Waveguide polarizer and a circularly polarized antenna

Abstract

A waveguide polarizer for converting between a linearly polarized electromagnetic field in a first waveguide and a circularly polarized electromagnetic field in a second waveguide is provided. The waveguide polarizer includes a structure interconnecting the first and second waveguide which includes a waveguide excitation arrangement with a bifilar helical shape. A circularly polarized antenna arranged to be connected to the first waveguide of the waveguide polarizer and a satellite arrangement are also provided.

Claims

1. A waveguide polarizer for converting between a linearly polarized electromagnetic field in a first waveguide and a circularly polarized electromagnetic field in a second waveguide, wherein the waveguide polarizer comprising: a structure interconnecting the first and second waveguide comprising a waveguide excitation arrangement with a bifilar helical shape, wherein the structure comprises a transition waveguide interconnecting the first waveguide to a third waveguide, wherein the transition waveguide provides an impedance match between the first waveguide and the third waveguide.

2. The waveguide polarizer according to claim 1, wherein the waveguide excitation arrangement with the bifilar helical shape is galvanically connected to the first waveguide on opposing sides.

3. The waveguide polarizer according to claim 2, wherein the waveguide excitation arrangement with the bifilar helical shape is galvanically connected to ridges on opposing sides of the first waveguide.

4. The waveguide polarizer according to claim 1, wherein the first waveguide has a super-elliptical cross-section.

5. The waveguide polarizer according to claim 1, wherein the first waveguide has a rectangular cross-section.

6. The waveguide polarizer according to claim 1, wherein the first waveguide has a rectangular cross-section with rounded edges.

7. The waveguide polarizer according to claim 1, wherein the first waveguide has a cross-section including ridges.

8. The waveguide polarizer according to claim 1, wherein the second waveguide has a super-circular cross-section.

9. The waveguide polarizer according to claim 1, wherein the second waveguide has a circular cross-section.

10. The waveguide polarizer according to claim 1, wherein the second waveguide has a square cross-section.

11. The waveguide polarizer according to claim 1, wherein the second waveguide has a square cross-section with rounded edges.

12. The waveguide polarizer according to claim 1, wherein the transition waveguide has a length that is a quarter of the wavelength of the propagating electromagnetic field in the first waveguide.

13. A circularly polarized antenna arranged to be connected to a second waveguide of a waveguide polarizer for converting between a linearly polarized electromagnetic field in a first waveguide and the circularly polarized electromagnetic field in the second waveguide, wherein the waveguide polarizer comprising: a structure interconnecting the first and second waveguide comprising a wave-guide excitation arrangement with a bifilar helical shape, wherein the structure comprises a transition waveguide interconnecting the first waveguide to a third waveguide, wherein the transition waveguide provides an impedance match between the first waveguide and the third waveguide.

14. The circularly polarized antenna according to claim 13, wherein the length of the second waveguide of the waveguide polarizer is such that evanescent modes generated by the waveguide excitation arrangement contribute significantly to the antenna radiation properties.

15. The circularly polarized antenna according to claim 13, wherein the length of the second waveguide of the waveguide polarizer is such that no evanescent modes generated by the waveguide excitation arrangement contribute significantly to the antenna radiation properties.

16. The circularly polarized antenna according to claim 13, further comprising one or more choke rings arranged around the second waveguide.

17. A satellite arrangement comprising a waveguide polarizer for converting between a linearly polarized electromagnetic field in a first waveguide and a circularly polarized electromagnetic field in a second waveguide, wherein the waveguide polarizer comprising: a structure interconnecting the first and second waveguide comprising a wave-guide excitation arrangement with a bifilar helical shape; wherein the structure comprises a transition waveguide interconnecting the first waveguide to a third waveguide, wherein the transition waveguide provides an impedance match between the first waveguide and the third waveguide.

Description

BRIEF DESCRIPTION OF FIGURES

(1) Features and advantages of the embodiments will become readily apparent to those skilled in the art by the following detailed description of exemplary embodiments thereof with reference to the accompanying drawings, wherein:

(2) FIG. 1 shows a schematic illustration comparing a circularly polarized pipe antenna according to prior art (left) and a circularly polarized antenna according to some embodiments (right),

(3) FIGS. 2-3 shows a first and a second cross-sectional view of a circularly polarized antenna according to some embodiments,

(4) FIGS. 4-5 shows diagrams illustrating examples of input return loss and directivity, respectively, for a circularly polarized antenna according to some embodiments,

(5) FIG. 6 shows a perspective view of a circularly polarized antenna according to some embodiments, and

(6) FIG. 7 shows a first and second cross-sectional view of a waveguide polarizer according to some embodiments.

DETAILED DESCRIPTION

(7) The figures are schematic and simplified for clarity, and they merely show details which are essential to the understanding of the embodiments presented herein, while other details have been left out. Throughout, the same reference numerals are used for identical or corresponding parts or steps.

(8) FIG. 1 shows a circularly polarized antenna 20 (right) according to some embodiments. The circularly polarized antenna 20 is a compact radiator which may provide circular polarization to a wave feed from a linear polarized wave guide. The circularly polarized antenna 20 comprises a waveguide polarizer 30 for achieving the circular polarization. Embodiments of the waveguide polarizer 30, which may also be referred to herein as a bifilar helix radiator, is described in more detail below with reference to FIGS. 2-7. The circularly polarized antenna 20 may either be configured for a right-hand circular polarization, RHCP, or left-hand circular polarization, LHCP.

(9) Furthermore, the waveguide polarizer 30 is here placed or located inside the pipe of the circularly polarized antenna 20 enabling a significantly more compact antenna assembly for the circularly polarized antenna 20. This is illustrated in FIG. 1 by the total length B of the circularly polarized antenna 20 being significantly shorter that the total length A of the circularly polarized pipe antenna 10 according to prior art. Here, it should also be noted that no septum polarizer is implemented, or needed, in the circularly polarized antenna 20.

(10) FIG. 2-3 shows a first and a second cross-sectional view of a circularly polarized antenna 20 comprising a waveguide polarizer 30 according to some embodiments. The circularly polarized antenna 20 comprises a first waveguide 70 and a second waveguide 80. The first waveguide 70, or input waveguide, may be provided with a wave feed producing a linearly polarized electromagnetic field in the first waveguide 70. Here, the first waveguide 70 may be arranged to be connected to a feed component or network (not shown) configured to provide the wave feed for the first waveguide 70. According to one example, the first waveguide 70 may have a rectangular cross-section. However, according to other examples, the first waveguide 70 may also have a super-elliptical cross-section, a rectangular cross-section with rounded edges, or a cross-section including ridges. Further, according to one example, the second waveguide 80 may have a circular cross-section. However, according to other examples, the second waveguide 80 may also have a super-circular cross-section, a square cross-section, or a square cross-section with rounded edges. Furthermore, it should also be noted that, although not mentioned explicitly above, other cross-sections of the first and second waveguide 70, 80 may also be envisioned.

(11) In the example shown in FIGS. 2-3, the waveguide polarizer 30 is arranged to convert the linearly polarized electromagnetic field in the first waveguide 70 into a circularly polarized electromagnetic field in the second waveguide 80. However, it should also be noted that the waveguide polarizer is reciprocal and may thus also be used to convert a circularly polarized electromagnetic field in one waveguide into a linearly polarized electromagnetic field in another waveguide. The waveguide polarizer 30 comprises a structure 30, 50A, 50B interconnecting the first and second waveguide 70, 80. The structure 30, 50A, 50B further comprises a waveguide excitation arrangement with a bifilar helical shape 40A, 40B, also referred to herein as a bifilar helix.

(12) In some embodiments, the structure 30, 50A, 50B may comprise two matching sections 50A, 50B. The first matching section may be a transition waveguide 50A and the second matching section may be a third waveguide 50B. The transition waveguide 50A may interconnect the first waveguide 70 with the third waveguide 50B. The transition waveguide 50A may also provide an impedance match between first waveguide 70 and the third waveguide 50B. Here, the transition waveguide 50A may be said to comprise a transmission line with a characteristic impedance and a specific length. The length of the transition waveguide 50B may typically be a quarter of a wavelength of the propagating electromagnetic field in the first waveguide 70. The third waveguide 50B may interconnect with, or form part of, the waveguide excitation arrangement with a bifilar helical shape 40A, 40B.

(13) According to some embodiments, the waveguide excitation arrangement with a bifilar helical shape 40A, 40B, may consist of two helical filaments 40A that are connected to opposite sides of the first waveguide 70. In some embodiments, the waveguide excitation arrangement with the bifilar helical shape 40A, 40B may be galvanically connected to the first waveguide 70 on opposing sides. In some embodiments, the waveguide excitation arrangement with the bifilar helical shape 40A, 40B is galvanically connected to ridges 40B on opposing sides of the first waveguide 70. Here, it should also be understood that the bottom part of the two helical filaments 40A may form the ridges 40B on the opposing sides of the first waveguide 70. The ridges 40B may also provide matching of the bifilar helix and some mechanical advantages. In some embodiments, the two helical filaments 40A may be shorted or open at the top.

(14) FIG. 3 shows a diagram illustrating an example of input return loss of a circularly polarized antenna 20 according to some embodiments. FIG. 4 shows a diagram illustrating an example of directivity of a circularly polarized antenna 20 according to some embodiments. The directivity is here shown for a number of frequency points defined by the centre frequency f0 and a frequency bandwidth of ±10%. The frequency bandwidth of the circularly polarized antenna 20 is significantly large, i.e. about 20%, and diagrams of FIGS. 3-4 demonstrates the performance for the circularly polarized antenna 20 for a 20% frequency bandwidth.

(15) FIG. 5 shows a perspective view of a circularly polarized antenna 20 according to some embodiments. As may be seen in the example shown in FIG. 5, the circularly polarized antenna 20 may comprise a reflector or cup 21. Optionally, the reflector or cup 21 may be surrounded by one or more choke rings 22, 23. Here, it may be noted that it is the size and shape of the bifilar helix 40A, 40B and the reflector 21 that together shapes the radiation pattern of the circularly polarized antenna 20. The optional choke rings 22, 23 may also assist in the shaping of the radiation pattern of the circularly polarized antenna 20, but may also be used to reduce the back radiation from being received by the circularly polarized antenna 20.

(16) FIG. 6 shows a first and second cross-sectional view of a waveguide polarizer 60 according to some embodiments. As may be seen in the example shown in FIG. 6, the waveguide polarizer 60 may also be used the same way as a septum polarizer. In this example, the first waveguide 70, or first waveguide port, is a rectangular waveguide, while the opposite second waveguide 80, or second waveguide port, is a circular waveguide.

(17) Furthermore, in some embodiments, the length of the second waveguide 80 of the waveguide polarizer 30, 60 may be adapted such that evanescent modes generated by the waveguide excitation arrangement with a bifilar helical shape 40A, 40B contribute significantly to the antenna radiation properties. This provides more degrees of freedom to optimize the design, but may be considered a more complicated case. Optionally, in some embodiments, the length of the second waveguide 80 of the waveguide polarizer 30, 60 may be adapted such that no evanescent modes generated by the waveguide excitation arrangement with a bifilar helical shape 40A, 40B contribute significantly to the antenna radiation properties. This would advantageously ensure that there is no interaction with the evanescent modes, which could be advantageous in some cases.

(18) The description of the example embodiments provided herein have been presented for purposes of illustration. The description is not intended to be exhaustive or to limit example embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives to the provided embodiments. The examples discussed herein were chosen and described in order to explain the principles and the nature of various example embodiments and its practical application to enable one skilled in the art to utilize the example embodiments in various manners and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products. It should be appreciated that the example embodiments presented herein may be practiced in any combination with each other.

(19) It should be noted that the word “comprising” does not necessarily exclude the presence of other elements or steps than those listed and the words “a” or “an” preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the example embodiments may be implemented at least in part by means of both hardware and software, and that several “means”, “units” or “devices” may be represented by the same item of hardware.

(20) The embodiments herein are not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be construed as limiting.