EP0484241B1 - Printed circuit antenna for a dual polarized antenna array - Google Patents

Description

The present invention relates to an elementary printed antenna in plated technology for a network for receiving and / or transmitting telecommunications signals, having a small footprint for boarding purposes in a machine, such as satellite.

More specifically, the antenna comprises, in a known manner, a dielectric substrate, a ground conductor plane of a microwave power supply line disposed on one face of the substrate, and a radiating element disposed on another face of the substrate, said conductive plane having a coupling slot for coupling the supply line to the radiating element.

In such an antenna, as illustrated in Figure 14.6, page 824, from the book "MICROSTRIP ANTENNAS", Vol. 2, edited by J.R. James & P.S. Hall, 19 .., the radiating element is constituted by a metal plate printed on the face of the substrate opposite the slot made in the ground plane. The supply line is for example a microstrip line.

The radiating plate is similar to an open resonator which is the seat of waves essentially polarized along the width of the underlying coupling slot. The resonances mainly depend on the dimensions of the slot and of the plate. The bandwidth is a function of the overvoltage coefficient of the resonator, which itself depends on the thickness and the electrical characteristics of the substrate.

To constitute a dual polarization network, the latter comprises a first sub-network comprising antennas subject to a first polarization, for example Ex, and a second sub-network comprising antennas subject to a second polarization Ey orthogonal to the first. The antennas in the first and second subarrays are interleaved and are therefore in close proximity to one another.

The two polarizations are obtained by perpendicular coupling slots. The measurements show that the electromagnetic field is not perfectly polarized in the vicinity of an elementary antenna. Indeed, for example, the electric field lines curve in proportion to the distance from the center of the coupling slot, along the longitudinal axis of the latter. This curvature of the field line thus makes polarization imperfect, and consequently generates harmful couplings between elementary antennas in the same sub-array, but also between elementary antennas in the two sub-arrays. These couplings are all the more pronounced the closer the antennas are to each other.

The gain of such a network is therefore low. The surface occupied by this one is all the greater as the gain is improved, to the detriment of the congestion of the network and therefore unlike the search for compactness for the materials on board in vehicles.

The present invention aims to provide an elementary printed antenna which generates an almost perfect polarization, that is to say almost rectilinear, which makes it possible to bring together such antennas having crossed polarizations and therefore to reduce the size of a network. antennas.

To this end, a printed antenna according to the invention and as defined in the introduction, is characterized in that the radiating element consists of several narrow conductive strips extending perpendicular to the coupling slot.

The narrow bands maintain polarization along their longitudinal direction and thus prevent excitation of the mode orthogonal to the polarization thus defined. Under these conditions two elementary antennas having coplanar and perpendicular conductive bands between them offer an almost zero coupling, which makes it possible to bring them together, and therefore to increase the antenna density and the compactness in a dual polarization network.

• la fig. 1 est une vue éclatée en perspective d'une antenne imprimée à fente de couplage et plaque rayonnante selon la technique antérieure ;
• les figs. 2 et 3 sont respectivement une vue en coupe transversale à la fente de couplage et une vue de dessus de la plaque rayonnante, montrant des répartitions de lignes de champ électrique et du courant surfacique dans l'antenne de la fig. 1 ;
• la fig. 4 est analogue à la fig. 3 et montre une plaque rayonnante elliptique ;
• la fig. 5 est une vue éclatée en perspective d'une antenne imprimée à bandes rayonnantes selon l'invention ;
• les figs. 6 et 7 sont des vues de dessus de bandes rayonnantes inscrites globalement dans un rectangle et une ellipse, respectivement ; et
• la fig. 8 est une vue schématique de dessus d'un réseau d'antennes à deux polarisations orthogonales selon l'invention.

Other advantages and characteristics of the invention will appear more clearly on reading the following description of several preferred embodiments of the invention with reference to the corresponding appended drawings in which:

• fig. 1 is an exploded perspective view of a printed antenna with coupling slot and radiating plate according to the prior art;
• figs. 2 and 3 are respectively a cross-sectional view of the coupling slot and a top view of the radiating plate, showing distributions of electric field lines and surface current in the antenna of FIG. 1;
• fig. 4 is similar to FIG. 3 and shows an elliptical radiating plate;
• fig. 5 is an exploded perspective view of a printed antenna with radiating bands according to the invention;
• figs. 6 and 7 are top views of radiating bands inscribed generally in a rectangle and an ellipse, respectively; and
• fig. 8 is a schematic top view of an array of antennas with two orthogonal polarizations according to the invention.

In order to better discern the characteristics of the invention, the structure of an elementary printed antenna 1a with coupling slot according to the prior art is recalled with reference to FIG. 1.

According to this example, the antenna 1a is supplied by a microwave microstrip line supported by a first dielectric substrate 2a of thickness d₂ and of relative permittivity εr₂ predetermined. The substrate 2a is printed on both sides. The underside of the substrate comprises a conductive strip 3a of predetermined width W₃. The upper face of the substrate 2a is covered with a ground conducting plane 4a. A rectangular portion of the upper face of the substrate 2a is devoid of conductive material to form a coupling slot 5a. The longitudinal axis of the slot 5a is perpendicular to the microstrip 3a, while the transverse axis of the slot 5a is parallel to and vertically aligned with the axis of the microstrip. The length and width of the slot 5a are denoted by L₅ and W₅ in FIG. 1.

The elementary antenna 1a also comprises a conductive plate 6a ("patch" in English terminology) constituting the radiating element of the antenna. The plate 6a is superimposed above the ground plane 4a, opposite the underside of the substrate 2a supporting the microstrip 3a, by means of a second dielectric substrate 7a. The substrate 7a has a thickness d₇ and a relative permittivity εr₇ generally different from d₂ and εr₂ respectively, the constant εr₇ often being less than ε _r2 and close to unity to increase the bandwidth of the antenna. The substrate 7a is fixed to the conductive plane 4a of the first substrate, for example with epoxy cement.

The plate 6a is full, unlike the openwork character of the ground plane 4a imparted by the presence of the slot 5a.

The plate 6a is rectangular and has predetermined width W₆ and length L₆ much larger than the dimensions of the slot 5a, as shown in FIG. 3. According to other variants, the radiating plate can be square, circular, trapezoidal, polygonal or else elliptical as shown in FIG. 4. The centers of the slot 5a and of the plate 6a are superimposed vertically, that is to say aligned perpendicular to the longitudinal axis of the microstrip 3a. The transverse and longitudinal axes of the slot 5a are here parallel to the transverse and longitudinal axes of the plate 6a, respectively.

A thin dielectric plate (not shown) serving as a protective cover can be glued to the upper face of the second substrate 7a supporting the printed plate 6a.

The two substrates possibly with the protective cover thus form a monolithic elementary antenna.

Fig. 2 illustrates electric field lines E in the antenna 1a which are seen in the vertical plane comprising the longitudinal axis of the microstrip 3a and the transverse axis of the slot 5a, and therefore which extend perpendicular to the slot 5a. Fig. 3 shows surface current lines on the radiating plate 6a. These figures show, as already said, current lines which are curvilinear on either side of the transverse axis of the slot 5a and therefore field lines not perpendicular to the slot which disturbs any field polarization in the environment close to the antenna 1a, and in particular causes this antenna 1a to couple with any other neighboring elementary antenna in a flat antenna array.

An elementary printed antenna 1b with coupling slot and microstrip microwave power supply line according to the invention is illustrated in FIG. 5. This antenna 1b is therefore of the same type as the known antenna 1a described above and comprises elements 2b, 3b, 4b, 5b and 7b, identified with the index b, respectively analogous to those 2a, 3a, 4a , 5a and 7a of antenna 1a.

The antenna 1b comprises, in place of the metal plate 6a, several narrow parallel metal strips 8b forming the radiating element of the antenna 1b. The strips 8b are printed on the upper face of the second substrate 7b. For example, according to fig. 5, the bands 8b are seven in number, each have a length L₈ = W₆ and a width W₈ approximately equal to L₆ / 14, and are equidistant by intervals of width I = W₈ along the longitudinal axis of the slot 5b . The strips 8 thus extend parallel to the microstrip 3b and perpendicular to the slot 5b, and are distributed symmetrically on either side of the transverse axis of the slot 5b.

The contour formed by the ends of the strips 8b can be similar to that of the plate 6a, and is for example rectangular as shown in FIGS. 5 and 6, or elliptical as shown in fig. 7, or even circular or polygonal.

In figs. 6 and 7 are indicated by arrows of the surface current lines which are confined in the conductive strips 8b. Compared to figs. 3 and 4, these streamlines are perfectly rectilinear and parallel, having regard to the small width W₈ of the conductive strips 8b relative to the length L₆ of the plate 6a. Thanks to the straightness of the bands 8b, the electric field polarization E is perfectly perpendicular to the coupling slot 5b, and cannot be disturbed by and cannot disturb a polarized orthogonal electric field emitted by an elementary antenna according to the invention located at neighborhood of antenna 1b, as will be seen below in an array of antennas.

By way of example, a double polarization array comprising two sub-arrays each having sixteen elementary antennas according to the invention is shown in FIG. 8.

The first sub-array includes sixteen 1X₁ to 1X₁₆ antennas with Ex polarization which are uniformly distributed in four parallel rows 1X₁ to 1X₄, 1X₅ to 1X₈, 1X₉ to 1X₁₂ and 1X₁₃ to 1X₁₆, forming linear networks. The first antenna sub-network is supplied by a microstrip line 9X which ends in a tree line in the network by means of power dividers by two 10X in order to supply the four rows, then pairs of antennas and finally each of the elementary antennas of a pair. The 1X₁ to 1X₁₆ antennas are thus regularly distributed in a square matrix.

The second sub-network also includes four linear antenna sub-networks 1Y₁ to 1Y₄, 1Y₅ to 1Y₈, 1Y₉ to 1Y₁₂ and 1Y₁₃ to 1Y₁₆ forming lines of a square matrix interleaved two by two with the lines of the first sub-network . A microstrip line 9Y also arborescent through power dividers by two 10Y supplies the second sub-network. Line 9Y is analogous to line 9X and originates from a side opposite line 9Y with respect to the array, and the antennas in the first subarray are staggered relative to the antennas in the second subarray, the subnetwork columns also being interleaved two by two.

The two sub-arrays have in common the two dielectric substrates 2b and 7b between which extends the ground plane 4b with slots 5X and 5Y associated with the antennas 1X₁ to 1X₁₆ and 1Y₁ to 1Y₁₆, and under the first 2b of which are printed the 3X and 3Y line microstrips associated with said antennas, respectively. The radiating bands 8X and 8Y of the two sub-arrays are thus coplanar on the upper face of the substrate 7b.

The antennas 1X₁ to 1X₁₆ have their radiating bands 8X, extending in a direction Ex, while the antennas 1Y₁ to 1Y₁₆ have their radiating bands 8Y extend in a direction Ey perpendicular to the direction Ex. The antennas according to the invention thus associated with orthogonal pure polarizations can be very close to one another, unlike networks according to the prior art, since the Ex and Ey polarizations are perfectly rectilinear and orthogonal, and therefore do not disturb each other. For example, a 1X, 1Y antenna is "framed" by four other 1Y, 1X antennas according to fig.8. This results in greater compactness which is particularly advantageous when the antenna network is embedded for example in a satellite, a missile or other device.

Although the invention has been described with reference to microstrip supply lines (microstrip), a person skilled in the art will know how to replace these by triplate lines (stripline) or coaxial lines. For a three-ply line, a third dielectric substrate is fixed under the underside of the first substrate 2b; a reflective ground conductor plane is printed under the underside of the third substrate.

On the other hand, the distribution of antennas in a network can be different from that shown in fig. 8.

Claims (6)

1. Printed antenna (1b) comprising a dielectric substrate (7b), an earth conducting plane (4b) of a hyperfrequency supply line (3b) arranged on one side of the substrate, and a radiating element arranged on another side of the substrate, said conducting plane having a coupling slot (5b) for coupling the supply line to the radiating element, characterised in that the radiating element consists of a plurality of narrow conducting bands (8b) extending perpendicularly to the coupling slot (5b).
2. Antenna according to claim 1, characterised in that the bands (8b) are distributed symmetrically on both sides of the transverse axis of the slot (5b).
3. Network of antennae comprising a plurality of first antennae (1X₁ to 1X₁₆) according to claim 1 or 2 and the bands (8X) of which are parallel to one another.
4. Network of antennae according to claim 3, characterised in that it comprises a plurality of second antennae (1Y₁ to 1Y₁₆) according to claim 1 or 2 and the bands (8Y) of which are parallel to one another and extend in the same plane as and perpendicular to the bands (8X) of the first antennae (1X₁ to 1X₁₆).
5. Network of antennae according to claim 4, characterised in that the antennae closest to a first or second antenna (1X, 1Y), respectively, are second or first antennae (1Y, 1X), respectively.
6. Network of antennae according to claim 4 or 5, characterised in that the first antennae (1X₁ to 1X₁₆) are distributed along the rows of a first matrix which are interconnected, two by two, with the rows of a second matrix along which the second antennae (1Y₁ to 1Y₁₆) are distributed.

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