EP0481417A1 - Device for feeding an antenna element radiating two orthogonal polarisations - Google Patents

Abstract

The present invention relates to a feed device for a radiating element operating with dual polarisation, comprising a first feed line (11) penetrating into a first cavity (13) situated beneath the said radiating element (10), and a second feed line (12) arranged according to a geometry orthogonal to the first line (11) and penetrating into a second cavity (14) situated in the continuation of the first, a conductive part (16) forming a coupling slot (19) between these two cavities (13, 14). Application in particular to the field of space transmissions. <IMAGE>

Description

The invention relates to a device for supplying a radiating element operating in double polarization, which may be of the printed antenna type or of the waveguide type.

The use of so-called printed antennas: patch antennas, dipoles, annular slots, etc. is increasing in the telecommunications field.

• . adéquation à la mission RF (Radiofréquence)
• . niveau de définition de la technologie ;
• . type d'interfaces requis, connectique ;
• . tenue en puissance ;
• . coût ; . encombrement, masse .....

Depending on the mission envisaged: fixed telecommunications, maritime or aeronautical telecommunications, "broadcasting", location, relay, etc., the choices of a type of radiating element on the one hand and a type of propagation line d on the other hand result from a compromise involving a large number of parameters:

• . adequacy to the RF (Radiofrequency) mission
• . level of technology definition;
• . type of interfaces required, connectivity;
• . power handling;
• . cost ; . size, mass .....

The integration of all these parameters as well as the development of active antennas makes it possible to offer printed antennas as very attractive and competitive solutions on most of the missions envisaged today.

• - montée vertigineuse des pertes ;
• - miniaturisation des éléments rayonnants ;
• - difficultés de connectique et de réalisation.

This is quite common for missions operating in L-band (1.5-1.6 GHz), in S-band (2 GHz), in C-band (4-6 GHz) and tends to become more and more so for K-band missions, today in Ku-band (12.4-18 GHz). However the increase in frequency can only be done at the cost of a great technological effort as the problems appear difficult:

• - vertiginous rise in losses;
• - miniaturization of radiating elements;
• - connection and implementation difficulties.

Many missions require only one polarization per frequency (linear or circular). In this case, the crossed polarization specifications are not generally very difficult to maintain. This is the case for L-band (aeronautical and maritime), S-band (relay), L and S-bands (localization) missions. For this kind of application, depending on the radiating element selected, different modes of supply can be envisaged.

• - l'alimentation à partir d'une ligne coaxiale ;
• - l'alimentation dans le plan à partir d'une ligne microruban ;
• - l'alimentation par couplage électromagnétique à partir d'une ligne microruban ou triplaque.

The most common excitation modes of a printed antenna are:

• - feeding from a coaxial line;
• - feeding in the plane from a microstrip line;
• - power supply by electromagnetic coupling from a microstrip or triplate line.

The first two approaches have been widely described and studied insofar as they are on the one hand a priori easy achievements and have a similarity in propagation behavior with the radiating element itself which can be approximated by a microstrip line.

The solutions belonging to the third category mark a step in the feeding technique by decoupling the radiating element from the main line. The increase in the number of parameters thus allows better management of the bandwidth performance of the assembly.

• - attaque par une jupe capacitive réalisée à l'aide d'une gaine de conducteur coaxial extérieur ;
• - attaque par une pastille capacitive sur ou sous le "patch".

Thus the supply of a printed antenna can be carried out using an orthogonal coaxial line. The basic configuration consists in connecting the central core of the coaxial to an impedance point under the "patch" corresponding to the impedance of the coaxial. This technique is very often insufficient in the context of a large band mission (> -_ 1%) due to the probe effect due to the non-zero diameter of the conductor. Also in order to increase the performance of such a transition, devices have been commonly developed for compensating the probe choke, namely:

• - attack by a capacitive skirt produced using an outer coaxial conductor sheath;
• - attack by a capacitive patch on or under the "patch".

These devices are widely known and described: for example in an article entitled "Conformal microstrip antennas" by Robert E. MUNSON (Microwave journal; March 1988) which describes several types of microstrip antennas, their applications and their performance.

The supply of a printed antenna ("patch" or dipole) can also be carried out from a microstrip line. Again these types of food are widely known. This feeding method is widely used and does not require any particular process other than that of the etching of the "patch" itself. It is thus possible to supply the radiating elements and produce the distribution elements according to the same surface.

The supply of a printed antenna can, finally, be carried out by electromagnetic coupling technique. This supply mode allows RE energy to be transferred from a main line without any contact or mechanical connection between the conductors. In addition, by the introduction of parameters, they allow better management of the adaptive capacities of aerials. From microstrip lines it is possible to supply a dipole or a patch-type antenna. It is also possible to supply a radiating element from a triplate line. This can offer certain interesting aspects in comparison with the electrical situation of the microstrip which is an open line.

• - alimenter les éléments rayonnants selon deux polarisations orthogonales ;
• - intégrer les circuits BFN ("Beam Forming Networks") dans la maille physique du réseau ;

All these widely known embodiments, however, become difficult to implement for missions requiring use in double polarization. Indeed for this kind of application the problems are increasing; Very often the basic radiating element is not alone, but constitutes a sub-network and the problem posed as a whole consists in:

• - supply the radiating elements according to two orthogonal polarizations;
• - integrate BFN circuits ("Beam Forming Networks") in the physical mesh of the network;

so as to produce a module making it possible to meet the objectives of polarization purity, bandwidth, efficiency, quality of radiation and ... with acceptable technology and costs.

Solutions of the type using two orthogonal coaxial attacks lead to complicated architectures for supplying the radiating element and for accessing each of the BFN circuits. Whatever the configuration, this requires at least a single-stage coaxial / triplate transition as well as a double-stage transition; which results in an increased technological complexity compared to simple polarization, associated in addition with low intrinsic performance. The coupling between the two coaxial probes is typically 20 dB for this type of excitation, thus causing cross-polarization re-radiation problems to be resolved by special sub-array devices (sequential rotations for example).

In any case, the development is not easy, due to parasitic phenomena. In addition, the solution requires a major effort in electrical and technological engineering.

The object of the present invention is to respond to the problem thus defined

To this end, the invention provides an original device for supplying a radiating element operating in double polarization, characterized in that it comprises a first supply line penetrating into a first cavity situated under said radiating element, and a second supply line, arranged in a geometry orthogonal to the first line, penetrating into a second cavity located in the extension of the first, a conductive part forming a coupling slot between these two cavities.

• - l'alimentation d'un élément rayonnant selon deux polarisations orthogonales ;
• - la sortie de chacune des polarisations sur des niveaux séparés, permettant ainsi une gestion indépendante des circuits BFN et une intégration complète de l'ensemble de ces répartiteurs sous le réseau de l'élément rayonnant sans nécessiter d'éléments de connexion autres que ceux existant entre le dispositif d'alimentation et l'élément rayonnant lui-même.

Advantageously, this device makes it possible to simultaneously ensure in a single unit, and without requiring a mechanical connection (connection):

• - the supply of a radiating element according to two orthogonal polarizations;
• - the output of each of the polarizations on separate levels, thus allowing independent management of the BFN circuits and complete integration of all of these distributors under the network of the radiating element without requiring connection elements other than those existing between the supply device and the radiating element itself.

In addition, the device of the invention makes it possible to considerably simplify the distribution architecture, the production technology, and the cost of the sub-networks of the radiating elements.

• - les figures 1 et 2 illustrent le dispositif de l'invention respectivement en vue en coupe et en vue de dessus ;
• - les figures 3 à 6 illustrent respectivement une réalisation du dispositif de l'invention et plusieurs courbes de fonctionnement ;
• - Les figures 7 et 8 illustrent une application du dispositif de l'invention à un sous-réseau à quatre éléments.

The characteristics and advantages of the invention will become apparent from the description which follows, by way of nonlimiting example, with reference to the appended figures in which:

• - Figures 1 and 2 illustrate the device of the invention respectively in sectional view and in top view;
• - Figures 3 to 6 respectively illustrate an embodiment of the device of the invention and several operating curves;
• - Figures 7 and 8 illustrate an application of the device of the invention to a four-element subnetwork.

• - l'alimentation d'un élément rayonnant selon deux modes orthogonaux avec un haut découplage entre les accès (>-_ 30 dB) ;
• - les changements de plan nécessaires à l'implantation de circuits formateurs de faisceaux (BFN) de chacune des polarisations.

The excitation of the radiating element 10, of composite or non-composite technology, represented in FIG. 1, is done by using a multifente and multicavity structure. Such a structure makes it possible to carry out in a single operation:

• - the supply of a radiating element according to two orthogonal modes with a high decoupling between the accesses (> -_ 30 dB);
• - the plan changes necessary for the installation of beam forming circuits (BFN) of each of the polarizations.

Typically two supply lines 11 and 12 corresponding to the ends of two beam formers are installed at different levels under a radiating element 10.

The first microstrip or triplate line 11, symmetrical or not, enters a first cylindrical cavity 13. This "open" cavity is produced by a set of conductive cylinder 15, for example metallic, of diameter 0 a and two metallic tracks 10 at level N, and 16 at level N-2, which thus produce the "covers" "of said cylinder. The access window 20 of the line 11 to the cavity 13 is dimensioned according to rules known to those skilled in the art in accordance with the distribution of the fields along the line 11.

In the same way, the second line 12 of the second distributor, arranged in a geometry orthogonal to the first line 11, enters a second cylindrical cavity 14 of diameter 0 b located at a level N-3 lower than that of the first cavity 13 and concentric with it. This second cavity 14 is produced by all of the electric cylindrical walls 17, a metallized bottom 18 as well as the metal part 16 which also constitutes the bottom of the first cavity 13.

The two cavities 13 and 14 are therefore located one above the other and have a common part 16 which has a vital role in the operation of the double-stage device which is described below. They contain, in the example shown, dielectric spacer devices 40, 41 and 42, 43 allowing the positioning of the two lines 11 and 12, arranged in two blocks 44 and 45 for example of brass.

• - d'une part une géométrie des conducteurs en présence optimisée de façon à réaliser l'adaptation d'impédance de l'élément rayonnant 10 à chaque ligne d'alimentation ;
• - d'autre part un soin extrême apporté à la géométrie de la pièce 16 et conséquemment à la nature de la fente de couplage 19 : Cette pièce 16 joue en quelque sorte un rôle de séparateur de polarisation, qui agit comme un court-circuit pour l'onde véhiculée par la première ligne 11 , de sorte que l'on a une condition de fermeture vis-à-vis des étages inférieurs. Typiquement la géométrie du conducteur 16 et de la fente 19 peut comporter une ou plusieurs fentes rectangulaires parallèles au conducteur 11.

An electromagnetic wave is carried by the first line 11 inside the first cavity 13. The whole of this cavity acts as a suitable directive hexapole; which therefore requires

• - On the one hand, a geometry of the conductors in the presence optimized so as to achieve the impedance adaptation of the radiating element 10 to each supply line;
• - on the other hand, extreme care given to the geometry of the part 16 and consequently to the nature of the coupling slot 19: This part 16 acts in a way as a polarization splitter, which acts as a short circuit for the wave carried by the first line 11, so that there is a closing condition vis-à-vis the lower floors. Typically, the geometry of the conductor 16 and of the slot 19 may include one or more rectangular slots parallel to the conductor 11.

Thus the cavity 13 acts as a directional coupler with respect to the lower stages so that no transfer of energy takes place from the first line 11 to the second line 12 which therefore has a high degree of coupling . The energy conveyed by the first line 11 is therefore completely transferred to the radiating element 10 without coupling to the line 12.

The second line 12 which is located at level N-3 has a configuration of compatible field lines of the slot (s) 19. Therefore, these make it possible to couple the RF energy contained in the second cavity 14 to the first cavity 13. At this level, the only suitable outlet presented by the assembly is the radiating element 10 so that no energy initially conveyed by line 12 can couple to line 11, due to the orthogonality conditions imposed field lines with respect to line 11. The excitation of the radiating element 10 according to the polarization of the second line 12 therefore involves the two cavities 13 and 14 as well as a selective coupling device 16 and 19 in polarization. The adaptation of the radiating element 10 to the line 12 therefore brings into play all of the characteristics of the conductors and their respective geometries.

• /c ≦ φb < oa ; Elle a pour objet d'augmenter le nombre de paramètres permettant de réaliser l'adaptation de l'ensemble à la ligne 12. Ainsi une succession de n cavités superposées peut être utilisée de façon à dégager des paramètres d'optimisation.

In an alternative embodiment, the cavity 14 has a more elaborate shape bringing into play a third cavity of diameter 0c, located under the first two and in the extension of the latter with:

• / c ≦ φb <oa; Its purpose is to increase the number of parameters making it possible to adapt the assembly to line 12. Thus a succession of n superimposed cavities can be used so as to release optimization parameters.

FIG. 3 shows the geometry of a radiating element with double orthogonal polarizations, produced in KU band, which corresponds to the principles described above.

Typical performances of such a device are presented in Figures 4 to 6.

• - un élément rayonnant 10 à double étage comprenant :
  • . un patch carré 21 en cuivre de longueur 6 mm, et d'épaisseur 0,2 mm qui est actif pour l'accès supérieur ;
  • . une couche 22 en Nida ("Nid d'Abeille") de hauteur 4,2 mm ;
  • . une couche 23 de scotch Kapton ;
  • . un patch 24 circulaire en laiton collé sur la surface inférieure du scotch Kapton de diamètre 6,8 mm, et d'épaisseur 0,3 mm ;
• - une plaque 25 en laiton d'épaisseur 0,4 mm ;
• - une fente 26 de largeur 14 mm ;
• - un triplaque 27 d'épaisseur 0,8 mm ;
• - une ligne 100 ohms 28 d'épaisseur environ 0,01 mm, de longueur débouchante 5 mm ;
• - une feuille de quartz polyamide 29 d'épaisseur environ 0,1 mm ;
• - une première cavité 30 de diamètre 14 mm, de hauteur 5,8 mm réalisée dans un premier bloc de laiton 36 ;
• - une feuille de quartz polyamide 31 d'épaisseur environ 0,1 mm sur laquelle est disposée un "patch" en laiton de diamètre 7 mm et d'épaisseur 0,3 mm réalisant un court-circuit dans le sens de la polarisation supérieure ;
• - un triplaque 32 d'épaisseur 0,8 mm ;
• - une ligne 100 ohms 35 d'épaisseur environ 0,01 mm, de longueur débouchante 5 mm ;
• - une feuille de quartz polyamide 33 d'épaisseur environ 0,1 mm ;
• - une seconde cavité 34 de diamètre 14 mm et de hauteur 5,8 mm réalisée dans un second bloc de laiton 37 ; Les figures 4 et 5 représentent des courbes illustrant l'adaptation des polarisations en fonction de la fréquence, soient respectivement :
• - R.O.S. accès supérieur (figure 4) : -20 dB de 10.50 GHz à 12,75 GHz soit environ 20% de bande passante à R.O.S. = 1,22 ;
• - R.O.S. accès inférieur (figure 5) performance similaire traduisant 20% de bande passante à R.O.S. = 1,22.

This device has the following characteristics:

• - a double-stage radiating element 10 comprising:
  • . a square patch 21 of copper 6 mm long and 0.2 mm thick which is active for the upper access;
  • . a layer 22 of Nida ("Honeycomb") 4.2 mm high;
  • . a layer 23 of Kapton tape;
  • . a circular brass patch 24 glued to the lower surface of the Kapton scotch with a diameter of 6.8 mm and a thickness of 0.3 mm;
• - a brass plate 25 of thickness 0.4 mm;
• - A slot 26 of width 14 mm;
• - a triplate 27 of 0.8 mm thickness;
• a 100 ohm line 28 of thickness approximately 0.01 mm, of through length 5 mm;
• - a polyamide 29 quartz sheet about 0.1 mm thick;
• - A first cavity 30 of diameter 14 mm, height 5.8 mm made in a first block of brass 36;
• - a polyamide 31 quartz sheet of thickness approximately 0.1 mm on which is placed a brass "patch" with a diameter of 7 mm and a thickness of 0.3 mm producing a short circuit in the direction of the higher polarization;
• - a triplate 32 with a thickness of 0.8 mm;
• a 100 ohm 35 line about 0.01 mm thick, 5 mm through length;
• - a polyamide 33 quartz sheet about 0.1 mm thick;
• a second cavity 34 with a diameter of 14 mm and a height of 5.8 mm produced in a second block of brass 37; FIGS. 4 and 5 represent curves illustrating the adaptation of the polarizations as a function of the frequency, namely:
• - ROS upper access (Figure 4): -20 dB from 10.50 GHz to 12.75 GHz, i.e. around 20% of bandwidth at ROS = 1.22;
• - ROS lower access (Figure 5) similar performance translating 20% of bandwidth at ROS = 1.22.

FIG. 6 is a curve illustrating the decoupling between accesses as a function of the frequency. The device has decoupling in the entire band greater than 30 dB and on average close to 33 dB between the upper and lower ports.

After studying the radiation patterns measured on each of the accesses at central frequency, it appears that due to the absence of coupling between the accesses, an excellent polarization purity is obtained at all points in accordance with the results concerning the same type of radiating element used in monopolarization.

• - d'une part l'alimentation des sous-réseaux 1 par 4 est facilement réalisée sous la maille des éléments rayonnants.
• - d'autre part l'alimentation de chacune des polarisations, réalisées séparément en deux plans distincts, permet de pousser très loin l'intégration du répartiteur associé à chaque polarisation. A titre d'exemple il est possible de réaliser un circuit 1 par 32 implanté en totalité sur le même niveau sans qu'il soit nécessaire d'effectuer une opération de changement de plan autre que celle du dispositif d'excitation de l'élément rayonnant.

In an embodiment of a sub-network of 32 radiating elements, it is clearly seen for a level of BFN that:

• - On the one hand, the supply of the sub-networks 1 by 4 is easily carried out under the mesh of the radiating elements.
• - On the other hand the supply of each of the polarizations, produced separately in two distinct planes, makes it possible to push very far the integration of the distributor associated with each polarization. For example, it is possible to make a 1 by 32 circuit located entirely on the same level without the need to perform a plane change operation other than that of the excitation device of the radiating element. .

A similar distributor for the other polarization can be integrated completely independently at the corresponding level.

Thus the approach proposed at the level of the radiating element: exciter with integrated level change therefore has very interesting repercussions at the level of the subnetworks, of which it considerably simplifies the distribution architecture, the production technology, and therefore, at the level industrial, the cost.

• - quasi-impossibilité de loger les circuits BFN ("Beam Forming Networks") dans la maille du réseau ;
• - nécessiter de prévoir des opérations de changement de plan.

In a technology in an "all planar" version, fundamental installation problems appear even at the level of a sub-network of four elements:

• - it is almost impossible to accommodate BFN ("Beam Forming Networks") circuits in the network;
• - require planning operations to change plans.

• Il est bien entendu que la présente invention n'a été décrite et représentée qu'à titre d'exemple préférentiel et que l'on pourra remplacer ses éléments constitutifs par des éléments équivalents sans, pour autant, sortir du cadre de l'invention.

While using the device of the invention solves all these problems. Thus Figure 7 shows the detail of the circuits and cavities located under the radiating elements for a first distributor. FIG. 8 shows the detail of the circuits and cavities for a second distributor located at a second level. The drawings are the same, only the topology has rotated 90 °.

• It is understood that the present invention has only been described and shown as a preferred example and that its constituent elements can be replaced by equivalent elements without, however, departing from the scope of the invention.

Thus the radiating element 10 can excite a passive resonator so as to produce a broadband radiating element.

In the same way, the device thus described, whether or not using a passive resonator, can be used to supply, in a manner known to those skilled in the art, a microwave element of the waveguide or radiating horn type (corrugated, dual mode , etc ....).

Claims (8)

1. Device for supplying a radiating element operating in double polarization, characterized in that it comprises a first supply line (11) penetrating into a first cavity (13) located under said radiating element (10), and a second supply line (12), arranged in a geometry orthogonal to the first line (11) penetrating into a second cavity (14) located in the extension of the first, a conductive part (16) forming a coupling slot ( 19) between these two cavities (13, 14). 2. Device according to claim 1, characterized in that the conductive part (16) has a role of polarization splitter which acts as a short circuit for the wave conveyed by the first line (11). 3. Device according to any one of claims 1 or 2, characterized in that the two cavities (13, 14) are cylindrical and concentric, the second cavity (14) having a diameter (0b) less than or equal to that (0a ) of the first cavity (13). 4. Device according to claim 3, characterized in that the first cavity (13) is produced by a metal cylinder (17) located between the radiating element (10) and the conductive part (16). 5. Device according to claim 3, characterized in that the second cavity (14) is produced by a conductive cylinder (17), a metallized bottom (18) and the part (16). 6. Device according to any one of claims 4 or 5, characterized in that it comprises a third concentric cavity with the first two, located in the extension ment of these and of diameter (φc) less than or equal to that of the other two (φa, φb). 7. Device according to claim 1, characterized in that it comprises spacers (40, 41; 42, 43) allowing the positioning of the two lines (11, 12) in the first two cavities (13, 14). 8. Device according to claim 1, characterized in that the two lines (11, 12) are microstrip or triplate lines.

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