Wideband orthomode transducer

Abstract

An orthomode transducer and to a satellite transmission chain includes the orthomode transducer, for transmitting a first signal and a second signal in orthogonal propagation modes. The 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.

Claims

1. An orthomode transducer for transmitting a first signal and a second signal in orthogonal propagation modes, the orthomode transducer comprising: a primary waveguide with a square or a rectangular cross section and two guided access means comprising: a free end via which the first signal and the second signal are respectively injected or recovered; and two arms connected to the primary waveguide, wherein each guided access means of the two guided access means comprises a junction configured to connect the free end to the two arms of the respective guided access means, the two arms of each guided access means being connected to the primary waveguide at two off-centered locations on one or more sides of the primary waveguide, the two off-centered locations being symmetrical about an axis of symmetry of the primary waveguide.

2. The orthomode transducer according to claim 1, wherein the two-off centered locations where the two arms of each of said guided access means are connected to the primary waveguide comprise two corners of the same side of the primary waveguide.

3. The orthomode transducer according to claim 1, wherein the junction of each of the two guided access means is configured such that the signals transmitted on the pair of arms of the respective guided access means are in phase or in phase opposition depending on their propagation mode in the primary waveguide.

4. The orthomode transducer according to claim 1, wherein the two arms of the same guided access means have substantially identical dimensions.

5. The orthomode transducer according to claim 1, wherein the guided access means are arranged symmetrically about an axis of symmetry of the primary waveguide.

6. The orthomode transducer according to claim 1, wherein the junction of a first guided access means of said two guided access means defines one of an E-plane T-junction or an H-plane T-junction, wherein the junction of a second guided access means of said two guided access means defines one of an E-plane T-junction or an H-plane T-junction, wherein the two arms of said first guided access means are different than the two arms of said second guided access means.

7. The orthomode transducer according to claim 1, wherein the junction of each of the two guided access means is a common shared junction that defines a magic T-junction and wherein the two arms of the two guided access means share a common shared pair of arms, lateral ports of the common shared junction being connected to the common shared pair of arms, and the first and the second signal being transmitted via two separate ports of the magic T-junction.

8. A device comprising: the orthomode transducer according to claim 1, and a 90° coupler connected to the free ends of the guided access means of the orthomode transducer so as to circularly polarize the first and the second signal.

9. A transmission chain for a satellite antenna, the transmission chain comprising: the orthomode transducer according to claim 1, and a source connected to the orthomode transducer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIG. 1a shows, highly schematically, a transmission chain for an antenna, for example a satellite antenna,

(3) FIG. 1b shows, highly schematically, the components of an antenna array on board a satellite,

(4) FIG. 2a shows a three-dimensional view of an orthomode transducer with two branches according to the prior art,

(5) FIG. 2b describes the principle of polarizing signals in a waveguide with two branches,

(6) FIG. 2c shows an assembly for circularly polarizing and combining signals in an orthomode transducer with two branches,

(7) FIG. 2d shows the electric field of the signal injected onto the guided access means 203 of an orthomode transducer with two branches,

(8) FIG. 2e shows an assembly for improving the decoupling of an orthomode transducer with two branches,

(9) FIG. 2f shows an orthomode transducer with two offset branches,

(10) FIG. 3a shows a three-dimensional view of an orthomode transducer with four branches according to the prior art,

(11) FIG. 3b describes the principle of polarizing signals in an orthomode transducer with four branches,

(12) FIG. 4a roughly shows the electric field in the corner of a waveguide with a square or rectangular cross section,

(13) FIG. 4b schematically shows the physical principles applicable when injecting a signal via two access means located on the edges of one side of the primary waveguide,

(14) FIG. 4c shows a configuration for injecting a signal in an off-centred manner on the sides of a waveguide,

(15) FIG. 4d shows a configuration for injecting a signal in an off-centred manner on the sides of a waveguide,

(16) FIG. 4e shows a configuration for injecting a signal in an off-centred manner on the sides of a waveguide,

(17) FIG. 5a shows one embodiment of an orthomode transducer with two branches according to the invention,

(18) FIG. 5b shows the electric field of the signal injected onto the access means 510 of an orthomode transducer with two branches according to one embodiment of the invention,

(19) FIG. 5c is a three-dimensional depiction of an orthomode transducer according to one embodiment of the invention,

(20) FIG. 5d distinguishes between the various parts of an orthomode transducer according to one embodiment of the invention for manufacture through milling,

(21) FIG. 6a shows one embodiment of an orthomode transducer with two branches according to the invention,

(22) FIG. 6b distinguishes between the various parts of an orthomode transducer according to one embodiment of the invention for manufacture through milling.

(23) Identical references are used in different figures when the elements that are denoted are identical.

DETAILED DESCRIPTION

(24) 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.

(25) It is based on the properties of the electromagnetic field, which is oriented perpendicular to the metal walls of the waveguide.

(26) FIG. 4a roughly shows the direction of the electric field in the corner of a waveguide 401 with a square or rectangular cross section. Since the electromagnetic field is always perpendicular to the support, in the corner of the waveguide, it is inclined as a function of the distance to the two walls.

(27) 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. FIG. 4b schematically shows the physical principles applicable when injecting a signal via two access means located on the edges of the same side of the primary waveguide.

(28) FIG. 4b adopts the example of injecting a first signal into the primary waveguide 401 of an orthomode transducer through a guided access means 410, so that this signal propagates in TE10 mode (vertical linear). The solid arrows show the orientation of the electric field. The signal injected onto the guided access means 410 is split into two signals of the same power by a junction 411 acting as a means for splitting the signals. The junction is connected to two arms 412 and 413 of the same length. The junction may be for example an E-plane microwave T-junction, dividing the signal into two signals in phase opposition and of the same power. The arms of each access means are connected to the primary waveguide 401 via two off-centred slots located at the ends of the right-hand edge of the primary waveguide 401, symmetrically about the axis xx′. The electric fields thereby applied in the corners of the primary waveguide (represented by solid arrows) are not vertical in the corners. However, vector combination of these two injections gives the desired electric field, here a perfectly vertically polarized electric field.

(29) 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.

(30) 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 FIG. 4b, in which the arms 412 and 413 of the guided access means 410 are positioned in the corners of a vertical wall of the primary waveguide 401, the junction 411 splits the signal into two signals in phase opposition so as to vertically polarize the signal, or two in-phase signals so as to horizontally polarize it.

(31) 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.

(32) The layout described in FIG. 4b is not the only one possible for a guided access means with two arms in an orthomode transducer according to the invention. FIGS. 4c, 4d and 4e describe other configurations for injecting a signal in an off-centred manner on the sides of a primary waveguide 401.

(33) In FIG. 4c, the junction 421 is an E-plane T-junction, which generates two signals in phase opposition on the two arms 422 and 423, which inject the signals into the two corners of a horizontal side of the primary waveguide 401, symmetrically about the axis yy′. The propagation mode in the primary waveguide is therefore TE01 mode, that is to say horizontal linear polarization. Using a junction 421 configured so as to generate in-phase signals, such as an H-plane T-junction, the propagation mode that is obtained is TE10 mode, that is to say vertical linear polarization.

(34) In FIG. 4d, the two arms are connected to off-centred access means located on two opposing edges of the primary waveguide 401. The access means are always symmetrical about the axis xx′. The electric field evolves as in FIG. 4b, in TE10 mode, even though the injection points of the arms 432 and 433 into the primary waveguide are different from those of the arms 412 and 413 in FIG. 4b. By using an H-plane T-junction rather than an E-plane T-junction, the signal is horizontally polarized (TE01 mode).

(35) In FIG. 4e, the two arms are connected to the same horizontal side of the primary waveguide 401, and are off-centred symmetrically about the axis yy′, but without covering the corners. The electric field evolves in the same way as in FIG. 4c, even though the layout of the arms and their positioning with respect to the corners of the primary waveguide differ.

(36) 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.

(37) FIG. 5a shows one embodiment of an orthomode transducer with two branches according to the invention. The transducer is configured so as to transmit a first signal with a vertical linear polarization, and a second signal with a horizontal linear polarization.

(38) 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. FIG. 5a shows the orthomode transducer in a sectional view at the intersections with the guided access means, in a plane xy orthogonal to the axis zz′ in which the primary waveguide 501 extends.

(39) 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.

(40) 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.

(41) 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.

(42) FIG. 5b shows the electric field of the signal injected onto the access means 510 of an orthomode transducer with two branches according to one embodiment of the invention, in a sectional view in the plane xy at the intersection between the guided access means and the primary guide 501. The length and the direction of the arrows show the intensity and the direction of the electric field.

(43) 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 FIG. 2d, due to the symmetry of the access means with two branches: the decoupling between the polarizations is therefore greater.

(44) 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.

(45) 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.

(46) By virtue of the symmetry properties of the off-centred access means, the orthomode transducer according to the invention as shown in FIG. 5a makes it possible to improve decoupling performance by a few dB over orthomode transducers with two arms such as the one shown in FIG. 2a, by generating perfectly linear electric fields and by blocking the propagation of the signal from one guided access means to another by design. This orthomode transducer is furthermore more wideband than orthomode transducers with two branches from the prior art, since its symmetry properties mean that it constructs polarization alignments that are always well-oriented, independently of the frequency band under consideration. This is not the case with orthomode transducers with two arms, which are not symmetrical and therefore have to be optimized for a given frequency band.

(47) FIG. 5c is a three-dimensional depiction of an orthomode transducer according to one embodiment of the invention. It is possible here to see the primary waveguide 501, which has connected to it a first access means 510, for injecting the signal transmitted with a polarization, and a second access means 520, for injecting the signal transmitted with the cross polarization.

(48) 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 FIG. 3a, this being one of the desired aims of the invention. This compactness is important, notably for producing antenna arrays involving a large number of orthomode transducers arranged in a limited mesh. The reduction in mass is proportional thereto, this also being highly beneficial for producing antenna arrays embedded in the payload of satellites.

(49) 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.

(50) 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 FIG. 2c.

(51) 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 FIG. 5d, the part 533 representing a step for matching the orthomode transducer to the source of the antenna.

(52) Another embodiment of an orthomode transducer according to the invention is given in FIG. 6a. This embodiment still involves a primary waveguide 601, but the guided access means for the two signals with cross polarizations are injected via the same pair of arms.

(53) 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.

(54) 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′.

(55) 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.

(56) 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.

(57) The waveguide according to the embodiment shown in FIG. 6a makes it possible to obtain very high levels of decoupling, of the order of −70 dB, with an extremely compact device. In comparison with the embodiments presented above, it however operates on a reduced frequency band, given by the operating band of the magic T-junction.

(58) It is very simple to produce since it may be generated by additive manufacturing, or by milling requiring only the assembly of two parts. FIG. 6b shows the two parts 621 and 622 required to produce an orthomode transducer according to the invention through milling.

(59) 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.

(60) 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.