Abstract:
The invention relates to a radar sensor including a radar antenna, a radar lens and a funnel element between the radar antenna and the radar lens. The funnel element includes a material which absorbs the radar radiation emitted by the radar antenna.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a radar sensor, e.g., a radar sensor for distance measurement in a motor vehicle. 
         [0003]    2. Description of the Related Art 
         [0004]    In a motor vehicle, a radar sensor may be used for determining a distance to a surrounding object. Based on the determined distance, different comfort and convenience functions of the motor vehicle may be controlled. For example, a speed of the motor vehicle may be automatically controlled to a predetermined value, a forward distance measurement with the aid of the radar sensor ensuring that the vehicle maintains a predetermined safety distance to a preceding motor vehicle. Other applications of a radar sensor include an emergency brake function when rapidly approaching an object, a distance warning device for making it easier for a driver of the motor vehicle to maintain a safety distance to a preceding vehicle, or a parking assistant for collision warning in close range at a low driving speed. 
         [0005]    Such radar sensors are generally designed as an integrated module, the module providing already evaluated or partially evaluated distance or proximity signals to an electrical interface. All components, which are necessary for transmitting, receiving and correlating radar signals, are included in the module. 
         [0006]    Such a radar sensor generally includes a radar antenna, a high-frequency circuit for activating the radar antenna and a radar lens for focusing the radar radiation emitted by the radar antenna or radar radiation incident on it. To prevent high-frequency radiation of the radar antenna from adversely affecting the high-frequency circuit or high-frequency radiation of the high-frequency circuit from adversely affecting the function of the radar antenna, it is known to provide a metal plate or a metal cage, which includes a recess, through which the radar antenna transmits or receives radar radiation, to shield the radar antenna from the high-frequency circuit. This makes it possible to shield electromagnetic radiation and in particular the high-frequency radar radiation, so that the high-frequency circuit and the radar antenna do not mutually influence one another; however, this may also adversely affect the performance or characteristics of the radar antenna. 
         [0007]    The object of the present invention is to suppress stray radiation in the area of a radar antenna of a radar sensor. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    A radar sensor according to the present invention includes a radar antenna, a radar lens and a funnel element between the radar antenna and the radar lens. The funnel element includes a material which absorbs the radar radiation emitted by the radar antenna. 
         [0009]    This makes it possible to omit the use of a shielding metal surface which may reflect radar radiation and other electromagnetic radiation. A directional characteristic of the radar antenna may be immune to influence due to the absorbing material. This may result in improved operation of the radar sensor. Furthermore, it may be simpler to adapt the geometry of the radar sensor, in particular of the radar lens, to an emission characteristic of the radar antenna. This makes it possible to improve the control of the emission characteristic of the radar sensor and achieve savings in development and production costs. 
         [0010]    The funnel element&#39;s narrow side faces the radar antenna and its wide side faces the radar lens. In one preferred specific embodiment, the funnel element is in contact with the radar lens. This makes it possible to ensure that the radar radiation transmitted by the radar antenna is incident on a geometrical area of the radar lens, which is designed for focusing the radar radiation. This may reduce a distortion of the radar radiation, in particular in a radially outer edge area of the radar lens. 
         [0011]    A lens edge, which in particular does not contribute to the focusing of the radar radiation, may lie in the radially outer area of the radar lens, the funnel element being designed for shielding the lens edge from radar radiation of the radar antenna by absorption. The lens edge may be essential for structural reasons. In particular, the lens edge may be used for connecting the radar lens to a housing in order to encapsulate the radar sensor against environmental influences. The essential mechanical structure of a known radar sensor may thus be retained without distorting the radar radiation in the area of the lens edge. 
         [0012]    In one specific embodiment, the funnel element includes a cylindrical section in the area of the radar lens. The cylindrical section may contribute to better shielding the lens edge from radar radiation from the radar antenna. 
         [0013]    In another specific embodiment, the funnel element has a radially inward facing collar in the area of the radar antenna. The collar may contribute to improved suppression of radial electromagnetic radiation with respect to a main propagation direction of the radar radiation. In particular, when the radar antenna is mounted on a planar component such as a printed circuit board, the collar may suppress surface waves propagating along the surface of the component. Furthermore, the collar may be used for a mechanical connection of the radar lens to the radar antenna or to a planar element on which the radar antenna is mounted or formed. A contact force of the funnel element may be distributed by the collar to a larger area. A mechanical structure of a module-like encapsulated radar sensor may thus be made simpler or improved. 
         [0014]    The radar antenna may be situated together with other high-frequency components on a planar circuit substrate, in particular a printed circuit board. This makes it possible to integrate the radar antenna and the electronic high-frequency components on the circuit substrate, which may reduce the space requirements, weight and manufacturing costs of the radar sensor. The funnel element may nonetheless effectively suppress a mutual influencing of the radar antenna and the high-frequency components. 
         [0015]    The funnel element may have a fastening element for attaching it to the radar antenna, so that the radar lens including the funnel element forms a separately manageable unit. This may simplify an assembly of the radar sensor. 
         [0016]    The funnel element may be manufactured from a radar radiation absorbing plastic material. For this purpose, the plastic material may have predetermined dielectric properties, and resistive and/or magnetic substances may be added to the plastic material for converting radar radiation into heat. This makes it possible to achieve efficient absorption of the radar radiation. 
         [0017]    In one specific embodiment, the material of the funnel element is porous. Reflection and refraction of the radar radiation on pore boundaries may contribute to increasing the absorption capacity of the funnel element. 
     
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
         [0018]      FIG. 1  shows a radar sensor. 
           [0019]      FIG. 2  shows a section through a material of the funnel element of  FIG. 1 . 
           [0020]      FIG. 3  shows a section through an alternative material similar to  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]      FIG. 1  shows a radar sensor  100 . Radar sensor  100  is in particular designed for use in a motor vehicle. Radar sensor  100  is preferably a long-range radar sensor (LRR) for determining a distance and if necessary a speed of an object at a distance of up to several hundreds of meters. The radar radiation emitted by radar sensor  100  is preferably in the range of approximately 24 GHz or 77 GHz. 
         [0022]    Radar sensor  100  includes a base plate  105  and a radar lens  115 , which close a housing  110  at diametrically opposed ends. In other specific embodiments, the components of radar sensor  100  may also be protected from environmental influences in some other way than by housing  110  and base plate  105 . Radar lens  115  has a radially outer lens edge  120 , which may be attached to housing  110 . Furthermore, the radar sensor includes a circuit substrate or a printed circuit board  125 , on which a radar antenna  130  and a high-frequency circuit  135  are situated. Radar antenna  130  may be formed on printed circuit board  125  in the form of a printed circuit. Between printed circuit board  125  and radar lens  115  extends a funnel element  140 , the narrow side of which faces radar antenna  130  and its wide side faces radar lens  115 . In the area of radar lens  115 , a fastening element  145  is formed on funnel element  140  for attaching it to radar lens  115 . 
         [0023]    An interface  150  is optionally attached to base plate  105  in order to provide electrical signals with regard to a measuring result of radar sensor  100  to the outside and for connecting to a power supply. Interface  150  may be connected to other electronic components in radar sensor  100 , which will not be discussed in greater detail in the present case. 
         [0024]    High-frequency circuit  135  on printed circuit board  125  preferably maintains a predetermined radial distance to radar antenna  130  to make it possible to place funnel element  140  on printed circuit board  125  in this area. The narrow side of funnel element  140  lies in the area of radar antenna  130  and is preferably engaged with printed circuit board  125 . The wide side of funnel element  140  lies in the area of radar lens  115 , and is preferably axially in contact with radar lens  115 , so that funnel element  140  is fixed in the axial direction between radar lens  115  and printed circuit board  125 . 
         [0025]    The side of radar lens  115  facing funnel element  140  is preferably planar. An internal width of funnel element  140  on radar lens  115  is preferably sized in such a way that an area of radar lens  115  lying radially within lens edge  120 , which is relevant for the focusing of exiting or entering radar radiation, is adjacent to the cavity formed by funnel element  140 . 
         [0026]    Preferably, a cylindrical section  155  is formed on funnel element  140  in the area of radar lens  115 . Cylindrical section  155  may make it more difficult for radar radiation emitted from radar antenna  130  from reaching lens edge  120  where difficult to control reflections and a distortion of radar radiation may occur. 
         [0027]    On its narrow side facing radar antenna  130 , funnel element  140  preferably has a radially inward extending collar  160 . This makes it possible to enlarge a contact surface of funnel element  140  on printed circuit board  125 . As a result, surface waves between radar antenna  130  and high-frequency circuit  135  may be effectively damped. 
         [0028]    In the area of cylindrical section  155 , a fastening element  145  may be formed on funnel element  140  in order to attach funnel element  140  to radar lens  115 . This may result in a separately manageable unit, which makes assembly of radar sensor  100  easier. In the present specific embodiment, for example, printed circuit board  125  may be positioned in housing  110  before radar lens  115 , together with funnel element  140 , is placed on housing  110  from above, resulting in housing  110  being closed axially on the top, and printed circuit board  125  is optionally pressed axially onto a supporting structure of housing  110 . Before or after the assembly of radar lens  115  and funnel element  140 , base plate  105  may be attached on the underside of housing  110 . 
         [0029]    Funnel element  140  is made of a material whose properties and structure are conducive to absorption of radar radiation. Both the material and the structure are preferably optimized to a wavelength of radar radiation which is emitted upwards during normal operation by radar antenna  130  in  FIG. 1 . 
         [0030]    Funnel element  140  is primarily designed for keeping the radiation emitted by radar antenna  130  away from elements, which either may be impaired by radar radiation, in particular high-frequency circuit  135 , or which, due to their refractive properties, may interfere with a measurement with the aid of the radar radiation, such as lens edge  120 . Secondly, funnel element  140  is also designed for keeping high-frequency radiation which has neither been generated by radar antenna  130 , nor has entered into radar sensor  100  through radar lens  115 , away from radar antenna  130 . Such radiation may, for example, be generated in the form of a fundamental or harmonic wave frequency by high-frequency circuit  135 . 
         [0031]      FIG. 2  shows a section through a material of funnel element  140  of  FIG. 1 . Funnel element  140  is preferably manufactured from a plastic material. The plastic material of funnel element  140  preferably has semi-conductive properties, i.e., its conductivity lies between that of a conductor and an insulator, in particular in the range between 10 3  and 10 −8  S/cm. This makes it possible for a part of radar radiation, to which funnel element  140  is exposed, to be converted into heat within the material, as a result of which the radar radiation is effectively absorbed. 
         [0032]    In the preferred specific embodiment shown in  FIG. 2 , the material of funnel element  140  is furthermore interspersed with metalized beads or metal balls  205  of a predetermined diameter, which may be selected in particular as a function of a wavelength of the radar radiation. In a known manner, metal balls  205  may improve the absorption properties of funnel element  140 . In one variant of the shown specific embodiment, metal balls  205  may also be applied to an inner or outer surface of funnel element  105 , for example, with the aid of an appropriate paint coating. 
         [0033]      FIG. 3  shows a section through an alternative material of funnel element  140  similar to the diagram of  FIG. 2 . The shown specific embodiment may be combined with the specific embodiment of  FIG. 2 . The material of funnel element  140  is interspersed with pores  210 , whose size range is preferably adapted to a wavelength of the radar radiation emitted by radar antenna  130 . If radar radiation penetrates the material of funnel element  140 , it is partially reflected on boundaries of pores  210 , as a result of which interference effects may form, which increase the absorption of the radar radiation.