EP0518271A1 - Elemental microwave antenna with two polarisations - Google Patents

Abstract

Elemental microwave antenna able to constitute one of the elements of an array, this antenna being capable of transmitting or receiving two waves with orthogonal polarisations. <??>It consists of a cavity (1) containing the two orthogonal excitation probes (4, 6) separated by a polarisation-selective obstacle (9), forming a short-circuit plane for the wave transmitted by the upper probe (6) and a "patch" for the wave transmitted by the lower probe (4). Another "patch" (13) is common to these two nested antennas. A third "patch" (15), which is polarisation-selective in the sense that it is transparent to the wave transmitted by the lower probe (4), can moreover be provided. <IMAGE>

Description

The present invention relates to an elementary microwave antenna, that is to say an antenna which can either operate alone, or be one of the elements of an antenna array, or be used alone or in an array as a primary source of 'A reflector antenna system or focusing device, this antenna being able to operate with two orthogonal polarizations.

There are known elementary antennas of this type which are produced using often printed plates, and which comprise two orthogonal feed lines, generally coplanar, which are associated with one or two flat obstacles of the resonant paver type (more commonly known as "patches"), including a so-called "active" patch which is coupled to these two lines and possibly another so-called "passive" patch which overhangs the first patch and which has the role of widening the bandwidth.

These known structures have the major drawback of not allowing the achievement of a satisfactory decoupling between the two orthogonal polarizations over a wide bandwidth, so that this does not make it possible to obtain the purity characteristics which are often desired at actual hour.

• . de séparer électriquement et physiquement les réseaux d'éléments rayonnants de façon à obtenir un réseau pour chacune des deux polarisations croisées;
• . d'imbriquer géométriquement en un seul les deux réseaux rayonnants mono-polarisation ainsi réalisés;
• . de grouper des éléments rayonnants fonctionnant en mode bipolarisation selon des sous-réseaux bien définis et alimentés par l'intermédiaire de déphaseurs pour annuler le rayonnement en polarisation croisée dans l'axe de l'antenne.

In an attempt to improve the performance of antenna networks of this type, it has already been proposed:

• . electrically and physically separating the networks of radiating elements so as to obtain a network for each of the two crossed polarizations;
• . geometrically nesting in one the two radiating mono-polarization networks thus produced;
• . to group radiating elements operating in bipolarization mode according to well-defined sub-arrays and supplied by phase shifters to cancel the radiation in cross polarization in the axis of the antenna.

However, all of these ways of doing things do not make it possible to obtain networks having a space requirement and a weight low enough to be compatible with certain requirements, especially in the case of antennas on satellite. Furthermore, the quality of separation of the polarizations is still insufficient when it is desired to obtain a large bandwidth.

• . un premier organe d'exitation ou de captage d'une première onde hyperfréquence polarisée selon une première direction, cet organe d'excitation/captage étant donc placé au voisinage du fond de cette cavité;
• . un premier obstacle résonant, qui est sélectif en polarisation , et qui est conformé pour être un résonateur ou radiateur "actif", du genre pavé résonant ou "patch", pour cette première onde hyperfréquence, et à contrario pour former un plan de court-circuit pour une deuxième onde hyperfréquence polarisée de façon orthogonale par rapport à ladite première onde hyperfréquence;
• . un deuxième organe d'excitation ou de captage de cette deuxième onde hyperfréquence; et
• . un deuxième obstacle résonant, du genre pavé résonant ou "patch", qui n'est pour sa part pas sélectif en polarisation;
  de sorte que finalement ledit premier obstacle résonant, qui est sélectif en polarisation, constitue à la fois un radiateur dit "actif" pour ladite première onde hyperfréquence et un plan de court-circuit, formant fond de cavité, pour ladite deuxième onde hyperfréquence, tandis que ledit deuxième élément résonant, qui n'est pas selectif en polarisation, constitue à la fois un radiateur dit "passif" pour cette première onde hyperfréquence et un radiateur dit "actif" pour cette deuxième onde hyperfréquence.

The invention aims to remedy these drawbacks. To this end, it relates to an elementary microwave antenna, this antenna being able to operate with two waves of orthogonal polarizations, and comprising a cavity open in the direction of the radiation and at least containing successively, in the direction going from the bottom of the cavity towards its opening:

• . a first excitation or capture member for a first microwave wave polarized in a first direction, this excitation / capture member therefore being placed in the vicinity of the bottom of this cavity;
• . a first resonant obstacle, which is selective in polarization, and which is shaped to be an "active" resonator or radiator, of the resonant pad or "patch" type, for this first microwave wave, and conversely to form a short plane circuit for a second microwave wave orthogonally polarized with respect to said first microwave wave;
• . a second excitation or capture member for this second microwave wave; and
• . a second resonant obstacle, of the resonant block or "patch" type, which for its part is not selective in polarization;
  so that finally said first resonant obstacle, which is selective in polarization, constitutes both a so-called "active" radiator for said first microwave wave and a short-circuit plane, forming a cavity bottom, for said second microwave wave, while said second resonant element, which is not selective in polarization, constitutes both a so-called "passive" radiator for this first microwave wave and a so-called "active" radiator for this second microwave wave.

Advantageously, there can also be provided, downstream of said second resonant element and always in the direction of radio-emission from the bottom-opening of this cavity, at least one third resonant obstacle, this third resonant element being in turn a selective element in polarization and shaped so as to be transparent for said first microwave wave and conversely so as to constitute a so-called "passive" radiator or resonator, of the "patch" type also, for said second microwave wave.

• . Figure 1 est une coupe verticale d'une réalisation de principe de cette antenne élémentaire;
• . Figure 2 et 3 sont des vues en plan des deux éléments sélectifs en polarisation qui équipent cette antenne élementaire;
• . Figure 4 est une vue de dessus d'un exemple pratique de réalisation de cette même antenne; et
• . Figure 5 est une vue en coupe selon V-V de Figure 4.

In any case, the invention will be well understood, and its advantages and other characteristics will emerge during the following description of a non-limiting example of embodiment of this elementary antenna, with reference to the appended schematic drawing in which:

• . Figure 1 is a vertical section of a principle embodiment of this elementary antenna;
• . Figure 2 and 3 are plan views of the two selective polarization elements which equip this elementary antenna;
• . Figure 4 is a top view of a practical embodiment of this same antenna; and
• . Figure 5 is a sectional view along VV of Figure 4.

Referring first of all to FIGS. 1 to 3, it is a transmission / reception microwave antenna element, this antenna element being capable of transmitting or receiving two microwave waves. distinct and whose polarizations, which are for example linear polarizations, are orthogonal. this element antenna can, of course, operate alone, but it is more typically intended to be part of an antenna array comprising a greater or lesser number of antenna elements, of the same type or not.

This antenna element consists of a cavity 1, of circular section in this example, the bottom 2 and the circular side wall 3 are metallized. This cavity is completely open in the direction D of emission of the radiation, so that it constitutes a blind hole as seen in FIG. 1.

This cavity can be partially or entirely filled with dielectric material.

• . Une première onde hyperfréquence qui est excitée ou captée par une première sonde 4 constituée par l'âme d'une première ligne triplaque 5. Cette sonde est placée à environ un quart de longueur d'onde du fond de la cavité 1, à proximité de la surface 2, et est orthogonale à l'axe 8 de la cavité 1.
• . Une deuxième onde hyperfréquence qui est excitée ou captée par une deuxième sonde 6, qui est orthogonale à la première sonde 4 et qui est constituée par l'âme d'une deuxième ligne triplaque 7. Cette sonde 6 est contenue dans un plan qui est orthogonal à l'axe 8 de la cavité 1, et par conséquent parallèle au plan contenant l'autre sonde 4. Elle est située à l'intérieur de la cavité 1, à environ un quart de longueur d'onde de la première sonde 4.

In this cavity 1 are excited (or received) two microwave waves whose polarizations are orthogonal:

• . A first microwave wave which is excited or picked up by a first probe 4 formed by the core of a first triplate line 5. This probe is placed at about a quarter of a wavelength from the bottom of the cavity 1, near the surface 2, and is orthogonal to the axis 8 of the cavity 1.
• . A second microwave wave which is excited or picked up by a second probe 6, which is orthogonal to the first probe 4 and which is formed by the core of a second triplate line 7. This probe 6 is contained in a plane which is orthogonal to the axis 8 of the cavity 1, and therefore parallel to the plane containing the other probe 4. It is located inside the cavity 1, about a quarter of a wavelength from the first probe 4.

According to axis 8, between the probe 4 and the probe 6, is placed an obstacle 9, plane and orthogonal to the axis 8, which is shown in plan view in FIG. 2 and which is selective in polarization in this direction that it constitutes a short-circuit plane, orthogonal to axis 8, for the wave radiated or received by the upper probe 6, while it forms a circular obstacle plane, also called "radiating pad" or "patch", defining a non-looped radiating slot 10 consisting of at least two half-slots, here semicircular 10A, 10B, physically separated from each other and of the same radius, for the wave radiated or received by the lower probe 4.

In the example considered, the selective patch 9 has a planar, quasi-circular shape, with two diametrically opposite "ears" 11 and 12 which electrically connect the central disc 13 to the circular lateral wall 3 of the cavity 1. It constitutes by following a short circuit for the electric field E2, relating to the probe 6, which is directed along these ears 11 and 12, while it forms a quasi-circular patch for the electric field E1, orthogonal to the field E2 and relating to probe 4.

Continuing to move along the axis 8 and in the direction D, we find the aforementioned probe 6, then, above this probe 6 and in this case at the level of the upper opening of the cavity 1, an ordinary patch 13 defining, with the cavity 1, a looped radiating slot 14.

Finally, above this patch 13 is provided a patch 15 which is selective in polarization in the sense that it is designed to be transparent for the electric field wave E1 relative to the probe 4, while it forms a real patch for the E2 wave relative to the probe 6. To do this, and as can be seen in FIG. 3, this selective patch 15 consists of a set of parallel conducting wires 16 which are directed in the direction of the field E2.

The operation of this elementary antenna is as follows:
The selective member 9 is a short-circuit plane for the field wave E2 which is emitted or received by the upper probe 6. For this wave, the bottom of the cavity 1 is therefore constituted by this member 9. Furthermore, still for this field wave E2, the patch 13 constitutes a first patch, conventionally called "active", while the member 15, which behaves like a patch, plays the role of the so-called "passive" patch, the essential role of which is to widen the bandwidth of the microwave signal emitted or received by this probe 6.

As regards, on the other hand, the field wave E1 which is emitted or received by the lower probe 4, the member 15 is completely transparent, and is therefore absent from the electrical point of view, while the member 9 plays the role of an "active" patch and that patch 13 is then, for this wave, a "passive" patch.

In this concept, element 15 plays the same role with respect to elements 6 and 13 as element 13 with respect to elements 5 and 9.

These bandwidth extensions can be different depending on the performance requested from the system.

Finally, it can be seen that this antenna element can transmit or receive two waves of orthogonal polarizations E1, E2 without these two waves, which are then completely dissociated from the electrical point of view, interfering with each other.

Furthermore, it may be bandwidth waves which are sufficiently wide because, for each of them, the presence of a "passive" patch, respectively patch 13 for the E1 wave and patch 15 for the E2 wave.

Finally, this antenna element has good characteristics of mass and size due to the fact that it is in fact made up of two conventional antenna elements (cavity, active patch, and passive patch) which are physically " nested "one inside the other, in fact constituting a geometric multilayer structure at two different levels.

A practical example of embodiment of the antenna element which has just been described is shown in FIGS. 4 and 5, where the corresponding elements are designated by the same reference numbers.

In this embodiment, the cavity 1 is produced in a dielectric body 17, the walls of which intended to be at ground potential are either metallized or coated with metallic layers 18. The two aforementioned "ears" 11 and 12 are here made of two parallel metal wires, respectively 11A, 11B and 12A, 12B, which are welded to the central metal disc 9 on the one hand and to a metal ring 19 taken in the body of the body 17 on the other hand. Of course, the members 13 and 15 are held in place by conventional insulating means and not shown.

It goes without saying that the invention is not limited to the embodiment which has just been described. Thus, the upper selective patch 15 could not be provided, so that the antenna part relating to the probe 6 (wave E2) would then not include a passive patch. Likewise, instead of triplate lines, other models of supply or reception lines could be used.

The geometric shapes and reliefs of the cavity and its associated organs can be other than those shown here. In particular, the cavity can be produced in a metal block.

Likewise, patch 9 can be produced in any way, in particular the electrical contacts 11 and 12 between patch 9 and the walls of the cavity 1 can be provided in multiple ways.

An increase in the number of patches, selective in polarization or not according to the need, can be envisaged. Other types of selective surfaces can be used. These two nested antennas can operate at different frequencies, and their Orthogonal polarizations can be circular instead of linear. In particular, by supplying the two ports 4 and 6 with signals in quadrature phase and of the same amplitude, for example by means of a 3dB hybrid coupler, it is possible to produce an element emitting or receiving two strongly decoupled orthogonal circular polarizations. on the ports of this coupler.

In the same network, different radiating elements can be used, such as elements radiating a single polarization, combined with bipolarization elements according to the invention.

This antenna can be used alone or in a network to illuminate a focusing system.

Claims (6)

Elementary microwave antenna capable of operating with two waves of orthogonal polarizations (E1, E2), characterized in that it comprises a cavity (1) open in the direction (D) of the radiation, this cavity at least containing successively, in the direction ( D) going from its bottom (2) towards its opening: . a first member (4) for exciting or capturing a first microwave wave (E1) polarized in a first direction, this member (4) being close to the bottom (2) of the cavity (1); . a first obstacle (9) resonant and selective in polarization, which is shaped to be an "active" resonator, of the resonant block or "patch" type, for this first microwave wave (E1), and conversely to be a short plane -circuit for a second microwave wave (E2) polarized orthogonally to this first microwave wave (E1); . a second member (6) for exciting or capturing this second microwave wave (E2); and . a second resonant obstacle (13), of the resonant block or "patch" type, which for its part is not selective in polarization;
so that finally this first resonant obstacle (9) constitutes both an "active" resonator for the first microwave wave (E1) and a short-circuit plane, forming the bottom of the cavity, for the second microwave wave (E2), while this second resonant obstacle (13) constitutes both a "passive" resonator for the first wave (E1) and an "active" resonator for the second wave (E2). Elementary microwave antenna according to claim 1, characterized in that it comprises at least further downstream of said second resonant obstacle (13) in the direction of radio transmission (D), a third resonant obstacle (15), selective in polarization, which is shaped so as to be transparent for the first microwave wave (E1) and conversely so as to constitute a "passive" resonator, of the resonant block or "patch" type, for the second microwave wave (E2). Elementary antenna according to claim 1 or claim 2, characterized in that said first resonant obstacle (9) is shaped to define, with the wall (3) of the cavity (1), at least one non-looped slot (10) formed at least two separate half-slots (10A, 10B). Elementary antenna according to one of claims 1 to 3, characterized in that it operates in circular polarization by combined use of its ports (4,6). Array of microwave antennas, characterized in that it consists of elementary bipolarization antennas according to one of claims 1 to 4, associated with elements of different type. Antenna according to one of claims 1 to 4, characterized in that it is used, alone or in an array, to illuminate a focusing system.

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