EP0899814B1 - Radiating structure - Google Patents

Description

The invention relates to an antenna, or radiating structure, comprising an exciter chip associated with a set of radiating secondary pellets.

Pad printed antennas are of common use because their cost of implementation is low and they have a reduced mass and volume, which is particularly useful for space applications. They are generally made by etching or lithography of pellets, or conductive blocks, on dielectric substrates.

An antenna of this kind is described in particular in the European patent application no. 627,783 entitled "Multi-layered radiating structure with variable directivity". In this patent application is described an antenna in which the secondary pads are arranged in one (or more) plane (s) parallel (s) to the plane of the exciter pad.

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

It has been found that antennas of this type make it possible to obtain a circular polarization of good quality, that is to say a very low ellipticity rate in the axis of the antenna, perpendicular to the planes of the pellets. By cons the rate ellipticity increases significantly for inclined directions relative to the axis of the antenna.

The document "Antennas and propagation society symposium, 1991 digest, no.1" titled "Circular polarization characteristics of parasitic microstrip antennas" by Lee et al relates to the circular polarization characteristics of the microstrip antennas. The document WO 96/38728 relates to a pellet cavity antenna.

The invention provides a radiating structure for maintaining the purity of circular polarization over a wide angular sector.

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

In the antenna according to the invention, there is provided a reflecting surface surrounding the exciter pad and the secondary pads constitute semi-reflecting surfaces for the exciting wave, the relative position of the secondary pads between them and with respect to the reflecting surface being such that the transmitted waves are in phase.

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

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

Of course the quality of the radiated signal depends on the signal applied to the exciter chip.

In one embodiment, the emitting pellet is located in (or near) a first plane constituting the reflecting surface, or ground plane, and the secondary pellet is at a distance equal to about half the length (λ ) of the wave to be transmitted. Under these conditions a wave emitted by the exciter chip to a secondary pellet travels a distance of half a wavelength. The corresponding beam is partially transmitted, and thus radiated outward, and is partially reflected by the secondary pellet. The reflected beam is directed to the surface reflective from where it is returned to the same secondary pellet or other secondary pellet, from where it is transmitted and thus radiated. The beam reflected on a secondary pellet and which returns to another secondary pellet, thus travels a wavelength. In this way, the two transmitted rays are in phase.

The total opening of the radiated beam depends on the reflection coefficient of the secondary pellets. The opening can be all the more important as the reflection coefficient is greater. In fact, the part of the beam which is furthest from the central part, where the excitation pellet is, is that which 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 exciter pad provided to give this pellet a shape that moves away from the circular shape.

In one embodiment, the primary and secondary pellets are disposed in a conductive cavity in order to orient the emitted radiation and / or to limit the coupling with other neighboring elements. In this case it has been found that the reflection of the excitatory waves on the walls of the cavity causes an alteration of the polarization quality. Therefore, in this embodiment, it is intended to provide at least peripheral secondary pellets a shape and orientation to restore the circular polarization. For example, the peripheral secondary pellets all have substantially the same shapes and the same dimensions and are elongated along a determined axis, with or without a distinct orientation of the radial orientation, and the angle between the axes of two successive pellets corresponds to the angle whose vertex is constituted by the center around which the secondary pellets are arranged and whose sides are the lines joining this vertex to the centers of the pellets concerned.

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

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

de cette sur-face, on comprend que, les faisceaux réfléchis étant inclinés par rapport à la normale à ces plans, le chemin électrique parcouru par le faisceau entre deux pastilles secondaires est supérieur à la longueur d'onde λ. Ce déphasage est négligeable pour une réflexion, mais pour des réflexions multiples il peut en résulter des déphasages gênants. Ce défaut intervient notamment pour des antennes à large ouverture, c'est-à-dire des antennes pour lesquelles des pastilles secondaires périphériques reçoivent un signal résultant de plusieurs réflexions.However, in order to benefit from both the good quality of circular polarization and broadband, it is preferable to take special precautions. Indeed, if the secondary pellets are in a plane parallel to the plane of the reflective surface and distant from $\frac{\lambda }{2}$

from this surface, it is understood that, the reflected beams being inclined relative to the normal to these planes, the electrical path traveled by the beam between two secondary pellets is greater than the wavelength λ. This phase shift is negligible for reflection, but for multiple reflections it can result in troublesome phase shifts. This defect occurs especially for wide-aperture antennas, that is to say antennas for which peripheral secondary pellets receive a signal resulting from several reflections.

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

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

When circular pellets are provided, this variation is obtained, for example, either by conferring on the secondary pellets furthest from the center a smaller diameter than that of the central pellets, or by conferring an annular shape on the pellets, the internal diameter of the central pellets. being larger than the inner diameter of the peripheral secondary pellets.

A second embodiment of phase-shift compensation consists in modulating the distance separating the reflecting surface from the surface of the secondary pellets, for example by providing a distance between the secondary pellets and the reflecting surface, which is all the smaller the distance of the secondary pellets in 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 become apparent with the description of some of its embodiments, this being done with reference to the attached drawings in which:

• the figure 1 is a sectional diagram of an antenna according to the invention,
• the figure 2 is a top view of the antenna of the figure 1 ,
• the figure 3 is a sectional view for another embodiment of the antenna of the invention,
• the Figures 4, 5 and 6 are pellet diagrams of the antenna of the figure 3 ,
• the figure 7 shows secondary pellets for another embodiment of the invention,
• the figure 8 is a diagram of an antenna variant according to the invention, and
• the figure 9 is a diagram similar to that of the figure 8 but still for another variant.

We first refer to Figures 1 and 2 .

The antenna shown in these figures is intended to emit waves in the microwave range around a center frequency of 8 GHz.

It comprises, on the one hand, an exciter pad 20 and, on the other hand, secondary pads 22 ₁ to 22 ₇ .

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

The pellet 22 ₁ is at the right of the pellet 20, that is to say that the centers of the pellets 20 and 22 ₁ are on the same normal to the plane of the parallel faces 24 ₁ and 24 ₂ .

The other secondary pellets 22 ₂ to 22 ₇ are evenly distributed around the central pellet 22 ₁ .

According to an important aspect of the invention the distance separating the faces 24 ₁ and 24 ₂ is substantially equal to half a wavelength $\frac{\lambda }{2}\mathrm{.}$

The face 24 ₁ is at a short distance from a conducting surface 26 forming a ground plane.

The characteristics of the secondary pellets 22 ₁ to 22 ₇ are chosen such that these pellets are semi-reflective, that is to say that a beam 28 received by a secondary pellet is partially reflected, in a beam 30, by this secondary pellet and is partially transmitted in a beam 32.

The antenna works as follows:

The beam 30 reflected by the central secondary pellet 22 ₁ is again reflected on the ground plane 26 to be returned, according to the beam 34, to a peripheral secondary pellet 22 ₄ . The pellet 22 ₄ partially transmits the beam at 36. The beam 32 transmitted by the central pellet 22 ₁ is parallel to the beam 36 transmitted by the pellet 22 ₄ and the beams 32 and 36 are substantially 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 purity of circular or linear polarization over a wide angular sector up to an inclination of about 50 ° relative to the normal to the faces 24 ₁ and 24 ₂ .

As will be seen below, the excitation signal applied to the wafer 20 may be applied to a single access of the latter, provided that the wafer has a shape that deviates from the circular shape, with an axis inclined by example of about 45 ° with respect to the direction of the incident current.

It has been indicated above that the secondary pellets 22 ₁ to 22 ₇ have a semi-reflective character. Reflective "semi" 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 modulated according to the needs, including the desired aperture for the antenna. In particular the reflection coefficient will be higher as the number of secondary pellets succeed each other in the radial direction. Indeed, at each reflection on a secondary pellet, the energy of the beam decreases in proportion to the reflection coefficient. It will therefore require a high reflection coefficient so that sufficient energy remains for the beams reflected several times on the secondary pellets. It can be noted here that the reflection coefficient on the ground plane is practically 100%.

Of course the radial extension ( figure 2 The greater the number of radially succeeding pellets, the larger the radiated beam.

In the example described above, a dielectric substrate 24 is used. In a variant, the exciter chip and the secondary pellets may be deposited on different substrates 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 emitted beam and to limit the coupling with other neighboring antennas, for example identical or similar antennas forming a network in which there is the antenna shown.

In this example, two exciter pads 42 and 44 are provided. The first exciter pad 42, of lower position (that is to say the 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 tile. The secondary pellets 46 ₁ to 46 ₇ are in a plane 48 distant from the plane 45 of the pellet 44 of about half a wavelength.

As shown on the figure 4 , the pellet 42 constitutes a metal deposit on a substrate 47 and this pellet has the shape of a semi-curvilinear rectangle with two parallel straight sides 50 and 52 and two curvilinear sides 54 and 56 forming arcs of the same circle.

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

The conductor 60 has the direction of the diagonal of the curvilinear rectangle which ends at the top 58. The angle between this diagonal and the sides 50 and 52 is about 30 °.

On the substrate 47 is also provided a scalloped conductive deposit, 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 direction of the diagonal, the channel 64 being provided to let the driver pass 60.

The pellet 44 ( figure 5 ) has a shape similar to that of the pellet 42. Its dimensions are slightly smaller than those of this pellet 42. Its center is at the right of the center of the lower pellet. The orientation of the straight sides 70 and 72 of the wafer 44 differs from the orientation of the straight sides of the wafer 42: the inclination of the sides 70 and 72 with respect to the direction of the conductor 60 is about 45 °.

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

The central secondary pellet 46 ₁ , at the right of the pellet 44, has a circular shape while the peripheral secondary pills 46 ₂ to 46 ₇ have an elongate shape, similar to that of the pellets 42 and 44, that is to say in the shape of a semi-curvilinear rectangle ( figure 6 ).

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

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

The double resonator formed by the pellets 42 and 44 makes it possible, with respect to a single patch, to increase the bandwidth of the antenna.

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

Finally, the shape, arrangement and orientation of the secondary pellets 46 ₂ to 46 _{7 make it} possible to 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 on the Figures 7 to 9 relates to a large aperture antenna, that is to say having a large number of secondary pellets and whose radial extension from the central pellet 80 ₁ , is important.

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

A beam emitted from the exciter pad (not shown) towards the central secondary pellet 80 ₁ is reflected by this central pad 80 ₁ from which it is reflected on the ground plane and, from the ground plane, the beam is reflected towards an intermediate pellet. On the intermediate pellet the beam is reflected back to the ground plane and finally to a peripheral pellet. It is recalled that these multiple reflections require a relatively high reflection coefficient on the secondary pellets so that the beam arriving at the peripheral secondary pellets has an intensity which is not too low compared to the beam transmitted by the central pellet.

The reflected beams not being strictly perpendicular to the plane of the pellets, it follows that the electrical path traveled by the beam between two adjacent secondary pellets is greater than one wavelength. The resulting phase shift is insignificant from a secondary pellet to an adjacent pellet but becomes sensitive when phase shifts add up. This results in troublesome side lobes.

To remedy this drawback, means are provided for re-phasing.

In a first category of reshaping means, a lower resonance frequency is given in the center than at the periphery. In other words, the wavelength is adapted to the electric paths traveled so that the waves emitted by all the secondary pellets are in phase.

The variation of the resonance frequencies is favorable to a wide bandwidth.

In the example shown on the figure 7 , all the pellets have substantially the same outer diameter and have an annular shape, but the diameter of the central opening depends on the position of the pellet. The diameter of the opening of the wafer 80 ₁ is greater than the diameter of the opening of the peripheral wafers 80 ₂ to 80 ₇ and the diameter of the opening of the peripheral wafers 80 ₈ to 80 ₁₉ is the smallest.

Alternatively (not shown) the resonant frequency is varied by varying the outer diameter of the pellets, the central pellet having the largest diameter.

In a second category of phase compensation means is varied the distance between the reflective surface and the semi-reflective pellets from the center to the periphery.

In the example of the figure 8 , the secondary pellets are in a plane 90 and the reflecting surface 92 has circular steps, about the axis 94. These steps are even closer to the plane 90 that they are distant from the axis 94.

In the example shown on the figure 9 the reflective surface 96 is planar while the secondary patches are on circular steps 98. The center pellet is farthest from the plane 96 and the peripheral pads are closest to the plane 96.

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

Claims (13)

1. A radiating structure, or antenna, comprising an exciter patch (20; 44) intended to receive an excitation signal and a plurality of secondary patches (22; 46; 80) intended to radiate the waves received from the exciter patch, characterized in that it comprises a reflective surface (26) in the vicinity of the exciter patch and in that the secondary patches constitute semi-reflective surfaces, the distance between the exciter patch and the reflective service at one end, and the secondary patches at the other, being roughly equal to half the wavelength to be transmitted.
2. A structure according to claim 1, characterized in that the secondary patches are disposed concentrically and that they exhibit a reflection coefficient that grows higher as more secondary patches extend in a radial direction.
3. A structure according to any one of the claims 1 to 2, characterized in that the plurality of secondary patches comprises first, a central patch (22; 46; 80) and second, at least one multiplicity of peripheral patches around the central patch.
4. A structure according to any one of the preceding claims, characterized in that the exciter patch (42) exhibits a shape elongated in one direction and in that that exciter patch is fed from a single access path (58) by a circular polarization wave.
5. A structure according to any one of the preceding claims, characterized in that the exciter patch (44) receives the excitation energy from another patch (42) separated from the exciter patch by a short distance compared to the distance between the exciter patch and the secondary patches.
6. A structure according to any one of the preceding claims, characterized in that it comprises a conductive cavity (40) housing the exciter patch, and the secondary patches.
7. A structure according to claim 6, characterized in that the secondary patches exhibit a multiplicity of peripheral patches (462 to 467) whose shapes and orientations are such that they compensate for the depolarization caused by the conductive cavity (40).
8. A structure according to claim 7, characterized in that the peripheral patches are extended in a direction that is tilted compared to the radial direction connecting the center of those patches to the center of the set of secondary patches, the tilt of all peripheral patches with respect to their radial direction being the same.
9. A structure according to any one of the preceding claims, characterized in that the secondary patches are disposed around a center with at least one set of patch(es) a first distance away from the center and at least one multiplicity of peripheral patches further from the center, the resonance frequency of the patch(es) closest to the center being lower than the resonance frequency of the patches further from the center,
10. A structure according to claim 9, characterized in that the patches have a circular shape and in that the patches closest to the center have a greater diameter than the patches further from the center.
11. A structure according to claim 9, characterized in that the patches have a ring shape and are all roughly the same outer diameter, the inner diameter of the patches closest to the center being greater than the inner diameter of the patches further from the center.
12. A structure according to any one of the preceding claims, characterized in that the secondary patches are disposed around a center and in that the secondary patches' distance from the reflective surface decreases from the center towards the periphery.
13. A structure according to claim 12, characterized in that the reflective surface and/or the surface on which the secondary patches are disposed has/have steps (92; 98).

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