Patent Grant
11476553
This application claims priority to foreign French patent application No. FR 2004878, filed on May 15, 2020, the disclosure of which is incorporated by reference in its entirety.
The invention lies in the field of microwave transmissions, and relates more particularly to an orthomode transducer used to transmit two signals with orthogonal polarizations.
Although the proposed solution is particularly useful in the field of antenna sources, and in particular satellite antennas, it is not limited to these applications, and the orthomode transducer according to the invention may also be used for other devices, such as for example for producing microwave filters or duplexers.
In order to maximize their spectral efficiency, satellite-based transmission systems generally use polarization diversity, which consists in transmitting two orthogonally polarized signals on the same frequency band (for example a vertical polarization and a horizontal polarization, or a right-hand circular polarization and a left-hand circular polarization). When the polarizations between the two signals are perfectly orthogonal, the signals may be recovered independently, thereby making it possible to transmit or to receive two signals simultaneously in the same frequency band, or else to transmit and to receive simultaneously in the same frequency band, from a single antenna.
In theory, the decoupling between the two signals is infinite, thereby allowing them to be perfectly dissociated. In practice, asymmetries in the transmission equipment create an angular factor in the electric fields. In this case, a subcomponent of each polarization is coincident with the cross polarization, thereby leading to coupling phenomena between the signals. Those skilled in the art therefore take care to ensure that the two orthogonally polarized signals are transmitted with the greatest possible decoupling.
Orthomode transducers, or signal duplexers (also known by the name orthogonal mode transducer, or OMT) are devices belonging to the power supply chain of an antenna, in particular of a satellite antenna.
Numerous telecommunications satellites are equipped with an antenna array, consisting of a large number of transmission chains such as the one shown in
The antenna array on board satellites may comprise several tens of transmission chains, and therefore the same number of orthomode transducers. The bulk and the mass of these devices are therefore highly decisive elements when designing satellite antennas.
In the remainder of the description, and in order to simplify understanding of the applicable physical phenomena, the explanations are given considering the case of application of two signals injected onto the orthomode transducer for the purpose of being orthogonally polarized and combined and then transmitted by the source of the satellite antenna. However, the invention is applicable identically in the case of two signals with orthogonal polarizations and received from the source of the satellite antenna and transmitted and split by the orthomode transducer, or in the case in which one signal is transmitted and the other one is received.
Orthomode transducers have a square central core that is configured so as to allow the transmission of a first signal in a TE10 propagation mode, in which the electric field of the signal is linear and vertical, and a second signal in a TE01 propagation mode, in which the electric field of the signal is linear and horizontal. The two signals are then orthogonally polarized and may be transmitted simultaneously. The central core may be rectangular in order to propagate signals in separate frequency bands. Likewise, the signals may be transmitted with circular polarizations by combining for example a coupler with the orthomode transducer, such that each signal is transmitted in a first mode, on the one hand, and in delayed and phase-offset form in a second mode, on the other hand. The resultant electric field is then rotating, thereby creating a circularly polarized signal.
Several different structures of orthomode transducers are known from the prior art.
The primary waveguide is connected, at a first side, along its longitudinal axis zz′, to a source, a radiating element matching the waveguide and free space. The primary waveguide 201 is connected to two guided access means 202 and 203 via which the two signals to be transmitted are injected. The junctions between the guided access means and the primary waveguide are formed at the same level of the primary waveguide, in a plane xy orthogonal to the axis zz′, through slots produced in the middle of orthogonal walls of the primary guide, with the result that signals injected via the two guided access means are combined with orthogonal polarizations in the primary waveguide before being transmitted to the source (and by contrast, allowing the orthogonally polarized signals to be extracted from each of the access means). The back of the primary waveguide 201 along the longitudinal axis zz′ may be connected for example to other access means for injecting signals in a separate frequency band.
As shown in
The signal injected via the guided access means 203 propagates within the primary waveguide 201 with the propagation mode TE01, that is to say that it is linear and horizontal. Within the primary waveguide, the electric fields are not perfectly aligned. These slight distortions are linked to the sensitivity of the electric field to the asymmetries present on a centred access means, and have the effect of producing coupling phenomena between the two orthogonally polarized signals.
Furthermore, a small portion of the signal injected via the access means 203 propagates into the guided access means 202. Since the electric field is always perpendicular to the support, it rotates while entering the guided access means 202. Residuals of the signal transmitted on the access means 203 are then encountered on the guided access means 202 with the same polarization as the signal transmitted on this access means (vertical linear), thereby causing additional stray coupling phenomena. For this reason, the decoupling generally achieved using an orthomode transducer with two branches is of the order of −20 dB. This level of decoupling may prove to be too poor for a certain number of applications, such as for example for satellite antennas, where losses linked to decoupling translate into a degradation in the link budget and therefore in achievable throughputs.
One known way of improving decoupling between the paths of an orthomode transducer with two guided access means is described in patent EP 2,202,839 B1 and shown in
This solution makes it possible to achieve high levels of decoupling, but is difficult to implement and bulky.
Another way of improving decoupling of an orthomode transducer with two access means is shown in
Orthomode transducers with four branches are also known from the prior art, making it possible to achieve greater decoupling than those with two branches. Such an orthomode transducer is shown in
The signal intended to be vertically polarized is injected onto the primary waveguide 301 from the guided access means 303 and 305, which are opposite one another with respect to the primary waveguide 301. The signals injected from the two guided access means are identical, synchronized, in-phase and have the same power level. They then combine constructively in the primary waveguide, and the signal propagates in TE10 mode. Likewise, the second signal, intended to be horizontally polarized, is injected synchronously and in-phase onto the primary waveguide 301 from the guided access means 304 and 306, which are opposite one another with respect to the primary waveguide 301. In this case too, the two injected signals combine constructively, and the signal propagates in the primary waveguide in TE01 propagation mode.
The symmetry of the orthomode transducer with four branches means that the electric field lines are more rectilinear than in a transducer with two branches.
In the same way as in the waveguide with two access means, a portion of the signal injected from the guided access means 303 is encountered in the guided access means 302 with an electric field 310 that is pivoted by 90° and therefore horizontally polarized. Likewise, a portion of the signal injected from the guided access means 305 is encountered in the guided access means 302 with an electric field 311 that is pivoted by 90° and therefore horizontally polarized. Since the signals are injected in-phase from the guided access means 303 and 305, the electric field 310 and the electric field 311 of the residuals of these signals transmitted in the guide 302 are then in phase opposition (180°). They combine destructively, and the residuals of the signals injected via the guided access means 303 and 305 encountered in the guided access means 302 vanish. The principle is the same in each of the waveguides 302 to 305.
The symmetry properties of orthomode transducers with four branches therefore make it possible to obtain a perfectly linear electric field, the cross polarization naturally vanishing in the cross access means. They generally exhibit high levels of decoupling, of the order of −40 dB.
However, generating two identical and in-phase signals for each polarization introduces upstream complexity since it is then necessary to duplicate the generation of the signals, the signals transmitted to one pair of access means having to be perfectly identical and synchronized. The orthomode transducer having four independent access means is also not optimal in terms of compactness.
As an alternative, the guided access means used to inject a given signal may be combined in pairs, taking care that the paths to each injection point are of the same length so that the signals are injected simultaneously and in-phase. The combination circuits are then complex, all the more so since the two guided access means are interwoven, and require a large number of elementary connection components, thus increasing dispersion. The performance ultimately obtained is limited, and ohmic losses are significant, for a bulky and heavy device.
One object of the invention is therefore to describe an orthomode transducer having a high level of decoupling, that is both easy to implement and compact.
To this end, the present invention describes an orthomode transducer for transmitting a first signal and a second signal in orthogonal propagation modes. The orthomode transducer comprises:
a primary waveguide with a square or rectangular cross section, two guided access means having firstly a free end via which the first signal and the second signal are respectively injected or recovered, and secondly two arms connected to the primary waveguide.
Each guided access means comprises a junction configured so as to connect the free end to the two arms of the guided access means, the two arms of each guided access means being connected to the primary waveguide at two off-centred locations on one or more sides of the primary waveguide, symmetrically about an axis of symmetry of the primary waveguide.
Advantageously, the connection between the primary waveguide and the two arms of a guided access means comprises the two corners of the same side of the primary waveguide.
According to the embodiment of the orthomode transducer according to the invention, the junction of each guided access means is configured such that the signals transmitted on the two arms of a guided access means are in phase or in phase opposition depending on their propagation mode in the primary waveguide.
Advantageously, the two arms of the same guided access means have substantially identical dimensions.
Advantageously, the guided access means are arranged symmetrically about an axis of symmetry of the primary waveguide.
In one embodiment of the described orthomode transducer, each guided access means comprises a particular junction chosen from among an E-plane T-junction and an H-plane T-junction, and two particular arms.
In one alternative embodiment, the two guided access means comprise the same junction in the form of a magic T-junction whose lateral ports are connected to a common pair of arms, the first and the second signal being transmitted via two separate ports of the magic T-junction.
The described invention also relates to a device for transmitting the signals with orthogonal circular polarizations. It comprises:
Lastly, the invention addresses a transmission chain for a satellite antenna comprising a source connected to an orthomode transducer as described above, or a device as described above for transmitting signals with orthogonal circular polarizations.
The invention will be better understood and other features, details and advantages will become more clearly apparent from reading the following non-limiting description, and by virtue of the following appended figures, given by way of example, among which:
Identical references are used in different figures when the elements that are denoted are identical.
Although they exhibit good performance in terms of decoupling, orthomode transducers with four branches from the prior art are difficult to implement and bulky. The invention therefore naturally targets orthomode transducers with two branches.
It is based on the properties of the electromagnetic field, which is oriented perpendicular to the metal walls of the waveguide.
The invention proposes to inject the signals not via access means centred on the sides of the cavity of the primary waveguide of the orthomode transducer, but via off-centred access means located on the edges of one or more sides of this primary waveguide. With just one off-centred injection point, the propagation mode in the waveguide is not controlled, since it is not certain that the electric field in the waveguide will be perfectly linear and oriented in the desired direction. The invention proposes to inject each signal not via one but via two off-centred access means on one or more sides of the primary waveguide, and to do so symmetrically about an axis of symmetry of the primary waveguide.
The junction 411 may also be an H-plane microwave T-junction, dividing the signal into two in-phase signals of the same power. In this case, the electric field of the signals (shown by the dotted arrows) at the output of the junction 411 is in-phase. The signal in the primary waveguide 401, resulting from the vector combination of the signals injected via the arms 412 and 413, is then horizontally polarized (TE01 mode, horizontal linear). The type of junction is therefore chosen depending on the desired propagation mode in the primary waveguide.
By injecting the same signal, in phase or in phase opposition, through two off-centred and symmetrical access means in the primary waveguide of an orthomode transducer, it is therefore possible to “force” the propagation mode of the electromagnetic wave. In the example in
Using arms having the same dimensions (same length, same width and same height) makes it possible to inject the signal into the primary waveguide synchronously and with the same power level. One simple means of obtaining arms of the same length is to arrange the entire guided access means symmetrically about the axis of symmetry xx′ of the primary waveguide 401.
The layout described in
In
In
In
The arms of a guided access means therefore do not necessarily meet the primary waveguide 401 in one of its corners, on the condition that the injection points into the primary waveguide are symmetrical about an axis of symmetry of the primary waveguide 401, such that combining the signals injected from the two arms generates a perfectly rectilinear electric field. However, the proximity of the corners improves the performance of the orthomode transducer according to the invention, since the joining slots between the access arms and the central waveguide create magnetic coupling (H field), positioning them in the corners optimizing the efficiency of this coupling.
It comprises a primary waveguide 501 with a square cross section, but the invention would also apply identically to a waveguide with a rectangular cross section, in the case of two injected signals operating in different frequency bands. The primary waveguide 501 extends along an axis zz′ in which a source for an antenna system may for example be located. It is designed to propagate signals in the two TE10 and TE01 fundamental modes in the one or more frequency bands under consideration.
A first guided access means 510 is configured so as to inject the first signal into the primary waveguide 501. It comprises a waveguide 511 having a free end via which the signal to be transmitted with vertical polarization is injected, a junction 512 configured so as to divide the first signal into two identical signals of the same power and in phase opposition, such as an E-plane T-junction, and two arms 513 and 514, connected firstly to the junction 512 and secondly to the same side of the primary waveguide in a manner off-centred and symmetrical about its axis xx′. The elements forming the guided access means 510 are dimensioned so as to allow the first signal (the electromagnetic field of which is shown by solid arrows in the figure) to propagate in a fundamental mode in the frequency band under consideration. They may be connected to the primary waveguide 501 through irises that perform impedance matching. The vector combination of the electric fields of the signals injected via the two arms 513 and 514 into the waveguide 501 forms the propagation mode of the signal in the waveguide, that is to say here TE10 mode, corresponding to vertical linear polarization.
In an identical manner, a second guided access means 520 is configured so as to inject the second signal into the primary waveguide 501, at the same level as the first guided access means. It comprises a waveguide 521, via which the signal is injected, connected to a junction 522, configured so as to divide the second signal into two identical signals of the same power and in phase opposition. The two outputs of the junction 522 open onto the arms 523 and 524. The two arms are respectively connected to the edges of the same side of the primary waveguide, symmetrically about its axis of symmetry yy′. The side of the waveguide that is chosen here is the side orthogonal to the one where the arms of the first guided access means are connected. However, in the orthomode transducer according to the invention, any other side could have been selected, since the final polarization of the signal depends on the combination of the positions where the signal is injected by the two arms and on the chosen junction type. The elements forming the guided access means 520 are dimensioned so as to allow the second signal (the electromagnetic field of which is shown by dotted arrows in the figure) to propagate in a fundamental mode in the frequency band under consideration. They may be connected to the primary waveguide 501 via slots provided with irises for the impedance matching. The vector combination of the electric fields of the signals injected via the two arms 523 and 524 makes it possible to form the propagation mode of the signal in the waveguide, here TE01 mode, corresponding to horizontal linear polarization.
The orthomode transducer according to the invention therefore makes it possible, from two access means 510 and 520, to combine two signals with the desired cross polarizations in the primary waveguide 501.
The electric field in the access means 510 evolves such that the vector combination of the signal injected in-phase through the arms 513 and 514 propagates in the primary waveguide in TE10 mode, that is to say vertically polarized. It is observed that the electric field is oriented far more precisely than in an orthomode transducer with two access means shown in
A portion of the energy injected from the guided access means 510 propagates in the arms 523 and 524 of the guided access means 520, where the electric field rotates so as to be oriented horizontally. The in-phase junction 522 (E-plane T-junction) then acts as a means for combining the signals in phase opposition. Since the position of the two arms is symmetrical about the axis of symmetry yy′ of the primary waveguide 501, the signals transmitted in the two arms are identical and of the same power. The orientation of the electric field means that they are in phase opposition (180°) in the access means 521. They therefore cancel one another out, and the residuals of the signal transmitted by the guided access means 510 and received in the junction 522 naturally vanish in the waveguide 521. There are therefore no or only few coupling effects caused by residuals of a signal in the guided access means for the cross polarization signal.
The phenomenon is the same in the other direction, where residuals of the signal transmitted by the access means 520 are in phase opposition in the arms 513 and 514. Their combination by the junction 511 in phase opposition means that the horizontally polarized signal vanishes at output. There are therefore no or only few coupling effects in this direction as well.
By virtue of the symmetry properties of the off-centred access means, the orthomode transducer according to the invention as shown in
This device has the advantage of being particularly simple and of occupying a volume close to 75% lower in comparison with orthomode transducers with four branches that are connected in pairs, such as the one shown in
Another advantage of the orthomode transducer according to the invention is that the bottom of the cavity of the orthomode transducer (the back of the primary waveguide along the axis zz′) remains free. It is therefore possible thereafter to add other access means for processing the polarizations of signals transmitted in another frequency band, or a load acting as termination of the primary waveguide.
Although the orthomode transducer according to the invention, in which each of the access means comprises a pair of separate arms, makes it possible to polarize signals with orthogonal linear polarizations, it may be combined with a coupler so as to circularly polarize the signals, in a manner comparable to what happens with orthomode transducers with two arms that are known from the prior art, such as the one shown in
Lastly, it may be contemplated to produce the orthomode transducer according to the invention through additive manufacturing (three-dimensional metal printing) for a low cost or through a milling technique, in only three parts 531, 532 and 533 shown in
Another embodiment of an orthomode transducer according to the invention is given in
To this end, the orthomode transducer comprises a device known to those skilled in the art, called magic T-junction. A magic T-junction is a three-dimensional microwave component with four ports: two lateral ports, a sum port and a difference port. It jointly performs the function of an E-plane T-junction and an H-plane T-junction, the lateral ports and the sum port forming the H-plane T-junction and the lateral ports and the difference port forming the E-plane T-junction.
The first access means to the primary waveguide is formed by a waveguide 603 having a free end via which the first signal is injected, and connected to the difference port of the magic T-junction. The two lateral ports of the magic T-junction are connected to two arms 610 and 611, which are themselves connected to the primary waveguide 601 via off-centred access means positioned on the edges of the same side of the primary waveguide, symmetrically about its axis of symmetry yy′.
The second access means to the primary waveguide is formed by a waveguide 604 having a free end via which the second signal is injected, and connected to the sum port of the magic T-junction. The arms of this access means are the arms 610 and 611 connected to the lateral ports of the magic T-junction, just like the first access means.
Using a magic T-junction makes it possible to be able to partition the arms between the two guided access means with orthogonal polarizations. The positioning of the access means makes it possible to obtain orthogonal propagation modes in the primary waveguide 601 with perfectly formed electric fields. Lastly, the positioning and the structure of the access means, associated with the magic T-junction, makes it possible to avoid coupling effects between the two signals with cross polarizations.
The waveguide according to the embodiment shown in
It is very simple to produce since it may be generated by additive manufacturing, or by milling requiring only the assembly of two parts.
The embodiments presented above for an orthomode transducer according to the invention make it possible to combine signals with orthogonal polarizations in a simple, space-saving and highly effective manner.
The orthomode transducer according to the invention has been described in the case of application of injecting two signals from the free ends of the guided access means into the primary waveguide. However, the invention applies identically to extracting signals from the primary waveguide into the two guided access means. In this case, the T-junctions act as means for combining the signals received by the arms from the primary waveguide. The invention also applies in the same way to injecting a first signal and simultaneously extracting a second signal with cross polarization.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004878 | May 2020 | FR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3715688 | Woodward | Feb 1973 | A |
| 11081766 | Wrigley | Aug 2021 | B1 |
| 20130307719 | Granet et al. | Nov 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 2 202 839 | Jun 2010 | EP |
| 835 575 | May 1960 | GB |
| 2 054 974 | Feb 1981 | GB |
| Number | Date | Country | |
|---|---|---|---|
| 20210359383 A1 | Nov 2021 | US |
