RADIOFREQUENCY EXCITER OF A RECEIVING AND TRANSMITTING ANTENNA

Abstract

A compact radiofrequency driver includes at least one axial port intended to be connected to a radiating antenna, at least one output intended to collect received signals and at least one input intended to transmit signals, comprising first and second septum polarizers and a frequency filter, the second polarizer being connected, via its common port, to a first rectangular port of the first polarizer and the frequency filter being connected to the second rectangular port of the first polarizer and being configured to filter a reception or transmission frequency band, these two bands being different, and wherein at least one of the polarizers is configured to convert a circularly polarized signal received on said axial port of the driver into a linearly polarized signal in a reception frequency band and in that at least a second polarizer is configured to convert a linearly polarized signal transmitted to the driver by the input into a circularly polarized signal in a transmission frequency band.

Claims

1. A compact radiofrequency driver comprising at least one axial port (AA) intended to be connected to a radiating antenna, at least one output (DRx, GRx) intended to collect signals received by said antenna and at least one input (DTx, GTx) intended to transmit signals via said antenna, further comprising: a first septum polarizer (PS1); a second septum polarizer (PS2); and a frequency filter (F1), the two septum polarizers each comprising three ports, one of the ports being a common port (AC1, AC2) and the other two ports, which are called the right port (AD1, AD2) and the left port (AG1, AG2), being rectangular ports (AD1, AD2, AG1, AG2), the second septum polarizer being connected via its common port to a first rectangular port of the first polarizer and the frequency filter being connected to the second rectangular port of the first polarizer and being configured to filter a reception frequency band or a transmission frequency band, the axial port being connected to the common port of the first polarizer, the input and the output being connected to the filter or to a rectangular port of the second polarizer, and wherein the septum of the first polarizer (PS1) is configured to convert, in a transmission frequency band, a linearly polarized signal received on one of its rectangular ports (AD1, AG1) into an elliptically polarized signal on its common port (AC1), and to preserve, in a reception frequency band different from said transmission frequency band, an elliptical polarization between an elliptically polarized signal received on its common port (AC1) and the signal output from its rectangular ports (AD1, AG1).

2. The radiofrequency driver as claimed in claim 1, wherein the septum of the first polarizer is configured so that a phase shift between a signal received on one of its rectangular ports (AD1, AG1) and a signal output from its common port (AC1), in a transmission frequency band, is 90°±7° and the septa of the first and second polarizers are configured so that a phase shift between a signal received on the common port (AC1) of the first polarizer (PS1) and a signal output from one of the rectangular ports (AD2, AG2) of the second polarizer (PS2), in a reception frequency band, is 90°±7°.

3. The radiofrequency driver as claimed in claim 1, wherein the septum of the first polarizer is configured so that a phase shift between a signal received on its common port (AC1) and a signal output from one of its rectangular ports (AD1, AG1), in a reception frequency band, is 90°±7° and the septa of the first and second polarizers are configured so that a phase shift between a signal received on one of the rectangular ports (AD2, AG2) of the second polarizer (PS2) and a signal output from the common port (AC1) of the first polarizer (PS1), in a transmission frequency band, is 90°±7°.

4. The radiofrequency driver as claimed in claim 1, wherein the common port of said two polarizers has a square or circular cross section.

5. The radiofrequency driver as claimed in claim 1, wherein the rectangular ports of said two polarizers have a rectangular or elliptical cross section.

6. The radiofrequency driver as claimed in claim 1, comprising a second frequency filter (F2) and a third septum polarizer (PS3), said second filter being connected to said first rectangular port (AD1) of said first polarizer in parallel with said second polarizer (PS2) and being configured to reject a reception frequency band or a transmission frequency band, and said third polarizer (PS3) being connected to said second rectangular port (AG1) of said first polarizer in parallel with said first frequency filter (F1) and being configured to convert said circularly polarized signal received on said axial port (AA) of the driver into a linearly polarized signal in a reception frequency band or to convert said linearly polarized signal transmitted to said driver by said input into a circularly polarized signal in a transmission frequency band.

7. The radiofrequency driver as claimed in claim 1, comprising a frequency filter (F2) placed between one of the rectangular ports of said first polarizer (AD1) and the common port of said second polarizer (AC2) or of said third polarizer (AC3).

8. The radiofrequency driver as claimed in claim 1, comprising a second frequency filter (F3) and a third septum polarizer (PS4), said second filter being connected to one of said rectangular ports of said second polarizer (PS2) and being configured to reject the same frequency band as said first filter (F1), and said third polarizer (PS4) being placed between said first polarizer (PS1) and said first filter (F1), its common port being connected to the first polarizer (PS1) and one of its rectangular ports being connected to the first filter (F1), and the third polarizer (PS4) being configured to convert said circularly polarized signal received on said axial port of the driver into a linearly polarized signal in a reception frequency band or to convert said linearly polarized signal transmitted to said driver by said input into a circularly polarized signal in a transmission frequency band.

9. The radiofrequency driver as claimed in claim 1, wherein the septum of each said septum polarizer has a profile chosen from a stepped profile, a profile expressed by a spline curve or a linear profile.

10. An antenna, comprising at least one compact driver (Einv) as claimed in claim 1.

11. A satellite, comprising at least one antenna (A) as claimed in claim 10.

Description

[0024] Other features, details and advantages of the invention will become apparent upon reading the description with reference to the appended drawings, which are given by way of example and which show, respectively:

[0025] FIGS. 1 to 3, an antenna driver according to the prior art;

[0026] FIG. 4a, an antenna driver according to a first embodiment of the invention and FIGS. 4b to 4e, an antenna driver according to variants of this first embodiment;

[0027] FIG. 5, an antenna driver according to a second embodiment of the invention;

[0028] FIG. 6, an antenna driver according to a third embodiment of the invention;

[0029] FIGS. 7a, 7b and 7c, the profile of septum-polarizer plates able to be used in various embodiments of the invention;

[0030] FIG. 8, a comparison between a driver according to the prior art and a driver according to one embodiment of the invention; and

[0031] FIG. 9, a satellite including a driver according to an embodiment of the invention.

[0032] FIG. 4a shows a driver according to a first embodiment of the invention.

[0033] This first embodiment corresponds to a single-polarization application. The ports DRx and GTx define the transmission port (GTx) and reception port (DRx) of the device. The latter comprises two septum polarizers PS1 and PS2 placed in cascade, and a frequency filter F1.

[0034] The two septum polarizers each possess three ports: a common port and two rectangular ports, called the right and left ports. A waveguide CLT is connected to the first polarizer PS1 via its common port AC1 and the second polarizer PS2 is connected to the right port AD1 of the first polarizer PS1 via its common port AC2. Lastly, the left port AG1 of the first polarizer PS1 is connected to a frequency filter F1. The filter F1 may be connected to this port AG1 directly (case of FIG. 4a) or indirectly and for example by virtue of another septum polarizer (case of FIG. 6). The filter F1 is then optionally connected to a waveguide taper T or to a “stepped transition” and forms the transmission port GTx of the device. The right port AD2 of the second polarizer is optionally connected to a taper T and forms the reception port DRx. The left port AG2 of the second polarizer PS2 is in this example connected to ground.

[0035] In this example, the filter F1 lets pass only the transmission frequency band and therefore rejects the frequencies of the reception band. The waveguide CLT is, for example, an adapter allowing a component of circular cross section to be connected to a component of square cross section. An antenna, a horn antenna for example, may thus be connected to the first polarizer PS1 by virtue of this waveguide CLT via the port AA. A taper T is a waveguide the input and output of which have different dimensions, this allowing the field passing through it to be increased or decreased.

[0036] When a right polarization signal is received by the device by virtue of a horn connected to the waveguide CLT, a right circularly polarized signal is delivered to the first polarizer PS1 via its common port AC1. This circular signal comprises two linear components: a vertical component and a horizontal component. The vertical component is considered to be parallel to the septum (or plate) of the septum polarizer PS1 and the horizontal component is considered to be perpendicular to the septum (or plate) of the polarizer PS1. The parallel component of the signal enters via the common port AC1 into the polarizer PS1, and leaves the polarizer PS1 via the rectangular port AD1, the port AG1 being provided for the left polarization signal. For the parallel component, the cut-off frequency of the polarizer PS1 is modified by the septum of the polarizer PS1, this causing, for the parallel component, a modification of the dispersion within the polarizer PS1. The septum, and more particularly the profile of the plates of the septum, is configured so that the wavelength of this component is shorter than that of the perpendicular component. The parallel component therefore takes more time to travel through the polarizer than the perpendicular component, and is therefore delayed with respect to the perpendicular component by a phase shift of ϕ.sub.R-PS1 on exiting the rectangular port AD1 of the first polarizer PS1. The signal therefore emerges elliptically polarized from the rectangular port of the polarizer PS1.

[0037] The frequency filter F1 is configured so as to reject signals that do not belong to the transmission frequency band, and the signal at the port AG1 of the first polarizer due to decoupling from the right port AD1 is therefore sent back to the polarizer PS1, and more particularly to the second rectangular port AD1. This is possible because the short-circuit plane of the filter F1 is positioned so as to put said signal back in phase.

[0038] Via the second rectangular port AD1 of the first polarizer PS1, the signal passes into the second septum polarizer PS2, a phase shift ϕ.sub.R-PS2 between the vertical component (i.e. parallel to the septum) and horizontal component (i.e. perpendicular to the septum) being generated therein. Now, said polarizer, and in particular the profile of the plates of the septum of the polarizer PS2, is configured so that the elliptically polarized signal emerges linearly polarized. The signal is collected almost entirely by the right port AD2 of the second polarizer PS2 by virtue of a decoupling function that is naturally generated by the plates from which the septum of the first polarizer is formed. The sum of the two phase shifts ϕ.sub.R-PS1±ϕ.sub.R-PS2 is equal to 90°, and this sum applied by the two polarizers PS1 and PS2 allows a linearly polarized signal to be obtained on the reception port DRx.

[0039] When the device transmits, it transmits a left polarization signal (inverse of the polarization used on reception), and to this end a linearly polarized signal is sent to the device via the port GTx. This signal first passes through filter F1, then on exiting the filter, it is sent to the first polarizer PS1. On exiting the first polarizer PS1 via its common port AC1, the transmitted signal is circularly polarized with a phase shift ϕ.sub.R-PS1 of 90° then is sent to an antenna connected to the waveguide CLT.

[0040] In this example, the first polarizer PS1, and more particularly the profile of the plates of the septum of the polarizer PS1, is configured to convert a linearly polarized signal into a circularly polarized signal during transmission, i.e. it is configured to create a phase shift of 90° between the two, horizontal and vertical, components of a signal entering the device via the transmission port GTx. As the first polarizer PS1 is configured for transmission, it induces a phase shift, of as close to 90° as possible, on the horizontal and vertical components of a signal received on its common port AC1. The second polarizer PS2 is therefore configured so that the sum of the phase shift induced by the first polarizer PS1 and of the phase shift induced by the second polarizer PS2 is 90° for received signals, this allowing a linearly polarized signal to be output from the right port AD2 of the second polarizer PS2.

[0041] It is possible to adjust the phase shift between the horizontal and vertical components of the signals, and therefore the polarization between a signal entering and exiting a septum polarizer, by virtue of the number of steps present in the septum of the two polarizers PS1 and PS2, in the case where the septum of the two polarizers has a stepped profile (FIG. 6a). Numerical simulations are for example carried out, to adjust the number thereof. In addition, the purity of the circular polarization is characterized by the degree of ellipticity. The latter depends on the phase tolerance with respect to the theoretical phase shift of 90°. For example, it is considered to be possible, with a tolerance of plus or minus 7°, i.e. a phase shift comprised between 83′ and 97°, to generate a circular polarization from a linear polarization, and vice versa. Advantageously, the tolerance is plus or minus 2°.

[0042] More generally, the phase shift induced by a septum polarizer may be adjusted by modifying the profile of the plates of the septum. This adjustment is generally made by virtue of numerical simulations in which the profile of the plates of the septum is varied (number of steps, linear or curved profile, etc.) in order to obtain the desired phase shift. Thus, in the example of FIG. 4a, the profile of the septum of the first polarizer PS1 is configured so that the phase shift between a signal received on the rectangular port AG1 and output via the common port AC1 is 90°±7° in a transmission frequency band. The profile of the septa of the first polarizer PS1 and second polarizer PS2 is also configured so that the phase shift between a signal received on the common port AC1 of the first polarizer PS1 and output via the rectangular port AD2 of the second polarizer PS2 is 90°±7° in a reception frequency band.

[0043] According to another embodiment of the invention, the second polarizer PS2 is connected to the first polarizer PS1 via its left port AG1, and the filter F1 is connected to the first polarizer PS1 via its right port AD1 (FIG. 4b). In this case, the reception port GRx is still connected to one of the rectangular ports of the second polarizer PS2, and the transmission port DTx to the filter F1. In this embodiment, the profile of the septum of the first polarizer PS1 is configured so that the phase shift between a signal received on the rectangular port AD1 and output via the common port AC1 is 90°±7° in a transmission frequency band. The profile of the septa of the first polarizer PS1 and second polarizer PS2 is also configured so that the phase shift between a signal received on the common port AC1 of the first polarizer PS1 and output via the rectangular port AD2 of the second polarizer PS2 is 90°±7° in a reception frequency band.

[0044] According to another embodiment of the invention, the filter F1 is a filter that rejects the frequencies of the transmission band. In this case, the first polarizer PS1 is configured to obtain a phase shift of 90°, with for example a tolerance of ±7°, between the vertical component and the horizontal component of received signals and the second polarizer PS2 is configured so that the sum of the phase shift induced by the first polarizer PS1 and the phase shift induced by the second polarizer PS2 is 90°, with for example a tolerance of 7°, between the two components of transmitted signals. The phase shift introduced by the two polarizers PS1 and PS2 thus allows the received circularly polarized signal to be converted into a linearly polarized signal and the transmitted linearly polarized signal to be converted into a circularly polarized signal. The receiving port GRx is therefore located on the output of the filter F1 and the transmission port DTx is located on one of the rectangular ports of the second polarizer PS2 (FIG. 4c).

[0045] In other words, in this embodiment, the profile of the septum of the first polarizer PS1 is configured so that the phase shift between a signal received on the common port AC1 and output via the rectangular port AG1 is 90°±7° in a reception frequency band. The profile of the septa of the first polarizer PS1 and second polarizer PS2 is also configured so that the phase shift between a signal received on the rectangular port AD2 of the second polarizer PS1 and output via the common port AC1 of the first polarizer PS1 is 90°±7° in a transmission frequency band.

[0046] According to another embodiment of the invention, a second frequency filter may be placed between the two polarizers PS1 and PS2 so as: [0047] to reject signals belonging to the transmission frequency band, if the first polarizer PS1 is configured to obtain a phase shift of 90°, with for example a tolerance of ±7°, for transmitted signals and to convert a transmitted linearly polarized signal into a circularly polarized signal (FIG. 4d)—in this case, the transmission port GTx is connected to the output of the filter F1 and the reception port DRx is connected to one of the rectangular ports of the second polarizer PS2; or [0048] to reject signals belonging to the reception frequency band, if the first polarizer PS1 is configured to obtain a phase shift of 90°, with for example a tolerance of ±7°, for received signals and to convert a received circularly polarized signal into a linearly polarized signal (FIG. 4e)—in this case, the transmission port DTx is connected to one of the rectangular ports of the second polarizer PS2 and the reception port GRx is connected to the output of the filter F1.

[0049] In the example of FIG. 4d, the profile of the septum of the first polarizer PS1 is configured so that the phase shift between a signal received on the rectangular port AG1 and output via the common port AC1 is 90°±7° in a transmission frequency band. The profile of the septa of the first polarizer PS1 and second polarizer PS2 is also configured so that the phase shift between a signal received on the common port AC1 of the first polarizer PS1 and output via the rectangular port AD2 of the second polarizer PS2 is 90°±7° in a reception frequency band.

[0050] In the example of FIG. 4e, the profile of the septum of the first polarizer PS1 is configured so that the phase shift between a signal received on the common port AC1 and output via the rectangular port AG1 is 90°±7° in a reception frequency band. The profile of the septa of the first polarizer PS1 and second polarizer PS2 is also configured so that the phase shift between a signal received on the rectangular port AD2 of the second polarizer PS1 and output via the common port AC1 of the first polarizer PS1 is 90°±7° in a transmission frequency band.

[0051] The architecture illustrated in FIGS. 4a to 4e is dedicated to single-polarization applications, this meaning that, on the reception port DRx, the received signal issued from the right circular polarization will not be collected. To collect the received signal issued from the left circular polarization, the reception port would have to be placed on the second rectangular port of the polarizer PS2.

[0052] FIG. 5 shows a driver according to a second embodiment of the invention. This architecture is dedicated to dual-polarization applications, and it allows a Feed with four ports, namely two transmission ports GTx and DTx and two reception ports GRx and DRx, to be produced. Compared to the driver of FIG. 4, this driver additionally comprises a second frequency filter F2 placed in parallel with the second polarizer PS2 on the right rectangular port AD1 of the first polarizer PS1; and a third septum polarizer PS3, placed in parallel with the filter F1 on the left port AG1 of the first polarizer PS1.

[0053] The operating principle is similar to that of FIG. 4. On transmission, the transmitted signal is delivered to the input of the device via the transmission ports GTx and DTx. This signal is linearly polarized and comprises a vertical component and a horizontal component. The two filters F1 and F2 are configured to reject signals not comprised in the transmission frequency band. The transmitted signal is therefore sent to the first polarizer PS1 via its two rectangular ports AD1 and AG1. The polarizer PS1 (in particular its septum) is configured so as to phase shift by 90°, with for example a tolerance of ±7°, the two components of the transmitted signal in order to convert the linearly polarized signal into a circularly polarized signal. The transmitted signal output from the first polarizer PS1 via its common port AC1 is therefore circularly polarized.

[0054] On reception, the received signal is delivered as input to the first polarizer PS1 via its common port AC1. The input signal is circularly polarized. On exiting the polarizer PS1, this signal is left and/or right elliptically polarized, and exits via the left port AG1 and right port AD1 of the first polarizer PS1. It is then sent to the common ports AC2 and AC3 of the two polarizers PS2 and PS3. The polarizers PS2 and PS3, and in particular their respective septum, are configured so that the phase shift induced by the first polarizer PS1 and by the polarizer PS2 or PS3 is 90° between the horizontal and vertical components of the received signal, with a tolerance of ±7°. This allows two linearly polarized signals to be obtained as output from the polarizers PS2 and PS3, on the ports AD2 and AD3, one of these signals resulting from the received left circularly polarized signal and the second resulting from the received right circularly polarized signal.

[0055] As above, it is possible for the polarizer PS2 and the filter F2 to be on the left port AG1 of the first polarizer PS1, and for the polarizer PS3 and the filter F1 to be on the right port AD1 of the first polarizer PS1. Likewise, according to another embodiment of the invention, the first polarizer PS1 may be configured so that the phase shift between the two, vertical and horizontal, components of received signals is 90°, with for example a tolerance of ±7° (i.e. to convert a received circularly polarized signal into a linearly polarized signal), the filters F1 and F2 may be configured to reject frequencies not belonging to the reception frequency band, and the polarizers PS2 and PS3 may be configured so that the phase shift between the two components of transmitted signals, i.e. the phase shift induced by the two polarizers PS1 and PS2 or PS1 and PS3, is 90°, with for example a tolerance of ±7° (i.e. to convert a linearly polarized transmitted signal into a circularly polarized signal).

[0056] FIG. 6 shows a driver according to a third embodiment. This architecture has four ports: a right reception port DRx, a left reception port GRx, a right transmission port DTx and a left transmission port GTx. This driver comprises three polarizers PS1, PS2 and PS4 and two filters F1 and F3. Compared to the previous architecture, the filters F1 and F3 are each placed at the output of one of the rectangular ports of the polarizers (PS2 for F3 and PS4 for F1). The filters F1 and F3 are for example configured so as to let pass only the frequencies of the transmission band. In this case, the polarizer PS1 generates, in the transmission band, the entire 90° phase shift. The phase shift in the reception band is then either generated, for right received signals, by the combination of the polarizers PS1 and PS2, or, for left received signals, by the combination of the polarizers PS1 and PS4. The polarizers PS2 and PS4 are also, in this example, dimensioned so that the transmitted signal is able to propagate in the plane perpendicular to the septum of PS2 and PS4, but unable to propagate in the plane parallel to the septum. The polarizers PS2 and PS4 are then equivalent to rectangular guides in the transmission band. The transmission and reception bands are filtered via the filters F1 and F3 so that the frequencies of the reception band do not pass to the transmission ports DTx and GTx and via a sub-cutoff guide so that the frequencies of the transmission band do not pass to the reception ports DRx and GRx.

[0057] FIGS. 7a, 7b and 7c show the profile of the plates of a septum polarizer present in an antenna driver according to one embodiment of the invention. The plates may have a stepped profile (FIG. 7a), a profile given by a spline curve (FIG. 7b) or a linear profile (FIG. 7c). Regarding a profile given by a spline curve, it is possible to adjust the phase shift of the polarizer by varying the number of points, or knots, interpolated by the curve. For a linear profile, the phase shift may be adjusted by varying the number of sections (or segments) and their slope. The plate profile used will depend on the manufacturing technology. For example, a stepped profile will be preferred when manufacturing by machining, whereas a linear or spline profile will be preferred for additive manufacturing.

[0058] FIG. 8 compares a driver according to the prior art E.sub.ant and a driver according to one embodiment of the invention E.sub.inv in a dual-polarization application. The mass of the driver according to the invention is up to 77% lower than in the prior art and its manufacturing cost is up to 82% lower.

[0059] FIG. 9 shows a satellite S comprising a plurality of horn antennas A on which a driver E according to the invention is placed. In this example, compared to a prior-art driver, mass is lower by about thirty kilograms.