Mode extractor of an electromagnetic signal

Abstract

The present invention relates to a mode extractor device (500) of an electromagnetic signal comprising, from upstream to downstream: - a first turnstile junction (1), comprising: - an input waveguide (11) comprising a multimodal coaxial transition zone (12) and four first output ports (13), the input waveguide (11) having an outer diameter decreasing from upstream to downstream; - a second turnstile junction (3) comprising: - an output waveguide (31) extending along the longitudinal axis A from an upstream end (34), located towards a second output port (311); - a coaxial output (32) inserted into the output waveguide (31) by projecting from the output waveguide (31) and extending inside a portion of the length of the output waveguide (31) from the upstream end (34) of the output waveguide (31). Figure for the abbreviation: Fig. 4

Description

Title of the invention: Mode extractor of an electromagnetic signal Technical field

[0001] The present application relates generally to the field of satellite telecommunications, whether civil or military, and more particularly to the antennas with which ground stations are equipped, antennas operating in transmission and reception respectively on frequency bands K and Ka (i.e. the frequency bands between 17.3 and 21.2 GHz and between 27.5 and 31 GHz), in circular polarization and implementing tracking of the satellite using a monopulse reception channel. STATE OF THE ART

[0002] Satellite telecommunications ground stations generally concentrate communications transmitted with user terminals on a single link and, to ensure this function, comprise a parabolic reflector antenna, which makes it possible to obtain high directivity and high gain in communications with the satellite. During reception operation, the electromagnetic field is reflected by the parabolic reflector towards a horn, which injects the field thus collected into an input waveguide generally of circular section, or more rarely of rectangular or square section, adapting it towards a vertical or horizontal polarization of the transverse electric mode TEn, that is to say a TEnV mode for vertical polarization or TEnh for horizontal polarization over a reception bandwidth, denoted Rx.During transmission operation, this adaptation is reversible, the transverse electrical mode TEn going from the input waveguide to the horn over a transmission bandwidth, noted Tx.

[0003] These modes must be extracted downstream of the horn and made available on different accesses depending on the bandwidth for reception and tracking of the signal.

[0004] A sum channel is useful for receiving and transmitting the signal while a difference channel is only useful for receiving and tracking the signal: the signal of the sum channel is maximum and that of the difference channel zero when the antenna is in the axis of the satellite. The signal ratio between the sum channel and the difference channel defines a deviation slope which makes it possible to determine an angular misalignment of the antenna pointing towards the satellite and therefore allows tracking of the satellite.

[0005] In the solutions of the prior art, the difference path ARx is formed by extracting the TE2i mode, which has the advantage of operating in rectilinear as well as circular polarization, but this TE2i mode has a significantly higher cutoff frequency. (of the order of 60%) than the fundamental TEn mode, which requires to extract it a first waveguide with a cross-section diameter significantly larger than that of the waveguide used for the sum channel, as well as the use of protrusions placed symmetrically around this first waveguide, which must then be recombined. This, however, forms a very bulky mode extractor.

[0006] To reduce the size of the mode extractor, it has been proposed to use the TMOi mode which has a transverse magnetic field and is radial. It has the advantage of having a cut-off frequency which is a little higher than the fundamental mode (+30%) and, moreover, the quasi-radial nature of its electric field means that it couples very naturally with the fundamental TEM (transverse electromagnetic) mode of a simple coaxial device.

[0007] Document US 2,892,982 describes the extraction of the TM01 mode by a waveguide while injecting the fundamental modes of the guide into the branches of a turnstile splitter. The turnstile splitter, or turnstile junction, is a hybrid junction with five ports formed of four rectangular cross waveguides arranged concentrically in a plane perpendicular to the axis of a circular or square guide, connected by 90° elbows to four branches in a rectangular waveguide. These four rectangular guides being of smaller thickness operate in the fundamental mode TEi0. The symmetrical fundamental mode of the main guide is transformed in an appropriate manner into two waves of opposite phase on opposite branches. The two axes of the cross make it possible to process the orthogonal modes TEnh and TEnV.

[0008] Furthermore, document EP 3 060 397 B1 also describes a compact embodiment which has a wide operating frequency band (18GHz-30GHz) which consists of extracting the TMOi tracking mode by a hybrid junction towards a cylindrical central guide. The four lateral branches in a rectangular guide form a bridge towards a second hybrid junction with four branches so as to recombine the two modes TEnv and TEnh necessary to generate the circular polarization on the “sum” channel. Such a solution is well suited to on-board antennas transmitting in K band, i.e. in the low band and receiving in Ka band, in the high band.

[0009] A problem with this solution is that the extraction of the TMOi mode is not optimal. Indeed, this solution is well suited to on-board antennas, which transmit on a frequency band lower than their reception band, respectively the K and Ka bands, it is not for a ground station where the configuration is reversed with a Tx transmission band belonging to the Ka frequency band and an Rx reception band belonging to the K frequency band. Furthermore, for wideband operation of this TMOi mode extractor, it is necessary that the majority of the power of this mode be directly transmitted from the horn to the ARx difference path. This is not the case. Indeed, there is insufficient isolation between the TEi0 wave of the input waveguide branches and the output of the TEM mode.

[0010] In particular, the transverse magnetic mode TMOi can be partially transmitted in the branches of the turnstile junction according to waves of identical phases on the opposite branches.

[0011] This insulation defect causes the coupling of a portion of this power onto the four branches and these identical phase conditions do not allow recombination on the second turnstile junction, which leads to the generation of a standing wave sufficient to initiate resonances at periodic frequencies in the reception band K. Such resonances in turn couple with the difference channel ARx, which significantly disrupts its response by greatly reducing its operating bandwidth by creating transmission attenuations at certain frequencies. This phenomenon also appears in the total bandwidth of the mode extractor, which also degrades the performance of the reception band of the sum channel Rx. These performance degradations make such a mode extractor unusable for a ground station.

[0012] Finally, such a junction is designed to operate so that only the lontisymmetric TE modes, generated by the two modes TEnh and TEnv, circulate in the four branches, i.e. the turnstile junction of the prior art is single-mode. Consequently, only these modes can be reconstituted and transmitted to the second downstream waveguide. As a result, a portion of the symmetric TEi0 modes are reflected in the opposite direction in the branches because they cannot be transmitted to the second downstream waveguide, which is an additional source of disturbance. Statement of the invention

[0013] An aim of the present application is to remedy the aforementioned drawbacks, by proposing a TMoI mode extractor which is compact and suitable for ground stations for reception and transmission in the respective K and Ka bands.

[0014] To this end, according to a first aspect of the invention, a mode extractor device for an electromagnetic signal circulating from upstream to downstream along a longitudinal axis of the mode extractor device is proposed, the mode extractor device comprising, from upstream to downstream:

[0015] - a first turnstile junction, comprising:

[0016] - an input waveguide extending along the longitudinal axis from a first input port to a downstream end, the input waveguide comprising a multimode coaxial transition zone and four first rectangular output ports gular, orthogonal to the longitudinal axis and arranged in a cross, the first turnstile junction being configured to be connected to an antenna for collecting an electromagnetic field via the first input port, the input waveguide having an outer diameter decreasing from upstream to downstream;

[0017] - the multimodal coaxial transition zone comprising a coaxial waveguide disposed within the input waveguide coaxially, the coaxial waveguide comprising a central core whose diameter increases from upstream to downstream and extends from one end over a portion of the input waveguide;

[0018] - four rectangular branches, each of the rectangular branches being connected orthogonally to one of the first rectangular output ports;

[0019] - a second turnstile junction comprising:

[0020] - an output waveguide extending along the longitudinal axis from one end upstream, located towards a second exit port;

[0021] - four second rectangular input ports arranged in a cross, orthogonal to the axis longitudinal and each connected orthogonally to a rectangular branch and to the upstream end of the output waveguide;

[0022] - a coaxial output inserted into the output waveguide by protruding from the guide output waveguide and extending within a portion of the length of the output waveguide from the upstream end of the output waveguide.

[0023] The invention also relates to a mode extractor device for an electromagnetic signal, in which the second turnstile junction comprises: - a coaxial output inserted into the output waveguide by projecting from the output waveguide and extending within a portion of the length of the output waveguide from the upstream end of the output waveguide and surrounded by a series of metal discs;

[0024] - a protrusion extending along the longitudinal axis, inside a part of the length of the output waveguide from the upstream end of the output waveguide.

[0025] A second aspect of the invention relates to a mode extractor device for an electromagnetic signal, comprising an intermediate turnstile junction placed between the first turnstile junction and the second turnstile junction, the intermediate turnstile junction comprising:

[0026] - four T-links, each connected orthogonally to a rec branch tangular and comprising a main guide perpendicular to the rectangular branch and a lateral branch integrated into the rectangular branch in its length and extending parallel to the longitudinal axis;

[0027] - four rectangular intermediate input ports arranged in a cross, orthogonal to the longitudinal axis and each connected to a rectangular branch by a T-shaped connection;

[0028]

[0029]

[0030]

[0031]

[0032]

[0033] - an intermediate waveguide with a square or circular section; the mode extractor device of an electromagnetic signal comprising four successions of capacitive irises, configured to constitute bandpass filters, each of the successions being respectively placed between two sections of a rectangular branch, downstream of the T-shaped connection and upstream of the second rectangular input port of the second turnstile junction. The second aspect of the invention also relates to a mode extractor device, in which: - the successions of capacitive adaptation irises are configured to form bandpass filters having a bandwidth of 17.3 GHz to 21.2 GHz; - each respective main guide of a T-link comprises an inductive matching iris positioned perpendicular to the respective main guide and each respective side branch of a T-link comprises at its end closest to the second turnstile link a capacitive matching iris positioned perpendicular to the respective side branch, the inductive matching irises and the capacitive matching irises being configured to optimize the performance of the T-links. The first or second aspect of the invention is advantageously supplemented by the following characteristics, taken alone or in one of their technically possible combinations: - the outer diameter of the coaxial waveguide around the central core increases continuously from upstream to downstream; - the coaxial waveguide around the central core comprises at least four successive stages, each stage having respectively a diameter greater than the upstream stage and a diameter less than the downstream stage so that the external diameter of the coaxial waveguide increases discontinuously from upstream to downstream; - the input waveguide has a circular section and the output waveguide a square section, or the input waveguide has a square section and the output waveguide a circular section; - the output waveguide is a ridge-shaped waveguide; - the coaxial output of the second turnstile junction is sized for extract the Transverse Electromagnetic mode TEM from the electromagnetic signal received by the second turnstile junction; The invention finally relates to a transmitting / receiving station comprising an antenna connected to a mode extractor device according to the invention. The invention consists of chaining two turnstile junctions (or hybrid junctions) connected to each other by means of four rectangular waveguide branches. tangular to allow coupling of the two TEn modes and the TMOi mode of the main guide of a signal from a horn connected to the device of the invention.

[0034] The first turnstile junction is designed for multimode operation, that is to say it allows to convert not only the two TEn modes but also the TMOi mode coming from the cylindrical waveguide of a horn into four TE 10 modes of the rectangular guides constituting the four branches, while preserving a good impedance adaptation in the total Rx and Tx band (K / Ka). The TEnh mode of the input guide is thus divided into two antisymmetric contributions of the fundamental TEio mode in two orthogonal accesses of the cross. The TEnV mode generates two TE10 waves in the branches orthogonal to that where the waves are generated by the TEnh mode. As for the TMOi mode of the input guide, it is divided into four symmetric contributions, therefore of the same amplitude and phase, of TE10 waves in all the branches. It should be noted that the phase of the fields changes after a 90° bend.Therefore, the fields that were in phase opposition before the first bend become in phase and vice versa. The second bend then allows another phase change of 90° allowing the initial state (at the input branches of the first turnstile junction) to be returned to a phase shift of 180° (contribution of the two bends).

[0035] The second downstream hybrid junction allows the waves of the four rectangular branches to be recombined to restore the three modes present upstream of the first junction on different paths, while ensuring perfect decoupling between these sum (S) and difference (A) paths. To achieve this, the output waveguide, which provides the sum path S, is sized smaller than the input waveguide upstream of the first junction, so that its cutoff frequency of the TM mode oi is higher than the maximum frequency of use in transmission Tx. Thus, any recombination of the symmetrical TE10 waves coming from the rectangular branches will be forced into the coaxial output which provides the difference path A located in the opposite direction to the guide which provides the sum path S.Even if this reconstitution of the TMqi mode of the upstream input waveguide in coaxial TEM mode on the difference access is poorly adapted, the lost energy would be reflected in the rectangular branches, then upon arriving at the first junction would recombine into a mode re-emitted by the horn since this first junction is designed to be perfectly adapted. There is therefore no trapping phenomenon as is the case in document EP 3 060 937 B1 which causes resonances is therefore eliminated. Even when the branches have a path imbalance, then a recombination in TEn mode appears next to the TMOi mode on the input waveguide.

[0036] This is the major advantage of this assembly, unlike previous solutions, because in the absence of coupling between S and A, the risks of resonances are eliminated. Another advantage is to use a ridged square guide at the output of the second junction in order to better isolate the passage from TMOi mode to the square guide. DESCRIPTION OF FIGURES

[0037] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0038] [Fig.l] illustrates a satellite telecommunications ground station according to one embodiment of the invention;

[0039] [Fig.2] illustrates a sectional view of the entire device according to a first embodiment of the invention;

[0040] [Fig.3] illustrates a schematic detail view of the first turnstile connection

[0041] [Fig.4] illustrates a schematic view of the entire device according to a first embodiment of the invention;

[0042] [Fig.5] illustrates a sectional view of the entire device according to a second embodiment of the invention;

[0043] [Fig.6] illustrates a schematic view of the entire device according to a second embodiment of the invention.

[0044] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION Ground station

[0045] [Fig.l] illustrates a satellite telecommunications ground station 100 comprising a parabolic antenna 200 which comprises a parabolic reflector 300 associated with a horn antenna 400 (hereinafter horn 400) and a mode extractor 500. The mode extractor 500 makes it possible to extract the modes useful for determining the sum S and difference A channels presented in the introduction. During reception operation, the electromagnetic field is reflected by the parabolic reflector 300 towards the horn 400, which injects the field thus collected into the mode extractor 500. First embodiment

[0046] In the following, upstream and downstream are defined with respect to the direction of propagation of the waves in reception, that is to say from the parabolic reflector 300 to the accesses of the sum E and difference A channels of the mode extractor 500. Consequently, the elements defined as being respectively “input” and respectively “output” or any similar formulation must be considered, for operation of the mode extractor 500 in transmission, as being respectively “output” and respectively “input”.

[0047] Furthermore, the longitudinal axis is called the axis of revolution of the cylinder formed by a input waveguide or respectively by an output waveguide.

[0048] Figures 2 to 4 illustrate a mode extractor device 500 according to a first embodiment. Such a device makes it possible to extract the modes of an electromagnetic signal coming from the horn 400 and connected to the mode extractor device 500 and circulating from upstream to downstream along a longitudinal axis A, along the mode extractor device 500. From upstream to downstream, the mode extractor device 500 comprises a first turnstile junction 1 (or hybrid junction) and a second turnstile junction 3, connected to each other by four rectangular branches 2 forming waveguides.

[0049] The first turnstile junction 1 comprises an input waveguide 11 which extends along the longitudinal axis A from upstream to downstream from a first input port 111 to a multimodal coaxial transition zone 12. The first turnstile junction 1 is configured to be connected to a horn 400 for collecting the electromagnetic field via the first input port 111. The input waveguide 11 has an outer diameter which decreases from upstream to downstream. Preferably, this reduction is done continuously or discretely. In the case of a discrete decrease, the reduction in diameter is carried out in successive steps 112, that is to say that the input waveguide 11 is in the form of several hollow cylinders or parallelepipeds of different diameters, for example four hollow cylinders or parallelepipeds end to end forming a continuous input waveguide 11.

[0050] The multimodal coaxial transition zone 12 comprises a coaxial waveguide 120 disposed inside the input waveguide 11, with which it is coaxial. The coaxial waveguide 120 extends from the multimodal coaxial transition zone 12 over a portion of the input guide 11. The multimodal coaxial transition zone 12 is therefore not over the entire length of the input waveguide 11. The coaxial waveguide 120 comprises a central core 121 whose diameter increases from upstream to downstream. Preferably, the diameter of the coaxial waveguide 120 increases in successive steps 122, so that a transition zone 12, in which the diameter of the input waveguide 11 decreases while the diameter of the coaxial waveguide 120 increases, is established along the longitudinal axis A.The diameter of the coaxial waveguide 120 increases with, preferably, a minimum of four successive steps 122, the difference in radius of a step 122 with a preceding step 122 preferably being at least two to four wavelengths.

[0051] A series of metal discs 15, for example a series of two metal discs 15, may be placed around the distal end of the coaxial waveguide 120 relative to the horn 400, which also includes a protrusion 35.

[0052] At the downstream end of the input waveguide 11 are arranged four first ports output ports 13 of rectangular section, each of them being orthogonal to the longitudinal axis A and arranged concentrically to form a cross, each first output port 13 being perpendicular to its two neighbors and aligned with the opposite first output port 13 (see [Fig.3]). From each first output port 13 extends a rectangular branch 2 consisting of a waveguide of rectangular section, orthogonal to the corresponding first output port 13, so that each rectangular branch 2 is parallel to the longitudinal axis A. The multi-modal coaxial transition zone 12 opens at the center 14 of the cross formed by the four rectangular branches 2 connected to the input waveguide 11.

[0053] The second turnstile junction 3 is placed opposite the first turnstile junction 1 and comprises four second input ports 33, similar in their nature and their cross arrangement to those of the first turnstile junction 1. To each second input port 33 is connected the second end of a rectangular branch 2, in order to join the first junction 1 to the second junction 3.

[0054] Still from upstream to downstream, from the center 14 of the cross formed by the second output ports 33 extends an output waveguide 31 along the longitudinal axis A. The center of the cross is an upstream end 34 of the turnstile junction 3, from which the output waveguide 31 extends to a second output port 311 at its end. Furthermore, a coaxial outlet 32 ​​projects from the upstream end 34 upstream and inside the output waveguide 31 downstream. At the end of the coaxial outlet 32 ​​is placed a protrusion 35 surrounded by metal discs 15.

[0055] In operation, the coaxial output 32 provides the difference path A and the second output port 311 of the output waveguide 31 provides the sum path S.

[0056] An operation of the mode extractor device 500 according to the first embodiment is described below in the case where the input waveguide 11 has a circular section and the output waveguide 31 a square section (see FIGS. 2 to 4). The mode extractor device 500 described is therefore connected to a horn 400 which collects an electric field by adapting it towards vertically polarized modes TEn v and horizontally polarized modes TEnh. The horn 400 also collects a magnetic field of mode TMOi. These modes TEnh, TEnV, TMOi and TMn are propagated to the first turnstile junction 1 via the input waveguide 11. The input waveguide 11 is configured to preserve the impedance adaptation of the main modes TEn, TMOi and TMn.The multimodal coaxial transition zone 12 of the input waveguide 11 and the coaxial waveguide 120, which has the function of allowing the multimode operation of the first turnstile junction 1, converts the TMOi mode into the fundamental TEM mode, without impedance break thanks to the progressive increase in the diameter of the coaxial waveguide. 120. The TEnh, TEnV modes are propagated without reflections in the input waveguide 11 on the Rx and Tx bands. The succession of steps 112 also makes it possible to control the relative power level of the higher mode TMn with respect to the two modes TEnh and TEnV in order to generate two hybrid modes HEnh and HEnV minimizing the level of cross-polarization radiated by the sum path E of the horn 400. This also makes it possible to minimize losses in the event of coupling of the fundamental mode TE h with higher order modes. These advantages are made possible by a number of steps 112 and 122 of evolution of the diameters of the input waveguide 11 and of the coaxial waveguide 120 and a longer length of the multimodal coaxial transition zone 12.

[0057] In order to adapt the transient coaxial modes to the first four output ports 13, one or more metal discs 15 and a protrusion are arranged around the coaxial waveguide 120 in order to capture the symmetrical components forming again a TEM mode and transmitted via the coaxial output 32, which makes it possible to optimize the transition of the modes from the input waveguide 11 to the first output ports 13.

[0058] The modes are then propagated in the four rectangular branches 2 via the first four output ports 13 in the form of two antisymmetric TE io modes and two symmetric TEi0 modes, before being received by the corresponding second output ports 33 of the second turnstile junction 3, the output waveguide 31 of the second turnstile junction 3, of square section, being dimensioned so that the fundamental modes TE10 and TEOi can propagate but the TMOi mode is cut off there, unlike the coaxial output 32 configured to recombine the symmetric waves of TE10 mode into a TEM mode, so as to extract the TEM mode for the output of the difference path ARx towards the upstream.The symmetrical waves of the TE10 modes from the four branches 2 recombine thanks to the outgrowth 35, which is surrounded by metal discs in order to maximize the coupling of the TE10 modes with the ARx difference voice in order to extract the maximum of the tracking mode.

[0059] Preferably, the output waveguide 31 of square section is a “ridged” or crest-shaped waveguide, which makes it possible to avoid any downstream propagation of the reconstituted TEM mode and therefore the reflection of the latter so that the mode residues are again captured by the difference path ARx, which optimizes the extraction. The recombination of the TEi0 modes of the rectangular branches 2 towards the coaxial output 32 is similar to the phenomena occurring in the first turnstile junction 1.

[0060] Alternatively, the input waveguide 11 has a square section and the output waveguide 31 has a circular section.

[0061] In this configuration, the TEoi, TEi0, TMOi and TMn modes are then propagated by the horn 400 to the first turnstile junction 1 via the input waveguide 11. The input waveguide 11 is configured to preserve the impedance matching of the main TEOi, TMOi and TMn modes. In the multimode coaxial transition zone 12 of the input waveguide 11 and the coaxial waveguide 120, which has the function of allowing the multimode operation of the first turnstile junction 1, the TMOi mode is converted into the fundamental TEM mode, without impedance break thanks to the progressive increase in the perimeter of the section of the coaxial waveguide 120. The TEOi and TEi0 modes are themselves propagated without reflections in the input waveguide 11 on the Rx and Tx bands. The succession of steps 112 also makes it possible to control the power level of the parasitic upper mode TMn in order to minimize the coupling with the cross-polarization which would be radiated in reflection by the horn 400.This also makes it possible to minimize losses in the event of coupling of the fundamental mode TEn with higher order modes. These advantages are increased by a number of steps 112,122 of evolution of the perimeters of the input waveguide sections 11 and of the coaxial waveguide 120 and a longer length of the multimodal coaxial transition zone 12.

[0062] The modes are then propagated in the four rectangular branches 2 via the first four output ports 13 in the form of two antisymmetric TE io modes and two symmetric TEi0 modes, before being received by the corresponding second output ports 33 of the second turnstile junction 3, the output waveguide 31 of the second turnstile junction 3, of circular section, being dimensioned so that the TEnV and TEnh modes can propagate but the TMOi mode is under cut-off there, unlike the coaxial output 32 configured to recombine the symmetric waves of TE10 mode into a TEM mode, so as to extract the TEM mode for the output of the ARx difference path towards the upstream.The symmetrical waves of the TE10 modes from the four rectangular branches 2 recombine thanks to the outgrowth 35, which is surrounded by metal discs in order to maximize the coupling of the TE10 modes with the ARx difference voice in order to extract the maximum of the tracking mode.

[0063] In comparison with the devices of the prior art, the mode extractor 500 described here therefore eliminates any possibility of resonance thanks to the multimode and wideband character of the first turnstile junction 1, which cannot in any way trap the energy coupled between the modes. The proposed architecture is also very compact in comparison with existing devices, while operating over a very wide frequency band. Second embodiment

[0064] Figures 5 and 6 illustrate a mode extractor device 500 according to a second embodiment. The mode extractor device 500 according to the second embodiment embodiment comprises, in addition to the characteristics of the device of the first embodiment, an intermediate turnstile junction 4, placed between the first turnstile junction 1 and the second turnstile junction 3. This intermediate turnstile junction 4 comprises, like the first turnstile junction 1 and the second turnstile junction 3, four rectangular intermediate inlet ports 43 arranged in a cross, orthogonal to the longitudinal axis A. Each intermediate inlet port 43 is connected to a rectangular branch 2 via a T-shaped connection 42. There are thus four T-shaped connections 42, each being connected orthogonally to a rectangular branch 2 and comprising a main guide 421 perpendicular to the rectangular branch 2 and a lateral branch 422 integrated into the rectangular branch 2 in its length.The turnstile junction 4 is placed similarly to the second turnstile junction 3, opposite the first turnstile junction 1. An intermediate waveguide 41 whose cross-section is square extends downstream along the longitudinal axis A and is connected to the four intermediate input ports 43.

[0065] Furthermore, in this same embodiment, there is placed between two sections of a rectangular branch 2, downstream of the T-shaped connection 42 and upstream of the rectangular intermediate input port 43 of the second turnstile junction 3, a succession 5 of capacitive adaptation irises 51, configured to constitute bandpass filters, each of the successions 5 being respectively placed between two sections of a rectangular branch 2, downstream of the T-shaped connection 42 and upstream of the rectangular intermediate input port 43 of the second turnstile junction 3. Each succession 5 of capacitive adaptation irises 51 forms a bandpass filter which preferentially lets the K band pass towards the second turnstile junction 3 and rejects the Ka band.This bandpass filter is a rectangular "corrugated" waveguide with a very wide rejection band, which supports high powers without breakdown or multi-actor effect, while presenting low ohmic losses and being of low machining cost.

[0066] The T-junctions 42 are critical elements because they cause an insertion loss in both the K and Ka bands and interact with the bandpass filters formed by the successions 5 of capacitive irises 51. This is the reason why preferably, each respective main guide 421 of a T-link 42 comprises an inductive matching iris 431 and each respective lateral branch 422 of a T-link 42 comprises at its end closest to the second turnstile link 3 a capacitive matching iris 432, the inductive matching irises 431 and the capacitive matching irises 432 being configured to optimize the performance of the T-links 42. These irises are for example metal plates or slats, placed on the lateral inner walls of the waveguides. The inductive adapting irises 431 comprise slats placed perpendicular to the magnetic field, while the Capacitive matching iris 432 comprises slats placed perpendicular to the electric field, their respective reactance being optimized to improve the performance of the T-links 42.

[0067] This configuration improves the ellipticity rate of the system and therefore makes it possible to create a high-purity circular polarization. The operating principle consists of separating the Rx and Tx channels from the sum channel E before the recombination of the second turnstile junction 3 by taking advantage of the fact that all the signals are of TEi0 mode in the rectangular branches 2. This separation is carried out by a duplexer formed by the T-links 42 in association with the successions 5 of capacitive irises 51. The successions 5 of capacitive irises 51 rejecting the Ka band, the associated Tx band rushes into the main guide 421 of the respective T-link 42, the main guide 421 being under cut-off for the Rx band thanks to its dimension smaller than that of the branch 2.The intermediate turnstile junction 4 then recombines the four TEi0 modes into TEiO and TEOi modes if the section of the intermediate waveguide 41 is square and into TEnhe and TEnv modes if the section of the intermediate waveguide 41 is circular. We can then extract the sum channel ETx following the intermediate waveguide 41 of the intermediate turnstile junction 4 and the sum channel ERx following the output waveguide 31 of the second turnstile junction 3, which then makes it possible to integrate polarizers specific to each band, the specific polarizers having better performances than a total band polarizer, which acting on the entirety of the Rx and Tx bands, is poor in ellipticity rate at the bandwidth limit.

[0068] The new mode extractor 500 of this second embodiment makes it possible to obtain performances in terms of isolation between the sum E and difference A channels, less than -35 dB on the Rx band and between the Rx and Tx channels less than -110 dB. In terms of cross-polarization and ellipticity ratio, the performances are also improved since the latter is less than 0.3 dB. A final advantage of this second embodiment is its capacity to be used within an antenna 200 of a ground station 100 as well as within an on-board antenna in which the Tx and Rx bands are inverted and correspond respectively to the Ka and K bands. The conversion from one use to the other is carried out in a simple manner, by moving the coaxial output 32 between the second turnstile junction 3 and the intermediate turnstile junction 4 for the acquisition of the difference A channel.

Claims

Claims

1. Mode extractor device (500) of an electromagnetic signal circulating from upstream to downstream along a longitudinal axis A of the mode extractor device (500), the mode extractor device (500) comprising, from upstream to downstream: - a first turnstile junction (1), comprising: - an input waveguide (11) extending along the longitudinal axis A from a first input port (111) to a downstream end (14), the input waveguide (11) comprising a multimodal coaxial transition zone (12) and four first rectangular output ports (13), orthogonal to the longitudinal axis A and arranged in a cross, the first turnstile junction (1) being configured to be connected to an antenna (200) for collecting an electromagnetic field via the first input port (111), the input waveguide (11) having an outer diameter decreasing from upstream to downstream; - the multimodal coaxial transition zone (12) comprising a coaxial waveguide (120) arranged inside the input waveguide (11) in a coaxial manner, the coaxial waveguide (120) comprising a central core (121) whose diameter increases from upstream to downstream and extends from one end (14) over a portion of the input waveguide (11); - four rectangular branches (2), each of the rectangular branches (2) being orthogonally connected to one of the first rectangular output ports (13); - a second turnstile junction (3) comprising: - an output waveguide (31) extending along the longitudinal axis A from an upstream end (34), located towards a second output port (311); - four second rectangular input ports (33) arranged in a cross, orthogonal to the longitudinal axis A and each connected orthogonally to a rectangular branch (2) and to the upstream end (34) of the output waveguide (31); - a coaxial output (32) inserted into the output waveguide (31) projecting from the output waveguide (31) and extending within a portion of the length of the output waveguide (31) from the upstream end (34) of the output waveguide (31).

2. Mode extractor device (500) of an electromagnetic signal in

3.

4.

5. which the second turnstile junction (3) comprises: - a coaxial output (32) inserted into the output waveguide (31) projecting from the output waveguide (31) and extending within a portion of the length of the output waveguide (31) from the upstream end (34) of the output waveguide (31) and surrounded by a series of metal discs (15); - a protrusion (35) extending along the longitudinal axis A, within a portion of the length of the output waveguide (31) from the upstream end (34) of the output waveguide (31). Mode extractor device (500) of an electromagnetic signal according to one of claims 1 or 2, comprising an intermediate turnstile junction (4) placed between the first turnstile junction (1) and the second turnstile junction (3), the intermediate turnstile junction (4) comprising: - four T-shaped connections (42), each being connected orthogonally to a rectangular branch (2) and comprising a main guide (421) perpendicular to the rectangular branch (2) and a lateral branch (422) integrated into the rectangular branch (2) in its length and extending parallel to the longitudinal axis A; - four intermediate rectangular inlet ports (43) arranged in a cross, orthogonal to the longitudinal axis A and each connected to a rectangular branch (2) by a T-shaped connection (44); - an intermediate waveguide (41) with a square or circular section; the mode extractor device (500) of an electromagnetic signal comprising four successions (5) of capacitive irises (51), configured to constitute bandpass filters, each of the successions (5) being respectively placed between two sections of a rectangular branch (2), downstream of the T-shaped connection (42) and upstream of the second rectangular input port (33) of the second turnstile junction (3). Mode extractor device (500), in which the successions (5) of capacitive adaptation irises (51) are configured to form bandpass filters having a bandwidth of 17.3 GHz to 21.2 GHz.Mode extractor device (500) according to one of claims 3 or 4, wherein each respective main guide (421) of a T-link (42) comprises an inductive adaptation iris (431) positioned perpendicular to the respective main guide (421) and each respective lateral branch (422) of a T-link (42) comprises at its end closest to the second turnstile link (3) an adaptation iris. capacitive (432) positioned perpendicular to the respective side branch (422), the inductive matching irises (431) and the capacitive matching irises (432) being configured to optimize the performance of the T-links (42).

6. Mode extractor device (500) according to one of claims 1 to 5, in which the outer diameter of the coaxial waveguide (120) around the central core (121) increases continuously from upstream to downstream.

7. Mode extractor device (500) according to one of claims 1 to 5, in which the coaxial waveguide (120) around the central core (121) comprises at least four successive bearings (122), each bearing (122) having respectively a diameter greater than the bearing (122) upstream and a diameter less than the bearing (122) downstream so that the external diameter of the coaxial waveguide (120) increases discontinuously from upstream to downstream.

8. Mode extractor device (500) according to one of claims 1 to 7, wherein the input waveguide (11) has a circular section and the output waveguide (31) a square section, or the input waveguide (11) has a square section and the output waveguide (31) a circular section.

9. Mode extractor device (500) according to one of claims 1 to 8, wherein the output waveguide (31) is a ridge-shaped waveguide.

10. Mode extractor device (500) according to one of claims 1 to 9, wherein the coaxial output (32) of the second turnstile junction (3) is sized to extract the Transverse Electromagnetic mode TEM from the electromagnetic signal received by the second turnstile junction (3).

11. A transmitting / receiving station (100) comprising an antenna (200) connected to a mode extractor device (500) according to any one of claims 1 to 10.

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