Patent Publication Number: US-11646479-B2

Title: Method for producing a waveguide, circuit device and radar system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to German Patent Application No. 102019200689.2 filed on Jan. 21, 2019, and to German Patent Application No. 102019200893.3 filed on Jan. 24, 2019, the contents of which are incorporated by reference herein in their entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to methods for producing a waveguide, circuit devices and radar systems comprising a waveguide, and to methods, circuit devices and radar systems in which a waveguide is integrated into a multilayer substrate. 
     BACKGROUND 
     In radio-frequency circuit arrangements, it is typically necessary to transfer radio-frequency signals between different circuit structures. By way of example, radar systems can comprise transmitting/receiving circuits, local oscillator circuits and antennas, between which radio-frequency signals are transferred. In this case, radio-frequency signals can be in a frequency range of 50 to 100 GHz and higher. 
     The requirements in respect of recognizing and differentiating various objects are constantly increasing particularly in the case of radar systems in the automotive sector. One influencing variable here is the size of the antenna aperture, which is substantially determined by the number of different transmission and reception channels. Typical radar systems can thus have a plurality of transmitting/receiving circuits, which are sometimes also referred to as transceivers, wherein a typical radar system can comprise for example three transmission channels, TX channels, and four reception channels, RX channels. In order to increase an object differentiability, however, ever more channels are desirable, for example eight transmission channels and sixteen reception channels. Each transmission channel and each reception channel is generally assigned a corresponding transmitting antenna and a corresponding receiving antenna. It may generally be desirable for all transceivers to use the same, as far as possible phase-synchronous, radio-frequency local oscillator signal in order to down-convert received radar signals to the baseband. 
     In order to transfer or to distribute such radio-frequency signals (RF signals) in a circuit device, expensive printed circuit boards have been used hitherto, wherein microstrip lines are provided on a specific radio-frequency substrate, RF substrate, in order to minimize the losses. However, such known solutions have problems with regard to conduction losses, crosstalk and manufacturing tolerances. In particular, expensive materials are required for producing such RF substrates, wherein the RF substrates have a low tolerance vis-à-vis process fluctuations and vis-à-vis variations of the dielectric. 
     Overview 
     Therefore, solutions enabling RF signal transfer in circuit devices with improved properties in particular with regard to conduction loss and crosstalk would be desirable. 
     Examples of the present disclosure provide methods, circuit devices and radar systems comprising at least one waveguide in a multilayer substrate, such that RF signals can be transferred by way of the waveguide in the multilayer substrate. 
     Examples of the present disclosure provide a method for producing a waveguide in a multilayer substrate which involves producing at least one cutout corresponding to a lateral course of the waveguide in a surface of a first layer arrangement comprising one or a plurality of layers. A metallization is produced on surfaces of the cutout. A second layer arrangement comprising one or a plurality of layers is applied on the first layer arrangement, wherein the second layer arrangement comprises on a surface thereof a metallization which, after the second layer arrangement has been applied on the first layer arrangement, is arranged above the cutout and together with the metallization on the surfaces of the cutout forms walls of the waveguide. 
     Examples of the present disclosure provide a circuit device, having the following features: a multilayer substrate; at least one waveguide integrated into the multilayer substrate; a first layer arrangement comprising one or a plurality of layers, wherein the first layer arrangement comprises a cutout corresponding to a lateral course of the waveguide in a surface thereof; a metallization on the surfaces of the cutout; a second layer arrangement, which comprises one or a plurality of layers and is applied on the surface of the first layer arrangement, wherein a metallization on the second layer arrangement is arranged above the cutout and together with the metallization on the surfaces of the cutout forms the waveguide, wherein the metallization on the second layer arrangement leaves open predetermined lateral regions of the cutout in a vertical direction; and coupling elements for coupling signals into and out of the waveguide at the regions of the cutout that are left open in a vertical direction. 
     Examples of the present disclosure provide a radar system having the following features: a multilayer substrate; at least one waveguide formed in the multilayer substrate; and a first semiconductor radar transmitting/receiving circuit and a second semiconductor radar transmitting/receiving circuit, wherein the first semiconductor radar transmitting/receiving circuit is coupled to the second semiconductor radar transmitting/receiving circuit by way of the waveguide, or wherein the first semiconductor radar transmitting/receiving circuit and the second semiconductor radar transmitting/receiving circuit are coupled to a local oscillator circuit by way of a respective waveguide. 
     Examples of the present disclosure are based on the insight that the integration of a waveguide into a multilayer substrate in the manner described makes it possible to transfer and to distribute radio-frequency signals in a circuit device comprising the multilayer substrate, wherein firstly conduction losses and crosstalk can be reduced or minimized and secondly expensive RF substrates can be omitted. The integration of waveguides in multilayer substrates in the manner described makes it possible to integrate waveguides flexibly in circuit devices comprising a multilayer substrate, on and in which RF elements, for example in the form of semiconductor circuits, such as e.g. semiconductor chips, and/or antenna elements are provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Examples of the present disclosure are explained in greater detail below with reference to the accompanying drawings, in which: 
         FIGS.  1 A- 1 F  show schematic illustrations for an example of a method for producing a waveguide in a multilayer substrate; 
         FIGS.  2 A- 2 F  show schematic illustrations for a further example of a method for producing a waveguide in a multilayer substrate; 
         FIGS.  3  and  4    show schematic illustrations of layers of a multilayer substrate which comprise waveguide structures; 
         FIGS.  5 - 8    show schematic illustrations of various examples of circuit devices in which a waveguide is integrated into a multilayer substrate; and 
         FIG.  9    shows a circuit diagram of an example of a radar system. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, examples of the present disclosure are described in detail using the accompanying drawings. It should be pointed out that identical elements or elements having the same functionality may be provided with identical or similar reference signs in the drawings, in which case a repeated description of such elements may be omitted. Therefore, descriptions for elements having identical or similar reference signs may be mutually interchangeable. 
     In the following description, a plurality of details are set out in order to yield a more thorough explanation of examples of the present disclosure. However, it is evident to those skilled in the art that examples of the present disclosure can be implemented without these specific details. In other cases, sufficiently known structures and devices are shown in a schematic cross-sectional view or plan view instead of their details being shown, in order not to obscure the description of examples. Moreover, features of the various examples described hereafter can be combined with other features of other examples, unless a contrary indication is expressly given herein. 
     An example of a method for producing a waveguide in a multilayer substrate will now be described with reference to  FIGS.  1 A to  1 F . Firstly, a cutout  12  is produced in a surface of a first layer arrangement  10 . The layer arrangement  10  can comprise one or a plurality of layers, for example layers composed of a ceramic or dielectric material.  FIG.  1 A  schematically shows a plan view of the first layer arrangement  10  and  FIG.  1 B  schematically shows a cross-sectional view along the line B-B in  FIG.  1 A . A direction perpendicular to the main surfaces of the layer arrangement shall be defined as a vertical direction, and a direction parallel thereto shall be defined as a lateral direction. In plan view, the cutout  12  corresponds to a lateral course of the waveguide to be produced. To put it another way, the waveguide to be produced extends laterally in the first layer arrangement and the cutout produced corresponds to a lateral course of the waveguide from a first lateral section thereof to a second lateral section thereof. The first lateral section can be a first lateral end of the waveguide and the second lateral section can be a second lateral end of the waveguide. 
     As is shown in  FIG.  1 C , a metallization  14  is produced on surfaces of the cutout. The metallization  14  can continuously cover all surfaces of the cutout. After the metallization  14  has been produced, a second layer arrangement  20  comprising a metallization  22  on a surface thereof is applied on the first layer arrangement  10 . The second layer arrangement  20  can in turn comprise one or a plurality of layers, for example ceramic or dielectric layers. After the second layer arrangement  20  has been applied on the first layer arrangement  10 , the metallization  22  of the second layer arrangement is arranged above the cutout  12  and together with the metallization  14  on the surfaces of the cutout  12  forms the waveguide, as is shown in  FIG.  1 D . The metallization  22  can likewise be continuous in the region of the waveguide formed, such that together with the metallization  14  a waveguide with a continuous metallization in the entire inner surface region of the waveguide is formed. 
     In examples of the present disclosure, the metallization on the second layer arrangement may not cover regions of the cutout at predetermined lateral regions thereof, such that signal coupling into and signal coupling out of the waveguide can take place by way of these regions. In other examples, the metallization on the second layer arrangement is removed in regions of the cutout at predetermined lateral regions thereof after the second layer arrangement has been applied.  FIGS.  1 A  to IF show one such example. As is shown in  FIG.  1 E , the metallization  22  is removed at predetermined lateral regions  24  and  26  of the cutout  12 . The lateral regions  24 ,  26  can be lateral ends of the cutout  12  in examples. In examples, the removal can be carried out through openings  28 ,  30  in the second layer arrangement  20 . In examples, the second layer arrangement  20  can have the openings  28 ,  30  when it is applied. In the example shown, the openings  28 ,  30  in the second layer arrangement  20  are produced at the predetermined lateral regions of the cutout after the second layer arrangement  20  has been applied on the first layer arrangement  10 , in order to make it possible to remove the metallization  22  in the regions  24 ,  26 . 
     In examples of the disclosure, the openings in the second layer arrangement have been or are metallized and form an extension of the waveguide through at least parts of the second layer arrangement. 
     In the example shown in  FIGS.  1 A to  1 F , producing the openings  28  and  30  through the second layer arrangement  20  is followed by forming metallizations  32  and  34  on surfaces of the openings  28  and  30  in the second layer arrangement  20 . The metallizations  32  and  34  constitute an extension of the waveguide through the second layer arrangement  20 , in a vertical direction in the example shown. The waveguide produced thus comprises vertical sections formed by the metallizations  32  and  34  and a lateral section formed by the metallizations  22  and  14 . 
     In the example shown in  FIGS.  1 A to  1 F , the cutout  12  does not completely penetrate through the first layer arrangement  10  in a vertical direction with respect to a main surface of the first layer arrangement  10 . The lateral section of the waveguide is thus formed by the metallization  14  on the surface of the cutout  12  and the metallization  22  on the surface of the second layer arrangement  20 . In other example implementations, the cutout can completely penetrate through the first layer arrangement in a direction perpendicular to a main surface of the first layer arrangement, e.g. in a vertical direction. One such example will now be described with reference to  FIGS.  2 A to  2 F , these figures in each case again showing different method stages during production. 
       FIG.  2 A  once again shows a schematic plan view of the first layer arrangement  10 , in which a cutout  36  corresponding to a lateral course of the waveguide is formed. As can be discerned in  FIG.  2 B , the cutout  36  completely penetrates through the first layer arrangement  10  in this example. In the example shown, the cutout  36  completely penetrates through the first layer arrangement  10  over the entire lateral course. In other examples, the first cutout can completely penetrate through the first layer arrangement  10  at least in sections along the lateral course. 
     As is shown in  FIG.  2 C , a metallization  14  is produced on surfaces of the cutout  36 . Afterward, a second layer arrangement  20  having a metallization  22  is applied on a first main surface of the first layer arrangement  10 . Furthermore, as shown in  FIG.  2 D , a third layer arrangement  40  having a metallization  42  is applied on a second main surface of the first layer arrangement  10 . The third layer arrangement  40  can comprise one or a plurality of layers, for example ceramic or dielectric layers. The second layer arrangement  20  and the third layer arrangement  40  are applied on opposite sides of the first layer arrangement  10 , such that the metallization  22  is arranged on a first side of the cutout  36  and the metallization  42  is arranged on a second side of the cutout  36  opposite the first side. The metallizations  22  and  42  together with the metallization  14  on surfaces of the cutout  36  thus form the waveguide. 
     As is shown in  FIGS.  2 E and  2 F , afterward the metallization  22  can once again be removed at predetermined regions  24  and  26 , which can once again be carried out by way of openings  28  and  30  in the second layer arrangement  20 . The openings  28  and  30  in the second layer arrangement  20  can then once again be metallized in order to produce metallizations  32  and  34  constituting an extension of the waveguide through the second layer arrangement  20 . 
     In examples, waveguides are thus produced in a multilayer substrate by virtue of metallizations being provided on various layer arrangements and the layer arrangements being connected to one another in such a way that the metallizations define walls of the waveguide. Waveguides having various courses can thus be integrated into a multilayer substrate in a flexible manner. The multilayer substrate can be for example a substrate which is additionally configured for receiving semiconductor components at regions provided therefor. Accordingly, the multilayer substrate can comprise e.g. contact connection regions and electric lines, as known for instance from printed circuit boards for semiconductor components. 
     In examples, the metallization on the surfaces of the cutout and the metallization on the second layer arrangement and, if present, the third layer arrangement extend continuously between the predetermined lateral regions. It is thus possible to form a waveguide having continuous metallic surfaces, which waveguide enables low conduction losses and low crosstalk, in a multilayer substrate. 
     In examples of the present disclosure, provision can be made of coupling elements for coupling signals into and out of the waveguide at the predetermined lateral regions at which the metallization on the second layer arrangement does not cover the cutout. Coupling elements  50  and  52  are schematically illustrated by dashed lines in  FIGS.  1 F and  2 F . The coupling elements can be formed for example by patch antennas designed to couple electromagnetic RF signals into the waveguide and/or to couple electromagnetic RF signals out of the waveguide. 
     In examples of the present disclosure, therefore, at least one coupling element can be formed by an antenna, wherein the antenna can be formed in or on a housing of an RF circuit chip fitted in or on the multilayer substrate, or wherein the antenna can be fitted on the multilayer substrate. In examples, furthermore, reflectors can be provided on a side of the coupling elements facing away from the first layer arrangement. 
     In examples, the cutout can be formed in the first substrate arrangement by any suitable methods, for example by milling, by a laser treatment, by etching methods or the like. In examples, the first layer arrangement can comprise a plurality of layers of the multilayer substrate, in which layers signal routing structures comprising vias and conductor tracks are formed. In examples, the second layer arrangement can comprise a plurality of layers of the multilayer substrate, in which layers signal routing structures comprising vias and conductor tracks are formed. In examples, the first and second layer arrangements are fitted on a plurality of layers of the multilayer substrate, in which layers signal routing structures comprising vias and conductor tracks are formed. 
     Examples of the present disclosure provide methods for producing a circuit comprising a multilayer substrate. The multilayer substrate is produced comprising a plurality of layers, in which signal routing structures comprising vias and conductor tracks are formed. The multilayer substrate comprises RF elements on or in the multilayer substrate. The RF elements can comprise transmitting/receiving circuits and local oscillator circuits, for example. The RF elements can be formed by semiconductor circuits in the form of semiconductor chips. At least one waveguide is formed in the multilayer substrate by methods as described herein, wherein at least one terminal of a first RF element is coupled by way of the at least one waveguide to a terminal of a second RF element for signal transfer between same. 
     In examples, the RF elements can comprise a local oscillator circuit, at least one transmitting/receiving circuit and at least one antenna, wherein producing at least one waveguide comprises producing a waveguide that couples the local oscillator circuit to the at least one transmitting/receiving circuit, and/or producing a waveguide that couples the at least one transmitting/receiving circuit to the at least one antenna. In examples, the circuit can be a radar circuit, wherein the RF elements comprise a plurality of transmitting/receiving circuits, a plurality of receiving antennas, a plurality of transmitting antennas, and a local oscillator circuit, wherein producing at least one waveguide comprises producing a plurality of waveguides in order to couple the local oscillator circuit to each of the transmitting/receiving circuits, and to couple the transmitting/receiving circuits to the plurality of receiving antennas and transmitting antennas. 
     Examples of the present disclosure are described below on the basis of a radar circuit device. However, there is no need to mention separately that other circuit devices in which RF signals are transferred can also be implemented using methods and devices such as are described herein. Generally, examples of the present disclosure are applicable to circuit devices in which RF signals are transferred between RF elements, in particular RF semiconductor circuits, e.g. semiconductor chips. 
     As was mentioned in the introduction, the requirements made of radar systems in the automotive sector with regard to recognizing and differentiating various objects are constantly increasing, wherein, in order to attain a desired number of channels, by way of example, a plurality of radar transceivers in a cascade circuit can be used. In the case of such a cascade circuit, it is desirable for all transceivers to use the same, as far as possible phase-synchronous, radio-frequency local oscillator signal, LO signal, to down-convert the received radar signals to the baseband. In examples, the radio-frequency local oscillator signal can have a frequency of more than 50 GHz, for example between 76 and 81 GHz. The distribution of signals of such high frequency entails a number of problems. Firstly, signals of such high frequency are subject to specific losses on the printed circuit board, which has the effect that the power of the radio-frequency signals be correspondingly high, which results in unnecessary heating of the circuit that provides the radio-frequency signal. The circuit that provides the radio-frequency signal can be e.g. an LO master. The high power consumption of the LO master can be a burden on the thermal budget of the entire radar circuit and thus restrict the performance thereof and/or require expensive, complex measures for removing the heat. Furthermore, undesired crosstalk between the radio-frequency LO signal and the transmission and/or reception paths of the radar transceivers on the printed circuit board can reduce the performance of the radar circuit, which is sometimes also referred to as a radar sensor. Furthermore, expensive printed circuit boards have been required hitherto, wherein the properties of the printed circuit board materials, for example the dielectric conductivity and the coefficient of thermal expansion, have been permitted to fluctuate very little, in order to keep the influences, for example the signal damping, on the various LO paths as constant as possible. 
     Besides the distribution of the radio-frequency LO signal, feed lines from the transceivers to the transmitting-receiving antennas are also affected by the problems mentioned. Here, too, it is beneficial to keep losses low and crosstalk low. Examples of the present disclosure serve to alleviate the problems mentioned using the integration of waveguides integrated into a multilayer substrate. 
       FIG.  9    schematically shows a circuit diagram of a radar circuit comprising an LO circuit  60  and four transceiver circuits  62 ,  64 ,  66  and  68 . The circuits can be formed in each case by integrated circuits, IC, or integrated circuit chips. The LO circuit  60  constitutes an LO master, which makes a radio-frequency LO signal available to the transceiver circuits  62  to  68 . The transceiver circuits  62  to  68  thus constitute LO slaves. In order to distribute the LO signal, the LO circuit  60  is connected to the transceiver circuits  62  to  68  by way of an LO distribution network  70 . To put it more precisely, a respective transmission output TX 1 , TX 2 , TX 3  and TX 4  is connected to a local oscillator input LO_IN of a respective transceiver circuit  62 ,  64 ,  66 ,  68  by way of an assigned signal line  72 ,  74 ,  76 ,  78 . Each of the transceiver circuits  62  to  68  has a plurality of transmission outputs and a plurality of reception inputs. In the example shown, each transceiver circuit  62  to  68  has two transmission outputs TX 1 , TX 2  and four reception inputs RX 1 , RX 2 , RX 3  and RX 4 . The transmission outputs and reception inputs of the transceiver circuits are connected to receiving antennas  82  and transmitting antennas  84  by way of RF signal feed lines  80 . The receiving antennas  82  and the transmitting antennas  84  can be formed by patch antennas, as is shown in  FIG.  9   .  FIG.  9    thus shows a typical LO distribution network and RF signal feed lines to the antennas for a radar frontend circuit having eight transmission channels and sixteen reception channels. It goes without saying that comparable circuits can also be implemented with a different number of channels. Furthermore, passive RF elements such as e.g. ring coupler structures having a plurality of inputs/outputs can also be formed by the waveguide having a corresponding shape and routing. In the case of cascaded radar devices, such ring coupler structures can make it possible that, in the event of failure of a transceiver circuit operating as master, which transceiver circuit, in the original configuration, distributes the LO signal to the radar devices operating as slaves, in a new configuration, a transceiver circuit operating hitherto as a slave becomes the new master, which undertakes the LO distribution to the further MMIC, without the need for an active switchover in the LO distribution network. Likewise, in the present examples, the lateral course of the waveguide can be configured arbitrarily and have for example straight subsections, round subsections or angular subsections. 
     In examples of the present disclosure, one or more of the signal lines  72 ,  74 ,  76 ,  78  and one or more of the RF signal feed lines  80  to the antennas can be implemented by a waveguide as described herein. In examples, a corresponding waveguide can be implemented for each RF signal path of the radar circuit, e.g. both for all signal lines  72 ,  74 ,  76  and  78  and for all RF signal feed lines  80  to the receiving antennas  82  and the transmitting antennas  84 . 
     In this case, a waveguide should be understood herein to mean a waveguide which is not filled with a solid material, e.g. which is material-free. To put it more precisely, the interior between the walls of the waveguide is not filled with a solid material, but rather with a fluid, such as e.g. air. In this case, the dimensions of the waveguide can be adapted to the desired frequency range. By way of example, Table 1 shows typical dimensions and frequency ranges of waveguides having a rectangular cross section. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Recommended 
                   
                   
               
               
                 Waveguide 
                 frequency range 
                 Dimension A 
                 Dimension B 
               
               
                 designation 
                 [GHz] 
                 [mm] 
                 [mm] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 WR12 
                 60-90 
                 3.0988 
                 1.5494 
               
               
                 WR10 
                  75-110 
                 2.54 
                 1.27 
               
               
                 WR8 
                  90-140 
                 2.032 
                 1.016 
               
               
                 WR6 
                 110-170 
                 1.651 
                 0.8255 
               
               
                 WR5 
                 140-220 
                 1.2954 
                 0.6477 
               
               
                   
               
            
           
         
       
     
     In Table 1, the first column shows generally used designations of waveguides. The dimensions A and B represent the inner side lengths of the rectangular waveguide. Table 1 reveals that the dimensions of the waveguide decrease as the frequency increases. Examples of the present disclosure are thus suitable in particular for circuit devices, for example radar circuits, for high frequency ranges of 60 to 220 GHz, for example. 
     As has been explained above, in the case of a circuit arrangement as shown in  FIG.  9   , for example, all the RF signal lines can be implemented by waveguides. In this case, the arrangement of the elements of the circuit diagram shown in  FIG.  9    can be regarded as a layout which advantageously enables a corresponding connection of a local oscillator circuit  60  to transceiver circuits  62 ,  64 ,  66  and  68  and of the transceiver circuits  62  to  68  to respective antennas  82  and  84 . In order to implement the signal connections, it is possible to use for example waveguides having a layout as shown in  FIG.  3   . In this case,  FIG.  3    shows a plan view of a first layer arrangement, and cutouts, only two of which are designated by the reference signs  12  by way of example, have been produced in the first layer arrangement, as has been described above. As is shown schematically in  FIG.  4   , the first layer arrangement  10  can comprise a plurality of layers  10   a  to  10   d , in which corresponding cutouts for waveguides are formed. To put it more precisely, in plan view respectively overlapping cutouts in the various layers  10   a  to  10   d  jointly form a waveguide. It should be noted here that  FIG.  4    represents an exploded illustration and the layers  10   a  to  10   d  are connected to one another at main surfaces thereof. In this case, the cutouts in the individual layers are generally produced after the layers have been connected. Consequently, by way of example, the cutouts  12   a ,  12   b ,  12   c  and  12   d  overlap in plan view and form a continuous cutout, the lateral course of which corresponds to the lateral course of the waveguide that is integrated into a multilayer substrate in accordance with the present disclosure. Furthermore, in one example of a layer arrangement  10 , it may be possible to form respective waveguides in different layers, which can avoid crossing of waveguides e.g. in specific layouts. 
     In examples, the individual layers are firstly pressed in order to produce the first layer arrangement  10 , wherein cutouts are then produced in the correspondingly pressed layers, the cutouts corresponding to the lateral course of the waveguide structures to be produced. In examples, this cutout can have a U-shape in a vertical section. In examples, the cutout can be produced by laser treatment or be milled. The milled-out U-shape is then metallized and an upper layer, which constitutes a second layer arrangement in accordance with the present disclosure and has a metallization, is applied on the side in which the cutout is formed. The upper layer is then pressed with the other layers, such that the metallization on the upper layer and the metallization on the surfaces of the cutout give rise to the waveguide. 
     Examples of the present disclosure provide circuit devices which can be produced using methods as described herein. To put it more precisely, each waveguide as described herein can be produced using individual or all method features as described herein. 
     Examples of such circuit devices in which a first RF circuit is connected to a second RF circuit by way of a corresponding waveguide will now be explained in greater detail with reference to  FIGS.  5  to  8   . It is assumed in this description that the first RF circuit is an LO master, e.g. a circuit that provides an LO signal, and the second circuit is an LO slave, e.g. a circuit that receives an LO signal. However, there is no need to mention separately that the first and second RF circuits can also be formed by other RF circuits. 
     As is shown in  FIGS.  5  to  8   , the circuit devices each comprise a multilayer substrate  100 , into which a waveguide  102  is integrated. The waveguide here may have been produced in each case by a method as described herein, wherein in such a case a possible boundary between a first layer arrangement and a second layer arrangement is indicated by a dashed line  104  in  FIGS.  5  to  8   . 
     In the example shown in  FIG.  5   , an LO master  110  and an LO slave  112 , for example each in the form of an MMIC (monolithic microwave integrated circuit) are provided on the top side of the multilayer substrate  100 . In examples, the LO master  110  and the LO slave  112  can comprise an eWLB housing (eWLB=embedded wafer level ball grid array). Vias  114  and signal layers  116  can be provided in the multilayer substrate  100 . These constitute other signal routing structures  118  in the multilayer substrate. In the example shown in  FIG.  5   , the part of the multilayer substrate  100  below the dashed line  104  can be regarded as a first layer arrangement comprising a plurality of layers. The part of the multilayer substrate  100  above the dashed line  104  can be regarded as a second layer arrangement. The first layer arrangement has a cutout corresponding to a lateral course of the waveguide  102  in a surface thereof. A metallization is provided on the surface of this cutout. The second layer arrangement has on an underside thereof a metallization, which together with the metallization on the surfaces of the cutout forms the waveguide. The metallization on the second layer arrangement leaves open predetermined lateral regions  24 ,  26  of the cutout in the vertical direction, e.g. upward in  FIG.  5   . In the example shown, the predetermined lateral regions are lateral ends of the cutout. Furthermore, the second layer arrangement has openings  28 ,  30  at the predetermined lateral regions  24 ,  26 , wherein surfaces of the openings  28 ,  30  in the second layer arrangement are metallized and form an extension of the waveguide  102  through at least parts of the second layer arrangement. This extension can extend in a vertical direction, while the rest of the waveguide  102 , e.g. in the first layer arrangement, extends in a lateral direction. 
     Coupling elements in the form of patch antennas  150 ,  152  are provided in a manner overlapping the openings  28 ,  30  in order to couple RF signals into the waveguide  102  and to couple the signals out of the waveguide. The patch antennas  150 ,  152  can be connected to a respective RF solder ball  158 ,  159  of the LO master  110  and of the LO slave  112  by way of a respective line structure  154 ,  155  and a respective RF-suitable via  156 ,  157 . The line structure  154 ,  155  can comprise for example a microstrip line and a matching structure for impedance matching. In examples, the microstrip line itself can fulfill the function of impedance matching. 
     In the example of a circuit device as shown in  FIG.  5   , an RF signal is conducted into the interior of the multilayer substrate  100  by way of the RF solder ball  158  and the RF-suitable via  156 . In the interior, impedance matching can be carried out by way of the line structure  154  and the RF signal can be routed to the patch antenna  150  by way of a microstrip line of the line structure  154 . The patch antenna  150  emits the RF signal into the waveguide  102  integrated into the multilayer substrate  100 . The RF signal is received again on the part of the LO slave  112  by way of the further patch antenna  152 . From the patch antenna  152 , the RF signal can be routed to the RF solder ball  159  of the LO slave  112  by way of the line structure  155  and the RF-suitable via  157 . 
     The example shown in  FIG.  5    may be advantageous to the effect that the MMIC circuits do not have to be integrated into the multilayer substrate, but rather can be provided on a surface of the multilayer substrate. It is thus possible to reuse customary heat dissipation concepts since the MMIC circuits are not covered. 
       FIG.  6    shows one example of a circuit device in which the MMIC circuits  110  and  112  are recessed into the multilayer substrate  100  and the waveguide  102  is not integrated downward into the multilayer substrate, but rather is emplaced from above. The MMIC circuits  110 ,  112  are arranged in cutouts in a surface of the multilayer substrate. In the example shown in  FIG.  6   , that part of the multilayer substrate  100  which is arranged above the dashed line  104  can be regarded as a first layer arrangement, and that part of the multilayer substrate  100  which is arranged below the dashed line  104  can be regarded as a second layer arrangement. The waveguide is once again formed by corresponding metallizations on surfaces of a cutout in the first layer arrangement and on the second layer arrangement. Once again vertical sections of the waveguide extend through openings  28  and  30  in the second layer arrangement, the waveguide being open downward in this example. Once again patch antennas  150  and  152  are coupled to the openings in order to couple corresponding RF signals into the waveguide and to couple them out of the latter. Since the MMIC circuits  110  and  112  are recessed into the multilayer substrate  100 , RF-suitable vias are not required in this example. Rather, the line structures  154 ,  155  are directly connected to respective solder balls  158 ,  159  of the assigned MMIC element  110 ,  112 . The example shown in  FIG.  6    may be advantageous to the effect that customary layer constructions of a multilayer substrate can be reused. 
       FIG.  7    shows a further example of a circuit device in which the MMIC elements  110  and  112  are recessed into the multilayer substrate  100  and the waveguide  102  is integrated downward into the multilayer substrate. The MMIC elements are arranged in cutouts in a surface of the multilayer substrate  100 . In this example, once again the part of the multilayer substrate below the dashed line  104  can be regarded as a first layer arrangement and the part above the line can be regarded as a second layer arrangement. The waveguide  102  can thus be formed in the multilayer substrate  100  in a manner similar to that in the case of the example shown in  FIG.  5   . Since the MMIC elements  110  and  112  are once again recessed in the multilayer substrate, an RF-suitable via is not required and the respective patch antennas  150  and  152  can once again be connected directly to a respective solder ball  158 ,  159  of the respective MMIC element  110  and  112  by way of a respective line structure  154 ,  155 . In order to prevent emission from the patch antennas  150  and  152  upward, reflectors  170  and  172  can respectively be provided, which are arranged on sides of the patch antennas  150  and  152  facing away from the waveguide  102 . The reflectors  170  and  172  can be formed for example by corresponding metallizations in that layer of the multilayer substrate  100  which is arranged above the patch antennas  150  and  152 . The reflectors  170  and  172  can thus be integrated into the printed circuit board. Since, in the example shown in  FIG.  7   , the waveguide extends from the patch antennas  150  and  152  downward into the multilayer substrate  100  and reflectors  170  and  172  are provided, the MMIC elements  110  and  112  need not be recessed into the multilayer substrate  100  as far as in the example shown in  FIG.  6   . 
     A further example of a circuit device is shown in  FIG.  8   . In the example shown in  FIG.  8   , the MMIC elements  110  and  112  are integrated into the multilayer substrate. To put it more precisely, the MMIC elements  110  and  112  are inserted in cutouts in the multilayer substrate. In this example, the multilayer substrate comprises a first part  100   a  and a second part  100   b . The MMIC elements are inserted in cutouts of the first part  100   a  which are open upward. The second part  100   b  is placed onto the first part  100   a . The waveguide  102  is formed in the second part  100   b , as described herein. In this case, that part of the multilayer substrate which is situated above the dashed line  104  can be regarded as a first layer arrangement, and that part of the multilayer substrate  100  or of the second part  100   b  of the multilayer substrate which is situated below the dashed line  104  can be regarded as a second layer arrangement. Openings  28  and  30 , which penetrate through the second layer arrangement completely or partly, depending on the standpoint, are arranged in such a way that they are arranged opposite patch antennas  180  and  182  integrated into the housing of the MMIC elements  110  and  112 . 
     In the example shown in  FIG.  8   , the first part  100   a  and the second part  100   b  of the multilayer substrate can be produced separately from one another, and the second part  100   b , which comprises the waveguide  102 , can be placed onto the first part  100   a . In this variant, the antennas can be situated in the housing, package, on the rear side of the MMIC elements. In the case of such an arrangement, an RF transition from the respective MMIC element to the multilayer substrate is not necessary, with the result that fewer losses occur and more expedient printed circuit boards can be used. 
     It is evident to those skilled in the art that other implementations are possible besides the examples shown in  FIGS.  5  to  8   . Generally, examples of the present disclosure provide a circuit device in which a waveguide is integrated into a multilayer substrate in order to transfer RF signals between RF elements formed in or on the multilayer substrate. In this case, the RF elements can comprise RF circuits, such as, for example, RF circuit chips, and/or antennas. In examples, the multilayer substrate can comprise signal routing structures comprising vias and conductor tracks, wherein the circuit device comprises RF elements on or in the multilayer substrate, wherein at least one terminal of a first RF element is coupled by way of the at least one waveguide to a terminal of a second RF element for signal transfer between same. In examples, the RF elements can comprise a local oscillator circuit, at least one transmitting/receiving circuit and at least one antenna, wherein the at least one waveguide is configured to transfer an output signal of the local oscillator circuit to the transmitting/receiving circuit, and/or wherein the at least one waveguide or a further waveguide couples the at least one transmitting/receiving circuit to the at least one antenna. In this case, the local oscillator circuit can be part of a transmitting/receiving circuit, such that two transmitting/receiving circuits, with at least one of the transmitting/receiving circuits comprising a local oscillator circuit, can be connected by way of the waveguide. 
     In examples, the circuit arrangement is a radar circuit arrangement, wherein the RF elements comprise a plurality of transmitting/receiving circuits, a plurality of receiving antennas, a plurality of transmitting antennas, and a local oscillator circuit, wherein a plurality of corresponding waveguides are provided, which couple the local oscillator circuit to each of the transmitting/receiving circuits and couple the transmitting/receiving circuits to the plurality of receiving antennas and transmitting antennas. One example of such a circuit device is shown in  FIG.  9   . 
     Examples of the disclosure provide a radar system comprising a multilayer substrate, at least one waveguide formed in the multilayer substrate, a first semiconductor radar transmitting/receiving circuit and a second semiconductor radar transmitting/receiving circuit, wherein the first semiconductor radar transmitting/receiving circuit is coupled to the second semiconductor radar transmitting/receiving circuit by way of the waveguide, or wherein the first semiconductor radar transmitting/receiving circuit and the second semiconductor radar transmitting/receiving circuit are coupled to a local oscillator circuit by way of a respective waveguide. One example of such a cascaded radar system is shown in  FIG.  9   , wherein a plurality of semiconductor radar transmitting/receiving circuits  62 ,  64 ,  66 ,  68  are coupled to a local oscillator circuit  60 . In other examples, the LO master is not implemented as a separate LO circuit, but rather is formed by a local oscillator in one of the transmitting/receiving circuits. One of the transmitting/receiving circuits can thus act as LO master, which forwards the local oscillator signal to one or more other transmitting/receiving circuits. 
     In examples, the first and second semiconductor radar transmitting/receiving circuits are configured to generate frequency ramps using a local oscillator signal, wherein at least either the first or the second semiconductor radar transmitting/receiving circuit is configured to receive the local oscillator signal by way of the at least one waveguide. By way of example, the transmitting/receiving circuits  62  to  68  shown in  FIG.  9    can receive an LO signal by way of waveguides of the LO distribution network  70 . All transmitting/receiving circuits, transceivers, can thus use the same radio-frequency LO signal phase-synchronously to down-convert received radar signals to the baseband, for example. 
     In examples of the present disclosure, the waveguide or the waveguides of the radar system is or are produced by methods as described herein. Examples of the radar system can thus be produced using individual or all features of methods as described herein for producing a waveguide in a multilayer substrate. In the same way, radar systems as described herein can have some or all features of circuit devices as described herein. 
     Examples of the present disclosure make it possible to transfer RF signals in radar devices, for example automobile radar devices, with low losses and little crosstalk. Examples enable radar sensors having an increased angular resolution since a larger number of channels can be integrated in a multilayer substrate with longer RF feed lines on account of the lower signal losses and the lower crosstalk. As a result, examples of the present disclosure enable increased object differentiability on account of the increased angular resolution. Examples thus enable a cascading of a plurality of radar MMICs each comprising a plurality of transmitting and receiving antennas. 
     Although some aspects of the present disclosure have been described as features in association with a device, it is clear that such a description can likewise be regarded as a description of corresponding method features, in particular production method features. Although some aspects have been described as features in association with a method, in particular a production method, it is clear that such a description can also be regarded as a description of corresponding features of a device or of the functionality of a device. 
     In the detailed description above, in some instances different features have been grouped together in examples in order to rationalize the disclosure. This type of disclosure ought not to be interpreted as the intention that the claimed examples have more features than are expressly indicated in each claim. Rather, as represented by the following claims, the subject matter can reside in fewer than all features of an individual example disclosed. Consequently, the claims that follow are hereby incorporated in the detailed description, wherein each claim can be representative of a dedicated separate example. While each claim can be representative of a dedicated separate example, it should be noted that although dependent claims refer back in the claims to a specific combination with one or more other claims, other examples also comprise a combination of dependent claims with the subject matter of any other dependent claim or a combination of each feature with other dependent or independent claims. Such combinations shall be encompassed, unless an explanation is given that a specific combination is not intended. Furthermore, the intention is for a combination of features of a claim with any other independent claim also to be encompassed, even if this claim is not directly dependent on the independent claim. 
     The examples described above are merely illustrative for the principles of the present disclosure. It should be understood that modifications and variations of the arrangements and of the details described are obvious to those skilled in the art. Therefore, the intention is for the disclosure to be limited only by the appended patent claims and not by the specific details set out for the purpose of the description and explanation of the examples.