EP0899814A1 - Radiating structure - Google Patents

Abstract

Semi-reflecting secondary pastilles are provided to re-transmit signals in phase for wide angle transmission. The radiating aerial comprises an excitation pastille which is intended to receive an excitation signal, and a number of secondary pastilles which are intended to radiate the waves received from the first excitation pastille. The structure includes a reflecting surface (26) near to the excitation pastille (20), with the secondary pastilles comprising semi-reflecting surfaces (221, 224, 227). The assembly is such that the waves radiating from the secondary pastilles are in phase. The distance between the reflecting surface (26) and the secondary pastilles is preferably equal to a half wavelength.

Description

The invention relates to an antenna, or structure radiant, comprising an excitation patch associated with a set of radiating secondary pads.

The antennas printed with tablets are of use common because their cost of realization is low and they present reduced mass and volume, which is particularly useful for space applications. They are generally made by engraving or lithography of pastilles, or paving stones conductors, on dielectric substrates.

An antenna of this kind is described in particular in the European patent application n ° 627,783 entitled "Structure radiant multilayer with variable directivity ". In this patent application is described an antenna in which the pellets secondary are arranged in one (or more) plan (s) parallel (s) to the plane of the excitation patch.

This antenna is well suited to radiate in a directivity range from 9 to 13 dbi, range that would be difficult to obtain by networking elementary radiators.

It has been found that antennas of this type allow to obtain a good quality circular polarization, i.e. a very low ellipticity rate in the axis of the antenna, perpendicular to the planes of the pellets. However the rate ellipticity increases significantly for directions inclined to the axis of the antenna.

The invention provides a radiating structure allowing to maintain the purity of circular polarization over a wide angular sector.

It results from the observation that in the antennas known the degradation of the quality of polarization for inclined directions comes from the nature of the coupling between the excitatory and radiating pellets, this coupling being of the electromagnetic or proximity type.

In the antenna according to the invention, a surface is provided reflective surrounding the excitation patch and the pellets secondary constitute semi-reflective surfaces for the excitation wave, the relative position of the pellets secondary to each other and to the reflecting surface being such that the transmitted waves are in phase.

In other words, the secondary pellets are not excited by an electromagnetic coupling but are excited in dichroic fashion.

It has been found that this excitation mode makes it possible to maintain good circular polarization quality over a wide angular sector, with inclinations up to 50 ° from to the axis, or more.

Of course the quality of the radiated signal depends on the signal applied to the excitation pad.

In one embodiment, the emitting pad is found in (or in the vicinity of) a foreground constituting the reflective surface, or ground plane, and secondary patches lie at a distance of approximately half the length (λ) of the wave to be transmitted. Under these conditions a wave emitted by the excitation patch towards a secondary patch travels a distance of half a wavelength. The beam correspondent is partially transmitted, and therefore radiated outward, and is partially reflected by the patch secondary. The reflected beam is directed towards the surface reflective from where it is returned to the same secondary patch or another secondary patch, from which it is transmitted and therefore radiated. The beam reflected on a secondary patch and which returns to another secondary patch, thus traverses a wavelength. In this way, the two rays transmitted are well in phase.

The total opening of the radiated beam depends on the coefficient of reflection of the secondary pellets. The opening could be all the more important as the coefficient of reflection is bigger. Indeed the part of the beam which is furthest from the central part, where the patch is located is the one who undergoes the greatest number of reflections and which is therefore the most weakened by these reflections.

Furthermore, it has been found that it is possible to excite a circular polarization signal with a single access on the excitation tablet provided that this tablet is given a shape that moves away from the circular shape.

In one embodiment the primary pastilles (s) and secondary are arranged in a conductive cavity so orient the radiation emitted and / or limit the coupling with other neighboring elements. In this case it was found that the reflection of excitation waves on the walls of the cavity causes an alteration in the quality of polarization. That is why, in this embodiment, provision is made to give the minus the peripheral secondary pads a shape and a orientation to restore circular polarization. For example, the peripheral secondary pads all have substantially the same shapes and dimensions and are elongated along a determined axis, of distinct orientation or not of the radial orientation, and the angle between the axes of two pads successive corresponds to the angle of which the vertex is made up by the center around which the pellets are arranged secondary and whose sides are the straight lines joining this vertex at the centers of the pastilles concerned.

These orientations of the peripheral secondary pads increase the directivity of the antenna because the illumination secondary pastilles is standardized.

Whatever its embodiment, it has been found that the invention made it possible to emit waves over a wide band of frequencies.

However, in order to benefit from both the good quality of circular polarization and broadband it is better to take special precautions. Indeed, if the secondary pellets are in a plane parallel to the plane of the reflecting surface and λ / 2 away from this surface, we understand that, the reflected beams being inclined by compared to normal to these planes, the electric path traveled by the beam between two secondary pads is greater than the wavelength λ. This phase shift is negligible for a reflection, but for multiple reflections it may result annoying phase shifts. This defect occurs in particular for wide-opening antennas, i.e. antennas for which peripheral secondary pads receive a signal resulting from several reflections.

To remedy this defect, the invention provides means to compensate for the phase shift.

A first embodiment of this compensation consists in making the resonant frequency depend on each secondary dot of its distance from the center around of which are placed the secondary pellets, this frequency of resonance being all the more important as the distance to center is great.

When circular pads are planned this variation is obtained, for example, either by conferring on the pellets secondary farthest from the center smaller diameter than that of the central pellets, either by giving a form annular to the pellets, the internal diameter of the pellets being larger than the internal diameter of the secondary peripheral pastilles.

A second embodiment of phase shift compensation consists in modulating the distance between the reflecting surface of the surface of the secondary pellets, for example in providing a distance between the secondary pads and the surface reflective which is all the weaker the larger the distance of the secondary pads to the center.

la figure 1 est un schéma en coupe d'une antenne selon l'invention,

la figure 2 est une vue de dessus de l'antenne de la figure 1,

la figure 3 est une vue en coupe pour un autre mode de réalisation de l'antenne de l'invention,

les figures 4, 5 et 6 sont des schémas de pastilles de l'antenne de la figure 3,

la figure 7 montre des pastilles secondaires pour un autre mode de réalisation de l'invention,

la figure 8 est un schéma d'une variante d'antenne selon l'invention, et

la figure 9 est un schéma analogue à celui de la figure 8, mais encore pour une autre variante.

Other characteristics and advantages of the invention will appear with the description of some of its embodiments, this being carried out with reference to the attached drawings in which:

FIG. 1 is a diagram in section of an antenna according to the invention,

FIG. 2 is a top view of the antenna of FIG. 1,

FIG. 3 is a sectional view for another embodiment of the antenna of the invention,

FIGS. 4, 5 and 6 are diagrams of pads of the antenna of FIG. 3,

FIG. 7 shows secondary pads for another embodiment of the invention,

FIG. 8 is a diagram of an alternative antenna according to the invention, and

Figure 9 is a diagram similar to that of Figure 8, but again for another variant.

We first refer to Figures 1 and 2.

The antenna shown in these figures is intended for emit waves in the microwave domain, around with a central frequency of 8 GHz.

It comprises, on the one hand, an excitation tablet 20 and, on the other hand, secondary tablets 22 ₁ to 22 ₇ .

The pad 20 is deposited on one face 24 ₁ of a dielectric substrate 24 while the pads 22 ₁ to 22 ₇ are arranged on the opposite face 24 ₂ of the dielectric 24. All the pads constitute metallic deposits and have a shape of a circle of the same diameter in the example.

The pad 22 ₁ is in line with the pad 20, that is to say that the centers of the pads 20 and 22 ₁ are on the same normal to the plane of the parallel faces 24 ₁ and 24 ₂ .

The other secondary pads 22 ₂ to 22 ₇ are distributed regularly around the central pad 22 ₁ .

According to an important aspect of the invention, the distance separating the faces 24 ₁ and 24 ₂ is substantially equal to a half wavelength λ / 2.

The face 24 ₁ is a short distance from a conductive face 26 forming a ground plane.

The characteristics of the secondary pads 22 ₁ to 22 ₇ are chosen so that these pads are semi-reflecting, that is to say that a beam 28 received by a secondary pad is partially reflected, according to a beam 30, by this secondary patch and is partially transmitted in a beam 32.

Le faisceau 30 réfléchi par la pastille secondaire centrale 22₁ est de nouveau réfléchi sur le plan de masse 26 pour être renvoyé, selon le faisceau 34, vers une pastille secondaire périphérique 22₄. La pastille 22₄ transmet partiellement le faisceau en 36. Le faisceau 32 transmis par la pastille centrale 22₁ est parallèle au faisceau 36 transmis par la pastille 22₄ et les faisceaux 32 et 36 sont pratiquement en phase car le chemin parcouru par les faisceaux 30 et 34 est sensiblement égal à λ.

The antenna thus works as follows:

The beam 30 reflected by the central secondary patch 22 ₁ is again reflected on the ground plane 26 so as to be returned, according to the beam 34, to a peripheral secondary patch 22 ₄ . The patch 22 ₄ partially transmits the beam at 36. The beam 32 transmitted by the central patch 22 ₁ is parallel to the beam 36 transmitted by the patch 22 ₄ and the beams 32 and 36 are practically in phase because the path traveled by the beams 30 and 34 is substantially equal to λ.

This characteristic makes it possible to maintain a circular or linear polarization purity over a wide angular sector going up to an inclination of approximately 50 ° relative to the normal on the faces 24 ₁ and 24 ₂ .

As will be seen below the excitation signal applied to patch 20 can be applied to a single access of the latter, provided that this pellet is given a shape that deviates from the circular shape, with an inclined axis for example about 45 ° from the direction of the current incident.

It was indicated above that the secondary pads 22 ₁ to 22 ₇ have a semi-reflecting character. "Semi" reflective does not necessarily mean properties such that 50% of the energy is reflected and 50% of the energy is transmitted. The reflection coefficient can be adjusted as required, in particular the desired opening for the antenna. In particular, the reflection coefficient will be higher the greater the number of secondary pads which follow one another in the radial direction. Indeed, with each reflection on a secondary patch, the energy of the beam decreases in proportion to the reflection coefficient. A high coefficient of reflection will therefore be required for sufficient energy to remain for the beams reflected several times on the secondary pads. It can be noted here that the reflection coefficient on the ground plane is practically 100%.

Of course the radial extension (figure 2) of the beam the greater the number of pellets succeeding in the radial direction is great.

In the example described above, we use a dielectric substrate 24. As a variant, the excitation patch and the secondary pellets can be deposited on substrates different separated by vacuum or air.

We now refer to Figures 3 to 6.

In this embodiment, the antenna is housed in a metal cavity 40. This cavity makes it possible to orient the beam transmitted and limit the coupling with other neighboring antennas, for example identical or similar antennas forming a network in which the antenna represented is located.

In this example, two exciting pads are provided, 42 and 44 respectively. The first exciting pad 42, in a lower position (that is to say the one furthest from the surface of the secondary pads), receives the excitation signal while the second exciter pad 44 is coupled, by proximity effect, or electromagnetic coupling, with the pitch; lower tille. The secondary pads 46 ₁ to 46 ₇ are in a plane 48 distant from the plane 45 of the pad 44 by about half a wavelength.

As shown in FIG. 4, the patch 42 constitutes a metallic deposit on a substrate 47 and this pellet has the shape of a semi-curved rectangle with two sides parallel rectilinear 50 and 52 and two curvilinear sides 54 and 56 forming arcs of the same circle.

The vertex 58 common to the sides 50 and 54 is connected to a conductor 60 also constituted by a metallic deposit on the substrate 47.

Conductor 60 shows the direction of the diagonal of the curved rectangle which ends at the vertex 58. The angle between this diagonal and the sides 50 and 52 is approximately 30 °.

On the substrate 47 a deposit is also provided conductor indented, on the one hand, by a circle 62 surrounding the patch 42 and, on the other hand, by two channels 64 and 66 having the diagonal direction, channel 64 being provided to leave pass the driver 60.

The pad 44 (Figure 5) has a shape similar to that of the patch 42. Its dimensions are slightly less than those of this patch 42. Its center is at the right of the center of the lower pad. The orientation of the straight sides 70 and 72 of the pad 44 differs from the orientation of the straight sides of the patch 42: the inclination of the sides 70 and 72 by relative to the direction of the driver 60 is about 45 °.

The elongated or chamfered shape of the pellets 42 and 44 makes it possible to excite the pellets using a wave with circular polarization with a single access (vertex 58, FIG. 4) without altering the quality of this circular polarization after excitation secondary pads 46 ₁ to 46 ₇ .

The central secondary pad 46 ₁ , in line with the pad 44, has a circular shape while the peripheral secondary pads 46 ₂ to 46 ₇ have an elongated shape, similar to that of the pads 42 and 44, that is to say in the shape of a semi-curved rectangle (Figure 6).

The rectilinear sides of the peripheral pads which are diametrically opposite have the same orientation. Two successive peripheral pads have rectilinear sides with different orientations. The angle formed between the rectilinear sides of these successive peripheral pads is practically equal to the angle at the center a (60 ° in the example) formed by the lines 73 and 74 connecting the centers of the corresponding pads 46 ₂ and 46 ₃ to the center of central patch 46 ₁ .

Thus all the peripheral pads have the same inclination with respect to their radial direction (the direction joining the center of the patch to the center of the patch central).

The double resonator formed by the pads 42 and 44 allows, compared to a single pellet, to increase the strip bandwidth of the antenna.

The shape and relative orientation of the pellets 42 and 44 allows excitation by a wave polarized circularly by a single access 58 (FIG. 4).

Finally, the shape, the arrangement and the orientation of the secondary pellets 46 ₂ to 46 ₇ compensate for the depolarization induced by the conductive cavity 40.

This results in an increase in the directivity caused by the standardization of illumination.

The embodiment shown in Figures 7 to 9 relates to a large aperture antenna, that is to say comprising a large number of secondary pads and whose radial extension, from the central pad 80 ₁ , is significant .

In the example shown, 19 secondary pads 80 ₁ to 80 _{19 are provided} with a central pad 80 ₁ , surrounded by 6 intermediate pads 80 ₂ to 80 ₇ , which are surrounded by 12 peripheral pads 80 ₈ to 80 ₁₉ .

A beam emitted from the excitation pad (not shown) towards the central secondary pad 80 ₁ is reflected by this central pad 80 ₁ from which it is returned to the ground plane and, from the ground plane, the beam is reflected towards a intermediate patch. On the intermediate patch the beam undergoes a reflection again towards the ground plane and finally towards a peripheral patch. It will be recalled that these multiple reflections require a relatively high reflection coefficient on the secondary pellets so that the beam reaching the peripheral secondary pellets has an intensity which is not too weak compared to the beam transmitted by the central patch.

The reflected beams are not strictly perpendicular in terms of the pellets it follows that the path electric traversed by the beam between two secondary pads adjacent is greater than one wavelength. The phase shift which results is not very sensitive since a secondary pellet towards an adjacent patch but it becomes sensitive when the phase shifts add up. This results in side lobes troublesome.

To remedy this drawback, means are provided allowing reshaping.

In a first category of means of recovery phase, we give a lower resonance frequency in the center than on the outskirts. In other words we adapt the wavelength to the electrical paths traveled so that the waves emitted by all the secondary pads are in phase.

The variation in resonant frequencies is favorable broad bandwidth.

In the example shown in Figure 7, all the pellets have substantially the same outside diameter and have an annular shape, but the diameter of the central opening depends on the position of the patch. The diameter of the opening of the patch 80 ₁ is greater than the diameter of the opening of the peripheral pads 80 ₂ to 80 ₇ and the diameter of the opening of the peripheral pads 80 ₈ to 80 ₁₉ is the smallest.

As a variant (not shown), the frequency is varied resonance by varying the outside diameter of the tablets, the central tablet having the largest diameter.

In a second category of means of compensation phase shifts vary the distance between the reflecting surface and semi-reflective pads from the center towards the periphery.

In the example in Figure 8, the secondary pads lie in a plane 90 and the reflecting surface 92 has circular steps, around the axis 94. These steps are all the closer to plane 90 the further they are from axis 94.

In the example shown in Figure 9, the surface reflective 96 is flat while the secondary pads are on circular bleachers 98. The central tablet is furthest from plane 96 and the peripheral pads are closest to plan 96.

Alternatively, instead of steps, surfaces are provided inclined. It is also possible to provide surfaces inclined or bleachers for both the reflective surface and for secondary tablets.

Claims (14)

Radiant structure, or antenna, comprising a exciter pad (20; 44) for receiving a signal excitation and a plurality of secondary pellets (22; 46; 80) intended to radiate the waves received from the pellet exciter, characterized in that it has a surface reflective (26) in the vicinity of the excitation patch and in that the secondary pellets constitute surfaces semi reflective, the whole being such as radiated waves (32, 36) by the secondary pads are substantially in phase. Structure according to claim 1, characterized in what the distance between, on the one hand, the excitation pad and the reflecting surface and, on the other hand, the secondary patches, is substantially equal to half a wavelength at transmit. Structure according to claim 2, characterized in what the secondary pads are arranged concentrically and in that they have a reflection coefficient which is the higher the higher the number of pellets secondary extending in radial direction. Structure according to any one of the claims 1 to 3, characterized in that the plurality of pellets secondary includes, on the one hand, a central patch (22; 46; 80) and, on the other hand, at least a multiplicity of peripheral pads around the central pad. Structure according to any one of the claims previous, characterized in that the exciter pad (42) has an elongated shape in one direction and in that this excitation patch is supplied, by a single access (58), by a wave with circular polarization. Structure according to any one of the claims previous, characterized in that the exciter pad (44) receives excitation energy through another pad (42) separated from the exciter pad by a distance small compared to the distance between the exciter pad and secondary lozenges. Structure according to any one of the claims previous, characterized in that it includes a cavity conductor (40) housing the exciter pad and the pads secondary. Structure according to claim 7, characterized in that the secondary pads have a multiplicity of peripheral pads (46 ₂ to 46 ₇ ) of shapes and orientations such that they compensate for the depolarization induced by the conductive cavity (40). Structure according to claim 8, characterized in that the peripheral pads are elongated according to a inclined direction with respect to the radial direction connecting the center of these pads in the center of the pad set secondary, the inclination of all peripheral pads with respect to their radial direction being the same. Structure according to any one of the claims previous, characterized in that the secondary pellets are arranged around a center with at least one set of pastille (s) at a first distance from the center and at least one multiplicity of peripheral pads further from the center, the resonant frequency of the pellet (s) the most close to the center being lower than the resonant frequency pellets further from the center. Structure according to claim 10, characterized in that the pellets have a circular shape and that the pellets closest to the center have an outside diameter higher than the pads farther from the center. Structure according to claim 10, characterized in that the pellets are ring-shaped and all have substantially the same outside diameter, the inside diameter of pellets closest to the center being higher than the diameter inside of the pads furthest from the center. Structure according to any one of the claims previous, characterized in that the secondary pellets are arranged around a center and in that the distance of secondary pads with reflective surface have been decreasing since the center to the periphery. Structure according to claim 13, characterized in what the reflective surface and / or the surface on which are arranged the secondary pads have steps (92; 98).

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