Mode extractor of an electromagnetic signal

Abstract

The present invention relates to a mode-extracting device (500) for an electromagnetic signal comprising, from upstream to downstream: - a first orthomode junction (1) comprising: - a central core (121) and - a first coaxial waveguide (120) extending to a coaxial transition zone (11); - a second coaxial waveguide (140) extending from the coaxial transition zone (11) to a downstream end (15); - four first output ports (14); - a waveguide (150) extending from the end (15); - four first branches (2a); - a second junction (3, 4) comprising an output waveguide (31, 41), a second output port (311, 411), and four second input ports (33, 43), each connected orthogonally to one of the four second branches (2b) and to the waveguide output waves (31, 41). Figure for the abstract: Fig. 2

Description

Title of the invention: Mode extractor for 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 K and Ka frequency bands (i.e. the frequency bands between 17.3 and 21.2 GHz and between 27.5 and 31 GHz), in circular polarization and implementing satellite tracking by means of a monopulse reception channel. STATE OF THE ART

[0002] Satellite telecommunications ground stations generally concentrate communications transmitted with user terminals onto a single link and include, to perform this function, a parabolic reflector antenna, which provides high directivity and high gain in communications with the satellite. During receive operation, the electromagnetic field is reflected by the parabolic reflector towards a horn, which injects the field thus collected into an input waveguide, generally circular in cross-section, or more rarely rectangular or square in cross-section, adapting it to a vertical or horizontal polarization of the transverse electric mode TEn, i.e., a TEnV mode for vertical polarization or TEnh for horizontal polarization over a receive 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, denoted Tx. .

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

[0004] A sum channel is useful for both receiving and transmitting the signal, while a difference channel is useful only for receiving and tracking the signal: the sum channel signal is at its maximum and the difference channel signal is zero when the antenna is aligned with the satellite. The signal ratio between the sum channel and the difference channel defines a slope that allows for the determination of an angular offset of the antenna's pointing towards the satellite, thus enabling satellite tracking.

[0005] In prior art solutions, the ARx difference channel is formed by extracting the TE2i mode, which has the advantage of working in linear as well as circular polarization, but this TE2i mode exhibits a significantly higher cutoff frequency The mode is significantly higher (around 60%) than the fundamental mode TEN, which necessitates a first waveguide with a cross-sectional diameter considerably 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, results in a very bulky mode extractor.

[0006] To reduce the size of the mode extractor, it has been proposed to use the TM oi mode, which exhibits a transverse magnetic field and is radial. It has the advantage of having a cutoff frequency that is slightly 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] US patent 2,892,982 describes the extraction of the TM01 mode by a waveguide while injecting the fundamental modes of the waveguide into the branches of a tumstile. The tumstile, or junction, is a hybrid five-access junction formed by four rectangular waveguides arranged concentrically in a cross in a plane perpendicular to the axis of a circular or square waveguide, connected by 90° bends to four rectangular waveguide branches. These four rectangular waveguides, being thinner, operate in the fundamental mode TEi0. The symmetrical fundamental mode of the main waveguide is transformed appropriately into two waves of opposite phase on opposite branches. The two axes of the cross allow the orthogonal modes TEnh and TEnv to be processed.

[0008] Furthermore, document EP 3060397 also describes a compact embodiment with a wide operating frequency band (18 GHz–30 GHz) that extracts the tracking mode TMOi via a hybrid junction to a cylindrical central waveguide. The four lateral rectangular waveguide branches bridge to a second four-branch hybrid junction 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 onboard antennas transmitting in the K-band, i.e., in the lower band, and receiving in the Ka-band, in the upper band.

[0009] One problem with this solution is that the extraction of the TMOi mode is not optimal. Indeed, this solution is well suited to airborne antennas, which transmit on a frequency band lower than their receive band, namely the K and Ka bands respectively, but it is not suitable for a ground station where the configuration is reversed, with a transmit band (Tx) belonging to the Ka frequency band and a receive band (Rx) belonging to the K frequency band. The waveguide diameters must, in fact, be increased so that the The TMqi mode must not be cut off at the minimum reception frequency, i.e., 17.7 GHz. This necessitates control of the higher modes TE2i, TEOi, and TMn, which appear in the Tx band when the four branches are not exactly the same length, thus imposing very tight production tolerances.

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

[0011] This insulation defect causes a portion of this power to couple across the four branches, and these identical phase conditions prevent recombination at the second twisted junction. This results in the generation of a standing wave sufficient to initiate resonances at periodic frequencies in the K-band receive signal. Such resonances, in turn, couple with the ARx difference channel, significantly disrupting its response by drastically reducing its operating bandwidth and creating transmission attenuation at certain frequencies. This phenomenon also appears in the total bandwidth of the mode extractor, which also degrades the performance of the Rx sum channel's receive band. These performance degradations render such a mode extractor unusable for a ground station.

[0012] Finally, such a junction is designed to operate so that only the antisymmetric TEio modes, generated by the two modes TEnh and TEnv, circulate in the four branches; that is, the prior art turnstile junction is single-mode. Consequently, only these modes can be reconstructed and transmitted to the second waveguide downstream. As a result, some of the symmetric TEio modes are reflected back in the branches because they cannot be transmitted to the second waveguide downstream, which is an additional source of interference. Description of the invention

[0013] One object of the present application is to remedy the aforementioned disadvantages, by proposing a TM0iCompact mode extractor adapted for ground stations for reception and transmission in the respective K and Ka bands, improving the isolation between the sum and difference paths without significant reduction in bandwidth.

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

[0015] - a first orthomode junction comprising: - a central core extending along the longitudinal axis from a first entry port to a free downstream end and - a first coaxial waveguide comprising a first tube containing air surrounding the central core and extending along the longitudinal axis from the first inlet port to a coaxial transition zone, the first coaxial inlet waveguide being configured to be connected to an electromagnetic field collection antenna via the first inlet port, the outside diameter of the first tube decreasing in steps from upstream to downstream to the coaxial transition zone; - the coaxial transition zone comprising a second tube surrounding the central core and extending from the first tube to a third tube, the diameter of the central core in the coaxial transition zone being less than the diameter of the central core in the first coaxial waveguide so as to form a circular groove opening upstream into the first tube and downstream into the second tube, the third tube extending coaxially from the second tube to a second coaxial waveguide, the third tube having an outside diameter less than the diameter of the second tube and an inside diameter greater than the diameter of the central core; - the second coaxial waveguide extending from the coaxial transition zone to a downstream end and comprising a dielectric surrounding the central core, the dielectric having an outside diameter equal to the inside diameter of the third tube, an upstream end of the dielectric being in contact with a downstream end of the third tube; - four first rectangular output ports, orthogonal to the longitudinal axis and arranged in a cross on either side of the coaxial transition zone so that their longer sides are parallel to the longitudinal axis; - a waveguide, comprising a cylindrical portion extending upstream from the end, so as to surround a portion of the second coaxial waveguide, a rectangular waveguide and a rectangular waveguide section extending perpendicularly to the longitudinal axis from the cylindrical portion diametrically opposite each other and on either side of the end, an outer perimeter of the rectangular waveguide increasing in steps with the distance to the longitudinal axis and a length of the rectangular waveguide being greater than a length of the rectangular waveguide section; - four first rectangular branches joined to four second rectangular branches, each of the first rectangular branches being connected orthogonally to one of the first rectangular output ports and comprising an adaptation iris adjacent to this first output port; - a second junction comprising an output waveguide extending along the longitudinal axis from an upstream end, located opposite the downstream end, to a second output port and four rectangular second input ports arranged in a cross orthogonally to the longitudinal axis, each connected orthogonally to one of the four second rectangular branches and to the upstream end of the output waveguide.

[0016] The mode-extracting device according to the invention is advantageously complemented by the following features, taken alone or in one of their technically feasible combinations: - the coaxial transition zone includes irises configured to match the impedance of an electromagnetic transverse mode between the first coaxial waveguide and the second coaxial waveguide; - the second junction is an orthomode junction, the output waveguide being a coaxial waveguide and the four second input ports being arranged so that their greatest length is parallel to the longitudinal axis; - the second junction is a turnstile junction, further comprising a coaxial output extending from an upstream end to the upstream end, each second rectangular branch being joined to a first rectangular branch by means of a respective twisted waveguide inclined at 45° to the first and second rectangular branches, the mode extractor device also comprising an intermediate turnstile junction placed between the orthomode junction and the turnstile junction, the intermediate turnstile junction comprising: • four T-shaped links, each being orthogonally connected to a second rectangular branch and comprising a main guide perpendicular to the second rectangular branch and a lateral branch integrated into the second rectangular branch along its length and extending parallel to the longitudinal axis A; • four rectangular intermediate input ports arranged in a cross, orthogonal to the longitudinal axis A and each connected to a second rectangular branch by a T-junction; • an intermediate waveguide with a square or circular cross-section; - four successions of capacitive adaptation irises configured to constitute bandpass filters, each of the successions being respectively placed between two sections of a second rectangular branch, downstream of the T-link and upstream of the inlet port of the turnstile junction; - 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 main guide each respective lateral branch of a T-link includes at its end closest to the tourniquet link a capacitive matching iris positioned perpendicular to the respective lateral branch, the inductive matching irises and the capacitive matching irises being configured to optimize the performance of the T-links; - the coaxial output of the turnstile junction is sized to extract parasitic Transverse Electromagnetic (TEM) modes from the electromagnetic signal received by the turnstile junction and the output waveguide is sized to extract the Transverse Electromagnetic (TEM) mode from the electromagnetic signal received by the turnstile junction; - the rectangular waveguide of the orthomode junction is dimensioned to extract the Transverse Electric mode TEi0 from the electromagnetic signal received by the first orthomode junction.

[0017] The invention also relates to a transmitting / receiving station comprising an antenna connected to a mode extractor device according to one of the modes of the present disclosure. DESCRIPTION OF THE FIGURES

[0018] Other features, objectives and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which:

[0019] Fig. 1 illustrates a satellite telecommunications ground station according to a first embodiment of the invention;

[0020] Fig. 2 illustrates a cross-sectional view of the entire device according to the first embodiment of the invention;

[0021] Fig. 3 illustrates a view of the entire device according to the first embodiment of the invention;

[0022] Figure 4 illustrates a schematic detail view of the first orthomode link;

[0023] Figure 5 illustrates another schematic detail view of the first connection orthomode;

[0024] Fig. 6 illustrates a cross-sectional view of the entire device according to a second embodiment of the invention;

[0025] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION OF THE INVENTION Ground station

[0026] Figure 1 illustrates a ground-based satellite telecommunications station comprising a parabolic antenna 200 which includes a parabolic reflector 300 associated with a horn antenna 400 (hereinafter horn 400) and a mode extractor 500. The extractor The 500 mode extractor allows the extraction of 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 collected field into the 500 mode extractor. Fashion extractor

[0027] In what follows, upstream and downstream are defined with respect to the direction of wave propagation in reception, i.e., from the parabolic reflector 300 to the sum E and difference A inputs 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".

[0028] Furthermore, the longitudinal axis is the axis of revolution of the cylinder or tube formed by an input waveguide or, respectively, by an output waveguide. In what follows, a coaxial waveguide is understood to be a core coaxially surrounded by a coaxial hollow tube or cylinder, for example, metallic; the space between the core and the tube may contain air or a dielectric material.

[0029] The described device allows the modes of an electromagnetic signal originating from the horn 400 and connected to the mode extractor device 500 and traveling 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 orthomode junction 1 and a second junction 3, connected to each other by four rectangular branches 2 forming waveguides. Each orthomode junction comprises 6 ports.

[0030] The first orthomode junction 1 extends from a first input port 111 to a downstream end 15. A central core 121 extends along the longitudinal axis A from upstream to downstream from a first input port 111 to a downstream end 15. The first orthomode junction 1 is configured to be connected to an electromagnetic field collection horn 400 by the first input port 111.

[0031] The first coaxial waveguide 120 comprises the central core 121 surrounded by a suitable insulating medium, preferably air, the medium being contained by a first tube 122 coaxial with the central core 121. Near a coaxial transition zone 11, the tube 122 has an outer diameter that decreases from upstream to downstream. Preferably, this reduction occurs discretely, in successive steps, and between the first four output ports 14; that is to say, the coaxial waveguide 120, over a length parallel to the longitudinal axis A and between the upstream end of the first output ports 14 and the coaxial transition zone 11, takes the form of several tubes of different inner diameters centered around the central core 121. . This reduction in diameter allows for a wideband impedance matching of the TEnhet TEnV modes corresponding to the sum channel S since the conversion bandwidth of the TEi0 modes of the rectangular guides 2a to the TEn modes of the first coaxial guide 120 is increased.

[0032] As illustrated in detail in [Fig. 4] and [Fig. 5], the first coaxial waveguide 120 and a second coaxial waveguide 140 join in the coaxial transition zone 11. The second coaxial waveguide 140 comprises the same central core 121 as the first coaxial waveguide 120 and a dielectric 141 surrounding the central core 121 such that the outer diameter of the dielectric 141 is substantially equal to the inner diameter of a third tube 13. In the coaxial transition zone 11, the diameter of the central core 121 decreases compared to its diameter in the first coaxial waveguide 120. On the other hand, the diameter of the central core 121 in the coaxial transition zone 11 is equal to its diameter in the second coaxial waveguide 140.The coaxial transition zone 11 comprises a second tube 12 surrounding the central core 121 and extending from the first tube 122 to the third tube 13. The diameter of the central core 121 in the coaxial transition zone 11 is smaller than the diameter of the central core 121 in the first coaxial waveguide 120, thus forming a circular groove 10, or annular slot 10, made of the same medium as the contents of the tube 122, that is, preferably air. Upstream, the circular groove 10 opens partly onto the internal volume of the tube 122 and partly onto a portion of the circumference of the central core 121. In other words, the reduction in the outer diameter of the central core 122 in the coaxial transition zone 11 creates a space communicating with the volume of the tube 122.

[0033] Downstream, the circular groove 10 opens onto a third tube 13 surrounding the central core 121 from the circular groove 10 to the second coaxial waveguide 140, the third tube 13 being a hollow cylinder that forms the sheath of the second coaxial waveguide 140. The outer diameter of the third tube 13 is smaller than the diameter of the second tube 12 and its inner diameter is larger than the diameter of the central core 121. In particular, the inner diameter of this third tube 13 is the same as that of the dielectric 141 and the downstream surface of the third tube 13 is in contact with the upstream surface of the dielectric 141.

[0034] The transition zone 11, the circular groove 10, the second tube 12, the third tube 13 and the dielectric 141 are coaxial with the longitudinal axis A.

[0035] To improve the impedance matching between the input coaxial waveguide 120 and the second coaxial waveguide 140, the third tube 13 of the coaxial transition zone 11 preferentially includes impedance matching irises 113.

[0036] At the coaxial transition zone 11 are arranged four first output ports 14 of rectangular cross-section, each of them being orthogonal to the longitudinal axis A and arranged concentrically to form a cross, each first output port 14 being perpendicular to its two neighbors and aligned with the opposite first output port 14 (see [Fig. 4]). The rectangular cross-section of the first output ports 14 is such that the longer sides are parallel to the longitudinal axis A. From each first output port 14 extends a first rectangular branch 2a consisting of a waveguide with a rectangular cross-section, orthogonal to the corresponding first output port 14, so that each first rectangular branch 2a is parallel to the longitudinal axis A. In the immediate vicinity of each output port 14, each rectangular branch 2a has a matching iris 21. The coaxial transition zone 11 opens at the center of the cross formed by the first four rectangular branches 2a connected to the input waveguide.

[0037] Still from upstream to downstream, the second coaxial waveguide 140 extends from the coaxial transition zone 11 to a downstream end 15, at which it is short-circuited, that is to say the central core 121 is in contact with a conductor.

[0038] On the other hand, the downstream end 15 comprises a waveguide 150. The waveguide 150 comprises a cylindrical portion 151 extending upstream from the downstream end 15, so as to coaxially surround a portion of the second coaxial waveguide 140, a rectangular waveguide 152, and a rectangular waveguide segment 153 extending perpendicularly to the longitudinal axis A from the cylindrical portion 151 in diametrically opposite directions, from the downstream end 15 and without exceeding it. The outer perimeter of the rectangular waveguide 152 increases in steps with the distance to the longitudinal axis A, and a length of the rectangular waveguide 152 is greater than a length of the rectangular waveguide segment 153. The rectangular waveguide 152 thus extends between two first branches 2a and constitutes the port exit of the difference A channel.The rectangular waveguide 153 terminates in a short circuit at a distance approximately equal to one quarter of a wave from the central core 121, which allows a transition from the second coaxial waveguide 140 to the rectangular waveguide 152.

[0039] The first four rectangular branches 2a are joined to four second rectangular branches 2b, each of the first rectangular branches 2a being connected orthogonally to one of the first rectangular output ports 14.

[0040] The branches 2a, 2b are rectangular waveguides that connect the first orthomode junction 1 to a second junction 3. The second junction 3 comprises four rectangular second input ports 33 arranged in a cross orthogonally to the longitudinal axis A, each connected orthogonally to one of the four rectangular second branches 2b and to the upstream end 34 of the output waveguide 31, which extends along the longitudinal axis A from an upstream end 34, located opposite the downstream end 15, to a second output port 311. The second port of output 311 constitutes the output port of the sum channel S, while the rectangular waveguide 152 constitutes the output port of the difference channel A.

[0041] The configuration of the first orthomode junction 1 allows, in particular thanks to the geometry of the coaxial transition zone 11, a transition from, on the one hand, a multimode input coaxial waveguide 120 to a second single-mode coaxial waveguide 140 that propagates only the TEM mode and corresponds to channel A, and on the other hand, to a third dual-mode coaxial waveguide 311 that propagates only the TE1 Ih and TE1 Iv modes corresponding to the H and V polarizations of channel S. This junction allows the two channels to be separated with excellent isolation. A much wider bandwidth is thus obtained. Other advantages are provided by the embodiments detailed below. First method of implementation

[0042] In a first embodiment illustrated in Figures 2 and 3, the second junction 3 is a second orthomode junction 3, positioned opposite the first orthomode junction 1 and comprising four second input ports 33, similar in nature and cross-shaped arrangement to those of the first orthomode junction 1. The second end of a first rectangular branch 2a is connected to each second input port 33, in order to join the first junction 1 to the second orthomode junction 3. An output waveguide 31 extends along the longitudinal axis A from an upstream end 34, located opposite the downstream end 15, to a second output port 311. The second output port 311 constitutes the sum channel port S. The output waveguide of the second orthomode junction 3 is therefore sized to extract the Transverse Electromagnetic (TEM) mode from the electromagnetic signal received by the second orthomode junction 3.

[0043] The following describes the operation of the mode extractor device 500 according to the first embodiment. The mode extractor device 500 described is connected to a horn 400 which collects an electric field, adapting it to vertically polarized modes TEnv and horizontally polarized modes TEnh. The horn 400 also collects a magnetic field of mode TEM. These modes TEnh, TEnv, and TEM are propagated to the first orthomode junction 1 via the coaxial input waveguide 120. The coaxial transition zone 11, thanks to the geometry of the circular groove 12, allows only the K-band TEM mode to pass. As illustrated [Fig. 4], the TEM mode always remains radially distributed and therefore cannot couple with the first four output ports 14, which provides much better isolation compared to a turnstile-type junction.On the other hand, the conversion in the coaxial transition zone 11 generates two modes at the same time. TMn which will hybridize with the two modes TEnh, TEnV to create two optimal HEn modes in order to minimize the counter-polarization of the 400 horn.

[0044] The modes TEnh, TEnV are then propagated in the first four rectangular branches 2a via the first four output ports 14 in the form of two symmetrical TEi0 modes, before being received by the corresponding second input ports 33 of the second orthomode junction 3, and recombined in the coaxial output waveguide 31 to provide the sum channel S. Indeed, as the first four rectangular branches 2a are oriented so that their length is parallel with the longitudinal axis A, the TEi0 modes generated in two opposite rectangular branches 2a are in phase and symmetrical with respect to a plane perpendicular to the longitudinal axis A.The orientation of the first four rectangular branches 2a in rectangular guides has the advantage of filtering the TEM mode coming from the coaxial guide 120 to the S channel and thus allows better isolation of the S channel to the A channel since this TEM mode is fully transmitted to the guide 120 via the annular slot 10.

[0045] The adaptive irises 21, associated with the various successive cylindrical bearings of the tube 122, whose diameters decrease from upstream to downstream, allow the impedance adaptation of the TEi0 modes to the TEn modes between the cylindrical guide 122 and the rectangular branches 2a.

[0046] 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 orthomode junction 1.

[0047] Finally, the rectangular waveguide 152 allows the difference A channel used for tracking to be extracted in the form of TEi0 mode.

[0048] Compared with prior art devices, the mode extractor 500 described herein eliminates any possibility of resonance thanks to the multimode and broadband nature of the first orthomode junction 1, which cannot trap the coupled energy between the modes. The proposed architecture is also very compact compared to existing devices, while operating over a much wider frequency band.

[0049] An isolation of 60dB is obtained between channels A and S over a frequency range from 17.3GHz to 31 GHz and it is possible not to use filters on the first four side branches to protect channel A from the power emitted in the transmission bandwidth Tx on channel S.

[0050] In this same frequency band, the reflection coefficients of the entire mode extractor 500, consisting of the first orthomode junction 1 and the second orthomode junction 3, remain below -20dB on the sum channel S and those The difference A channel is around -15dB between 17.3GHz and 21.2 GHz, which is a clear improvement over the previous art.

[0051] Furthermore, the mode extractor configuration proposed in this description can be modified by replacing the second orthomode junction 3 with another junction to absorb phase imbalances between the first branches 2a, directing them towards loads. In particular, the use of magic tees (or hybrid tees) with loads on their difference channel makes it possible to compensate for imbalances caused by length differences due to machining between the first branches 2a and thus to avoid the occurrence of resonances. Second embodiment

[0052] Figure 6 illustrates a mode 500 extractor device according to a second embodiment. The mode 500 extractor device according to the second embodiment comprises a first orthomode junction 1 similar to that of the first embodiment, but this junction is connected to a second junction 3, which is a tourniquet junction 4.

[0053] The turnstile junction 4 includes an output waveguide 41 extending downstream along the longitudinal axis A from an upstream end 44, located towards a second output port 411 and four input ports 43 arranged in a cross orthogonally to the longitudinal axis A and each connected orthogonally to a second rectangular branch 2b and to the upstream end 44 of the output waveguide 41. The turnstile 4 also includes a coaxial output 42 which extends upstream from the upstream end 44, i.e. a coaxial waveguide protrudes from the turnstile 4 opposite the output waveguide 44. Unlike an orthomode junction, the rectangular input ports 43 are arranged so that their shorter sides are parallel to the longitudinal axis A. The second rectangular branches 2b are therefore at 90° to the first rectangular branches 2a placed opposite them.A twisted waveguide 60, inclined at 45°, connects each first and second rectangular branches 2a, 2b opposite each other. For a first pair of diametrically opposed rectangular branches 2a, 2b, the twisted waveguides 60 are inclined at 45° in a positive direction with respect to the longitudinal axis A, while another pair comprising the other diametrically opposed branches 2a, 2b comprises two twisted waveguides 60 inclined at 45° in a negative direction with respect to the longitudinal axis A. Preferably, the outer perimeter of the second rectangular branches 2b decreases discretely in the vicinity of a twisted waveguide 60.

[0054] Furthermore, an intermediate turnstile 5 is placed between the orthomode junction 1 and the turnstile junction 4, the intermediate turnstile 5 comprising four T-links 52, each being orthogonally connected to a second rectangular branch 2b and comprising a main guide 521 perpendicular to the second rectangular branch 2b and a lateral branch 522 integrated into the second rectangular branch 2b in its length and extending parallel to the longitudinal axis A. Each T-link 54 connects a second rectangular branch 2b to an intermediate inlet port 53, rectangular and arranged in a cross orthogonal to the longitudinal axis A, similarly to the turnstile junction 4.

[0055] Optionally, each respective main guide 521 of a T-link 52 includes an inductive matching iris 531 positioned perpendicular to the respective main guide 521 and each respective side branch 522 of a T-link 52 includes at its end closest to the turnstile 4 a capacitive matching iris 532 positioned perpendicular to the respective side branch 522, the inductive matching irises 531 and the capacitive matching irises 532 being configured to optimize the performance of the T-links 52.

[0056] Preferably, four successions 6 of capacitive matching iris 61 are placed between two sections of a second rectangular branch 2b, downstream of the T-link 52 and upstream of the rectangular input port 43 of the turnstile junction 4. The successions 6 of capacitive matching iris 61 are configured to constitute bandpass filters, advantageously with a bandwidth of 17.3 GHz to 21.2 GHz.

[0057] The use of twisted waveguides 60 thus allows the use of an orthomode junction 1 followed by two twisted-loop junctions 4 and 5, which makes it possible to duplex the K7 Ka bands and create circular bias. The twisted-loop junction 4 also allows, thanks to its coaxial output 42, the extraction of parasitic TEM modes generated by manufacturing defects in the filters, defects which cause phase imbalances between the first four and second branches 2a, 2b. These phase imbalances can lead to the appearance of resonances on the S channels. Advantageously, these parasitic modes are sent to a load by the coaxial output 42, which prevents the appearance of these resonances. Since the first orthomode junction 1 does not allow these TEM modes to pass through, no parasitic interaction is possible with the TEM mode of the difference channel A.

[0058] The invention described herein makes it possible to achieve an isolation of the order of 100dB between the two sum S and difference A channels, while widening the bandwidth up to 60% on the S channel and 20% on the difference A channel.

Claims

1. Demands Mode extractor device (500) of an electromagnetic signal traveling 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 orthomode junction (1) comprising: - a central core (121) extending along the longitudinal axis A from a first inlet port (111) to a free downstream end (15) and - a first coaxial waveguide (120) comprising a first tube (122) containing air surrounding the central core (121) and extending along the longitudinal axis A from the first inlet port (111) to a coaxial transition zone (11), the first coaxial inlet waveguide (120) being configured to be connected to an electromagnetic field collection antenna (200) via the first inlet port (111), the outside diameter of the first tube (122) decreasing in steps from upstream to downstream to the coaxial transition zone (11); - the coaxial transition zone (11) comprising a second tube (12) surrounding the central core (121) and extending from the first tube (122) to a third tube (13), the diameter of the central core (121) in the coaxial transition zone (11) being less than the diameter of the central core (121) in the first coaxial waveguide (120) so as to form a circular groove (10) opening upstream into the first tube (122) and downstream into the second tube (12), the third tube (13) extending coaxially from the second tube (12) to a second coaxial waveguide (140), the third tube (13) having an outer diameter less than the diameter of the second tube (12) and an inner diameter greater than the diameter of the central core (121); - the second coaxial waveguide (140) extending from the coaxial transition zone (11) to a downstream end (15) and comprising a dielectric (141) surrounding the central core (121), the dielectric (141) having an outside diameter equal to the inside diameter of the third tube (13), an upstream end of the dielectric (141) being in contact with a downstream end of the third tube (13); - four first rectangular exit ports (14), orthogonal to the longitudinal axis A and arranged in a cross on either side of the area coaxial transition (11) such that their longer sides are parallel to the longitudinal axis A; - a waveguide (150), comprising a cylindrical part (151) extending upstream from the end (15), so as to surround a part of the second coaxial waveguide (140), a rectangular waveguide (152) and a rectangular waveguide section (153) extending perpendicularly to the longitudinal axis A from the cylindrical part (151) diametrically opposite to each other and on either side of the end (15), an outer perimeter of the rectangular waveguide (152) increasing in steps with the distance to the longitudinal axis A and a length of the rectangular waveguide (152) being greater than a length of the rectangular waveguide section (153);- four first rectangular branches (2a) joined to four second rectangular branches (2b), each of the first rectangular branches (2a) being connected orthogonally to one of the first rectangular output ports (14) and comprising an adaptive iris (21) adjacent to this first output port (14); - a second junction (3, 4) comprising an output waveguide (31, 41) extending along the longitudinal axis A from an upstream end (34, 44), located opposite the downstream end (15), to a second output port (311, 411) and four second rectangular input ports (33, 43) arranged in a cross orthogonally to the longitudinal axis A, each connected orthogonally to one of the four second rectangular branches (2b) and to the upstream end (34, 44) of the output waveguide (31, 41).

2. Mode extractor device (500) of an electromagnetic signal according to claim 1, wherein the coaxial transition zone (11) comprises irises (113) configured to match the impedance of a transverse electromagnetic mode between the first coaxial waveguide (120) and the second coaxial waveguide (140).

3. Mode extractor device (500) of an electromagnetic signal according to any one of claims 1 or 2, wherein the second junction (3) is an orthomode junction, the output waveguide (31) being a coaxial waveguide and the four second input ports (33) being arranged so that their greatest length is parallel to the longitudinal axis A.

4. Mode extractor device (500) of an electromagnetic signal according to any one of claims 1 or 2, wherein: - the second junction (3, 4) is a turnstile junction (4), further comprising a coaxial output (42) extending from an upstream end (44) upstream; - each second rectangular branch (2b) being joined to a first rectangular branch (2a) by means of a respective twisted waveguide (60) inclined at 45° with respect to the first and second rectangular branches (2a, 2b);the mode extractor device (500) also comprising an intermediate turnstile junction (5) placed between the orthomode junction (1) and the turnstile junction (4), the intermediate turnstile junction (5) comprising: - four T-links (52), each being orthogonally connected to a second rectangular branch (2b) and comprising a main waveguide (521) perpendicular to the second rectangular branch (2b) and a lateral branch (522) integrated into the second rectangular branch (2b) along its length and extending parallel to the longitudinal axis A; - four rectangular intermediate input ports (53) arranged in a cross, orthogonal to the longitudinal axis A and each connected to a second rectangular branch (2b) by a T-link (52); - an intermediate waveguide (51) with a square or circular cross-section.

5. Mode extractor device (500) according to claim 4, comprising four successions (6) of capacitive matching irises (61) configured to constitute bandpass filters, each of the successions (6) being respectively placed between two sections of a second rectangular branch (2b), downstream of the T-link (52) and upstream of the inlet port (43) of the turnstile junction (4).

6. Mode extractor device (500) according to claim 5, wherein the successions (5) of capacitive matching iris (51) are configured to form bandpass filters having a bandwidth of 17.3 GHz to 21.2 GHz.

7. A mode-extracting device (500) according to any one of claims 4 to 6, wherein each respective main guide (521) of a T-link (52) comprises an inductive matching iris (531) positioned perpendicular to the respective main guide (521) and each respective side branch (522) of a T-link (52) comprises at its end closest to the tourniquet link (4) a capacitive matching iris (532) positioned perpendicular to the respective lateral branch (522), the inductive matching irises (531) and the capacitive matching irises (532) being configured to optimize the performance of the T links (52).

8. Mode extractor device (500) according to any one of claims 4 to 7, wherein the coaxial output (42) of the turnstile junction (4) is sized to extract spurious Transverse Electromagnetic TEM modes from the electromagnetic signal received by the turnstile junction (4) and the output waveguide (41) is sized to extract the Transverse Electromagnetic TEM mode from the electromagnetic signal received by the turnstile junction (4).

9. Mode extractor device (500) according to any one of claims 1 to 8, wherein the rectangular waveguide (152) of the orthomode junction (1) is sized to extract the Transverse Electric mode TEi0 from the electromagnetic signal received by the first orthomode junction (1).

10. Transmitting / receiving station (100) comprising an antenna (200) connected to a mode extractor device (500) according to any one of claims 1 to 9.