EP2430705B1 - Compact multibeam antenna - Google Patents

Description

GENERAL TECHNICAL FIELD

The invention relates to the field of single-frequency or multi-frequency multibeam antennas intended to transmit / receive a radio frequency signal in a plurality of directions.

STATE OF THE ART

Obtaining one or more directional antenna beams is to the detriment of the size of the antenna.

Indeed, the more the antenna must be directive (that is to say that it is desired to have an antenna that can radiate in a preferred direction or several directions and must have several independent beams) plus its radiating surface must be important.

The figure 1 illustrates a multi-beam antenna of known type.

This antenna, consisting of three panels P ₁ , P ₂ , P ₃ , can operate in three directional beams.

This antenna - see figure 2 comprises a ground plane P and a dielectric substrate 11 having a dielectric constant ε ₁ . The substrate 11 is disposed on the plane P of mass.

The antenna furthermore comprises a plurality of sets E _i of antenna elements, these antenna elements S _ij are arranged on the substrate 11 (i corresponds to the number of the set and j to the number of the element antenna in the set i).

The antenna elements S _ij are adapted to transmit / receive a radiofrequency signal in a given direction so that each set E _i is associated with a direction of the antenna. The antenna is considered to transmit / receive the signal in one or more frequency bands in different directions defined by each panel.

The figure 2 schematically illustrates a set E _i of antenna elements S _ij .

The elements S _ij are fed according to a distribution law (a _ij , Φ _ij ), a _ij being the amplitude of the transmitted or received signal and Φ _ij its phase. This law is applied to each group of sets i (formed of antenna elements j) of the same panel in order to form a coherent radiation pattern and favoring a determined direction A ₁ , A ₂ , A ₃ , normally an azimuth given in the horizontal plane. In its simplest form, the elements E _i are fed in series or in tree structure.

The Figures 3a and 3b respectively illustrate a top view and a profile view of the ground plane P with the substrate 11 and an antenna element S _i1 used in the antennas of known type.

In multibeam antennas of this type (see figure 1 ), the sets corresponding to the same direction are arranged in several columns, typically up to four columns. The columns are also arranged side by side.

A problem is that such an arrangement is cumbersome in particular in view of having more and more directional antennas, that is to say, can radiate in several directions. Indeed, it would be necessary to add columns.

PRESENTATION OF THE INVENTION

The invention makes it possible to have a multibeam antenna of reduced size compared with known antenna solutions of the same type.

According to a first aspect, the invention relates to a multibeam antenna for transmitting / receiving a radiofrequency signal in a plurality of directions in at least one frequency band, the antenna comprising: a ground plane; a dielectric substrate having a permittivity, the substrate being disposed on the ground plane; a plurality of sets of antenna elements disposed on the substrate, each set corresponding to a direction of the antenna.

The antenna according to the invention is characterized in that it further comprises a dielectric superstrate, having a permittivity greater than the permittivity of the substrate, arranged on the sets of antenna elements, and in that the sets are interlaced one below the other so as to form a column, the sets corresponding to the same direction of the antenna being separated by an assembly number equal to the number of directions of the antenna minus one.

• ▪ les éléments d'antennes d'un même ensemble sont espacés d'une distance inférieure à une longueur d'onde λ, la longueur d'onde λ correspondant dans le cas monofréquence à la fréquence à laquelle l'antenne doit fonctionner et dans le cas multifréquence à la fréquence centrale définie par (f_max-f_min)/2 où f_max est la fréquence maximale à laquelle l'antenne doit fonctionner et f_min est la fréquence minimale à laquelle l'antenne doit fonctionner ;
• ▪ les éléments d'antennes appartenant à des ensembles différents sont espacés d'une distance inférieure à λ/n, où λ correspond à : dans le cas monofréquence, à la fréquence à laquelle l'antenne doit fonctionner ; dans le cas multifréquences, à la fréquence centrale définie par (f_max-f_min)/2 où f_max est la fréquence maximale à laquelle l'antenne doit fonctionner et f_min est la fréquence minimale à laquelle l'antenne doit fonctionner ; et où n est le nombre d'ensembles différents (E_i) ;
• ▪ pour chaque direction de l'antenne un nombre identique d'ensembles d'éléments d'antennes ;
• ▪ les ensembles correspondant à une même direction de l'antenne sont connectés en série ou en arborescence ;
• ▪ chaque ensemble comprend un nombre identique d'éléments d'antennes ;
• ▪ les éléments d'antennes sont des patchs carrés, en forme de triangle équilatéral ou en forme ellipsoïdale ;
• ▪ chaque côté de chaque élément d'antenne est de dimension égale à $\frac{{\mathrm{<figure-callout\; id="0"\; label="\lambda "\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_0}{4\sqrt{{\mathrm{<figure-callout\; id="1"\; label="\epsilon "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_1+\delta {\mathrm{<figure-callout\; id="2"\; label="\epsilon "\; filenames="imgf0004.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_2}}$
  
  où ε₁ est la permittivité du substrat et ε₂ est la permittivité du superstrat, λ₀ est la longueur d'onde correspondant à la fréquence associée à l'élément d'antenne, la valeur δ est approximativement égale à : δ = h₁ / (h₁ + d) ;
• ▪ les éléments d'antennes sont des patchs à double polarisation orthogonale disposant de deux accès indépendants permettant de réaliser la diversité de polarisation.

The antenna according to the invention may furthermore have one or more of the following characteristics:

• The antenna elements of the same set are spaced apart by a distance less than a wavelength λ, the corresponding wavelength λ in the single-frequency case at the frequency at which the antenna is to operate and in the multi-frequency case at the center frequency defined by (f _max -f _min ) / 2 where f _max is the maximum frequency at which the antenna is to operate and f _min is the minimum frequency at which the antenna is to operate;
• ▪ the antenna elements belonging to different sets are spaced apart by a distance less than λ / n, where λ corresponds to: in the single-frequency case, to the frequency at which the antenna must operate; in the multifrequency case, at the central frequency defined by (f _max -f _min ) / 2 where f _max is the maximum frequency at which the antenna must operate and f _min is the minimum frequency at which the antenna must operate; and where n is the number of different sets (E _i );
• ▪ for each direction of the antenna an identical number of sets of antenna elements;
• ▪ the sets corresponding to the same direction of the antenna are connected in series or in tree structure;
• ▪ each set includes an identical number of antenna elements;
• ▪ Antenna elements are square patches, in the shape of equilateral triangle or in ellipsoidal shape;
• ▪ each side of each antenna element is equal in size to $\frac{{\mathrm{<figure-callout\; id="0"\; label="\lambda "\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_0}{4\sqrt{{\mathrm{<figure-callout\; id="1"\; label="\epsilon "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_1+\delta {\mathrm{<figure-callout\; id="2"\; label="\epsilon "\; filenames="imgf0004.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_2}}$
  
  where ε ₁ is the permittivity of the substrate and ε ₂ is the permittivity of the superstrate, λ ₀ is the wavelength corresponding to the frequency associated with the antenna element, the value δ is approximately equal to: δ = h ₁ / (h ₁ + d);
• ▪ Antenna elements are orthogonal dual polarization patches with two independent accesses to achieve polarization diversity.

The antenna according to the invention is single frequency or multifrequency and in each frequency band can have several beam directions.

According to a second aspect, the invention relates to a cellular communication network comprising an antenna the first aspect of the invention.

PRESENTATION OF FIGURES

• la figure 4 illustre une antenne multifaisceaux selon l'invention ;
• les figures 5a et 5b illustrent respectivement une vue de dessus et une vue de profil du plan de masse avec un substrat et un superstrat diélectriques et un élément d'antenne de l'antenne de l'invention ;
• les figures 6a et 6b illustrent respectivement un patch carré et un patch en forme de triangle équilatéral mis en oeuvre dans l'antenne de l'invention ;
• la figure 7 illustre une antenne à trois faisceaux monofréquence conforme à l'invention ;
• la figure 8 illustre un arrangement des éléments d'antennes dans un ensemble pour une antenne bifréquences conforme à l'invention ;
• la figure 9 illustre la variation du couplage entre deux ensembles d'éléments d'antennes en fonction de l'écart entre les éléments pour les éléments d'une antenne de type connu et pour des éléments plus petits, mis en oeuvre dans une antenne de l'invention, ayant des caractéristiques de rayonnement identique ;
• la figure 10 illustre les performances en termes de gain isotrope des éléments d'antennes d'une antenne de type connu et pour une antenne avec des éléments plus petits mis en oeuvre dans une antenne de l'invention, ayant des caractéristiques de rayonnement identique ;
• les figures 11a et 11b illustrent la réduction de taille d'un dipôle en un monopole utilisé dans l'antenne de l'invention ;
• la figure 12 illustre une vue de profil du plan de masse avec un substrat et un superstrat diélectriques et un élément d'antenne de l'antenne de l'invention pour expliciter les dimensions de l'élément d'antenne.

Other features and advantages of the invention will become apparent from the description which follows, which is purely illustrative and nonlimiting, and should be read with reference to the accompanying drawings in which, in addition to the Figures 1, 2, 3a and 3b already discussed:

• the figure 4 illustrates a multibeam antenna according to the invention;
• the Figures 5a and 5b respectively illustrate a top view and a side view of the ground plane with a dielectric substrate and superstrate and an antenna element of the antenna of the invention;
• the Figures 6a and 6b respectively illustrate a square patch and an equilateral triangle-shaped patch implemented in the antenna of the invention;
• the figure 7 illustrates a three-beam antenna with single frequency according to the invention;
• the figure 8 illustrates an arrangement of the antenna elements in a set for a two-frequency antenna according to the invention;
• the figure 9 illustrates the variation of the coupling between two sets of antenna elements as a function of the difference between the elements for the elements of an antenna of known type and for smaller elements, implemented in an antenna of the invention , having identical radiation characteristics;
• the figure 10 illustrates the performance in terms of isotropic gain of the antenna elements of an antenna of known type and for an antenna with smaller elements implemented in an antenna of the invention, having identical radiation characteristics;
• the Figures 11a and 11b illustrate the reduction in size of a dipole into a monopole used in the antenna of the invention;
• the figure 12 illustrates a profile view of the ground plane with a dielectric substrate and superstrate and an antenna element of the antenna of the invention for explaining the dimensions of the antenna element.

DETAILED DESCRIPTION OF THE INVENTION Antenna structure

• The figure 4 illustrates a multibeam antenna having a small footprint compared to multibeam antennas of known type (see antenna of the figure 1 ).
• The Figures 5a and 5b illustrate, respectively, a top view and a profile view of the ground plane P with the substrate 11, the superstrate 12 and an antenna element S _i1 .

This antenna comprises a ground plane P, a dielectric substrate 11 having a dielectric constant ε ₁ disposed on the ground plane P and a plurality of sets E _i of antenna elements S _ij disposed on the substrate 11.

As already mentioned, each set E _i corresponds to a direction of the antenna.

To reduce the size of the antenna, the sets E _i of antenna elements S _ij are intertwined one below the other so as to form a column and the sets E _i which correspond to the same direction of the antenna are separated by a set number equal to the number of direction of the antenna minus one.

In other words, the same antenna direction is found on the column of set of antenna elements periodically, the period being equal to the number of direction of the antenna.

Such interleaving can generate a coupling between antenna elements that are closer than in antennas of known type.

To avoid coupling between the antenna elements, the size of the antenna elements is reduced.

This reduction in size is possible by the fact that the antenna comprises a dielectric superstrate 12 having a permittivity ε ₂ greater than the permittivity ε ₁ of the dielectric substrate 11.

The use of this superstrate 12 makes it possible to maintain radiation characteristics that are identical to a larger antenna element.

Moreover, a resistor R is connected between the ground plane P and each antenna element S _ij . The resistance R is typically equal to one Ohm. This resistor R serves to short-circuit one of the radiating sides of the antenna element. This short-circuit serves to transform the radiating element of size λ / 2, consisting of two monopolies, each of size λ / 4 on each side of the dipole, into a single monopole of size λ / 4 and consequently allows to divide by two the electrical dimensions of the radiating element (see figure 11 ).

This resistor R also makes it possible to substantially increase the bandwidth of the antenna in its resonant behavior.

In order to obtain good performance for each direction of the antenna, the sets E _i which correspond to the same antenna direction are connected together in series.

• ▪ dans le cas monofréquence, à la fréquence à laquelle l'antenne doit fonctionner ;
• ▪ dans le cas multifréquences, à la fréquence centrale définie par (f_max-f_min)/2 où f_max est la fréquence maximale à laquelle l'antenne doit fonctionner et f_min est la fréquence minimale à laquelle l'antenne doit fonctionner ; et où
• ▪ n le nombre d'ensembles différents (E_i).

The antenna elements belonging to different sets are spaced apart by a distance less than λ / n, where λ corresponds to:

• ▪ in the case of single frequency, at the frequency at which the antenna must operate;
• ▪ in the multifrequency case, at the central frequency defined by (f _max -f _min ) / 2 where f _max is the maximum frequency at which the antenna must operate and f _min is the minimum frequency at which the antenna must operate; and or
• ▪ n the number of different sets (E _i ).

Typically we will take a spacing of less than 0.9λ / n.

The antenna elements of the same set are spaced apart by a distance less than λ.

The spacing constraints make it possible to obtain a radiation pattern of the different elements with a single main lobe in an angular aperture (-90 °, + 90 °) of the plane of the assembly relative to the main axis of perpendicular radiation. to all.

Beyond this spacing, additional main lobes appear at each end of the angular aperture (-90 °, + 90 °) degrading the directivity performance of the assembly.

Single frequency case

We illustrated on the figure 7 a three-beam antenna A, B, C single frequency. In this figure, in each set E ₁ , E ₂ , E ₃ the antenna elements S _ij are connected to each other.

In addition, all sets E ₁ are connected to obtain a first beam A, all sets E ₂ are connected to obtain a second beam B and all sets E ₃ are connected to obtain a third beam C.

The antenna elements of the same set are separated by a distance of 0.5λ and the antenna elements of different sets are separated by a distance of 0.3λ (there are three different beams).

Compared to known type antennas using a single beam, the use of several beams (including the use of a single UMTS carrier with a different scrambling code per beam) uses independent and physically similar antennas with radiation patterns with different azimuths in the horizontal plane.

This approach results in an increase in the overall surface of the antennal solution, comprising a plurality of specific antennas.

Multifrequency case

We illustrated on the figure 8 the arrangement of the antenna elements S _ij in a set E _i for a two-frequency antenna. The number of antenna elements S _ij is doubled with respect to a single-frequency antenna (see figure 7 ).

Compared to antennas of known type, the use of several near frequencies for different telecommunications standards (including the use of the 880-960 MHz spectrum for GSM and UMTS) uses independent and physically similar antennas with the same radiation pattern.

This approach results in an increase in the overall surface of the antennal solution, comprising a plurality of specific antennas.

Antenna elements S _ij

où ε₁ est la constante diélectrique du substrat et ε₂ est la constante diélectrique du superstrat, λ₀ est la longueur d'onde dans le vide δ est la contribution partielle du diélectrique ε₂ dans le rayonnement de la cavité de l'élément rayonnant.The antenna elements S _ij are preferably square or equilateral triangle-shaped patches of side dimension d: $$d=\frac{{\mathrm{<figure-callout\; id="0"\; label="\lambda "\; filenames="imgf0003.png,imgf0004.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_0}{4\sqrt{{\mathrm{<figure-callout\; id="1"\; label="\epsilon "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\epsilon </figure-callout>}}_1+\delta {\epsilon }_2}}$$

where ε ₁ is the dielectric constant of the substrate and ε ₂ is the dielectric constant of the superstrate, λ ₀ is the wavelength in the vacuum δ is the partial contribution of the dielectric ε ₂ in the radiation of the cavity of the radiating element .

This radiation takes place in effective dimensions taking into account the physical dimension d of the element and an overflow of the fields which extends over a distance approximately the value of the thickness h ₁ of the substrate (see figure 12 ). Note that the value δ is approximately equal to: $\delta =\frac{h_1}{{\mathrm{<figure-callout\; id="1"\; label="h"\; filenames="imgf0001.png"\; state="\{\{state\}\}">h</figure-callout>}}_1+d}\mathrm{.}$

The Figures 6a and 6b illustrate respectively a square patch and an equilateral triangle shaped patch, each side is of dimension d (see above).

Thanks to the reduction of the dimensions of the antenna elements S _ij , the interleaving of the sets E _i is possible and the space obtained is identical to the space required for a single direction of the antenna of known type (see the comparison between the configuration of the figure 1 and the configuration of the figure 4 ).

performances

The figure 9 illustrates the coupling between two sets of antenna elements as a function of the difference between the elements for known antenna elements (curve 20) and for the smaller elements (curve 30) having radiation characteristics identical. To ensure proper operation between different systems, it is sought to obtain a coupling between different antennas less than -30 dB.

With a typical distance of 0.45 λ between the antenna elements, the two antennas of known type have a coupling between them of about -10 dB whereas with the same spacing, the two antennas with the smaller antenna elements have a coupling below -50dB between them.

The figure 10 illustrates the performance in terms of isotropic gain of antenna elements of the antenna of known type (curve 40) and for the antenna with smaller elements (curve 50).

It is observed that, despite the addition of the superstrate and the substantial reduction of the physical dimensions of the compact radiating element, its gain is about 3 dBi at the resonance frequency, barely 0.2 dB below the gain of a conventional radiating element (about 3.2 dBi).

Claims (10)

1. Multibeam antenna for emitting/receiving a radiofrequency signal in a plurality of directions in at least one band of frequencies, the antenna comprising:

   - a ground plane (P);

   - a dielectric substrate (11), having a permittivity (ε₁), the substrate (11) being arranged on the ground plane (P);

   - a plurality of assemblies (E_i) of antenna elements arranged on the substrate (11), each assembly (E_i) corresponding to a direction of the antenna;

   characterised in that the antenna further comprises a dielectric superstrate (12), having a permittivity (ε₂) greater than the permittivity (ε₁) of the substrate (11), arranged on the assemblies (E_i) of antenna elements, and in that the assemblies (E_i) are interleaved one under the other so as to form a column, the assemblies (E_i) corresponding to a single antenna direction being separated by a number of assemblies equal to the number of antenna directions minus 1.
2. Antenna according to claim 1, in which the antenna elements of a single assembly are spaced apart by a distance less than one wavelength λ, the wavelength λ corresponding in the monofrequency case to the frequency at which the antenna has to operate and in the multifrequency case to the central frequency defined by (f_max-f_min)/2 where f_max is the maximum frequency at which the antenna has to operate and f_min is the minimum frequency at which the antenna has to operate.
3. Antenna according to one of the preceding claims in which the antenna elements belonging to different assemblies are spaced apart by a distance less than λ/n, where λ corresponds to:

   • in the monofrequency case, the frequency at which the antenna has to operate;

   • in the multifrequencies case, the central frequency defined by (f_max-f_min)/2 where f_max is the maximum frequency at which the antenna has to operate and f_min is the minimum frequency at which the antenna has to operate; and where

   • n is the number of different assemblies (E_i).
4. Antenna according to one of the preceding claims, comprising for each direction of the antenna an identical number of assemblies of antenna elements.
5. Antenna according to one of the preceding claims, in which the assemblies corresponding to a single antenna direction are connected in series or in arborescence.
6. Antenna according to one of the preceding claims, in which each assembly comprises an identical number of antenna elements.
7. Antenna according to one of the preceding claims, in which the antenna elements are square, equilateral triangle shaped or ellipsoidal shaped patches.
8. Antenna according to the preceding claim, in which each side of each antenna element is of dimension equal to $\frac{{\lambda }_0}{4\sqrt{{\epsilon }_1+\delta {\epsilon }_2}}$

   

   where ε₁ is the permittivity of the substrate and ε₂ is the permittivity of the superstrate, λ₀ is the wavelength corresponding to the frequency associated with the antenna element, the value 5 is approximately equal to: δ = h₁ / (h₁ + d).
9. Antenna according to one of the preceding claims, in which the antenna elements are patches with double orthogonal polarisation having two independent accesses making it possible to achieve diversity of polarisation.
10. Cellular communication network comprising an antenna according to one of the preceding claims.

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