EP3499636A1

EP3499636A1 - A rotator device for connecting non-aligned waveguides and a method of manufacture thereof

Info

Publication number: EP3499636A1
Application number: EP17306760.4A
Authority: EP
Inventors: Armel Le Bayon; Denis Tuau
Original assignee: Nokia Shanghai Bell Co Ltd
Current assignee: Nokia Shanghai Bell Co Ltd
Priority date: 2017-12-13
Filing date: 2017-12-13
Publication date: 2019-06-19
Anticipated expiration: 2037-12-13
Also published as: EP3499636B1

Abstract

A rectangular waveguide rotator device for connecting first and second waveguides, the first and second waveguides being arranged at an angle to each other is disclosed. The rotator device comprises: at least one rotator portion, the at least one rotator portion comprising a passage formed by outer walls comprising two longer walls connected by two shorter end walls; the at least one rotator portion comprising a ridge protruding from each of the longer side walls across a width of the longer side walls, the ridge lying between a first and a further section of the rotator portion; the first and further sections of the rotator portion being configured such that they are at an angle with respect to each other, one section being rotated through an angle with respect to the other.

Description

FIELD OF THE INVENTION

The invention relates to the field of rotator device for connecting non-aligned waveguides and a method of manufacture thereof.

BACKGROUND

Devices for rotating the polarisation of an electromagnetic signal transmitted through rectangular waveguides find their application in many microwave systems where polarization rotation is required such as in microwaves links. Microwave links are widely used for connectivity in modern digital IP networks. Often the ODU (OutDoor Unit) is directly mounted to a microwave antenna. A 45° or a 90° rotator may be required to allow the ODU to be mounted in the same orientation whatever the vertical or horizontal antenna polarization.
Microwaves components are generally machined with a high accuracy. Several parts may be mounted end to end and the final radioelectric result needs to be in line with stringent customer specifications. Furthermore, it is desirable for the different components to be simple and compact as this not only provides reduced costs but also reduces the risk of machining dimensions exceeding permitted tolerances.
One simple solution is to link two waveguides with different angles is by using one or several step twists. These are formed from straight rectangular waveguide twisted about their common axis at their junction surface (see for example Wheeler and Schiebert, "Step-Twist Waveguide Components" IRE Transactions - Microwave Theory and Techniques, October 1955). To get high broadband performances, two or more steps are necessary and, of course, the dimensions and the cost of the complete device increases.
A second solution is disclosed in Ruiz-Cruz et al. "Multi-Section Bow-Tie Steps for Full-Band Waveguide Polarization Rotation", IEEE Microwave and Wireless Component Letters Vol. 20, n07 July 2010. This provides a similar solution to the previous one but in this case each step twist has a bow-tie shape. The result is a more compact rotator. However, it is more complex to machine requiring several parts. Furthermore, several rotational steps are required to achieve the required performances so that the rotator is manufactured from several pieces with a total higher cost.
It would be desirable to provide a compact rotator manufactured by a simple machining process and with a high radioelectric performance.

SUMMARY

A first aspect of the present invention provides a rectangular waveguide rotator device for connecting first and second waveguides, said first and second waveguides being arranged at an angle to each other, said rotator device comprising: at least one rotator portion, said at least one rotator portion comprising a passage formed by outer walls comprising two longer walls connected by two shorter end walls; said at least one rotator portion comprising a ridge protruding from each of said longer side walls across a width of said longer side walls, said ridge lying between a first and a further section of said rotator portion; said first and further sections of said rotator portion being configured such that they are at an angle with respect to each other, one section being rotated through an angle with respect to the other.
The inventors of the present invention recognised that although the conventional form of two waveguides twisted about an angle to provide a desired rotation as is shown in figure 7 provides effective polarisation rotation, such a device suffers from a lack of compactness. They have addressed this by in effect allowing the two angled adjoining portions of waveguide to overlap, by rotating one part of the cross section of the waveguide with respect to the other part. Thus, the substantially parallel longer side wall are angled at a point towards the middle of each of the walls, such that the waveguide comprises two angled sections. At the point where the two angled sections intersect, a ridge is provided that protrudes into the rotator portion. The ridge improves the performance of the rotator device by lowering the cut-off frequency of the dominant mode and raising the cut-off frequency of the next higher order mode.
The rotator is arranged so that the longer side walls are substantially parallel with each other and are bent or angled towards a mid-point of the length of the wall. For the sake of the application walls are considered to be substantially parallel, if the difference in the distance between the walls at each end is less than 10% of the median distance between the walls. The angle in the longer side walls and the location of the protrusion or ridge occurs towards the centre of the waveguide, so that the length of the longer side walls in each section are the same or differ from each other by less than 25% of the median length of a section's side wall.
Arranging the rotator device, so that at least some of the rotation of the polarisation of the wave occurs within a section rather than between adjacent sections allows the size of the rotator device to be reduced and a more compact device provided.
In some embodiments a cross section of said rotator portion is rotationally symmetrical about a centre of said rotator portion, when cut through a line passing through a centre of said rotator portion and joining said two ridges.
The rotator portion is configured such that one section of it is bent with respect to the other section and there are ridges between the two sections which protrude from the long side walls into the passage of the rotator portion. This results in the cross-section of the rotator portion being rotationally symmetrical about a centre of the rotator portion when cut along the line that joins the two ridges and passes through a centre of the rotator portion.
In some embodiments, the rotator device may comprise a single rotator portion while in other embodiments it may comprise a plurality of rotator portions, said first and further sections of each rotator portion being successively rotated with respect to said first and said further sections of a next rotator portion.
One rotator portion may be sufficient to provide the polarisation rotation of the transmitted wave that is required for it to travel between the two angled waveguides. However, where the angle between the two waveguides is large or where the frequency band that is supported by the waveguides is relatively wide, then it may be more advantageous if the rotation is done in a number of steps using a plurality of rotator portions arranged one after the other within the rotator device. Each rotator portion will be successively rotated with respect to the previous one. In this regard, the first section will be rotated in one direction while the further section will be rotated in the other. The final result being that the polarisation of the wave travelling through the rotated device is rotated through an angle that is equal to the angle between the input and output waveguides that the rotator device connects.
Although the ridges may have an offset with respect to each other in different portions, in some embodiments said ridges of each of said plurality of rotator portions are aligned.
In some embodiments, each of said at least one rotator portion is located between two adjacent portions, said adjacent portions having a substantially rectangular cross section, one being aligned with said first section and the other being aligned with said further section.
In some cases, the rotator portions may be located adjacent to each other while in other embodiments there are intermediate or adjacent portions located on either side of each rotator portion and these are substantially rectangular in shape and aligned with one of the first or further sections. These adjacent portions do not have a bend such that the longer side walls are substantially straight. They may in some embodiments have a ridge extending across them while in other embodiments, there may be no ridge. Where there is a ridge in the adjacent portion, then it will be aligned with the ridge in the rotator portion.
In some embodiments, the adjacent portions are thinner than the rotator portions.
It is desirable to provide a compact rotator device, and as the rotator portion provides the rotation of the polarisation then the length of this section may need to have a certain size for this to be effective, the adjacent portions can be thinner and the device will still function well.
In some embodiments, said rotator device comprises adjacent portions at each end of the device, one of said end adjacent portions being configured to connect to said first rectangular waveguide, and the other of said end adjacent portions being configured to connect to said second waveguide.
The adjacent portions not having a bend in them are substantially the same shape as the waveguides to which the rotator device is to connect and thus, there may be adjacent portions at either end of the rotator device arranged to connect with the waveguides. In some embodiments the adjacent portions align with the waveguide to which they connect while in others one or both of them is offset to the waveguide providing the first rotational step. The angle to which they are offset may be the same or less than the angle between the first and further sections.
Where the rotator device rotates the wave in a single twist then the rotator device will comprise one rotator portion with two adjacent portions, on either side these adjacent portions connecting to the waveguides.
In some embodiments, said first waveguide is a different size to said second waveguide, and an end of said rotator device configured to connect with the larger waveguide comprises a connecting portion and two linking portions for linking said connecting portion to a closest rotator portion, a first of said two linking portions adjacent to said connecting portion comprising a first section aligned with said adjacent connecting portion and a further section aligned with a first section of said closest rotator portion, and a second of said two linking portions comprising a substantially rectangular cross section aligned with said first section of said adjacent rotator portion.
Generally, the two waveguides being connected by the rotator device have the same dimensions, but in some embodiments they may have different dimensions and in which case there may be a linking or transition portion that enables the transition from one size waveguide to the other, this transition portion may also provide some rotation. In conventional systems where there are different sized waveguides to be connected there is generally a separate transition portion for transitioning one waveguide to the size of the other. By combining the rotating and transition devices within a single device and providing some rotation within the linking transition portion a smaller more compact overall device is provided.
In some embodiments, a length and width at a widest point of said rotator portions are substantially the same as a length and width of said rectangular waveguides.
Although the dimensions of the rotator device may vary, in some embodiments, they are substantially the same as the waveguides to which they connect, in that the longest length and largest width of the passage within the rotator device are the same or are within 10% of the corresponding lengths and widths of the waveguides to which they are connected. Where the cross section does not vary greatly through the device, the machining is made simpler and is able to be performed within a single metallic piece which leads to a cost effective and robust device.
In some embodiments, said at least one rotator portion comprises curved corners between said longer side and shorter end walls.
Furthermore, it has been found that providing the rotator portion with curved corners and indeed providing the adjacent portions and any other connecting portions with curved corner walls makes them easy to machine and does not unduly affect performance.
In some embodiments, said ridges of said at least one rotator portion comprise a substantially triangular cross section.
Although the ridge may have a number of forms provided that it protrudes into the passage and disrupts some modes of the polarisation, in some embodiments it comprises a substantially triangular cross-section.
The ridge which may have a symmetric or a non-symmetric shape, acts to lower the cut-off frequency of the dominant mode and raise the cut-off frequency of the next higher order mode.
In some embodiments, the width of the at least one rotator portion at its widest point is between a fifth and a half of its length.
Although the rotator portion may have a number of forms, in some embodiments it is found that the dimensions outlined above provide a device which is particularly effective for rotating microwaves. It should be noted that the adjacent portions will have the same restriction on dimensions as the rotator portion.
In some embodiments, an angle between said first and further sections of said at least one intermediate section is between 10° and 25°.
It has been found effective to have an angle of between 10° and 25° between the first and further sections. Any larger angle and the rotation is not so effective. Thus, where the rotation needs to be through a larger angle than this, then several rotator sections in series may need to be used to provide the desired overall rotation.
Although the two waveguides being connected by the rotator device may be arranged at any angles with respect to each other, in some embodiments they are arranged at an angle of 45°.
In microwave antenna horizontal and vertically polarised waves may be received and transmitted and thus, it may be convenient for an outdoor box to be arranged with a waveguide half way between the two, at say 45°. In such a case a rotator device to provide the rotation from the vertical to 45° and a further rotator device from the horizontal to the 45° is required.
Although the waveguides may be configured to transmit a number of different waves, in some embodiments they are configured to transmit microwaves. Microwaves are generally transmitted along rectangular waveguides and their rotation using a rotator device according to embodiments is particularly effective.
A second aspect provides a microwave antenna comprising an antenna dish, a linking waveguide for transmitting at least one of horizontally polarised and vertically polarised waves, at least one outdoor unit comprising a waveguide port arranged at an angle of 45°, said microwave antenna further comprising at least one rotator device according to a first aspect, arranged between said linking waveguide and said at least one outdoor box.
Allowing the outdoor box to be arranged at a known angle is advantageous and thus, providing rotator devices that allow it to be arranged with its waveguide angled at 45°, provides an effective and compact solution for a microwave antenna. In some embodiments, the microwave antenna may have a linking waveguide for both horizontally polarised and vertically polarised waves and it may have two outdoor units, each comprising a waveguide port at an angle of 45°. In such a case there will be two rotator devices according to a first aspect arranged between the linking waveguide and the two outdoor boxes, one outdoor box treating the originally horizontally polarised waves and the other outdoor box treating the originally vertically polarised waves.
A third aspect provides a method of manufacturing a rotator device according to any preceding claim, said method comprising: machining in a metal block a substantially rectangular first passage to a first depth; continuing to machine a fraction of a cross section of said passage, such that said fraction of said first passage extends to a further depth; machining a substantially rectangular second passage in an opposing end of said block and at a corresponding position to said first passage to a second depth, said rectangular second passage being at an angle to said first passage and machining a fraction of said second passage to a further depth said fraction of said second passage overlapping in depth with a fraction of an other passage, said fraction of said other passage joining with said fraction of said passage and being at an angle therewith.
In some embodiments, said further depths overlap such that said first and further fractions meet to form a twisted mid section; wherein said machining of said fractions is done such that a ridge is provided between said two fractions.
In some embodiments said first depth and second depth are equal.
In some embodiments said substantially rectangular passages have rounded corners.
In embodiments where the rotator device comprises a single rotator portion, it may be machined from either side in two steps. Where there are additional rotator portions additional steps may be required and a machining tool with a lateral cutting edge may be required.
In some embodiments, the total length of the rotator is greater than half the longest depth that the first passage is machined to plus the longest depth that the second passage is machined to and less than the sum of their longest depths.
Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.
Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figure 1 shows an overview from the outside of a rotator being two rectangular waveguides;
Figure 2 schematically shows the construction of the rotator;
Figure 3 shows the dimensions of the rotator;
Figure 4 shows the performance of the rotator of an embodiment in the 7GHz frequency band where the length of the rotator of 21.64mm;
Figure 5 shows a rotator device having three twists according to an embodiment;
Figure 6 shows a microwave antenna according to an embodiment; and
Figure 7 shows a twisted waveguide according to the prior art.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided.
Embodiments provide a rotator device for rotating the polarisation of waves, such that two rectangular waveguides angled with respect to each other can be connected. The rotator device is designed so that it can be machined in one part and yet provides the performance of a rotator device formed of multiple parts. Furthermore, owing to the design of a bent waveguide portion, which in effect, squeezes two adjacent sections of non-aligned waveguides into a single section improved compactness is achieved. A twist is imparted within a waveguide portion rather than between two different waveguide portions and a ridge is provided to lower the cut-off frequency of the dominant mode and raise the cut-off frequency of the next higher modes.
Furthermore, by making the width of the rotator and the height of the rotator very close to those of the input or output waveguides, machining can be effectively provided within a single component using a machining tool.
Figure 1 shows one waveguide arranged here at 0° and a further waveguide arranged at 45°. Between the two waveguides is a rotator device according to an embodiment. This rotator device comprises straight sided adjacent portions for connecting to the waveguides and a rotator portion lying between them. This rotator portion has one section that is aligned with one adjacent portion and one section that is aligned with the other adjacent portion and has a bend in the middle allowing the two sections to be differently aligned.
Figure 2 schematically shows how a single twist rotator device such as that shown in Figure 1 is machined in two steps. A first step machines from one end of a metallic piece that will form the rotator device, a passage comprising a substantially rectangular cross section corresponding to the cross section of the waveguide to which it is to be connected. The machining is performed such that the whole rectangular cross section is machined to a first depth and then a section, shown here as the lower half of the cross section, is machined to a greater depth. A second step which may comprise machining from the other end of the metallic piece machines a substantially rectangular cross section corresponding to the cross section of the waveguide to which it is to be connected, this rectangular cross section being angled with respect to the first machined cross section. The machining is performed such that the whole rectangular cross section is machined to a first depth and then a section, shown here as the upper section is machined to a greater depth that overlaps with the other extended depth, such that a rotator portion is formed in the middle of two fractions or sections of non-aligned passages. A ridge is provided in the point at which the two sections join. As can be appreciated, this shape allows the device to be machined in two steps in a single piece of material. Thus, a low cost device with a high performance is provided that can be machined in one simple part without the need for many steps and different components.
In summary the rotator device can be manufactured by a two step machining process. One step machines a passage or partial passage oriented at one angle, while the other step provides a passage machined from the other end of the device at a different angle. The mid part is formed as a combination of the two machining steps, one of the steps forming one section of the mid part, while the other machining step forms the other section of the mid part. Thus, the machining from one end provides a complete substantially rectangular passage at one end and is continued further into the solid body to form say an upper section of a mid part, while the machining from the other end provides a substantially rectangular passage at a different angle to the passage at the one end, this machining continuing for say the lower section of the mid part. Thus, the mid part is formed of an "upper" section oriented one way and a "lower" section oriented at an angle to this and a slight geometric modification is provided between the two sections in the form of a triangular ridge.
In this simple way a rotator device is provided where at least some of the rotation occurs in a compact middle rotator portion.
The result is a compact rotator device that is machined in one piece and has the performances of a 2 component twist and which can achieve -40dB return loss value on 25% frequency band for a 45° rotation.
An embodiment was described above for a 45° twist using 2 steps. Embodiments can be used for other angular values and/or with more steps and with further rotator portions.
Embodiments are based on one or more rotator portions within a rotator device which has 2 sections arranged with a step twist and has a light geometric modification of the middle part to improve the radioelectrical performances. This light geometric modification may have the form of a ridge and may have a symmetric or non-symmetric shape and will lower the cut-off frequency of the dominant mode and raise the cut-off frequency of the next higher order modes.
Figure 3 shows the dimensions of a rotator according to an embodiment. The angle between the 2 sections is P. The dimensions of this angle are: 10° ≤ β ≤ 25°. The width a of the rotator and the height b are very close to the corresponding values of the input or output waveguides. l1 is the length of the portion machined in the first step, while l2 is the length of the portion machined in the second step.
The dimensions are such that $0.5 \leq \frac{t 2}{t 1} \leq 1.$
lt is the total length of this single twist rotator and (l1+l2)/2≤lt>(l1+l2).
Although l1 can be seen as the length of the first machining step it corresponds to the width of the straight portion adjacent to the rotator portion plus the width of the rotator portion, while the second machining step corresponds to the width of the straight portion adjacent to the other side of the rotator portion plus the width of the rotator portion.
The height h of the central part is $\frac{b}{2} \leq h \leq b$
and the width w is $\frac{a}{6} \leq w \leq \frac{a}{2}$
Figure 4 shows the Return Loss values for a rotator according to an embodiment in the 5.5 - 9 GHz frequency band. To get the performances of -35db for this broadband from a rotator with 2 steps a length of around 30mm is generally required. Embodiments of the invention provide a device with similar characteristics and a length of just 21.6mm, providing a 28% reduction in length. Thus, embodiments provide a reduction in size of the rotator device, a simplification of the machining process and a reduced cost.
Figures 1 to 4 disclose a two step, single twist device, while Figure 5 shows a further embodiment with an additional rotator portion. As can be seen there are two rotator portions with intermediate portions surrounding each rotator portion the intermediate or adjacent portions having straight sides. The rotator device may be formed of a number of rotator portions depending on the desired angle of rotation and supported bandwidth. Rotating the polarisation in several steps may improve performance but does reduce compactness. The machining of the device may be done in a single piece of material, owing to the similar dimensions of each piece. A machining tool with a cutting portion that extends laterally from the tool may be required, where there are several rotator portions.
Figure 6 shows a microwave antenna according to an embodiment. The antenna comprises an antenna dish 10 for receiving and transmitting microwaves a linking waveguide, which in this embodiment comprises an orthomode transducer 20 for transmitting both horizontally and vertically polarised waves from the antenna towards two outdoor units 40 which each receive one of the vertically or horizontally polarised waves. Rotator devices 30 according to an embodiment are located between the orthomode transducer 20 and the outdoor units and act to rotate the polarisation of the waves from the vertical or horizontal to the 45° of the input waveguide of the devices.
The description and drawings merely illustrate the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.

Claims

A rectangular waveguide rotator device for connecting first and second waveguides, said first and second waveguides being arranged at an angle to each other, said rotator device comprising:
at least one rotator portion, said at least one rotator portion comprising a passage formed by outer walls comprising two longer side walls connected by two shorter end walls;

said at least one rotator portion comprising a ridge protruding from each of said longer side walls across a width of said longer side walls, said ridge lying between a first and a further section of said rotator portion;

said first and further sections of said rotator portion being configured such that they are at an angle with respect to each other, one section being rotated through an angle with respect to the other.
A rotator device according to claim 1, wherein
a cross section of said rotator portion is rotationally symmetrical about a centre of said rotator portion, when cut through a line passing through a centre of said rotator portion and joining said two ridges.
A rotator device according to any preceding claim, comprising a plurality of rotator portions, said first and further sections of each rotator portion being successively rotated with respect to said first and said further sections of a next rotator portion.
A rotator device according to any preceding claim, wherein each of said at least one rotator portion is located between two adjacent portions, said adjacent portions having a substantially rectangular cross section, one being aligned with said first section and the other being aligned with said further section.
A rotator device according to claim 4, wherein at least one of said adjacent portions comprises a ridge extending from each of said longer side walls in a direction perpendicular to said longer side walls, said ridge being aligned with said ridge of said at least one rotator portion.
A rotator device according to claim 4 or 5, wherein said rotator device comprises adjacent portions at each end, one of said end adjacent portions being configured to connect to said first rectangular waveguide, and the other of said end adjacent portions being configured to connect to said second waveguide.
A rotator device according to any one of claims 1 to 6, wherein said first waveguide is a different size to said second waveguide, and an end of said rotator device configured to connect with the larger waveguide comprising a connecting portion for connecting to said rectangular waveguide and two linking portions for linking said connecting portion to a closest rotator portion, a first of said two linking portions adjacent to said connecting portion comprising a first section aligned with said adjacent connecting portion and a further section aligned with a first section of said closest rotator portion, and a second of said two linking portions comprising a substantially rectangular cross section aligned with said first section of said adjacent rotator portion.
A rotator device according to any preceding claim, wherein a length and width at a widest point of said rotator portions are substantially the same as a length and width of said rectangular waveguides.
A rotator device according to any preceding claim, wherein said at least one rotator portion comprises curved corners between said longer and shorter end walls.
A rotator device according to any preceding claim, wherein said ridges of said at least rotator portion comprise a substantially triangular cross section.
A rotator device according to any preceding claim, wherein a width of said at least one rotator portion between said ridges is greater than a half of the width of said at least one rotator portion at its widest point.
A rotator device according to any preceding claim, wherein the width of the at least one rotator portion at its widest point is between a fifth and a half of its length.
A rotator device according to any preceding claim, wherein an angle between said first and further sections of said at least one intermediate section is between 10° and 25°.
A microwave antenna comprising an antenna dish, a linking waveguide for transmitting at least one of horizontally polarised and vertically polarised waves, at least one outdoor unit comprising a waveguide port arranged at an angle of 45°, said microwave antenna further comprising at least one rotator device according to any preceding claim, arranged between said linking waveguide and said at least one outdoor box.
A method of manufacturing a rotator device according to any preceding claim, said method comprising:
machining in a metal block a substantially rectangular first passage to a first depth;

continuing to machine a fraction of a cross section of said first passage, such that said fraction of said first passage extends to a further depth;

machining a substantially rectangular second passage in an opposing end of said block and at a corresponding position to said first passage to a second depth, said rectangular second passage being at an angle to said first passage; and

machining a fraction of said second passage to a further depth, said fraction of said second passage overlapping in depth with a fraction of an other passage, said fraction of said other passage joining with said fraction of said passage and being at an angle therewith.