EP0108463A1 - Radiating element for cross-polarized microwave signals and planar antenna consisting of an array of such elements - Google Patents

Abstract

Radiating element or receiver of microwave signals with orthogonal polarizations, this element comprising, on either side of a first layer with a first recess, first and second perpendicular microwave transmission lines, and on the other side of the transmission, a second layer with a second recess and a third layer with a third recess located opposite the other two but short-circuited so as to constitute a reflective plane, the transmission lines being made up of symmetrical grooves and conductive tapes (21 ) and (31) carried in the median plane of these lines and the ends of which penetrate inside the recesses to form exciting probes (24) and (34) whose lengths are distinct and chosen so that, for a thickness determined any of the first layer, the pairs of values lengths of the end of a probe-distance from the probe to the single reflective plane corresponds are due to an experimentally maximum coupling or close to this maximun between each of the probes and the propagation medium. Application: microwave transmitting or receiving antennas.

Description

The present invention relates to an element for receiving microwave signals with orthogonal polarizations or, according to the principle of reciprocity of antennas, a radiating element for such signals produced in a similar manner, this element comprising on either side of a microwave transmission line. the end of which constitutes an excitation probe a dielectric layer.

The invention also relates to a planar antenna comprising an array of such juxtaposed elements, and finds in particular an application in the field of reception of 12 gigahertz television signals retransmitted by means of satellites. 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 words reception, receive, receiver may always be replaced by the words send, transmit, radiant.

A planar antenna comprising such elements is described in the article "New wideband high-gain stripline planar array for 12 GHz satellite TV" by E. Rammos, published in the journal Electronic letters, Volume 18, n ° 6, 18 March 1982, pages 252 and 253. Despite encouraging performance, this antenna is not entirely satisfactory with regard to its performance.

The object of the invention is to propose a receiver element and an antenna (composed of a network of such elements) in which the efficiency is improved.

To this end, the invention relates to a receiving or radiating element as defined in the preamble and characterized in that it also comprises a second transmission line and a third dielectric layer arranged such that this element comprises respectively, on either side of the first layer in which a first recess is provided, the first and second microwave transmission lines arranged along two perpendicular axes, and also comprises, the other side of one of the transmission lines, the second layer with a second recess located opposite the first and, on the other side of the other transmission line, the third layer with a third recess located opposite of the other two but short-circuited at a distance from this other transmission line less than the thickness of this third layer so as to constitute a reflective plane, the first and second transmission lines being constituted on the one hand by grooves produced symmetrically in the adjacent layers and on the other hand of conductive tapes carried in the median plane of these lines and whose ends penetrate followed nt said axes inside the recesses to constitute the excitation probes achieving with the propagation medium a coupling which allows the reception or the radiation of said microwave signals, and in that the lengths of these ends constituting said excitation probes are distinct and chosen so that, for any given thickness of the first layer, the pairs of end length values of a probe-distance from the probe to the single reflective plane correspond to an experimentally maximum coupling or close to this maximum between each of said probes and the propagation medium contained in the recesses.

In the structure thus proposed, the use of transmission lines with suspended substrate and the possibility, mainly resulting from the use of such lines, to carry out an adaptation of the excitation probes by a different choice of their lengths according to the distance between these probes help to significantly increase the radiation characteristics. Furthermore, this structure allows a very simple mechanical production while making it possible to space the planes in which the two exciting probes are located, which allows in particular the installation, in the layers, of the grooves forming with the conductors the transmission lines (this guidance in the air then makes it possible to use a dielectric of ordinary quality from the point of view of its microwave properties, without its losses become troublesome).

• - la figure 1 montre un mode de réalisation de l'élément récepteur selon l'invention ;
• - la figure 2 montre une disposition des sondes excitatrices permettant d'obtenir un gain élevé pour l'élément récepteur ;
• - la figure 3 est une vue en coupe partielle suivant l'axe AA de la figure 1 et met en évidence la disposition des lignes de transmission selon la structure dite à substrat suspendu.

The invention relates, on the other hand, to a planar microwave antenna composed of an entire network of such elements and produced with similar characteristics. The features and advantages of the element and the antenna thus concerned will now appear more precisely in the description which follows and in the appended drawings, given by way of nonlimiting example and in which:

• - Figure 1 shows an embodiment of the receiver element according to the invention;
• - Figure 2 shows an arrangement of the excitation probes to obtain a high gain for the receiving element;
• - Figure 3 is a partial sectional view along the axis AA of Figure 1 and highlights the arrangement of the transmission lines according to the so-called suspended substrate structure.

This element comprises the following structure: on either side of a first layer 10, in which a first recess 11 (in this example, circular) of metallized interior surface is provided, a first transmission line 20 and a second transmission line 30 consisting of conductive strips 21 and 31 carried in the median plane of grooves 22 and 32 by a thin dielectric sheet 23 and 33 providing mechanical support for the conductors. The end of the central conductors of these suspended ribbon microwave transmission lines referenced 24 and 34 penetrates along two perpendicular axes inside the recesses, thus constituting two excitation probes which achieve coupling with the propagation medium allowing reception of the signals microwave; these two ends have a penetration length opposite the recess which is distinct, as specified below. The other end of each line constitutes its output, in the case of reception.

On the other side of the line 20 is provided a second layer 40 also comprising a second recess 41 of metallized interior surface located opposite the first recess 11, and, similarly, on the other side of the line 30 is provided a third layer 50 with a third recess 51 of metallized interior surface located opposite the other two. This recess 51 is short-circuited in a plane parallel to the faces of the layers, at a distance from the line 30 of course less than the thickness of the layer 50, so as to constitute a single reflective plane for the received microwave signals. The element thus described behaves like a waveguide-line transition with a suspended substrate, in which the axis of the guide is perpendicular to the plane of the lines.

The first, second and third layers 10, 40 and 50 may be metallic, or else made of a dielectric material with metallization of the walls of the recesses 11, 41 and 51 which pass through them respectively. Furthermore, the diameter of the recesses must be both sufficiently small, relative to the wavelength associated with the frequency of the microwave signals, to avoid the appearance or attenuate the propagation of the undesirable higher modes and sufficiently large to allow the propagation of the main mode in the considered bandwidth. Finally, the recess 41 ends with a tapered flare 61 possibly covered with a polyurethane type screen, these arrangements helping to enhance the gain and improve the characteristics of the radiation.

The tests carried out with a receiving element having the structure which has just been described have led to studying the influence, on the performances obtained, of the end length of the lines 20 and 30 actually situated opposite the recesses 11, 41, 51 aligned. These experimental measurements, essentially relating to the coupling between these ends of lines 20 and 30 and the propagation medium, that is to say the cavity formed by all of the aligned recesses, have led to an optimization of this coupling when said two ends, or excitation probes, have a different length. More specifically, for a determined length of one of the excitation probes, the distance from this probe to the single reflective plane (formed by the bottom of the layer 50) is sought which provides a satisfactory and if possible maximum adaptation in the frequency band concerned (here substantially 11 , 7 to 12.5 gigahertz); Figure 2 shows an example of arrangement of the two probes of different lengths.

It is thus possible to have tables of correspondence between the probe lengths and the distance to the reflector, giving the best possible adaptations. The distance between the probes is then fixed by the thickness of the layer 10 (chosen according to the electromechanical requirements imposed: mechanical production of the layer, installation on the one hand in the layers 10 and 40 and on the other hand in the layers 10 and 50 of the grooves of the transmission lines 20 and 30, ...), we look in such correspondence tables for two length values for which the associated values of distance to the single reflective plane differ from this value of the thickness of layer 10.

• - côté du carré égal à 0,31 λg soit ici 15 millimètres (la longueur d'onde Xg étant celle dans la partie guide de l'élément récepteur) et rayon de courbure des sommets arrondis égal à 3 millimètres ;
• - distance sonde de la ligne 20 - plan réflecteur : 0,27 Xg ;
• - distance sonde de la ligne 30 - plan réflecteur : 0,17 λg ;
• - longueur d'extrémité de la sonde de la ligne 20 dépassant dans l'évidement : 0,12 Xg ;
• - longueur d'extrémité de la sonde de la ligne 30 dépassant dans l'évidement : 0,10 Xg ;
• - distance verticale entre ces deux sondes : 0,10 Xg (soit, à 12 gigahertz, 5 millimètres, ce qui est suffisant pour la mise en place, par usinage, des cannelures des lignes de transmission 20 et 30).

In the framework of tests carried out with square receiving elements with rounded tops, it was possible to obtain at the end of the transmission line, the end of the central conductor of which constitutes the excitation probe, a standing wave rate of less than 1 , 6 (which corresponds to transmission losses of less than 0.25 dB) under the following conditions:

• - side of the square equal to 0.31 λg or here 15 millimeters (the wavelength Xg being that in the guide part of the receiving element) and radius of curvature of the rounded vertices equal to 3 millimeters;
• - probe distance from line 20 - reflector plane: 0.27 Xg;
• - probe distance from line 30 - reflector plane: 0.17 λg;
• - end length of the probe of line 20 protruding into the recess: 0.12 Xg;
• - end length of the probe of line 30 protruding into the recess: 0.10 Xg;
• - vertical distance between these two probes: 0.10 Xg (that is, at 12 gigahertz, 5 millimeters, which is sufficient for the installation, by machining, of the grooves of the transmission lines 20 and 30).

These values, corresponding as indicated above to the example of square elements with rounded vertices, are valid for a line impedance of approximately 70 ohms, with a width of the central conductors of 1.4 millimeters, in grooves of dimensions 2.5 x 1.8 millimeters.

For the establishment of lines 20 and 30 between layers 10 and 40 on the one hand, 10 and 50 on the other hand, it will be noted that the grooves mentioned above, of rectangular shape in general, are known for example d 'after figure 4 of the patent of the United States of America n ° 3.587.110 granted on June 22, 1971 in the name of the company RCA Corporation, figure whose principle is repeated in figure 3 of the present application (one can see see also the article "Careful MIC design prevents waveguide modes", published in the journal Microwaves, May 1977, p. 188 et seq., figure 1). It will also be noted that at the output of these lines 20 and 30, to allow the reconstruction of the signals with right circular polarization and with left circular polarization, a 3 dB hybrid coupler can be provided, with its two inputs connected respectively to the outputs of lines 20 and 30 and its two outputs providing said right or left circularly polarized signals. It is also possible, instead of the coupler, to provide a depolarizing structure in front of the receiving element. Finally, without a coupler or depolarizing structure, signals are obtained having two perpendicular linear polarizations.

Of course, the present invention is not limited to the receiving or radiating element described above, from which variants can moreover be proposed without thereby departing from the scope of the invention. In particular, the invention also relates to a planar microwave antenna which is composed of a whole network of such receiving elements, the conditions seen previously and relating to the diameter of the recesses being then supplemented by the fact that, for a positioning of the elements satisfactorily next to each other, this diameter must be sufficiently small (compared to the wavelength in vacuum associated with the frequency of the microwave signals) so that the distance between the elements can be less than said wavelength. It is indeed only with this last condition that the appearance of undesirable secondary lobes, called lobes of the network, is avoided.

The structure of this radiating or receiving antenna is quite similar to that of the radiating or receiving element, and everything that has been said above about it can be transposed as is in the case of the antenna , except for transmission lines. In fact, the antenna no longer comprises only two transmission lines leading from the receiving element to two output connections but, more precisely, two networks of microwave transmission lines, electrically independent like lines 20 and 30 and intended , like them, to ensure the transmission of the microwave signals received towards the electronic circuits external to the antenna. In this case, it is now at the output of these two networks that a 3 dB hybrid coupler can be provided (or, instead of the coupler, a depolarizing structure in front of the entire antenna) for the reconstruction of the polarized signals. left and right circular.

These networks are each composed, in a manner well known in numerous embodiments (see in particular the network structure shown in FIG. 1 of French patent application No. 7011449), of a succession of combination stages. If the antenna comprises n receiving elements, the first n ends of each network are used, as already described for a single receiving element, for coupling with the propagation space of the signals to be received, while the opposite opposite end of each of the two networks, the point of convergence of all the transmission lines across the successive combination stages, is connected to the electronic reception circuits external to the antenna (and, for example, in the first place to one and the other of the two entrances from 3 dB coupler which allows the reconstruction of signals with right and left circular polarizations).

An antenna produced in this way lends itself particularly well to a low-cost modular embodiment, in which elementary blocks forming subsets of receiving elements can be used in an appropriate number and by joined assembly for the constitution of antennas of dimensions , gain and directivity diagram well determined, either for example a symmetrical antenna of square shape, or more generally asymmetrical antennas, in particular of rectangular shape, having different radiation patterns in two orthogonal planes. This last characteristic is particularly interesting for the antennas of reception of television signals with 12 gigahertz retransmitted by satellites, since an opening with 3 dB lower than 2 ° is in this case, essential only in the equatorial plane to separate the signals of two "distant" satellites, in this plane, of 3 ° (see the recommendations of the CCIR, Geneva, 1977).

Another modular type embodiment can also be advantageously proposed: if it is desired to have a planar antenna which must receive or transmit microwave signals only of one type of polarization (linear, or circular while maintaining a depolarizing structure) , said antenna can be obtained from that described above simply by omitting the central layer 10 and one of the two supply networks 20 or 30.

It is clear, finally, that the application of the invention to the reception of 12 gigahertz television signals retransmitted by satellites is not limiting, although the antenna described is in fact mainly intended for coupling with one or more reception heads of such signals (an example of these reception heads is described in particular in the review "L'Onde Electrique", volume 62, n ° 3, March 1982, pages 39 and 40). On the one hand, the invention is applicable to all kinds of networks of purely terrestrial microwave transmission, and on the other hand the choice of an example of application at the frequency of 12 gigahertz is not exclusive of any other possible operating frequency in the microwave range, linked to the intended application.

Claims (6)

1. Receiving or radiating element of microwave signals with orthogonal polarizations comprising on either side of a microwave transmission line, the end of which constitutes an excitation probe, a dielectric layer, characterized in that it also comprises a second line of transmission and a third dielectric layer arranged so that this element comprises respectively, on either side of the first layer in which a first recess is provided, the first and second microwave transmission lines arranged along two perpendicular axes, and comprises also, on the other side of one of the transmission lines, the second layer with a second recess located opposite the first and, on the other side of the other transmission line, the third layer with a third recess located opposite the other two but short-circuited at a distance from this other transmission line less than the thickness of this e third layer so as to constitute a reflecting plane, the first and second transmission lines being constituted on the one hand by grooves produced symmetrically in the adjacent layers and on the other hand by conductive tapes (21) and (31) carried in the median plane of these lines and the ends (24) and (34) of which penetrate along said axes inside the recesses to constitute the exciting probes producing a coupling with the propagation medium allows reception or radiation of said microwave signals, and in that the lengths of these ends constituting said excitation probes are distinct and chosen so that, for any given thickness of the first layer, the pairs of values of length of end d 'A probe-distance from the probe to the single reflective plane corresponds to an experimental maximum or close to this maximum coupling between each of said probes and the propagation medium contained in the recesses. 2. Planar microwave antenna for the reception, or the emission, of microwave signals with orthogonal polarizations, characterized in that it is composed of a whole network elements according to claim 1, juxtaposed and arranged so that this antenna comprises, on either side of a first layer in which are provided first recesses, first and second networks of microwave transmission lines ensuring by via a succession of combination stages, the connection, for each of the two networks, between the receiving or radiating elements and a single corresponding output connection, and in such a way that it also comprises, on the other side from one of these networks of transmission lines, a second layer where there are provided second recesses located opposite the first and, on the other side of the other network of transmission lines, a third layer where are provided third recesses located opposite the first and second but short-circuited at a distance from this other network of transmission lines less than the thickness of this third layer so as to constitute a reflective plane inside each element, the diameter of the recesses being also sufficiently small compared to the wavelength associated with the frequency of the microwave signals so that the distance between the elements can be less than said length of wave. 3. Antenna according to claim 2, characterized in that the first, second and third layers are made of a dielectric material, with metallization of the walls of the recesses which pass through them. 4. Antenna according to claim 2, characterized in that the first, second and third layers are metallic. 5. Antenna according to one of claims 2 to 4, characterized in that it comprises, for a modular embodiment, elementary blocks forming subsets of receiving or radiating elements and which can be used in appropriate numbers and by assembly joint for the constitution of antennas of determined dimensions, gain and directivity diagram, and in particular of asymmetrical antennas presenting different radiation diagrams according to the considered plans.

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