Patent ID: 12224494

DETAILED DESCRIPTION

According to one embodiment of the invention that is illustrated inFIGS.4and5, the quasi-optical beam former comprises an upper parallel-plate waveguide2and a lower parallel-plate waveguide3that are superposed one with respect to the other. They thus share a common conductive plane4, which forms the lower wall of the upper parallel-plate waveguide2, and the upper wall of the lower parallel-plate waveguide3. The upper and lower parallel-plate waveguides occupy the XY plane, and they are therefore superposed in the Z direction.

The upper and lower parallel-plate waveguides are not superposed over the entire extent of the quasi-optical beam former, but only over a portion thereof. Beyond a certain distance from the focal array of beam ports, the upper parallel-plate waveguide2and the lower parallel-plate waveguide3form, in the absence of metal plane, a common parallel-plate waveguide5.

The quasi-optical beam former also comprises a set of upper beam ports6intended to feed the upper parallel-plate waveguide2. The upper beam ports6are located in the plane of the upper parallel-plate waveguide2.

In the same way, the quasi-optical beam former comprises a set of lower beam ports8intended to feed the lower parallel-plate waveguide3. The lower beam ports8are located in the plane of the lower parallel-plate waveguide3.

The quasi-optical beam former also comprises a set of network ports (7,9), which may be placed in one and the same level, in order to transmit signals to the radiating elements.

The upper beam ports6and the lower beam ports8are located in the focal plane of the quasi-optical device10. Each beam port comprises a source for generating a TEM wave (TEM standing for Transverse ElectroMagnetic), a TE wave (TE standing for Transverse Electric) or indeed both.

According to one embodiment of the invention, the sources are horn antennas, in particular H-plane horn antennas, which are particularly suitable for performing beam reconfiguration, each source of the beam port defining one spot-beam feed.

However, it will be noted that other well-known types of sources may be used (monopole arrays, transitions between micro-strips and parallel-plate guide, transitions between striplines and parallel-plate guide, transitions between coaxial guides and parallel-plate guide, etc.). Horn antennas may easily be designed and manufactured in PCB technology.

According to another embodiment, the quasi-optical beam former comprises a single beam-port stage, one set of upper network ports7, and one set of lower network ports9.

At the junction between the upper waveguide and the lower waveguide on the one hand, and the common waveguide on the other hand, a resistive film is placed in the continuity of the conductive plane that separates the upper waveguide and the lower waveguide, as illustrated inFIG.5.

The resistive film is a layer that has a resistivity squared such that when current lines pass through the resistive film, a certain amount of energy is dissipated, this decreasing coupling between the beam ports.

In embodiments, the resistive film11may be closer to the beam ports than the quasi-optical device, or in contrast be closer to the quasi-optical device than the beam ports. Similarly, the resistive film may be relatively wide (width corresponding to the dimension in the longitudinal direction X).

As a variant, the resistive film11may be adjacent to the beam ports and/or adjacent to the network ports, i.e. in direct connection with these ports. In this case, the beam former comprises only a single parallel-plate waveguide, in one and only one stage.

It is possible to define the dimensions and characteristics of the resistive film11by means of empirical measurements carried out during a simulating phase or during a computing phase, so as to obtain the desired level of decoupling between the beam ports.

The dimension of the resistive film, in the direction of propagation X, may advantageously be larger than or equal to λg/4, where λgis the wavelength guided in the quasi-optical beam former1.

The resistive film may for example comprise a nickel-phosphorus alloy.

It is advantageous to place the resistive film11over the entire length of the metal plane4, in the transverse direction Y, so as to dissipate energy even for the beam ports that are most off-centre, with respect to the main axis of the quasi-optical device.

The presence of the resistive film, in the continuity of the conductive plane (either directly in contact with the beam ports or network ports, or at the junction between the superposed guides and the common parallel-plate waveguide), allows losses related to overlap of the beams to be minimized.

Moreover, the presence of the resistive film near (adjacent to) the superposed beam ports (or near the junction with a common parallel-plate waveguide) allows space to be freed to accommodate the size of the sources, so that they may perfectly irradiate the network ports, with an apodized pattern, also allowing side lobes to be decreased. Sources of larger size also allow the amplitude of the field on the edges of the quasi-optical beam former to be limited, and parasitic reflections therefrom to be minimized.

According to one embodiment of the invention, the beam ports (6,8) and network ports (7,9) are superposed in at least two stages (33,34).

According to another embodiment, illustrated inFIG.6, the upper beam ports6and the lower beam ports8may be shifted with respect to each other in the transverse direction Y, by a predefined distance. The shift is therefore in the focal plane of the quasi-optical device10.

The predefined distance is advantageously equal to the width of the beam port divided by the number of stages (33,34) of beam ports, this allowing a compact array of beam ports to be obtained.

Thus, as illustrated inFIG.6, for a beam former comprising two stages (33,34), the predefined distance is equal to a half-width of the beam port (d2/2, d2corresponding to the width of one beam port) and the centre of an upper beam port coincides with the junction between two lower beam ports, and vice versa.

FIG.7illustrates, schematically, the operation of the quasi-optical beam former according to the invention, at the junction between the upper parallel-plate waveguide2and the lower parallel-plate waveguide3on the one hand, and the common parallel-plate waveguide5on the other hand.

The resistive film11makes it possible to isolate the upper and lower beam ports6,8and to obtain, at the output port24, which is located in the common parallel-plate waveguide5, a summation without loss of the signals delivered by the input beam ports when said signals are in phase and of same amplitude (schematic (a) inFIG.7).

Specifically, in the balanced (or even) mode, the electric potential on either side of the resistive film11being identical, there is no current line created in the resistive part.

In contrast, in the case of an imbalance between the input signals (uneven mode, schematic (b) inFIG.7), the resistive film11is subjected to current lines that lead to the absorption, through dissipation, of the imbalance between the input signals.

The resistive film11thus allows coupling problems that were potentially encountered in the prior art to be solved.

FIG.8illustrates the radiation pattern of a multibeam active antenna comprising a quasi-optical beam former according to the invention, in which the beam ports are superposed in two levels. The multibeam active antenna also comprises a radiating panel connected to the output of the beam former. The abscissa represents the pointing angle of the antenna.

The number of the beam port (1to22), visible in the right-hand portion of the figure in which the quasi-optical beam former is shown, corresponds to the number of the main lobe in the left-hand portion of the figure. With the quasi-optical beam former according to the invention, the level of overlap is about ⅔ dB, this greatly minimizing losses related to overlap of the beams, in comparison with the 9 dB observed when the beam ports are located in one and the same level.

The resistive film11thus makes it possible to match the upper and lower parallel-plate waveguides to the common parallel-plate guide, while ensuring a low degree of mutual coupling between the sources.

With such a level of overlap, the beam former according to the invention thus guarantees high-throughput transmissions between satellites and users whether the latter be stationary or rapidly moving (trains, aeroplanes, etc.).

The level of overlap may be improved by increasing the number of stages, and for example by placing the beam ports in four stages.

Thus, according to one embodiment, illustrated inFIG.9, the quasi-optical beam former comprises more than two stages, and in the present case four stages (33,34,35,36). A resistive film (37,38,39) is placed between each stage, adjacently to the beam ports. The beam ports of two superposed stages may advantageously be shifted by a predefined distance equal to the width of the beam port divided by the number of stages of beam ports. Provision may also be made, in a configuration employing four or more stages, as illustrated inFIG.10, for the length of each conductive plane (41,42,43) in the direction X of propagation of a wave through the quasi-optical beam former1to be variable from one stage to the next, so as, for example, to balance coupling between the beam ports, gradually.

For example, the conductive plane42located mid-height is the longest, among all the conductive planes. Considering the stages located between the upper portion44of the waveguide and the middle conductive plane42, the conductive plane41located mid-height is attributed a length smaller than that of the middle conductive plane42, and so on (dichotomized shortening). The resistive films (111,112,113) are arranged at the end of the conductive planes (41,42,43).

This embodiment ensures balanced coupling between the beam ports, and a good distribution of the E-field in even modes.

According to one particularly advantageous embodiment, the quasi-optical beam former according to the invention is produced in the form of a multilayer printed circuit board (PCB). Specifically, the permittivity εrof the dielectrics integrated into the beam former allows the wavelength guided inside the quasi-optical beam former to be decreased by a factor √{square root over (εr)}, and the dimensions of the beam former to be decreased by the same factor. The quasi-optical device10is integrated into a parallel-plate guide filled with dielectric, and the beam ports may be produced in SIW technology (SIW standing for Substrate Integrated Waveguide).

The process for manufacturing the quasi-optical beam former thus comprises a step of etching the resistive film, in the locations where the resistive film is provided. The technique for manufacturing a PCB quasi-optical beam former lends itself particularly well to the addition of a resistive film to the beam former.

Quasi-optical beam formers in multilayer-PCB format may lead to higher losses than beam formers in metal-guide format. Nevertheless, in active antennas, the amplifiers are integrated into the radiating panel (all the amplifiers contribute to the formation of the beam); they are therefore not located before the beam former, and hence there is more tolerance to losses.

According to one embodiment, illustrated inFIG.11, the dimensions of the beam ports differ from one stage to the next. In this case, the number of beam ports differs from one stage to the next. For example, inFIG.11, stage37comprises three beam ports70, and stage38comprises four beam ports71. The beam ports of stage37are wider (in the transverse direction Y) than the beam ports of stage38. A segment of resistive film11lies at the junction between stage37and stage38, at the output of the beam ports.

The embodiment illustrated inFIG.11may be extended to more than two stages, and for example to four or even more stages, the length of the conductive plane remaining the same or varying from one stage to the next.

The fronts of the cylindrical waves excited by the beam ports of the quasi-optical beam former are oriented toward the centroid of the network ports. The transmitted electric field is therefore maximum at the centre of the network ports, and the strength of the electric field may decrease for ports located on the periphery. There is however a residual electric field on the edges of the quasi-optical beam former.

In order to decrease the residual electric field on the edges, the quasi-optical beam former, such as illustrated inFIG.12, comprises, on its lateral edges (25,26), a first absorbing device12in the upper stage33, and a second absorbing device13in the lower stage34. The lateral edges (25,26) are the edges located in the transmission line, between the beam ports and the quasi-optical device (FIG.4).

The absorbing devices are configured to absorb energy not transmitted between the beam ports (6,8) and the network ports (7,9), and thus to minimize parasitic reflections from the edges of the quasi-optical beam former.

The first absorbing device12and the second absorbing device13may extend over the entire length of the corresponding lateral edge, namely all the way between the most off-centre beam ports and the quasi-optical device. As a variant, the absorbing devices may extend from the resistive film11to the quasi-optical device10in the longitudinal direction X.

The position of the first absorbing device12and of the second absorbing device13is advantageously shifted by a distance corresponding to λg/4 in the transverse direction Y, where λgis the wavelength guided in the quasi-optical beam former1. The direction of the shift, i.e. which absorber is set back with respect to the other, is of no importance. Moreover, the resistive film11is placed between the first absorbing device12and the second absorbing device13. The resistive film11may extend beyond the absorbing devices, in the transverse direction Y. The resistive film11may be placed in the continuity of the metal plane and between the first absorbing device12and the second absorbing device13, as illustrated inFIG.12.

Shifting the position of the first absorbing device12and of the second absorbing device13by a distance corresponding to λg/4 in the transverse direction Y generates a phase opposition between parasitic reflections generated by the absorbers. The signal resulting from the combination in phase opposition is absorbed by the resistive film11.

Decreasing parasitic reflections from the lateral edges (25,26) allows the levels of signals generating interference with the amplitude and phase relationships desired on the network ports to be limited and thus the levels of the side lobes of the antenna to be attenuated.

The absorbing devices may comprise an absorbent material, for example an epoxy foam filled with magnetic particles.

According to one variant (illustrated inFIG.13), the absorbing devices may comprise dummy ports33. Each dummy port may take the form of a structure equipped with a segment of resistive film71, with conductive sidewalls72, and with a conductive transverse link70lying on either side of each sidewall.

According to another variant, the absorbing devices may comprise a plurality of dummy ports loaded with resistive loads.

FIG.14illustrates a variant of arrangement of the network ports, in which variant the network ports50of one stage33are configured to all be coupled to an antenna, and the network ports51of an adjacent stage34are configured to all be coupled to a load52not connected to the antenna, which may be a resistive film. Coupling to a load52not connected to the antenna may be achieved using horn antennas connected to loads via transitions between rectangular guides and micro-strips53.

Another variant of arrangement is illustrated inFIG.15. Network ports on two levels use transitions between parallel-plate guides and coaxial guides54. The ports56of one of the two levels are connected to loads55, which may comprise a resistive film. The ports57of the adjacent level are connected to the antenna.

Another variant of arrangement is illustrated inFIG.16. Network ports on two levels use transitions between parallel-plate guides and micro-strips57. The ports60of one of the two levels are connected to loads58(resistive films for example). The ports59of the adjacent level are connected to the antenna.

These various types of ports and of transitions may also be used for the beam ports.

This arrangement allows parasitic reflections of high angles of incidence to be decreased and network-port widths larger than 0.6λgto be used. Conventionally, network ports of widths smaller than 0.6λgare used to limit these parasitic reflections.

Specifically, the incident waves are partially reflected from the network ports of each stage. This reflection increases with the size of the network ports and with the angle of incidence of the wave. The partial reflections from each stage are then in phase opposition when the network ports are shifted by one half-period. They are then absorbed by the resistive film.

This cancellation of partial reflection works for port widths up to 0.8λgor even 0.9λg, in order to decrease the angle of incidence θQOof the waves of the quasi-optical beam former necessary to feed to the antenna.

Specifically, the angle of incidence θQOis directly related to the spacing d2between the network ports through the following equation, θradbeing the pointing angle of the antenna, d1the spacing between the radiating elements of the antenna, and εr2being the permittivity of the quasi-optical beam former:

θQ⁢O=sin-1(d1d2⁢εr⁢2⁢sin⁢θr⁢a⁢d)

The spacing d1between the radiating elements of the antenna is set by the constraint that requires the grating lobes of the antenna to be placed outside of the coverage of the antenna.

Typically, for an active antenna of a satellite in geostationary orbit having to operate over θrad=±8.7°, the spacing between the radiating elements is of the order of 3.1λ where λ is the wavelength in vacuum.

Thus, in the case of an active antenna operating in a geostationary orbit, increasing the periodicity of the network ports from 0.6λgto 0.8λgallows the constraint on the angle of incidence of the waves inside the quasi-optical beam former to be relaxed, from 51.4° to 38.5°, which seems less critical.

This is possible as a result of use of two superposed rows of network ports spaced with a period of 0.8λg, in combination with implementation of a shift of one half-period between the two superposed rows. Only one of the two rows of ports is then connected to the radiating elements, and the ports of the other row are connected to loads (seeFIGS.14,15and16), this allowing specular reflections to be avoided.

According to another embodiment illustrated inFIG.17, the upper and lower network ports are configured to be alternately coupled, in the transverse direction Y, to an antenna and to a load that is not connected to the antenna.

Thus, the set of upper network ports comprises in alternation an upper network port27connected to the antenna (not shown inFIG.17), and a network port28connected to a load that is not connected to the antenna.

In the same way, the set of lower network ports comprises in alternation a lower network port29connected to a load that is not connected to the antenna, and a network port30connected to the antenna.

Considering two superposed network ports (for example ports27and29, or ports28and30), only one of the two ports is connected to the antenna, the other being connected to a load not connected to the antenna.

This mode of operation, which has been explained with reference to a receive antenna, is also transposable to the case of a transmit antenna. In this case, a wave incident on the network ports at an oblique angle of incidence is partially reflected in the direction of the grating lobe. The partial reflections are then converted into an uneven mode, which dies out in the resistive film.

The invention also relates to an active antenna comprising a quasi-optical beam former such as mentioned above, and a radiating panel connected to the output of the beam former.