FR2842025A1 - RADIANT BI-BAND DEVICE WITH COPLANAR POLARIZATIONS - Google Patents

Abstract

The radiating device comprises a first radiating element (1) operating in a first frequency band F1 and a second radiating element (2) operating in a second frequency band F2. The first radiating element (1) is formed by a half-wave "patch" antenna comprising a rectangular radiating plate (4). The second radiating element (2) is formed by at least one dipole comprising two radiating strands (7) and (8) arranged parallel to the direction of the electric field radiated by said radiating plate (4). Application: Cellular radiocommunication networks.

Description

Bi-band radiating device with coplanar polarizations.

  The invention relates to antennas and their radiating elements. In some applications, such as the base stations of cellular radio networks, it is desirable to have radiating elements of small footprint, dual-band, and capable of working, in each band, on two parallel polarizations or

  orthogonal, for the reasons developed later.

  Low-profile bi-band radiating elements are known in the form of superimposed radiating plate "patch" antennas emitting on two different frequencies in parallel or orthogonal polarization planes. However, with this type of radiating elements, the decoupling between two parallel polarization transmission paths is far from reaching the minimum value of 20 to 30 dB, required for example for

  GSM and UMTS cellular radio networks.

  It is generally difficult to obtain decouples as high when the polarizations

2 0 are coplanar.

  The invention aims to improve the situation.

  For this purpose, there is provided a radiating device which comprises a first radiating element 25 operating in a first frequency band F1 and a second radiating element operating in a second frequency band F2, the two radiating elements having

  each one or two orthogonal channels of polarization.

  According to another aspect of the invention, the first radiating element comprises a half-wave "patch" antenna comprising a radiant plate of generally rectangular shape. The second radiating element may comprise at least one dipole comprising two radiating strands arranged in a plane of polarization of the radiating plate and oriented parallel to the plane of the radiating plate. The first radiating element and the strands of the dipole forming the second radiating element are arranged parallel to a plane of

  Mass also forming a reflector.

  Other features and advantages of the invention will appear in the description which follows

  made with reference to the appended drawings which represent:

  Figure 1, a first embodiment of a radiating device according to the invention.

  FIG. 2, a view along AA section of the radiating device of FIG.

  FIG. 3, a view along section BB of the radiating device of FIG.

  FIG. 4 is a perspective view of the radiating device of FIG.

  FIG. 5, a second embodiment of a radiating device according to the invention.

  FIG. 6, a view along section BB of the radiating device of FIG.

  Figure 7, a third embodiment of a radiating device according to the invention;

  FIG. 8, a perspective view of the radiating device of FIG. 7.

  Figures 9 and 10 show respectively perspective and top views of a fourth

  embodiment of a radiating device according to the invention.

  The drawings contain, for the most part, elements of a certain character. They could

  so not only to make the description better understood, but also to contribute

  2 5 to the definition, if any.

  Reference is made to Figures 1 to 3, in which the counterparts are

  represented with the same references.

  The radiating device comprises a first radiating element 1 of the type known under the Anglo-Saxon "patch" designation (or "keypad") operating in a first frequency band in the vicinity of a nominal frequency F1, and a second radiating element. 2 of the dipole type surmounting the first, operating in a second frequency band near a nominal frequency F2 greater than the frequency F1. The two nominal frequencies are in a ratio F2 / F1 at least equal to 1.5, preferably significantly higher. In the example described, the radiating elements 1 and 2 radiate two electric fields polarized vertically, that is to say in the vertical plane containing the line W 'of FIG. 1. More precisely, the radiating element 1 comprises two conducting radiating plates. 3 and 4 superimposed which form, with a mass conducting plane 5 having the role of reflector, a double resonator. The bottom plate 3 forms with the ground plane 5 a first resonator which is excited by an inductive coaxial probe or a coaxial cable 6 and the upper plate 4 forms with the lower plate 3 a second resonator which is excited by the lower plate 3 by Capacitive coupling This is similar to the known principle

  broadband "patch" antennas.

  More generally, to allow expansion of the frequency band radiated by the first radiating element 1, a radiating plate 4 is superimposed on the lower radiating plate 3; the two plates are of nearly equal dimensions, arranged parallel to each other, and in the same general direction; one of the two plates is

  Excited directly; the other is excited by coupling with the first.

  Here, the lower radiating plate 3 is excited in the fundamental mode around its half-wave resonance. There appears in the middle of each of the plates a line of neutral potential. These neutral potential lines can then be used to pass through these two lines, or in their immediate vicinity, fixing elements and / or supplying the dipole.

  forming the second radiating element.

  Other ways to obtain these neutral lines can be used. Indeed, according to other embodiments of the invention, not shown, the excitation of the first resonator, described by an inductive coxial probe, can also be done with a capacitive coaxial probe, or by a slot on the reflector 5, and a line

  printed micro tape placed behind the reflector 5 which constitutes the ground plane.

  Whatever the mode of excitation of the first resonator, it is advisable to locate the excitation point of the first resonator on the line VV 'of symmetry of the lower plate 3 and to position it with respect to one of the edges of the plate so as to adapt the impedance

  from the "patch" to the impedance of the power line which is usually 50 Ohms.

  The fact of implementing a double "patch" (two resonators) provides a relative bandwidth of about 10% around the nominal frequency F1, while it would be only about 2% with a " patch "containing only one resonator, this for a report

  stationary wave at 50 Ohms less than 2: 1.

  In other words, and according to one aspect of the invention, the "patch" is excited in the fundamental mode around the half-wave resonance (known as TMO mode 1) so that the respective lengths A and B, plates 3 and 4, measured in the direction of the vertical axis VV ', are close to the half wavelength of the wave which propagates in the dielectric substrate component "patch", this substrate being advantageously of the air, or

  a dielectric constant of 1, for a larger bandwidth.

  Under these conditions, the horizontal line nn 'of symmetry of the lower plate 3 constitutes a neutral line: all the points of this line are at the same potential as that of the ground plane 5 constituting the reflector. It is the same with the horizontal line nn'de symmetry

of the upper plate 4.

  This characteristic, which is related to the excitation mode of the "patch", is advantageously used according to the invention for electrically connecting the two lines mm 'and nn' to the ground plane 5 by conducting pins and arranging the radiating element. 2 above the "patch" which does not alter in

  nothing the proper functioning of the "patch".

  For its part, the radiating element 2 comprises two conducting radiating strands 7 and 8 electrically connected to a symmetrizer 9 of a type known under the designation "balun". The dipole thus formed is similar to the so-called "half-wave symmetrical" or "doublet half-wave" type. The balun 9 serves to support the radiating strands 7 and 8. These are arranged vertically in the direction of the axis VV ', at a given height H of the top plate 4 of the "patch", in order to radiate an electromagnetic field vertically polarized in the same plane as that radiated by the "patch", ie the plane

vertical line containing the line VV '.

  The top plate 4 of the "patch" serves as the main reflector of the dipole formed of the strands 7 and 8, so that the radiation of the dipole is unidirectional. Typically, the height H is close to a quarter of the wavelength of the frequency F2; but this height can be adjusted according to the desired half-power aperture in the frequency band F2

of the dipole.

  The two conducting feet 9a and 9b of the balun 9 together form a bifilar line which is arranged horizontally, in the plane of the neutral lines mm 'and nn' of the "patch", preferably symmetrically with respect to the vertical axis of symmetry. VV. The two feet 9a, 9b pass through the plates 3 and 4 perpendicularly until they come into electrical contact with the reflector 5. This crossing is preferably made with electrical contact with the plates 3 and 4. The advantage of a crossing with contact is the grounding of the two radiating plates 3 and 4, which improves the operating stability of the "patch" and discharge the electrostatic charges to the ground plane forming the reflector 5. 2 0 One Feet 9a of the balun 9 is constituted by a tube traversed throughout its length by a central conductor 10, which forms with the tube a coaxial line for the excitation of the strands 7 and 8 of the dipole constituting the radiating element 2. one of the strands, for example 7, is connected to one end of the central conductor 10 and the other strand 8 is connected to the corresponding end of the tube 9a. The end of the central conductor 10 opposite to that connected to one end of the dipole 2 is connected to the central conductor of a coaxial connector 11 fixed to the end of the tube 9a passing through the reflector 5 or to the central conductor of a cable coaxial 1 1 whose sheath is electrically connected to the ground plane forming the reflector 5. The coaxial line thus formed serves as an impedance transformer of the dipole to bring it back to a standard value of 50 ohms, for example. The cross section of the tube 9a can take different forms and can be for example circular, square or rectangular. It is also possible to envisage other embodiments of symmetrizer 9 of the "balun" type with non-tubular feet, as is known from the state of the art. For example, the diameter of the straight sections of the feet 9a and 9b can be chosen short in front of the length

  at frequencies F2, for example less than X / 20.

  In other words, according to a first embodiment, the strands of the dipole constituting the second radiating element are connected to a balun-type balun formed by two parallel conducting rods, arranged in the plane formed by the two neutral lines of symmetry of the plates. and perpendicularly crossing the plates, the plane formed by the two rods being perpendicular to the plane of the electric field radiated by the first radiating element. According to a second embodiment, the two parallel conducting rods form a plane perpendicular to the plane formed by the two neutral lines of symmetry of the plates and are arranged on both sides and close to these, crossing the plates perpendicularly. plates, the plane formed by the two rods being parallel to the plane of the

  electric field radiated by the first radiating element.

  The power supply and the impedance matching of the dipole to the transmission / reception circuits are obtained by traversing along its longitudinal axis one of the rods of the balun carrying a first strand of the dipole, by an impedance transformer conductor of which one end is connected to the end of the second strand of the dipole and the other end is connected to the central core of a connector or a coaxial cable whose sheath is electrically connected to the ground plane forming a reflector, while the other rod of the balun carrying the second

  The strand of the dipole is connected to the ground plane forming the reflector.

  To facilitate the flow of electrostatic charges on the ground plane and improve the operating stability, the balancer rods can be in electrical contact with the ground plane.

  the radiating plates which it crosses and with the ground plane forming the reflector.

  According to a variant of the first embodiment of the invention, the first radiating element comprises a first radiating plate and a second lower radiating plate in the form of a square of approximately equal dimensions, excited on two lines of symmetry of the "patch" respectively parallel to the adjacent sides of the squares formed by the plates for generating two orthogonal polarization waves of the same frequency F1, and the second radiating element comprises a second dipole oriented perpendicularly to the first dipole and fed by a second balun type balun to generate two orthogonal polarization waves having a second frequency F2 whose radiated electric fields are respectively coplanar with those radiated by the first

radiating element.

  The radiating elements 1 and 2 are supported by the reflector 5. The width of the reflector 5 is greater than the width of the "patch" forming the radiating element 1. The reflector 5 may be bordered by walls 5a and 5b of determined height as illustrated. in Figure 2. The width of the reflector 5 and the height of the walls 5a and 5b are adjustable parameters that depend on the applications. By reflection and diffraction, these parameters have an effect of widening or narrowing of the half-power aperture of the diagrams of

1 0 radiation.

  Two connecting conductive tabs 12 and 13 may be provided at the ground plane of the reflector 5 connected to the edges of the lower plate 3 and in the plane of symmetry mm ', nn'. The width of these metal strips can be chosen smaller than the length

  wave, for example less than one thirtieth of the wavelength of the frequency wave FI.

  It has been found that this improves the adaptation of the "patch" impedance; this also stabilizes its operation with respect to climatic variations; finally, this limits the neighborhood couplings in the case of a network composed of several radiating elements,

  which can then be implanted closer to each other.

  In the operating frequency band F2 of the radiating element 2, the decoupling between the channels of two radiating elements 1 and 2 can be very high, typically 30 dB and more if the frequency F1 is close to the nominal frequency of the "patch". is enough

  away from the nominal frequency F2 of the dipole.

  In contrast to the embodiment of FIGS. 1 to 3, the embodiment of FIGS. 6 (where the homologous elements are represented with the same references), the feet 9a and 9b of the balun of the radiating element 2 pass through the plates. 3 and 4 of the "patch" forming the first radiating element in the vertical plane of symmetry VV ', and the strands 7

  30 and 8 of the dipole forming the second radiating element are oriented in this plane.

  In this configuration, the decoupling in the frequency band F1 between the channels of the two radiating elements is typically 20 dB, therefore less favorable compared to the configuration of FIGS. 1 to 3 for which the decoupling is typically 30 dB. It is believed that this less favorable decoupling is due to the appearance of a potential difference between the feet of the balun, at the operating frequency FI of the first radiating element 1. This is because the vertical line V 'is not not a neutral line of the radiating element 1 and that the potential on its upper half is equal and opposite to the potential on its lower half relative to the neutral line nn '. However, the decoupling of the two channels in the frequency band F2 is of the same order of magnitude typically

  30 dB than that of the configuration of Figures 1 to 3.

  The embodiments described above relate to bi-band radiators whose polarization is linear vertically in two frequency bands F1 and F2.

  It is also possible to adapt them to the production of two-band radiating elements having two orthogonal polarizations inclined at an angle equal to, for example, +/- 45, with respect to the vertical axis VV 'as represented according to a first example in FIGS. 7 and 8 and according to a second example in FIGS. 9 and 10, where the homologous elements of

  previous figures are represented with the same references.

  In these two examples, the "patch" constituting the first radiating element 1 is in the form of a square "patch" with two superposed plates 3 and 4. The two polarization channels are obtained by exciting the lower plate 3 of the embodiment of FIG. 7 by two probes 14 and 15 placed on two orthogonal lines of symmetry xx 'and yy' of the "patch" respectively parallel to the sides of the square plates 3 and 4 and oriented +/- 45 relative to the direction of the vertical axis VV 'or as shown in the embodiment of Figure 10, by exciting the lower plate 3 by two probes 14 and 15 placed on the diagonals of the "patch". The second radiating element 2 is formed by two orthogonal dipoles 16 and 17 which surmount the first radiating element 1. The two dipoles radiate two waves of frequency F2> 1.5 IF with orthogonal polarizations inclined by

+/- 45 with respect to the axis VV '.

  In Figures 7 and 8 the radiating strands 16a, 16b; 17a, 17b of the dipoles 16 and 17 are parallel to the lines of symmetry xx 'and yy'du "patch" and inclined by +/- 45 with respect to the vertical axis VV'. In the case of FIGS. 9 and 10, the radiating strands of dipoles 16 and 17 are

  parallel to the diagonals of the "patch".

  As in the previous embodiments, a reflector 5 with potential walls 5a

  and 5b supports all the radiating elements 1 and 2.

  More generally in this alternative embodiment of the invention, the first radiating element and the second radiating element are oriented in space to respectively radiate two orthogonal polarized waves inclined by +/- 45 with respect to the vertical. In the base stations of the cellular radiocommunication networks, the role of the antennas is to transmit and / or receive information or data transmitted between base stations and mobile subscribers to the network. The way in which these antennas are realized depends on the geographical area covered and the quality of reception of information circulating

  inside the elementary cells of networks.

  Thus, to obtain a good reception quality at any point in a network, it may be necessary to bring the base stations more or less together, depending on the propagation conditions. These depend for a large part on land irregularities in general, as well as the disposition of buildings in urban areas. In addition, it is in urban areas that the concentration in base stations is the largest. The resulting multiplicity of antennas is often perceived as detrimental to the aesthetics of the buildings and neighborhoods in which they are installed. It is possible to reduce the number of base stations in a given territory, using two different transmission frequencies, between which the transmission system can switch according to criteria related to the quality of reception. In such a case, it is desirable to provide orthogonal polarization planes for radiated waves on the first frequency and the second frequency, in order to avoid interference from one receive channel to the other. This poses different problems as to the realization of the antennas, and, first of all, to the

  design of antenna elements.

  The invention has the advantage that it allows in particular the realization of two-band directional networks comprising several radiating devices and having good inter-band isolation. It has been seen that the invention provides a scribing device having two supply paths, each operating in a distinct frequency band, the two frequency bands being in a ratio greater than 1.5. In addition, polarizations can be coplanar

  and / or orthogonal in the two frequency bands.

  Beside this, the invention can also provide a radiating device operating in two different frequency bands enjoying a strong decoupling between the two frequency channels. Moreover, each channel can radiate according to a unidirectional diagram of which

  the half-power aperture in the horizontal plane is close to 90.

  More specifically, for operating modes in the GSM900 frequency bands and in the GSM1 800 and UMTS band as a whole, the decoupling obtained between two IF and F2 frequency channels is greater than 30 dB for the embodiment illustrated by the FIG. Figures 1 to 3; it is 20dB in the embodiment of FIGS. 5 to 6. The standing wave ratio with respect to 50 Ohms is less than 1.7: 1 in the GSM band and less than 1.5: 1 in the GSM1800 band or UMTS. Mid-power openings of diagrams

  of radiation are close to 90 in both frequency bands.

  It can be seen that the radiating device is particularly well suited for the realization of reduced space base station antennas for cellular radio networks such as those known as GSM 900 (870 to 970 MHz), GSMI800 (1710 to 1880 MHz) or the new UMTS system (1920 to 2170 MHz) for which the links with the mobiles must be carried out according to one or two orthogonal polarizations, identical for all the frequency bands. For example, for suburban areas the requested polarization is vertical, whereas for urban areas two

  Orthogonal polarizations inclined +/- 45 from the vertical are required.

  In the embodiment illustrated in FIGS. 7 to 8, practical embodiments have shown that the decoupling obtained in the band F1 between the frequency channels F1 (GSM900) and F2 (GSM1800 + UMTS) is greater than 30 dB for the channels polarization (coplanar) and greater than 25dB for orthogonally polarized channels. In the F2 band, this decoupling is greater than 30 dB for the parallel polarization channels as well as for the perpendicularly polarized channels. Mid-power openings are

  neighboring 650 in the band Fl and close to 90 in the band F2.

  In the embodiment illustrated in FIGS. 9 to 10, practical embodiments have shown that the decoupling obtained in the IF band between the frequency channels F1 (GSM900) and F2 (GSM 1800 + UMTS) is greater than 23 dB for the parallel (coplanar) polarization channels and greater than 40dB for orthogonal polarization channels. In the F2 band, this decoupling is greater than 30 dB for the parallel polarization channels and 40 dB for the perpendicular polarization channels. Mid-power openings are

  neighboring 650 in the band Fl and close to 90 in the band F2.

  The antennas of base stations must therefore integrate two or even three frequency bands, transmit and receive in these frequency bands with polarizations

  identical and a high level of decoupling between these frequency bands.

  The radiating device according to the invention can be used for other applications and other frequency bands requiring two channels with identical polarizations and

separate frequencies.

  It can also be used for other applications requiring for example to emit and receive electromagnetic waves with right or left circular polarization in

  combining the two orthogonal polarization channels in quadrature phase.

Claims (10)

Claims.   1-radiating device for dual-band radio waves with coplanar polarizations, comprising a first radiating element (1) operating in a first frequency band F1 and a second radiating element (2) operating in a second frequency band F2, characterized in in that the first radiating element (1) is formed by a half-wave "patch" antenna comprising a rectangular radiating plate (4) and in that the second radiating element (2) is formed by at least one dipole comprising two radiating strands (7) and (8) arranged in a plane of polarization of the radiating plate (4) and oriented   parallel to the radiating plate (4).   2-radiating device according to claim 1, characterized in that the first radiating element (1) and the second radiating element (2) are arranged parallel to a plane   mass (5) also forming a reflector.   3-radiating device according to claims 1 and 2, characterized in that the plate   radiating (4) of the first radiating element (1) is superimposed on a lower radiating plate (3) of approximately equal dimensions, arranged in parallel and in the same direction as the radiating plate (4), between the latter and the ground plane (5) for   form with the ground plane (5) a double resonator.   4-radiating device according to claim 3, characterized in that the radiating plate   (3) is excited in the fundamental mode around its resonance demionde.   Radiation device according to any one of claims 1 to 4, characterized in that   the strands (7, 8) of the dipole constituting the second radiating element (2) are connected to a balun-type balun formed by two parallel conducting rods (9a, 9b) disposed in the plane of symmetry formed by the neutral lines mm 'and nn' respectively of the plates 3 0 (3) and (4) and passing through the plates (3, 4) in a direction perpendicular to the plane of the plates (3,4).   6-radiating device according to any one of claims 1 to 4, characterized in that   the strands (7, 8) of the dipole constituting the second radiating element (2) are connected to a balun-type balun formed by two parallel conducting rods (9a, 9b), forming a plane perpendicular to the plane of symmetry formed by the neutral lines mm 'and nn' respectively of the plates (3) and (4) and arranged on both sides and close to those ci, and passing through the plates (3, 4) in a direction perpendicular to the plane of the plates (3,4).   7-Device according to one of claims 5 and 6, characterized in that one of the rods (9a)   is traversed at its center by a central conductor (10) whose one end is connected to the end of one of the strands (7) and the other end is connected to the central conductor of a coaxial connector (11) fixed to the plane mass forming the reflector (5), the rod (9a) being connected by a first end to the end of the other strand (8) and by a second end to the ground plane (5) and in that the another rod (9b) is fixed by a first end to one end of the strand (7) and by a second end to the ground plane forming the reflector (5).   8-Device according to one of claims 5 and 6, characterized in that one of the rods (9a)   is traversed in its center by a central conductor (10) whose end is connected to the end of one of the strands (7) and the other end is connected to the central conductor of a coaxial cable (11) whose sheath is electrically fixed to the ground plane forming the reflector 20 (5), the rod (9a) being connected at one end to the end of the other strand (8) and at a second end to the ground plane (5). ) and in that the other rod (9b) is fixed by a first end to one end of the strand (7) and by a second end to the plane of mass forming the reflector (5).   9-radiating device according to any one of claims 5 and 6, characterized in that   that the rods (9a, 9b) of the balun are in electrical contact with the radiating plates   (3, 4) that it pass through and with the ground plane forming the reflector (5).   10-radiating device according to any one of claims 3 to 9, characterized in that   That the lower radiating plate is fixed at its edges by two conductive tabs   (12) and (13) located in the plane of symmetry mm ', nn' of the plates.   11-radiating device according to any one of claims 1 to 9, characterized in that   the first radiating element comprises a first radiating plate (4) and a second square-shaped radiating plate (3) of roughly equal dimensions excited on two lines of symmetry of the "patch" respectively parallel to the adjacent sides of the formed squares; by the plates (3, 4), for generating two orthogonal polarization waves of the same frequency F1, and in that the second radiating element (2) comprises a second dipole oriented perpendicular to the first dipole and fed by a second symmetric type " balun "for generating two waves with orthogonal polarizations according to a second frequency F2 whose radiated electric fields are   respectively coplanar with those radiated by the first radiating element.   12-radiating device according to claim 10, characterized in that the first radiating element (1) and the second radiating element (2) are oriented in space to radiate respectively two orthogonal polarized waves inclined by +/- 45 by vertical ratio.   13-radiating device according to any one of claims 1 to 10, characterized in   the ratio of the frequency bands radiated by the first (1) and the second   radiating element (2) is substantially greater than 1.5.