Patent Application
20240421481
The invention relates to an antenna device with two dipole arrays and an associated communication system.
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) broadcasting service and a digital terrestrial radio service, also referred to by the acronym DTR.
Patent GB1247629 describes an antenna device with a high azimuthal aperture for broadcasting UHF (Ultra High Frequency) signals. This antenna device comprises an array of vertically aligned low-frequency dipoles and an array of high-frequency dipoles also vertically aligned. The antenna device also comprises a support for the dipoles, in the form of a vertical mast.
To limit coupling between arrays, patent GB1247629 proposes placing, along the mast, one array 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 support of the mast.
The addition of low-frequency services on an existing pylon already hosting high-frequency services is particularly restrictive insofar as the low-frequency array must be positioned at the top of the pylon to preserve quasi-symmetrical radiation around the mast, while limiting interference with arrays already present on the mast.
Thus, the addition of a low-frequency array intended to, for example, provide an FM broadcasting service operating between 87.5 MHz and 108 MHZ, has the disadvantage of condemning the top of the pylon exclusively to 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.
Thus, it may be desired to provide an antenna device which makes it possible to overcome at least part of the aforementioned problems and constraints.
An antenna device is therefore proposed 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 following each other vertically; and a support of the low-frequency dipoles and the high-frequency dipoles, wherein 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.
Thus, the high-frequency dipoles are vertically nested 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.
The invention may further comprise one or more of the optional features that will be described below, in any technically possible combination.
The support comprises a main support, along which the low-frequency dipoles are vertically arranged. The support further comprises an auxiliary support, along which the high-frequency dipoles are vertically arranged. Preferably, the auxiliary support is attached to the main support.
The main support is a hollow, 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 array, such that the main mast constitutes a return line to a common electrical ground.
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 on the main mast and connected to the inner conductor of the coaxial line of the low-frequency array.
The decoupling device is a coaxial low-pass filter arranged at the input of the low-frequency array. The filter consists of alternating high and low impedance coaxial sections.
The center of each low-frequency dipole is arranged vertically in the middle of the centers of the pair of high-frequency dipoles.
The centers of the high-frequency dipoles of each pair are vertically aligned.
The centers of the high-frequency dipoles of at least one pair of high-frequency dipoles 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.
The pairs of high-frequency dipoles are arranged alternately on either side of the low-frequency dipoles.
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.
The low-frequency dipoles and the high-frequency dipoles are inclined relative to each other.
At least one high-frequency dipole is arranged at the center of a low-frequency dipole.
The low-frequency dipoles and/or the high-frequency dipoles comprise two co-linear arms of the same length, preferably equal to a quarter of the wavelength associated with an operating frequency of said respective array.
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 inner 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 array, so that said at least one mast constitutes a return line to a common electrical ground.
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 array.
The decoupling device comprises one or more frequency rejection filters.
The antenna device further comprises, for each low-frequency dipole, at least one quarter-wave trap arranged around a leg of the low-frequency dipole.
The leg of the low-frequency dipole comprises two fixing tubes parallel to each other, the quarter-wave trap comprising two hollow cylindrical bodies, longitudinally truncated 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.
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.
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:
In the description that 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 and 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.
With reference to
This communication system 100 is configured to transmit and/or receive at the same time two radiofrequency signals from two distinct respective services. For example, one of the services is an FM (Frequency Modulation) broadcasting service and the other is a digital terrestrial radio service (also known as DAB, or Digital Audio Broadcasting).
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 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.
Generally speaking, low frequency and high frequency do not necessarily belong to distinct frequency domains (i.e. metric, decimetric, etc.). For example, the low frequency is an FM frequency (e.g. 88, 98 or 108 MHZ) and the high frequency is a DAB frequency (e.g. 174, 200 or 225 MHZ), in which case the low and high frequencies both belong to the same metric frequency domain.
The communication system 100 thus comprises an antenna device 102 grouping:
Each dipole array is designed to transmit and/or receive in a frequency band centered around a so-called central frequency. Subsequently, it will be considered that this central frequency is the operating frequency of the dipole array, in transmission or in reception.
In transmission mode, each transmitter/receiver 108, 110 is designed to convert data to be transmitted from the associated service into a radiofrequency signal supplied to the dipoles 112, 114 of the associated array 104, 106. These dipoles 112, 114 are then designed to emit the radiofrequency signal in free space.
In reception mode, the dipoles 112, 114 of each array 104, 106 are designed to capture 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 considered.
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.
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 co-linear. Thus, the two arms of each dipole have the same current density to limit the electromagnetic radiation instabilities of the dipole.
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 λ/8 and λ/2, where A designates the reference wavelength associated with the central frequency of the frequency band used for the service concerned.
Preferably, the arms 112a of the low-frequency dipoles 112 are longer than the arms 114a of the high-frequency dipoles 114. In a known manner, the greater the length of the arms of the dipole, the more the dipole is adapted to radiate at low frequency.
In the example of
Each dipole 112, 114 further comprises a leg 112b, 114b for fixing the two arms 112a, 114a. The leg 112b, 114b is for example attached to the central ends of the two arms 112a, 114a. The leg 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 leg, the two tubes are respectively fixed to the central ends of the arms 112a, 114a.
In all the embodiments described in the present application, each dipole 112, 114 has a double leg. However, according to other embodiments not described, each dipole may have a single leg, in particular the low-frequency dipoles and/or the high-frequency dipoles.
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 leg, the length of the leg, 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, not all dipoles in the same array will necessarily be identical.
In general, the arms of each dipole are co-linear and each have a free end. This means that this free end is not connected to any other element. For example, the free end of the arms of each dipole is not connected to the dipole support. Thus, a dipole is clearly distinguished from a batwing or Schmetterling (in German) type of antenna, consisting of two M-shaped arms, as described in document U.S. Pat. No. 5,497,166. Unlike the dipole, each M-shaped arm of such an antenna does not have any free ends, as is the case, for example, with a T-shaped dipole where only the leg of the T is fixed to the support.
In the example of
The centers 112c of the low-frequency dipoles 112 are aligned along the same vertical axis A1. By “aligned” is meant that the low-frequency dipoles 112 are substantially aligned along a vertical line, that is to say that their centers 112c can be offset horizontally relative to the vertical axis A1, for example at less than one fifteenth of the reference wavelength associated with the low-frequency array 104 as previously defined.
For example, in the case where the low-frequency array 104 operates at a frequency f1 equal to 100 MHz in an FM band, the associated reference wavelength Δ1 is equal to 3 m (λ1=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 λ1/15=0.2 m perpendicular to the axis A1.
Still in the example of
A first pair of high-frequency dipoles 114 (called the upper pair) is fixed on an upper portion of an auxiliary mast 118a, while a second pair of high-frequency dipoles 114 (called the lower pair) is fixed on a lower portion of another auxiliary mast 118b.
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.
As illustrated in
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.
Thus, the dipoles of the upper pair have a vertical plane of symmetry called upper, while the dipoles of the lower pair have a vertical plane of symmetry called lower. 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 π. As illustrated, the legs of the dipoles of the lower pair are included in the lower vertical plane π. In order not to make
This configuration allows to correct the edge effects at the ends of the high-frequency array, which has the effect of improving the radiation pattern of the array (e.g. symmetrization in the azimuthal plane, and/or reductions in radiation attenuation) as well as the overall impedance adaptation of the array by playing on the mutual impedances.
In other embodiments, the extreme dipoles may be co-linear with the central dipoles, so as to significantly simplify the manufacture of the array from a mechanical point of view in particular.
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.
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 arrays.
To support the dipoles 112, 114, the antenna device 102 further comprises a support 115 to which the dipoles 112, 114 are fixed by their respective legs 112b, 114b.
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
Preferably, the auxiliary mast(s) 118a, 118b are attached to the main mast 116. Thus, to deploy an additional service, the high-frequency array 106 can be easily added to the low-frequency array 104 previously deployed. Conversely, the main mast 116 could be attached to the auxiliary mast(s) to add the low-frequency array 104 to the high-frequency array 106 previously deployed.
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
The support 115 is, for example, of hollow tubular structure and circular section, as illustrated in
Generally speaking, the support 115 is of multi-tubular structure in the sense that it comprises at least two tubular longitudinal parts (i.e. masts) of any section, preferably rounded, such as circular or oval.
Thus, the support 115 is not a planar reflector, unlike the case of sector antennas typically used in mobile radio arrays whose azimuthal aperture at −3 dB is generally limited to 120° precisely because of the presence of a reflector plane.
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 portion of the same array grouping a subset of dipoles of this array.
Therefore, the support 115 is designed so that, on the one hand, all the low-frequency dipoles of the low-frequency array and, on the other hand, all the high-frequency dipoles of the high-frequency array 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.
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 stresses imposed by the structure of the communications system.
The support 115 is sized 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, low-frequency radiation and high-frequency radiation can remain quasi-constant around the A1 axis.
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.
This angular bulk E has a bisector A2. The front-rear direction X is taken along this bisector A2. Thus, the support 115 is located, in the direction X, at the rear of the low-frequency dipoles 112, as well as at the rear of the high-frequency dipoles 114.
Generally, the support 115 has a sufficiently small footprint to allow each of the arrays to have a radiation pattern presenting an azimuthal opening at −3 dB of at least 180°.
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 D1 less than 10%, preferably 5%, of the central operating wavelength of the low-frequency array 104. Similarly, the auxiliary masts 118a, 118b have a diameter D2 less than 10% of the central operating wavelength of the high-frequency array 106.
For example, in the case of an DTR service, the central operating wavelength of the high-frequency array (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 array (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 Y direction approximately equal to the sum of the diameter D1 of the main mast 116 and the diameters D2 of the auxiliary masts 118a, 118b, i.e. D1+2×D2=30+2*15*=60 cm, assuming that the auxiliary masts have the same diameter D2.
In the example of
With reference to
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
As explained previously, the low-frequency dipoles 112 are aligned vertically along the vertical axis A1. These are spaced regularly by a distance d1 corresponding to the pitch of the low-frequency array. The value of this distance d1 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 array. For example, in the case where the low frequency is equal to 100 MHZ, the distance d1 is adjusted so that d1=0.72.λ, where A denotes the wavelength associated with the operating frequency of the low frequency array. Generally speaking and without other constraints, the pitch d1 of the low frequency array is between 0.7.λ and 0.8.λ so as to maximize the radiation in all directions contained in a horizontal plane, and more generally between 0.5.λ and λ.
For their part, the high-frequency dipoles 114 are arranged on the auxiliary masts 118a, 118b, such that each low-frequency dipole 112 is positioned vertically between a respective pair P1, P2 of high-frequency dipoles 114.
For example, the high-frequency dipoles 114 are divided into distinct pairs P1, 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 P1, P2.
The two high-frequency dipoles 114 of each pair P1, 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 P1, 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 P1, P2.
Preferably, the high-frequency dipoles 114 of each pair P1, P2 are aligned vertically.
In the example illustrated in
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.
This right and left offset simplifies the addition of the high-frequency dipoles 114, since it is possible to fix each pair P1 of high-frequency dipoles 114 offset to the left on the auxiliary mast 118a, and each pair P2 offset to the right is fixed on the other auxiliary mast 118b.
Furthermore, thanks to this offset 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.
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 deformation of the radiation pattern of the low-frequency dipoles 112.
More preferably, the pairs P1, P2 of high-frequency dipoles 114 are alternately offset to the right and to the left. This also improves the compensation of the deformation of the radiation pattern of the low-frequency dipoles 112.
Still to improve this compensation, the offset to the right and to the left is, preferably, the same and noted by the reference “e” in
In other embodiments (not shown), the offset of the pairs may be different on the right and left of the low-frequency dipoles 112.
With reference to
This low frequency electrical connection 119 comprises, for example, an outer electrical connection 121 connecting the transmitter/receiver 108 to the support 115. This outer electrical connection 121 is, for example, a coaxial cable.
The low-frequency electrical connection 119 further comprises, carried by the support 115, an input/output connector 120, called low frequency, to which the outer electrical connection 121 is designed to be wired. In particular, the low-frequency connector 120 is carried by the main mast 116. Preferably, the low-frequency connector 120 is a coaxial connector.
The low-frequency electrical connection 119 further comprises, in the support 115, for each low-frequency dipole 112, an inner electrical conductor 122a, 122b electrically connecting the low-frequency connector 120 to the low-frequency dipole 112 considered. Each inner 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 leg 112b of the low-frequency dipole 112 considered, to reach one of its arms 112a. In the case where the leg 112b is double, the inner conductor 120 runs in one of its tubes.
The arm 112a reached by the inner conductor 122a, 122b is the one pointing downwards in the example of
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.
Alternatively, the conductive section 124 is not electrically connected to the downward-pointing arm 112a but capacitively coupled to the latter through the gap between the two arms 112a of the low-frequency dipole 112.
The inner electrical conductor 122a may comprise a plurality of electrical junctions placed end to end as illustrated in
Each inner conductor 122a, 122b may have a variable section along its length, as illustrated in
Furthermore, the main mast 116 and the leg 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 leg 112b surrounding the inner conductor 122a, 122b thus form a coaxial connection.
Using the main mast 116 and each leg 112b as a return line has several advantages.
On the one hand, it contributes to making the antenna device 102 electrically symmetrical, so that it generates little imbalance of the electrical 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.
On the other hand, it facilitates the impedance matching of the low-frequency array 104 in line with the characteristic impedance of the coaxial line 121 (generally of the order of 50Ω) when the latter is connected to the low-frequency connector 120.
Furthermore, the support 115 comprises, for example, a plurality of decoupling devices 126 configured to limit disturbances produced by the high-frequency array 106, for example by intermodulation phenomena, on the low-frequency array 104.
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 inner conductor 122a, 122b of this low-frequency dipole 112. In the illustrated example, 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.
Preferably, the decoupling devices 126 are rejection filters comprising, for example, an open angled coaxial line. The angled coaxial line 126 includes an outer conductor 126b and an inner conductor 126a extending inside the outer conductor 126b and electrically insulated therefrom. 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 (ε ″/ε′) less than or equal to 0.001, where ε″ and ε′ represent respectively the imaginary portion and the real portion of the electrical permittivity.
The inner conductor 126a is in contact with the inner conductive line 122a, 122b. As illustrated, the open angled coaxial line is L-shaped and has a longitudinal portion of length L1z extending parallel to the main mast 116 along the Z axis and a transverse portion of length L1x extending perpendicular to the main mast 116 along the X direction. Thus, each open angled coaxial line has a developed length L1 equal to the sum of the lengths of the longitudinal and transverse portions, i.e. L1=L1z+L1x.
Preferably, the developed length L1 of each open angled line is between λg/6 and λg/3, where λg is the guided wavelength corresponding to the central operating frequency of the high-frequency array 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 array, as defined above.
In other embodiments (not described), other decoupling devices may be considered, such as an open coaxial line without conductor or any other equivalent device.
In the example of
For example, the filters of a pair of rejector filters 126 are vertically spaced 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 λg, i.e. L4<3×λg.
The positioning of the rejection filters 126 relative to the low-frequency dipoles 112 may be adjusted so as to limit their interaction with the low-frequency dipoles 112 as much as possible. For this purpose, the rejection filters 126 are arranged, for example, two by two at the leg 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 array as little as possible, in other words so that they deform the radiation pattern of the low-frequency array as little as possible.
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.
The developed length L1 and the intra-pair separation length L4 may be adjusted so as to take into account the inter-array frequency spacing and their respective bandwidth, by rejecting as best as possible the frequency band associated with the other array, by facilitating or at least not degrading the impedance matching of the array on which they are installed and by making it possible to achieve the average and peak power capacities required according to the use considered.
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 reduce possible interaction with a metal plug located at the end.
The inner conductors 126a and outer conductors 126b have respective diameters which can be adjusted so as to obtain an impedance of the open angled coaxial line 126 of between 10 and 200Ω and to support average and maximum (peak) electrical powers required for reception and/or transmission.
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 inner 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 was 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, i.e. varying by approximately +/−10% around a median value.
With reference to
This high-frequency electrical connection 127 shown in simple dotted lines, comprises for example an outer electrical connection 125 connecting the transmitter/receiver 110 to the support 115. This outer electrical connection 125 is for example a coaxial cable.
The high-frequency electrical connection 127 further comprises, carried by the support 115, an input/output connector 128, called high-frequency, to which the outer electrical connection 125 is designed to be wired. 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.
The high-frequency array 106 further comprises a coaxial line 130 configured to preferentially connect in parallel all of the high-frequency dipoles 114 of the array to the high-frequency connector 128. Thus, from the high-frequency connector 128, the coaxial line 130 splits into two separate branches 103c, 130′c which themselves split into two sub-branches {130a, 130b}, {130′a, 130′b) respectively, as illustrated in
In alternative embodiments (not shown), 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.
As with the coaxial line of the low-frequency array, the coaxial line 130 of the high-frequency array 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.
The inner conductive portion of the coaxial line is a filiform electrical conductor running inside the auxiliary masts 118a, 118b and inside the legs 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 can itself have subsections of different impedances.
In the illustrated example, the two dipoles fixed on an upper portion of the auxiliary mast 118a are connected to the connector 128 via the sections 130a, 130b, 130c. The two dipoles fixed on a lower portion of the other auxiliary mast 118b are connected to the connector 128 via the sections 130′a, 130′b, 130′c. Section 130′c comprises a portion running inside a hollow crosspiece 132 connecting the two auxiliary masts 118a, 118b.
Given 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 hz1 from one pair of high-frequency dipoles and at a distance hz2 from the other pair of high-frequency dipoles, such 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. hz1=hz2+hy, so that the currents flowing inside the lines are balanced between the high-frequency dipoles 114.
The outer conductive portion of the coaxial line comprises the auxiliary masts 118a, 118b and the legs 114b of the high-frequency dipoles 114. The outer conductive portion thus formed serves as a return line for the currents of the coaxial line, so that all the dipoles of the high-frequency array 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 dipoles 112 and high-frequency dipoles 114 to the same reference potential, the radiation patterns of the low-frequency arrays 104 and high-frequency arrays 106 are stabilized.
Preferably, the leg of each dipole has a length approximately equal to one quarter of the wavelength associated with the operating frequency of the array to which it belongs. This particular length has several advantages.
On the one hand, it contributes to making the antenna system more symmetrical in terms of the distribution of electric currents across the coaxial line connecting each of the dipoles of the same array, 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.
On the other hand, it makes it possible to avoid excessive deformation of the azimuthal radiation pattern of the dipole array that may result from an interaction of the dipoles with their support mast. For example, a leg length that is too long will have the effect of crushing the azimuthal radiation pattern until the pattern becomes bidirectional.
As illustrated in
Preferably, the tubular part 129a is fixed on 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 also fixed to the other mast by means of this additional crosspiece.
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.
The high-frequency array 106 will now be described with reference to
On the left part of
As previously described with reference to
As illustrated in
The dipoles of the upper pair belong to the same vertical plane denoted π1 comprising the auxiliary mast 118a, while the dipoles of the lower pair belong to the same other vertical plane π2 comprising the auxiliary mast 118b hidden behind the auxiliary mast 118a according to the plane of
In the case where the high-frequency array comprises a plurality of upper pairs (instead of a single pair as shown in
Similarly, if the high-frequency array comprises a plurality of lower pairs (instead of a single pair as shown in
In general, dipoles will be considered to be vertically aligned if they belong to the same vertical plane (i.e. including the Z direction).
As described above, for each of the two pairs of dipoles, the extremal dipoles are larger than the central dipoles. For example, the extremal dipole has a leg of length H1 greater than that H2 of the leg of the central dipole. The extremal dipole has a section of diameter greater than that of the section of the central dipole.
Referring to
Advantageously, the connecting device 129 is configured to reject the frequency band in which the low-frequency array 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 portion 129a of the connecting device 129.
The decoupling device 136 comprises two rejector filters 136a, 136b configured to reject low frequencies. Each rejector filter comprises a pair of open angled coaxial lines 138 disposed head-to-tail on either side of the tubular portion 129a near a crosspiece 129b.
Each rejector filter is associated with a pair of high-frequency dipoles. However, in other embodiments (not shown), a plurality of pairs of rejection filters may be associated with each pair of high-frequency dipoles; the number of filters may vary between 1 and 3 typically.
As previously described for the low-frequency array, 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 λ′g/6 and λ′g/3, where λ′g denotes a guided wavelength corresponding to the central operating frequency of the high-frequency array.
As previously described for the low-frequency array, the outer conductor of these angled coaxial lines 138 is preferably slightly elongated relative to the inner conductor, so as to limit radiation at the open end of the 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 angled coaxial lines can be advantageously adjusted to obtain an impedance between 10 and 200Ω and allow the desired average and peak power resistances 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.
The transmission performance results of the antenna device 102 according to the first embodiment described above with reference to
This figure shows the normalized radiation pattern at 0 dB of the low-frequency array expressed in dB in the azimuthal plane (X,Y) as a function of an azimuthal angle φ expressed in degrees.
This pattern shows that the radiation of the low-frequency array 104 is symmetrical although not perfectly isotropic (i.e. quasi/pseudo-omnidirectional) with a lower gain at the rear (φ=) 0° of the array than at the front (φ)=180°. The gain is almost constant to within about −2 dB, on the front part of the array, i.e. for an azimuthal angle q between −180° and −90° and between 90° and 180°. At the rear of the low-frequency array 104, the attenuation varies between 2 dB and 6 dB depending on the azimuthal angle q, i.e. for −90°<φ<0° and −0°<φ90°.
Such radiation shows that the low-frequency array has an azimuthal opening at −3 dB at least equal to 180°. These results remain generally valid for the three FM frequencies tested.
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.
This pattern 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°<θ<−60° (at the front of the array) and 60°<θ<120° (at the back of the array).
Such radiation shows that the high-frequency array 106 has an azimuthal aperture at −3 dB of at least 180° at the front of the array (i.e. for −180°<φ<−90° and 90°<φ<) 180°. The gain at the rear of the antenna is all the more reduced as the operating frequency is high.
In view of this pattern, it can be seen that despite the presence of two secondary lobes, on either side of the horizontal plane, the high-frequency array 106 radiates substantially forward (θ=−90°) and backward (θ=90°) to a lesser extent.
With reference to
The pattern in
In
These results show that for the DTR band between 174 and 225 MHZ, an additional maximum isolation of approximately 40 dB is obtained thanks to the decoupling devices 126, 136.
Thus, the use of the rejection filters 126 of the low-frequency array 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 array 104 to the high-frequency array 106 in the operating frequency band of the high-frequency array 106.
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 array 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 array 106 to the low-frequency array 104 in the operating frequency band of the low-frequency array 104.
The input/output connector 120 of the low-frequency array 104 is moved to the end of the coaxial low-pass filter 140. However, it can be left in its original place in the event that the coaxial low-pass filter itself is equipped with its own coaxial input and output connectors.
Preferably, the coaxial low-pass filter 140 comprises an alternation of high and low impedance coaxial sections, denoted respectively 141.k and 142.k-1, where k is a natural integer preferably varying from 2 to 6. In the illustrated example, the 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.
The coaxial sections will be sized so that their impedance varies preferably between 10 and 200Ω and in line with the average and peak power ratings to be supported in the context of the exploitation of the invention.
Similarly, the order of the filter 140 thus constituted will be adjusted to reach 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 one pole.
The length of the coaxial sections will preferably be between λg/20 and λg/5, where λg represents the guided wavelength associated with the central operating frequency of the high-frequency array 106.
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.
An alternative embodiment of the high-frequency array will now be described with reference to
According to a particularity of this variant, the decoupling devices 126 of the high-frequency array 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 relative to the support 116 of the low-frequency array.
As previously described, the high-frequency dipoles 214 are connected to the input/output of the high-frequency array by a coaxial line 230 comprising a plurality of junctions 130a, 130b, 130c to feed the upper dipole pair and a plurality of junctions 130′a, 130′b, 130′c to feed the lower dipole pair. However, unlike what has been previously described with reference to
The high-frequency array 206 comprises four dipoles 214a, 214b, 214c, 214d of different dimensions. For example, the extremal dipoles 214a, 214d do not have the same dimensions as the central dipoles 214b, 214c. The two extremal 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.
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 array 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.
As previously described with reference to
According to a particular feature of the present variant, each decoupling device 236 comprises an angled coaxial line 238b and an open coaxial line 238a, the latter 238a being integrated inside an auxiliary mast 118a, 118b.
Furthermore, this variant differs from the embodiment described with reference to variant a) of
From a radioelectric point of view, this embodiment variant has the advantage that the antenna device is perfectly symmetrical on its outer 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 array 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.
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/rear ratio of the radiation pattern of the high-frequency array compared to an equivalent less integrated solution.
With reference to
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 legs of the low-frequency dipoles on the radiation of the high-frequency array 106.
In
More generally, all or part of the low-frequency dipoles of the low array may be equipped with one or more quarter-wave traps.
According to the example illustrated in
For example, each quarter-wave trap 150 is made up 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 leg 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.
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 to thus limit the contribution of the low-frequency dipoles 104 to the radiation of the high frequency array 106.
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 array 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/(4×L5), where c=3.108 m/s.
Thus configured, the quarter-wave trap 150 has the effect of avoiding or at least limiting deformation of the azimuthal radiation patterns of the high-frequency array 106, over its operating frequency band.
According to the example of
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 array 104.
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 tubes 112b constituting the legs of the low-frequency dipoles 112.
In the example illustrated, each cylindrical body has a circular section. However, in other embodiments (not shown), this section can be adapted depending on the shape of the section of the leg of the dipole. For example, the section could be chosen square, rectangular or elliptical.
Advantageously, the cylindrical body is truncated longitudinally along a horizontal plane (X,Y), that is to say parallel to the extension dimension of the leg 112b of the low-frequency dipole 112. Thus, the cylindrical body 150 comprises a flat portion 150a (i.e. truncated portion) extending over the entire length L5 of the body, so that the body is asymmetrical.
Advantageously, the two truncated cylindrical bodies 150 are arranged respectively on the tubes 112b constituting the leg, so that the planar (truncated) parts 150a face each other, as illustrated in
To the extent that the two truncated cylinders 150 are a pair, we can consider that the assembly constituted by these two cylinders forms the quarter-wave trap of a double-legged dipole. In alternative embodiments where the leg of the dipole is single (i.e. made up of a single tube), it will be understood that the quarter-wave trap is made up of a single cylinder arranged around the single tube.
The addition of such traps is particularly advantageous in the case where the legs of the low-frequency dipoles have a length approximately equal to half a wavelength associated with the frequencies broadcast on the high-frequency array.
According to this radiation pattern, the high-frequency array 106 has an azimuthal aperture at −3 dB greater than 180° with uniform radiation at the front of the array, i.e. for an azimuthal angle between 90° and 180° and between −180° and −90°.
Furthermore,
By comparing the two radiation patterns of
In the absence of a quarter-wave trap on the low-frequency array, the azimuthal radiation pattern of the high-frequency array presents a crushing as illustrated in dotted lines in
The radiation patterns in
With reference to
As in the first embodiment, the antenna device 202 comprises a low-frequency array and a high-frequency array. In the example illustrated, the low-frequency array comprises two low-frequency dipoles 212 with double legs 212b. The high-frequency array includes four high-frequency dipoles 214 with double legs 214b and a low-frequency connector 220.
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.
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).
In the present example, the two arms of each dipole are co-linear with each other. In this case, the direction of the dipole corresponds to the line along which the two arms are aligned. More generally, the direction of a dipole is defined by the line perpendicular to the bisector of the angle formed between the two arms of the dipole.
Conversely, in a variant 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.
Thus, more generally, the low-frequency dipoles 212 and the high-frequency dipoles 214 are inclined relative to each other according to the invention.
The inclination of the dipoles of one of the arrays relative to the direction of the dipoles of the other array at an angle between −90° and 0° or between 0° and 90° makes it possible to promote inter-service decoupling (or inter-array when each array provides a service in a distinct frequency band) by adding polarization decoupling.
In the example illustrated, the low-frequency dipoles are suitable 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 will only receive vertically polarized electric fields.
The inclination of the dipoles also makes it possible to reduce the influence of the dipole supports on the rear radiation of the array, thus reducing the front/back ratio of the radiation pattern of the array whose dipoles are inclined.
As described for the first embodiment, the low-frequency array comprises a decoupling device including rejector filters 226 arranged along the main mast 216.
For example, in the extreme case where one of the arrays is configured to transmit and/or receive in horizontal polarization (i.e. having a horizontal orientation of its dipoles) and the other array is configured to transmit and/or receive in vertical polarization (i.e. presenting a vertical orientation of its dipoles), the decoupling devices associated respectively with the low-frequency array and the high-frequency array could possibly be eliminated. This makes it possible to simplify the structure and weight of the antenna device, in the event that the necessary inter-array decoupling would be 30 to 40 dB maximum.
In the example illustrated in
With reference to
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 relative to the high-frequency dipoles 314, so as to form a right angle) (β=90°. This spatial quadrature configuration of the two arrays has the advantage of facilitating their respective decoupling.
In alternative embodiments (not shown), other inclinations could obviously be considered.
As for the first and second embodiments, each low-frequency dipole 312 is framed vertically by a pair of high-frequency dipoles 314 but another particularity of the third embodiment is that a high-frequency dipole 314′ is arranged at the center of each low-frequency dipole 312.
In the example shown, the three masts are all aligned in the Y direction.
Other variants of arrangement of the dipoles of the antenna device according to the invention will be described below with reference to
In the examples of
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 can be adapted depending on whether the legs of the dipoles are single or double.
Thus, the alternating positioning of the pairs of high-frequency dipoles, i.e. on one side and on the other alternately, in relation to the low-frequency dipoles, makes it possible to nest the two arrays over a reduced height thus limiting the bulk of the antenna device, while ensuring effective decoupling of the arrays leading to symmetry of their respective radiation in the azimuthal plane.
In this example, each group G1, G2 is made up 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 array.
This central symmetry ensures that the deformations 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.
This embodiment also 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.
In this example, each low-frequency dipole is framed vertically to the left by a pair of high-frequency dipoles and opposite to the right with 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.
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 framed obliquely 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.
In alternative embodiments (not illustrated), each low-frequency dipole may not be positioned equidistant from the high-frequency dipoles of the associated pair.
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 of its variants as described above makes it possible to vertically nest the high-frequency and low-frequency arrays so as to reduce vertical footprint while limiting coupling between these arrays.
It should also be noted that the invention is not limited to the embodiments or variants as described above. It will indeed appear to the person 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 him/her.
In the detailed presentation of the invention which is made previously, the terms used should not be interpreted as limiting the invention to the embodiments set out in the present description, but must be interpreted to include all the equivalents for which the prediction is within the reach of the person skilled in the art by applying his/her general knowledge to the implementation of the teaching which has just been disclosed to him/her.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR2114034 | Dec 2021 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/080870 | 11/4/2022 | WO |
