PT1516393E - 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

1

DESCRIPTION " DUAL-BAND RADIANT DEVICE WITH DOUBLE POLARIZATION " The invention relates to antennas and their radiant elements which can be used especially in the base stations of GSM or UMTS cellular radio communication networks, for example.

A radiant element with double polarization can be formed by two radiant dipoles, each dipole being constituted by two wires of colinear conductors. The length of each wire is roughly equal to the quarter of the working wavelength. The dipoles are mounted on a structure allowing them to be fed and positioned on top of a reflector (PLAN-MASSE). This allows, by reflection of the radiation behind the dipoles, to fine-tune the directivity of the radiation pattern of the array thus formed. It is known to realize a radiant device operating in two frequency bands and in orthogonal biases, to provide a first radiant element, formed by four quadrature dipoles operating on a first frequency Fl, around a second radiant element formed by two crossed dipoles in quadrature operating on a second frequency F2, the set of said elements being arranged at the top of a reflector.

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

However the interband decoupling depends fundamentally on the relative orientation of the second radiant 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 loose in the upper frequency band F2 for which the peripheral dipoles have a large dimension with respect to the wavelength corresponding to the frequency F2. In fact, the interaction between the peripheral dipoles operating at the frequency F1 and the crossed dipoles operating at the frequency F2 is due in turn to the direct radiation, the dipoles being in direct visibility, but also to the radiation reflected by the reflector. On the contrary, the perpendicular paths of the two radiating elements are very loose by the power of this geometric orthogonality. But if this orthogonality is no longer respected, especially if the dipoles of the central radiant element have arbitrary orientations to those of the peripheral dipoles forming the first radiant element then an overly strong interband coupling appears between the different transmission or reception paths of the two elements radiant

A further disadvantage of this structure is that the radiation of the central radiant element is disturbed by the peripheral radiant element. In effect, this radiation is partially diffracted in particular by the dipoles of the peripheral radiant element, so that the resulting radiation diagram exhibits at best ripples and, for an arbitrary relative orientation of the 3 dipoles of the central radiant element, this diagram is relatively dissimetric to the main axis of radiation perpendicular to the plane of the dipoles.

It is therefore difficult to obtain a simple dual-band radiant element to be manufactured having two orthogonal, linearly-biased orbitals in a wide frequency band. It is a fortiori difficult to realize a bipolarized directive network constituting several radiating elements of this kind, and offering a good purity of polarization.

In another plane, it would be desirable to obtain a radiating element having two orthogonal bias paths each having a unidirectional radiation pattern and the half-power aperture in the diagonal planes i.e. the planes ± 45 ° of the principal planes E and H of each dipole, is substantially less than 90Â °. The invention aims to improve the situation. The dual polarized dual-radiant radiant device according to the invention comprises a first radiant element operating in a first frequency band F1 which is formed by four dipoles arranged in a square and a second radiant element operating in a second frequency band F2 which is formed by at least one dipole arranged in the center of the square of the dipoles forming the first radiant element, each dipole being fed at its center by a symmetrix. The first and second radiant elements are arranged at the top of a reflector. 4

According to an advantageous arrangement, the dipoles forming the first radiant element and the symmetrizers are realized on the same metal plate, each symmetrix of a dipole being formed by a short-circuit grooved line cut into the metal plate following a direction perpendicular to the axis of the dipole. The second radiant element is formed by at least one dipole disposed within a cavity open to 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 by drawing. The second radiant element operating in the frequency band F2 is then fixed to the interior and center of the cavity whose bottom serves as the electric short-circuit plane and at least one symmetrix or "balun " serving the power of the second radiant element.

Thus realized the first radiant element and the second radiant element exhibit 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 whatever the relative orientation of the dipole (s) forming the second radiant element within the cavity, i.e. its polarization.

Further features and advantages of the invention will appear in the detailed description given below with reference to the accompanying drawings, in which: figure 1 represents a first embodiment of a first dual polarization radiant device 5 and can operate in two frequency bands FIG. 2 is a sectional view AA of FIG. 1; FIG. 3 is a perspective view of the device shown in FIGS. 1 and 2; FIG. 4 is a variant embodiment of the present invention; FIG. the first radiant element of Figure 1. Figure 5 shows a second embodiment of a device according to the invention. Figure 6 is a sectional view AA of the device of Figure 5. Figure 7 is a perspective view of the device of Figures 5 and 6. Figure 8 is a partial perspective view of a collinear network formed by one side of dual-band and bipolarized radiating elements of the type described in figure 7 and of mono-band and bipolarized radiating elements of the same type as the central radiating elements of figure 7.

The drawings contain, for the essential, elements of certain character. They may therefore serve not only to make the description better understood, but also to contribute to the definition of the invention where appropriate. The device shown in Figures 1, 2 and 3 wherein the homologous elements are represented with the same references, shows four dipoles referenced from 1 to 4 forming a square, cut into a metal plate 5 constituting a central hole 6 in which it unloads the open end of a radiating cavity 7. The side of the square formed by each dipole has a typical length equal to a half wavelength of the frequency wave F1 F1 radiated by the dipoles to a half power aperture of the neighboring beam of 65 ° in the horizontal plane. It should be noted, however, that it is the separation (d) between two parallel dipoles of the radiant 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 plane horizontal arrangement of these dipoles, that is to say 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 may be more or less large according to the thickness and width of the dipole. The larger this thickness the shorter the length of the dipole. In other words the side (d) of the square is determined as a function of the half-power aperture which is intended and which may have a value other than 65 ° and the length of the dipoles is adjusted to ensure impedance matching, generally 50 Ohms of the pair of parallel dipoles associated to form a directional diagram bias path. According to an advantageous embodiment the dipoles 1 to 4 and the cavity 7 can be realized in one piece by cutting and drawing the metal plate 5.

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

Each symmetrix is a support arm of the corresponding dipole. To do so, the plate 5 is formed around the through hole 6 of the cavity 7 into a concentric crown 7 constituting on its outer periphery and following two directions of right angles, excrescences 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 non-zero, for example greater than 0.05λ1 in order to avoid direct contact of the inner edge of the dipoles with the the outer edge of the crown 12 and thus minimize the interaction between the current flowing over the dipoles and the chains circulating over the crown 12. The arms' average width (w) is typically 5 to 10 times the width of the notched line which is otherwise very small side in front of the wavelength λΐ corresponding to the frequency Fl. The width of the crown 12 is determined by being sufficient at the same time on the mechanical plane to support the dipoles and the radio plane to stabilize the directivity of the radiation patterns of the cavity 7 in the second frequency band F2, making the aperture half-power of the radiation diagrams as a function of frequency. This width is preferably greater than 5/100-ima of the wavelength X2 corresponding to the frequency F2.

The dipoles 1 to 4 are fed at their base, ie at the open end of the grooved lines of the symmetrizers 8 to 11 by, for example, coaxial cables respectively referenced from 17 to 20. On the cross-sectional view of figure 2 dipoles 2 and 4 geometrically parallel on two opposite sides of the square are fed in phase and amplitude equality by two identical coaxial lines 18 and 20 and an Association Tea 21 to form a directional diagram bias path, such as a classic network of two parallel dipoles. The coaxial feed lines 17, 18, 19, 20 of the dipoles are arranged respectively along and on one side of the symmetrizers 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 polar orthogonal paths are thus obtained, the radiation patterns of which are substantially identical. However this mode of association is not limiting, and other modes may be considered.

The dipoles symmetrizers are grooved lines carved into the meandering plate 5. The intricacies of each slotted line should be sufficient in number so that the slotted line has a length substantially equal to the quarter of the wavelength of the frequency wave F1 radiated by the first radiant element. However, the grooved lines may overlap other shapes, for example as shown in Figure 4 where the elements homologous to those in Figure 1 bear the same references, are formed by a circular segment followed by a rectilinear segment terminating in the feed base of a dipole. The circular segment may be no matter where on the crown 12. However to avoid coupling between the frequency waves F1 and F2, it is preferred that it is not near the edge of the bore 6 but preferably in the middle of the crown 12.

The metal cavity 7 may be formed into a cylindrical or slightly conical shape of circular or more generally polygonal cross-section at power N equal sides with N = 2, 3, 4 ... The radiant plate 5 is in electrical contact with the edge 7a of the cavity. The cavity 7 is activated at its center by a radiant element 23 running on the second frequency F2. This radiant element 23 may be of simple dipole type for the case of operation in single polarization or cross-dipole type operation, or tourniquet commonly called in English " turnstile ", in the case of operation in orthogonal polarization mode , or any other type of radiating element adapted to other types of polarization comprising circular. The bottom 7b of the cavity 7 is closed so that the radiation of the inner radiant element 23 is unidirectional and directional forward from the cavity 7. The feed of the dipoles forming the radiating element 23 is effected by the " balun ". On the cross-sectional view of Figure 2 each symmetrix is formed by a first conductive tube 24 and a second conductive tube 25 of lengths substantially equal to the fourth of the wavelength of the frequency wave F2. The conductors 24 and 25 are in electrical connection at their respective ends with the feed base of each half of a dipole of the radiant element 23 and the bottom 7b of the cavity. The first tube 24 is traversed along its longitudinal axis by a central conductor 26 of which one end is connected to the feed base of the dipole means opposite to that to which it is connected at one of its ends and whose other end can be connected to the conductor of a power connector or, if appropriate, to the central conductor of a coaxial cable, not shown. The tubes 24 and 25 thus form with the central conductor 10 a coaxial impedance transforming line for the dipole to which they are connected.

Advantageously the depth of the cavity 7 is close to the fourth of the wavelength X2 of the frequency wave F2 of the radiant element 23 inside the cavity. The height of the radiant element 23 relative to the bottom 7b of the cavity is also close to the fourth of the wavelength X2 being less than the depth of the cavity 7. The diameter of the cavity 7 may vary in wide proportions, for example 0.45X2 and X2, for half-power apertures of less than 90 ° of the radiation diagrams in inclined diagonal planes of ± 45 ° relative to the principal planes E and H of the dipole within the cavity. However according to the ratio of the F1 / F2 frequencies the required deviation between the dipoles 1 to 4 of the radiant plate 5 operating in the frequency F1 may limit the maximum diameter of the cavity 7. For example, with a deviation of 170mm between two parallel dipoles of the radiant plate running on the GSM900 band, a diameter of 80mm and a depth of cavity of 40mm are suitable for a roughly 65 ° half-power opening diagram in the GSM1800 or UMTS band.

As shown in Figures 2 and 3 the cavity 7 supporting the plate 5 is fixed on a reflector 24 of sufficient size to allow the electromagnetic fields radiated behind the dipoles on the reflector to be forwarded forward. In addition to its mechanical role, the reflector 24 is intended to make unidirectional radiation from the radii of the radiant structure. The reflector 24 may constitute walls whose role is to harden the structure but also to act on the directivity of the radiating diagrams. The height of the dipoles of the radiant plate 5 relative to the reflector 24 can typically range from λ 1/8 to λ 1/4 in the frequency band F1 of wavelength λ 1.

According to a further embodiment shown in figures 5 to 7 in which the elements homologous to those of Figures 1 to 4 bear the same references, the dipoles 1 to 4 of the plate 5 are in part raised with respect to the plane formed by the opening of the cavity 7, each dipole being divided into three parts, a lower part respectively 1b; 2b, 3b, 4b lying in the plane of the plate 5 and two respec- tively high parts 1c; 2a, 2c; 3a, 3c; 4a, 4c situated on either side of the lower part. This elevation, which preferably preserves the geometrical symmetry of the structure, can also be done by tilting the parts of the dipoles situated beyond the zones of the corresponding symmetrizers 8 to 11. Several other geometric forms can be considered to make the dipoles, the only condition being respect for the symmetry of the radiant structure, ie the identity of the dipoles, if not the four of at least two to two by pairs of parallel dipoles. The symmetry of the dipoles per pair 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 relative to the center (0) of the square formed by the four dipoles. 12

The structures of the radiating elements of Figures 1 to 7 are very simple and allow to realize at a lower cost dual-band radiant structures having two orthogonal bias paths in each frequency band inclined for example as shown in figures 1 and 5 of ± 45 ° relative to a vertical direction v '. The four channels thus formed are strongly decoupled therebetween, typically 30dB, and radiate in each frequency band following unidirectional directivity diagrams having half-power apertures of less than 90ø in the horizontal plane, for example 65ø. Advantageously, collinear alignments of a plurality of such radiating structures may be realized to form high gain, e.g. 18dBi, dual-band vertical linear networks having two inclined orthogonal biases of ± 45 ° relative to a vertical direction vv 'on each band frequency. The embodiment of the network shown in Figure 8 comprises, on the one hand, dual-band and bipolarized radiating elements of the type described in figure 7 operating on the bands F1 (GSM900) and F2 (UMTS and / or DCS) and on the other hand radiant mono elements band bands operating in the F2 band of the same type as the central elements of Figure 7. The pitch of the network to the band F2 is half the pitch of the network to the band Fl. A highly directional, dual-band and bipolarized stepping network can thus be constructed having a good polarization purity and a strong decoupling between the different paths. It will be appreciated that all radiant elements operating in the band F2 have substantially the same phase center as a consequence of their identity, being located on the central axis of the cavity, axis perpendicular to the opening plane of the cavity. This property greatly facilitates the electrical control (or Tilt) of the beam per action over the mismatches between the radiant elements and also allows better alignment of the phases of the radiant elements in the frequency band for a greater directivity of the antenna.

Radiant elements embodied in accordance with the invention described above and operating in the frequency bands GSM1800, GSM1900 and UMTS have achieved insulation between the paths close to 30dB, with standing wave connections relative to 50 Ohms for all radiating elements less than 1 , 7: 1 and half-power apertures of the directivity diagrams close to 65 ° in the horizontal plane for neighboring gains of 9dBi in the two frequency bands.

Lisbon, April 7, 2010

Claims (17)

Radiant device of the type comprising a first radiant element operating in a first frequency band Fl, formed by four dipoles (1, 2, 3, 4) arranged in a square and a second radiant element (23) operating in a second band of (1, 2, 3, 4) forming the first radiant element, each dipole being fed at its center by a symmetrix, the set of radiant elements being arranged in the part (1, 2, 3, 4) forming the first radiating element and the associated symmetrizers (8, 9, 10, 11) are formed on the same metal plate ( 5) in that the symmetrizator of each dipole of the first radiant element is formed by a short-circuit grooved line cut into the metal plate (5) following a direction perpendicular to the dipole axis, and that the dipole of the the second radiant element is arranged inside a metal cavity (7) placed in the center of the metal plate (5). Device according to claim 1, characterized in that the cavity (7) is cylindrical, conical or of polygonal cross-section having power equal sides N = 2, 3, 4 ... etc. Device according to claims 1 and 2, characterized in that the cavity is formed by drawing the metal plate (5). 2 Device according to one of Claims 1 to 3, characterized in that the symmetrizers (8, 9, 10, 11) are formed by short-circuit grooved lines of length substantially equal to the fourth operating wavelength of the first element radiant. Device according to claim 4, characterized in that the grooved lines (8, 9, 10, 11) are in the form of meanders. Device according to claim 4, characterized in that the grooved lines (8, 9, 10, 11) form a first rectilinear segment followed by a second circular segment. Device according to one of Claims 1 to 6, characterized in that each dipole (1, 2, 3, 4) of the first radiant element is fed by a coaxial cable (17, 18, 19, 20) arranged along the the outer conductive sheath of said cable being in electrical contact with one half of said dipole, and the central conductor of said cable being connected to the base of the other half of said dipole. Device according to one of Claims 1 to 7, characterized in that the dipoles (1, 2, 3, 4) forming the first radiant element are in part raised relative to the plane formed by the opening of the cavity (7). 3 Device according to one of Claims 1 to 8, characterized in that the cavity (7) forms a bottom (7b) on which rests the dipole (s) of the second radiant element (23) by means of support tubes (24, 25). A device according to claim 9, characterized in that the support tubes (24, 25) each form a " balun " for feeding a respective dipole. Device according to claim 10, characterized in that the second radiant element (23) is formed by two right-angled cross-dipoles. Device according to one of Claims 9 and 10, characterized in that the height of the radiant element (23) relative to the bottom (7b) of the cavity (7) is close to the fourth of the wavelength radiated by the second radiant element being less than the depth of the cavity. Device according to one of Claims 1 to 12, characterized in that the depth of the cavity (7) is substantially equal to the quarter of the wavelength of the wave radiated by the second radiating element (23). Device according to claim 13, characterized in that the diameter of the cavity (7) or that of the circle circumscribed to the polygonal section is substantially in the range of 0.457 × 2 for the cylindrical cavities of circular cross-section or for the cavities of polygonal section, and X2, X2 designating the wavelength of the wave radiated by the second radiant element (23). Device according to one of Claims 1 to 14, characterized in that the first radiant element (1, 2, 3, 4) and the second radiant element (23) are oriented in the space to respectively irradiate two inclined orthogonal bias waves ± 45 ° relative to a longitudinal axis of the reflector (24). An antenna network, characterized in that it comprises an alignment of several devices according to one of Claims 1 to 15 arranged on a same reflector (24) and in order to form two inclined orthogonal bias paths of ± 45 ° relative to the direction of said alignment. The antenna network of claim 16, further comprising a plurality of second radiant elements (23) interspersed in said alignment. Lisbon, April 7, 2010