Compact high-gain antenna

Abstract

The invention relates to a panel antenna comprising: a ground plane (P); a dielectric substrate (11) having a permittivity (∈1), the substrate (11) being located on the ground plane (P); at least one radiating source (Si), each radiating source consisting of a plurality of antenna elements (Eij), the antenna elements (Eij) being located on the substrate (11) and furthermore consecutively spaced apart, relative to one another, by a distance (de) shorter than one wavelength λ, the wavelength λ corresponding to the antenna operating frequency. The antenna is characterized in that it furthermore comprises a dielectric superstrate (12) having a permittivity (∈2) higher than the permittivity (∈1) of the substrate (11), the superstrate being located above the antenna elements (Eij), and in that the antenna elements (Eij) are all identical and have, in operation, identical radiation characteristics.

Description

GENERAL TECHNICAL FIELD

The invention relates to the field of panel antennas, particularly those used in cellular networks.

STATE OF THE ART

Base transceiver stations (BTS) are subject to major constraints in terms of height arrangement (church louvers, bas-reliefs of the façades of protected buildings, etc.).

Cellular networks currently resort to isotropic high-gain antennas in order to maximise their radio range. These gains are obtained by means of panels of heights commonly varying between 1.2 m for the 1800/2100 MHz band and 2.4 m for the 900 MHz band.

A panel antenna comprises in the familiar manner a plurality of antenna elements arranged in a vertical row on a substrate.

FIG. 1 illustrates a panel antenna of known type.

The panel antenna in FIG. 1 comprises eight antenna elements E_i (i=1 to 8) arranged on a substrate 11; each antenna element E_i comprises an access point A_i and is spaced apart at a distance d_e of approx. 0.9λ, wherein λ is the vacuum wavelength at the central frequency of the frequency band of the antenna. The distance is understood between two access points A_i of the antenna elements E_i.

The antenna elements E_i are supplied in a tree structure for example: the adjacent antenna elements E_i are connected two by two by means of a first supply line L₁ in order to form four pairs of antenna elements.

The pairs are furthermore connected two by two by means of a second supply line L₂ in order to form two quadruplets of antenna elements and the quadruplets are finally interconnected by means of a third supply line L₃.

It is observed that the supply lines are defined between two access points A_i of each antenna element E_i.

FIGS. 2 a and 2b respectively illustrate a top view and a side view of an antenna element E_i arranged on a substrate 11. The antenna element E_i arranged on the substrate forms a radiating source termed a “patch”.

The dielectric substrate 11 has a dielectric constant ∈₁ and is arranged on a ground plane P, wherein the antenna element E_i is arranged on the substrate 11.

The antenna element E_i is arranged on the dielectric substrate 11 connected to a connector A_i in order to supply the antenna element E_i.

Each antenna element E_i displays during operation a unit gain of approx. 8 dBi; the antenna in FIG. 1 therefore displays a gain of 8 dBi+10 log(8)=17 dBi for a height of 8×0.9λ=7.2λ.

The tables in FIGS. 3a and 3b show the ratio between the gain of the antenna and its height for two main frequency bands used in cellular networks (the 880-960 MHz band, known as “900 MHz” and the 1710-2170 MHz band, known as “2100 MHz”) at the central frequency of the antenna frequency band. It is noticed in particular that in order to progress from a gain of 15 dBi to 17 dBi, the antenna height needs to be approximately doubled for a given central frequency.

It can therefore be seen that the height of the antenna is dictated by the number of antenna elements E_i. Hence, the greater the gain of the antenna, the more elements are required and the larger the size of the antenna.

This is not unproblematic, since the current trend involves imposing maximum heights for panel antennas or indeed reductions in height.

A solution is known for reducing the size of a panel antenna, involving eliminating some antenna elements E_i. Such elimination however results in a loss in terms of antenna gain and therefore deterioration in the antenna performances.

PRESENTATION OF THE INVENTION

One aim of the invention is to enable an increase in the gain of an antenna without having to increase the size of the antenna.

Another aim of the invention is to enable a reduction in the height of an antenna without any decrease in the gain of the antenna.

Hence, the invention relates to a panel antenna comprising a ground plane, a dielectric substrate, having a permittivity, wherein the substrate is arranged on the ground plane, at least one radiating source, wherein each radiating source is formed of a plurality of antenna elements, wherein the antenna elements are arranged on the substrate and are furthermore consecutively spaced apart in relation to one another at a distance of less than a wavelength λ, said wavelength λ corresponding to the antenna operating frequency.

The antenna according to the invention is characterised in that it furthermore comprises a dielectric superstrate, having a permittivity greater than the permittivity of the substrate, wherein the superstrate is arranged above the antenna elements and the antenna elements are all identical and possess during operation identical radiating characteristics.

The arrangement of the antenna elements forming each radiating source makes it possible to achieve a reduction in height with constant gain or obtain an increase in the gain with constant height.

Preferably, the antenna furthermore comprises a dielectric superstrate, having a permittivity greater than the permittivity of the substrate, wherein the superstrate is arranged on the antenna elements.

The combination of the superstrate with the arrangement of the antenna elements makes it possible to achieve either the reduction in height with constant gain or an increase in the gain with constant height.

The invention is advantageously supplemented by the following characteristics, considered alone or in any of their technically feasible combinations:

• • each radiating source comprises four antenna elements connected successively in pairs by the means of a first supply line, wherein said pairs are connected to each other by means of a second supply line, wherein the centre of the second supply line comprises an access point of the radiating source adapted for supply of said radiating source;
  • it comprises several radiating sources, wherein the radiating sources are arranged in relation to each other such that their access points are spaced apart by a distance equal to the distance between two antenna elements, wherein each radiating source possesses identical radiating characteristics;
  • the antenna elements are arranged in relation to one another with a distance d_e equal to d_s(N−1)/N, wherein d_s is the distance between two access points of two radiating sources and N is the number of antenna elements of each radiating source;
  • each radiating source preferentially comprises between two and six antenna elements;
  • the antenna elements are patches having a shape selected from among the following group: square, equilateral triangle, elliptical;
  • the antenna elements are derived from the following technologies: horns or wire antennas;
  • it comprises a resistance connected between the ground plane and each antenna element.

The invention also relates to a cellular communication network comprising a panel antenna according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates apanel antenna of known type;

FIGS. 2 a and 2b respectively illustrate a top view and a side view of an antenna element;

FIGS. 3 a and 3b respectively illustrate the ratio between the gain of the antenna and its height for two main frequency bands;

FIG. 4 illustrates a panel antenna according to a first embodiment of the invention;

FIG. 5 illustrates a panel antenna according to a second embodiment of the invention;

FIGS. 6 a and 6b respectively illustrate a top view and a side view of an antenna element of the antenna according to the invention;

FIG. 7 illustrates and elemental source according to the invention;

FIG. 8 illustrates a panel antenna of known type displaying during operation the same gain as the antenna according to the first embodiment of the invention;

FIG. 9 illustrates a panel antenna of known type having the same height as the antenna according to the second embodiment of the invention.

In all the figures, similar elements bear identical numerical references.

DETAILED DESCRIPTION OF THE INVENTION

Two embodiments of the invention are described below in relation to FIGS. 4 to 9.

“Antenna element” is taken to mean a radiating element having a preferably flat conducting body.

“Radiating source” is taken to mean the combination of several antenna elements.

“Panel antenna” is taken to mean a planar antenna comprising several antenna elements.

For each embodiment, the panel antenna comprises a dielectric substrate 11 having a permittivity ∈₁, wherein the substrate 11 is arranged on a ground plan P. Furthermore, the panel antenna comprises at least one radiating source S_i.

Each radiating source S_i is formed of a plurality of antenna elements E_ij consecutively spaced apart in relation to one another. Two consecutive antenna elements are spaced apart by a distance d_e less than the wavelength λ, said wavelength λ corresponding to the antenna operating frequency.

The antenna in FIG. 4 comprises two radiating sources S₁, S₂ and the antenna in FIG. 5 comprises six radiating sources.

Advantageously, each radiating source S_i comprises four antenna elements E_i1, E_i2, E_i3, E_i4 connected in pairs in a tree structure for example by means of a first supply line L₁.

Each antenna element comprises an access point A_ij for connection of the antenna elements in pairs by means of the supply line L₁.

The pairs of antenna elements E_ij are connected by means of a second supply line L₂. The centre of the second supply line L₂ comprises an access point A_i of the radiating source S_i. Such an access point A_i is adapted for supply of the radiating source S_i to which it refers.

As can be seen, there are as many access points A_i as there are radiating sources S_i. Hence, the antenna in FIG. 5 comprising six radiating sources therefore comprises six access points A₁, A₂, A₃, A₄, A₅, A₆.

The radiating sources S_i are arranged in relation to each other such that their access points A_i are spaced apart by a distance equal to the distance d_s between two consecutive access points of two radiating sources S_i.

Furthermore, the antenna elements E_ij of a radiating source S_i are arranged in relation to one another with a distance d_e equal to d_s(N−1)/N, wherein d_s is the distance between the radiating sources S_i and N is the number of antenna elements E_ij of each radiating source S_i. The distance d_e is in turn the distance between two consecutive access points A_ij of each antenna element E_ij.

To be more precise, in defining a main axis passing through the centres of symmetry of each antenna element, the access points A_ij of each antenna element are located on an axis perpendicular to the main axis, the first and second supply lines L₁, L₂ being parallel to the main axis.

Preferably, each radiating source S_i comprises four radiating elements E_ij.

The antenna furthermore comprises (those of FIGS. 4 and 5) a dielectric superstrate 12 having a permittivity ∈₂ greater than the permittivity ∈₁ of the substrate 11 which is arranged on the antenna elements E_ij.

In relation to an antenna element E_i forming a radiating source of the patch type, of known type, the antenna element E_ij is thus immersed in a medium with high permittivity, which allows a reduction in the size of the antenna element in order to reduce its operating wavelength, or rather retain it and reduce its physical dimensions.

Use of the substrate 12 makes it possible to retain radiating characteristics identical to those of an antenna element of greater height.

Furthermore, a resistance R is connected between the ground plane P and each antenna element E_ij (refer to FIGS. 6a and 6b). The resistance R is typically equal to one Ohm. This resistance 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, formed of two monopoles, each of size λ/4 on each side of the dipole, into a single monopole of size λ/4 and consequently makes it possible to halve the electrical dimensions of the radiating element.

This resistance R also allows an appreciable increase in the passband of the antenna in its resonant behaviour.

Finally, the permittivity ∈₁ is for example between 1 and 4 and is preferably equal to 2.2 and the permittivity ∈₂ is for example between 10 and 50 and is preferably equal to 30.

By way of example, in relation to the antenna element E_i of a patch of known type, for an operating frequency in the GSM band at a central frequency of 920 MHz, the side of the antenna element E_i is of dimensions equal to 94 mm whereas the side of the antenna element E_ij (with the superstrate) is of dimensions equal to 21.5 mm.

Still by way of example, one may consider antenna elements E_ij which are square, in the shape of an equilateral triangle or elliptical in shape or derived from the following technologies: horns or wire antennas allowing combination of sources owing to their small size or small radiating aperture.

Reduction in Height—Constant Gain

The antenna illustrated in FIG. 4 allows a reduction in height of a panel antenna of known type while retaining the same gain of 17 dBi.

It comprises two radiating sources S₁, S₂ spaced apart by a distance d_s=0.9λ, each consisting of four antenna elements spaced apart by a distance d_e=0.9λ (4−1)/4=0.675λ (refer to FIG. 7).

Each radiating source displays a gain of 14 dBi during operation such that the antenna in FIG. 4 displays a gain of 17 dBi during operation.

Nevertheless, in relation to the antenna as illustrated in FIG. 8, the height is halved: the reduction is from 7.2λ (8×0.9λ) to 3.6λ (4×0.9λ).

The radiating sources S₁ and S₂, each having an access point A₁, A₂, are nested along the longitudinal axis of the antenna (refer to FIG. 4) such that the points of access A_i of the sources S_i are set apart by the same distance d_s. In order to facilitate understanding of the supply circuit of the different sources, each access point is arranged on a side opposite the following access point.

The distance between two consecutive radiating elements belonging to two different radiating sources varies between d_s/N and d_s(N−1)/N, i.e. between 0.225λ and 0.675λ.

Increase in Gain—Constant Height

The antenna illustrated in FIG. 5 allows an increase in gain of the antenna while retaining the same height as a panel antenna of known type.

It comprises six radiating sources, each consisting of four antenna elements (refer to FIG. 7).

As in the preceding embodiment, each radiating source displays a gain of 14 dBi during operation such that the antenna in FIG. 5 displays a gain of 21.8 dBi during operation instead of 17 dBi obtained by the antenna of the same height, as illustrated in FIG. 9 (height equal to 7.2λ).

As above, the radiating sources, each having an access point A₁, A₂, A₃, A₄, A₅, A₆, are nested along the longitudinal axis of the antenna (refer to FIG. 5) such that the access points A_i of the sources S_i are set apart by the same distance d_s. In order to facilitate understanding of the supply circuit of the different sources, each access point is arranged on a side opposite the following access point.

The distance between two consecutive radiating elements belonging to two different radiating sources varies between d_s/N and d_s(N−1)/N, i.e. between 0.225λ and 0.675λ.

Claims

1. Panel antenna comprising a ground plane (P),a dielectric substrate (11), having a permittivity (e1), wherein the substrate (11) is arranged on the ground plane (P),at least one radiating source (Si) formed of at least one pair of antenna elements (Eij) arranged on the substrate (11), the antenna elements being all identical and have during operation identical radiating features and are furthermore consecutively spaced apart in relation to one another at a distance (de) of less than a wavelength λ, said wavelength λ corresponding to the antenna operating frequency, the antenna elements being connected successively in pairs by a first supply line (L1), wherein said pairs are connected to each other by a second supply line (L2), the centre of the second supply line (L2) comprising an access point (Ai) of the radiating source (Si) adapted for supplying said radiating, source (Si);a dielectric superstrate (12), having a permittivity (∈2) greater than the permittivity (e1) of the substrate (11), wherein the superstrate is arranged above the antenna elements (Eij) and the antenna elements (Eij);a resistance (R) connected between the ground plane (P) and each antenna element (Eij).

2. Antenna according to claims 1 wherein each radiating source (S1) comprises four antenna elements (Ei1, Ei2, Ei3, Ei4).

3. Antenna according to claim 2, comprising several radiating sources (Si), wherein the radiating sources (Si) are arranged in relation to each other such that their access points (Ai) are spaced apart by a distance equal to the distance between two antenna elements (Eij), wherein each radiating source (Si) possesses identical radiating characteristics.

4. Antenna according to claim 1, wherein the antenna elements (Eij) are arranged in relation to one another with a distance de equal to ds(N−1)/N, wherein ds is the distance between two access points (Ai) of two radiating sources (Si) and N is the number of antenna elements (Eij) of each radiating source (Si).

5. Antenna according to claim 1, wherein each radiating source (Si) preferentially comprises between two and six antenna elements (Eij).

6. Antenna according to claim 1, wherein the antenna elements (Eij) are patches having a shape selected from among the following group: square, equilateral triangle, elliptical.

7. Antenna according to claim 1, wherein the antenna elements (Eij) are derived from the following technologies: horns or wire antennas.

8. Cellular communication network comprising a panel antenna according to claim 1.