Comb-shaped waveguide filter with an omnidirectional resonator

Abstract

Additively manufacture a comb waveguide filter with a degree of freedom in configuration. 【Solution means】The present invention is a comb waveguide filter (1) manufactured by metal additive manufacturing, comprising at least two resonators (2) interconnected by a main iris (24), each resonator comprising a cavity (20) having a first axis (z), each cavity (20) is in particular delimited in the range of the cavity by a flat bottom (21) extending perpendicular to the first axis (z), relating to a waveguide filter (1). The present invention also relates to a method for manufacturing the described comb waveguide filter, which method includes additive manufacturing of the at least two resonators and the main iris connecting those resonators.

Description

Technical Field

[0001] The present invention relates to a comb waveguide filter having an all-directional resonator obtained by additive manufacturing.

Background Art

[0002] Radio frequency (RF) signals can propagate in free space or waveguide devices.

[0003] An example of such a conventional waveguide is described in Patent Document 1. The content thereof is incorporated herein by reference. The waveguide consists of a hollow device, and its shape and dimensions determine the propagation characteristics for a predetermined wavelength of an electromagnetic signal. The cross-section of the internal waveguide of this device is rectangular. In this document, other waveguide cross-sections including circular shapes are proposed.

[0004] This prior art waveguide includes a core manufactured by additive manufacturing by stacking layers one by one. This core defines an internal waveguide as a wave guide having a cross-section determined by the frequency of the electromagnetic signal to be propagated. The inner surface of the core is covered with a conductive metal layer. The outer surface may also be covered with a conductive metal layer that contributes to the rigidity of the device.

[0005] Waveguide devices are used, for example, to form waveguide filters, propagate RF signals, or operate in the spatial or frequency domain. The present invention relates to a passive waveguide filter that can filter RF signals without using active electronic components in particular.

[0006] Conventional waveguide filters used for radio frequency signals generally have internal openings with rectangular or circular cross-sections. The main purpose of these filters is to suppress unwanted frequencies and pass the desired frequencies with minimal attenuation. For example, one or both filters for a receiving system and a transmitting system in the spatial domain may require attenuation exceeding 100 dB or 120 dB.

Prior Art Documents

Patent Document

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] One object of the present invention is to provide a comb-type waveguide filter that is not subject to the limitations of known waveguide filters.

[0009] Another object of the present invention is to provide a comb-type waveguide filter suitable for additive manufacturing.

[0010] Another object of the present invention is to provide a comb-type waveguide filter that is more compact and less bulky.

[0011] Another object of the present invention is to provide a comb-type waveguide filter that can filter a wider frequency range (only signals of a certain frequency are propagated, and signals of other frequencies are not propagated).

Means for Solving the Problems

[0012] According to this invention, these objects are achieved, in particular, a comb-type waveguide filter manufactured by metal additive manufacturing, comprising at least two resonators interconnected by a main iris, each resonator having a cavity with a first axis, in the waveguide filter, each cavity being delimited, in particular, by a flat bottom extending perpendicular to the first axis, characterized in that each cavity is further delimited by a roof converging towards a single point, by a waveguide filter.

[0013] The fact that the resonator has a roof converging towards a single point facilitates or enables additive manufacturing of the waveguide filter by avoiding (there being no overhanging beam portion) the overhanging beam portion which is complex to manufacture. Second, the fact that the roof converges towards a single point means that the "axial" property of conventional filters, where the shape of the resonator is restricted in the propagation direction of the electromagnetic signal within the filter, is avoided.

[0014] Each roof may comprise a first lateral portion adjacent to the flat bottom and a second lateral portion converging towards a single point.

[0015] Each resonator may have rotational symmetry about a first axis.

[0016] Each flat bottom is circular or a polygon having at least three sides and may preferably be circular, square, pentagonal, hexagonal, or octagonal.

[0017] Each resonator may further comprise a post rising parallel to the first axis from the flat bottom.

[0018] At least one post may be made integrally with the flat bottom of the resonator.

[0019] The post of each resonator may have a circular or a cross-section having at least three sides, preferably a circular, square, pentagonal, hexagonal, or octagonal cross-section.

[0020] Advantageously, the post may be helical and extend along the first axis. This configuration allows the length of the post to be increased, and thus the impedance matching of the cavity of the resonator can be made greater.

[0021] In one embodiment, the diameter of the post may vary along the first z-axis.

[0022] The roof of at least one resonator may comprise a protrusion extending parallel to the first axis towards the inside of the cavity of at least one resonator.

[0023] At least one main iris may comprise a connection portion that is not parallel to the flat bottom. This connection portion extends between two resonators connected by at least one main iris.

[0024] The connection portion may connect the single point of a plurality of resonators connected by at least one main iris.

[0025] At least one resonator may comprise a plurality of main irises that are not coaxially arranged.

[0026] The waveguide filter may comprise at least three resonators that are continuously connected by main irises. The first and second resonators of the three resonators are connected to each other by a secondary iris.

[0027] This mutual coupling (in French, "couplage croisé") improves the selectivity of the filter in a specific frequency band.

[0028] The secondary iris may have a cross-section different from that of the main iris (24).

[0029] At least one secondary iris may comprise a secondary connection portion that extends between resonators connected by at least one secondary iris

[0030] A plurality of main irises of a plurality of resonators may be coaxially arranged along the propagation axis of the electromagnetic signal.

[0031] The waveguide filter may comprise at least four resonators. One of these at least four resonators may be connected to at least three separate resonators.

[0032] In particular, this matter makes it possible to obtain, for example, a filter, or a filter that combines the functions of one or both of a distributor and a polarizer.

[0033] At least one resonator may comprise one or both of a polarizer and a septum (polarization converter).

[0034] According to the present invention, these objects are also achieved by a method for manufacturing a comb waveguide filter having at least one of the above-described characteristics. This method includes additive manufacturing of at least two resonators and a main iris connecting these resonators.

[0035] Embodiments of the present invention are described with reference to the accompanying drawings.

Brief Description of the Drawings

[0036]

Figure 1a

Figure 1b

Figure 1c

Figure 1d

Figure 1e

Figure 1f

Figure 2a

Figure 2b

Figure 3a

Figure 3b

Figure 4a

Figure 4b

Figure 4c

Figure 4d

Figure 4e

Figure 5a

Figure 5b

Figure 6a

Figure 6b

Figure 7

Figure 8

Figure 9

DETAILED DESCRIPTION OF THE INVENTION

[0037] The present invention relates to a comb waveguide filter 1 comprising at least two resonators 2 obtained by additive manufacturing and connected to each other by a main iris 24. Each resonator 2 comprises a cavity 20 defined by a flat bottom 21 and a roof 22, in particular perpendicular to a first axis z.

[0038] Figures 1a to 1f show examples of resonators 2 that can be used in the comb waveguide filter 1 according to the present invention. The main iris 24 connecting a plurality of resonators is not shown in these figures.

[0039] The first z-axis generally corresponds to the direction of additive manufacturing.

[0040] By converging the roof 22 of each resonator 2 toward a single point 23, it is possible to avoid a cantilever surface with respect to the first axis z, which is difficult or impossible to manufacture by additive manufacturing. Furthermore, the manufacture of the roof 22 converging toward the zenith point enables a resonator 2 that does not have a preferred direction for the propagation of electromagnetic waves because it does not converge toward the ridge of the roof. In fact, while the propagation direction is determined to some extent by two roofs intersecting at a ridge, the roof according to the present invention converges to a single point, so that the propagation direction of waves in the waveguide filter can be selected more freely. In other words, the resonator is omnidirectional (non-directional) in the sense that it can be connected to other resonators in almost any direction. Due to the flexibility (in arrangement) brought about by the shape of the roof 22 according to this invention, for example, even if the resonators are not aligned in a straight line along the axis but form a bent portion, a filter can be created as a comb waveguide filter. Therefore, by selecting a shape that conforms to specific constraints, it becomes possible to significantly reduce the overall dimensions of such a filter.

[0041] The roof 22 of the resonator 2 may be inclined away from the flat bottom 21 as shown in FIGS. 1a, 1c, and 1e. Alternatively, the roof 22 may be provided with a first vertical side portion 26 adjacent to the flat bottom 21 and a second side portion 27 that is inclined and converges toward a single point 23 as shown in FIGS. 1b, 1d, and 1f. In this way, the roof 22 can be designed as a pyramid having the flat bottom 21 as the bottom, or as a combination of a rectangular parallelepiped having the flat bottom 21 and a pyramid disposed on the rectangular parallelepiped.

[0042] Other embodiments include a resonator having a roof 22 that converges towards a single point 23, where the contour is not linear as in the case of a pyramid, but rather, for example, polygonal, parabolic, hyperbolic, or any other contour that enables additive manufacturing.

[0043] Generally, the angle that the inclined portion of the roof 22 makes with the first axis is between 10° and 60°, preferably between 25° and 50°. This is because if the angle is too large, additive manufacturing of the inclined portion becomes difficult.

[0044] As shown in FIGS. 1a to 1f, the resonator may have at least one rotational symmetry about the first z-axis. Preferably, the resonator has multiple rotational symmetries about the z1-axis.

[0045] FIGS. 1a and 1b show embodiments where the roof 22 is conical or consists of a cone that overrides a cylinder. In these cases, since the contour of the roof is obtained as a rotational surface about the first axis z, maximum rotational symmetry is achieved.

[0046] FIGS. 1c and 1d show embodiments where the roof 22 is a pyramid with a square base or a pyramid with a square base is formed on a prism (i.e., a parallelepiped) with a square base. Thus, the roof 22 is invariant with respect to rotation about the first axis z by an angle of kx90°, where k is an integer.

[0047] FIGS. 1e and 1f show embodiments where the roof 22 is a pyramid with a regular hexagonal base or a pyramid placed on a prism with a pyramid having a regular hexagonal base. Thus, the roof 22 is invariant with respect to rotation about the first axis z passing through an angle of kx60°, where k is an integer.

[0048] More generally, the roof 22 may comprise any rotational surface about the first axis z, such that the roof converges towards a single point 23. Additionally or alternatively, the roof 22 may comprise a pyramid whose base is shaped by any polygon.

[0049] The first side portion 26 of the roof 22 may be cylindrical. Alternatively or complementarily, a rectangular parallelepiped with an arbitrary polygon at the bottom may be provided.

[0050] In a preferred embodiment, the flat bottom 21 that separates the cavity 20 of the resonator 2 according to the present invention has, like the roof 22, the property of invariance under rotation about the first axis z. In particular, the flat bottom may be circular, a polygon having at least three sides, preferably circular, square, pentagonal, hexagonal or octagonal. Other shapes of the flat bottom 21 such as elliptical or non-convex can also be envisaged without departing from the scope of the present invention.

[0051] The plurality of resonators 2 of the comb waveguide filter according to the present invention are interconnected by the main iris 24. As will be explained below, some resonators may include secondary irises, which explains the term "main" iris. These main irises 24 enable the propagation of electromagnetic waves from one resonator to another within the filter.

[0052] In one embodiment, two consecutive resonators 2 of the filter 1 have a geometry that allows them to be arranged relative to each other in a sufficient proportion, i.e., when most of the roof 22 of the first resonator is arranged relative to most of the roof 22 of the second resonator, the main iris 24 may be formed by an opening in the continuous portion of the roof.

[0053] The cross-section of this opening determines the cut-off frequency of the wave propagating between these two resonators via the main iris 24. Therefore, this cross-section conforms to the specific requirements intended for the filter 1.

[0054] In another embodiment, the shape of resonator 2 requires an opening larger than the continuous portion of the resonator. As shown in FIGS. 2A and 2B, the main iris 24 includes an opening extending to both the first lateral portion 26 and the second lateral portion 27 of the roof 22. The connecting portion 25 extends between at least a portion of the two second lateral portions 27 of the two roofs 22 connected by the main iris 24.

[0055] As shown in FIGS. 2a and 3a, the connection portion between the resonators may include an inclined portion to facilitate additive manufacturing or to enable those connection portions to be additively manufactured as well. The connection portion may be composed of, for example, a gable roof.

[0056] In one embodiment, the connecting portion 25 can connect the two roofs 22 over the entire height of the roof 22 or over the entire height of the second lateral portion 27 of the roof. Alternatively or complementarily, a single point 23 of the two roofs 22 can be connected by the connecting portion 25.

[0057] In an embodiment not shown, due to the shape of the resonators 2, they cannot be arranged adjacent to each other. Thus, the main iris 24 connecting such two resonators includes a connecting portion 25 connecting the two resonators. This connecting portion can be, for example, a rectangular waveguide having the same cross-section as the opening of the main iris that determines the cut-off frequency.

[0058] Generally speaking, the length, width, and height of the main iris and the connecting portion affect the coupling position (level) between the two resonators. Therefore, these variables are adapted according to requirements.

[0059] As shown in FIGS. 2A and 2B, the cavity 20 of the resonator 2 may include a post 28 rising from a flat bottom 21 parallel to the first axis z. By using the post 28 in the cavity 20, the impedance of the cavity can be changed, thereby controlling the resonance frequency of the circuit formed by the cavity 20 and the main iris 24.

[0060] These posts 28 differ from any adjustment screws in that their resonant frequency cannot be adapted or changed by addition.

[0061] These posts 28 can be integrally formed with the flat bottom 21. This method is advantageous from the perspective of additive manufacturing because it can avoid subsequent machining for forming such posts.

[0062] The shape of these posts, and more particularly, their cross-section in a plane parallel to the flat bottom 21, can be adapted as required and also as a function of the geometry of the roof 22. The geometric shape of the cross-section of the post 28 does not necessarily have to be the same as the cross-sectional geometry of the flat bottom 21 or the cross-sectional geometry of the roof 22 of the resonator.

[0063] As shown in FIGS. 4a to 4e, the resonator 2 may comprise a post 28 which is a cuboid whose cross-section has a bottom which is a circle or a polygon with at least three sides. Preferably, the bottom of the post is circular, square, pentagonal, hexagonal or octagonal. The circular geometries of the flat bottom 21 and the roof 22 in FIGS. 4a to 4e are by no means restrictive and, in combination with these posts, all the alternative structures described above can be realized.

[0064] To facilitate the additive manufacturing of such posts 28, the upper surface of the post, i.e., the surface facing the flat bottom 21, may comprise a curved portion or an inclined portion. These curved portions are also useful when the filter is for high-power applications.

[0065] In an alternatively implemented embodiment shown in FIGS. 7 to 9, the post 28 is helical with its main direction coinciding with the first z-axis. When it is said that a helical post extends parallel to an axis, it means that the main direction of the helix is parallel to the axis.

[0066] Using such a helical post makes it possible to obtain a post 28 that is longer than a straight post. In particular, this makes it possible to increase the impedance matching of the cavity 20 to a greater extent.

[0067] The pitch of the propeller, i.e., the vertical distance between two consecutive points on the propeller in a plane containing the first z-axis line, may be constant or variable.

[0068] The diameter of the helix can also be constant or variable. In a preferred embodiment shown in FIGS. 7 to 9, the diameter of the helix decreases as a function of the height relative to the flat bottom 21 of the resonator 2. In particular, this configuration makes it possible to adapt the outer diameter of the helical post to the inner diameter of the cavity 20 of the resonator 2. The rotating surface on which the helix is formed is a cone.

[0069] However, in certain configurations where it is not necessary to reduce the diameter of the helix, the diameter of the helix may be kept constant in order to further increase the overall length of the helical post.

[0070] Alternatively or additionally, the rotating surface on which the propeller rests may be an inverted cone, a cylinder, a sphere, or a surface with alternating positive and negative curvatures. Thereby, the diameter of the propeller can be made to increase and decrease alternately.

[0071] Such a helical post 28 can be additively manufactured integrally with the rest of the resonator. Alternatively or additionally, the helical post may be manufactured separately from the resonator and placed inside the cavity during or after the additive manufacturing of the resonator.

[0072] As shown in FIG. 9, two adjacent resonators 2 may each comprise a helical post 28. The winding direction of the helix, i.e., the direction, may be the same or, alternatively, opposite.

[0073] The upper part of the cavity 20 of the resonator 2 may be provided with protrusions extending from the inner surface of the roof 22 towards the inside of the cavity so as to change the impedance of the cavity. These protrusions extend substantially parallel to the first axis. These protrusions are integral with the resonator and are thus also distinguished from conventional adjustment screws which are movable elements with respect to the resonator.

[0074] In a preferred embodiment, the protrusion is integral with the roof 22 of the resonator. Similar to the post 28, the surface of the protrusion facing the roof 22 can be flat or curved according to specific requirements, especially with respect to additive manufacturing and high-power use of the filter.

[0075] The resonator 2 of the waveguide filter 1 may be provided with adjustment screws that allow for fine-tuning when the filter is in use. Different from the post 28, these screws are movable elements with respect to the resonator structure and are used to make slight changes to the impedance of the resonator cavity 20.

[0076] As described above, one of the main advantages of the waveguide filter according to the present invention lies in its omnidirectionality (in the sense that the resonators are non-coaxial, i.e., not necessarily connected along one axis).

[0077] Figs. 3a and 3b show an embodiment in which a plurality of resonators 2 are arranged non-coaxially. More specifically, for example, the first resonator 2, which is the left resonator in Fig. 3a, has a port 31 that allows it to receive an electromagnetic signal at the input of the filter. This first resonator is connected to the second resonator 2 by a main iris 24 having a connection portion 25. The main iris 24 is not located at a position directly opposite the port 31. On the one hand, the straight line passing through the center of the port 31 and the flat bottom 21, and on the other hand, the straight line passing through the center of the flat bottom and the main iris 24 intersect, forming an angle between 90° and 150°.

[0078] The second resonator is also connected to the third resonator 2 (the rightmost in Fig. 3a) via a main iris 24 that also has a connection portion 25. The third resonator is provided with a port 31 through which the electromagnetic signal can be emitted from the filter 1. Similarly, the angle formed by the straight line passing through the center of the flat bottom 21 and the straight line passing through the center of the flat bottom and the port 31 through the main iris 24 connecting the second resonator and the third resonator is between 90° and 150°.

[0079] The filter obtained by this resonator arrangement thus forms a bent portion with the second resonator, and compared with the conventional coaxial arrangement, the overall length of the filter can be significantly shortened for a given number of resonators.

[0080] Due to the circular shape of the roof 22 of the resonator in this design, a great degree of freedom is obtained in the relative positioning of the resonators. In fact, since it is invariant with respect to rotation about the first z-axis, it is virtually possible to arrange the circular resonator at any position around another circular resonator. Therefore, by connecting the resonators in this way, a very diverse filter shape can be obtained.

[0081] Another advantage resulting from the omnidirectionality of the resonator is the fact that by introducing "knees" into the filter, certain non - continuous resonators that are not connected by the main iris can be placed very close to each other. In Fig. 3b, the two resonators with ports 31 are not connected by the main iris but are very close. Therefore, by utilizing the property of being close, a secondary coupling (sub - coupling) can be introduced between the non - continuous resonators.

[0082] In particular, these sub - couplings make it possible to introduce alternative propagation paths for the waves in the filter. Depending on the phase of the signal, transmission zeros may appear in the transfer function of the filter as a result of multiplying the paths of the waves in the filter. This means that sub - couplings between non - continuous resonators can be applied, for example, to achieve a linear phase response, or to improve the selectivity of the filter by enhancing filtering at specific locations at specific frequencies by generating finite transmission zeros. In this way, by introducing transmission zeros into the frequency response, the number of resonators required to meet the specifications of a specific filter selectivity can be reduced. As a result, the insertion loss, installation area, and manufacturing cost can be reduced.

[0083] These secondary coupling portions take the form of a secondary iris 29. This secondary iris 29 may comprise a secondary connection portion between two roofs 22 of the resonator connected by the secondary iris. Similar to the case of the connection portion, the secondary connection portion may comprise a portion inclined with respect to the first axis to facilitate additive manufacturing.

[0084] Figure 3b shows a second connection portion 29 connecting a first resonator with an input port 31 and a third resonator with an output port 31.

[0085] The cross-section of the secondary iris 29 may be different from that of the main iris 24. The cross-section of the secondary iris is, for example, rectangular (the longest side of the rectangle is arranged parallel or perpendicular to the first z-axis).

[0086] Another embodiment of a filter with non-coaxial resonators is shown in FIGS. 5a and 5b. A plurality of resonators 2 designed according to a square-bottom model are arranged vertically and horizontally so that each resonator has at least two sides in continuity with other resonators. The main iris 24 with a connection portion 25 connects the resonators 2 and forms the electromagnetic wave propagation path in the filter 1. For example, in FIG. 5b, an electromagnetic wave enters the filter 1 via the port 31 of the rightmost resonator 2, then propagates counterclockwise by 90° via the main iris and reaches the second resonator 2 (the second resonator) (below in FIG. 5b). Then, it propagates clockwise by 90° via the main iris to the third resonator 2 (the third resonator) (left in FIG. 5b) and then propagates clockwise by 90° via the main iris to the fourth resonator 2 (the fourth resonator) (above in FIG. 5b). Finally, it rotates counterclockwise by 90° from the filter and is output from the port 31 of the fourth resonator.

[0087] As shown in FIGS. 5a and 5b, the first resonator and the fourth resonator are additionally connected by a second iris 29 having a second connection portion 30. The cross-section of the secondary iris 29 is different from that of the main iris in order to improve filtering. In this embodiment, the secondary iris 29 has a square cross-section, and one of its diagonals is parallel to the first z-axis.

[0088] Due to the shape of the resonator, a non-coaxial arrangement of the filter is possible, but it is also possible to obtain a filter in which all the resonators 2 are aligned on the same axis of propagation of the electromagnetic signal, as illustrated, for example, in FIG. 2a.

[0089] In a particular embodiment, the waveguide filter of the present invention comprises at least four resonators, one of which is connected to at least three separate resonators via a main iris 24. Such a configuration makes it possible, in particular, to obtain a filter with a plurality of resonator branches, in other words, for example, a filter having one input port and a plurality of output ports, or a plurality of input ports and one output port. This makes it possible, for example, to create a comb-shaped waveguide filter having a power divider or polarization splitter function.

[0090] FIG. 6a shows a comb-shaped waveguide filter 1 in which at least one of the resonators 2 (the third from the left in the figure) is connected to the other three resonators. Thus, the resonator 2 located on the left side of the filter in FIG. 6a has a port 31 for inputting an electromagnetic signal to the filter, and the two resonators located on the right side of the filter in FIG. 6a each have a port 31 for outputting an electromagnetic signal from the filter.

[0091] FIG. 6b shows a further embodiment of the present invention in which the first resonator on the left side of the figure has an input port 31 for an electromagnetic signal to the filter 1 and propagates the signal to two separate resonators via the main iris 24. The last resonator on the right side of the figure receives two electromagnetic signals via the main iris and propagates them outside the filter via the output port 31.

[0092] At least one resonator of the filter may include one or both of a polarizer and a septum (polarization converter) so as to perform one or both of splitting and combining of one or more electromagnetic signals. Other standard passive RF components may be combined with the filter without departing from the scope of the present invention.

[0093] The present invention also relates to a method for manufacturing a waveguide filter as described above.

Explanation of Signs

[0094] 1 Comb-shaped waveguide filter 2 Resonator 20 Cavity 21 Flat bottom 22 Roof 23 Single point 24 Main iris 25 Connection part 26 First side part 27 Second side part 28 Post 29 Sub-iris 30 Sub-connection part 31 Coaxial port Z First axis X Propagation axis

Claims

1. A comb waveguide filter (1) manufactured by metal additive manufacturing, comprising at least two resonators (2) interconnected by a main iris (24), each resonator comprising a cavity (20) having a first axis (z), in the waveguide filter (1), each cavity (20) being delimited in particular by a flat bottom (21) extending perpendicular to the first axis (z), characterized in that each cavity (20) is further delimited by a roof (22) converging towards a single point (23), a waveguide filter (1).

2. The waveguide filter (1) according to claim 1, characterized in that each roof (22) comprises a first lateral part (26) adjacent to the flat bottom (21) and perpendicular to the bottom (21), and a second lateral part (27) converging towards the single point (23).

3. The waveguide filter (1) according to claim 1 or 2, characterized in that each resonator (2) has rotational symmetry about the first axis (z).

4. The waveguide filter (1) according to any one of claims 1 to 3, characterized in that each flat bottom (21) is circular or polygonal with at least three sides, preferably circular, square, pentagonal, hexagonal or octagonal.

5. The waveguide filter according to any one of claims 1 to 4, characterized in that each resonator (2) further comprises a post (28) rising parallel to the first axis (z) from the flat bottom (21).

6. The waveguide filter (1) according to claim 5, characterized in that at least one of the posts (28) is made integrally with the flat bottom (21) of the resonator (2).

7. The waveguide filter (1) according to claim 6, characterized in that the post (28) of each resonator has a circular or cross-section with at least three sides, preferably a circular, square, pentagonal, hexagonal or octagonal cross-section.

8. The waveguide filter (1) according to any one of claims 1 to 6, characterized in that the post (28) is helical and extends along the first axis (z).

9. The waveguide filter (1) according to claim 8, characterized in that the diameter of the post (28) varies along the first axis (z).

10. The roof (22) of at least one resonator (2) is provided with a protrusion extending parallel to the first axis (z) towards the inside of the cavity (20) of the at least one resonator, the waveguide filter (1) according to any one of claims 1 to 9.

11. At least one main iris (24) comprises a connecting portion (25) that is not parallel to the flat bottom (21), the connecting portion extending between two resonators connected by the at least one main iris (24), the waveguide filter (1) according to any one of claims 1 to 10.

12. The connecting portion (25) connects the single point (23) of a plurality of resonators (2) connected by at least one main iris (24), the waveguide filter (1) according to claim 11.

13. At least one resonator (2) comprises a plurality of main irises (24) that are not coaxially arranged, the waveguide filter (1) according to any one of claims 1 to 11.

14. The waveguide filter comprises at least three resonators (2) continuously connected by the main iris (24), the first and second resonators (2) being connected to each other by a secondary iris (29), the waveguide filter (1) according to any one of claims 1 to 13.

15. The secondary iris (29) has a cross-section different from that of the main iris (24), the waveguide filter (1) according to claim 14.

16. At least one of the secondary irises (29) comprises a secondary connecting portion (30) extending between a plurality of resonators (2) connected by at least one secondary iris (29), the waveguide filter (1) according to claim 13 or 14.

17. A plurality of the main irises (24) of the plurality of resonators (2) are coaxially arranged along the propagation axis (x) of the electromagnetic signal, the waveguide filter (1) according to any one of claims 1 to 11.

18. The waveguide filter comprises at least four resonators (2), one of the at least four resonators being connected to at least three separate resonators, the waveguide filter (1) according to any one of claims 1 to 17.

19. The waveguide filter (1) according to any one of claims 1 to 18, characterized in that at least one resonator (2) comprises one or both of a polarizer and a septum.

20. A method for manufacturing a comb-shaped waveguide filter (1) according to any one of claims 1 to 19, comprising at least two resonators (2) and an additive manufacturing process of the main iris (24) connecting the resonators.

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