WO2018171903A1

WO2018171903A1 - Waveguide junction for a feeding structure

Info

Publication number: WO2018171903A1
Application number: PCT/EP2017/057128
Authority: WO
Inventors: Fabio Morgia
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2017-03-24
Filing date: 2017-03-24
Publication date: 2018-09-27
Also published as: EP3526853B1; EP3526853A1

Abstract

The present invention provides a waveguide junction (100) for a feeding structure (1100) of a slot antenna array (1700). The waveguide junction (100) comprises a first waveguide (101), and a second waveguide (102) above the first waveguide (101). Further, it comprises a slot waveguide (103) arranged between the first waveguide (101) and the second waveguide (102) to couple the first and second waveguides (101, 102). The longitudinal axis of the slot waveguide (103) is rotated by 40-50°, preferably by 45°, with respect to the longitudinal axis of the first waveguide (101) and with respect to the longitudinal axis of the second waveguide (102). Additionally, the first waveguide (101) is cut parallel to the longitudinal axis of the slot waveguide (103) at one of its ends.

Description

WAVEGUIDE JUNCTION FOR A FEEDING STRUCTURE

TECHNICAL FIELD

The present invention relates to a waveguide junction for a feedings structure of a slot antenna array. The present invention further relates to a feedings structure of a slot antenna array, and to a slot antenna array. The feeding structure and the slot antenna array of the present invention are realized using waveguide junctions of the present invention as power dividers.

BACKGROUND

Conventional waveguide slot antenna arrays are suitable for multitude of applications that require high gain. A slot antenna array has two fundamental parts, a radiating part and a complicated three-dimensional feeding structure, which is arranged below the radiating part. The feeding structure is typically realized by using combinations of conventional E- plane and H-plane power dividers or power splitters, like T junctions. T junctions are the simplest of the commonly used waveguide junctions.

Fig. 18 shows (lower part) an H-plane T junction 1800, which is a type of waveguide junction that has gained its name, because a top of the "T" in the T junction, i.e. the waveguide forming the two T-arms 1801, is parallel to the plane of the magnetic field H lines in the waveguide. An electromagnetic field (indicated by arrows in Fig. 18, which indicate the direction of the electromagnetic field) can be fed into the waveguide forming the T-leg 1802, and in-phase outputs can be obtained from the two T-arms 1801. That is, the H-plane T junction 1800 is able to split an input signal into two in-phase (0°) output signals. Fig. 18 also shows (upper part) an E-plane T Junction 1810, which is a type of waveguide junction that has gained its name, because a top of the "T" in the T junction, i.e. the waveguide forming the two T-arms 1811, extends from the main waveguide forming the T-leg 1812 in the same plane as the electric field E in the waveguide. In contrast to the H- plane T junction 1800, the two output signals of the E-plane T junction 1810 will be out of phase (180°) with each other.

The main issue of conventional slot antenna arrays is related to ETSI requirements. The ETSI document (ETSI EN 302 217-4-2) addresses these ETSI requirements for directional fixed beam antennas to be utilized with new Point-to-Point (P-P) systems. The document defines specifically a Radiation Pattern Envelope (RPE) in terms of Co- and Cross- polarization. In case of an equal illumination at every radiator element of a conventional slot antenna array, the RPE of the slot antenna array is not compliant with the ETSI requirements.

In order to meet the ETSI requirements for the RPE, peak side lobe levels may be reduced via an amplitude control, which is called tapering. For this tapering, non-uniform amplitude weighting functions must be defined. In addition, in order to assign the right value of output power to each radiator element for obtaining the required RPE, the feeding structure of the slot antenna array must be properly designed. The most prominent trade-off, when implementing amplitude weighting functions in such a feeding structure, is between low side lobe levels and a physical implementation of the distribution over the whole frequency band.

The physical implementation requires combinations of equal and unequal waveguide power dividers, respectively. These power dividers should have several important characteristics: wideband, flexibility, compactness and symmetry. Some proposed combinations are just too complex to manufacture. For instance, one such complex combination proposes connecting two waveguides in a cross configuration, wherein the waveguides lie in two different planes.

Nevertheless, some conventional cross configurations that address the issue are known. However, these conventional cross configurations are either compact, but their output signals are in-phase, which is not desired. Or their structure is not symmetrical, i.e. the input waveguide is not symmetrical with the output waveguides. However, size and symmetry of waveguide junctions used for a feeding structure are very important, in order to reduce as much as possible the distance between the antenna radiators. SUMMARY

In view of the above-mentioned issue and disadvantages, the present invention aims to improve conventional waveguide junctions, and thus conventional feedings structures of conventional slot antenna arrays. The present invention has the object to provide a waveguide junction, which is compact and symmetrical, in order to build an improved feeding structure, and a slot antenna array that fulfills ETSI requirements. Further, the waveguide junction should be flexible in use. In particular, a rotation of the phase of the output signals should be easily possible, without changing the symmetry of the waveguide junction, and without variation of the phase of the input signal. Further, a physical rotation of the input of the waveguide junction should also be possible, without increasing return loss and splitting. Another object of the present invention is to provide a feeding structure for a slot antenna array, such that the slot antenna array can be operated with a RPE complying with ETSI requirements.

The objects of the present invention are achieved by the solutions provided respectively in the enclosed independent claims. Advantageous implementations of the present invention are further defined in the dependent claims. A first aspect of the present invention provides a waveguide junction for a feeding structure of a slot antenna array, the waveguide junction comprising a first waveguide, a second waveguide above the first waveguide, and a slot waveguide arranged between the first waveguide and the second waveguide to couple the first and second waveguides, wherein the longitudinal axis of the slot waveguide is rotated by 40-50°, preferably by 45°, with respect to the longitudinal axis of the first waveguide and with respect to the longitudinal axis of the second waveguide, and wherein the first waveguide is cut parallel to the longitudinal axis of the slot waveguide at one of its ends.

The slot waveguide, which is rotated by preferably 45°, realizes the coupling between, for instance, an input (first) waveguide and an output (second) waveguide. The coupling effect is supported by means of the 45° cut of the first waveguide.

The waveguide junction of the present invention can be used in realizing a feeding structure of a slot antenna array, and has several advantages. Firstly, it is very compact and symmetric. Secondly, a rotation of the phase of the output signals is easily possible, without any variation of the waveguide junction symmetry, and without any variation of the phase of the input signal. It is also possible to physicaly rotate the first waveguide, wherein return loss and splitting value stay the same after the rotation.

In an implementation form of the first aspect, the second waveguide is cut parallel to the longitudinal axis of the slot waveguide at one of its ends.

Thereby, a waveguide junction with a very compact two-plane bend design can be achieved. The longitudinal axis of the first waveguide is here perpendicular to the longitudinal axis of the second waveguide. This waveguide junction has one input and only one output. Signals can be coupled into one of the waveguides, and are coupled out from the other one of the waveguides. In a further implementation form of the first aspect, the first waveguide and/or the second waveguide comprises, arranged along its longitudinal axis, at least one narrower portion and at least one broader portion.

Such a shape of the waveguide(s), i.e. with different kinds of portions, improves the return loss of the waveguide junction. A waveguide having such different portions has accordingly different waveguide widths arranged along its longitudinal axis.

In a further implementation form of the first aspect, the second waveguide comprises, close to the slot waveguide, a step or groove on one of its surfaces (surface area or face), preferably on a surface (surface area or face) facing away from the first waveguide. In other words, the groove reduces the section of the waveguide, thereby allowing to split the power in non-equal parts.

The step or groove introduced, for instance, inside the second waveguide realizes an unequal power distribution between the two ends of the second waveguide. The step or groove, when placed close to the slot waveguide, may thus lead to a redistribution of the power among output ports of the waveguide junction. The output ports can be at the opposite ends of the second waveguide, while an input port of the waveguide junction is at the end of the first waveguide, which is not cut parallel to the slot waveguide. In other words, the end of the first waveguide, at which the input port is located, is not parallel to the slot waveguide. The distance between the slot waveguide and the step or groove, and the size of the step or groove, determine the value (ratio) of the power division between the output ports of such a waveguide junction. Despite very high values of unequal splitting (power division) in such a waveguide junction, results still show a very good wideband behavior. In particular, the waveguide junction can successfully be used in the design of, for example, a V-Band antenna with frequencies between 57 to 66 GHz.

In a further implementation form of the first aspect, the longitudinal axis of the first waveguide is perpendicular to the longitudinal axis of the second waveguide.

In a further implementation form of the first aspect, the longitudinal axis of the first waveguide is parallel to the longitudinal axis of the second waveguide. Thus, different geometries of power dividers can be fabricated, which makes the waveguide junction of the present invention very flexible in use, specifically simplifies integration into a feeding structure.

In a further implementation form of the first aspect, the waveguide junction is for transferring a signal in a frequency range of 40 -100 GHz, preferably 57-66 GHz between the first waveguide and the second waveguide.

The proposed transition has been successfully used in the design of V-Band antennas with 57 to 66 GHz.

A second aspect of the present invention provides a feeding structure for a slot antenna array, the feeding structure comprising at least one waveguide junction according to the first aspect or any implementation form. In an implementation form of the second aspect, the first waveguide of the at least one waveguide junction is connected to an input port in the feeding structure, and the second waveguide of the at least one waveguide junction is connected to at least one output port in the feedings structure. In a further implementation form of the second aspect, the at least one waveguide junction is configured as a power divider (power splitter) in the feeding structure.

In a further implementation form of the second aspect, multiple waveguide junctions according to the first aspect or any implementation form of the first aspect are arranged on different levels and connected together to form at least one power splitter element a with an input port and a plurality of output ports, wherein a power division value (a power splitting value) of waveguide junctions at the same level is the same. In a further implementation form of the second aspect, the first waveguides of the multiple waveguide junctions are arranged with their longitudinal axes parallel to each other, and are connected to a common input port.

With a feeding structure according to the second aspect and its implementation forms, a slot antenna array having a RPE complying with ETSI requirements can be realized. This is due to the various advantages of the waveguide junction described above. In particular, the waveguide junctions are arranged and connected in the feeding structure as power dividers. The power division of each waveguide junction can be adapted as needed, and particular high values of power division can be used. This enables designing the feeding structure according to ETSI requirements. Further, the waveguide junctions are very compact, particularly in the depth direction. Accordingly, many levels of waveguide junctions can be arranged in the feeding structure, without the feeding structure becoming too large for practical use. A third aspect of the present invention provides a slot antenna array comprising a feeding structure according to the second aspect or any implementation form of the second aspect.

In an implementation form of the third aspect, the slot antenna array further comprises a radiating part, wherein the feedings structure is arranged below and is connected to the radiating part.

The slot antenna array of the third aspect can be provided with a RPE that complies with ETSI requirements. It has to be noted that all devices, elements, units and means described in the present application could be implemented in the software or hardware elements or any kind of combination thereof. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. Even if, in the following description of specific embodiments, a specific functionality or step to be performed by external entities is not reflected in the description of a specific detailed element of that entity which performs that specific step or functionality, it should be clear for a skilled person that these methods and functionalities can be implemented in respective software or hardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS The above described aspects and implementation forms of the present invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

Fig. 1 shows a waveguide junction according to an embodiment of the present invention.

Fig. 2 shows a waveguide junction according to an embodiment of the present invention. Fig. 3 shows a waveguide junction according to an embodiment of the present invention.

Fig. 4 shows simulations for a waveguide junction according to an embodiment of the present invention.

Fig. 5 shows a waveguide junction according to an embodiment of the present invention. shows a waveguide junction according to an embodiment of the present invention. shows a waveguide junction according to an embodiment of the present invention. shows simulations of a waveguide junction according to an embodiment of the present invention. shows simulations of a waveguide junction according to an embodiment of the present invention. shows simulations of a waveguide junction according to an embodiment of the present invention. shows a generic feeding structure of a slot antenna array. shows feeding structure according to an embodiment of the present invention. shows an H-plane splitting element of a feedings structure according to an embodiment of the present invention. shows simulations of an H-plane splitting element of a feedings structure according to an embodiment of the present invention. shows an H-plane splitting element of a feedings structure according to an embodiment of the present invention. shows an E-plane splitting element of a feedings structure according to an embodiment of the present invention. shows a slot array antenna according to an embodiment of the present invention. Fig. 18 shows conventional H-plane and E-plane T junctions.

DETAILED DESCRIPTION OF EMBODIMENTS

Fig. 1 shows a waveguide junction 100 according to an embodiment of the present invention, which is suitable for a feeding structure 1100 (see e.g. Fig. 11) of a slot antenna array 1700 (see e.g. Fig. 17) of the present invention. The waveguide junction 100 comprises a first waveguide 101, and a second waveguide 102 arranged above the first waveguide 101. A slot waveguide 103 is further arranged between the first waveguide 101 and the second waveguide 102, in order to couple the first and second waveguides 101, 102. That means, a signal that is input, for instance, to the first waveguide 101 is coupled to, and can be output from, the second waveguide 102.

The arrangement of the three different waveguides 101-103 in the waveguide junction 100 is advantageously as follows. A longitudinal axis (extension direction) of the slot waveguide 103 is rotated by 40-50°, preferably by 45°, with respect to the longitudinal axis (extension direction) of the first waveguide 101, and with respect to the longitudinal axis (extension direction) of the second waveguide 102. The longitudinal axes of the first waveguide 101 and of the second waveguide 102, respectively, may be perpendicular to another.

In addition, in order to support and improve the coupling between the first and second waveguides 101, 102, the first waveguide 101 is cut parallel to the longitudinal axis of the slot waveguide 103 at one of its ends. That is, the first waveguide 101 has an end face, which runs parallel to the longitudinal axis (extension direction) of the slot waveguide 103.

Fig. 2 shows the waveguide junction 100 of Fig. 1 in more detail. The waveguide junction 100 of Fig. 2 includes three waveguides, namely the first waveguide 101, the second waveguide 102, and the slot waveguide 103 rotated by here 45°, which realizes the coupling between the two waveguides 101, 102. Further, here in Fig. 2, the first waveguide 101 is specifically an input waveguide, and the second waveguide 102 is specifically an output waveguide. That is, a signal input to an input port 200 of the first waveguide 101 can be coupled via the slot waveguide 103 to the second waveguide 102, is (power) divided in the second waveguide 102, and is output at the two opposite ports 201a, 201b of the second waveguide 102. Notably, the first waveguide 101 and the second waveguide 102 are perpendicular to each other, when considering their longitudinal axes.

Fig. 3 shows that, advantageously, the signal output at a first output port 201a of the waveguide junction 100 is out-of-phase with the signal output at a second output port 201b. Further, the waveguide junction 100 is, advantageously, very compact and also symmetric with respect to the input and output ports 200, 201a, 201b, and the two waveguides 101, 102, respectively.

Fig. 4 shows that the waveguide junction 100 of Fig. 3 can be successfully used in the design of a V-Band antenna, i.e. for an operating frequency band between 57 and 66 GHz. In this frequency band, an E-field input into the input port 200 of the first waveguide 101 is coupled well to the output ports 201a, 201b of the second waveguide 102, and this particularly over the complete frequency range (see results (b) in Fig. 4 (continued)). It can also be seen (see results (a) in Fig. 4) that the E-field (power) distribution in the waveguide junction 100 is very symmetrical. Figs. 5 and 6 show the flexible usability of the waveguide junction 100. In particular, the Figs. 5 and 6 demonstrate that a rotation of the phase of the output signals at the output ports 201a, 201b of the second waveguide 102 is possible by changing the orientation of the first waveguide by 180° with respect to the x axis, wherein the x axis is the axis parallel to the longitudinal axis of the first waveguide; and by rotating the slot waveguide by 90° with respect to the z axis, wherein the z axis is perpendicular to the plane of the first waveguide. A phase rotation is thus possible without changing the overall symmetry of the waveguide junction 100, and without variation of the phase of the input signal input at the input port 200 of the first waveguide 101. In this respect, Fig. 5 shows in a perspective view (left side) and a top view (right side) of the waveguide junction 100, that the first waveguide 101 is below the second waveguide 102, and the slot waveguide 103 is arranged between them. In the top view, the slot waveguide 103, and the parallel cut of the first waveguide 101, extend from upper left to lower right. The output signals at the output ports 201a, 201b are phase-rotated to another by 180°.

Fig. 6 shows in a perspective view (left side) and a top view (right side) of the waveguide junction 100, which correspond to the views in Fig. 5 that the slot waveguide 103, and the parallel cut of the first waveguide 101, extend from upper right to lower left (differently than in Fig. 5). This difference effects that the signal output from output port 201a in Fig. 5 is phase-rotated by 180° compared to the signal output from output port 201a in Fig. 6. Likewise, the signal output from port 201b in Fig. 5 is phase-rotated by 180° compared to the signal output from port 201b in Fig. 6.

Fig. 7 shows another waveguide junction 100 according to an embodiment of the present invention, which bases on the waveguide junctions 100 shown in the previous figures. In such a waveguide junction 100 as in Fig. 7, the first waveguide 101 and/or the second waveguide 102 has at least one narrower portion 701 and at least one broader portion 702, which portions 701, 702 are arranged along the longitudinal axis of the respective waveguide 101, 102. Particularly, here in Fig. 7, it is the first waveguide 102 that has two narrower portions 701 close to the output ports 201a, 201b, and has a broader portion 702 between the two narrower portions 701, particularly at the overlap of the first waveguide 102 with the slot waveguide 103. At a broader portion 702, the respective waveguide 102 is widened in a direction perpendicular to, but in-plane with, its longitudinal axis. In other words, at a broader portion 702, the respective waveguide 101, 102 extends wider outwardly than in a narrower portion 701. In particular, a broader portion 702 arranged close to the slot waveguide 103 on a waveguide junction 102 improves the return loss of the waveguide junction 100. Same holds also true for the first waveguide 101.

In some application may also be advantageous to design the waveguide junction so that the first waveguide 101 and/or the second waveguide 102 has two broader portions close to the output ports 201a, 201b, and has a narrower portion between the two broader portions.

Fig. 8 shows further flexible usability of the waveguide junction 100. In the waveguide junction 100 shown in part (a) of Fig. 8, the first waveguide 101 is perpendicular to the second waveguide 102, i.e. with respect to their longitudinal axes. In the waveguide junction 100 shown on part (b) of Fig. 8 (see Fig. 8 (continued)), the longitudinal axis of the first waveguide 101 is parallel to the longitudinal axis of the second waveguide 102. For both waveguide junctions 100 shown in Fig. 8, a good coupling is simulated over the whole frequency band (57-66 GHz). Thus, within the waveguide junction 100, it is also possible to physicaly rotate the input (first) waveguide 101, whereby specifically return loss and splitting value stay the same after the rotation.

Fig. 9 shows a waveguide junction 100 according to another embodiment of the present invention, which bases on the waveguide junction 100 shown in the previous figures. In particular, with the waveguide junction 100 of Fig. 9, an unequal power divider can be realized. Such an unequal power divider is usable for achieving ETSI Class 2 requirements of a slot antenna array, since for these requirements output power tapering of the radiators of the slot antenna array is required. Here in Fig. 9, the second waveguide 102 comprises, close to the slot waveguide 103, a step or groove 900 on one of its surfaces, preferably on a surface facing away from the first waveguide 101. The step or groove 900 effects a power redistribution among the output ports 201a, 201b of the second waveguide 102. To this end, the step or groove 900 is placed preferably close to the slot waveguide 103. The distance between the slot waveguide 103 and the step or groove 900, and the size of the step or groove 900, determines the value (ratio) of the power division. Thus, the value (ratio) of the power division can be adjusted according to practical needs. Even for a very high value of the power division, simulation results show a wideband behavior between particularly the frequencies of 57 to 66 GHz.

Fig. 10 shows a waveguide junction 100 according to another embodiment of the present invention, which bases on the waveguide junction 100 shown in the Figs. 1 and 2. Here, both the first waveguide 101 and the second waveguide 102 are cut parallel to the longitudinal axis of the slot waveguide 103 at one of their ends. That is, the second waveguide 102 is additionally cut (in Figs. 1 and 2 only the first waveguide 101 is cut), and accordingly has an end face running parallel to the slot waveguide 103. This design of the waveguide junction 100 has one input port 200 and only one output port 201, namely at the uncut end of the second waveguide 102. Therefore, the waveguide junction 100 of Fig. 9 realizes a two-plane bend structure, which is very compact, while still its wideband behavior is very good between 57-66 GHz. All the waveguide junctions 100 according to embodiments of the present invention can particularly be used in a feeding structure of a slot antenna array, as described in the following. Fig. 11 shows a feeding structure 1100 for a slot antenna array 1700 (e.g. in Fig. 17) with one input 1101 and 2^N outputs 1102, where N denotes a number of power splitting levels within the feeding structure 1100, and is an integer. Due to the 2^N outputs 1102, (2^N -1) power dividers 1103 (also called power splitters) are required. In the example of Fig. 11 (here the case is N=3), the feeding structure 1100 has seven power dividers 1103. In a conventional case of using no-uniform amplitude weighting functions (e.g. Binomial, Chebyshev, etc.), the power dividers 1103 have to be dimensioned, in order to obtain the desired output power at the radiators level. However, not all functions that are needed can be physically implemented. Sometimes, it is not possible to realize the right value of the power division of a power divider 1103, and some other times it is possible, but only for a narrow frequency band. By using, however, in the feeding structure, waveguide junctions 100 according to the present invention as selected power dividers 1103, this issue can be resolved. A particular constraint for the possible values of the power dividers 1103 is added in this feeding structure 1100, namely that all the power dividers 1103 at the same level m, where m e [1, 2, ... , N] of the feeding structure 1100 have the same power division value (power splitting value).

Fig. 12 shows a feeding structure 1100 according to an embodiment of the present invention. The feeding structure 1100 includes the input 1101, the multiple outputs 1102, and the plurality of power dividers 1103. In particular, the feeding structure 1100 preferably includes a plurality of waveguide junctions 100 as selected ones of the power dividers 1103. The power dividers 1103 are arranged on different levels m, where m e

[1, 2, ... , N], and are connected together to form a power- splitting feeding structure 1100. Again, values of power division of the power dividers 1103 at the same level m are the same. The feeding structure 1100 of Fig. 12 is specifically divided into different kinds of power splitting elements, namely at least one splitting element 1200 for splitting power along the H-plane, and at least one splitting element 1201 for splitting power along the E- plane. Fig. 13 shows the H-plane splitting element 1200, which is part of the feedings structure 1100 shown in Fig. 12. It is called H-plane splitting element 1200, since it realizes power splitting along the H-plane. In particular, the element 1200 is shown with an input (which corresponds to the input port 1101 of the feeding structure in Fig. 12) and with 16 output ports 1300. Selected power dividers 1103 of the element 1200 (as shown by dotted circles for one side of the element 1200, repeated likewise on the other side of the element 1200) are realized by waveguide junctions 100 according to the present invention. Each waveguide junction 100 thus individually serves as a power divider 1103 (power splitter) in the feeding structure 1100. The first waveguide 101 of each waveguide junction 100 is connected directly or indirectly to the input port 1101 of the feeding structure 1100, and the second waveguide 102 of each waveguide junction 100 is connected directly or indirectly to at least one output port 1300 in the feedings structure 1100. Each waveguide junction 100 can thus act as a power splitter for the power of the input signal. The first waveguides 101 of the multiple waveguide junctions 100 are further arranged with their longitudinal axes parallel to each other.

The multiple power dividers 1103 are arranged on different levels N of the element 1200 (and thus also the feeding structure 1100 shown in Fig. 12), and are connected together to form the element 1200. The power division value (power splitting ratio) of the power dividers 1103 at the same level m is the same, m e [1, 2, ... , N] . Power dividers 1103, which are provided displaced from another perpendicular to the longitudinal axes of the first and second waveguides 101, 102, are at different levels N of the element 1200.

Fig. 14 shows that in the H-plane splitting element 1200 of Fig. 13, the power distribution is symmetric in each level m, and the power is split evenly towards higher levels of the N levels.

Fig. 15 shows the H-plane splitting element 1200 of Fig. 13 in another perspective. It can particularly be seen, which power dividers 1103 are implemented by waveguide junctions 100. Preferably, all power dividers 1103 except for the one on the lowest level of the N levels are implemented by waveguide junctions 100. That is, the power divider 1103 on the lowest level directly at the input port 1101 of the signal is preferably a conventional power divider 1103, preferably a conventional T-junction, while all further power dividers 1103 (shown by dotted circles on one side of the element 1200, repeated likewise on the other side of the element 1200) are waveguide junctions 100. One advantage of the waveguide junctions 100 is here their very low depth, which allows reducing size and costs of a feedings structure with several layers N. Fig. 16 shows the E-plane splitting element 1201 of Fig. 12. The element 1201 has an input port 1600, multiple power dividers 1103, and radiator elements 1601, which are connected to the power dividers at the highest level of the N levels. Again, selected ones of the power dividers 1103 are implemented by waveguide junctions 100. In particular, all power dividers 1103 except for those on the highest level (connected to the radiator elements 1601) are implemented by waveguide junctions 100.

Fig. 17 shows a slot antenna array 1700 according to an embodiment of the present invention. The slot antenna array 1700 comprises a radiating part 1701 and a feeding structure 1100, for instance, as shown in Fig. 12. The feedings structure 1100 is arranged below, and is connected to the radiating part 1701. The feeding structure 1100 includes a plurality of waveguide junctions 100 as selected power dividers 1103, preferably connected together as shown in the Figs. 13-16, respectively.

The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those persons skilled in the art and practicing the claimed invention, from the studies of the drawings, this disclosure and the independent claims. In the claims as well as in the description the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.

Claims

1. Waveguide junction (100) for a feeding structure (1100) of a slot antenna array (1700), the waveguide junction (100) comprising

a first waveguide (101),

a second waveguide (102) above the first waveguide (101), and

a slot waveguide (103) arranged between the first waveguide (101) and the second waveguide (102) to couple the first and second waveguides (101, 102),

wherein the longitudinal axis of the slot waveguide (103) is rotated by 40-50°, preferably by 45°, with respect to the longitudinal axis of the first waveguide (101) and with respect to the longitudinal axis of the second waveguide (102), and

wherein the first waveguide (101) is cut parallel to the longitudinal axis of the slot waveguide (103) at one of its ends.

2. Waveguide junction (100) according to claim 1, wherein

the second waveguide (102) is cut parallel to the longitudinal axis of the slot waveguide (103) at one of its ends.

3. Waveguide junction (100) according to claim 1 or 2, wherein

the first waveguide (101) and/or the second waveguide (102) comprises, arranged along its longitudinal axis, at least one narrower portion (701) and at least one broader portion (702).

4. Waveguide junction (100) according to one of the claims 1 to 3, wherein

the second waveguide (102) comprises, close to the slot waveguide (103), a step or groove (900) on one of its surfaces, preferably on a surface facing away from the first waveguide (101).

5. Waveguide junction (100) according to one of the claims 1 to 4, wherein

the longitudinal axis of the first waveguide (101) is perpendicular to the longitudinal axis of the second waveguide (102).

6. Waveguide junction (100) according to one of the claims 1 to 4, wherein the longitudinal axis of the first waveguide (101) is parallel to the longitudinal axis of the second waveguide (102).

7. Waveguide junction (100) according to one of the claims 1 to 6 for transferring a signal in a frequency range of 40 -100 GHz, preferably 57-66 GHz between the first waveguide (101) and the second waveguide (102).

8. Feeding structure (1100) for a slot antenna array (1700), the feeding structure (1100) comprising at least one waveguide junction (100) according to one of the claims 1 to 7.

9. Feeding structure (1100) according to claim 8, wherein

the first waveguide (101) of the at least one waveguide junction (100) is connected to an input port (1101) in the feeding structure (1100), and

the second waveguide (102) of the at least one waveguide junction (100) is connected to at least one output port (1102) in the feedings structure (1100).

10. Feeding structure (1100) according to claim 8 or 9, wherein

the at least one waveguide junction (100) is configured as a power divider (1103) in the feeding structure (1100).

11. Feeding structure (1100) according to one of claims 8 to 10, wherein

multiple waveguide junctions (100) according to one of the claims 1 to 7 are arranged on different levels and connected together to form at least one power splitter element (1200, 1201) with an input port (1101, 1600) and a plurality of output ports

(1300, 1601), wherein a power division value of waveguide junctions (100) at the same level is the same.

12. Feeding structure (1100) according to claim 11, wherein

the first waveguides (101) of the multiple waveguide junctions (100) are arranged with their longitudinal axes parallel to each other, and are connected to a common input port (1101).

13. Slot antenna array (1700) comprising a feeding structure (1100) according to one of the claims 8 to 12.

14. Slot antenna array (1700) according to claim 13, further comprising

a radiating part (1701),

wherein the feedings structure (1100) is arranged below and is connected to the radiating part (1701).