EP3761442A1

EP3761442A1 - Waveguide

Info

Publication number: EP3761442A1
Application number: EP19184837.3A
Authority: EP
Inventors: Ahmed Halid Akgiray; Nikolov Biser
Original assignee: Alcan Systems GmbH
Current assignee: Alcan Systems GmbH
Priority date: 2019-07-05
Filing date: 2019-07-05
Publication date: 2021-01-06

Abstract

A Waveguide (1) for transmitting a radio frequency signal with a hollow waveguide body (2) extending along a central axis (3) between a first open end (4) and a second open end (5). A body wall (8) of the hollow waveguide body (2) is fabricated from an electrically conductive material and encloses a waveguide cavity of the waveguide body (2). At least in a first section (12) of the waveguide (1) adjacent to the first end (4) of the waveguide body (2) the waveguide (1) comprises a first pair (6) and a second pair (7) of opposing ridge elements of the electrically conductive material. Each of the respective ridge elements arranged at the body wall (8) of the waveguide body (2) is projecting inwardly from the body wall (8) and extending along the central axis (3). Each of the ridge elements comprises a ridge tail surface (9) that is closer to the central axis (3) than the adjacent parts of the body wall (8). At least in the first section (12) an adapting element (10) comprising a dielectric material (11) with a relative permittivity larger than air is arranged in between the opposing ridge tail surfaces (9) of the first pair (6) and the second pair (7) of ridge elements.

Description

Technical Field

The invention relates to a waveguide for transmitting a radio frequency signal with a hollow waveguide body extending along a central axis between a first open end and a second open end, whereby the waveguide body comprises a body wall of an electrically conductive material, whereby the body wall encloses a waveguide cavity, wherein at least in a first section of the waveguide adjacent to the first end of the waveguide body the waveguide comprises a first pair and a second pair of opposing ridge elements of the electrically conductive material, with each of the respective ridge elements arranged at the body wall of the waveguide body projecting inwardly from the body wall and extending along the central axis, whereby each of the ridge elements comprises a ridge tail surface that is closer to the central axis than the adjacent parts of the body wall.

Background of the invention

In the area of microwave technology hollow metallic waveguides are commonly used to transmit a radio frequency signal along the hollow waveguide as for instance from a radio frequency amplifier to an antenna. Within this application radio frequency comprises a range of frequencies from 30 MHz to 300 GHz. In hollow waveguides the radio frequency signal propagates as electromagnetic waves along the hollow waveguide. For frequencies below a cut-off frequency, being dependent on the dimensions perpendicular to a central axis of the hollow waveguide, electromagnetic waves cannot propagate along the hollow waveguide.
For frequencies higher than the cut-off frequency the radio frequency signal can propagate as electromagnetic waves along the waveguide in a fundamental mode and potentially in higher order modes. When increasing the frequency above the cut-off frequency of the hollow waveguide initially the radio frequency signal is propagating only in the fundamental mode. With further increase of the frequency there is an onset of the propagation of the radio frequency signal in a higher order mode. The propagation of the radio frequency signal as well as the coupling of the radio frequency signal out of the hollow waveguide in higher order modes can lead to losses. Hence, it is desired to transmit the radio frequency signal exclusively in the dominant mode without a participation of the higher order modes. An operational bandwidth of the hollow waveguide where the radio frequency signal can propagate exclusively in the dominant mode is limited between a lower frequency limit equal to the cut-off frequency of the hollow waveguide, and an upper frequency limit, equal to the frequency onset at which propagation in the higher order modes occurs.
An operational bandwidth ratio for which the radio frequency signal propagates solely in the dominant mode is defined as a ratio of the upper frequency limit divided by the lower frequency limit. As the cut-off frequency is inversely related to the largest dimension of a waveguide cavity orthogonal to the central axis of the waveguide, a minimal size requirement for the waveguide for a given frequency can hamper the use of waveguides where a space saving integration is necessary as for instance in waveguide feeds and open waveguide radiating elements of antenna arrays. For instance, in a planar phased array antenna with a multitude of open waveguide radiating elements arranged next to each other on an antenna plane a lateral spacing between a central axis of the open waveguide radiating elements is typically around half a wavelength of the radio frequency signal the phased array antenna is designed to operate at. Notably, the cut-off frequency of the dominant mode of a quadratic hollow waveguide coincides with a minimal lateral extension of a side of the waveguide cavity of half a wavelength of the radio frequency signal. Hence, a spacing of this sort is not feasible taking twice a thickness of a body wall surrounding the waveguide cavity into account.
It is known in the art to reduce the cut-off frequency of the dominant mode of a hollow waveguide by filling the hollow wave guide completely with a dielectric material. Hereby the cut-off frequency of the dominant mode of the waveguide can be lowered by the inverse of the square root of a relative permittivity of said dielectric material. Hence, for a given cut-off frequency the waveguide filled with the dielectric material can be manufactured using smaller lateral dimensions compared to the hollow waveguide. For filling the hollow waveguide several dielectric materials are available with a relative permittivity predetermined for a respective dielectric material. Therefore, a reduction of the lateral size is only feasible in predetermined discrete steps, being dependent on the relative permittivity of the used dielectric material.
Furthermore, it is well known in the art to use quadruple ridge waveguides with two opposing pairs of ridges protruding into the waveguide cavity to lower the cut-off frequency of the dominant mode of the ridged waveguide for a given dimension. By varying ridge dimensions of the two opposing pairs of ridges protruding into the waveguide cavity the cut-off frequency of the dominant mode can be lowered continuously, allowing a continuous reduction of the dimensions of the quadruple ridge waveguide with a constant cut-off frequency of the dominant mode. When introducing the two opposing pairs of ridges into the hollow waveguide it is possible that the radio frequency performance of the considered device at the upper frequency of the operational bandwidth is decreased more than at the lower frequency of the operational bandwidth, effectively reducing the operational bandwidth ratio. This can result from the excitation of one or more higher order modes into the operational bandwidth due to introduction of the two opposing pairs of ridges into the hollow waveguide.
Accordingly, there is a need for a quadruple ridge waveguide with an increased operational bandwidth ratio as compared to the known quadruple ridge wave guides.

Summary of the invention

The present invention relates to a waveguide as described above, characterized in that at least in the first section an adapting element comprising a dielectric material with a relative permittivity larger than air is arranged in between the opposing ridge tail surfaces of the first pair and the second pair of ridge elements. By arranging the adapter element inside at least the first section of the waveguide the operational bandwidth ratio of the waveguide can be increased by lowering the lower frequency limit and/or increasing the higher frequency limit. The first section of the waveguide can extend from the first open end to the second open end. Alternatively, the waveguide can also comprise multiple sections. The hollow waveguide body can be fabricated from a suitable metallic conductor as e.g. copper or aluminium. Advantageously, the hollow waveguide has a tubular shape with a circular cross section. An inwardly oriented side of the waveguide body is advantageously coated with silver or gold. The ridge elements projecting inwardly from the body wall can have a rectangular cross section with each of the ridge elements comprising the ridge tail surface and two sidewall surfaces, with the latter two connecting the respective ridge tail surface with the adjacent part of the body wall. The opposing ridge tail surfaces of the respective pair of ridge elements are advantageously plane and arranged parallel to each other. The dielectric material can be fabricated from suitable materials as polytetrafluoroethylene (PTFE), acrylonitrile butadiene styrene (ABS), silicone dioxide, silicone dioxide, epoxy resin, aluminium dioxide or a combination thereof. Particularly, the dielectric material can be a composite material as for instance glass-reinforced epoxy laminate.
According to an advantageous aspect of the invention, at least in the first section the adapting element is in contact with the ridge tail surface of each of the respective ridge elements. In such a way an electrical field formed between the opposing ridge tail surfaces when the radio frequency signal propagates along the waveguide can efficiently be concentrated in the adapting element.
According to an advantageous embodiment of the invention, the adapting element is spaced apart from the body wall. For the adapting element in contact with the ridge tail surfaces and being spaced apart from the body wall the adapting element can have a different influence on the electric field formed between the opposing ridge tail surfaces and an electric field between adjacent sections of the body wall between two neighbouring ridge elements, resulting in an increased operational bandwidth ratio of the waveguide.
According to an advantageous aspect of the invention, the first pair of ridge elements and the second pair of ridge elements are arranged orthogonal towards each other.
It is advantageous that at least in the first section the adapting element has a cross-shaped cross section orthogonal to the central axis. With the cross shaped adapting element arranged in between and contacting the ridge tail surfaces of the two orthogonal pairs of ridge elements the different influence of the adapting element on the electric field formed between the opposing ridge tail surfaces and the electric field between adjacent sections of the body wall between two neighbouring ridge elements can be further increased.
According to an advantageous embodiment of the invention, at least in the first section orthogonal to the central axis a cross section of the waveguide body with the first pair and the second pair of ridge elements and the adapting element are symmetric with respect to the first pair of ridge elements and/or the second pair of ridge elements arranged orthogonal towards each other. In such a way the fabrication of the waveguide can be simplified. The cross section can be circular or oval. In case of the oval cross section, one of the pairs of ridge elements is advantageously arranged along the smallest distance between opposing sections of the body wall, with the other pair of ridge elements being arranged orthogonal to said pair.
According to an advantageous aspect of the invention, orthogonal to the central axis the cross section of the wave guide body is rectangular, preferably quadratic. In case of the rectangular or the quadratic cross section of the wave guide body, one of the pairs of ridge elements is arranged along the smallest distance between opposing sections of the body wall, with the other pair of ridge elements being arranged orthogonal to said pair. A quadratic cross section of the wave guide body is particularly advantageous in case of the use of the waveguide as open waveguide radiating element in a planar phased array antenna. In this way an angular dependence of the radiation properties of the open waveguide radiating element can be optimized.
According to an advantageous embodiment of the invention, in a second section of the waveguide extending from the second open end of the waveguide body to the first section of the wave guide the first pair and/ or the second pair of ridge elements are extended from the first section along the central axis at least sectionwise into the second section. For instance, when used as an open waveguide antenna the waveguide can radiate the radio frequency signal through an aperture formed by the first open end in the first section of the waveguide. The second section of the waveguide can be modified as to couple in the radio frequency signal into the waveguide.
According to an advantageous aspect of the invention in the second section a distance between the respective ridge tail surfaces of the first or the second pair of ridge elements is staggered. The distance between the opposing ridge tail surfaces of one of the pairs of ridge elements can be staggered for example as to match an impedance of the waveguide to an impedance of a radio frequency signal amplifier connected to the second section of the waveguide. The distance of the respective opposing ridge tail surfaces in different staggered sections of the second section can be symmetric with respect to the central axis. It is advantageous, that only a height of one of the ridge elements of the staggered opposing pair of ridge elements is variable. The adapting element can be adapted to contact the ridge tail surface of the staggered pair of ridge elements.
It is advantageous that at the second open end of the waveguide body the ridge tail surfaces of the first or the second pair of ridge elements are merged. The staggered pair of ridge elements can be staggered in such a manner, that the respective ridge elements are merged at the second open end, preferably with only the height of one of the respective ridge elements being variable. In such a way the opposing, stepped ridge elements can form a septum polarizer. Thus, a linear polarized signal fed to the waveguide at the second open end can be transformed into a circular polarized signal at the first open end and vice versa. For use of the waveguide as a polarizer it is advantageous that the cross section of the waveguide body is circular or square.
According to an advantageous embodiment of the invention, the waveguide body comprises a groove formed at least sectionwise along the central axis with the groove being arranged along a circumferential direction between two neighbouring ridge elements. The waveguide comprising a groove can for example be used to transform the linear polarized signal fed to the waveguide at the second open end into a circular polarized signal at the first open end and vice versa. Advantageously, the groove is spaced apart from the first and the second open end. For a depth of the groove shallower than a thickness of the body wall the groove can be formed as a non-continuous recess in the body wall extending from the inside of the waveguide body. For a groove with a thickness larger than the body wall thickness the groove can be formed by a continuous recess in the body wall with the recess covered on the outside of the wave guide body with a lid element connected to the waveguide body. The waveguide can comprise a second groove, preferably arranged along the circumferential direction opposite to aforementioned groove.
To further increase the operational bandwidth ratio according to an advantageous aspect of the invention, the body wall between two neighbouring ridge elements is curved. It is also possible, that the curved body wall between two neighbouring ridge elements extends to the respective ridge tail surface. According to an advantageous aspect of the invention, the waveguide is a radiating element. The waveguide can be e.g. the open-ended waveguide antenna.

Brief description of the drawings

The present invention will be more fully understood, and further features will become apparent, when reference is made to the following detailed description and the accompanying drawings. The drawings are merely representative and are not intended to limit the scope of the claims. In fact, those of ordinary skill in the art may appreciate upon reading the following specification and viewing the present drawings that various modifications and variations can be made thereto without deviating from the innovative concepts of the invention. Like parts depicted in the drawings are referred to by the same reference numerals.

Figure 1 illustrates a perspective view of a waveguide,
Figure 2 illustrates a sectional view of the waveguide shown in figure 1 along a central axis and a first pair of ridge elements,
Figure 3 illustrates a sectional view along the central axis and the first pair of ridge elements of an alternative embodiment,
Figure 4 and figure 5 illustrate cross sections orthogonal to the central axis of two alternative embodiments of the waveguide,
Figure 6 and figure 7 illustrate top views of a first end and a second end of an alternative embodiment of the waveguide,
Figure 8 and figure 9 illustrate sectional views along the line I-I and II-II of the waveguide shown in figure 6 and figure 7,
Figure 10 and figure 11 illustrate cross sections orthogonal to the central axis of two alternative embodiments of the waveguide,
Figure 12 illustrates an electrical field formed inside the waveguide in an H₁₀ dominant mode, and
Figure 13 illustrates an electric field formed inside the waveguide in an H₁₁ higher order mode.

Figure 1 illustrates a perspective view of a waveguide 1. The waveguide 1 depicted in figure 1 comprises a square waveguide body 2 extending along a central axis 3 from a first open end 4 to a second open end 5. The waveguide 1 comprises a first pair 6 of opposed ridge elements and a second pair 7 of opposed ridge elements projecting inwardly from a body wall 8 of the waveguide body 2. The first pair 6 and the second pair 7 of ridge elements are arranged orthogonal to each other. The waveguide body 2 and the two pairs of ridge elements 6, 7 can be manufactured from a metallic material as copper. Each of the respective ridge elements of the two pairs of opposing ridge elements 6, 7 comprises a plane ridge tail surface 9.
Furthermore, the waveguide 1 comprises an adapting element 10 fabricated from a dielectric material 11 having a cross-shaped cross section. The dielectric material can be a polymer as polytetrafluoroethylene (PTFE). In a first section 12 of the waveguide 1 the adapting element 10 and the two pairs of ridge elements 6, 7 extend along the central axis 3. In the first section 12 the adapting element 10 is in contact with the ridge tail surfaces 9 of each of the respective ridge elements. In the embodiment of the waveguide 1 depicted in figure 1 the first section 12 extends from the first open end 4 to the second open end 5.
Figure 2 illustrates a sectional view of the waveguide 1 depicted in figure 1 along the central axis 3 and the first pair 6 of ridge elements. The adapting element 10 extends from the first open end 4 to the second open end 5 and contacts the ridge tail surfaces 9 of the opposing ridge elements of the first pair 6 and the second pair 7 of ridge elements.
Figure 3 illustrates a sectional view of an alternative embodiment of the waveguide 1 with the square waveguide body 2 with the two pairs of ridge elements 6, 7 as shown in figures 1 and 2. Here the first section 12 with the adaptive element 10 having a cross-shaped cross section extends along the central axis from the first open end 4 to a second section 13 of the waveguide 1. The second section 13 extends from the first section 12 to the second end 5.
Figure 4 and figure 5 illustrate sectional views orthogonal to the central axis 3 of the first section 12 of alternative embodiments of the waveguide 1. The waveguide body 2 of the waveguide 1 shown in figure 4 has a circular cross section. Each of the opposing ridge elements of the first pair 6 and the second pair 7 of ridge elements have a rectangular cross section comprising the ridge tail surface 9 and two side wall surfaces 14 with the ridge tail surface 9 being connected to the body wall 8 via the two side wall surfaces 14. The adapting element 10 is connected to all of the four ridge tail surfaces 9.
For the embodiment depicted in figure 5 an outline 15 of the cross section of the waveguide body 2 is square shaped. The ridge tail surfaces 9 of neighbouring ridge elements are connected via curved sections 16 of the body wall 8.
Figures 6 to 9 depict an alternative embodiment of the waveguide 1. Figure 6 and figure 7 illustrate schematic top views of the first open end 4 and the second open end 5 of the waveguide 1, respectively. Figure 8 and figure 9 illustrate respective sectional views along a line I-I and a line II-II as depicted in figure 7. A distance 17 between the first pair 6 of ridge elements is staggered. At the second open end 5 the first pair 6 of ridge elements is connected. The adapting element matches the staggered shaping of the first pair of ridge elements. In such a way the first pair 6 of ridge elements forms a septum polarizer.
Figure 10 and figure 11 illustrate schematic sectional views orthogonal to the central axis 3 of the first section 12 of alternative embodiments of the waveguide 1. The respective waveguide 1 depicted in figure 10 and figure 11 comprises a groove 18. The groove 18 is arranged along a circumferential direction between two neighbouring ridge elements. For the embodiment shown in figure 10 the groove is formed via a non-continuous recess 19 in the body wall 8. In case of the embodiment shown in figure 11 the groove 18 is formed via a continuous recess 20 in the body wall 8 and a lid element 21. The lid element 21 is matched to the continuous recess 20 and bonded to the body wall 8.
Figure 12 illustrates an electric field formed inside the waveguide 1 in a dominant mode Hio. A direction and a length of electric field lines 22, 23 depicts an orientation and an intensity of the electric field formed in the dominant mode Hio. The intensity of the field lines 23 extending between the ridge tail surfaces 9 of the first pair 6 of opposing ridge elements is larger than the intensity of the field lines 22 between opposing sections of the body wall 8 adjacent to the first pair 6 of opposing ridge elements. Thus, the dielectric material 11 of the adapting element 10 has a major effect on the electric field lines 23 of the dominant mode H₁₀ extending within the adapting element 10.
Figure 13 illustrates an electric field formed inside the waveguide 1 in a higher order mode H₁₁. The direction and the length of electric field lines 24, 25 depicts the orientation and the intensity of the electrical field formed in the higher order mode H₁₁. The curved electrical field lines 24 extend between sections of the side wall 8 between neighbouring ridge elements and are therefore not influenced by the dielectric material 11 of the adapting element 10. The electric field lines 25 extend between the opposing ridge elements within the dielectric material 11 of the adapting element 10. The electric field lines 24, 25 of the higher order mode H₁₁ are only partially extending within the adapting element 10, with the intensity of the electrical field lines 25 being smaller compared to the electrical field lines 23 of the dominant mode Hio, as depicted in figure 12. Hence, the influence of the dielectric material 11 of the adapting element 10 on the higher order mode H₁₁ is smaller as compared to the effect of the adapting element 10 on the dominant mode H₁₀.

Claims

Waveguide (1) for transmitting a radio frequency signal with a hollow waveguide body (2) extending along a central axis (3) between a first open end (4) and a second open end (5), whereby the waveguide body (2) comprises a body wall (8) of an electrically conductive material, whereby the body wall (8) encloses a waveguide cavity, wherein at least in a first section (12) of the waveguide (1) adjacent to the first end (4) of the waveguide body (2) the waveguide (1) comprises a first pair (6) and a second pair (7) of opposing ridge elements of the electrically conductive material, with each of the respective ridge elements arranged at the body wall (8) of the waveguide body (2) projecting inwardly from the body wall (8) and extending along the central axis (3), whereby each of the ridge elements comprises a ridge tail surface (9) that is closer to the central axis (3) than the adjacent parts of the body wall (8), characterized in that at least in the first section (12) an adapting element (10) comprising a dielectric material (11) with a relative permittivity larger than air is arranged in between the opposing ridge tail surfaces (9) of the first pair (6) and the second pair (7) of ridge elements.
Waveguide (1) according to claim 1, characterized in that at least in the first section (12) the adapting element (10) is in contact with the ridge tail surface (9) of each of the respective ridge elements.
Waveguide (1) according to any of the claims 1 or 2, characterized in that the adapting element (10) is spaced apart from the body wall (8).
Waveguide (1) according to any of the preceding claims, characterized in that the first pair (6) of ridge elements and the second pair (7) of ridge elements are arranged orthogonal towards each other.
Waveguide (1) according to claim 4, characterized in that at least in the first section (12) the adapting element (10) has a cross-shaped cross section orthogonal to the central axis (3).
Waveguide (1) according to any of the claims 4 or 5, characterized in that at least in the first section (12) orthogonal to the central axis (3) a cross section of the waveguide body (2) with the first pair (6) and the second pair (7) of ridge elements and the adapting element (10) are symmetric with respect to the first pair (6) of ridge elements and/or the second pair (7) of ridge elements arranged orthogonal towards each other.
Waveguide (1) according to any of the claims 4 to 6, characterized in that orthogonal to the central axis (3) the cross section of the wave guide body (2) is rectangular, preferably quadratic.
Waveguide (1) according to any of the preceding claims, characterized in that in a second section (13) of the waveguide (1) extending from the second open end (5) of the waveguide body (2) to the first section (12) of the wave guide (1) the first pair (6) and/ or the second pair (7) of ridge elements are extended from the first section (12) along the central axis (3) at least sectionwise into the second section (13).
Waveguide (1) according to claim 8, characterized in that in the second section (12) a distance (17) between the respective ridge tail surfaces (9) of the first pair (6) or the second pair (7) of ridge elements is staggered.
Waveguide (1) according to any of the claims 8 to 9, characterized in that at the second open end (5) of the waveguide body (2) the ridge tail surfaces (9) of the first pair (6) or the second pair (7) of ridge elements are merged.
Waveguide (1) according to any of the preceding claims, characterized in that the waveguide body (2) comprises a groove (18) formed at least sectionwise along the central axis (3) with the groove (18) being arranged along a circumferential direction between two neighbouring ridge elements.
Waveguide (1) according to any of the preceding claims, characterized in that along the cross section orthogonal to the central axis (3) the body wall (8) between two neighbouring ridge elements is curved.
Waveguide (1) according to any of the preceding claims, characterized in that the waveguide (1) is a radiating element.