EP0064313B1 - Circularly polarised microwave radiating element and flat microwave antenna using an array of such elements - Google Patents

Description

The present invention relates to a receiver element for microwave signals with circular polarizations, produced in a planar structure according to the printed circuit technique associated with a dielectric support, as well as a planar antenna comprising an array of such elements. It goes without saying that, given the reciprocity of an antenna, a reception element (or an antenna composed of a network of reception elements) is capable of functioning as a radiating element (as a radiating antenna) without any modification of its characteristics. This remark remains valid without exception throughout the description which follows, and the word reception can always be replaced by the word emission.

French patent application FR-A-2 408 921 describes an antenna comprising on the one hand radiating elements or receivers of microwave signals and on the other hand, associated with these, microwave transmission line termination structures . However, this termination structure only allows the reception of microwave signals of a single type of circular polarization and, moreover, the radiating and receiving elements consist of a set of three annular slots operating in a different and more complex way than the elements provided in this case.

The object of the invention is to propose a new structure for an element for receiving microwave signals, these signals being able to be indifferently with left circular polarization or with right circular polarization, as well as an antenna composed of such elements.

The invention firstly relates, for this purpose, to a receiver element for microwave signals with circular polarizations produced in planar structure according to the printed circuit technique associated with a dielectric support, or, according to the principle of reciprocity of antennas, a radiating element. such signals produced in a similar manner, said element comprising on the one hand two superimposed planar dielectric layers (12) and (13) each comprising on their outer face an electrically conductive surface (14) or (15) which constitutes a plane called mass and on the other hand, in the median plane (10) located between these layers, two separate triplate lines (3) and (4) of microwave transmission whose ends, called first, are respectively arranged along two substantially perpendicular and radial axes , characterized in that it is provided in each of the conductive surfaces with circular coaxial recesses with a diameter close to half the wavelength signals to be received, these recesses revealing the dielectric layers (12) and (13) and being situated opposite said first line ends to achieve with them a coupling allowing the transmission of the microwave signals to be received, and in that each of the other two ends, called second ends, of the three-plate lines (3) and (4) constitutes a connection intended to be connected to the electronic reception circuits.

In a particular embodiment of the invention, the receiving element also comprises in the same median plane at least two dipoles each consisting of an electrically conductive strip of length substantially equal to half the wavelength of the signals to receive and arranged along said axes to allow effective coupling between these dipoles and the corresponding triplate transmission lines, an insulating sheet being interposed between, these dipoles for. electrically separate from each other at least the portions of these two dipoles which are opposite one another, and this pair of dipoles being situated opposite the recesses.

Whatever the embodiment chosen, both of these two structures have the same essential advantages, namely the possibility of receiving signals with left or right circular polarization at the same time, and the almost total absence of coupling between the circuits corresponding to these two types of received signals since in the center of the dipoles, the coupling is only capacitive, and precisely where the electric field is zero or very weak.

• A) dans un plan médian, un ensemble de (m x n) paires de dipôles répartis en premiers et deuxièmes dipôles disposés respectivement suivant deux axes pratiquement perpendiculaires, les premiers dipôles d'une part, les deuxièmes dipôles d'autre part, étant parallèles les uns aux autres d'une paire de dipôles à l'autre ;
• B) dans le même plan médian, deux réseaux plans distincts de lignes triplaques de transmission hyperfréquence composés chacun d'une succession d'étages de combinaison des signaux reçus, les (m x n) extrémités de chacun de ces réseaux étant situées en regard d'une extrémité des (m x n) premiers dipôles pour l'un des réseaux et d'une extrémité des (m x n) deuxièmes dipôles pour l'autre réseau de façon à réaliser entre chaque réseau et les (m x n) dipôles qui lui sont associés un couplage capacitif suffisant pour permettre la transmission des signaux hyperfréquences à recevoir, et l'extrémité opposée de chacun de ces deux réseaux constituant une connexion destinée à être reliée aux circuits électroniques du dispositif de réception ;
• C) de part et d'autre de ce même plan médian, deux couches diélectriques planes comportant chacune sur leur face extérieure une surface électriquement conductrice qui constitue un plan dit de masse et, dans chacune de ces surfaces conductrices, (m x n) évidements non conducteurs laissant apparaître la couche diélectrique correspondante et situés en regard des (m x n) paires de dipôles.

The invention also relates to an antenna with an array of receiving elements as defined above, and comprising the following symmetrical structure:

• A) in a median plane, a set of (mxn) pairs of dipoles distributed in first and second dipoles arranged respectively along two substantially perpendicular axes, the first dipoles on the one hand, the second dipoles on the other hand, being parallel to each other to others from one pair of dipoles to another;
• B) in the same median plane, two distinct plane networks of three-plate microwave transmission lines each composed of a succession of stages of combination of the received signals, the (mxn) ends of each of these networks being located opposite a end of the (mxn) first dipoles for one of the networks and one end of the (mxn) second dipoles for the other network so as to achieve between each network and the (mxn) dipoles associated with it sufficient capacitive coupling to allow the transmission of the microwave signals to be received, and the opposite end of each of these two networks constituting a connection intended to be connected to the electronic circuits of the reception device;
• C) on either side of this same median plane, two planar dielectric layers each comprising on their outer face an electrically conductive surface which constitutes a ground plane and, in each of these conductive surfaces, (mxn) non-conductive recesses revealing the dielectric layer corresponding and located next to the (mxn) pairs of dipoles.

An antenna in a so-called stripline or triplate structure is already described in United States patent No. 4,170,013, filed on July 28, 1978 and issued on October 2, 1979 in the name of the United States of America represented by Secretary of the Navy, but can in no case apply, unlike the embodiment of the antenna which has just been proposed, to the reception of microwave signals capable of being left or right circularly polarized at the same time. Furthermore, the structure of the antenna receiving elements described in this patent is that of magnetic, not electrical, dipole elements.

• la figure 1a est une vue de dessus d'un élément de réception conforme à l'invention et la figure 1 une coupe suivant l'axe bb de la figure la ;
• la figure 2 montre deux dipôles dans lesquels ont été prévus des évidements non conducteurs 20 autour du point d'intersection des axes de disposition des dipôles ;
• la figure 3a est une vue de dessus d'une antenne plane comprenant un réseau d'éléments récepteurs conformes à l'invention et la figure 3b une coupe suivant l'axe bb de la figure 3a ; et
• la figure 4 montre une variante de réalisation de l'élément de réception selon l'invention.

Other particularities and advantages of the elements and antennas produced in accordance with the invention will appear more precisely in the description which follows and in the appended drawings, given by way of nonlimiting examples and in which:

• Figure 1a is a top view of a receiving element according to the invention and Figure 1 a section along the axis bb of Figure la;
• FIG. 2 shows two dipoles in which non-conductive recesses have been provided around the point of intersection of the axes of arrangement of the dipoles;
• Figure 3a is a top view of a planar antenna comprising an array of receiver elements according to the invention and Figure 3b a section along the axis bb of Figure 3a; and
• Figure 4 shows an alternative embodiment of the receiving element according to the invention.

The receiving element shown in FIGS. 1a and 1b is produced according to the technique of the printed circuit associated with a dielectric support and comprises the following symmetrical planar structure. In a first plane 10, said median and which constitutes a plane of symmetry for the structure described, there are provided two completely separate dipoles 1 and 2, each consisting of an electrically conductive strip whose length is substantially equal to half the length of the microwave signals to be received. These dipoles 1 and 2 are here arranged in an electrically symmetrical cross, along two perpendicular axes, and separated by a thin insulating sheet 11 (the dimensions of this sheet can, if desired, be limited to those necessary to isolate one of the other the portions of the dipoles which are actually opposite one another).

This same median plane 10 also contains two triplate lines 3 and 4, intended to ensure the transmission of the signals received by the dipoles to a reception device not shown. These two lines 3 and 4 must be independent and have no electrical connection between them. A first end 3a of the line 3 is located opposite one end of the dipole 1 and aligned with it, so as to achieve with this dipole a capacitive coupling and, similarly, a first end 4a of the line 4 is located in sight of one end of the dipole 2 and aligned with it, to also carry out a capacitive coupling. The second ends 3b and 4b of line 3 and line 4 are fitted with connectors 5 and 6 respectively and each constitute a connection intended to be connected to the electronic reception circuits, not shown.

To complete this structure, the receiving element finally comprises, on either side of the median plane 10, two pin dietary layers 12 and 13 each comprising on their outer face an electrically conductive surface, 14 and 15 respectively, which constitutes a ground plan. In these conductive surfaces are provided non-conductive recesses 7 and 8 respectively, the recess 7 in the surface 14 revealing the dielectric layer 12 and the recess 8 in the layer 15 revealing the dielectric layer 13. The recesses 7 and 8 are circular, with a diameter slightly greater than the length of each dipole, and are located opposite the dipoles so that they are entirely contained in the cylindrical contour which these recesses define.

The element thus proposed is interesting in several respects: (a) the line-dipole and space-dipole couplings can be strong simultaneously, thanks to the presence of ground planes preventing parasitic radiation from the triplate transmission lines and to that of the recesses authorizing reception exclusively with regard to the dipoles; (b) reception is that of circular polarization signals, both left and right, since the proposed structure does not eliminate either of the two possibilities, the separation of one or the other only taking place later; (c) the coexistence of these two possibilities of reception of signals of different circular polarizations is accompanied by good electrical insulation between the corresponding circuits, thanks to the complete separation of the two dipoles 1 and 2 (opposite to that which is described in patent No. 4,054,874 already cited).

The element can be equipped with a reflective metal surface 16, arranged on one side of the element (see FIG. 1b) and parallel to the median plane 10 of the latter. This conventional arrangement (see for example FIG. 2 of French patent application No. FR-A-2 408 921 reinforces the reception efficiency, the waves received which reach said surface 16 being returned to the dipoles. This reinforcement is optimal if the distance between this surface 16 and the median plane 10 is equal to or substantially equal to a quarter of the wavelength associated with the frequency of the useful signals to be received (by equal is meant electrically equivalent taking into account the media crossed; between the surface 16 and plane 10, there is indeed an air layer and a dielectric layer, layer 13).

• a) si les rubans qui constituent les dipôles ont des longueurs différentes, chaque dipôle peut recevoir des signaux dont les fréquences sont, de façon correspondante, différentes.
• b) si l'on donne aux extrémités des rubans une largeur supérieure à celle de leur zone centrale, chaque dipôle peut soit assurer la réception de signaux de même fréquence mais avec des dimensions un peu réduites par rapport au cas où la largeur de chaque dipôle reste constante, soit, à dimensions maintenues égales, assurer la réception de signaux de fréquence inférieure.
• c) enfin on peut améliorer encore l'absence quasi totale de couplage entre les dipôles, (1) soit en les disposant l'un par rapport à l'autre de telle sorte que l'intersection des deux axes perpendiculaires suivant lesquels ils sont placés coïncide, pour chacun des dipôles, avec son minimum électrique, (2) soit même en ménageant (voir la figure 2) un petit évidement non conducteur 20 dans la surface de chaque dipôle autour du point correspondant à l'intersection de ces deux axes (en réduisant le couplage résiduel éventuel entre les dipôles, les évidements permettent de rendre encore plus mince la feuille isolante 11 dont une trop grande épaisseur pourrait perturber la symétrie de la structure de l'élément récepteur et diminuer les avantages de celle-ci), (3) soit en combinant ces deux dispositions.

The following features can also be adopted, as required:

• a) if the ribbons which constitute the dipoles have of different lengths, each dipole can receive signals whose frequencies are correspondingly different.
• b) if the ends of the ribbons are given a width greater than that of their central zone, each dipole can either ensure reception of signals of the same frequency but with slightly reduced dimensions compared to the case where the width of each dipole remains constant, that is, for dimensions maintained equal, ensuring the reception of signals of lower frequency.
• c) finally, it is possible to further improve the almost total absence of coupling between the dipoles, (1) either by placing them one with respect to the other so that the intersection of the two perpendicular axes along which they are placed coincides, for each of the dipoles, with its electrical minimum, (2) or even by providing (see FIG. 2) a small non-conducting recess 20 in the surface of each dipole around the point corresponding to the intersection of these two axes ( by reducing the possible residual coupling between the dipoles, the recesses make it possible to make the insulating sheet 11 even thinner, too large a thickness which could disturb the symmetry of the structure of the receiving element and reduce the advantages thereof), ( 3) or by combining these two provisions.

The element which has just been described can, in accordance with the invention, be used for the production of a planar microwave antenna composed of a whole array of such elements, according to the same technique of the printed circuit associated with a dielectric support, with the structure described below with reference to Figures 3a and 3b.

In a first median plane 100 is provided a whole set of (mxn) pairs of dipoles 1 _min and 2 _m . _n (referenced in the same way as the dipoles 1 and 2 of the element considered in isolation, but with the indices m, n to characterize them each, m and n being, in the example here considered, equal to 25, but being able to naturally take other values). In each pair, the dipoles 1 _m . _n and 2 _m . _n are, as before, arranged in an electrically symmetrical cross, along two perpendicular axes, but being completely distinct, with electrical insulation provided again by an insulating sheet (either a single sheet with the same surface area as the complete antenna, or pieces of insulating sheet provided only in the dipole area, these pieces possibly themselves being limited to the dimensions just sufficient for the portions of dipoles facing each other to be effectively isolated. one in relation to the other).

The 2- (mxn) dipoles (1 _m . _N ), (2 _m . _N ) each consist of a conductive tape whose electrical length is substantially equal to half the wavelength of the microwave signals to be received. To simplify the description of their arrangement, the dipoles are grouped into (mxn) first dipoles 1 _min and (mxn) second dipoles 2 _m . _n . all the first dipoles on the one hand being parallel to one another from a pair of dipoles to the other, all the second - my dipoles on the other hand being also parallel to each other for a pair of dipoles at the other.

The median plane 100 contains, in addition to the (mxn) pairs of dipoles, the association of two networks of triplate microwave transmission lines, not shown to simplify the figures. These networks are, like lines 3 and 4, electrically independent of each other, intended to ensure the transmission of the signals received by the dipoles to the reception device (not shown), and for this purpose each composed of a succession of stages of combination of the received signals. Such networks are known in numerous embodiments (see, by way of nonlimiting example, the network shown in FIG. 1 of French patent application No. 2,050,408). The first (mxn) ends of one of the networks are located opposite one end of the 1 _min dipoles (mxn) (the same for all these dipoles) and each aligned with the corresponding dipole end, so as to achieve with the dipoles concerned a capacitive coupling; similarly, the first (mxn) ends of the other network are located opposite one end of the (mxn) 2 _m dipoles. _n and aligned with them respectively, to also perform a capacitive coupling of the dipoles to the networks. The opposite end, or second end, of the first network is the point of convergence of all the transmission lines composing this network; it is equipped with a first connector and constitutes a connection intended to be connected to the electronic circuits of the reception device; it is the same for the second end of the second network, equipped with a second connector.

To complete said structure, the antenna finally comprises, on either side of the median plane 100, two planar dielectric layers 112 and 113 each having on their outer face an electrically conductive surface, 114 and 115 respectively, which constitutes a plane of mass. These conductive surfaces 114 and 115 each comprise a set of (mxn) non-conductive recesses revealing the corresponding dielectric layer 112 or 113. These 107 _{m, n} and 108 _min recesses are circular, with a diameter slightly greater than the length of the dipoles and are located opposite them, in such a way that each pair of dipoles is entirely contained in the cylindrical contour delimited by the corresponding recesses.

The antenna thus proposed has the same advantages as the single element described above (quality of the useful couplings, almost total absence of harmful couplings, possibility of simultaneous reception of signals with left or right circular polarization, variations in the characteristics of the dipoles, etc. ...)

Of course, the present invention is not limited to the exemplary embodiments which have just been described and shown, from which other variants can also be proposed without departing from the scope of the invention.

In particular, the element and the antenna as described comprise dipoles, but an embodiment without dipoles (all other things almost equal) can be proposed, with the same essential advantages recalled above. In this case, the dimensions of the recesses are such that these become resonant diaphragms for the frequency of the signals to be received, the intensity of the coupling diaphragms-triplate lines then being linked to the importance of the penetration of the end of these lines in the cylindrical contour limited by the recesses.

On the other hand, when the dipoles are provided, their inclination remains similar from one pair to another, but can be chosen in various ways, one of the most interesting orientations being that where the dipoles are inclined at 45 degrees, this which allows symmetrical installation of the first and second networks of triplate lines.

If the element or antenna according to the invention is equipped with a metallic reflecting surface such as 16 (see the element in FIG. 1b), this surface can, in particular to avoid any coupling between neighboring receiving elements, be limited by (mxn) lateral metal walls with a diameter slightly greater than that of the recesses. These walls are perpendicular to the reflecting surface which now constitutes a bottom wall and placed on the ground plane of the corresponding dielectric layer (see FIG. 4 where an element is shown equipped with such a wall 17). The element or the antenna can also be equipped, in particular to avoid any horizontal radiation from one receiving element to another, with a metal ring 18 of diameter identical to that of the wall 17 and placed on the ground plane on the other dielectric layer.

Whatever the embodiment chosen, the element and the antenna which have been described above find an essential application in the field of television transmitted by satellite, for equipping the systems for receiving these television signals.

Claims (9)

1. A receiving element for circularly polarised high-frequency signals realised in a planar structure in accordance with the printed circuit technology on a dielectric support, or, in accordance with the reciprocity principle of the antennas, an element radiating such signals realised in a similar fashion, said element comprising two superposed planar dielectric layers (12) and (13), each layer having on its outer surface an electrically conducting surface (14) or (15) forming a plane which is commonly referred to as a ground plane, and also having, in the median plane (10) between the two layers, two distinct strip-lines (3) and (4) for high-frequency transmission, whose first ends are respectively disposed along two substantially perpendicular and radial axes, characterized in that in each conducting surface coaxial circular cavities are provided having a diameter approximately half the wavelength of the signals to be received, these cavities exposing the dielectric layers (12) and (13) and being situated opposite said first line ends for forming therewith a coupling allowing the transmission of the high-frequency signals to be received, and. in that each of the two other ends, called the second ends of the strip lines (3) and (4) form a connection intended to be connected to electronic receiving circuits.

2. An element as claimed in Claim 1, characterized in that it also comprises in the same median plane (10) at least two dipoles (1) and (2) each in the form of an electrically conducting strip having a length which is substantially equal to half the wavelength of the signals to be received and provided along said axes to allow an effective coupling between these dipoles and the corresponding transmission strip-lines (3) and (4), an insulating sheet (11) being inserted between these dipoles for electrically separating from each other at least those portions of these two dipoles which are facing each other, this pair of dipoles being located opposite the cavities.

3. An element as claimed in Claim 2, characterized in that the strips forming the dipoles (1) and (2) have different, but not much different, lengths.

4. An element as claimed in one of the Claims 2 and 3, characterized in that the strips forming the dipoles (1) and (2) are wider at their ends than in their central region.

5. An element as claimed in one of Claims 2 to 4, characterized in that in top view the intersection of the two axes along which the dipoles (1) and (2) are arranged coincides for each dipole with its electrical minimum.

6. An element as claimed in anyone of the Claims 2 to 5, characterized in that a small non-conducting cavity (20) is provided in the surface of each dipole (1) or (2), around the point corresponding to the intersection of the two axes along which these dipoles are arranged.

7. A planar high-frequency antenna formed from a network of receiving elements in accordance with Claim 1, characterized in that the antenna comprises the following symmetrical structure :

(A) two superposed planar dielectric layers (112) and (113), each having on its exterior surface an electrically conducting surface (114) or (115) which constitute a plane which is commonly referred to as a ground plane, and, in each of these conducting surfaces (m x n) non-conducting cavities (107_m,n), (108_m._n) exposing the corresponding dielectric layer and being situated pair-wise with respect to each other ;

(B) in the median plane (100) between the two layers (112) and (113), two distinct planar networks of high-frequency strip-lines each formed by a sequence of combining stages of the received signals, the (m x n) ends of each network being located opposite the 2.(m x n) cavities to realise therewith a coupling allowing the transmission of the high-frequency signals to be received, and the opposite end of each of these two networks forming a connection intended to be connected to electronic circuits of the receiving apparatus.

8. A planar high-frequency antenna formed by networks of receiving elements, each element as claimed in anyone of the Claims 2 to 6, characterized in that the antenna comprises the following symmetrical structure :

(A) in a median plane (100) an assembly of (m x n) pairs of dipoles divided into first and second dipoles (1 _m,n) and (2m,") arranged respectively along two substantially perpendicular axes, the first dipoles (1_m.n) on the one hand and the second dipoles (2_m._n) on the other hand being in parallel with each other in pairs of dipoles ;

(B) in the same median plane (100), two distinct planar networks of high-frequency transmission strip-lines, each formed by a sequence of combining stages for the received signal, the (m x n) ends of each network being located opposite an end of the (m x n) first dipoles (1 m.n) for one of the networks and opposite an end of the (m x n) second dipoles (2_m._n) for the other network, so as to realise an adequate capacitive coupling between each network and the (m x n) dipoles associated therewith to enable the transmission of the high-frequency signals to be received, and the opposite end of each of these two networks forming a connection intended to be connected to the electronic circuits of the receiving apparatus ;

(C) on both sides of the same median plane (100) two planar dielectric layers (112) and (113) each having on the exterior surface an electrically conducting surface (114) or (115) which forms a plane which is commonly referred to as a ground plane and, in each of these conducting surfaces (m x n) non-conducting cavities (7_m,_n) or (8_m._n) exposing the corresponding dielectric layer and being situated opposite the (m x n) pairs of dipoles.

9. An antenna as claimed in one of the Claims 7 and 8, characterized in that it comprises (m x n) metal collars (18) having a contour identical to the contours of the non-conducting cavities (7_m,_n) located on the corresponding sides, these collars being supported by the ground plane and being perpendicular thereto.

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