Radar sensor having a waveguide structure

Abstract

Radar sensor having a plate-like substrate (12) which has at least one layer composed of electrically non-conductive material and on one side has a waveguide structure and on the opposite side has a radiofrequency source / sink which is connected to the waveguide structure via a radiofrequency bushing (22), which passes through the substrate, characterized in that a wall of the radiofrequency bushing (22) is formed by a sequence of circular-cylindrically curved surface segments (30) which have a uniform cross section over at least part of the length of the radiofrequency bushing.

Description

[0001] Description

[0002] title

[0003] Radar sensor with a waveguide structure

[0004] The invention relates to a radar sensor having a plate-shaped substrate which has at least one layer of electrically non-conductive material and has a waveguide structure on one side and a high-frequency source / sink on the opposite side, which is connected to the waveguide structure via a high-frequency feedthrough passing through the substrate.

[0005] In particular, the invention relates to a radar sensor for motor vehicles.

[0006] State of the art

[0007] Radar sensors are used in motor vehicles to implement comfort functions such as adaptive cruise control and safety features such as emergency braking. The radar sensors transmit high-frequency radar beams via an antenna structure and receive the beams reflected by objects. The detected objects can be stationary or moving. Using the received radar beams, the distance and direction (angle) to the object can be calculated. Furthermore, the speed of the object relative to the radar sensor can be calculated. Radar sensors typically operate in a frequency range between 76 and 81 GHz.

[0008] Driver assistance functions with higher functionality in the comfort or safety area, such as NCAP AEB emergency braking functions for pedestrians or cyclists, as well as future autonomous functions in the Level 3 to Level 5 range, lead on the one hand to a large number of sensors that must be arranged at different positions around the vehicle in order to cover the necessary field of vision, and on the other hand to sensors with an increasingly wider azimuthal detection range.

[0009] Radar sensors with a wide azimuthal detection range and long range can be implemented using waveguide antennas, among other things. The waveguide antenna can be fed through a metallized opening through a circuit board, so that the waveguide antenna and a high-frequency source (or a high-frequency sink, i.e., a receiver) can be arranged on opposite sides of the circuit board. It is known to create such openings in the circuit board, which serve as high-frequency feedthroughs, by drilling or milling a hole with the desired cross-section into the circuit board and then metallizing the circuit board, including the surface of the hole, using a standard process.

[0010] Disclosure of the invention

[0011] The object of the invention is to create a radar sensor with a high-frequency feedthrough that has a geometry optimized for the respective application and yet can be manufactured cost-effectively. This object is achieved according to the invention in that a wall of the high-frequency feedthrough is formed by a sequence of circularly cylindrically curved surface segments that have a uniform cross-section over at least part of the length of the high-frequency feedthrough.

[0012] These high-frequency feedthroughs can be manufactured cost-effectively in any desired cross-sectional shape by arranging holes whose cross-sections overlap or at least almost touch each other, following the contour of the wall of the high-frequency feedthrough. Although the resulting wall of the high-frequency feedthrough exhibits a certain waviness because each individual hole forms at least one circular-cylindrical curved segment of the wall, with a relatively small number of holes and correspondingly low effort, it is possible to ensure that the waviness has no adverse effect on the transmission properties of the high-frequency feedthrough for microwaves, especially if the wall irregularities are smoothed by subsequent metallization.

[0013] A key advantage of this manufacturing process is that no complex milling process is required to create a desired geometry of the high-frequency feedthrough that deviates from the circular shape.

[0014] The holes can be produced efficiently with a single drill or an assortment of a few drills and can be arranged in such a way that only low transverse forces act on the drill during the drilling process.

[0015] The invention also relates to a method for producing a radar sensor with the features specified above, in which the high-frequency feedthrough is formed by arranging a plurality of holes in a row corresponding to the profile of the wall of the high-frequency feedthrough to be produced. Advantageous embodiments and further developments are specified in the dependent claims. The holes can be made in the substrate such that their cross-sections overlap one another, i.e. the distance between the axes of two adjacent holes is smaller than the diameter of the holes or, if these diameters are different, smaller than the sum of the radii of the two holes. The lined-up holes then create a straight or curved slot in the substrate.

[0016] In one embodiment, the high-frequency feedthrough is formed directly by this slot. In another embodiment, the curved or multi-angled slot forms a closed line. Within this line, the remaining material of the circuit board then forms an island that is not connected to the surrounding material and therefore falls out, resulting in a high-frequency feedthrough whose width is greater than the width of the slot. Each individual hole creates a circular-cylindrically curved wall segment in the wall of the high-frequency feedthrough, and the adjacent wall segments form a series of ridges along the wall of the high-frequency feedthrough that protrude into the interior of the feedthrough. The smaller the distance between the axes of the individual holes, the flatter and blunt these ridges are.Increasing the distance between the axes of the holes results in higher and sharper ridges. However, this has the advantage that lower transverse forces act on the drill when drilling a single hole, as the surfaces with which the drill bit engages the substrate wall are more evenly distributed. Finally, if the distance between the axes of the holes is increased to the point where it equals the diameter of the holes, the circular-cylindrical wall segments form a series of semicircles. If the distance between the axes is increased even further, narrow ridges remain between the individual holes.However, if the slot formed by the holes forms a closed line, the island enclosed by the line, which is then connected to the surrounding material via narrow webs, can be broken out with little force, so that with a comparatively small number of holes, in which practically no transverse forces occur, a high-frequency feedthrough with a relatively large cross-sectional area is obtained.

[0017] The substrate will generally be a multilayer printed circuit board having at least two electrically conductive layers on its two opposite surfaces. Optionally, however, additional electrically conductive layers may be provided inside the printed circuit board. After one or more high-frequency feedthroughs have been produced using the method described above, the metallized layers on both surfaces of the printed circuit board and the metallized layers on the inner surfaces of the high-frequency feedthroughs can be produced in a single operation using known chemical or electrochemical metallization processes. Preferably, the metallization layer on the inner surfaces of the high-frequency feedthroughs should have a thickness of 1 μm or more, as this reliably covers the aforementioned burrs and eliminates the dependence of the high-frequency properties on the metallization thickness.

[0018] Since the method according to the invention allows a high degree of flexibility in the design of the cross-sectional geometry of the high-frequency feedthroughs, the bandwidth can be easily optimized, and desired filter or attenuation properties can be realized by a suitable choice of geometry, if necessary also selectively for certain polarization directions. In a known manner, the attenuation properties and the permittivity of the high-frequency feedthroughs can also be influenced by

[0019] The five openings forming these high-frequency feedthroughs are filled with suitable materials. Additional conductor structures can then be applied to the filler material at the opposite ends of the high-frequency feedthrough, if necessary.

[0020] It is also not necessary for the holes used to create the walls of the high-frequency feedthroughs to extend from one side of the circuit board to the other. For example, a first contour can be formed by a sequence of shallow holes, and then, within this first contour, a sequence of deeper holes can be used to create another contour, the geometry of which is, within certain limits, independent of the geometry of the first contour. In this way, stepped structures can also be realized in the high-frequency feedthrough.

[0021] In the following, exemplary embodiments are explained in more detail using the drawings.

[0022] They show:

[0023] Fig. 1 shows a partial section through a radar sensor according to a

[0024] 25 Embodiment of the invention;

[0025] Fig. 2 shows a section through a substrate of the radar sensor according to

[0026] Fig. 1 and a high-frequency feedthrough formed therein; uO Figs. 3 and 4 examples of high-frequency feedthroughs with a different geometry; and

[0027] Fig. 5 shows a section through a substrate with a high-frequency feedthrough according to another embodiment.

[0028] The radar sensor 10, shown in a partial section in Fig. 1, has a substrate 12 formed by several layers 14 of electrically non-conductive material and alternating layers 16 of electrically conductive material. The top and bottom surfaces of the substrate 12 are metallized and thus also form layers 16 of electrically conductive material.

[0029] Arranged on the top side of the substrate 12 is a waveguide structure 18, which may be, for example, a waveguide antenna or a connecting structure leading to a waveguide antenna (not shown). On the opposite side of the substrate 12, at the bottom in Fig. 1, a radio-frequency source / sink 20 is arranged, which is formed, for example, by an integrated radio-frequency component (MMIC) and serves to generate a microwave signal and feed it into the waveguide structure 18 and / or to detect and evaluate a microwave signal received by the waveguide antenna.

[0030] The waveguide structure 18 and the high-frequency source / sink 20 are signal-connected to each other by a high-frequency feedthrough 22. This high-frequency feedthrough 22 is formed by a perforation, which in the example shown extends from the top to the bottom of the substrate 12 with a uniform cross-section and whose wall has a metallization 24.

[0031] The high-frequency feedthrough 24 is thus capable of transmitting microwave signals from a connection point of the waveguide structure 18 to a connection point of the high-frequency source / sink 20 and vice versa. The transmissivity of the high-frequency feedthrough 22 for microwave signals with different frequencies and polarizations depends on the geometry, in particular the cross-section of the aperture forming the high-frequency feedthrough 22.

[0032] Fig. 2 shows a cross-section of the high-frequency feedthrough 22. It can be seen that the high-frequency feedthrough 22 is formed by four adjacent holes 28, the outlines of which are shown in dash-dotted lines in Fig. 2. The four holes 28 have a uniform radius and are arranged at uniform center-to-center distances, with this center-to-center distance being slightly smaller than the diameter of the holes, so that the cross-sections of the holes overlap. The upper and lower walls of the high-frequency feedthrough 22 shown in Fig. 2 therefore have a wavy cross-sectional shape and are formed by circular-cylindrical wall segments 30, each of which corresponds to a portion of the circumference of one of the holes 28 and which adjoin one another to form ridges 32.

[0033] The high-frequency feedthrough 22 thus has the overall shape of an elongated straight slot, the opposite walls of which are formed by diametrically opposite wall segments 30 of the same bores.

[0034] The high-frequency feedthrough can be manufactured, for example, by clamping the substrate 12 into an XY table that enables controlled movements of the substrate in a two-dimensional XY plane, and by successively forming the holes 28 using a drill clamped in a drill chuck stationary in the XY plane. The substrate 12 is then metallized to form the metallization 24 on the walls of the high-frequency feedthrough 22 as well as the metallizations on the top and bottom of the substrate. Fig. 3 shows a high-frequency feedthrough 22a that differs from the embodiment according to Fig. 2 in that the holes 28 have different diameters. In the example shown, the diameters are selected such that the slot forming the high-frequency feedthrough has a waist in the middle and its width increases towards both ends.

[0035] Fig. 4 shows a high-frequency feedthrough 22b according to another embodiment. In this case, the holes 28 again have a uniform diameter, but their center axes are arranged on a curved line, so that the slot forming the high-frequency feedthrough has an overall curved shape.

[0036] Fig. 5 shows a cross-section of a substrate 12c with a high-frequency feedthrough 22c that is stepped in its longitudinal section. This high-frequency feedthrough was manufactured by drilling holes of different diameters into the substrate from opposite sides.

[0037] The walls of the high-frequency feedthrough 22c are therefore defined by circularly cylindrically curved wall segments 30c, which have a smaller radius of curvature and a smaller width in the upper part of the feedthrough (see Fig. 5) than in the lower part. Accordingly, the center axes of the holes drilled into the substrate from above are also spaced closer than the center axes of the holes drilled from below.

[0038] Overall, a high-frequency feedthrough with a step 34 is obtained. The contours defined by the wall segments 30c above and below this step can be different from each other.

Claims

CLAIMS 1. Radar sensor with a plate-shaped substrate (12) which has at least one layer (14) of electrically non-conductive material and has a waveguide structure (18) on one side and a high-frequency source / sink (20) on the opposite side, which is connected to the waveguide structure (18) via a high-frequency feedthrough (22; 22a-c) passing through the substrate, characterized in that a wall of the high-frequency feedthrough (22; 22a-c) is formed by a sequence of circular-cylindrically curved surface segments (30; 30c) which have a uniform cross-section over at least part of the length of the high-frequency feedthrough.

2. A method for producing a radar sensor according to claim 1, characterized in that for producing the high-frequency feedthrough (22; 22a-c), a plurality of holes (28) extending at right angles to the plane of the substrate are arranged in a row such that the peripheral walls of the holes (28) form the wall segments (30; 30c).

3. A method according to claim 2, wherein by arranging the holes in a row The high-frequency feedthrough (22; 22a-c) is formed in the form of a slot whose width corresponds to the diameter of the holes (28).

4. Method according to claim 2 or 3, wherein the axes of the successively produced holes (28) lie on a straight line.

5. Method according to one of claims 2 to 4, wherein the bores (28) have different diameters.

6. Method according to one of the preceding claims, in which the bores (28) are formed continuously from one side of the substrate (12) to the other side.

7. Method according to one of claims 2 to 6, in which the substrate is metallized after the holes (28) have been made, a metallization (24) having a layer thickness of 1 m or more is formed.

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