EP2009735A1 - Antenna with diversity of polarisation for transmitting and/or receiving audio and/or video signals - Google Patents

Abstract

The antenna has a set of identical antenna elements supplied radio-electrically with currents of same phase and amplitude. The antenna elements respectively have biquad type identical and separated radiating elements (1, 2) each formed of two polygonal geometrical figures reunited by a common part, and reflectors associated with the corresponding radiating element. The radiating elements have respective longitudinal symmetry axes (X, X') orthogonally crossing at the level of feed centers (4, 5) that are isolated from one another and supplied individually.

Description

The present invention relates, in general, to a polarization diversity antenna for transmitting and / or receiving audio and / or video signals.

More specifically, the invention relates to a polarization diversity antenna for transmitting and / or receiving audio and / or video signals, of the kind comprising a plurality of identical antenna elements powered electrically by currents of substantially the same phase and the same amplitude, each antenna element comprising a radiating element formed of two polygonal geometric figures joined by a common vertex, a feed center and a reflector associated with this radiating element.

Microstrip patch antennas used in particular in wireless computer networks (Wi-Fi) have certain advantages such as low weight, small footprint and low cost of use. They are available in either horizontal or vertical linear polarization or left or right circular polarization for telecommunications. However, these antennas also have limited possibilities. As examples, the narrow bandwidth is often associated with problems of geometric and physical tolerance and generally low gain (6 d Bi).

Moreover, most of them radiate only in the half-plane, support weak powers (100 w) and have radiation losses.

The object of the present invention is to propose an antenna of the type indicated above, of a non-prohibitive cost, which has a flexible use because it allows a diversity of polarization and whose performances are superior to those of antennas of the state of the technique, in particular antennas of the patch type, used in comparable applications.

To achieve this goal, the antenna according to the invention is characterized in that it comprises two identical and separate radiating elements whose respective longitudinal axes of symmetry intersect orthogonally at said feed centers which are isolated one of each other and fed individually.

According to a further feature of the invention, each antenna element comprises a radiating element or radiator configured according to a double continuous loop of perimeter substantially equal to two wavelengths (2 λ), these two loops being located in the same plane , having a common vertex and being selected from a set of polygonal geometrical shapes comprising quadrilaterals undistorted or deformed into a series of polygons whose vertices grow in number toward each other until they form a geometrical figure devoid of such highs.

According to a particular characteristic of the invention, the two loops are chosen from a set of polygonal geometrical shapes resulting from the deformation of a quadrilateral, these polygonal shapes being capable of to ensure a greater range of the bandwidth and to increase the gain compared to the undeformed quadrilateral.

As a result, the antenna element may represent a continuous double loop taking the form of, for example, two squares or, preferably, two pentagons, hexagons or other higher polygons until reaching and understanding geometric shapes without sharp angles. for example two ellipses.

In addition, according to another characteristic of the invention, each radiating element is configured according to a double continuous loop representing two identical polygonal geometric shapes.

According to a preferred embodiment, the two radiating elements are of identical shape and each configured in a double continuous loop representing two identical polygonal geometric shapes.

In such a case, a single polygonal geometric shape is, therefore, the basis of the configuration of these two radiating elements.

On the other hand, according to another advantageous and preferred feature of the invention, each antenna element comprises a radiating element configured according to a double continuous loop taking the geometric form of two pentagons.

In such a configuration, the radiating element takes the form, therefore, of a decagonal loop.

In addition, according to a particular and preferred feature of the invention, the two radiating elements are each configured in an identical decagonal loop.

When the radiating element is in the form of two pentagons, the three adjacent sides of each of them, with respect to the furthest sides of the feeding center, are advantageously located each along the sides of a single and even rectangle. Consequently, the two pentagons of the same radiating element each comprise two adjacent right angles.

In fact, the two pentagons in question correspond to two adjacent parallel quadrilaterals whose sides closest to each other are deformed towards each other so as to constitute the outline of a feeding center. .

For this reason, the radiating element taking the form of a double pentagon or double quadrilateral deformed thus described may be designated later in the description as in the claims by the name "biquad".

The radiating element is usually made from a wire advantageously copper, placed at a short distance from the receiver to which it is attached. However, this metal wire may be replaced preferably by a printed circuit on a dielectric support panel, printing performed according to known methods.

According to a preferred embodiment, the two printed circuits, each forming a radiating element, are respectively fixed on the opposite faces of the same support panel, for example a laminated panel formed of a glass fiber reinforced epoxy composite. Such a panel is generally thin usually less than 2 mm. These elements radiating, in particular their feeding centers, are found, therefore, in parallel planes however located at a very short distance from one another or, in other words, at substantially equal distance from the reflector.

For this reason, a single reflector will be advantageously used. This usually takes the form of a plate configured in support of said radiating elements which are directly attached thereto or, preferably, via a dielectric panel supporting them, in particular in the form of printed circuits.

This reflector consists of a metal plate generally made of copper or aluminum. Steel, especially stainless steel or polychlorinated biphenyl ("PCB") can be used as well. In this case, and in known manner, it may be advantageous to solder, for example copper to the coaxial power cable orifice, orifice formed in this reflector so as to ensure a good physical and electrical connection.

According to another characteristic of the invention, the different radiating elements are connected, via their respective supply center, to a divider / phase shifter circuit, in particular such a circuit capable of providing a phase shift of, for example, 90 °.

This connection is generally provided by means of a coaxial power supply cable.

1. a) L'isolation des centres d'alimentation entre eux permet, dans un système de réception, l'obtention de signaux de deux polarisations croisées de cette antenne en l'occurrence les polarisations verticale et horizontale. Toutefois, moyennant l'utilisation d'un circuit déphaseur de 90° alimentant séparément les deux centres d'alimentation en question à partir d'une source unique d'alimentation électrique, une polarisation circulaire peut être créée. Ainsi, un déphasage de +90° ou -90° entre ces centres d'alimentation provoqué par exemple par une commande électronique capable de les piloter, en particulier un circuit diviseur/déphaseur commandé et des commutateurs RF (radio-fréquence), permettra d'obtenir une polarisation circulaire respectivement droite ou gauche. Par conséquent, la configuration des deux centres d'alimentation ci-dessus couplée à un dispositif électronique de commande pour le pilotage de ces deux centres, permet la conception d'une antenne agile en polarisation.
2. b) L'alimentation d'un seul des deux centres d'alimentation est capable de créer une polarisation linéaire verticale ou horizontale selon que l'élément rayonnant alimenté est respectivement l'élément vertical ou l'élément horizontal. Par conséquent, l'antenne selon l'invention peut être utilisée, si nécessaire, dans une configuration fixe pour des applications ne nécessitant ni diversité de polarisation ni agilité en polarisation.

The antenna according to the invention thus conceived can be implemented in different ways:

1. a) The isolation of the power centers between them makes it possible, in a reception system, to obtain signals from two crossed polarizations of this antenna, in this case the vertical and horizontal polarizations. However, with the use of a 90 ° phase shifter separately feeding the two power centers in question from a single source of power, a circular polarization can be created. Thus, a phase shift of + 90 ° or -90 ° between these centers of supply caused for example by an electronic control capable of driving them, in particular a controlled divider / phase-shifter circuit and RF (radio-frequency) switches, will enable obtain a circular polarization respectively right or left. Therefore, the configuration of the two above feed centers coupled to an electronic control device for controlling these two centers, allows the design of an antenna agile polarization.
2. b) The feeding of only one of the two feed centers is capable of creating a vertical or horizontal linear polarization depending on whether the radiating element fed is respectively the vertical element or the horizontal element. Therefore, the antenna according to the invention can be used, if necessary, in a fixed configuration for applications requiring neither polarization diversity nor polarization agility.

• o La figure 1 est une vue schématique frontale d'une antenne selon l'invention,
• o La figure 2 est une vue latérale de l'antenne à la figure 1 couplée à un circuit de déphasage schématisé,
• o La figure 3 est une représentation du diagramme de rayonnement dans le plan horizontal d'une antenne à la figure 1.

The invention will be better understood and other purposes, features and advantages thereof will become apparent more clearly in the explanatory description which follows with reference to the accompanying drawings given solely by way of example illustrating an embodiment of the invention and in which:

• o The figure 1 is a front schematic view of an antenna according to the invention,
• o The figure 2 is a side view of the antenna at the figure 1 coupled to a schematic phase shift circuit,
• o The figure 3 is a representation of the radiation pattern in the horizontal plane of an antenna at the figure 1 .

EXAMPLE 868 MHz ANTENNA

As shown in figure 1 , the antenna according to the invention, the radiation pattern of which in rectilinear polarization is illustrated in FIG. figure 3 , comprises a set of two radiating elements of biquad type, namely a radiating element 1 placed horizontally and an identical radiating element 2 placed vertically. These two radiating elements are each configured in closed loop forming, in this case, two pentagons equal in the same plane and united by a common vertex. In addition, as evidenced by the longitudinal axes of symmetry X and X ', these biquads 1 and 2 intersect perfectly at 90 ° avoiding any interaction between them. On the other hand, it is observed that the farthest sides of the feed center 4 of the radiating element 1, that is to say the three sides adjacent a, b, c of the first pentagon and the three adjacent sides d, e, f of the second pentagon, are located along the edges of the same rectangle. Therefore, the sides a and b; b and c; d and e and e and f are orthogonal. In addition, the length of the sides b and e is about 55 mm, while the length of the sides a, c, d, and f is about 50 mm and the total length of this biquad 1 is about 120 mm. Since biquads 1 and 2 are equal, the characteristics listed above for biquad 1 are found at biquad 2.

On the other hand, these biquads 1 and 2 are in the form of printed circuits respectively on the opposite faces of a panel 3 of thickness 1.6 mm, made of woven and glued glass fibers, for example a FR4 board as shown in figure 2 .

The figure 1 also shows, in addition to the feeding center 4 of the biquad 1, the feeding center 5 of the biquad 2. These feeding centers, isolated from each other, are spaced about 40 mm from the reflector 6 visible to the figure 2 which consists of an aluminum plate G3 of about 250 mm × 250 mm and about 1.5 mm thick.

On the other hand, each of these biquads is connected via its respective power supply center to a divider / phase-shifter circuit 7 of the type having 4 inputs, which is shown in FIG. figure 2 . This phase-shifting circuit, printed on a double-sided FR4 panel, is loaded on 50 Ω and has an input 8 in connection with an electric power source (not shown) while the inputs 9 and 10 are connected respectively to the biquad 1 through its feed center 4 and biquad 2 via its center of supply 5. This connection is provided, on the other hand, by means of coaxial cables 11 and 12 with an impedance of 50Ω, power supply cables covered with electrically neutral material. Thus, when the centers 4 and 5 are powered, or the input 9 connected to the horizontal biquad 1 may be out of phase + 90 ° or the input 10 connected to the biquad 2 may be, in turn, out of phase -90 ° and this, so as to put in phase these two radiating elements 1 and 2 and configure the antenna in circular polarization respectively right or left.

The polarization diversity antenna according to the invention provides undeniable advantages over the state of the art represented in particular by the patch antenna and can be developed at a low cost, in any event comparable to that of this type of antenna.

By way of examples, the bandwidth and the gain, close to 9 dBi, offered by the antenna according to the invention in circular polarization prove to be greater than with a patch antenna. On the other hand, in circular polarization, the opening of the main lobe of the antenna according to the invention is greater than 40 °.

Consequently, the efficiency exhibited by the circular polarization antenna according to the invention at the radiation and gain level could be validly exploited for use in radio frequency communications (RFID: "Radio Frequency Identification"), for example at 868MHz or 960MHz.

On the other hand, the circularly polarized antenna according to the invention could also be used in Wi-Fi in particular at 2.4 GHz for the transmission of images, for example from drones used for terrestrial observation, real time and from the sky.

Furthermore, in vertical or horizontal linear polarization, the antenna according to the invention may be used for the polarization decoupling measurement and in particular in specific cases where the antenna polarization switching is frequent.

Claims (12)

A polarization diversity antenna for transmitting and / or receiving audio and / or video signals, of the kind comprising a plurality of identical antenna elements, electrically powered by currents of substantially the same phase and amplitude, each element antenna comprising a radiating element formed by two polygonal geometrical figures joined by a common vertex, a feed center and a reflector associated with this radiating element, characterized in that it comprises two identical radiating elements (1,2) and separated, whose respective longitudinal axes of symmetry intersect orthogonally at said feed centers (4,5) which are isolated from each other and fed individually. Antenna according to claim 1, characterized in that each radiating element is configured according to a double continuous loop of perimeter substantially equal to two wavelengths (2 λ), these two loops being located in the same plane, having a common vertex and being chosen from a set of polygonal geometrical shapes comprising quadrilaterals that are not deformed or deformed into a series of polygons whose vertices grow in number while approaching each other until they form a geometrical figure devoid of such vertices. Antenna according to Claim 1 or 2, characterized in that the two radiating elements are of a shape identical and each configured in a double continuous loop representing two identical polygonal geometric shapes. Antenna according to claim 2 or 3, characterized in that the radiating element (1,2) is configured according to a double continuous loop taking the geometric form of two pentagons. Antenna according to claim 4, characterized in that the three adjacent sides of each pentagon of a radiating element, adjacent sides represented by the furthest sides of the feed center (4,5), are located each along the sides of one and the same rectangle. Antenna according to one of claims 1 to 5, characterized in that the two antenna elements are in the form of printed circuits on opposite sides of a dielectric support panel (3). Antenna according to one of claims 1 to 6, characterized in that the radiating elements (1, 2) are associated with a single reflector (6) forming a support panel therefor, these radiating elements being fixed either directly or by via a dielectric panel (3) supporting them in the form of printed circuits. Antenna according to one of claims 1 to 7, characterized in that the radiating elements (1, 2) are respectively in parallel planes at a substantially equal distance from the reflector (6). Antenna according to one of claims 1 to 8, characterized in that the radiating elements (1,2) are connected, via their respective feed centers, to a divider / phase shifter circuit (7). Antenna according to one of claims 1 to 9, characterized in that it is used in right or left circular polarization according to a phase shift of respectively + 90 ° or - 90 ° is applied between the feed centers. Antenna according to one of Claims 1 to 10, characterized in that it is used for wireless (Wi-Fi) or radio frequency (RFID) applications. Antenna according to one of claims 1 to 8, characterized in that it is used in vertical or horizontal linear polarization depending on whether the supplied radiating element is respectively the vertical element or the horizontal element.

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