Dual-channel polarization correction

Abstract

Embodiments relate to a device for correcting the polarization twist of two linearly polarized signals using two polarization converters connected in series, wherein the second polarization converter can be rotated about an axis. In this way, the skew angle of an antenna can be compensated with respect to a satellite using a rotatable waveguide circuit. By converting the polarization from linear to circular, it is easier to rotate the now circularly polarized signals, using a second polarization converter, which reestablishes a linear polarization for the circularly polarized signals. Given the dual-channel signal outcoupling, the PCU may allow two orthogonal linear polarizations to be corrected at the same time using a simpler mechanical composition.

Claims

1. A device for correcting a polarization shift of two linearly polarized signals, comprising: a first polarization converter configured to convert the two linearly polarized signals from a linear polarization into a circular polarization, such that the signals are converted into two circularly polarized signals that rotate in opposite directions from one another; and a second polarization converter connected in series to the first polarization converter and configured to receive the circularly polarized signals, wherein the second polarization converter is configured to rotate about an axis to correct the polarization shift of the linearly polarized signals, the axis extending longitudinally through a center of the second polarization converter.

2. The device according to claim 1, wherein the first polarization converter is a septum polarizer.

3. The device according to claim 2, wherein the septum polarizer further includes a plurality of restrictions disposed linearly along the length of the septum polarizer, wherein the plurality of restrictions are configured to convert the two signals from the linear polarization into the circular polarization.

4. The device according to claim 3, wherein each of the plurality of restrictions has a stepped cross-section that progressively decreases in size along the length of the septum polarizer towards the second polarization converter.

5. The device according to claim 3, wherein the septum polarizer has a substantially rectangular cross-section, and the plurality of restrictions are disposed on a single internal wall of the septum polarizer.

6. The device according to claim 1, wherein the second polarization converter converts the two converted signals, received from the first polarization converter, from a circular polarization into a linear polarization.

7. The device according to claim 1, wherein the second polarization converter is a quad-ridge polarizer.

8. The device according to claim 7, wherein: the quad-ridge polarizer includes a plurality of restrictions, such that restrictions on opposing walls are identical and restrictions on neighboring walls are different from each other.

9. The device according to claim 8, wherein the restrictions along the axis of the quad-ridge polarizer are symmetrical, wherein the axis extends longitudinally through a center of the second polarization converter.

10. The device according to claim 1, further comprising: an outcoupling unit connected to the second polarization converter, wherein the outcoupling unit includes first and second outcoupling elements configured for outcoupling the signals into coaxial conductors, wherein: the second polarization converter includes a plurality of restrictions rotated by 45 degrees in relation to the first and second outcoupling elements.

11. The device according to claim 10, wherein: the first and second outcoupling elements are oriented perpendicularly to each other, and the outcoupling unit further includes one or more restrictions disposed between the first and second outcoupling elements for constricting the outcoupling unit.

12. The device according to claim 1, further comprising: an incoupling unit connected to the first polarization converter including two conductors, each conductor including an incoupling element for converging the signals towards each other.

13. The device according to claim 12, wherein the incoupling unit further includes a tuning screw associated with each incoupling element, wherein the tuning screw is disposed on a wall proximate the associated incoupling element.

14. The device according to claim 1, wherein the device is configured to operate in a frequency range of 10.7 to 12.75 GHz or 13.75 to 14.5 GHz.

15. A dual channel polarization control unit for correcting the polarization shift of two linearly polarized signals, comprising: a first polarization converter configured to convert the two linearly polarized signals from a linear polarization into a circular polarization, such that the signals are converted into two circularly polarized signals that rotate in opposite directions from one another; and a second polarization converter connected in series to the first polarization converter and configured to receive the circularly polarized signals, wherein the second polarization converter is configured to rotate about an axis to correct the polarization shift of the linearly polarized signals, the axis extending longitudinally through a center of the second polarization converter.

16. The control unit according to claim 15, wherein the second polarization converter converts the two converted signals, received from the first polarization converter, from the circular polarization into the linear polarization.

17. The control unit according to claim 15, wherein the first polarization converter is a septum polarizer, the septum polarizer further comprising: a plurality of restrictions disposed linearly along the length of the septum polarizer, wherein the plurality of restrictions are configured to convert the two signals from the linear polarization into the circular polarization.

18. The control unit according to claim 17, wherein each of the plurality of restrictions has a stepped cross-section that progressively decreases in size along the length of the septum polarizer towards the second polarization converter.

19. The control unit according to claim 15, wherein the second polarization converter is a quad-ridge polarizer, the quad-ridge polarizer comprising: a plurality of restrictions, such that restrictions on opposing walls are identical and restrictions on neighboring walls are different from each other.

20. The control unit according to claim 15, further comprising: an outcoupling unit connected to the second polarization converter, wherein the outcoupling unit includes first and second outcoupling elements configured for outcoupling the signals into coaxial conductors, wherein: the second polarization converter includes a plurality of restrictions rotated by 45 degrees in relation to the first and second outcoupling elements.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a schematic composition of the signal transmission from a satellite to an airplane-based receiver using dual-channel polarization shift correction;

(2) FIGS. 2 and 3 shows sectional views of the device according to an exemplary embodiment;

(3) FIG. 4 shows a sectional view of an exemplary incoupling unit;

(4) FIG. 5 shows a sectional view of an exemplary septum polarizer;

(5) FIG. 6 shows a sectional view of an exemplary quad-ridge polarizer;

(6) FIG. 7 shows a sectional view of an exemplary outcoupling unit; and

(7) FIGS. 8a-d show exemplary E-field distributions at different skew angles.

DETAILED DESCRIPTION

(8) FIG. 1 shows the operating principles of an exemplary device according to the present disclosure for correcting the polarization shift of two linearly polarized signals. The device is also referred to as a dual channel polarization control unit (PCU).

(9) The skew angle is defined as the angle between the polarization of a signal of a satellite S and of a signal at the antenna A, for example the angle between V and V (or H and H).

(10) Skewing the antenna A with respect to the satellite S connects the signals H/V from the antenna A as H/V to the PCU 1. A septum polarizer 2, serving as the first polarization converter, converts each of the two linearly polarized components H/V into a respective circularly polarized wave RHCP/LHCP, which differ in the sense of rotation (right-hand or left-hand). The resultant wave may be elliptically polarized at a transition to a quad-ridge polarizer 3 serving as the second polarization converter. The septum polarizer converts V and H into two circular waves which rotate in opposite directions. The sense of rotation of the general ellipse resulting from the superimposition of the two circular sub-waves is dependent on the amplitudes of the sub-waves. The axial ratio and the sense of rotation of the ellipse are dependent on the skew angle between the antenna A and the satellite S.

(11) The quad-ridge polarizer 3 is not static and rotates about an axis, serving as a rotor R, in keeping with the skew angle, for example driven by a motor, and breaks the ellipse into the two linear components, which thereafter are again available as linear original signals H/V for outcoupling and further processing.

(12) The rotation of the quad-ridge polarizer 3 is controlled by a processor (not shown) which knows the position of the airplane or other vehicle on which the antenna and the PCU are mounted, and the position of the satellite, and generates the correction signal for the rotation.

(13) Alternatively, the signal quality may be continuously evaluated by the processor. When a signal deteriorates as a result of a polarization shift, this may be corrected by a rotation of the quad-ridge polarizer.

(14) FIGS. 2 to 7 show an exemplary device developed for the Ku band in a frequency range from 10.7 to 12.75 GHz. The number and dimensions of the restrictions discussed in greater detail below are an exemplary compromise between an easy-to-produce mechanical composition and sufficiently good properties in terms of attenuation, reflections and polarization separation in the desired frequency band having the desired bandwidth.

(15) FIG. 2 shows a top view onto a sectional illustration of the PCU. Hereafter, the reception scenario where signals of the satellite are received by the antenna A and supplied to a receiver is shown in each case. The device can also be used for the transmission scenario so that transmission signals are appropriately corrected in advance prior to emission via the antenna A. With the exception of the incoupling and outcoupling, the device is composed of waveguides that may be generally square having rounded edges, except for the quad-ridge polarizer 3 which has a substantially cylindrical interior.

(16) The signals V, H arriving from the antenna A are coupled into an incoupling unit 5 by way of symmetrical coaxial wave-guide couplers and converted from a linear into a circular polarization in the septum polarizer 2. A second conversion of the circularly polarized signals into linearly polarized signals takes place in the downstream quad-ridge polarizer 3, which is connected in series, wherein a rotation of the quad-ridge polarizer 3 is used to compensate for a potential polarization shift. In an outcoupling unit 4 provided down-stream from the quad-ridge polarizer 3, the signals H/V are outcoupled by way of coaxial waveguide couplers. With the exception of the rotating quad-ridge polarizer 3, the other assemblies are static.

(17) FIG. 3 shows a side view of the same exemplary device of FIG. 2. Restrictions 11, 12 and 14 in the polarizers 2, 3 and the outcoupling unit 4 are more clearly apparent, as are the outcoupling elements 13 of the outcoupling unit 4. The restrictions 11 of the septum polarizer 2 are provided downstream from a partition between the waveguides of the incoupling unit and may be located on exactly one wall. From a complete separation of the two waveguides, these restrictions 11 progress into the septum polarizer 2 in a stepped manner. In the zero position (where no polarization shift that needs compensation is present), the restrictions 12 of the quad-ridge polarizer 3 are rotated 45 in relation to the restrictions 11 of the septum polarizer 2 and the outcoupling elements 13 of the outcoupling unit 4. In the worst case of a 45 polarization shift, this minimizes crosstalk between the two channels.

(18) The restrictions 14 of the outcoupling unit 4 may be disposed between the outcoupling points 13 and oriented perpendicularly to the outcoupling point 13 located furthest away from the quad-ridge polarizer 3. In this way, a /4 waveguide termination may be achieved for both outcoupling elements 13, minimizing reflections.

(19) The incoupling unit 5 according to FIG. 4 shows two physically separate inputs for the antenna-side signals V, H, which are connected to the waveguide via incoupling points 15 designed as coaxial waveguide couplers. From the incoupling points 15, the waves converge toward each other in a respective rectangular waveguide, but are separated by a partition provided downstream from the restrictions 11 of the septum polarizer. The waveguide is slanted in the transition to the partition so that the two waves can enter the septum polarizer parallel to each other. Tuning screws 16 are disposed in the waveguides opposite the incoupling point 15 and between the incoupling point 15 and the partition, respectively. The penetration depth of the tuning screws 16 can be set individually by rotating them, whereby it is possible to compensate for possible reflection differences of the co-axial conductors or incoupling points 15 separately for each of the waveguides.

(20) The septum polarizer 2 according to FIG. 5 includes restrictions 11 that are provided downstream from the partition of the incoupling unit. Starting from the incoupling unitthis is where the restrictions 11 separate the two halvesthe restrictions 11 become increasingly smaller, until they disappear entirely in the now one-piece rectangular wave-guide. The restrictions are used to convert the linearly polarized input waves (TE 1,0 mode) into corresponding RHCP/LHCP waves having a circular polarization. Reflections in the transition to the neighboring quad-ridge polarizer are minimized by rounding the corners of the otherwise rectangular waveguide, thereby minimizing the change in cross-section toward to the more cylindrical cross-section of the quad-ridge polarizer.

(21) FIG. 6 shows the quad-ridge polarizer 3. The quad-ridge polarizer 3 includes two differently designed restriction pairs 12 (i.e. ridge structures) in a rounded square waveguide. The restrictions 12 break a circular input signal back into the two orthogonal linear basic components thereof by way of a 90 phase shift. In this case, TE1,0 is delayed by the more pronounced restrictions (extending further into the waveguide) with respect to TE0,1 by 90. The restrictions 12 are symmetrical along the axis of the quad-ridge polarizer 3, so that the conversion takes place both in the reception scenario and in the transmission scenario. If restrictions 12 located opposite each other in the waveguide are identical, neighboring ones will differ from each other.

(22) An outcoupling unit 4 provided downstream from the quad-ridge polarizer is shown in FIG. 7. In a cylindrical round wave-guide, two outcoupling points 13 disposed perpendicularly to each other are provided as coaxial waveguide couplers. The waveguide tapers toward the end as a result of restrictions 14, which are oriented perpendicularly to the rear outcoupling element 13 and form a virtual waveguide termination for the front outcoupling element 13.

(23) The mode of action of the PCU will be described based on exemplary polarization shifts in FIGS. 8a-d, wherein the E-field distribution is represented, and the ports H, V denote the antenna-side signals and the ports H, V denote the receiver-side signals:

(24) FIG. 8a, skew=0: In this case, the planes of polarization between the satellite and the antenna are in perfect agreement (skew=0). The satellite signal H is seen completely at the port H by the antenna and is conducted directly to the port H. The quad-ridge polarizer is not being rotated.

(25) FIG. 8b, skew=0: In this case, the planes of polarization between the satellite and the antenna are in perfect agreement (skew=0). The satellite signal V is seen completely at the port V by the antenna and is conducted directly to the port V. The quad-ridge polarizer is not being rotated.

(26) FIG. 8c, skew=90: In this case, the planes of polarization between the satellite and the antenna are skewed by 90 (skew=90). The satellite signal H is seen at the port V by the antenna and is subsequently conducted back to the port H by the PCU by way of a 90 rotation of the quad-ridge polarizer.

(27) FIG. 8d, skew=45: In this case, the planes of polarization between the satellite and the antenna are skewed by 45 (skew=45). The satellite signal H is seen in equal parts at the ports H and V of the antenna. A rotation of the quad-ridge polarizer by 45 makes the signal completely visible again at the port H.

LIST OF REFERENCE NUMERALS

(28) 1 PCU 2 first polarization converter, septum polarizer 3 second polarization converter, quad-ridge polarizer 4 outcoupling unit 5 incoupling unit 11 restrictions of the septum polarizer 12 restrictions of the quad-ridge polarizer 13 outcoupling elements 14 restrictions of the outcoupling unit 15 incoupling elements 16 tuning screw A antenna field R rotor S satellite V, H antenna-side signals V, H receiver-side signals TE, LHCP, RHCP signal modes