dipoles, the extreme dipoles are larger than the central dipoles. For example, the The extremal dipole has a foot of length H1 greater than that H2 of the foot of the central dipole. The extremal dipole has a section of diameter greater than that of the section of the central dipole.

[0145] With reference to [Fig.8], the connecting device 129 shown in [Fig.6] will now be described in more detail.

[0146] Advantageously, the connecting device 129 is configured to reject the frequency band in which the low-frequency network 104 operates. For this purpose, the connecting device 129 comprises a decoupling device 136 for decoupling the high-frequency dipoles from the low-frequency dipoles, so that the high-frequency dipoles are not disturbed by the presence of the low-frequency dipoles. The decoupling device 136 is connected to the coaxial line 130'c running between the two auxiliary masts 118a, 118b. It is fixed along the tubular part 129a of the connecting device 129.

[0147] The decoupling device 136 comprises two rejection filters 136a, 136b configured to reject low frequencies. Each rejection filter comprises a pair of open angled coaxial lines 138 arranged head to tail on either side of the tubular portion 129a near a crosspiece 129b.

[0148] Each rejector filter is associated with a pair of high-frequency dipoles. However, in other embodiments (not shown), several pairs of rejector filters may be associated with each pair of high-frequency dipoles; the number of filters may vary between 1 and 3 typically.

[0149] As previously described for the low frequency network, each open angled coaxial line 138 includes an inner conductor in contact with the coaxial line 130'c running inside the tubular portion 129a used to connect the high frequency dipoles. Each open angled coaxial line 138 has a developed length between X'g / 6 and X'g / 3, where X'g denotes a guided wavelength corresponding to the center operating frequency of the high frequency network.

[0150] As described previously for the low-frequency network, the outer conductor of these bent coaxial lines 138 is preferably slightly elongated relative to the inner conductor, so as to limit radiation at the end of the open line or possible interaction with a metal plug located at the end. The ratio of the diameters of the inner and outer conductors constituting said open bent coaxial lines can be advantageously adjusted to obtain an impedance between 10 and 200 Q and allow the desired average and peak power handling depending on the use considered. The dielectric present between the inner and outer conductors may be air or any dielectric material having a low loss tangent.

[0151] The transmission performance results of the antenna device 102 according to the first embodiment described previously with reference to Figures 1, 3-8 will now be presented with reference to Figures 9 to 13.

[0152] [Fig.9] illustrates an azimuthal radiation pattern of the low frequency network 104 obtained for three distinct operating frequencies (88 MHz, 98 MHz, 108 MHz) selected from a frequency band of an FM broadcasting service.

[0153] This figure shows the normalized radiation pattern at 0 dB of the low-frequency network expressed in dB in the azimuthal plane (X,Y) as a function of an azimuthal angle q> expressed in degrees.

[0154] This diagram shows that the radiation of the low-frequency network 104 is symmetrical although not perfectly isotropic (i.e. quasi / pseudo-omnidirectional) with a lower gain at the rear (q> = 0°) of the network than at the front (q> =180°). The gain is almost constant to within about -2 dB, on the front part of the network, i.e. for an azimuthal angle q> between -180° and -90° and between 90° and 180°. At the rear of the low-frequency network 104, the attenuation varies between 2 dB and 6 dB depending on the azimuthal angle q>, i.e. for -90° <q>< 0° and -0° <q>< 90°.

[0155] Such radiation shows that the low-frequency network has an azimuthal opening at -3dB at least equal to 180°. These results remain generally valid for the three FM frequencies tested.

[0156] [Fig. 10] illustrates an elevation radiation pattern of the low frequency network 104 obtained under the same conditions as for [Fig.9].

[0157] This figure shows the normalized radiation pattern expressed in dB in the vertical plane (X,Y) as a function of the elevation angle 0 expressed in degrees.

[0158] This diagram shows the presence of some secondary lobes but these remain globally negligible, so that most of the energy is radiated in a horizontal dimension, i.e. for -120°<0<-60° (at the front of the array) and 60°<0<120° (at the rear of the array).

[0159] [Fig. 11] illustrates an azimuthal radiation pattern of the high frequency network 106 obtained for three distinct operating frequencies (174 MHz, 200 MHz, 225 MHz) selected from a frequency band of an RNT service.

[0160] Such radiation shows that the high frequency network 106 has an azimuthal opening at -3dB of at least 180° at the front of the network (i.e. for -180° <q>< -90° and 90° <q>< 180°). The gain at the rear of the antenna is reduced the higher the operating frequency.

[0161] [Fig. 12] illustrates an elevation radiation pattern of the high frequency network 106 obtained under the same conditions as for [Fig. 11].

[0162] In view of this diagram, it can be seen that despite the presence of two secondary lobes, on either side of the horizontal plane, the high-frequency network 106 radiates essentially forward (0=-90°) and backward (0=90°) to a lesser extent. measure.

[0163] With reference to [Fig. 13], the results of decoupling in transmission between the low frequency network 104 and the high frequency network 106 will now be described.

[0164] The diagram in [Fig. 13] illustrates the amplitude of the parameter S in transmission noted S12 and expressed in dB, as a function of the operating frequency expressed in MHz for the antenna device 102 operating in a frequency band of an FM service (88-108 MHz) and in a frequency band of an RNT service (174-225 MHz), these bands corresponding to those already used to produce the radiation diagrams described previously with reference to figures 9-12.

[0165] In [Fig. 13], the curve shown in solid line represents the parameter S12 in the case where the antenna device 102 comprises the decoupling devices 126, 136, as described with reference to FIGS. 4, 7, 8 respectively on the low frequency network 104 and on the high frequency network 106. In comparison, the curve in dotted line represents the parameter S12 in the absence of the decoupling devices 126, 136 respectively on the low frequency network and on the high frequency network.

[0166] These results show that for the RNT band between 174 and 225 MHz, an additional maximum isolation of approximately 40 dB is obtained thanks to the decoupling devices 126, 136.

[0167] Thus, the use of the rejection filters 126 of the low-frequency network 104 makes it possible to very significantly reduce (i.e. maximum reduction of approximately 40 dB) the quantity of radio waves transferred from the low-frequency network 104 to the high-frequency network 106 in the operating frequency band of the high-frequency network 106.

[0168] Similarly, by comparing the two curves in the FM domain (88-108 MHz), it clearly appears that the use of the rejector filters 136 of the high-frequency network 106 makes it possible to reduce to a lesser extent (i.e. maximum reduction of approximately 10 dB), the quantity of radio waves transferred from the high-frequency network 106 to the low-frequency network 104 in the operating frequency band of the low-frequency network 104.

[0169] [Fig. 14] illustrates an alternative embodiment of the low-frequency network 104 described with reference to [Fig. 4], according to which the decoupling device 126 of the low-frequency network 104 is replaced by a coaxial low-pass filter 140 configured to reject the frequencies of the high-frequency network 106.

[0170] The input / output connector 120 of the low-frequency network 104 is moved to the end of the coaxial low-pass filter 140. However, it may be left in its initial position in the event that the coaxial low-pass filter is itself provided with its own coaxial input and output connectors.

[0171] Preferably, the coaxial low-pass filter 140 comprises an alternation of high and low impedance coaxial sections, denoted respectively 141.k and 142.kl, where k is a natural integer preferably varying from 2 to 6. In the example illustrated, the filter coaxial low-pass filter 140 includes four high impedance sections 141.1, 141.2, 141.3, 141.4 and three low impedance sections 142.1, 142.2, 142.3.

[0172] The coaxial sections will be sized so that their impedance preferably varies between 10 and 200 Q and in line with the average and peak power requirements to be supported in the context of the exploitation of the invention.

[0173] Similarly, the order of the filter 140 thus constituted will be adjusted to achieve the desired rejection level. By definition, the order of the filter corresponds to the number of poles constituting it and in the present case, each section corresponds to a pole.

[0174] The length of the coaxial sections will preferably be between / .„ / 20 and Xg / 5, where Xg represents the guided wavelength associated with the central operating frequency of the high frequency network 106.

[0175] The coaxial elements (sections) will preferably be held in position by continuous or discontinuous dielectric elements, for example polytetrafluoroethylene, and whose relative permittivity will preferably be less than 3 and the loss tangent preferably less than 0.001.

[0176] An alternative embodiment of the high-frequency network will now be described with reference to FIGS. 15 and 16. This alternative is designated by the reference 206.

[0177] According to a particular feature of this variant, the decoupling devices 126 of the high frequency network are partly integrated and the coaxial line 127 in the auxiliary masts 118a, 118b allowing the input / output connector to be placed equidistant and symmetrically with respect to the support 116 of the low frequency network.

[0178] [Fig. 15] illustrates a sectional view in the (X,Z) plane of the high-frequency network according to this variant embodiment which will bear the reference 206.

[0179] As described above, the high-frequency dipoles 214 are connected to the input / output of the high-frequency network by a coaxial line 230 comprising several junctions 130a, 130b, 130c to feed the upper dipole pair and several junctions 130'a, 130'b, 130'c to feed the lower dipole pair. However, unlike what has been previously described with reference to [Fig. 6], the two auxiliary masts 118a, 118b are not connected by means of a tubular part 129a but by means of three hollow tubular crosspieces 249a, 249b, 249c, extending in the Y direction and through which the transverse sections 130c, 130c' run. These tubular crosspieces 249a, 249b, 249c are illustrated more clearly in [Fig. 16] which will be described below.

[0180] The high-frequency network 206 comprises four dipoles 214a, 214b, 214c, 214d of different dimensions. For example, the extreme dipoles 214a, 214d do not have the same dimensions as the central dipoles 214b, 214c. The two extreme dipoles 214a, 214d themselves have different dimensions relative to each other. Furthermore, the central dipoles 214b, 214c themselves have different dimensions relative to each other. compared to each other.

[0181] Advantageously, the dimensions of the high-frequency dipoles 214a, 214b, 214c, 214d may be adjusted so as to generate a particular phase distribution in the high-frequency network 206, for example to obtain a specific depointing of the vertical radiation pattern or else a filling (i.e. suppression) of the radiation zeros in this same vertical plane.

[0182] [Fig. 16] illustrates in the transverse plane (Y,Z) the high frequency network 206 of the [Fig.15].

[0183] As previously described with reference to [Fig.8], the high frequency network 206 comprises two decoupling devices 236.

[0184] According to a feature of the present variant, each decoupling device 236 comprises a bent coaxial line 238b and an open coaxial line 238a, the latter 238a being integrated inside an auxiliary mast 118a, 118b.

[0185] Furthermore, this variant differs from the embodiment described with reference to variant a) of [Fig.6], in particular in that a third crosspiece 249c is provided to connect the two auxiliary masts 118a, 118b in their center, where the input / output connector 228 of the high frequency network is placed, i.e. where the branches 230c, 230c' meet.

[0186] From a radioelectric point of view, this embodiment variant has the advantage that the antenna device is perfectly symmetrical on its external part, insofar as the input / output connector 228 can be placed equidistant from the two pairs of high-frequency dipoles (i.e. lower pair (214c, 214d) and upper pair (214a, 214b)). Furthermore, the two pairs of dipoles of the high-frequency network 206 are electrically connected to the input / output connector 228 along an equivalent electrical path. It follows that the antenna device according to this embodiment variant has symmetrical azimuthal radiation patterns in the (X,Y) plane.

[0187] Thus, by integrating into the auxiliary masts 118a, 118b, not only the entire high-frequency coaxial line used to connect the high-frequency dipoles, thanks in particular to the tubular crosspieces 249a, 249b, 249c, but also the open lines 238a used for decoupling, the antenna device has a reduced electrical size of the supports 118a, 118b as well as an improvement in the front / back ratio of the radiation pattern of the high-frequency network compared to an equivalent less integrated solution.

[0188] With reference to [Fig. 17], an alternative embodiment of the antenna device 102 according to [Fig.l] will now be described.

[0189] According to this variant, the antenna device 102 further comprises at least one quarter-wave trap 150 associated with each of the low-frequency dipoles 112, so as to limit the influence of the feet of the low-frequency dipoles on the radiation of the network. high frequency 106.

[0190] In [Fig. 17], only one low-frequency dipole 112 has been shown, but it will be understood that the other low-frequency dipole of the antenna device 102 according to [Fig.l] could also be equipped with the same quarter-wave traps.

[0191] More generally, all or part of the low-frequency dipoles of the low-frequency network may be equipped with one or more quarter-wave traps.

[0192] According to the example illustrated in [Fig.17], a quarter-wave trap 150 is arranged on each tube 112b constituting the foot of the low-frequency dipole 112.

[0193] For example, each quarter-wave trap 150 consists of a hollow metallic cylindrical body. Each cylindrical body 150 has one end forming a closed section in direct contact with the outer surface of the tube 112b constituting the foot of the dipole. The other end 150b of the cylindrical body 150 forms an open section. Each cylindrical body 150 is arranged around the associated tube 112b.

[0194] The quarter-wave traps 150 associated with the low-frequency dipoles 112 are designed to create a high impedance on the tubes 112b, precisely at the location of the end 150b forming an open section, and thus to limit the contribution of the low-frequency dipoles 104 to the radiation of the high-frequency network 106.

[0195] Each quarter-wave trap 150 is configured to operate in a frequency band around the frequency of interest, i.e. the central frequency fc of the service band used by the low-frequency network 104. Preferably, the frequency of interest f=fc is such that its corresponding wavelength is equivalent to four times the length of the quarter-wave trap 150. In other words, the quarter-wave trap 150 has a length L5 which is linked to the frequency of interest f according to the following expression f=c / (4xL5), where c=3.108 m / s.

[0196] Thus configured, the quarter-wave trap 150 has the effect of avoiding or at least limiting a deformation of the azimuthal radiation patterns of the high-frequency network 106, over its operating frequency band.

[0197] According to the example of [Fig.17], the inventors observed a significant improvement in the radiation patterns of the high-frequency network 106, over approximately 10% of its relative bandwidth, between a minimum frequency (fmin) equal to 174 MHz and a maximum frequency (fmax) equal to 192 MHz, said relative bandwidth being expressed by fmax-fmin / fc- However, this result will vary depending on the dimensions of the trap.

[0198] Preferably, each of these quarter-wave traps 150 has a length L5 approximately equal to a quarter of a wavelength associated with the operating frequency of the low-frequency network 104.

[0199] For example, the quarter-wave trap 150 is configured to reject a frequency range for which the radiation pattern of the low-frequency array 104 is likely to be impacted by the presence of the 112b tubes constituting the feet of the low-frequency dipoles 112.

[0200] In the example illustrated, each cylindrical body has a circular section. However, in other embodiments (not shown), this section may be adapted according to the shape of the section of the foot of the dipole. For example, the section may be chosen to be square, rectangular or elliptical.

[0201] Advantageously, the cylindrical body is truncated longitudinally along a horizontal plane (X,Y), that is to say parallel to the extension dimension of the foot 112b of the low-frequency dipole 112. Thus, the cylindrical body 150 comprises a flat part 150a (i.e. truncated part) extending over the entire length L5 of the body, so that the body is asymmetrical.

[0202] Advantageously, the two truncated cylindrical bodies 150 are arranged respectively on the tubes 112b constituting the foot, so that the flat (truncated) parts 150a are opposite each other, as illustrated in [Fig.17]. Such an arrangement makes it possible to limit the capacitive effects between the quarter-wave traps of the same dipole.

[0203] To the extent that the two truncated cylinders 150 go together, it can be considered that the assembly constituted by these two cylinders forms the quarter-wave trap of a double-footed dipole. In alternative embodiments where the foot of the dipole is simple (i.e. constituted by a single tube), it will be understood that the quarter-wave trap consists of a single cylinder arranged around the single tube.

[0204] The addition of such traps is particularly advantageous in the case where the feet of the low-frequency dipoles have a length approximately equal to half a wavelength associated with the frequencies broadcast on the high-frequency network.

[0205] [Fig. 18] illustrates, in a continuous line, a radiation pattern of the high-frequency network 106, when the low-frequency dipoles 112 are all equipped with quarter-wave traps 150 as previously described with reference to [Fig. 17].

[0206] According to this radiation pattern, the high-frequency network 106 has an azimuthal opening at -3 dB greater than 180° with uniform radiation at the front of the network, i.e. for an azimuthal angle between 90° and 180° and between -180° and -90°.

[0207] Furthermore, [Fig. 18] illustrates, in dotted lines, the radiation pattern of the high frequency network 106 obtained by removing the quarter-wave traps 150 from the low frequency network 104.

[0208] By comparing the two radiation patterns of [Fig. 18], it clearly appears that the presence of the quarter-wave traps 150 on the low-frequency dipoles 112 allows the high-frequency array 106 to maintain an azimuthal aperture of at least 180° at a level between 0 and -3 dB, with almost constant radiation at the front of the array.

[0209] In the absence of a quarter-wave trap on the low-frequency grating, the azimuthal radiation pattern of the high-frequency grating exhibits a flattening as illustrated in dotted lines in [Fig. 18]. This is due to the induced radiation from the feet of the low-frequency dipoles which interacts destructively with the direct radiation from the high-frequency grating, whether the low-frequency grating is active or inactive. Thus, the addition of the quarter-wave traps 150 on the feet 112b of the low-frequency dipoles 112 has the effect of reducing the excitation of these feet and consequently of reducing the distortions of the radiation pattern at the operating frequency of the high-frequency grating.

[0210] The radiation patterns of [Fig. 18] were obtained in the case where the high-frequency network 106 is configured to transmit signals in the RNT frequency bands, in particular at 174 MHz. Thus, the effect described above was illustrated for a high operating frequency equal to 174 MHz but a similar effect exhibiting a progressive decrease could also be observed at high frequencies up to approximately 192 MHz.

[0211] With reference to [Fig. 19], an antenna device according to a second embodiment of the invention which will bear the reference 202 will now be described.

[0212] As in the first embodiment, the antenna device 202 comprises a low-frequency array and a high-frequency array. In the illustrated example, the low-frequency array comprises two low-frequency dipoles 212 with double legs 212b. The high-frequency array comprises four high-frequency dipoles 214 with double legs 214b and a low-frequency connector 220.

[0213] The second embodiment differs from the first embodiment mainly in that the low frequency dipoles 212 are inclined relative to the high frequency dipoles 214 which remain oriented vertically.

[0214] Thus, the arms 212a of the low-frequency dipoles 212 are oriented so that they form a non-zero angle α, preferably equal to 45°, relative to the direction in which the arms 214a of the high-frequency dipoles 214 are oriented (i.e. relative to the vertical).

[0215] In the present example, the two arms of each dipole are collinear with each other. In this case, the direction of the dipole corresponds to the straight line along which the two arms are aligned. More generally, the direction of a dipole is defined by the straight line perpendicular to the bisector of the angle formed between the two arms of the dipole.

[0216] Conversely, in an alternative embodiment (not shown), it is the high-frequency dipoles which are inclined (or oriented) relative to the low-frequency dipoles while the low-frequency dipoles are aligned vertically on the main mast.

[0217] Thus, more generally, the low frequency dipoles 212 and the high frequency 214 are inclined relative to each other according to the invention.

[0218] The inclination of the dipoles of one of the networks relative to the direction of the dipoles of the other network at an angle between -90° and 0° or between 0° and 90° makes it possible to promote inter-service decoupling (or inter-network decoupling when each network provides a service in a separate frequency band) by adding polarization decoupling.

[0219] In the illustrated example, the low-frequency dipoles are adapted due to their orientation to emit and / or receive radiation comprising a horizontal component and a vertical component, while the high-frequency dipoles due to their vertical orientation will emit and / or receive only vertically polarized electric fields.

[0220] The inclination of the dipoles further makes it possible to reduce the influence of the dipole supports on the rear radiation of the array, thus reducing the front / rear ratio of the radiation pattern of the array whose dipoles are inclined.

[0221] As described for the first embodiment, the low frequency network comprises a decoupling device including rejection filters 226 arranged along the main mast 216.

[0222] For example, in the extreme case where one of the networks is configured to transmit and / or receive in horizontal polarization (i.e. having a horizontal orientation of its dipoles) and the other network is configured to transmit and / or receive in vertical polarization (i.e. having a vertical orientation of its dipoles), the decoupling devices associated respectively with the low-frequency network and the high-frequency network may possibly be eliminated. This makes it possible to simplify the structure and the weight of the antenna device, in the event that the necessary inter-network decoupling would be 30 to 40 dB at most.

[0223] In the example illustrated in [Fig. 19], all the high-frequency dipoles 214 are carried by a single auxiliary mast 218, while the low-frequency dipoles 212 are fixed both to the main mast 216 and to the single auxiliary mast 218, i.e. a respective foot 212b on each mast to allow the inclined dipoles to be fixed. Obviously, other dipole support configurations could be envisaged (e.g. one or more auxiliary masts), for example depending on whether the foot of the dipoles is single or double.

[0224] With reference to [Fig.20], an antenna device according to a third embodiment of the invention will now be described.

[0225] A particularity of this third embodiment is that the low-frequency dipoles 312 and the high-frequency dipoles 314 are inclined respectively by -45° and +45° relative to the direction of extension of the masts 316, 318a, 318b corresponding to the vertical direction Z. In other words, the low-frequency dipoles 312 are oriented with respect to the high-frequency dipoles 314, so as to form a right angle (|3=9O°). This spatial quadrature configuration of the two networks has the advantage of facilitating their respective decoupling.

[0226] In alternative embodiments (not shown), other inclinations may of course be considered.

[0227] As for the first and second embodiments, each low frequency dipole 312 is vertically framed by a pair of high frequency dipoles 314 but another particularity of the third embodiment is that a high frequency dipole 314' is arranged in the center of each low frequency dipole 312.

[0228] In the example illustrated, the three masts are all aligned along the Y direction.

[0229] Other variants of arrangement of the dipoles of the antenna device according to the invention will be described below with reference to Figures 21 to 25, where the location of a high-frequency dipole is represented schematically by a cross +, while the location of a low-frequency dipole is represented by a star *. The pairs or groups of high-frequency dipoles are represented by a closed outline in dotted lines.

[0230] In the examples of figures 21 to 24, we are in the case where the support of the low-frequency dipoles is constituted by a main mast 116 while the support of the high-frequency dipoles is constituted by two auxiliary masts 118a, 118b, such as those described with reference to the first embodiment.

[0231] In this case, it is assumed that the high-frequency dipoles are distributed in a balanced manner on the two auxiliary masts 118a, 118b, so that the arrangement of the dipoles is symmetrical. Obviously, according to alternative embodiments (not illustrated), the number of masts may be adapted depending on whether the feet of the dipoles are single or double.

[0232] [Fig.21] illustrates a first variant 402, in which the pairs PI, P2, P3, P4, high frequency dipoles are arranged alternately from left to right of the low frequency dipoles.

[0233] Thus, the alternating positioning of the pairs of high-frequency dipoles, i.e. on one side and the other alternately, relative to the low-frequency dipoles, makes it possible to nest the two networks over a reduced height, thus limiting the size of the antenna device, while ensuring effective decoupling of the networks leading to symmetry of their respective radiation in the azimuthal plane.

[0234] [Fig.22] illustrates a second variant 502, in which the pairs of dipoles high frequency are distributed on the two auxiliary masts, so as to form a group G1 called upper of high frequency dipoles arranged on an upper part of one of the auxiliary masts 118a and another group G2 called lower of high frequency dipoles arranged on a lower part of the other auxiliary mast 118b.

[0235] In this example, each group Gl, G2 consists of two pairs of high-frequency dipoles, so that the arrangement of these two groups is symmetrical with respect to a central point O of the low-frequency network.

[0236] This central symmetry ensures that distortions in the radiation patterns induced by one group of dipoles are compensated by the other group so that the radiation patterns remain symmetrical in the azimuthal plane.

[0237] [Fig.23] illustrates a third variant 602, in which only the pairs of high-frequency dipoles arranged to the left of the low-frequency dipoles vertically frame the latter respectively.

[0238] This embodiment further has the particularity that a high-frequency dipole of each of the pairs is common with the adjacent pair. In other words, each high-frequency dipole belongs to two adjacent pairs, except for the two dipoles located respectively at the two ends of the auxiliary mast 118a.

[0239] In this example, each low-frequency dipole is framed vertically on the left by a pair of high-frequency dipoles and opposite on the right by a high-frequency dipole. Thus, all the high-frequency dipoles arranged to the right of the low-frequency dipoles are aligned along the Y axis (horizontally) with the latter.

[0240] [Fig.24] illustrates a fourth variant 702, in which the high-frequency dipoles are alternately distributed to the right and left of the low-frequency dipoles, so that two consecutive low-frequency dipoles frame a low-frequency dipole in a direction oblique to the vertical.

[0241] Each low-frequency dipole is separated vertically, preferably by the same height h / 2 relative to the two high-frequency dipoles of the pair with which it is associated. Thus, each low-frequency dipole is obliquely framed by a pair of high-frequency dipoles so that the latter are fixed on two separate auxiliary masts 118a, 118b equidistant from the low-frequency dipole.

[0242] In alternative embodiments (not shown), each low-frequency dipole may not be positioned equidistant from the high-frequency dipoles of the associated pair.

[0243] [Fig.25] illustrates an embodiment 802 in which all the high-frequency dipoles are arranged on the same side (for example, to the left as illustrated) of the low-frequency dipoles. In this case, all the high-frequency dipoles are arranged on the same auxiliary mast 118.

[0244] It clearly appears that an antenna device or a communication system including such an antenna device according to any one of the embodiments or any one of its variants as described previously makes it possible to vertically nest the high frequency and low frequency networks so as to reduce the vertical size while limiting the couplings between these networks.

[0245] It will also be noted that the invention is not limited to the embodiments or variants as described above. It will indeed appear to those skilled in the art that various modifications can be made to the embodiments or variants described above, in light of the teaching which has just been disclosed to them.

[0246] In the detailed presentation of the invention which is made above, the terms used must not be interpreted as limiting the invention to the embodiments set out in the present description, but must be interpreted to include all equivalents whose prediction is within the reach of those skilled in the art by applying their general knowledge to the implementation of the teaching which has just been disclosed to them.< / q> < / q> < / q> < / q>

Claims

Claims

1. Antenna device (102; 202; 302; 402; 502; 602; 702; 802) comprising: - a low-frequency network (104; 204; 304) of low-frequency dipoles (112; 212; 312) having respective centers (112c) aligned on a so-called vertical axis (Al); - a high-frequency network (106; 206; 306) of high-frequency dipoles (114; 214; 314) having respective centers (114c) succeeding one another vertically; - a support (115) for the low-frequency dipoles (112; 212; 312) and the high-frequency dipoles (114; 214; 314), said support comprising: • a main support (116; 216; 316) along which the low-frequency dipoles (112; 212; 312) are arranged vertically; and • an auxiliary support (118; 118a, 118b; 218; 318a, 318b) along which the high-frequency dipoles (104; 214; 314) are arranged vertically, said auxiliary support being fixed to the main support; the high frequency dipoles (114;214;314) being arranged so that the center (112c) of each low frequency dipole (112;212;312) is positioned vertically between the centers (114c) of a pair (PI;P2) of two high frequency dipoles (114;214;314); said device being characterized in that: - the main support is a hollow and electrically conductive main mast (116;216;316), and - said device further comprises a coaxial line (122) comprising at least one inner conductor (122a, 122b) electrically connecting the low-frequency dipoles (112) to the same input / output connector (120) of the low-frequency network, so that the main mast constitutes a return line to a common electrical ground.

2. Device (102; 202; 302) according to claim 1, further comprising on the main mast (116; 216) a decoupling device (126; 226; 140) of the low frequency dipoles (112; 212) relative to the high frequency dipoles (114; 214), said decoupling device being fixed on the main mast and connected to the inner conductor (112a, 112b) of the coaxial line (122) of the low frequency network.

3. Device according to claim 2, in which the decoupling device is a coaxial low-pass filter (140) arranged at the input of the low-frequency network, said filter (140) comprising an alternation of coaxial sections (141.1, 142.1, 141.2, 142.2, 141.3, 142.3, 141.4) of high and low impedance.

4. Device (102; 202; 302) according to any one of claims 1 to 3, wherein the center (112c) of each low frequency dipole (112; 212; 312) is arranged vertically in the middle of the centers (114c) of the pair (PI; P2) of high frequency dipoles (114).

5. Device (102; 202; 302) according to any one of claims 1 to 4, wherein the centers (114c) of the high frequency dipoles (114) of each pair (PI; P2) are vertically aligned.

6. Device (102; 402; 502) according to any one of claims 1 to 5, wherein the centers (114c) of the high frequency dipoles (114) of at least one pair (PI) are horizontally offset to one side of the centers (112c) of the low frequency dipoles (112), while the centers (114c) of at least one other pair (P2) of high frequency dipoles (114) are horizontally offset to the other side of the low frequency dipoles (112).

7. Device (102; 402) according to claim 6, in which the pairs (PI, P2, P3, P4) of high frequency dipoles (114) are arranged alternately on either side of the low frequency dipoles (112).

8. Device (602; 802) according to claim 6, in which the two pairs (G1; G2) of high frequency dipoles associated with two consecutive low frequency dipoles are horizontally offset on the same side of the low frequency dipoles.

9. Device (202; 302) according to any one of claims 1 to 8, wherein the low frequency dipoles (212) and the high frequency dipoles (214) are inclined relative to each other.

10. Device (302) according to any one of claims 1 to 9, wherein at least one high frequency dipole (314') is arranged at the center of a low frequency dipole (312).

11. Device (102; 202; 302) according to any one of claims 1 to 10, wherein the low frequency dipoles (112; 212; 312) and / or the High frequency dipoles (114; 214; 314) comprise two arms (112a; 212a; 312a; 114a; 214a; 314a) which are collinear and of the same length, preferably equal to a quarter of the wavelength associated with an operating frequency of said respective network.

12. Device (102; 202; 302) according to any one of claims 1 to 11, wherein the auxiliary support comprises at least one hollow and electrically conductive auxiliary mast (118; 118a, 118b; 218; 318a, 318b), said device further comprising a coaxial line comprising at least one inner conductor (130a, 130b, 130c, 130a', 130b', 130c') running inside said at least one auxiliary mast and electrically connecting the high-frequency dipoles (114) to a same input / output connector (128) of the high-frequency network, so that said at least one mast constitutes a return line to a common electrical ground.

13. Device (102; 202; 302) according to claim 12, further comprising a device for decoupling the high frequency dipoles from the low frequency dipoles, said decoupling device being connected to the inner conductor of the coaxial line of the low frequency network.

14. Device (102; 202; 302) according to claim 2 or 13, wherein the decoupling device comprises one or more frequency rejection filters (126; 136).

15. Device (102; 202; 302) according to any one of claims 1 to 14, further comprising for each low frequency dipole (112), at least one quarter-wave trap (150) arranged around a foot (112b) of the low frequency dipole (112).

16. Device (102; 202; 302) according to claim 15, in which the foot (112b; 114b) of the dipole (112; 114) comprises two fixing tubes parallel to each other, the quarter-wave trap comprising two hollow cylindrical bodies (150) truncated longitudinally so as to each have a flat surface (150a), the two cylindrical bodies (150) being arranged respectively around each of the two fixing tubes (112b; 114b), so that the flat surfaces (150a) of the two cylindrical bodies are opposite each other.

17. Communication system (100) configured to transmit and / or receive radiofrequency signals in at least two distinct frequency bands, characterized in that it comprises an antenna device (102; 202; 302; 402; 502; 602; 702) according to any one of the re- claims 1 to 16.

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