WO2004001902A1

WO2004001902A1 - Double polarization dual-band radiating device

Info

Publication number: WO2004001902A1
Application number: PCT/FR2003/001745
Authority: WO
Inventors: Mostafa Jelloul
Original assignee: Arialcom
Priority date: 2002-06-25
Filing date: 2003-06-11
Publication date: 2003-12-31
Also published as: DE60331067D1; EP1516393A1; EP1516393B1; PT1516393E; FR2841391A1; FR2841391B3; ATE456168T1; CN100570953C; AU2003255660A1; ES2339764T3; CN1663075A

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

DUAL POLARIZATION TWO-BAND RADIATION DEVICE

The invention relates to antennas and their radiating elements usable in particular in the base stations of cellular radiocommunication networks of GSM or UMTS type for example.

A radiating element with double polarization can be formed of two radiating dipoles, each dipole being constituted by two strands of collinear conductors. The length of each strand is substantially equal to a quarter of the working wavelength. The dipoles are mounted on a structure allowing their supply and their positioning above a reflector (ground plane). This allows, by reflection of the rear radiation of the dipoles, to refine the directivity of the radiation diagram 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 dipoles in quadrature operating on a first frequency FI, around a second radiating element formed by two dipoles crossed in quadrature operating on a second frequency F2, all of these elements being arranged above a reflector.

Depending on their orientation in space, the dipoles can radiate or receive electromagnetic waves according to two polarization channels, for example a horizontal polarization channel and a vertical polarization channel or also according to two polarization channels offset by an angle of ± 45 "from horizontal or vertical.

However, inter-band decoupling basically depends 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 FI 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 FI and the crossed dipoles operating at the frequency F2 is due both to direct radiation, the dipoles being in direct visibility, but also to radiation reflected by the reflector. On the other hand, the perpendicular channels of the two radiating elements are well decoupled by virtue of this geometric orthogonality. But if this orthogonality is no longer respected, in particular 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 from 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 diagram presents in the best of cases ripples and, for an arbitrary relative orientation of the dipoles of the central radiating element , this diagram is asymmetrical with respect to the main axis of radiation perpendicular to the plane of the dipoles.

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

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

The invention aims to improve the situation.

The dual-polarized dual-band radiating device according to the invention comprises a first radiating element operating in a first frequency band FI which is formed by 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 second radiating elements are arranged above a reflector. According to an advantageous arrangement, the dipoles forming the first radiating element and the baluns are produced in the same metal plate, each balun of a dipole being formed by a short-slit line cut in the metal plate in a direction perpendicular to the axis of the dipole. The second radiating element is formed by at least one dipole disposed inside a cavity opening into the center of the metal plate.

According to another advantageous embodiment of the invention, the metal plate and the cavity can be made in one piece, by stamping for example. 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 electric short-circuit plane for at least one balun or balun used to supply the second element. radiant

Thus produced the first radiating element and the second radiating element exhibit a very weak electromagnetic interaction. This is only due to the diffraction of the edge of the cavity. In this way the decoupling between the two frequency bands is very strong whatever the relative orientation of the dipole (s) forming the second radiating element inside the cavity, ie its polarization.

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

- Figure 1 shows a first embodiment of a first radiating device with double polarization capable of operating in two different frequency bands according to the invention, - Figure 2 shows a view along section AA of Figure 1.

- Figure 3 is a perspective view of the device shown in Figures 1 and 2. - Figure 4 is an alternative embodiment of the first radiating element of Figure 1 - Figure 5 shows a second embodiment of a device according the invention, FIG. 6 is a view along section AA of the device in FIG. 5. - FIG. 7 is a perspective view of the device in FIGS. 5 and 6.

FIG. 8 is a partial perspective view of a collinear network formed on the one hand of dual-band and bipolarized radiating elements of the type described in FIG. 7 and of single-band and bipolarized radiating elements of the same type as the elements central radiators of figure 7. The drawings essentially contain 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 necessary.

The device shown in Figures 1, 2 and 3 where the homologous elements are represented with the same references, shows four dipoles referenced from 1 to 4 forming a square, cut from a metal plate 5 having a central hole 6 into which 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 IF wave radiated by the dipoles for an opening at half power of the neighboring beam 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 therefore 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, that is to say the half-power opening of this diagram and that this opening depends 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 greater this thickness, the shorter the length of the dipole. In other words the side (d) of the square is determined according to the half-power opening which is sought and which can have a value different from 65 ° and the length of the dipoles is adjusted to ensure the adaptation d impedance, usually 50 Ohms, of the pair of parallel dipoles associated to form a polarization path with directional diagram. According to an advantageous embodiment, the dipoles 1 to 4 and the cavity 7 can be made in one piece by cutting and stamping the metal plate 5.

Each dipole 1 to 4 is supplied by a balun referenced respectively from 8 to 11, of the "balun" type formed by a short slit line cut in the metal plate

5.

Each balun constitutes a support arm for the corresponding dipole. To do this, the plate 5 is formed around the hole 6 for the passage of the cavity 7 by a concentric ring 12 having on its outer periphery and in two directions at right angles protrusions or arms 13 to 16 of shapes for example, rectangular, bevelled or trapezoidal, respectively connecting the crown 12 to the dipoles 1 to 4. The radial length (h) of the arms is preferably not zero, for example greater than 0.05λl 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 slotted line which is moreover very small compared to the wavelength λl corresponding to the frequency FI.

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

The dipoles 1 to 4 are supplied at their base, that is to say at the open end of the slotted lines of the baluns 8 to 11 by means, for example, of coaxial cables referenced respectively from 17 to 20. In the sectional view of FIG. 2 the dipoles 2 and 4 geometrically parallel on two opposite sides of the square are supplied at equal phase and amplitude by two identical coaxial lines 18 and 20 and an association tee 21 to form a polarization path with directional diagram , like a classical network of two parallel dipoles. The coaxial supply lines 17, 18, 19, 20 of the dipoles are arranged respectively along and on one side of the baluns 8, 9, 10, 11. The external conductive sheath of the coaxial lines 17 to 20 is in electrical contact with the base of the first half of the dipole it supplies 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, the radiation patterns of which are substantially identical. However, this mode of association is not limiting, and other modes can be envisaged.

The symmetrizers of the dipoles are slit lines cut in the plate 5 in the form of meanders. The meanders of each slotted line must be in sufficient number so that the slotted line has a length substantially equal to a quarter of the wavelength of the IF frequency wave radiated by the first radiating element. However the slit lines can take other forms, they can for example as shown in Figure 4 where the elements homologous to those of FIG. 1 bear the same references, being formed by a circular section followed by a straight section leading to the supply base of a dipole. The circular section can be anywhere on the crown 12. However to avoid coupling between the waves of frequencies FI 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 can take a cylindrical or slightly conical shape, of circular or more generally polygonal section with 2 power N equal sides with N = 2, 3, 4 .... The radiating plate 5 is in electrical contact with the edge 7a of the cavity.

The cavity 7 is excited in its center by a radiating element 23 operating on the second frequency F2. This radiating element 23 can be of simple dipole type for the case of operation in single polarization mode or of crossed 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 from the interior radiating element 23 is unidirectional and directed towards the front of the cavity 7.

The dipoles forming the radiating element 23 are supplied by means of balun type baluns. In the sectional view of Figure 2 each balun is formed by a first conductive tube 24 and a second conductive tube 25 of lengths substantially equal to a quarter of the wavelength of the frequency wave F2. The conductors 24 and 25 are in electrical connection by 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 the other end of which 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 relative 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 within wide proportions, for example between 0.45λ2 and λ2, for half-power openings of less than 90 ° of the radiation patterns in the diagonal planes inclined by ± 45 ° relative to the planes principal E and H of the dipole inside the cavity. However, according to the ratio of the frequencies FI / F2, the spacing necessary between the dipoles 1 to 4 of the radiating plate 5 operating at the frequency FI 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 an aperture diagram at half power about 65 ° in the GSM1800 or UMTS band.

As it appears in Figures 2 and 3 the cavity 7 which supports the plate 5 is fixed on a reflector 24 of sufficient dimensions to allow the electromagnetic fields radiated behind the dipoles on the reflector to be returned to the front. In addition to its mechanical role, the reflector 24 is intended to render the radiation of the dipoles of the radiating structure unidirectional. The reflector 24 may include low 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 with respect to the reflector 24 can typically vary from λl / 8 to λl / 4 in the frequency band FI of wavelength λl.

According to another embodiment illustrated in Figures 5 to 7 where the elements homologous to those of Figures 1 to 4 bear the same references, the dipoles 1 to 4 of the plate 5 are partly raised relative to the plane formed by the opening of the cavity 7, each dipole being divided into three parts, a lower part respectively lb, 2b, 3b, 4b located in the plane of the plate 5 and two upper parts respectively la, le; 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 corresponding baluns 8 to 11. Various others geometric shapes can be envisaged to produce dipoles, the only condition being respect for the symmetry of the radiating structure, that is to say the identity of the dipoles, if not of the four at least two by two by pairs of parallel dipoles. The symmetry of the dipoles in pairs means that two parallel dipoles have the same total length so that they have the same impedance and that their respective radiation is substantially the same. The two pairs of dipoles are not necessarily identical because each pair of dipoles generates an independent bias 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 in FIGS. 1 to 7 are very simple and make it possible to produce dual-band radiating structures having two orthogonal polarization paths in each frequency band, inclined for example, as shown in FIGS. 1 and 5, at low cost. , ± 45 ° from a vertical direction w '. The four channels thus formed are strongly decoupled from each other, typically 30 dB, and radiate in each frequency band according to unidirectional directivity diagrams having half-power openings of less than 90 ° in the horizontal plane, for example 65 °. Advantageously, collinear alignments can be made of a plurality of such radiating structures to form vertical linear networks of high gain, for example 18dBi, dual-band having two orthogonal polarization channels inclined by ± 45 ° relative to a vertical direction. w 'in each frequency band.

The embodiment of the network shown in FIG. 8 comprises on the one hand dual-band and bipolarized radiating elements of the type described in FIG. 7 operating in the bands FI (GSM900) and F2 (UMTS and / or DCS) and d 'other hand of bipolarized single-band radiating elements operating in the band F2 of the same type as the central elements of Figure 7. The pitch of the network for the band F2 is half the pitch of the network for the band IF. It is thus possible to build a highly directive network with regular pitch, dual-band and bipolarized having good polarization purity and a strong decoupling between the different channels. It will be noted that all the radiating elements operating in the band F2 have substantially the same phase center due to their identity, this being located on the central axis of the cavity, axis perpendicular to the plane of the opening of the cavity . This property greatly facilitates the electrical pointing (or Tilt) of the beam by action 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 produced 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 insulation between the channels close to 30dB, with standing wave ratios relative to 50 Ohms for all radiating elements less than 1.7: 1 and half-power openings of the directivity diagrams close to 65 ° in the horizontal plane for gains close to 9dBi in the two frequency bands.

Claims

claims

1. A radiating device of the type comprising a first radiating element operating in a first frequency band FI, formed by four dipoles (1, 2, 3,4) arranged in a square and a second radiating element (23) operating in a second frequency band frequency F2 formed of at least one dipole arranged in the center of the square of the dipoles (1, 2, 3, 4) forming the first radiating element, each dipole being fed in its center by a balun, the set of radiating elements being arranged above a reflector (24), characterized in that the dipoles (1, 2, 3, 4) forming the first radiating element and the baluns (8, 9, 10, 11) associated therewith are produced in a same metal plate (5), each balun of a dipole being formed by a slit line in short circuit, cut in the metal plate (5) in a direction perpendicular to the axis of the dipole, and in that the second element radiant (23 ) is formed by at least one dipole disposed inside a metal cavity (7) placed in the center of the metal plate (5).

2-Device according to claim 1, characterized in that the cavity (7) is of cylindrical, conical shape or of polygonal section at 2 power N equal sides with N = 2, 3, 4, ... etc.

3-Device according to claims 1 and 2, characterized in that the cavity is made by stamping the metal plate (5).

4- Device according to one of claims 1 to 3, characterized in that the baluns (8, 9, 10, 11) are formed by lines with slits in short circuit of length substantially equal to a quarter of the operating length of the first radiating element.

5- Device according to claim 4, characterized in that the slit lines (8, 9, 10, 11) are in the form of meanders.

6- Device according to claim 4, characterized in that the slit 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, characterized in that the dipoles (1, 2, 3, 4) forming the first radiating element are supplied by coaxial cables (17, 18, 19, 20) arranged the along the baluns, the external conductive sheath of each cable being in electrical contact with the first half of the dipole which it supplies, its central conductor being connected to the base of the other half of this same dipole.

8-Device according to one of claims 1 to 7, characterized 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, characterized in that the cavity (7) has a bottom (7b) on which rests the second radiating element (23) by means of support tubes (24, 25) .

10-Device according to claim 9, characterized in that the support tubes (24, 25) form two-wire lines of the "Balun" type for supplying the dipoles of the second radiating element (23).

11 -Device according to claim 10, characterized in that the second radiating element (23) is formed of two dipoles crossed at right angles.

12-Device according to one of claims 9 and 10, characterized in that the height of the radiating element (23) relative to the bottom (7b) of the cavity (7) is close to a 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, characterized in that the depth of the cavity (7) is substantially equal to a quarter of the wavelength of the wave radiated by the second radiating element (23).

14-Device according to claim 13, characterized in that for the cylindrical cavities with circular section, or for the cavities with polygonal section, the diameter of the cavity (7) or that of the circle circumscribed in the polygonal section, is substantially between 0.45 X2 and λ2, λ2 designating the wavelength of the wave radiated by the second radiating element (23).

15-Device according to one of claims 1 to 14, characterized in that the first radiating element (1, 2, 3, 4) and the second radiating element (23) are oriented in space to radiate respectively two waves to orthogonal polarizations inclined ± 45 ° from the vertical.

16-Antenna network, characterized in that it comprises several devices according to one of claims 1 to 15, aligned vertically on the same reflector (24) and arranged on the reflector (24) so as to form two channels of orthogonal polarization inclined ± 45 ° from the vertical direction in each frequency band.