EP1516393B1 - Double polarization dual-band radiating device - Google Patents

Abstract

The invention concerns a device comprising a first radiating element operating in a first frequency band F1, consisting of four dipoles (1, 2, 3, 4) in square arrangement and a second radiating element (23) operating in a second frequency band F2 consisting of at least one dipole arranged in the center of the square of dipoles (1, 2, 3, 4) forming the first radiating element, each dipole being center-fed by a balun. The set of radiating elements is arranged above a reflector (24). The dipoles (1, 2, 3, 4) forming the first radiating element and the baluns (8, 9, 10, 11) associated therewith are produced in a common metal plate (5), each balun of a dipole consisting of a close-circuit slotted line cut out in the metal plate (5) along a direction perpendicular to the dipole axis. The second radiating element (23) consists of at least one dipole arranged inside a metal cavity (7) located in the center of the metal plate (5). The invention is applicable to cellular radio communication networks.

Description

The invention relates to antennas and their radiating elements that can be used in particular in the base stations of cellular radio communication networks of the GSM or UMTS type, for example.

A double polarization radiating element may be formed of two radiating dipoles, each dipole consisting of two collinear conductor strands. The length of each strand is substantially equal to one quarter of the working wavelength. The dipoles are mounted on a structure allowing their feeding and their positioning above a reflector (plane-mass). This makes it possible, by reflection of the rear radiation of the dipoles, to refine the directivity of the radiation pattern of the assembly thus formed.

It is known to produce a radiating device operating in two frequency bands and with orthogonal polarizations, to have a first radiating element, formed by four quadrature dipoles operating on a first frequency F1, around a second radiating element formed by two dipoles. crossed in quadrature operating on a second frequency F2, all of these elements being disposed above a reflector.

According to their orientation in space, the dipoles can radiate or receive electromagnetic waves in two polarization paths, for example a horizontal polarization path and a vertical polarization path, or else two polarization paths offset by an angle of ± 45 ° from horizontal or vertical.

However, the inter-band decoupling depends fundamentally on the relative orientation of the second radiating element placed in the center of the first. In particular, the parallel dipoles of the elements operating in the frequency bands F1 and F2 are insufficiently decoupled in the upper frequency band of frequency F2 for which the peripheral dipoles have a large dimension relative to the wavelength corresponding to the frequency F2. . Indeed, the interaction between the peripheral dipoles operating at the frequency F1 and the crossed dipoles operating at the frequency F2 is due to both the direct radiation, the dipoles being in line of sight, but also to the radiation reflected by the reflector. On the other hand, the perpendicular paths of the two radiating elements are well decoupled by virtue of this geometrical orthogonality. But if this orthogonality is no longer respected, especially if the dipoles of the central radiating element have arbitrary orientations relative to those of the peripheral dipoles forming the first radiating element, then a fairly strong inter-band coupling appears between the different channels of transmission or reception of the two radiating elements.

Another disadvantage of this structure is that the radiation of the central radiating element is disturbed by the peripheral radiating element. Indeed, this radiation is partially diffracted in particular by the dipoles of the peripheral radiating element, so that the resulting radiation pattern in the best case has undulations and, for an arbitrary relative orientation of the dipoles of the central radiating element this diagram is asymmetrical with respect to the principal axis of radiation perpendicular to the plane of the dipoles.

It therefore remains difficult to obtain a single-band radiating element that is simple to manufacture, having two linearly polarized orthogonal channels strongly decoupled in a wide frequency band. It is a fortiori difficult to achieve a bipolarized directional network comprising several radiating elements of this kind, and offering good polarization purity.

On another plane, it would be desirable to obtain a radiating element with two orthogonal polarization paths each having a unidirectional radiation pattern and whose half-power aperture in the diagonal planes, ie planes located at ± 45 ° of the main planes E and H of each dipole, substantially less than 90 °.

The invention aims to improve the situation.

The dual-polarization dual-band radiating device according to the invention comprises a first radiating element operating in a first frequency band F1 which is formed of four dipoles arranged in a square and a second radiating element operating in a second frequency band F2 which is formed of at least one dipole disposed in the center of the square of the dipoles forming the first radiating element, each dipole being fed at its center by a balun. The first and the second radiating elements are arranged above a reflector.

According to an advantageous arrangement, the dipoles forming the first radiating element and the baluns are made in the same metal plate, each balun of a dipole being formed by a short-circuit line cut into the metal plate in a direction perpendicular to the metal plate. axis of the dipole. The second radiating element is formed by at least one dipole disposed inside a cavity opening at the center of the metal plate.

According to another advantageous embodiment of the invention the metal plate and the cavity may be made in one piece, for example stamping. The second radiating element operating in the frequency band F2 is then fixed inside and in the center of the cavity, the bottom of which serves as an electrical short-circuit plane to at least one balun or balun serving to supply the second element. radiant

Thus, the first radiating element and the second radiating element have a very weak electromagnetic interaction. This is only due to the edge diffraction of the cavity. In this way the decoupling between the two frequency bands is very strong regardless of the relative orientation of the dipole or dipoles forming the second radiating element inside the cavity, that is to say its polarization.

• la figure 1 représente un premier mode de réalisation d'un premier dispositif rayonnant à double polarisation pouvant fonctionner dans deux bandes de fréquence différentes selon l'invention,
• la figure 2 représente une vue suivant la coupe AA de la figure 1.
• la figure 3 est une vue en perspective du dispositif représenté aux figures 1 et 2.
• la figure 4 est une variante de réalisation du premier élément rayonnant de la figure 1
• la figure 5 représente un deuxième mode de réalisation d'un dispositif selon l'invention.
• la figure 6 est une vue suivant la coupe AA du dispositif de la figure 5.
• la figure 7 est une vue en perspective du dispositif des figures 5 et 6.
• la figure 8 est une vue partielle en perspective d'un réseau colinéaire formé d'une part d'éléments rayonnants bi-bande et bipolarisés du type décrit à la figure 7 et d'éléments rayonnants monobande et bipolarisés du même type que les éléments rayonnants centraux de la figure 7.

Other characteristics and advantages of the invention will appear in the detailed description below, made with reference to the appended drawings, in which:

• the figure 1 represents a first embodiment of a first dual polarization radiating device that can operate in two different frequency bands according to the invention,
• the figure 2 represents a view according to the AA section of the figure 1 .
• the figure 3 is a perspective view of the device shown in figures 1 and 2 .
• the figure 4 is an alternative embodiment of the first radiating element of the figure 1
• the figure 5 represents a second embodiment of a device according to the invention.
• the figure 6 is a view along the AA section of the device of the figure 5 .
• the figure 7 is a perspective view of the device figures 5 and 6 .
• the figure 8 is a partial perspective view of a collinear network formed on the one hand of bi-band and bipolarized radiating elements of the type described in FIG. figure 7 and single-band and bipolarized radiating elements of the same type as the central radiating elements of the figure 7 .

The drawings contain, for the most part, elements of a certain character. They can therefore not only serve to better understand the description, but also contribute to the definition of the invention, if any.

The device represented in figures 1 , 2 and 3 where the homologous elements are represented with the same references, shows four dipoles referenced 1 to 4 forming a square, cut in a metal plate 5 having a central hole 6 into which opens the open end of a radiating cavity 7. The side of the square formed by each dipole has a typical length equal to the half wavelength of the frequency wave F1 radiated by the dipoles for a mid-power beam opening close to 65 ° in the horizontal plane.

It should be noted, however, that it is the spacing (d) between two parallel dipoles of the radiating plate 5 and consequently the length of the sides of the square formed by the four dipoles 1 to 4 which largely determines the directivity of the radiation pattern in the horizontal plane of these dipoles, ie the half-power aperture of this diagram and that this aperture depends very little on the length (1) of the dipoles. The length (1) of a dipole determines its impedance and can be greater or less depending on the thickness and width of the dipole. The larger this thickness is, the shorter the length of the dipole will be. In other words, the side (d) of the square is determined as a function of the half-power opening which is sought and which may have a value other than 65 ° and the length of the dipoles is adjusted to ensure the adaptation of impedance, generally 50 Ohms, of the pair of associated parallel dipoles to form a directional pattern polarization channel. In accordance with an advantageous embodiment, the dipoles 1 to 4 and the cavity 7 can be made in one piece by cutting and stamping of the metal plate 5.

Each dipole 1 to 4 is fed by a balun referenced 8 to 11, respectively, of the "balun" type formed by a short-circuit line cut in the metal plate 5.

Each balun constitutes a support arm of the corresponding dipole. To do this, the plate 5 is formed around the hole 6 through which the cavity 7 passes through a concentric ring 12 having on its outer periphery and along two right-angle directions, protuberances or arms 13 to 16 of shapes, for example, rectangular, chamfered or trapezoidal, respectively connecting the ring 12 to the dipoles 1 to 4. The radial length (h) of the arms is preferably non-zero, for example greater than 0.05λ1 so as to avoid direct contact of the inner edge of the dipoles with the outer edge of the ring 12 and thus minimize the interaction between the current flowing on the dipole and the currents flowing on the ring 12. The average width (w) of the arms is typically 5 to 10 times the width of the slit line which is otherwise very small in front of the wavelength λ1 corresponding to the frequency F1.

The width of the ring 12 is determined to be sufficient both mechanically to support the dipoles and on the radioelectric plane to stabilize the directivity of the radiation patterns of the cavity 7 in the second frequency band F2, by making less fluctuating half-power aperture of radiation patterns as a function of frequency. This width is preferably greater than 5/100-th of the wavelength λ2 corresponding to the frequency F2.

The dipoles 1 to 4 are fed at their base, that is to say at the open end of the slit lines of the baluns 8 to 11 by means for example of coaxial cables respectively referenced 17 to 20. On the sectional view of the figure 2 the geometrically parallel dipoles 2 and 4 on two opposite sides of the square are fed at equal phase and amplitude by two identical coaxial lines 18 and 20 and an association tee 21 to form a directional pattern polarization path, such as a classical network of two parallel dipoles. The coaxial feed lines 17, 18, 19, 20 of the dipoles are respectively disposed along and on one side of the baluns 8, 9, 10, 11. The outer conductive sheath of the coaxial lines 17 to 20 is in electrical contact with the base of the first half of the dipole it feeds and with the plate 5, and the central conductor is connected to the base of the other half of the same dipole. Two orthogonal polarization paths are thus obtained whose radiation patterns are substantially identical. However, this mode of association is not limiting, and other modes can be envisaged.

The baluns of the dipoles are slot lines cut into the meandering plate 5. The meanders of each slot line must be in sufficient number for the slot line to have a length substantially equal to one quarter of the wavelength of the frequency wave F1 radiated by the first radiating element. However, the slit lines can take other forms, they can for example as shown in FIG. figure 4 or the elements homologous to those of the figure 1 have the same references, be formed by a circular section followed by a rectilinear section leading to the feed base of a dipole. The circular section may be anywhere on the crown 12. However, to avoid the coupling between the frequency waves F1 and F2, it is preferable that it is not near the edge of the hole 6 but rather in the middle of the crown. 12.

The metal cavity 7 may take a cylindrical or slightly conical shape, of circular section or more generally polygonal at 2 N power sides equal to N = 2, 3, 4 .... The radiating plate 5 is in electrical contact with the edge 7a of the cavity.

The cavity 7 is excited at its center by a radiating element 23 operating on the second frequency F2. This radiating element 23 may be of simple dipole type for the case of operation in single polarization mode or cross dipole type, or turnstile commonly called in English "turnstile", for the case of operation in polarization mode orthogonal, or any other type of radiating elements suitable for other types of polarization including circular. The bottom 7b of the cavity 7 is closed so that the radiation of the inner radiating element 23 is unidirectional and directional towards the front of the cavity 7.

The power supply of the dipoles forming the radiating element 23 is effected by balun balun means. On the sectional view of the figure 2 each balun is formed by a first conductive tube 24 and a second conductive tube 25 of length substantially equal to one quarter of the wavelength of the frequency wave F2. The conductors 24 and 25 are in electrical connection at their respective ends with the supply base of each half of a dipole of the radiating element 23 and the bottom 7b of the cavity. The first tube 24 is traversed along its longitudinal axis by a central conductor 26, one end of which is connected to the supply base of the half-dipole opposite to that to which it is connected by one of its ends and whose other end can be connected to the central conductor of a power connector or possibly to the central conductor of a coaxial cable not shown. The tubes 24 and 25 thus form with the central conductor 26 a coaxial line transforming impedance for the dipole to which they are connected.

Advantageously, the depth of the cavity 7 is close to a quarter of the wavelength λ2 of the radiated wave of frequency F2 of the radiating element 23 inside the cavity. The height of the radiating element 23 with respect to the bottom 7b of the cavity is also close to a quarter of the wavelength λ2 while being less than the depth of the cavity 7.

The diameter of the cavity 7 can vary in large proportions, for example between 0.45λ2 and λ2, for half-power openings less than 90 ° radiation diagrams in the diagonal planes inclined by ± 45 ° with respect to the planes. main E and H of the dipole inside the cavity. However, according to the ratio of the frequencies F1 / F2 the necessary spacing between the dipoles 1 to 4 of the radiating plate 5 operating at the frequency F1 can limit the maximum diameter of the cavity 7. For example, with a spacing of 170mm between two dipoles Parallels of the radiating plate operating in the GSM900 band, a diameter of 80mm and a cavity depth of 40mm are suitable for producing a half-power aperture diagram of about 65 ° in the GSM1800 or UMTS band.

As it appears on Figures 2 and 3 the cavity 7 which supports the plate 5 is fixed on a reflector 24 of sufficient size to allow the electromagnetic fields radiated at the rear of the dipoles on the reflector to be returned to the front. In addition to its mechanical role, the reflector 24 is intended to unidirectional radiation of the dipoles of the radiating structure. The reflector 24 may comprise walls whose role is to stiffen the structure but also to act on the directivity of the radiated diagrams. The height of the dipoles of the radiating plate 5 relative to the reflector 24 can vary typically from λ1 / 8 to λ1 / 4 in the frequency band F1 of wavelength λ1.

According to another embodiment illustrated in Figures 5 to 7 where the elements homologous to those of Figures 1 to 4 have the same references, the dipoles 1 to 4 of the plate 5 are partially raised relative to the plane formed by the opening of the cavity 7, each dipole being divided into three parts, a lower part 1b respectively; 2b, 3b, 4b located in the plane of the plate 5 and two high parts respectively 1a, 1c; 2a, 2c; 3a, 3c; 4a, 4c located on either side of the lower part. This elevation, which preferably must retain the geometric symmetry of the structure, can also be done by tilting the parts of the dipoles located beyond the zones of the baluns 8 to 11 corresponding. Various others Geometric shapes can be envisaged to make dipoles, the only condition being the respect of the symmetry of the radiating structure, ie the identity of the dipoles, if not of the four at least two by two pairs of parallel dipoles. The symmetry of the pairs of dipoles means that two parallel dipoles have the same total length so that they have the same impedance and their respective radiation is substantially the same. The two pairs of dipoles are not necessarily identical because each pair of dipoles generates an independent polarization path. The symmetry in question is a symmetry with respect to the center (O) of the square formed by the four dipoles.

The structures of the radiating elements of Figures 1 to 7 are very simple and make it possible to realize at low cost two-band radiating structures having two orthogonal polarization paths in each frequency band, inclined, for example, as shown by FIGS. figures 1 and 5 , of ± 45 ° with respect to a vertical direction vv '. The four channels thus formed are strongly decoupled from each other typically of 30 dB, and radiate in each frequency band according to unidirectional directivity diagrams having half-power openings less than 90 ° in the horizontal plane, for example 65 °. Advantageously, collinear alignments of a plurality of such radiating structures may be made to form high gain vertical linear arrays, for example 18dBi, a dual band having two orthogonal polarization paths inclined by ± 45 ° with respect to a vertical direction. vv 'in each frequency band.

The embodiment of the network shown in figure 8 comprises on the one hand bi-band and bipolarized radiating elements of the type described in figure 7 operating in the F1 (GSM900) and F2 (UMTS and / or DCS) bands and on the other hand of bipolarized mono-band radiating elements operating in the F2 band of the same type as the central elements of the figure 7 . The network pitch for the F2 band is half the network pitch for the F1 band. It is thus possible to construct a highly directive, regular pitch, bi-band and bipolarized network having a good polarization purity and a strong decoupling between the different channels. It should be noted that all the radiating elements operating in the band F2 have substantially the same phase center because of their identity, this being situated on the central axis of the cavity, which axis is perpendicular to the plane of the opening of the cavity. . This property greatly facilitates the electrical pointing (or tilt) of the beam by acting on the phase shifts between radiating elements and also allows better alignment of the phases of the radiating elements in the frequency band for greater directivity of the antenna.

Radiating elements made in accordance with those of the invention described above and operating in the GSM1800, GSM 1900 and UMTS frequency bands have made it possible to obtain an insulation between the channels close to 30 dB, with standing wave ratios with respect to 50 Ohms for all radiating elements less than 1.7: 1 and half-power apertures of directivity patterns close to 65 ° in the horizontal plane for gains close to 9 dBi in both frequency bands.

Claims (17)

1. Radiating device of the type comprising a first radiating element operating in a first frequency band F1 formed by four dipoles (1, 2, 3, 4) arranged in a square and a second radiating element (23) operating in a second frequency band F2 formed by at least one dipole arranged in the centre of the square of dipoles (1, 2, 3, 4) forming the first radiating element, each dipole being supplied at its centre by a balancing unit, all the radiating elements being arranged above a reflector (24),
   characterised in that the dipoles (1, 2, 3, 4) forming the first radiating element and the balancing units (8, 9,10, 11) associated with them are produced from the same metal plate (5),
   in that the balancing unit of each dipole of the first radiating element is formed by a short-circuit slot line cut in the metal plate (5) in a direction perpendicular to the axis of the dipole, and
   in that the dipole of the second radiating element (23) is arranged inside a metal cavity (7) placed in the centre of the metal plate (5).
2. Device according to claim 1, characterised in that the cavity (7) is cylindrical, conical or polygonal in section with 2 power N equal sides with N=2, 3, 4, ...etc.
3. Device according to claims 1 and 2, characterised in that the cavity is formed by stamping the metal plate (5).
4. Device according to one of claims 1 to 3, characterised in that the balancing units (8, 9, 10, 11) are formed by short-circuit slot lines the length of which is substantially equal to a quarter of the operating wavelength of the first radiating element.
5. Device according to claim 4, characterised in that the slot lines (8, 9, 10, 11) are meandering in shape.
6. Device according to claim 4, characterised in that the slot lines (8, 9, 10, 11) comprise a first straight section followed by a second circular section.
7. Device according to one of claims 1 to 6, characterised in that each dipole (1, 2, 3, 4) of the first radiating element is supplied by a coaxial cable (17, 18, 19, 20) arranged along the balancing unit associated with it, the outer conductive sheath of said cable being in electrical contact with a first half of said dipole and the central conductor of said cable being connected to the base of the other half of said dipole.
8. Device according to one of claims 1 to 7, characterised in that the dipoles (1, 2, 3, 4) forming the first radiating element are partly raised relative to the plane formed by the opening of the cavity (7).
9. Device according to one of claims 1 to 8, characterised in that the cavity (7) comprises a base (7b) on which the dipole(s) of the second radiating element (23) rest(s) via support tubes (24, 25).
10. Device according to claim 9, characterised in that the support tubes (24, 25) respectively form a two-wire line of the "balun" type for supplying a respective dipole.
11. Device according to claim 1, characterised in that the second radiating element (23) is formed by two dipoles crossing at right angles.
12. Device according to one of claims 9 and 10, characterised in that the height of the radiating element (23) relative to the base (7b) of the cavity (7) is approximately one quarter of the wavelength radiated by the second radiating element while being less than the depth of the cavity (7).
13. Device according to one of claims 1 to 12, characterised in that the depth of the cavity (7) is substantially equal to one quarter of the wavelength radiated by the second radiating element (23).
14. Device according to claim 13, characterised in that for cylindrical cavities of circular section, or for cavities of polygonal section, the diameter of the cavity (7) or that of the circle circumscribed in the polygonal section is substantially between 0.45λ2 and λ2, where λ2 denotes the wavelength of the wave radiated by the second radiating element (23).
15. Device according to one of claims 1 to 14, characterised in that the first radiating element (1, 2, 3, 4) and the second radiating element (23) are oriented in space so as to radiate two waves, respectively, with orthogonal polarisations inclined at ± 45° to a longitudinal axis of the balancing unit (24).
16. Antenna network, characterised in that it comprises an alignment of a number of devices according to one of claims 1 to 15, arranged on a same reflector (24) so as to form two orthogonal polarisation pathways inclined at ± 45° to the direction of said alignment.
17. Antenna network according to claim 16, characterized in that it further comprises a plurality of second radiating elements (23) intercaled in said alignment.

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