Patent Application
20230238710
This application claims priority to foreign French patent application No. FR 2200694, filed on Jan. 27, 2022, the disclosure of which is incorporated by reference in its entirety.
The invention generally relates to the field of telecommunications, and in particular to quasi-optical beam formers (QOBF) for multibeam active antennas.
Quasi-optical beam formers may be installed on board satellites or in ground stations. Antennas using such formers may operate in transmission mode or in reception mode, reciprocally.
A quasi-optical beam former is a focusing (reception mode) and collimating (transmission mode) device.
The wavefronts are curved in the XY plane. In order to compensate for the curvature of the wavefront, a quasi-optical device 23 is inserted between the beam ports and the network ports. This quasi-optical device may for example be a lens such as used in continuous-delay-lens beam formers or a reflector such as used in pillbox beam formers. Each network port 18 is connected to an amplifier 19 followed by a radiating element 20 by a delay line 21 and an amplifier port 22. It converts the cylindrical waves emanating from the beam ports into planar waves radiated by the radiating panel of the multibeam active antenna.
Quasi-optical beam formers produce multiple beams that are aligned along an axis, and that usually overlap at a gain level that may be as much as 10 dB lower than the maximum gain of the beams, as illustrated in
This level of overlap of the beams is a result of a compromise in respect of the size of these sources, which must meet two opposing constraints: on the one hand, they must be large enough to adequately irradiate the optical system, and thus avoid spin-over losses, and on the other hand, they must be close together enough for the beams to overlap.
When a geographic region is covered by an antenna producing this beam overlap, certain ground stations are then exposed to an antenna gain decreased by these overlap losses. It is therefore desirable to minimize these overlap losses, and therefore to produce multiple beams that overlap at a high gain level.
A number of solutions have been envisaged with a view to minimizing losses related to the overlap of the beams.
It is for example known to use two quasi-optical beam formers with inserted sources, as for example disclosed in patent application WO 2013/110793 A1. Use of these two formers allows beam density in a given angular sector to be doubled. This solution however requires two quasi-optical beam formers, and a combining stage. This results in a greater mass, and a very substantial increase in complexity in the case of two-dimensional beam formation.
Other solutions use smaller sources with scanning recombination of two adjacent sources, as disclosed in the article “A theoretical limitation on the formation of lossless multiple beam antennas” (J. L. Allen, IRE Trans., 1961, AP-9, pp. 350-352). This approach makes it possible to produce equivalent sources that are large enough and that are superposed partially so that the associated beams overlap at a higher level. However, this solution requires a circuit associating divider and combiner to be added, this complexifying the beam former and generating additional losses.
In other solutions, apodization of the signal on the output ports is used to widen the main lobe of each beam while decreasing the level of their side lobes. Widening the main lobe allows a better overlap of the beams to be achieved but does not allow additional beams to be added. To perform this apodization, it is necessary to modulate the amplitude of the output signal as a function of the position of the radiating element in the array. This may be done passively using attenuators or indeed actively with a variable amplification as a function of the position of each element in the lattice of the array. This solution however leads to a decrease in the gain of the active antenna, for a given number of radiating elements, and is therefore undesirable.
In another approach described in the article “Reconfigurable Multi-Beam Pillbox Antenna for Millimeter Wave Automotive Radars” (M. Ettorre, R. Sauleau, Proc. ITST, pp. 87-90, 2009), sources are superposed in two different levels, this however generating substantial coupling between the feeds.
There is a need for improved quasi-optical beam formers capable of minimizing losses related to overlap of the beams, without significant increase in complexity and/or bulk.
One subject of the invention is therefore a quasi-optical beam former comprising a set of beam ports, a set of network ports, a quasi-optical device and at least one parallel-plate waveguide extending between the beam ports and the network ports, the beam ports and/or the network ports being superposed in at least two stages, each of the at least two stages being separated by a conductive plane common to two adjacent stages, the quasi-optical beam former comprising a resistive film placed in the continuity of the conductive plane.
Advantageously, the quasi-optical beam former comprises a plurality of superposed parallel-plate waveguides, each superposed parallel-plate waveguide being placed facing the beam ports and/or facing the network ports of a given stage, the beam former further comprising a common parallel-plate waveguide, placed in the continuity of the superposed parallel-plate waveguides, the resistive film being placed at the junction between each superposed parallel-plate waveguide and the common parallel-plate waveguide.
Advantageously, the resistive film is adjacent to the beam ports.
Advantageously, the resistive film is adjacent to the network ports.
Advantageously, each beam port having an identical width between two consecutive beam ports of the same stage, the beam ports of two adjacent superposed stages are shifted by the width of the beam port divided by the number of stages of beam ports.
Advantageously, the beam ports are superposed in at least four stages, the length of each conductive plane in the direction of propagation of a wave through the quasi-optical beam former being variable from one stage to the next.
Advantageously, the beam ports have different dimensions, from one stage to the next.
Advantageously, each network port having an identical width between two consecutive network ports of the same stage, the network ports of two adjacent superposed levels are shifted by the width of the network port divided by the number of stages of network ports.
Advantageously, the network ports of a stage are configured to all be coupled to one antenna, and the network ports of a superposed adjacent stage are configured to all be coupled to a load not connected to the antenna.
Advantageously, the quasi-optical beam former comprises, on each of the lateral edges, a plurality of absorbing devices configured to absorb energy not transmitted between the beam ports and the network ports, said absorbing devices being superposed in the at least two stages, the position of the absorbing devices being shifted by a distance corresponding to λg/4, where λg designates the wavelength guided in the quasi-optical beam former, the resistive film being placed between the absorbing devices of two superposed stages.
Advantageously, the absorbing devices comprise dummy ports or an absorber.
Advantageously, the network ports and/or the beam ports comprise coaxial lines, coaxial guides, striplines or micro-strips.
Advantageously, the quasi-optical beam former takes the form of a multilayer printed circuit board (PCB), the parallel-plate waveguide being filled with a dielectric, the beam ports being produced in SIW technology.
The invention also relates to an active antenna comprising a quasi-optical beam former such as mentioned above, and a plurality of radiating elements connected to the output of said beam former.
Advantageously, the dimensions of the network ports are smaller than the dimensions of the radiating elements.
Other features, details and advantages of the invention will become apparent on reading the description given with reference to the appended drawings, which are given by way of example.
According to one embodiment of the invention that is illustrated in
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 waveguide 2 and the lower parallel-plate waveguide 3 form, in the absence of metal plane, a common parallel-plate waveguide 5.
The quasi-optical beam former also comprises a set of upper beam ports 6 intended to feed the upper parallel-plate waveguide 2. The upper beam ports 6 are located in the plane of the upper parallel-plate waveguide 2.
In the same way, the quasi-optical beam former comprises a set of lower beam ports 8 intended to feed the lower parallel-plate waveguide 3. The lower beam ports 8 are located in the plane of the lower parallel-plate waveguide 3.
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 ports 6 and the lower beam ports 8 are located in the focal plane of the quasi-optical device 10. 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 ports 7, and one set of lower network ports 9.
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 in
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 film 11 may 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 film 11 may 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 film 11 by 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 λg is the wavelength guided in the quasi-optical beam former 1.
The resistive film may for example comprise a nickel-phosphorus alloy.
It is advantageous to place the resistive film 11 over the entire length of the metal plane 4, 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 in
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 in
The resistive film 11 makes it possible to isolate the upper and lower beam ports 6, 8 and to obtain, at the output port 24, which is located in the common parallel-plate waveguide 5, 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) in
Specifically, in the balanced (or even) mode, the electric potential on either side of the resistive film 11 being 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) in
The resistive film 11 thus allows coupling problems that were potentially encountered in the prior art to be solved.
The number of the beam port (1 to 22), 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 film 11 thus 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 in
For example, the conductive plane 42 located mid-height is the longest, among all the conductive planes. Considering the stages located between the upper portion 44 of the waveguide and the middle conductive plane 42, the conductive plane 41 located mid-height is attributed a length smaller than that of the middle conductive plane 42, 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 εr of 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 device 10 is 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 in
The embodiment illustrated in
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 in
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 device 12 and the second absorbing device 13 may 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 film 11 to the quasi-optical device 10 in the longitudinal direction X.
The position of the first absorbing device 12 and of the second absorbing device 13 is advantageously shifted by a distance corresponding to λg/4 in the transverse direction Y, where λg is the wavelength guided in the quasi-optical beam former 1. The direction of the shift, i.e. which absorber is set back with respect to the other, is of no importance. Moreover, the resistive film 11 is placed between the first absorbing device 12 and the second absorbing device 13. The resistive film 11 may extend beyond the absorbing devices, in the transverse direction Y. The resistive film 11 may be placed in the continuity of the metal plane and between the first absorbing device 12 and the second absorbing device 13, as illustrated in
Shifting the position of the first absorbing device 12 and of the second absorbing device 13 by 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 film 11.
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 in
According to another variant, the absorbing devices may comprise a plurality of dummy ports loaded with resistive loads.
Another variant of arrangement is illustrated in
Another variant of arrangement is illustrated in
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 0.6λg to be used. Conventionally, network ports of widths smaller than 0.6λg are 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 0.8λg or even 0.9λg, in order to decrease the angle of incidence θQO of the waves of the quasi-optical beam former necessary to feed to the antenna.
Specifically, the angle of incidence θQO is directly related to the spacing d2 between the network ports through the following equation, θrad being the pointing angle of the antenna, d1 the spacing between the radiating elements of the antenna, and εr2 being the permittivity of the quasi-optical beam former:
The spacing d1 between 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 0.6λg to 0.8λg allows 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 (see
According to another embodiment illustrated in
Thus, the set of upper network ports comprises in alternation an upper network port 27 connected to the antenna (not shown in
In the same way, the set of lower network ports comprises in alternation a lower network port 29 connected to a load that is not connected to the antenna, and a network port 30 connected to the antenna.
Considering two superposed network ports (for example ports 27 and 29, or ports 28 and 30), 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2200694 | Jan 2022 | FR | national |
