Method for manufacturing thin multi-layer waveguide assembly and a thin multi-layer waveguide assembly

Abstract

The present disclosure relates to a multi-layer waveguide arrangement and a method for manufacturing the multi-layer waveguide arrangement. The multi-layer waveguide arrangement comprises a stack of at least two metal layers (1, 2), each metal layer (1, 2) having two main surfaces (1a, 1b, 2a, 2b), wherein the at least two metal layers (1, 2) comprises structures (4, 5, 13) that form a waveguide between the at least two metal layers (1, 2) for guiding electromagnetic signals having an operational wavelength λ. Wherein the metal layers (1, 2) are held together by laser welds at a plurality of weld locations and wherein at least one of the at least two metal layers has a maximum thickness less than λ divided by four.

Description

[0001] METHOD FOR MANUFACTURING THIN MULTI-LAYER WAVEGUIDE ASSEMBLY AND A THIN MULTI-LAYER WAVEGUIDE ASSEMBLY

[0002] TECHNICAL FIELD OF THE INVENTION

[0003]

[0001] The present invention relates to a method for manufacturing a multi-layer waveguide and a multi-layer waveguide formed by said method.

[0004] BACKGROUND OF THE INVENTION

[0005]

[0002] Waveguiding arrangements, such as antenna arrangements for transmitting and receiving electromagnetic radiation or filters for filtering of electromagnetic signals are of great importance in modern society. For example, antennas are essential for wireless communication and are also used in RADAR applications for transmitting and detecting RADAR signals. To this end, multiple antennas are integrated into most modem automobiles (as well as other vehicles) for both wireless communication purposes and RADAR detection of the surroundings.

[0006]

[0003] In many applications, and especially for automotive, it is important the antennas are cost efficient to manufacture, made small and thin to enable simple integration and offer excellent radiation performance at high frequencies. These requirements have waveguide structures utilizing multi-layer structures with gap waveguides popular.

[0007]

[0004] However, a problem with multi-layer waveguide structures is that the manufacturing process can be costly and time consuming since the multiple layers must be riveted or glued together at a large number or locations.

[0008]

[0005] When using rivets, multiple through-holes must be formed through the layers and the rivets are installed one-by-one. In some cases riveting risks damaging the delicate layers when the tail is deformed. In international application WO21151538 by the current applicant a multi-layer waveguide arrangement with rivets integrated into one layer is proposed. According to this implementation, the rivets can be integrated with one of the layers whereby they are deformed or melted to hold all layers together. A drawback however is that the integrated rivets are fragile and must be formed by the same material as that of the layer with which they are integrated whereas it may be desirable to use a different material. Additionally, the rivets and necessary surrounding geometry require much space and cannot be placed at all wanted locations.

[0009]

[0006] A drawback with using an adhesive is that it generally does not provide an as secure mounting as rivets. Additionally, providing an adhesive between the layers will increase the spacing between the layers which may be detrimental for waveguiding performance in some implementations.

[0010] GENERAL DISCLOSURE OF THE INVENTION

[0011]

[0007] It is a purpose of the present invention to overcome at least some of the shortcomings of the prior solutions and provide a method for manufacturing a multi-layer waveguide arrangement that is accurate and reliable whereby the resulting multi-layer waveguide arrangement is securely assembled.

[0012]

[0008] According to a first aspect of the invention there is provided a multi-layer waveguide arrangement comprising a stack of at least two metal layers, each metal layer having two main surfaces, wherein the at least two metal layers comprises structures that form a waveguide between the at least two metal layers for guiding electromagnetic signals having an operational wavelength X. Wherein the metal layers are held together by laser welds at a plurality of weld locations, and wherein at least one of the at least two metal layers has a maximum thickness less than X divided by four.

[0013]

[0009] It has been found that by utilizing at least one very thin metal layer a multi-layer waveguide can be held together by means of laser welding. Even though very thin metal layers are delicate and sensitive to bending or deflection it has surprisingly been found that laser welding is an efficient method for holding the layers of multi-layer waveguides together.

[0014]

[0010] Since the metal layers comprise structures that, when the metal layers are held together, form a thin and lightweight waveguide suitable for very high frequencies can be realized with the metal layers. Additionally, due to the laser welding the reliability of the waveguide is increased and the manufacturing process is made more efficient. For example, compared to riveting, a laser weld does not require any additional components or specific structures to be provided on the metal layers whereas riveting required provision and alignment of rivets and provision of rivet holes in the metal layers. Laser welds can also be made very small, allowing the welds to only occupy a small area which enables the waveguides to be made more compact. Additionally, laser welds form very strong attachment points making the resulting waveguides robust and highly reliable. Yet another benefit with laser welds is that the process of forming the laser welds can be made highly efficient and cost efficient. For examples, compared to riveting there are fewer processing steps required for laser weld formation.

[0015] [Oil] According to a second aspect of the invention there is provided a method for manufacturing a multi-layer waveguide assembly. The method comprising providing at least two metal layers each having two main surfaces, the at least two metal layers comprising structures that, when the metal layers are held together, form a waveguide for electromagnetic signals having an operational wavelength X and holding the at least two metal layers together. The method further comprises when the metal layers are held together, laser welding the at least two metal layers by irradiating an external surface of at least one of the layers with a laser to form a laser weld at one or more weld locations, wherein at least one of the at least two metal layers has a maximum thickness less than X divided by four.

[0016]

[0012] The invention according to the second aspect features the same or equivalent benefits as the invention according to the first aspect. Any functions described in relation to the method for manufacturing a multi-layer waveguide may have corresponding features in a multilayer waveguide and vice versa.

[0017]

[0013] In some implementations laser welding the at least two metal layers by irradiating an external surface of at least one of the layers with a laser comprises irradiating two external surfaces with a same laser or different lasers at corresponding or different weld locations.

[0018]

[0014] With weld locations that are “corresponding” it is meant that the weld locations are at opposite and corresponding sides of the layer stack formed by the metal layers. In some implementations, the laser welding is performed from both sides at corresponding opposite weld locations whereby a combined laser weld is formed extending through all layers.

[0019]

[0015] By laser welding from both sides the multi-layer waveguide may be more reliantly held together. Additionally, the risk for causing deformations on or more layers is decreased since the strain caused by the laser welds can be more evenly distributed. Additionally, in some implementations the assembly of the metal layers together can also be made more quickly since it is not necessary to perform irradiation at each weld location until all layers have been reached by the laser weld. For example, in multi-layer waveguides comprising three metal layers, laser welds from one external surface extend through two layers and laser welds from the other external surface also extend through two metals. Forming additional laser welds extending through two metal layers may be quicker compared to forming fewer laser welds that extend through all three metal layers.

[0020]

[0016] In some implementations of the first or second aspect, wherein at least one of the at least two metal layers has a maximum thickness less than divided by five, preferably less than X divided by ten, preferably less than X divided by fifteen, or preferably less than X divided by twenty.

[0021]

[0017] Generally, the thinner the metal layer(s) are, the more quickly the laser welding can be performed. Traditionally, the metal layers of multi-layer waveguides are comparatively thick, having a thickness exceeding X / 2. However, it has been realized that laser welds may be used to hold much thinner metal layers together. In some implementations, the layers have a varying thickness, but typically at least one layer is still made very thin. For example, one of the outer layers is used as a radiating layer (with antenna aperture) and can be made very thin and / or one of the layers is an intermediate layer with a waveguiding channel and central conductor which can be made very thin. As a further example, when the operational frequency is 30 GHz the wavelength is approximately 10 mm and a layer having a maximum thickness of X / 10 is therefore less than 1 mm thick. As the frequency increases, the wavelength X decreases whereby the metal layers can be made even thinner.

[0022]

[0018] In some implementations, each layer has a maximum thickness which is at most 2.5 mm, at most 2.0 mm or at most 1.5 mm.

[0023]

[0019] Optionally, each of said at least two metal layers has a maximum thickness less than X divided by two, less than X divided by four, less than X divided by five, or less than X divided by six meaning that the multi-layer arrangement can be made very thin.

[0024]

[0020] The multi-layer waveguide arrangements described herein are suitable for high frequencies, such as frequencies of at least 30 GHz, at least 40 GHz or at least 50 GHz.

[0025]

[0021] In some implementations, wherein each laser weld has a welding outline in the outermost layer wherein the welding outline forms at least one of a line, oval (e.g. ellipse or circle) and a polygon.

[0026]

[0022] The welding outline may be defined as the general shape of the deformed material (that forms the weld) that is visible on the external surface. Line shaped outlines may enable the laser weld to more closely follow the shape of one or more waveguides, whereby the strain on the layers (particularly in the vicinity of the waveguide) becomes more evenly distributed so as to not cause bending or bucking to not degrade waveguiding performance.

[0027]

[0023] In some implementations, at least one laser weld has a line shaped outline, having a weld length, L, and weld width, W, wherein the weld length, L is at least two times the weld width, W. For example, the weld width, W, is smaller than 2 mm, smaller than 1 mm or smaller than 0.5 mm.

[0028]

[0024] In some implementations, wherein at least one laser weld has a welding outline which is elliptical or polygonal, having a largest dimension that is less than 5 mm, less than 3 mm, less than 1 mm or less than 0.5 mm. Defined differently, it is envisaged that at least one laser has a welding outline which is elliptical or polygonal, having a largest dimension that is less than X multiplied with 1.5, less than X, less than X divided by two, or less than X divided by four.

[0025] In some implementations, a plurality of weld locations are distributed along a path defining a parallel to the waveguide.

[0029]

[0026] For example, the weld locations may be arranged intermittently along the path that is parallel to the waveguide (on both sides or only on one side). If the waveguide follows a curved or straight path, two or more laser welds are arranged intermittently along a corresponding parallel curved or straight path. The separation distance between two neighboring laser weld locations may be at most divided by eight, at most X divided by five or at most X divided by two. This rather dense spacing is particularly beneficial for non-metasurface multilayer waveguide arrangements. For waveguide arrangements with metasurface the laser weld locations may be placed with the same, or greater, separation distances since the waveguide arrangements with metasurfaces are generally less sensitive to the layers not being arranged fully together.

[0030]

[0027] In some implementations, a continuous elongated laser weld is provided so as to extend along a path that is parallel to the waveguide.

[0031]

[0028] In some implementations, at least one of the metal layers comprises a metasurface delimiting a waveguide, the metasurface comprising thick sections and thin sections configured to stop electromagnetic signals from propagating along the metal layer in a direction other than along the waveguide.

[0032]

[0029] A metasurface as such is known by the person skilled in the art to stop propagation of electromagnetic signals in undesired directions, e.g. in directions other than along the waveguide. A metasurface is an example of an electromagnetic band gap (EBG) structure that stops the propagation of electromagnetic signal. The metasurface can be integrated (i.e. formed as single piece) with the metal layers. While layers provided with a metasurface can used to form very thin multi-layer waveguide arrangements, it is not necessary and the laser welds can be used to hold together multi-layer waveguide arrangements without metasurfaces, such as multi-layer waveguides wherein the multiple layers form rectangular waveguides with or without a coaxial conductor.

[0033]

[0030] In some implementations, a difference in height between the thick and thin sections is less than X divided by five, preferably less than X divided by eight, and most preferably less than X divided by ten.

[0034]

[0031] Accordingly, the metasurface envisaged in some implementations is very shallow, having a comparatively small height difference between the thick sections and the thin sections. This enables the total thickness of the metal layers to be made much thinner enabling a smaller waveguide arrangement and more efficient laser welding.

[0032] In some implementations, the metasurface is at least partially surrounded by a frame region having a substantially constant thickness that corresponds to the thick sections of the metasurface and wherein at least one weld location overlaps with the frame region.

[0035]

[0033] The frame region may be a region with substantially constant thickness which at least partially, or preferably fully, surrounds the waveguide. By providing one or more weld locations in the frame region the laser weld is provided at a location where there is plenty of metal material (which can be melted and cured). Additionally, it has been found that quality of the laser welds is much better when the laser welds are formed in an area where the metal layers are abutting each other.

[0036]

[0034] In some implementations, the laser welds are arranged with an average spatial density of less than 6 laser welds per2, preferably less than 3 laser welds per X2, more preferably less than 2 laser welds per I2, and most preferably less than 1 laser welds per2.

[0037]

[0035] It has also been found that by providing the laser welds in a comparatively sparse pattern the amount of layer deformation can be decreased. Additionally, fewer laser welds will mean that the manufacturing can be performed more rapidly.

[0038]

[0036] In some implementations, each metal layer is made of a material comprising copper, aluminum and / or steel, and preferably the material is a copper alloy with at least 90% copper, preferably at least 95% copper, most preferably pure copper.

[0039]

[0037] Copper has shown to exhibit excellent properties which makes it possible to form laser welds with a controlled weld shape and outline. Additionally, copper is an excellent conductor and can be formed into very thin metal layers enabling the multi-layer waveguide arrangement to be made very thin.

[0040]

[0038] In some implementations, at least one of said at least two metal layers, comprises a welding feature at one or more weld locations, the welding feature comprising a recess or a protrusion, wherein the laser weld is provided through the welding feature.

[0041]

[0039] That is, prior to welding at least one welding feature is provided at one or more weld locations wherein the welding feature is at least one of a recess, opening and protrusion. In some implementations, at least a portion of one or more welding features may still be visible. The welding features are envisaged to improve the resulting quality of the laser welds and / or facilitate more efficient laser welding due to there, locally, being less material (meaning that the laser weld will form more quickly) or more material (which could prohibit bubble formation and indentations from forming in the weld).

[0042]

[0040] In some implementations, the at least two metal layers are at least three layers.

[0041] In general, any number N > 2 of metal layers may be used to form the multiwaveguide arrangement, such as two or more layers, three or more layers, or four or more layers. With more metal layers more sophisticated waveguide structures can be formed.

[0043]

[0042] In some implementations with three metal layers, at least one metal layer is an intermediate metal layer with a channel having a central conductor suspended in the channel. The central conductor is attached to the intermediate metal layer using intermittently arranged supporting stubs that extend from the central conductor to the intermediate layer. Here, the plurality of weld locations are preferably provided close to each supporting stub as this has been found to improve the structural stability of the arrangement.

[0044]

[0043] Accordingly, each supporting stub may be associated with a laser weld and the distance between the laser weld and the corresponding supporting stub is preferably less than X divided by two, less than divided by four, less than X divided by eight, or less than X divided by fifteen, when seen along a normal to the metal layers.

[0045]

[0044] In some implementations, the at least three layers comprise a top layer, a bottom layer and at least one intermediate layer arranged between the top layer and the bottom layer, wherein the top and bottom layer comprise a respective metasurface facing the at least one intermediate layer and surrounding an elongated channel in the intermediate layer.

[0046]

[0045] The elongated channel forms a waveguide together with the metasurfaces and this is one example of a three layer multi-layer waveguide which can be made very thin and held together by laser welds while exhibiting excellent waveguiding properties.

[0047] BRIEF DESCRIPTION OF THE DRAWINGS

[0048]

[0046] Aspects of the present invention will be described in more detail with reference to the appended drawings, showing currently preferred embodiments.

[0049]

[0047] Figure la shows a cross-sectional and side view of a two metal layers according to some implementations.

[0050]

[0048] Figure lb shows a cross-sectional and side view of two metal layers while these layers are irradiated with two lasers, according to some implementations.

[0051]

[0049] Figure 1c shows a cross-sectional and side view of two metal layers fixed together with a laser weld, according to some implementations.

[0052]

[0050] Figure 2 is a flowchart illustrating a method for manufacturing a multi-layer waveguide according to some implementations.

[0053]

[0051] Figure 3a is a top-down view of a line-shaped weld according to some implementations.

[0052] Figure 3b is a top-down view of a circular weld according to some implementations.

[0054]

[0053] Figure 4a is a cross-sectional and side view of three metal layers held together using a laser weld.

[0055]

[0054] Figure 4b is a cross-sectional and side view of three metal layers held together using a laser weld, typically formed by moving the laser in a closed loop while forming the laser weld.

[0056]

[0055] Figure 4c-4e shows cross-sectional views, at progressively deeper layers of an exemplary laser weld formed by moving the laser in a closed loop, while forming the laser weld.

[0056] Figure 5a is a cross-sectional and side view of a multi-layer waveguide comprising three metal layers according to some implementations.

[0057]

[0057] Figure 5b is a top-down view of the central conductor overlaid the first metal layer of a multi-layer waveguide comprising three metal layers according to some implementations.

[0058] Figure 5c is a top-down view of the exterior surface of the second layer provided with antenna apertures according to some implementations.

[0058]

[0059] Figure 6a shows a cross-sectional and side view of three metal-layers wherein the first metal layer is provided with a welding feature in the form a recess according to some implementations.

[0059]

[0060] Figure 6b shows a cross-sectional and side view of three metal-layers wherein the first metal layer is provided with a welding feature in the form of a protrusion according to some implementations.

[0060]

[0061] Figure 6c shows a cross-sectional and side view of three metal-layers wherein a welding feature in the form a recess extending through two metal layers is provided, according to some implementations.

[0061]

[0062] Figures 7a-e show cross-sectional views of various multi-layer waveguide arrangements without metasurfaces, according to some implementations.

[0062]

[0063] Figures 8a-b shows a top down view of multi-layer arrangements with the various laser weld patterns, according to some implementations.

[0063] DETAILED DESCRIPTION OF CURRENTLY PREFERRED EMBODIMENTS

[0064]

[0064] Fig. la depicts a cross-sectional and side view of two metal layers 1, 2 that may be held together to form a multi-layer waveguide 10 for guiding electromagnetic signals. The multilayer waveguide 10 is configured for an operational frequency associated with an operational wavelength . The multi-layer waveguides presented herein are especially suitable for high frequencies above 30 GHz, above 50 GHz or even above 60 GHz. However, the same general structure of the multi-layer waveguide 10 may also be used for lower frequencies.

[0065]

[0065] The multi-layer waveguide 10 shown in fig. la comprises two metal layers, however, as will be described below this is merely an exemplary embodiment and the present disclosure generally covers many types of multi-layer waveguides 10 with two, three, four or more metal layers 1, 2.

[0066]

[0066] The first metal layer 1 comprises two main surfaces la, lb that are opposite to each other. The first metal layer 1 also comprises a minor edge surface that defines the thickness of the first metal layer 1. Similarly, the second metal layer 2 also comprises two opposite main surfaces 2a, 2b and a minor edge surface. In general, each metal layer used in the multi-layer waveguides 10 described herein will feature two respective main surfaces and a minor edge surface wherein waveguiding structures or openings (to e.g. form an antenna) are arranged on one or more of the main surfaces or, in the case of an opening being provided, extending between the two main surfaces.

[0067]

[0067] When the two metal layers 1, 2 of fig. la are held together, each metal layer will exhibit a respective internal main surface lb, 2b, facing another layer, and each metal layer will exhibit a respective external main surface la, lb, facing away from another layer. Generally, the external main surfaces la, lb are said to face outwards since these face away from the internal structures of the multi-layer waveguide 10. If more than two metal-layers are used to form the metal layer stack that constituted the multi-layer waveguide 10, there will in general still be two external surfaces la, 2a with at least one layer (arranged between two other layers) featuring only internal surfaces.

[0068]

[0068] At least one of the metal layers 1, 2 comprises structures that, when the two metal layers 1, 2 are held together with the internal main surfaces lb, 2b facing each other, form an electromagnetic waveguide 13 for electromagnetic signals with the operational wavelength . In fig. la it is seen that the second metal layer 2 comprises a recess 5 in the internal main surface 2b wherein the recess 5 is provided with a metasurface 4 comprising thick sections 41, sometimes referred to as pins, and thin sections 42 arranged between the thick sections 41. The metasurface 4 surrounds a waveguide 31. The waveguide 31 is here realized as region that is devoid of metasurface 4 structures that forms a space in which electromagnetic can be confined. Typically, the width of waveguide, i.e. the region devoid of, but surrounded by, the metasurface, is about divided by two. The spacing between adjacent thick sections 41 forming the metasurface is typically about X divided by four.

[0069] While a metasurface may enable realization of extra thin, high performance multilayer waveguides it is also envisaged that the multilayer waveguides described herein do not comprise a metasurface. For example, each layer may be a substantially flat layer with recesses, openings and / or protrusions that when the metal layers 1, 2 are held together form a rectangular waveguide as shown in e.g. figs. 7a-e.

[0069]

[0070] When the two metal layers 1, 2 of fig. la are held together, electromagnetic signals with wavelengths around the operational wavelength X are guided between the two metal layers 1, 2 and between the metasurface 4 along the waveguide 31. The metasurface 4 stops the electromagnetic signal from propagating in directions other than along a waveguiding path defined by the waveguide 31. Optionally, a ridge 51 may be arranged in the waveguide 31 wherein the electromagnetic signals are guided along the ridge 51 of the waveguide. Hereby, it is realized that electromagnetic waveguides that guide electromagnetic signals along any desirable path can be formed by providing at least two metal layers 1, 2 provided with the appropriate structures.

[0070]

[0071] The multi-layer waveguide arrangement 10 can also be used to realize an antenna. An antenna is formed by providing an antenna aperture 13 in one of the metal layers 1, 2 at a location overlapping with the waveguide 31. The antenna aperture 13 may thereby be used to transmit electromagnetic signals from the waveguide 31 into the environment or to receive electromagnetic signals from the environment and guiding the electromagnetic signals into the waveguide 31.

[0071]

[0072] In the embodiment shown in fig. la, the antenna aperture 13 is arranged in the first metal layer 13 thus enabling electromagnetic signals to be guided along the waveguide 31 to / from the antenna aperture 13. It is however understood that the antenna aperture 13 may also be located in the second layer 2 if desired and, in general, two or more antenna apertures 13 can be provided in the same metal layer 1, 2 to form an antenna array with high antenna performance, e.g. in terms of gain, beamwidth, and sidelobe levels.

[0072]

[0073] As mentioned above, the metasurface 4 comprises thick sections 41 and thin 42 sections arranged in a regular pattern, e.g. a matrix pattern with multiple rows of thick and thin sections 41, 42 on either side of the waveguide, or a random pattern. Preferably, the height difference between the thick and thin sections 41, 42 is less than X divided by five, or less than divided by six. Even more preferably, the height difference between the thick and thin sections 41, 42 is less than X divided by eight or X divided by ten. Accordingly, since the minimum depth of the recess 5 comprising the metasurface 4 is equal to the height difference between the thick and thin sections 41, 42 the recess 5 can be made very shallow. In turn, this enables the entire metal layer 2 to be made very thin, having a maximum thickness of less than X divided by four, or even smaller, such as less than X divided by five or less than X divided by six. Such a thin metal layer has been shown to be surprisingly well suited for laser welding.

[0073]

[0074] In general, at least one of the layers 1, 2 forming the waveguide 31 has a thickness which is less than X divided by four, or less than X divided by five. In some embodiments, each layer has a thickness which is less than divided by four, or less than X divided by five. It is envisaged that all layers may have the same thickness, or that the layers have different thicknesses.

[0074]

[0075] In the embodiment shown in fig. la, the second metal layer 2 is thicker than the first metal layer 1. For example, the first metal layer 1 may have been formed in an injection molding process which generally requires the structures of the metal layer to be thicker. The first layer 1, on the other hand, may be made much thinner. For example, the first layer 1 is manufactured from a thin sheet material which is stamped or etched to form the antenna aperture 13.

[0075]

[0076] It is understood that the metal layers 1, 2 shown in fig. la are merely exemplary and in some embodiments there are more than two layers. Additionally, it is understood that the main waveguiding structures, such as the recess 5, the metasurface 4 and / or the ridge 51, may be provided on both metal layers 1, 2 and not only on the second metal layer 2. For example, it is envisaged that both the first metal layer 1 and the second metal layer 2 comprise a respective metasurface 4, wherein the two metasurfaces 4 face each other. An additional example of a multi-layer waveguide with three metal layers will be described in connection to fig. 4a below.

[0077] With reference to fig. Ib-d and the flowchart of fig. 2 a laser welded waveguide assembly, and a method for manufacturing the laser welded multi-layer waveguide assembly 10 will now be described.

[0076]

[0078] At step SI at least two metal layers 1, 2 are provided. For example, two metal layers 1, 2 identical to those shown in fig. la are provided. At step S2 the two metal layers 1, 2 are held together with the internal surfaces facing each other to form the waveguide 31 and expose the two external main surfaces la, 2a as shown in fig. lb. For example, the metal layers 1, 2 are placed on top of each other on a horizontal surface with the second metal layer 2 being arranged below the first metal layer 1 to thereby expose the external main surface l of the first metal layer 1.

[0077]

[0079] With the metal layers 1, 2 arranged together the method goes to step S3 involving laser welding the at least two metal layers 1, 2 by irradiating at least one external surface with a laser 6, 6’ at each of one or more weld locations. The irradiation with the laser is continued until the at least two adjacent metal layers 1, 2 have melted at the weld location. The irradiation is stopped whereby the melted metal material is allowed to cool. Optionally, active cooling is used to cure the melted metal material more quickly.

[0078]

[0080] The melted and cured metal material at each weld location forms a cured structure of metal that holds the metal layers 1, 2 together by locally fusing the metal layers 1, 2. This forms a laser weld 7 of melted and then cured metal material as shown in fig. 1c which extends between the two adjacent metal layers 1, 2 and reliantly fixates the metal layers 1, 2 together.

[0081] Optionally, the method goes to step S4 involving repeating the laser welding at a second weld location, different from the first weld location. In this way a plurality of laser welds 7 may be provided at a plurality weld locations whereby the fixation of the metal layers becomes even more reliable. Another benefit with providing multiple laser welds 7 is that the strain exerted by the laser welds 7 on the metal layers becomes evenly distributed which mitigates the risk of damaging the metal layers or causing buckling of one or more of the metal layers 1, 2.

[0082] It is understood that the laser welding may be performed at the one or more weld locations at the same time, e.g. using multiple lasers, or in sequence.

[0079]

[0083] Optionally, the laser welding is performed by irradiating both external surfaces la, 2a either at the same time using different lasers 6, 6’ or in sequence using the same laser 6 or different lasers 6, 6’. In some implementations, and especially if many metal layers 1, 2 (such as six or more metal layers 1, 2) or one or more thick metal layer 1, 2 are used, laser welding from only one external surface la, lb may not be sufficient for the laser weld 7 to penetrate all metal layers 1, 2 whereby laser welding from both external surfaces la, 2a at corresponding and opposite weld locations, may be performed to form a laser weld 7 that goes through all layers 1, 2.

[0080]

[0084] It is also envisaged that if laser welding is performed from both external surfaces, it is not necessary that the weld locations are corresponding and opposite such that the laser welding from each side forms a single, large, laser weld. As also shown in fig. 1c, two laser welds 7a, 7b have been formed from different external surfaces la, lb whereby the weld location of each laser weld are not arranged at opposite locations.

[0081]

[0085] Additionally, it is noted that in some cases laser welding through many thick metal layers 1, 2 may be possible to achieve from the same external surface la, 2a if the laser power or irradiation time is increased. However, it has been realized that increased irradiation time and / or increased laser power may cause the resulting laser welds 7 to have irregular shapes which, during curing, may strain the metal layers 1, 2 causing them to bend, deform or even break. Additionally, increased irradiation time and / or power at each weld location will increase the total manufacturing time and cost for the laser welded multi-layer waveguide arrangement 10 which is undesirable. Therefore, it may be preferable to perform laser welding from both external surfaces in situations where many, or thick, metal layers 1, 2 are used and / or preferable to use thinner metal layers 1, 2.

[0082]

[0086] As illustrated in the cross-sectional view in fig. 1c, a laser weld 7 formed by laser welding from both sides at corresponding and opposite weld locations may exhibit a characteristic width / area profile similar to an hourglass shape. In general, each laser weld 7 will exhibit a cross-sectional width / area in a plane parallel to the metal layers 1, 2 which decreases for each layer from a maximum cross section at the external layer which faces the laser 6, 6’ during irradiation towards deeper layers further away from the external layer which faces the laser 6, 6’. Accordingly, if welding at a weld location has been performed from only one side the laser weld width / area profile will be generally cone-shaped, going from a large width / area at the external surface in layer facing the laser 6, 6’ to a gradually smaller width / area in deeper layers. Accordingly, when welding is performed from both sides, the resulting width / area profile of the laser weld along the layers is similar to an hourglass being a combination of a V-shape and an upside-down V-shape.

[0083]

[0087] Excellent laser welding results have been achieved with metal layers 1, 2 comprising copper, and preferably the metal layers 1, 2 are made of pure copper. In some implementations at least one metal layer 1, 2, or each layer, is made of pure copper or a copper alloy comprising at least 90% copper or preferably at least 95% copper. However, other metals than copper can also be used, such as aluminum, steel or even brass, and multi-layer waveguide arrangements 10 with metal layers 1, 2 comprising different metals or alloys are also envisaged.

[0088] Turning to fig. 3a and 3b, various exemplary weld outlines 71, 72 are shown. The weld outline is defined as the shape of the deformed metal (which has been melted and cured) that forms the weld as it appears on the external surface which faces the laser during laser welding.

[0084]

[0089] It is understood by moving the laser when irradiating the metal layers the shape of the outline of each laser weld can be adjusted. For example, each laser weld may have an elongated shape 71 as shown in fig. 3a having a weld length L and a weld width W wherein the weld length L is greater than the weld width W. For example, the weld length L is at least two times the weld width W, at least three times the weld width W or at least four times the weld width W.

[0085]

[0090] In some embodiments, the weld width W of the elongated laser weld 71 is less than 2 mm, or less than 1 mm, or less than 0.5 mm. The welding width can be even smaller still, such as less than 0.4 mm or even smaller than 0.3 mm. Preferably, the welding width of the elongated laser weld 71 is less than divided by 2, less than divided by four or less than divided by eight. The weld length L of elongated laser weld 71 may be e.g. at least 0.2 mm such as at least 0.5 mm. In one implementation, the elongated laser weld 71 has a weld width of about 0.25 mm and a weld length of about 0.5 mm. A narrow and elongated laser weld 71 can be formed quickly since a comparatively high laser power may be used while still the weld width / area profile can be controlled for the full welding depth. By comparison, laser welds that have a weld shape of a comparatively small spot or dot may require longer total irradiation time with a lower power laser to achieve laser welds with sufficient repeatability that do not grow to irregular shapes as the weld is formed. Accordingly, using elongated laser welds 71 facilitates more efficient manufacturing.

[0086]

[0091] To form an elongated laser weld 71 the laser can e.g. be moved in straight line during welding. However, it is further envisaged that the elongated laser weld 71 is not necessarily straight, it may e.g. be curved or comprise one or more bends. For example, the outline of the laser weld may be generally C-shaped, S-shaped or otherwise curved so as to follow the general path of a waveguide, as will be described below.

[0087]

[0092] Alternatively, each laser weld may have a generally elliptic outline 72 as shown in fig. 3b where the elliptic outline is in the form of a circle having a largest dimension D. An elliptic outline shaped weld may e.g. be formed by moving the laser in a circle or spiral when irradiating an outer surface of the metal layers. Other shapes are of course also possible, for example each weld may be substantially triangular, substantially rectangular or substantially polygonal. The laser weld outline may be “filled-in” with molten and cured metal, or it is envisaged that the outline forms a loop encircling an area without molten and cured metal.

[0088]

[0093] Each laser weld outline may have a largest dimension which is less than 3 mm, less than 2 mm or less than 1 mm. Laser weds with a smaller outline are also envisaged, for example each laser weld outline may have a largest dimension which is less than 0.5 mm, or less than 0.25 mm.

[0089]

[0094] In fig. 4a a cross-section in a plane perpendicular to the metal layers 1, 2, 3 is shown, illustrating how the laser weld 7 extends through three metal layers 1, 2, 3. As indicated above, the multi-layer waveguide may comprise more than two metal layers and in the embodiment shown in fig. 4a and fig. 4b the multi-layer waveguide comprises three metal layers, the first metal layer 1, the second metal layer 2, and an intermediate layer 3 between the first and second metal layers 1, 2.

[0095] In this embodiment, the laser weld has been formed by irradiating only the first external surface la of the first metal layer 1. As seen, the laser weld 7 is generally cone-shaped as is typical for laser welds formed by irradiating a single external surface la as opposed to irradiating both external surfaces at corresponding and opposite weld locations.

[0090]

[0096] The width of the weld 7 decreases as it goes from the outermost layer 1 towards deeper layers 2, 3 as is shown schematically in fig. 4a. The laser weld 7 may penetrate fully through all metal layers 1, 2, 3 as shown in fig. 3c but it is also envisaged that the laser weld penetrates only a portion of the deepest layer it reaches. The laser weld 7 may e.g. be the result of welding with the laser stationary, with the laser moving in a spiral, with the laser moving in a comparatively small diameter circle or with the laser moving along a path to form an elongated straight or curved weld.

[0091]

[0097] In some implementations, the aspect ratio of the laser weld 7 is below 10:1 indicating that the size of the laser weld 7 in the outermost layer 1 is at most ten times the size of the laser weld 7 at the deepest layer 2 it reaches. Accordingly, a laser weld 7 can in general be made to reach trough an arbitrarily deep stack of metal layers 1, 2, 3 provided the laser weld size at the outermost layer 1 is sufficiently large. It has been found that with an aspect ratio of 10: 1 or less a laser weld 7 having a diameter not exceeding 2 mm is sufficient to reach 20 mm of depth. Of course, if the laser weld size in the outermost layer 1 is increased the laser weld 7 can reach even deeper. Accordingly, in some implementations each laser weld is not deeper than 20 mm, or not deeper than 10 mm as this enables the laser to made very small.

[0092]

[0098] In some implementations, the laser is moved such that the center point of the irradiation point moves over the external surface in a closed path with a comparatively large inner dimension (e.g. the center point moves in a circle having a diameter of more than 1 mm) whereby the resulting laser weld, seen from the opposite external surface 2a, forms a concave shape as shown in fig. 4b. This type of laser weld forms a large diameter body of cured molten metal at one or more layers close to the external irradiated layer 1, whereby the body of cured molten metal transforms into an annular shape for the deeper layers leaving an intact, nonmelted, metal layers inside a substantially conical space defined by the annular body of cured molten metal.

[0093]

[0099] Fig. 7c-e depict a cross-section of the laser weld shown in fig. 4b in planes parallel to the metal layers at progressively deeper positions. Fig. 7c show a cross-section of the laser weld at the first metal layer 1, here the laser weld 7 is substantially disc shaped. Fig. 4d shows a cross-section of the laser weld at a deeper plane (e.g. at the intermediate metal layer 3) and at this depth the laser weld 7 as transitioned into an annular shape leaving a region 75 of unmolten metal layers inside the annularly shaped laser weld. Fig. 7e shows a cross-section of the laser weld at an even deeper plane (e.g. at the second metal layer 2) and at this depth the region 75 of unmolten metal layers inside the annularly shaped laser weld has grown and the outer dimension of the annular shape has become smaller, compared to fig. 4d.

[0094]

[0100] As will be appreciated by the person skilled in the art, the dimension of the annularly shaped portion of the laser weld, and the region 75 of unmolten metal layers inside the annularly shaped portion, can be configured by adjusting welding parameters such as welding power and the dimensions of the shape along which the laser is moved during welding.

[0095]

[0101] As described above, it is envisaged that more than two metal layers are laser welded together. It is appreciated that by adding additional layers it is possible to form more sophisticated waveguide structures that follow a path between two layers and goes up and / or down through one or more layers. As an example, at least two adjacent layers are used to form a routing structure routing electromagnetic to / from one or more input / output ports and one or more antenna ports wherein at least two additional adjacent layers are used to form a radiating structure for conveying electromagnetic signals from the one or more antenna ports to one or more radiating slots.

[0096]

[0102] In some implementations, more than two layers are used to form a waveguide arrangement. For example, at least three layers are used to form a multi-layer waveguide arrangement 10 as will now be described in connection with fig. 5a.

[0097]

[0103] The multi-layer waveguide arrangement 10 comprises a first metal layer 1 and a second metal layer 2. An intermediate layer 3 is arranged between the first and second metal layer 1, 2 and in the shown embodiment, the first and second metal layer 1, 2 each comprises a respective metasurface 4 that faces the intermediate metal layer 3. However, it is understood the one or both metasurfaces 4 may be arranged on the intermediate layer 3 instead.

[0098]

[0104] In general, a metasurface 4 is arranged in the multi-layer waveguide arrangement 10 such that there is at least one metasurface 4 between each pair of adjacent metal layers 1, 2, 3. That is, there is at least one metasurface 4 between the first metal layer 1 and the intermediate layer 3 and there is at least one metasurface between the second metal layer 2 and the intermediate layer 3. This will prohibit electromagnetic signals from leaking out between adjacent metal layers. Optionally, two metasurfaces 4 may be arranged between a pair of adjacent layers. For example, the intermediate layer 3 may comprise a metasurface 4 which faces the first metal layer 1 wherein the first metal layer 1 also comprises a metasurface 4 that faces the intermediate metal layer 3.

[0105] In this multi-layer waveguide arrangement 10, a waveguide 31 is formed by providing an elongated aperture that forms a channel 33 in the intermediate layer 3. The metasurface 4 of the first and second metal layer 1, 2 are arranged to surround the channel 33 in the intermediate layer 3. Additionally, in a region overlapping with the channel 33 the first and second metal layer 1, 2 is devoid of any metasurface 4 whereby a waveguide 31 extending parallel to the metal layers 1, 2, 3 is formed by the channel 33 in the intermediate layer 3, the first and second metal layer 1, 2 and the metasurface 4 arranged on each of the first and second metal layers 1, 2.

[0099]

[0106] This type of three-layer waveguide arrangement 10 may be realized with very thin metal layers. For example, at least one of the metal layers 1, 2, 3 has a total thickness below X divided by four, below divided by five or below X divided by six. Preferably, each metal layer 1, 2, 3 has a total thickness below X divided by four, below X divided by five or below X divided by six.

[0100]

[0107] The thickness of each individual layer is preferably less than 1 mm, although larger thicknesses are possible. In some implementations, the thickness of each layer is between 500 pm and 300 pm. All layers could have the same thickness, but it is also envisaged that the metal layers 1, 2, 3 may have different thicknesses. For example, the first metal layer 1 and second metal layer 2 may have a same thickness between 500 pm and 300 pm and the intermediate layer 3 is thinner, having a thickness between 50 pm and 200 pm, e.g. about 100 pm. The above exemplary thicknesses are suitable for simple and cost effective manufacturing but are merely exemplary and can vary outside of these ranges, e.g. depending on the operational frequency. The above exemplary thicknesses are suitable for an operational frequency around 77 GHz.

[0101]

[0108] The intermediate layer 3 may further comprise a central conductor 32 that extends in the channel 33. With the central conductor 32 the waveguide 31 becomes similar to a coaxial waveguide.

[0102]

[0109] The metasurface of the first and second metal layer 1, 2 is surrounded by a frame region 15, 25 of constant thickness. Preferably, the thickness of the frame region is substantially equal to, or slightly larger than, the thickness of a thick section 41 of the metasurface. For example, the first and / or second metal layer 1, 2 may have been formed by providing a metal sheet whereby the thin sections 42 of the metasurface 4 and the region devoid of metasurface 4 is formed by etching whereby the thick sections 41 remain as non-etched parts having a thickness substantially equal to the frame region 15, 25.

[0103]

[0110] Hereby, at least one, or preferably all, laser welds 7 are provided in the frame region 15, 25. In the frame region 15, 25, the metal layers 1, 2, 3 are contacting each other over a large area whereby the laser welds 7 will exert a clamping pressure on the layers 1, 2, 3 which is distributed over a large area. Preferably, any laser weld 7 is provided at some distance away from the metasurface 4 or waveguide 31 so as to avoid molten metal from reaching the metasurface 4 or waveguide 31 which could impact the waveguiding performance. For example, each laser weld is provided at a distance of at least the operational wavelength divided by two from the closest edge of the waveguide 31 or at least the operational wavelength from the closest edge of the waveguide 31.

[0104] [Ill] Fig. 5b shows a top-down view of the first metal layer 1 with the central conductor 32 outlined. To keep the central conductor 32 suspended in the channel 33, one or more suspension stubs 34 may be provided that extends from central conductor 32, across the channel 33, and connects to the rest of the intermediate layer 3. Fig. 5b also shows the region devoid of metasurface 4 in connection to the waveguide 31 formed by the channel 33. The region devoid of metasurface 4 may e.g. be formed as an area without thick sections 41 having thickness corresponding to the thin sections.

[0105] [H2] A plurality of elongated laser welds 71 have been provided in the frame region 15, 25 and preferably the plurality of elongated laser welds 71 follow the path of the waveguide 31 defined in part by the channel 33 in the intermediate layer 3. Of course, other laser welds, with outlines of other shapes may be used and multiple laser welds with varying shapes, or having the same outline, may be provided along the waveguide 31. Preferably, the laser welds 71 are arranged on both sides of the waveguide 31 to exert an even pressure on the metal layers 1, 2, 3 in the area surrounding the waveguide 31.

[0106] [H3] In some implementations, the multi-layer waveguide arrangement 10 comprises more than one waveguide and in fig. 5c a top down view of the second metal layer 2 is shown with the path of two waveguides 31 outlined. In some implementations, the waveguides 31 will lead to one or more antenna apertures 23. Here, the antenna apertures 23 are arranged in the second metal layer 2 but this is merely an example, and it is envisaged that the antenna apertures may be provided in anyone, or both, of the first and second metal layer 1, 2.

[0107]

[0114] Elongated laser welds 71 are provided at weld locations distributed intermittently along the waveguides 31 and optionally the elongated laser welds 71 are provided on both sides of at least one of the waveguides 31.

[0108] [H5] It is also envisaged that elongated laser welds 71 may be oriented differently with respect to each other to more accurately follow the path of the waveguide 31 which may comprise one or more bends. Additionally or alternatively, one or more elongated laser welds 71 may be curved to follow the shape of the waveguide 31 more accurately. In an extreme case, it is envisaged that a single elongated laser weld 31 follows shape of the entire waveguide 31 on one side, or even loops around the waveguide 31 to surround it on both sides.

[0109] [H6] The elongated laser welds 71 shown in fig. 5b and fig. 5c are merely exemplary and laser welds with other shapes may be used. For example, at least one of, or all, the laser welds have a circular shape, triangular shape, or other polygonal shape.

[0110]

[0117] Preferably, the spatial density of laser welds 71 on at least one of the main surfaces la, 2a is kept small since too densely packed laser welds generally makes it more difficult to design waveguides which do not overlap with one or more welds and may introduce excessive strain on the, potentially very thin, metal layers 1, 2, 3. Additionally, using fewer laser welds may speed up the manufacturing process.

[0111]

[0118] The spatial density of laser welds is determined as the number of laser welds divided by the surface area of the exterior surface la, 2a, optionally expressed in the operational wavelength squared. The spatial density is below 6 laser welds per X2, preferably below 4 laser welds per X2, more preferably below 2 laser welds per2and most preferably below 1 laser weld per X2. Even lower spatial densities may be used and, in some implementations, the spatial density is below 0.5 or 0.25 laser welds per X2.

[0112]

[0119] Depending on the shape of the outline of each laser weld, the smallest spacing between two neighboring laser welds could vary. In some implementations, the center-to-center distance between each pair of laser welds is at least X divided by six, preferably at least X divided by four and most preferably at least X divided by two.

[0113]

[0120] In some embodiments a welding structure 9a, 9b, 9c is provided at one or more, or each, weld location as will be described in connection to fig. 6a-c.

[0114]

[0121] In fig. 6a a welding structure in the form of a recess 9a is provided on the outermost, which in this case is the second metal layer 2. The laser weld is formed at least partially, or preferably fully, inside the recess 9a by arranging the laser 6 such that it irradiates an area inside the recess 9a when forming the laser weld. The recess 9a may for example be formed together with the second metal layer (i.e. in an injection molding process). The recess 9a may also be formed by etching the second metal layer 9a. It has been realized that by etching the second metal layer 2 to form the recess 9a the bottom surface of the recess 9a may exhibit an increased surface roughness. This in turn reduces surface reflections which may help realize a more controlled laser weld shape.

[0115]

[0122] In fig. 6b a protrusion 9b is shown, which is another example of a welding feature that may be used.

[0123] In fig. 6c a multi-layer recess 9c is shown which is yet another example of a welding that may be used. The multi-layer recess 9c is a recess which extends through at least one metal layer 2 and at least partially through an adjacent deeper metal layer 3. The multi-layer recess 9c may comprise slanting wall sections (for example linearly slanting wall sections as shown in fig. 6c) which expose an edge surface of the one or more metal layers 1, 3. The multilayer recess is irradiated with a laser 6, a laser weld can be formed which holds all metal layers 1, 2, 3 together e.g. by creating a circularly shaped laser weld or spiral laser weld inside the multi-layer recess. As the multi-layer recess 9c (and also the single layer recess 9a) feature a local reduction in material the laser welds can be formed more quickly, using a lower power laser, and / or in a way such that the laser weld reaches connects all metal layers 1, 2, 3 in a more evenly distributed manner.

[0116]

[0124] In figs. 6a-c the different welding structures 9a, 9b, 9c are shown for multi-layer waveguides comprising three metal layers where laser welding is performed from one side. It will however be appreciated that the same welding structures 9a, 9b, 9c may be used for multilayer waveguides with two metal layers or multi-layer waveguides with more than three metallayers and / or that the welding structures may be arranged on both external surfaces and used when welding is performed from both sides.

[0117]

[0125] In the above, various multi-layer waveguide arrangements have been described. While each mutli-layer waveguide arrangement comprises a metasurface it is understood that other types of multi-layer waveguide arrangements, without metasurfaces, can be provided with laser welds in accordance with the present invention. With reference to figs. 7a-e various waveguide arrangements without metasurfaces will now be described.

[0118]

[0126] In fig. 7a a cross-sectional view of a multi-layer waveguide arrangement with five layers 1, 2, 3a, 3b, 3c is shown. The multi-layer waveguide arrangement comprises a first (top) layer 1, a second (bottom) layer 2 and three intermediate layers 3a, 3b, 3c wherein each intermediate layer 3a, 3b, 3c comprises an elongated aperture. The elongated aperture of each intermediate layer 3a, 3b, 3c communicate so as together form a rectangular waveguide 33. Provided that all metal layers 1, 2, 3a, 3b, 3c are arranged together, the multiple metal layers cooperate to form a structure resembling a traditional rectangular waveguide. The position of one or more lasers 6 is shown schematically illustrating where the laser welds will be formed to hold the metal layers 1, 2, 3a, 3b, 3c together.

[0119]

[0127] Fig. 7b shows a cross-section of a waveguide arrangement with two layers 1, 2, a first layer 1 and a second layer 2. The first layer 1 is comparatively thick, and comprises a rectangular recess 5 forming a rectangular waveguide 33 when the comparatively thin second layer 2 is put on top of the second layer 2. Accordingly, a rectangular waveguide 33 may be formed with as few as two layers 1, 2 held together by laser welds.

[0120]

[0128] Fig. 7c shows a cross-section of a similar multi-layer waveguide arrangement as in fig. 7b. The only difference between the embodiment of fig. 7b and the embodiment of fig. 7c is that the rectangular recess 33 in the embodiment of fig. 7c which provided with a ridge 51 which forms a rectangular ridge waveguide. Accordingly, also a rectangular ridge waveguide can be realized with two metal layers.

[0121]

[0129] Fig. 7d shows a cross-section of a multi-layer waveguide arrangement with three layers 1, 2, 3, a first layer 1, a second layer 2, and an intermediate layer 3. The intermediate layer comprises an elongated aperture and a central conductor 32 suspended in the elongated aperture. The first and second layer 1, 2 each comprises a corresponding rectangular recess facing the intermediate layer 3 such that when the first and second layer 1, 2 are held together over the intermediate layer 3, they form a rectangular waveguide with a central conductor 32 together with the elongated aperture in the intermediate layer 3.

[0122]

[0130] A rectangular waveguide with a coaxial conductor can also be realized with the five layer arrangement from fig. 7a. As shown in fig. 7e, the elongated aperture of the central layer 3b of the three intermediate layers 3a, 3b, 3c is provided with a central conductor 32 such that when the layers 1, 2, 3a, 3b, 3c are held together the elongated aperture in each of the intermediate layers 3a, 3b, 3b cooperate to form a rectangular waveguide with a coaxial conductor 32.

[0123]

[0131] The rectangular waveguides realized without metasurfaces may be adapted based on the desired operational frequency. For example, each rectangular waveguide may resemble that of a standard rectangular waveguide size labelled “WR” or “WG”. For instance, rectangular waveguides labeled WR12 are adapted for frequencies between 60 and 90 GHz has a width of about 3.10 mm and height of about 1.55 mm.

[0124]

[0132] Rectangular waveguides realized without metasurface (see e.g. the exemplary embodiments in figs. 7a-e) are in general more sensitive to manufacturing errors. For example, it may be important for the waveguiding performance that the metal layers are in physical contact with each other whereas this is not as important for multi-layer waveguide arrangements with metasurfaces. To this end, waveguide arrangements without metasurfaces may be provided with more, or more densely arranged, laser welds compared to multi-layer waveguides realized with metasurfaces.

[0125]

[0133] Turning to fig. 8a and 8b a top view of a multi-layer waveguide arrangement with the waveguide channel 33 outlined is shown. Fig. 8a illustrates that the laser welds 7 can be provided intermittently with a regular or irregular spacing distance d along a path parallel to the waveguiding channel 33. Alternatively, an elongated laser weld 7’ can be provided so as to follow a path that is parallel to the waveguiding channel. The distance d between laser welds 7 is at least X / 10 and preferably less than X / 2 when the multi-layer waveguide arrangement does not comprise a metasurface. With such a tight spacing the layers will be accurately held together which improves performance for rectangular waveguides realized using multiple layers.

[0126]

[0134] In some implementations, the waveguide is a coaxial waveguide (with or without a metasurface) as shown in fig. 5a, 7d, and 7e. In such implementations, it may be preferable to provide laser welds 7 in close vicinity to the supporting stubs 34 that connect the central conductor 32 to the intermediate layer. Especially, when no metasurface is used, the laser welds 7 may be provided very close to the supporting stubs, such as within a distance of X / 2 , X / 4 or X / 8 from the point where supporting stubs 34 connect to the rest of the metal layer, when seen along a normal of the layers.

[0127]

[0135] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, various number of metal layers may be used and laser welds with various outline shapes may be used to realize multi-layer waveguide arrangements suitable for different applications.

[0128]

[0136] Such and other obvious modifications must be considered to be within the scope of the present invention, as it is defined by the appended claims. It should be noted that the above- mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting to the claim. The word "comprising" does not exclude the presence of other elements or steps than those listed in the claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

Claims

CLAIMS1. A multi-layer waveguide arrangement comprising: a stack of at least two metal layers (1, 2), each metal layer (1, 2) having two main surfaces (la, lb, 2a, 2b), wherein at least one of the metal layers (1, 2) comprises a structure (4, 5, 13) that, when the metal layers (1, 2) are held together form a waveguide between the at least two metal layers (1, 2) for guiding electromagnetic signals having an operational wavelength ; wherein the metal layers (1, 2) are held together by laser welds at a plurality of weld locations, and wherein at least one of the at least two metal layers has a maximum thickness less than X divided by four.

2. A method for manufacturing a multi-layer waveguide assembly comprising: providing at least two metal layers (1, 2) each having two main surfaces (la, lb, 2a, 2b), at least one of the metal layers (1, 2) comprising structures (4, 5, 13) that, when the metal layers (1, 2) are held together, form a waveguide for electromagnetic signals having an operational wavelength X; holding the at least two metal layers (1, 2) together; and when the metal layers (1, 2) are held together, laser welding the at least two metal layers (1, 2) by irradiating an external surface (la, 2a) of at least one of the layers (1, 2) with a laser (6) to form a laser weld at one or more weld locations, wherein at least one of the at least two metal layers has a maximum thickness less than divided by four.

3. The method according to claim 2, wherein laser welding the at least two metal layers (1, 2) by irradiating an external surface (la, 2a) of at least one of the layers (1, 2) with a laser (6) comprises irradiating two external surfaces (la, 2a) with a same laser (6) or different lasers (6, 6’) at corresponding or different weld locations.

4. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein at least one of the at least two metal layers has a maximum thickness less than X divided by five, less than X divided by ten, less than X divided by fifteen or less than X divided by twenty.

5. The method according to any of the preceding claims, wherein each layer has a maximum thickness below 2.5 mm, wherein each layer has a maximum thickness of 2.0 mm or wherein each layer has a maximum thickness of 1.5 mm.

6. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein each of said at least two metal layers has a maximum thickness less than X divided by two, less than divided by four, less than X divided by five, or less than X divided by six.

7. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein each laser weld has a welding outline in the outermost layer (la, 2a) wherein the welding outline forms at least one of a line (7a), oval (7b) or polygon.

8. The method or multi-layer waveguide arrangement according to claim 7, wherein at least one laser weld has a line shaped outline, having a weld length, L, and weld width, W, wherein the weld length, L is at least two times the weld width, W.

9. The method or multi-layer waveguide arrangement according to claim 8, wherein the weld width, W, is smaller than 2 mm, smaller than 1 mm or smaller than 0.5 mm.

10. The method or multi-layer waveguide arrangement according to any of claims 7-9, wherein at least one laser weld has a welding outline which is elliptical or polygonal, having a largest dimension that is less than 5 mm, less than 3 mm, less than 1 mm or less than 0.5 mm.

11. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein a plurality of distinct weld locations are distributed along a path that is parallel to the waveguide.

12. The method or multi-layer waveguide arrangement according to claim 11, wherein the distance between neighboring weld locations distributed along the path is less than X divided by two, or less than X divided by five, or less than X divided by eight.

13. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein a continuous elongated laser weld is provided so as to extend along a path that is parallel to the waveguide.

14. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein at least one of the metal layers (1, 2) comprises a metasurface (4) delimiting a waveguide (31), the metasurface (4) comprising thick sections (41) and thin sections (42) configured to stop electromagnetic signals from propagating along the metal layer (1, 2) in a direction other than along the waveguide (31).

15. The method or multi-layer waveguide arrangement according to claim 14, and wherein a difference in height between the thick and thin sections (41, 42) is less than X divided by five, preferably less than X divided by eight, and most preferably less than X divided by ten.

16. The method or multi-layer waveguide arrangement according to claim 14 or claim 15, wherein the metasurface (4) is at least partially surrounded by a frame region (15, 25) having a thickness that is at least equal to the thick sections (41) of the metasurface (4) and wherein at least one weld location (71a-e) overlaps with a frame region (15, 25).

17. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein the laser welds are arranged with an average spatial density of less than 6 laser welds per X2, preferably less than 3 laser welds per I2, more preferably less than 2 laser welds per X2, and most preferably less than 1 laser welds per X2.

18. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein each metal layer (1, 2) is made of a material comprising copper, aluminum and / or steel, and preferably the material is a copper alloy with at least 90% copper, preferably at least 95% copper, most preferably pure copper.

19. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein at least one of said at least two metal layers, comprises a welding feature(9a, 9b, 9c) at one or more weld locations, the welding feature comprising a recess or a protrusion, wherein the laser weld is provided through the welding feature.

20. The method or multi-layer waveguide arrangement according to any of the preceding claims, wherein the at least two metal layers (1, 2) are at least three layers (1, 2, 3).

21. The method or multi-layer waveguide arrangement according to claim 20, wherein the at least three layers comprises an intermediate layer (3, 3b) arranged between the first and second layer, wherein the third layer comprises a channel with a central conductor attached to the third layer via a plurality of supporting stubs (34), and wherein a plurality of welding locations are arranged along the waveguide at the position of each support stub (34).

22. The method or multi-layer waveguide arrangement according to claim 20 or claim 21, wherein the at least three layers comprises a top layer (1), a bottom layer (2) and at least one intermediate layer (3) arranged between the top layer (1) and the bottom layer (2), wherein the top and bottom layer (1, 2) comprises a respective metasurface (4) facing the at least one intermediate layer (2) and surrounding an elongated channel (33) in the intermediate layer.

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