Waveguide element and method for its manufacture

Abstract

The invention relates to a waveguide element comprising a channel (10) with an open side defined by at least one side wall (11, 12). The side wall (11, 12) has a plurality of separate electrical contact surfaces (20).

Description

The present invention relates to a waveguide element, in particular for a radar sensor. Furthermore, the present invention relates to a method for producing the waveguide element.Prior ArtRadar sensors are used in vehicles in order to implement comfort functions and safety functions. In this case, they measure the distance to a target directly without relying on an interpretation of images, as is effected, for example, in the case of an optical camera.Antenna structures for radar sensors may be designed as planar antennas on a printed circuit board, in particular as microstrip antennas. Furthermore, three-dimensional waveguide antennas are used. These have a lower power loss and a higher broadband characteristic compared to the planar antennas. Waveguide antennas usually consist of several layers, which must be glued or soldered to one another.DE 10 2020 216 362 A1 describes a radar sensor having a hollow conductor structure in the form of a channel open on one side. This channel is soldered with its open side onto a copper layer of a printed circuit board, so that the copper layer forms a wall of the waveguide.Disclosure of the InventionThe waveguide element is in particular configured to conduct an electromagnetic wave having a wavelength λ. It has a channel with an open side bounded by at least one side wall. For example, the channel may have a single side wall that completely surrounds it or may have multiple side walls. In addition to the side wall which delimits the open side or the side walls which delimit the open side, it can in particular have at least one wall which is opposite the open side and is connected to the side wall or the side walls. The at least one side wall has a plurality of electrical contact surfaces which are separate from one another. An electrical contact surface is understood to mean a surface which is provided and configured to solder or electrically conductively glue the side wall of the channel to a metal surface. This metal surface is in particular a metallic base surface of a printed circuit board. The open side can thus be closed by means of the metal surface. In one embodiment of the waveguide element, the channel can likewise consist of a metal. In another embodiment of the waveguide element, it consists of a carrier material, such as a plastic, for example, which has a metallization layer on the inside of the channel.In principle, it is possible to solder or glue the side walls of such a channel over the entire surface to a metal surface. Such a full-surface connection would, however, cause a rigid connection between the waveguide element and the metal surface, which entails a high risk of bending and breaking during the duration of the life of the waveguide element. It has been found that this risk can be reduced by a plurality of electrical contact surfaces which are separated from one another.A length and / or the width of each electrical contact surface is preferably in the range from 0.3 mm to 1.5 mm. An area of each electrical contact surface is preferably in the range of 0.09 mm 2 to 2.25 mm 2. Such electrical contact surfaces have the advantage that they guarantee a resilient connection between the channel and the metal surface on the one hand and keep the contact surface between the channel and the metal surface on the other hand so small that the waveguide element has a high tolerance to mechanical loads.A distance between two adjacent electrical contact surfaces is preferably in the range of 0.3 mm to λ / 4 and is particularly preferably smaller than λ / 8. As a result, the electrical contact surfaces are on the one hand close enough to connect the waveguide element reliably to the metal surface and on the other hand far enough apart to significantly reduce the sensitivity of the waveguide element to mechanical loads.The electrical contact surfaces are preferably separated by means of apertures through a side wall, which can be in particular round arc-shaped or rectangular. Such perforations have the effect that non-perforated regions of the side wall, which each end in an electrical contact surface, take the form of pins which are well suited for a defined point-by-point connection between the channel and a metal surface. At the same time, it has been found that such apertures do not have a negative influence on the waveguide properties of the channel. The apertures can be designed in particular as toothing of the side walls.The channel preferably has a rectangular cross section, whereby it is simple to produce. Its height from the open side to the side of the channel opposite this open side is preferably in the range of λ / 2 to λ, since this represents a monomodal rectangular waveguide.The channel is preferably arranged on a metallic base surface of a printed circuit board, the outer contour of which corresponds to the outer contour of the open side of the channel. This metallic base surface, which in particular consists of copper, can also be referred to as footprint. If the electrical contact surfaces are separated by means of apertures through the side wall, the outer contour of the metallic base surface has a toothed structure, by means of which an exact positioning of the channel on the printed circuit board is facilitated. In this case, the electrical contact surfaces of the channel are soldered or glued to the teeth protruding in the outer contour of the metallic base surface.A wall of the channel, which is opposite its open side, is widened in particular beyond the cross section of the channel and can function as an antenna structure for a radar sensor. One or more openings extend through this wall into the interior of the channel and can serve as radiation elements for a radar wave.The printed circuit board furthermore preferably has a circuit with integrated microwave conductors (monolithic microwave integrated circuit; MMIC) for a radar sensor, which circuit is connected in a waveguiding manner to the channel. This can be arranged on the same side of the printed circuit board as the channel in order to protect it from heat and parasitic radiation below the side of the channel extended to form an antenna structure, or it can be arranged on the side of the printed circuit board facing away from the channel, wherein the waveguiding connection extends through the printed circuit board.In a method for producing such a waveguide element, which has a printed circuit board, a waveguide element is first provided, which only has the channel open on one side. Furthermore, a printed circuit board with a metallic base surface is provided, the outer contour of which corresponds to the outer contour of the open side of the channel of the waveguide element. The channel is then fastened to the electrical contact points by soldering or electrically conductive bonding on the metallic base surface of the printed circuit board, in order to thus obtain a waveguide element which is bounded on one side by the metallic base surface of the printed circuit board and on its further sides by the walls of the channel. In this case, the channel is aligned precisely on the metallic base surface by surface tension effects of the solder paste or of the adhesive.Brief Description of the DrawingsExemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. FIG. 1 shows an isometric view of a waveguide element according to an exemplary embodiment of the invention. FIG. 2 shows an isometric view of a waveguide element according to another exemplary embodiment of the invention. FIG. 3 ashows an isometric representation of a channel of a waveguide element according to yet another embodiment of the invention. FIG. 3 bshows a top view of the channel according to FIG. 3 a. FIG. 4 shows a plan view of a printed circuit board which, in an exemplary embodiment of the invention, can be connected to a channel made of a waveguide element. FIG. 5 shows an isometric view of the channel according to FIGS. 3 aand 3 b, the open side of which has been largely closed by a metallic base surface of a printed circuit board. FIG. 6 shows an isometric view of a waveguide element according to an exemplary embodiment of the invention, which has the channel according to FIGS. 3 aand 3 band the printed circuit board according to FIG. 4. FIG. 6 bshows a sectional side view of the waveguide element according to FIG. 6 a. FIG. 7 shows a flow diagram of a method for producing a waveguide element according to an exemplary embodiment of the invention.Embodiments of the InventionA waveguide element according to a first exemplary embodiment of the invention is illustrated in FIG. 1. This has a channel 10 with a rectangular cross section. The channel 10 has two side walls 11, 12 which have electrical contact surfaces 20 on their underside. The side walls 11, 12 have semicircular apertures 21 which separate the electrical contact surfaces 20 from one another. The channel 10 is arranged on a printed circuit board 30 in such a way that the electrical contact pads 20 are soldered to a metallic base area 31 of the printed circuit board 30, which consists of copper. The metallic base 31 forms the underside of the channel 10.FIG. 2 shows a second exemplary embodiment of the waveguide element according to the invention. This differs from the first exemplary embodiment in the dimensioning of the channel 10. while in the first exemplary embodiment the width of the channel 10 is greater than its height, in the second exemplary embodiment the height of the channel 10 is greater than its width. In both exemplary embodiments, the outer contour of the metallic base surface corresponds exactly to the outer contour of the open side of the channel 10, which is bounded by the two side walls 11, 12.The channel 10 of a waveguide element according to a third exemplary embodiment of the invention is illustrated in FIGS. 3 aand 3 b. This channel 10 is T-shaped and is bounded by a single circumferential side wall 13. This side wall 13 has, in the same way for the side walls 11, 12 in the first two exemplary embodiments, semicircular apertures 21 and is thus toothed. The regions of the side wall 13 remaining between the apertures 21 end in each case in electrical contact surfaces 20. Four radiation openings 15 pass through the antenna surface 14 and thus connect the channel 10 in a waveguiding manner to the side of the antenna surface 14 opposite the channel 10.The channel 10 according to the third embodiment of the invention is intended to be soldered to a printed circuit board 30 shown in Fig. 4. This has a metallic base 31 made of copper, which has a toothed outer contour corresponding to the toothed contour of the side wall 13 of the channel 10. A waveguiding via 32 extends from the metallic base 31 through the printed circuit board 30 to its opposite side. The inner walls of via 32 are metallized.If the channel 10 is soldered onto the metallic base 31, a structure results which is shown in FIG. 5 with the omission of the remaining printed circuit board 30. The complete waveguide element obtained in this way is shown in FIGS. 6 aand 6 b. On the side of the printed circuit board 30 facing away from the channel 10, an MMIC is connected by means of a ball grid array 41 (BGA). This is configured to function as a transceiver for a radar sensor. Radar waves are conducted from the MMIC 40 through the via 32 and the channel 10 to the radiation elements 15 and are radiated by the radar sensor. Such a radar sensor can be used in particular in a motor vehicle.The sequence of a production method for a radar sensor according to the third exemplary embodiment of the invention is schematically illustrated in FIG. 7. After the start 50 of the method, the still unfinished waveguide element is first provided, which only consists of the channel 10 according to FIGS. 3 aand 3 b. Subsequently, the circuit board 30 is provided 52 according to FIG. 4, the electrical contact surfaces 20 of the side wall 13 of the channel 10 are provided with a solder paste, positioned exactly on the metallic base surface 31 of the circuit board 30 and then fastened 53 to the latter by means of soldering. In this case, the surface tension of the solder paste guarantees a correct positioning of the channel 10. The arrangement of further electronic components, such as the MMIC 40, on the printed circuit board 30 can be carried out before or after carrying out these method steps 50 to 54.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2020 216 362 A1

[0004]

Claims

A waveguide element, comprising a channel (10) having an open side which is bounded by at least one side wall (11 - 13), characterized in that the side wall (11 - 13) comprises a plurality of electrical contact surfaces (20) which are separated from one another.The waveguide element according to claim 1, characterized in that a height and / or width of each contact surface (20) is in the range of 0.3 mm to 1.5 mm.The waveguide element according to claim 1 or 2, characterized in that a distance between two adjacent contact surfaces (20) is in the range of 0.3 mm to λ / 4 mm, wherein λ is a wavelength of an electromagnetic wave for which the waveguide element is configured to be guided.Waveguide element according to one of Claims 1 to 3, characterized in that the contact surfaces (20) are separated by means of apertures (21) through the side wall (11-13).Hollow conductor element according to Claim 4, characterized in that the apertures (21) are round arc-shaped or rectangular.Hollow conductor element according to claim 4 or 5, characterised in that the apertures (21) are designed as toothing of the side wall (11-13).Hollow conductor element according to one of Claims 1 to 6, characterized in that the channel (10) has a rectangular cross section.Hollow conductor element according to one of Claims 1 to 7, characterized in that the channel (10) is arranged on a metallic base surface (31) of a printed circuit board (30), the outer contour of which corresponds to the outer contour of the open side of the channel (10).Waveguide element according to Claim 8, characterized in that the printed circuit board (30) has an MMIC (40) for a radar sensor, which is connected in a waveguiding manner to the channel (10).Method for producing a waveguide element according to Claim 8 or 9, comprising the following steps: - providing (51) a hollow conductor element according to one of Claims 1 to 7, - providing (52) a printed circuit board (30) having a metallic base surface (31), the outer contour of which corresponds to the outer contour of the open side of the channel (10) of the waveguide element, and - fastening (53) the channel (10) to the contact surfaces (20) on the metallic base surface (31) by means of soldering or electrically conductive adhesive bonding.

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