Antenna integrating delay lenses in the interior of a distributor based on parallel-plate waveguide dividers

Abstract

A quasi-optical beamformer includes a power distributor composed of a succession of parallel-plate dividers extending in a YZ-plane from a first stage to a last stage, each parallel-plate divider comprising, in each of the stages of the corporate structure located under a higher stage, first and second parallel-plate waveguide branches leading to respective parallel-plate dividers of the following stage of the corporate structure, the beamformer furthermore including a plurality of lenses extending longitudinally along the X-axis in at least one stage of the power distributor, so as to apply a delay that is continuously variable along the X-axis, the lenses being placed in each of the branches of the dividers of at least one stage in the power distributor.

Claims

1. A quasi-optical bears beamformer comprising a power distributor composed of a succession of parallel-plate dividers having a corporate structure made up of stages extending in a YZ-plane from a first stage (e.sub.i) to a last stage (e.sub.N), each parallel-plate divider comprising, in each of the stages of the corporate structure located under a higher stage, first and second parallel-plate waveguide branches leading to respective parallel-plate dividers of the following stage of the corporate structure, wherein the beamformer further comprising a plurality of lenses (6, 7) extending longitudinally along an X-axis, which is orthogonal to the YZ-plane, in at least one stage of the power distributor (1), so as to apply a delay that is continuously variable along the X-axis, wherein said lenses being placed in each of the branches of the dividers of at least one stage in the power distributor.

2. The quasi-optical beamformer according to claim 1, the lenses being placed in a plurality of stages (e.sub.1, . . . , e.sub.N) of the power distributor and having respective heights such that the continuously variable delay is applied gradually in the stages of the power distributor.

3. The quasi-optical beamformer according to claim 1, the lenses being placed in each stage (e.sub.1, . . . , e.sub.N) of the power distributor.

4. The quasi-optical beamformer according to claim 1, the lenses being placed solely in the last stage (e.sub.N) of the power distributor.

5. The quasi-optical beamformer according to claim 1, each of the lenses of a given stage being a straight-profile lens.

6. The quasi-optical beamformer according to claim 1, each of the lenses of a given stage being a curvilinear-profile lens.

7. The quasi-optical beamformer according to claim 5, the power distributor comprising only straight-profile lenses placed in each stage (e.sub.1, . . . , e.sub.N) of the power distributor.

8. The quasi-optical beamformer according to claim 1, said former being connected to a plurality of sources that are oriented in different directions in the XY-plane, each of the sources being able to inject a wave into the distributor, the waves propagating in said various directions in the XY-plane, respectively, the lenses being suitable for collimating these waves.

9. A multibeam antenna comprising at least one quasi-optical beamformer according to claim 1, and furthermore comprising a plurality of radiating horns, each radiating horn being connected to a branch of the last stage of the power distributor (e.sub.N).

10. The multibeam antenna according to claim 9, comprising a polarizer configured to circularly polarize the waves, which are emitted by the antenna with a linear polarization.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features, details and advantages of the invention will become more clearly apparent on reading the description given with reference to the appended drawings, which are given by way of example and which show, respectively:

(2) FIG. 1A: a prior-art lens-like quasi-optical beamformer;

(3) FIG. 1B: a straight-profile lens of a prior-art lens-like quasi-optical beamformer;

(4) FIGS. 1C and 1D: a prior-art curvilinear-profile-lens quasi-optical beamformer;

(5) FIG. 2A: a prior-art pillbox beamformer;

(6) FIG. 2B: a cross section in the plane A-A of the pillbox beamformer illustrated in FIG. 2A;

(7) FIG. 3A: a perspective view of a prior-art CTS antenna;

(8) FIG. 3B: a view of the YZ-plane of the CTS antenna illustrated in FIG. 3A;

(9) FIG. 4: an exploded view of the CTS antenna of FIGS. 3A and 3B;

(10) FIG. 5: a schematic illustration of the electrical paths travelled in the beamformer of FIGS. 3A and 3B;

(11) FIG. 6A: a schematic illustration of a first embodiment of the invention;

(12) FIG. 6B: a cross section cut in the YZ-plane of the last stage of the beamformer according to the first embodiment;

(13) FIG. 7A: a schematic illustration of a second embodiment of the invention;

(14) FIG. 7B: a cross section cut in the YZ-plane of the last stage of the beamformer according to the second embodiment;

(15) FIG. 7C: a cross section cut in the YZ-plane of the last stage of the beamformer according to the second embodiment;

(16) FIG. 8: an illustration of the antenna according to the second embodiment of the invention;

(17) FIG. 9: a schematic illustration of a third embodiment of the invention.

DETAILED DESCRIPTION

(18) FIG. 5 schematically illustrates electrical paths travelled in the prior-art beamformer also illustrated in FIGS. 3A and 3B. In a prior-art beamformer, the waves issued from the sources 10 travel an electrical length L.sub.1, then are converted into plane waves on passage through the pillbox junction 23. The central source 10c must be placed at the focal point of the pillbox junction 23. The pillbox beamformer, which is composed of parallel-plate waveguides 20 and the pillbox junction 23, thus defines an electrical length L.sub.1. The electrical length L2 then remaining to be travelled in the power distributor 1, which depends on the number of radiating elements and on the spacing between the radiating elements, is of the same order of magnitude as L.sub.1. Based on this observation, the inventors propose to carry out the conversion of cylindrical waves to plane waves within the distributor 1, and before the horns 5 (according to a first and a second embodiment) or gradually (according to a third embodiment).

(19) FIG. 6A illustrates a first embodiment, in which the wave conversion is carried out in the last stage of the distributor 1. The sources 10 emit waves, of cylindrical wave fronts, towards the power distributor 1. The power distributor 1 is composed of a plurality of stages e.sub.1, . . . , e.sub.N. In the first stage e.sub.1, which is directly connected to the sources 10, optionally via a straight 90 bend, a parallel-plate divider 3 composed of two branches B1 and B2 is located. It will be noted that the straight bend does not add any additional length to the beamformer; for this reason straight bends have no impact on the structure. The parallel-plate divider 3 is configured to distribute the electric field E issued from the sources 10. The parallel-plate dividers 3 may be unbalanced in order to modify the division of power and thus to control the distribution of power to the horns 5.

(20) As illustrated in FIG. 6B, in the last stage of the distributor, at the output of each branch B1, B2 of each divider 3 of this stage, optionally connected via a 90 bend 18, a straight-profile lens 6 is located. The straight-profile lens 6 may comprise a protrusion 13 equipped with an inset 17, a metal insert for example, that is placed between the parallel plates of each of the branches B1 and B2, just before the horns 5. The dimensions of the protrusion may be defined by a height variation of the insert along the Y-axis (see FIG. 1B). Typically, the height of the protrusion 13 may be zero or almost zero at the ends of the lens along the X-axis, whereas it may be maximal at the centre of the lens along the same axis. The insert may in particular be of I shape.

(21) In this first embodiment, the distributor 1 divides, in each stage e.sub.1, . . . , e.sub.N, the electric field E of the waves, the wave front of which remains cylindrical in the distributor. With respect to the CTS antenna of the prior art, for waves issued from the most off-axis sources, this distribution of the cylindrical waves generates far fewer reflections from the edges of the distributor 1. This is because, in the CTS antenna of the prior art, waves that are cylindrical (in the beamformer) then plane (in the distributor) propagate over a large distance (length of the beamformer added to the length of the distributor), whereas, according to the invention, the waves propagate in the distributor, directly from the sources, only over a length corresponding to that of the beamformer. The propagation distance of the waves is therefore shorter. Thus, it is no longer necessary with the antenna according to the invention, unlike in the prior art, to oversize the distributor 1 and the horns 5 along the X-axis with a view to preventing these reflections. Thus, in this embodiment, compactness along the X-axis is increased with respect to the CTS antenna of the prior art.

(22) Moreover, the straight-profile lenses 6, which comprise only a single protrusion, are small in size along the Z-axis; thus, they have a low profile along the same axis. This embodiment however requires a certain spacing between the horns 5, along the Y-axis, because of the height of the straight-profile lenses 6.

(23) FIG. 7A illustrates a second embodiment, in which the waves are converted in the last stage of the distributor 1. The sources 10 emit cylindrical waves into the power distributor 1. The power distributor 1 is composed of a plurality of stages e.sub.1, . . . , e.sub.N. A parallel-plate divider 3, composed of two branches B1 and B2, is located in the first stage e.sub.1, which is directly connected to the sources 10, optionally via a 90 bend. The parallel-plate divider 3 is configured to distribute the electric field E issued from the sources 10. A curvilinear-profile lens 7 is located in the last stage of the distributor, at the output of each divider of this stage, and optionally connected via a 90 bend. As for the first embodiment, the waves propagate in the distributor, directly from the sources, only over a length corresponding to that of the beamformer. Thus, in this second embodiment, a saving in the area along the X-axis with respect to the CTS antenna of the prior art is also obtained. Moreover, by adding a degree of freedom with respect to the first embodiment, it is thus possible to provide the beamformer with a plurality of focal points.

(24) In this second embodiment, the cylindrical waves are converted only in the last stage e.sub.N. Thus, the height (along the Y-axis) of certain protrusions of the curvilinear-profile lens requires there to be a spacing between the horns 5. Thus, in this second embodiment, the spacing between the horns 5 is set by the height of the lenses, as in the first embodiment described above.

(25) FIGS. 7B and 7C illustrate two cross sections, cut in the YZ-plane, of curvilinear-profile lenses 7 placed in the last stage of the distributor, at two different locations of the lens 7 along the X-axis. The curvilinear-profile lens 7 is placed between the parallel plates of each of the branches B1 and B2, just before the horns 5. The curvilinear-profile lens 7 may comprise a protrusion 13, folded on itself, having a portion p.sub.1 extending along the Y-axis, a portion p.sub.2 extending along the Z-axis, and a portion p.sub.3 extending along the Y-axis. The distance d between the two folded portions p.sub.1 and p.sub.3 that extend along the Y-axis increases from the ends of the lens along the X-axis (FIG. 7B) to reach a maximum at the centre of the lens (FIG. 7C). The height of the protrusion along the Y-axis also varies; it may be zero or almost zero at the ends of the lens along the X-axis, whereas it may be maximal at the centre of the lens along the same axis.

(26) FIG. 8 illustrates such an antenna, in particular the power distributor 1, the lenses 7 and the horns 5. It may be seen that this antenna is much less compact, along the Z-axis, than the antenna of the first embodiment because of the dimensions of the curvilinear-profile lenses 7.

(27) FIG. 9 illustrates a third embodiment of the invention. The sources 10 emit cylindrical waves towards the power distributor 1. The power distributor 1 is composed of a plurality of stages e.sub.1, . . . , e.sub.N. In the first stage e.sub.1, directly connected to the sources 10, optionally via a 90 bend, is located a parallel-plate divider 3 that is composed of two branches B1 and B2. The parallel-plate divider 3 is configured to distribute the electric field E issued from the sources 10.

(28) The lenses implemented in the third embodiment may take the form of straight-profile lenses comprising a protrusion (see FIG. 1B) in each of the branches B1, B2 of each divider. Each of the branches of the stage e.sub.1 leads to a divider in a higher stage e.sub.2. Thus, a parallel-plate divider 3 is connected to the first branch B1. This divider itself comprises two branches B1 and B2, each of the branches B1 and B2 of this parallel-plate divider 3 also comprising a straight-profile lens 6. The distributor 1 is thus defined by a corporate structure, in which the straight-profile lenses are located in each stage of the distributor 1, in the branches B1 and B2. Alternatively, the protrusion may be integrated into the junction of the branches B1 and B2; the contour of the junction is then no longer rectilinear, and must be modified so as to integrate the delay to be generated by the protrusion.

(29) As for the first and for the second embodiment, the waves propagate in the distributor directly from the sources, only over a length corresponding to that of the beamformer. Thus, in this third embodiment, a saving in area along the X-axis with respect to the CTS antenna of the prior art is also obtained.

(30) Such an arrangement provides an off-axis performance that is similar to the second embodiment, and therefore much better than that of the beamformers of the prior art. This is because, since the conversion to plane waves occurs gradually, there are no reflections from the edges of the distributor 1, contrary to the case in which the plane waves are highly inclined in the distributor 1. The multiplicity of protrusions allows the delays to be generated to be distributed and divided between the various protrusions, and thus a delay gradient, namely a delay that is a function of the position of the wave along the Z-axis, to be obtained. As in the second embodiment, this increase in the number of degrees of freedom with respect to the first embodiment thus prevents aberrations related to waves issued from highly off-axis sources, over a large angular sector. It is thus possible to endow the beamformer with a plurality of focal points. Moreover, the distribution of the lenses 6 makes it possible to decrease the amplitude of the delays to be generated in each protrusion, and therefore to limit the size thereof.

(31) The third embodiment was described with straight-profile lenses 6. This thus includes pillbox junctions, which are a certain type of straight-profile lens, as was described above. It may also be envisaged to distribute curvilinear-profile lenses 7 (see FIGS. 10 and 1D) in the distributor according to the third embodiment, while however taking into account the bulk of the curvilinear-profile lenses 7. Such a gradually distributed arrangement of curvilinear-profile lenses 7 according to the third embodiment allows additional degrees of freedom to be added in the case in which the use of straight-profile lenses does provide a sufficient number of degrees of freedom to allow a good performance to be obtained.

(32) A plurality of radiating horns 5 is located at the output of the distributor, each radiating horn 5 being connected to a branch (B1, B2) of the last stage of the power distributor e.sub.N. Each radiating horn 5 is configured to radiate the same field. Alternatively, the radiating horns 5 may have different power levels, in order to decrease the level of grating lobes. The beams thus generated are thinned in the E-plane, and may be circular, so as to be particularly suitable for spatial telecommunications. Since the conversion is gradual, the delay to be applied in the last stage e.sub.N in this embodiment is lower than that applied in the two preceding embodiments. Thus, contrary to the first two embodiments, the small height of the lens 6 (along the Y-axis) in the last stage e.sub.N allows the radiating horns 5 to be sufficiently close to one another along the Y-axis, and thus the problems created by grating lobes to be limited.

(33) Preferably, the heights of each of the lenses of the branches B1, B2 of a given stage are identical, so that the delay is uniformly and evenly applied in each stage, and so that the various beams transmitted to the horns are correctly in phase, thus improving the quality of the beams over a given angular sector.

(34) Other embodiments may be envisaged; in particular, one or more curvilinear-profile lenses 7 and one or more straight-profile lenses 6 may be placed in one stage.

(35) A limitation of linear radiating aperture array antennas resides in the polarization of the radiated wave. Said polarization is linear, and oriented in the direction orthogonal to the parallel plates. However, many applications, in particular spatial communications, require the radiative wave to be circularly polarized. To this end, the antenna that is one subject of the invention advantageously comprises a polarizer configured to circularly polarize the waves, which are emitted by the antenna with a linear polarization. A septum polarizer may be integrated into the antenna; alternatively, a polarizing radome 18, schematically shown in FIG. 9, may cover the antenna according to the invention.