Abstract:
A radar sensor and a radar antenna are for monitoring the environment of a motor vehicle. A compact construction is achieved by the planar array of both the control circuit and the radar antenna, so that the radar sensor may be located, for example, in the area of a motor-vehicle bumper. Example configurations consist of the separate line support for arranging lines to transmit high-frequency signals between the control circuit and the radar antenna and the configuration of the radar antenna as a Rotman lens, in relation to the signal propagation times and the layered arrangement of Rotman lens and group antenna.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a radar sensor and a radar antenna, which are particularly suitable for monitoring the vicinity of a motor vehicle. 
     BACKGROUND INFORMATION 
     Such radar sensors are needed for various comfort-related and safety-related driver-assistance systems. They use sensors aligned in the forward direction of travel, in order to gather information about the traffic and obstacles on the road. This information these information items are used by the corresponding driver-assistance system, in order to implement automatic vehicle-to-vehicle ranging or to carry out an automatic emergency-braking function, or for applications from the area of adaptive driving control, collision prevention, and for the future, autonomous driving of vehicles. 
     Described in IEEE Transactions on Microwave Theory and Techniques, VOL. 45, NO. 12, December 1997, “Millimeter-Wave Radar Sensor for Automotive Intelligent Cruise Control (ICC)”, M. E. Russell et al., is a radar sensor, which has a control circuit and a radar antenna, the control circuit being in the form of a transceiver module, and the radar antenna being connected to the control circuit by at least one lead. In this context, a part of the control circuit is in the form of an MMIC (monolithic millimeterwave integrated circuit). In addition, the radar antenna is in the form of a printed circuit and has a Rotman lens and a group antenna. The Rotman lens has a lenticular parallel-plate line, at least two supply leads, a plurality of coupling leads, and delay lines. In addition, the group antenna is made of a plurality of individual antennas, which are connected in series in at least two rows. Each of these rows of individual antennas is connected to a delay line, which transmits the high-frequency signal supplied by the parallel-plate line to the associated coupling lead, to the row of individual antennas. 
     In the case of the radar sensor represented above, there is a problem with the connection or coupling of the MMIC modules to the radar antenna, since differently dimensioned circuits situated on different substrates must be interconnected. In this case, losses often occur, since the connecting lines are not optimally adapted for the transmission of high-frequency signals. 
     A further disadvantage of the conventional radar antenna is that, in the case of transmitting high-frequency signals between the group antenna and the Rotman lens, a defined phase relation is indeed present between the specific rows of the individual antennas and the associated coupling leads of the Rotman lens. However, a variable amplitude distribution of the high-frequency signals to the separate rows of individual antennas of the group antenna is not possible in this radar antenna. Thus, the directional characteristic of the group antenna cannot be adjusted in an optimum manner. 
     In addition, the above-described conventional radar antenna has the problem of the entire radar sensor occupying a large volume, due to the Rotman lens and the group antenna being positioned at right angles to each other. Therefore, the dimensional requirements for a radar sensor cannot be fulfilled to an extent satisfactory for, e.g., positioning it in the region of the bumper of a motor vehicle. 
     Therefore, it is an object of the present invention to provide a radar sensor and a radar antenna in which the previously described disadvantages are eliminated. 
     SUMMARY 
     According to a first aspect of the present invention, the above-mentioned engineering problem is solved by providing a radar sensor having a control circuit, which is in the form of a transmitting and/or receiving module and has at least one MMIC (monolithic millimeter-wave integrated circuit), and having a radar antenna, which is connected to the control circuit by at least one lead and has a Rotman lens and a group antenna, the control circuit and the radar antenna essentially being positioned in parallel with each other. 
     The planar form of the entire radar sensor results in a more compact construction occupying a smaller volume, so that the radar sensor of the present invention may be easily integrated into the region of the bumper of a motor vehicle. 
     An example embodiment of the present invention provides for a conductor support, lines for transmitting high-frequency signals between the control circuit and at least one lead of the radar antenna being situated on the conductor support, and the conductor support being situated between the control circuit and the radar antenna. 
     The above-mentioned construction of the radar sensor allows the signal transmission between the variably dimensioned modules, e.g., the at least one MMIC component and the radar antenna, to be effectively implemented by an additional module. To this end, the lines situated on the additional conductor support may be manufactured prior to assembling the radar sensor, and therefore, the actual connections between the at least one MMIC component and the radar antenna may be manufactured in a simple manner, after assembly, including that of the conductor support. This ensures that the lines arranged on the conductor support are suitably dimensioned at their points of connection to the least one MMIC component and to the radar antenna. 
     In this context, the lines on the conductor support may essentially extend in one plane, parallelly to the printed circuit traces of the control circuit and to the at least one lead of the radar antenna. If these lines are also positioned essentially at the same elevation as the control circuit and the radar antenna, then the result is a configuration of the different line elements, which essentially extend in one plane. The consequently produced, electrical and electromagnetic connections between the different modules are therefore reduced to a minimum, so that occurring losses are minimized. 
     The lines may be in the form of microstrip transmission lines on the conductor support, which may be particularly suited for transmitting high-frequency electromagnetic signals. 
     A further example embodiment of the present invention provides for a circuit support, to which the at least one MMIC component of the control circuit, the conductor support, and at least part of the radar antenna are connected, e.g., using an adhesive. Therefore, the circuit support may also be referred to as a multichip module. Thus, a unit is formed by all of the components, which are interconnected by a circuit support. In addition, transmission lines for transmitting signals between the lines of the conductor support and the supply leads of the radar antenna may also be formed on the circuit support. Thus, the circuit support also assumes tasks that are partially functional. 
     On one hand, wire-bonding connections, and on the other hand, electromagnetic field couplings are possible as options for a connection between the lines of the conductor support and the at least one lead of the radar antenna. In the case of the wire-bonding connection, the connecting elements may be cut in a highly exact manner, since the electrical properties of the wire-bonding connection substantially depend on its precision. In addition, a connection using electromagnetic field coupling allows higher manufacturing tolerances of the individual elements, but requires more expenditure for circuit design. 
     An advantage of the above-mentioned configuration is the modularity, for different control circuits in the form of pre-fabricated MMIC components may be used with the same radar antennas for different application purposes. The assembly and connection are performed on the circuit support. 
     In addition, it should be pointed out that the arrangmenet of the above-described, present invention is independent of the particular form of the radar antenna. 
     According to a second aspect of the present invention, the above-mentioned engineering problem is solved by a radar antenna including a Rotman lens having a lenticular parallel-plate line, at least two supply leads, a plurality of coupling leads, and delay lines, and including a group antenna having a plurality of individual antennas, which, in each case, are connected in series in at least two rows. Each row is connected by an antenna terminal to a delay line, which transmits the high-frequency signals supplied by the parallel-plate line to the corresponding coupling lead, to the row of individual antennas. The lengths of the delay lines are selected for a predetermined frequency of the high-frequency signal, in such a manner, that, in response to the high-frequency signal being applied to each of the supply leads, signals having a predetermined phase distribution are applied to the antenna leads. For a predetermined frequency of the high-frequency signal, the signal propagation delays, which occur between the supply leads and the antenna leads, are changed by an essentially integral multiple of the signal period, for different delay lines, in order to preselect an amplitude distribution of the signals applied to the antenna terminals. 
     In this context, the signal propagation times for outer delay lines may be lengthened in comparison with inner delay lines. An advantage of this refinement is that, in comparison with the conventional radar antenna, not only is a suitable phase occupancy achieved at the rows of individual antennas of the group antenna, but it is possible to selectively set the amplitude distribution of the signals applied to the rows of individual antennas, as well. 
     In this context, different geometric lengths of the delay lines predetermine the signal propagation times along the delay lines. However, it is possible to preselect the signal propagation times along the delay lines, using different dielectric constants for the substrates utilized for the delay lines. The high-frequency signals having a phase relationship predetermined by the supplied signal may be sent to the different rows of individual antennas. This is possible due to the narrow-band characteristic of the high-frequency signal to be transmitted, since the frequency differences within the band width of the high-frequency signal only result in negligible phase differences based on different signal propagation times. This allows a very precise directivity characteristic to be achieved for the group antenna. 
     According to a third aspect of the present invention, the above-mentioned engineering problem is solved by a radar antenna including a Rotman lens having a lenticular parallel-plate line, at least two supply leads, a plurality of coupling leads, and delay lines, and including a group antenna having a plurality of individual antennas, which, in each case, are connected in series in at least two rows. The Rotman lens and the group antenna are positioned so as to be essentially parallel to each other and spaced apart. 
     This arrangement may achieve a space-saving configuration of the Rotman lens and group antenna, so that a planar design of the radar antenna and the radar sensor is possible, thereby simplifying their use in a motor vehicle. Thus, it is possible, for example, to integrate a flat radar sensor and a flat radar antenna into the bumper of a motor vehicle. The radar sensor includes the arrangement of the Rotman lens and the group antenna next to each other on a substrate. 
     The Rotman lens and the group antenna may be formed on two different substrates, the sides of the two substrates facing away from the Rotman lens and the group antenna being connected to each other, and a common metallic coating being situated between the two substrates. This metallic layer may be used as a common ground for the Rotman lens and the group antenna. 
     Coupling slits may be formed in the metallic layer, which electromagnetically couple the antenna terminals of the rows the group antenna&#39;s individual antennas, to the connection points of the delay lines. Two important advantages are associated with this. First of all, there is no need to produce a metallic connection between the delay lines and the rows of individual antennas. Secondly, the electromagnetic field generated by the Rotman lens only affects the group antenna at the coupling slits provided for this purpose. In addition, the metallic layer is used as a shield between the Rotman lens and the group antenna. 
     The connection points of the rows of individual antennas may be essentially situated in the center of the rows, whereby a symmetric amplitude distribution to the individual antennas inside a row of individual antennas is achieved. This further improves the directivity characteristic of the radar antenna. 
     Additional features and advantages of the present invention are explained in detail in the following description of example embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view of a motor vehicle having a radar sensor according to the present invention, where the radiation characteristic is illustrated. 
     FIG. 2 is a block diagram of the radar sensor according to the present invention. 
     FIG. 3 is a cross-sectional view of a first example embodiment of a radar sensor according to the present invention. 
     FIG. 4 is a cross-sectional view of a second example embodiment of a radar sensor according to the present invention. 
     FIG. 5 is an exploded view illustrating the assembly of a circuit support. 
     FIG. 6 is a plan view of a first example embodiment of a radar antenna according to the present invention. 
     FIG. 7 is an exploded view of a second example embodiment of a radar antenna according to the present invention. 
     FIG. 8 is a cross-sectional detail view of the radar antenna illustrated in FIG.  7 . 
     FIG. 9 is a plan view of an individual antenna. 
     FIG. 10 is a plan view of a detail cut away from a row of individual antennas. 
     FIG. 11 is a plan view of two rows of individual antennas, in which the position of the coupling slits is illustrated. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a motor vehicle  1 , which has a radar sensor  2  on its front end in the region of the bumper, the radar sensor including a radar antenna  4 , which has an azimuthal directivity characteristic possessing a separate sensitivity for different angular segments φ. Therefore, objects may be detected in an angularly resolved manner in order to characterize the vicinity of motor vehicle  1 . In addition to angle φ, it is also possible to determine distance R and relative speed v, so that vehicles traveling ahead or objects on the roadway may be detected, in order to consequently control the handling of motor vehicle  1 . 
     FIG. 2 illustrates the general configuration of the entire radar sensor, as well as that of a subsequent evaluation system, using a block diagram. Radar antenna  4 , a control circuit  8 , and an analog-digital converter  10  are situated in front end  6 . In this context, control circuit  8  takes the form of a transmitting and/or receiving module and has at least one MMIC component. Radar antenna  4  is connected to control circuit  8  by at least one lead  12 . 
     Analog-digital converter  10  is connected to a first control device  14 , which is in the form of an electronic control unit that is connected, in turn, to a second control device that, for example, takes the form of an evaluator inside the vehicle. The signals received by radar antenna  4  are evaluated in this evaluator, in order to control the handling of motor vehicle  1  in a suitable manner. However, the electronic control unit of first control device  14  is not only used to evaluate the signals received by radar antenna  4 , but also to activate radar antenna  4  so that it emits radar signals. The radar antenna  4  in the example embodiment illustrated in FIG. 2 is configured to be monostatic and is therefore used as both a transmitting antenna and receiving antenna. However, a bistatic example embodiment of the radar sensor, which has two different radar antennas  4 , of which one is used as a transmitting antenna and the other is used as a receiving antenna, is, of course, also possible. These may be dimensioned differently and may be adapted, in each case, to the requirements for a transmitting or receiving antenna. Thus, a small transmitting antenna may be sufficient for completely covering the range to be monitored, while the receiving antenna has a larger antenna surface because of the necessary angular resolution. 
     Control circuit  8 , which is configured as a transceiver module, is a central unit of the radar sensor  2  according to the present invention. First of all, the central unit has the task of providing radar antenna  4  with the frequency-modulated radar signal at a sufficient power. Secondly, control circuit  8  mixes the signal received by radar antenna  4  with a local oscillator signal, so that a signal is formed in the baseband. As the transceiver module, control circuit  8  therefore represents the interface between the signal processing and radar antenna  4  or radar antennas  4 . In the example embodiment of the radar sensor  2  according to the present invention, both radar antenna  4  and control circuit  8  are assembled using planar technology. As indicated above, control circuit  8  has MMIC components for this purpose. 
     A first example embodiment of a radar sensor according to the present invention is schematically illustrated in FIG.  3 . Control circuit  8  has two MMIC components  18  and  20 , which, inter alia, perform the functions of the oscillator and an I/O mixer. In addition, the radar sensor has a planar radar antenna  4 , which, as explained below in detail, has a Rotman lens  22  and a group antenna  24  that are deposited on a substrate  26 . 
     In addition, a conductor support  28  is provided, on which lines used for transmitting high-frequency signals between MMIC components  18  and  20  of control circuit  8 , and leads  12  of radar antenna  4 , are formed. For this purpose, conductor support  28  is positioned between control circuit  8 , i.e., MMIC components  18  and  20 , and radar antenna  4 . 
     As also illustrated in FIG. 3, lines  30  formed on conductor support  28  essentially extend in a plane parallel to the printed circuit traces of control circuit  8 , and parallel to leads  12  of radar antenna  4 . This arrangement may allow the connections between lines  30  and the leads  12  of radar antenna  4 , and the connections between the lines and MMIC components  18  and  20  to be configured to be short. In particular, this minimizes the losses during the transmission of the high-frequency signals. 
     This is especially true, when lines  30  essentially extend on the same level as the printed circuit traces of control circuit  8 , as is illustrated in FIG.  3 . Since the difference in elevation between conductor support  28  and the leads  12  to radar antenna  4  is also small, the advantageous effect of short connections is also produced in this case. A wire-bond connection  31  has been selected as the present connection. 
     Lines  30  are accommodated in a very effective manner for transmitting high-frequency signals, by configuring the lines to be microstrip transmission lines on conductor support  28 . To this end, conductor support  28  is manufactured, for example, from GaAs or AL 2 O 3 . 
     GaAs-based microstrip transmission lines are manufactured in a plurality of manufacturing steps. 
     In a first step, a wafer is divided into specimens, the sizes are of which suitable for manufacturing the conductor supports. This is done by using a diamond to scribe a rupture joint, and by breaking the wafer over an edge. The wafer piece is then thinned down to a necessary thickness, using a wet-chemical, etch-polishing process. Apart from the etching attack of the etching solution, e.g., bromine-methanol solution, the reduction in thickness is also aided by pure mechanical abrasion on a polishing cloth. The wafer pieces are subsequently scrubbed free of impurities, in order to insure that the metallic coating adheres well to the GaAs. To this end, both the intrinsic oxide and organic contaminants are removed from the semiconductor surface. The metallization is performed immediately afterwards, in order to prevent the intrinsic oxide from forming again on the surfaces of the specimens. The metallic coating includes a 10 nm thick chromium adhesive base, a 100 nm thick, vapor-deposited gold layer, and 3 μm of galvanically deposited gold. Since a microstrip transmission line has its ground potential on the bottom side of the substrate, both sides of the wafer piece used as a substrate may be metallized. Prior to the subsequent lithography, the specimen made up of the substrate and the metallic coating is bonded to a glass support, using a photosensitive resist. First of all, this step facilitates the handling of the sensitive GaAs, and secondly, the metallic coating on the back of the specimen is protected during etching. After the etching step, the photosensitive resist is dissolved in acetone, and the specimen is therefore detached from its support. In order to ensure that no photo-resist residues remain on the specimen, they undergo a photo-resist incineration step so that, above all, no photo-resist residues resulting in deteriorated adhesion of a bonding wire remain on the printed circuit traces. Finally, the specimens are cut to size in a highly precise manner, so as to match the GaAs conductor supports. 
     As FIG. 3 further illustrates, a circuit support  32  is provided, which represents a stable base for mounting sensitive MMIC components  18  and  20 , as well as a stable base for conductor support  28 . To this end, they are joined to circuit support  32  by an adhesive. In addition, a part of radar antenna  4  is connected to circuit support  32 , as well. In order to provide a stable base for the various elements, the material of circuit support  32  is adapted to the thermal expansion properties of the substrates of MMIC components  18  and  20 , circuit support  28 , and radar antenna  4 , since large temperature differences especially occur during use in a motor vehicle. For this purpose, AL 2 O 3  was selected in the present example embodiment. In addition, lines for the voltage supply and for connection to first control device  14  are directly formed on the substrate of circuit support  32 . 
     Circuit support  32  also has another function, which is explained in detail in connection with the second example embodiment illustrated in FIGS. 4 and 5. 
     As illustrated in FIG. 4, this example embodiment also provides for MMIC components  18  and  20 , conductor support  28 , and a part of radar antenna  4  being joined to circuit support  32 . In contrast to the example embodiment illustrated in FIG. 3, circuit support  28  is, however, not connected using a wire-bonding connection  31 , but rather with the aid of an electromagnetic field coupling  34 , as is explained in detail with reference to FIG.  5 . 
     On its upper side illustrated in FIG. 5, substrate  36 , on which at least a part of radar antenna  4  is formed, e.g., in the form of Rotman lens  22 , has a metallic grounding coating that includes a notch  40  and a coplanar line  42 . A metallic grounding coating  44 , a notch  46 , and a coplanar line  48  are formed on the upper surface of circuit support  32  illustrated in FIG. 5, so as to be symmetric to the shape of the surface of substrate  36 . As is indicated by arrows  50 , the upper surface of circuit support  32  illustrated in FIG. 5 is turned over and positioned on substrate  36 , whereby the two coplanar lines  42  and  48  abut against each other so as to at least partially overlap. Therefore, an electrical contact is formed between the two coplanar lines  42  and  48 . In addition, the configuration of coplanar lines  42  relative to leads  12  is illustrated in FIG.  7 . 
     A lead  12 , which is in the form of a microstrip transmission line, is indicated by dashed lines in FIG. 5, on the lower side of substrate  36 . In this context, arrow  52  points in the direction of radar antenna  4 , e.g., in the direction of Rotman lens  22 . 
     On the other side, conductor support  28 , which has a line  30  in the form of a microstrip transmission line, is attached to circuit support  32  on the surface opposite to line  30 , as is illustrated by arrow  54 . However, arrow  56  points in the direction of control circuit  8 , to which line  30  is connected. 
     Both lead  12  and line  30  are not electroconductively connected to coplanar lines  42  and  48 , respectively, but are set apart from coplanar lines  42  and  48 , respectively, by substrates  36  and  32 , respectively. Therefore, line  30  and lead  12  are electromagnetically interconnected by a series circuit of two coplanar microstrip junctions. The first junction connects conductor support  28  to circuit support  32 , and the second junction ensures that Rotman lens  22  is coupled to circuit support  32 . In this context, the two coplanar lines  42  and  48  are galvanically connected, using a flip-chip assembly. This not only simplifies assembly, but also reduces electrical losses in comparison with a wire-bonding connection. Last but not least, the above-described, modular construction of the radar sensor is simplified by the flip-chip assembly, since different MMIC components of different control circuits may be connected to circuit support  32  and radar antenna  4  without any serious adaptation problems. In addition, the above-described method of construction saves space. 
     Illustrated in FIG. 6 is a first example embodiment of a radar antenna  4  according to the present invention, which may be used in the above-described example embodiments of radar sensor  2 . Radar antenna  4  has a Rotman lens  22 , which includes a lenticular parallel-plate line  56 , five supply leads  58   a  through  58   e , a plurality of coupling leads  60 , and delay lines  62 . In addition, radar antenna  4  has a group antenna  24 , which includes a plurality of individual antennas  64  that are connected in series to form a plurality of rows  66 . Provided for each row  66  of individual antennas  64  is a delay line  62 , which transmits the high-frequency signal supplied by parallel-plate line  56  to the corresponding coupling lead  60 , to the row  66  of individual antennas. All other leads  68  are used to electrically terminate parallel-plate line  56  and are covered by an absorbing material, which may be in the form of a film. In order to prevent multiple reflections inside the region of parallel-plate line  56 , all of the leads, i.e., supply leads  58   a  to  58   e , coupling leads  60 , as well as terminating leads  68 , are converted into microstrip transmission lines in an impedance-matched manner, using Klopfenstein tapers. In this context, the supply leads  58   a  to  58   e  illustrated on the left in FIG. 6 lead into electronic control circuit  8 , and the coupling leads  60  illustrated on the right lead into group antenna  24 . 
     The shape of parallel-plate line  56  and delay lines  62  is such that, in response to a suitable excitation in the focal plane, which extends in the region of supply leads  58   a  through  58   e  in FIG. 6, a specific phase occupancy is produced at the antenna terminals  63  illustrated in FIG.  6 . Therefore, in the case of a high-frequency signal of narrow bandwidth and its being fed through central supply lead  58   c , a high-frequency signal having the same phase is applied to coupling leads  63 . But if the high-frequency signal is supplied to one of the two outer supply leads  58   a  or  58   e , then a signal is applied to coupling leads  63 , which specifies a fixed phase relationship but has a phase shift between individual coupling leads  60 . In this context, parallel-plate line  56  and delay lines  62  are configured in such a manner, that the phase relationship extends linearly from the upper to the lower coupling terminals  63  illustrated in FIG.  6 . Parallel-plate line  56  is configured so that an exactly linear phase characteristic is achieved for three focal points of the lens. For example, the two outer supply leads  58   a  and  58   e  and central supply lead  58   c  represent the three focal points of the Rotman lens. 
     According to the present invention, the signal propagation delays occurring between supply leads ( 58 ) and antenna terminals  63  are changed for different delay lines ( 62 ), for a predetermined frequency of the high-frequency signal, by essentially integral multiples of the signal period, in order to specify an amplitude distribution of the signals applied to antenna terminals ( 63 ). In this context, the signal propagation times for outer delay lines ( 62 ) are may be increased in comparison with inner delay lines ( 62 ). 
     On one hand, this ensures that the high-frequency signals, which are applied to coupling terminals  63  and have their predetermined phase relationship, are supplied to rows  66  of individual antennas  64 . If, for example, central supply lead  58   c  receives the high-frequency signal, then signals having a phase shift essentially equal to zero are formed at coupling terminals  63 . 
     But since, on the other hand, outer delay lines  62  purposely have a greater length than central delay lines  62 , the high-frequency signals are more sharply attenuated on the outside, so that an amplitude distribution having a higher amplitude in the middle and a lower amplitude on the outside forms inside group antenna  24 . This allows the directivity characteristic of group antenna  24  to be influenced in an advantageous manner. 
     In the example embodiment illustrated in FIG. 6, the different signal propagation times along delay lines  62  are predetermined by different geometric lengths. This may be seen from the greater or lesser degrees of curvature of the delay-line  62  contours. It is also possible to adjust the signal propagation times by using substrates for the delay lines, which have different dielectric constants, since the electromagnetic signals propagate along the delay lines, and their propagation time is affected by the dielectric constant of the substrate. 
     The phase-specific control of individual antennas  64  of group antenna  24  allows the directivity characteristic of radar antenna  4  to be adjusted in a very precise manner. In each case, the directivity characteristic of the antenna has a major lobe, while minor lobes, the intensity of which is markedly less than that of the major lobe, appear in both azimuthal directions. The azimuthal orientation of the major lobe may be controlled by variably activating the Rotman lens via different supply leads  58   a  through  58   e , for the direction of the major lobe is shifted as a function of the phase relationship between the different individual antennas  64 . In this manner, an angular resolution of radar antenna  4  may be achieved solely by electronics, without mechanically adjusting it. 
     As described above, the directivity characteristic of group antenna  24  may also be controlled by applying a signal to upper and lower rows  66  of individual antennas  64  illustrated in FIG. 6, the amplitude of the signal being less than that for central rows  66  illustrated in FIG.  6 . This concentrates the generation of electromagnetic radiation in the center of planar group antenna  24 . In this context, control by variable amplitude is achieved in that the delay lines for outer rows  66  are considerably longer than those for central rows  66 , which means that the high-frequency signal is more sharply attenuated before entering outer rows  66 , than in the case of central delay lines  62 . Therefore, attenuation effects alone achieve a suitable amplitude distribution of the high-frequency signals inside group antenna  24 . 
     As is illustrated in FIG. 6, each of the delay lines  62  is connected to one of the two ends of rows  66  of individual antennas  64 . In this context, Rotman lens  22  and group antenna  24  are formed on one substrate, which essentially corresponds to the example embodiment illustrated in FIG.  3 . Therefore, Rotman lens  22  and group antenna  24  are essentially situated in one plane, which allows a planar construction of the entire radar antenna. 
     Illustrated in FIG. 7 is an exploded view of a second example embodiment of a radar antenna  4  according to the present invention. In this case, Rotman lens  22  also has the previously described parallel-plate line  56 , supply leads  58 , coupling leads  60 , and delay lines  62 . In addition, group antenna  24  has individual antennas  64 , which are series-connected in rows  70 . In this case, rows  70  of individual antennas differ from those of the first example embodiment in that, as is described below in detail, the coupling of the electromagnetic signals mainly occurs in the center of rows  70 . The present invention provides for Rotman lens  22  and group antenna  24  being spaced apart and positioned in parallel with each other. In contrast to the planar construction in the first example embodiment, Rotman lens  22  and group antenna  24  are therefore positioned one over another, so as to at least partially overlap. For this purpose, Rotman lens  22  is formed on a first substrate  72 , and the group antenna is formed on a second substrate  74 . The sides of the two substrates  72  and  74  facing away from Rotman lens  22  and group antenna  24 , respectively, are interconnected by a common metallic coating  76 . In this context, metallic coating  76  is used as a common ground potential. The above-described two-layer construction of radar antenna  4  is likewise illustrated in FIG. 4, as well as in FIG.  8 . 
     Rotman lens  22  and group antenna  24  are coupled, using electromagnetic field coupling, as described above for the various components of radar sensor  2 . To this end, coupling slits  78  are formed in metallic coating  76 , which electromagnetically couple connecting points  80  of the rows  70  of individual antennas  64  to contact points  82  of delay lines  62 . 
     Therefore, the electromagnetic field, starting from contact points  82 , is transmitted through substrate  72 , through coupling slits  78 , through substrate  74 , to connecting points  80  of group antenna  24 . Since metallic coating  76  is also formed over the whole surface, Rotman lens  22  is effectively shielded from group antenna  24 . 
     The positioning and shape of a coupling slit  78  and two connecting points  80  and  82  is also illustrated in FIG.  8 . Since coupling slit  78  only stipulates a limited spatial region for electromagnetically coupling the two connecting points  80  and  82 , rows  70  are first of all energized in a precisely defined manner, and secondly, effective shielding is ensured in the regions outside coupling slits  78 . 
     The control of group antenna  24  as a transmitting antenna is described above, in which case the electromagnetic signals travel from Rotman lens  22  to group antenna  24 . When group antenna  24  is used as a receiving antenna, the signals propagate in the reverse direction. 
     A more precise refinement of the individual antennas, as well as of rows  70  and  66  of individual antennas  64 , is illustrated in detail in FIGS. 9 to  11 . 
     FIG. 9 illustrates an individual antenna  64 , which has a lead  84  that is in the form of a microstrip transmission line, and has a radiating surface  86  that is also referred to as a patch. The length of radiating surface  86 , which is indicated by y in FIG. 9, is predetermined by the frequency of the high-frequency signal and essentially corresponds to half the wavelength of the radiation in the substrate. However, width (b) and relative position of the supply point (x) may be selected within limits, the two parameters being matched to each other in order to ensure effective entrance adaptation. The edge of radiating surface  86  denoted by y is also designated as a non-radiating side of radiating surface  86 , and the two edges denoted by b are designated as radiating sides of the radiating surface. The two parameters, width (b) and length (y), may be changed within limits, whereby the magnitude of the power tapped from row  70  or  66  for the specific individual antenna  64 , and also the amplitude distribution inside row  70  or  66 , are adjustable. 
     To control a row  70  (or  66 ) of individual antennas  64 , a supply network is configured in the form of a three-gate series circuit, as is illustrated in FIG. 10. A triple gate includes two λ/4 transformers and an individual-antenna branch. On the condition that all individual antennas  64  operate in phase, the decoupling points may therefore be electrically spaced 360° from one another. Therefore, the connecting piece between two triple gates may produce an electrical phase shift of 180°. In addition, the individual triple gates are configured in such a manner that a specific portion of power Pin in the supply line is decoupled into the lead of individual antenna  64 , as a function of the desired amplitude distribution of individual antennas  64  along row  70 . 
     The following equations are valid for the individual impedances, in the case of a fixed portion α to be decoupled and a freely selected impedance level Z 0  of the supply line: 
     
       
         
           Z 
           1 
           ={square root over (αZ 0   Z   2 )}, 
         
       
     
     
       
           Z   3 ={square root over (α(1−α) −1   Z   0   Z   2 .)} 
       
     
     It can be inferred from the formulas that, in addition to impedance level Z 0 , the portion of the decoupled power may also be freely selected. Z 2  is the impedance level of lead  84  of individual antenna  64 , while Z 0  may be referred to as the impedance level of the supply line. 
     Apart from the configuration of branched individual antennas illustrated in FIG. 10, the individual antennas may also be arranged in series or threaded inside the line. The amplitude of each decoupled signal is then controlled by the width of the radiating surfaces. 
     The positioning of connecting points  80  along two rows  70  is illustrated in FIG.  11 . Connecting points  80  are essentially situated in the center of rows  70 , where, as illustrated in FIG. 11, a subdivision into λ/2 and λ is performed in order to ensure that the individual antennas  64  situated on the left and right of connecting point  80  are in phase, when electromagnetic waves propagate along rows  70  in two different directions. 
     In the above-described example embodiments of radar antenna  4 , the substrates of Rotman lens  22  and group antenna  24  are produced from a ceramic-filled composite of polytetrafluoroethylene (PTFE). This allows a flexible configuration of both radar antenna  4  and radar sensor  2 . 
     If substrates  72  and  74  also have different dielectric constants, then the size of Rotman lens  22  may be decreased independently of the dimensions predetermined by the external shape of group antenna  24 , when a high dielectric constant is used. 
     It should be pointed out that, in the case of the second radar-antenna example embodiment illustrated in FIG. 7, the routing of the delay lines may be&#39;selected within the framework of the arrangement. However, these delay lines  62  may be selected in a manner described with regard to the first example embodiment illustrated in FIG.  6 . Therefore, the adjustment of the signal propagation times represents an additional option for the radar antenna  4  according to the second example embodiment.