Abstract:
A system and technique for mounting a radar to a vehicle provides a mounting that does not interfere with the aesthetic appearance of a vehicle, that does not interfere with the aerodynamic performance of the vehicle, and offers optimal radar transmission efficiency. The vehicle can be an automobile or any other vehicle to which a radar system is applied.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/226,160, filed on Aug. 16, 2000 which application is hereby incorporated herein by reference in its entirety. 
     GOVERNMENT RIGHTS 
     Not Applicable. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to a system for mounting a radar system and more particularly to a system for mounting a radar system to a vehicle in a location behind a bumper section or other vehicle body part, for example, a lamp housing, a body panel, a license plate, or a side mirror housing. 
     BACKGROUND OF THE INVENTION 
     As is known in the art, radar systems have been developed for various applications in association with automobiles and other vehicles. For example, radar systems have been proposed and built that detect the presence of objects in proximity to an automobile on which the radar is mounted. 
     The radar system is typically optimized in shape and materials for the transmission and reception of radar energy and is not well suited to match the appearance of the body of the automobile. Thus, when mounted on the outer surface of the body of a vehicle, such as an automobile for example, a radar system is generally not aesthetically appealing. 
     Furthermore, automobile manufacturers, with a desire to optimize fuel efficiency, provide automobile shapes that are generally aerodynamically efficient. The radar system is not typically aerodynamically efficient when mounted to the body of an automobile since the shape of the radar system is typically optimized for effective transmission and reception of radar energy and not generally optimized for low drag. 
     It would, therefore, be desirable to provide a system for mounting a radar system on a vehicle that allows the vehicle on which the radar system is mounted to maintain its aesthetically pleasing shape. It would also be desirable to provide a system for mounting a radar system on a vehicle which results in the mounted radar system introducing little or no additional aerodynamic drag on the vehicle and which still allows the radar system to efficiently transmit and receive of radar energy. 
     It has, therefore, been recognized that it would be desirable to place the radar system behind a bumper section or other existing feature of the automobile. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a mounting system for mounting a radar system to a vehicle includes a spacer section between the radar system and a surface of the vehicle structure. The spacer section provides transmission thickness and an angular transmission thickness associated with the vehicle structure that increases the transmission efficiency of the radar energy from the radar system through the vehicle structure. The transmission thickness, or alternatively the angular transmission thickness, are made to be one half wavelength or a multiple thereof. 
     The mounting system for radar is adaptable to an automobile or to any vehicle upon which a radar system is mounted. 
     With this particular arrangement, a radar mounting system is provided that does not detract from the aesthetic appearance of the vehicle, and that does not detract from the drag characteristics of the vehicle. The radar mounting system for vehicles still provides efficient transmission and reception of radar energy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features of the invention, as well as the invention itself may be more fully understood from the following detailed description of the drawings, in which: 
     FIG. 1 is a partially exploded view of a radar system mounted to a vehicle bumper section; 
     FIG. 1A is an exploded isometric view of a radar system mounted to a vehicle bumper section; 
     FIG. 2 is a top isometric view of a radar system adapted for mounting to a vehicle; and 
     FIG. 2A is a bottom isometric view of the radar system of FIG. 2; 
     FIG. 3 is a top view of a radar system coupled to a bumper section of a vehicle; 
     FIG. 3A is a top view of an alternate embodiment of the radar system coupled to the bumper section of a vehicle; 
     FIG. 4 is a top view of another alternate embodiment of a radar system coupled to the bumper section of a vehicle; 
     FIG. 4A is a top view of yet another alternate embodiment of a radar system coupled to the bumper section of a vehicle; 
     FIG. 5 is a top view of yet another alternate embodiment of a radar system coupled to the bumper section of a vehicle; and 
     FIG. 5A is a top view of yet another alternate embodiment of a radar system coupled to the bumper section of a vehicle. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1 and 1A, in which like elements are provided having like reference designations, a pair of radar systems  12 ,  14  are mounted behind a rear automobile bumper  16 . The radar systems  14 ,  16  may be provided, for example, as radar systems described in U.S. patent application entitled Radar Transmitter Circuitry and Techniques, filed on Aug. 16, 2001, and assigned application Ser. No. 09/931,636, and U.S. patent application entitled Highly Integrated Single Substrate MMW Multi-Beam Sensor, filed on Aug. 16, 2001, and assigned application Ser. No. 09/931,277, each of which are assigned to the assignee of the present invention and incorporated herein by reference. It should be appreciated of course that other radar systems can be used in accordance with the present invention. It should also be appreciated that this invention applies equally well for mounting radar systems  12 ,  14  at various locations on an automobile, and is not limited to mounting in association with the rear bumper  16 , as will be described below. 
     The radar systems  12 ,  14  are each mounted behind a bumper section  16  provided from a material which allows radar signal energy to pass through with relatively little attenuation. The radar system  14  can be mounted to a mounting bracket  20  or can be mounted directly to the body of the automobile. A protective barrier section  22  is disposed between an inner wall of the bumper section  18  and a surface  14 A of the radar system  14 . Protective barrier section  22  provides additional protection for the radar system. 
     Referring to FIGS. 2 and 2A, in which like elements are provided having like reference designations, an exemplary radar system  24  includes mounting flanges  26   a - 26   c  that provide a mounting structure which can be used to mount the radar system to a portion of an automobile. A connector  28  provides an electrical interface both for power to the radar system and for communication of signals to and from the radar system. The radar system has a first surface  30  that faces toward the body of the automobile when the radar system  24  is disposed on the automobile. A second surface  32  of the radar system  24  faces away from the body of the automobile. In accordance with the mounting system of the present invention, the second surface  32  is directed toward an inner surface of the automobile bumper section or the inner surface of some other automobile structure. The second surface  32  is the surface through which radar signals are emitted from the radar system  24 . 
     An exemplary radar system  24  is provided having a length of 12.7 cm, a width of 7.6 cm and a thickness of 3.8 cm where the thickness corresponds to the distance between the two surfaces  30 ,  32 . It will be recognized by one of ordinary skill in the art that radar systems with other dimensions can be used with this invention. It will be further recognized that other mounting structures and techniques in addition to the flanges  26   a - 26   c  are possible with this invention. For example, other mounting structures include clips, snap features, adhesive, tape, and hook and loop (Velcro™). 
     It will be further recognized by one of ordinary skill in the art that other techniques in addition to the connector  28  can be used to provide power and data signals to the radar system. For example, a wiring harness can be molded into the radar system  24 , or terminal pins can be used. It will be further recognized by one of ordinary skill that the radar system  24  can be oriented in any azimuth orientation relative to the automobile. 
     Referring now to FIGS. 3 and 3A shown from top view, in which like elements are provided having like reference designations, a radar system  36  is disposed on a first surface of an automobile  38 . In this embodiment, radar system  36  is coupled to an outer surface of the body of the automobile  38 . The radar system  36  has disposed thereover an optional protective barrier section  52 . The barrier section  52  is disposed to prevent material matter or debris (e.g. snow) from entering the volume in front of radar system  36 . The barrier  52  also provides impact protection in the event of a vehicle collision. The barrier section  52  is provided from any material which will not absorb a significant amount of water. The barrier section  52  can be provided from any suitable material which is relatively transparent to radar signals propagating therethrough. In one embodiment, the barrier section  52  is provided from a closed cell foam rubber such as Neoprene™. In another embodiment, the barrier section  52  is provided from a polymethacrylimide rigid foam such as Rohacell™. The barrier section  52  can be shaped so as to enclose the radar system  36 . The barrier section  52  can be in contact with the radar system  36 , or alternatively a space can be provided between the barrier section  52  and the radar system  36 . 
     Disposed adjacent to the barrier section  52  is a spacer section  42 . In one embodiment, the spacer section  42  is disposed between the barrier section  52  and the bumper section  40 . 
     In an alternate embodiment, the spacer section  42  can be disposed on an outer surface of the bumper section  40  (i.e. the spacer section can be disposed so that it is visible to a person looking at the outside of an automobile). Though the spacer section  42  can be associated with either surface of the bumper section  40 , association with the inner surface as indicated is preferred so that the outer bumper appearance can be unaltered. 
     In one embodiment, the spacer section  42  can be an extension of the bumper section  40 , i.e. molded into the bumper section  40 . Alternatively, the spacer section  42  can be provided as a piece distinct from the bumper section  40  that is attached, for example with glue or a fastener structure such as a snap or clamp, to a surface of the bumper section  40 , whereby the spacer section  42  is the same type of material as the bumper section  40 . Alternatively, the spacer section  42  can be provided from a material which is a different material from that of the bumper section  40 . In discussion that follow, however, it will be recognized that in a preferred embodiment the spacer section  42  is provided from a material having the same dielectric constant as that of the bumper section  40 . In all cases, the spacer section  42  must be made of a material that, like the bumper section  40 , allows radar signal energy to pass through with relatively little attenuation. 
     The term transmission thickness as used herein will indicate the total thickness of material, at an angle perpendicular to the surface of the material, through which radar energy, represented by perpendicular radar beam  46   b , must propagate. The transmission thickness can include either the bumper thickness  48   a  of the bumper section alone, or, in the alternate embodiment, where the spacer section  42  is provided as a piece distinct from the bumper section  40 , the sum of the bumper thickness  48   a  plus the spacer thickness  48   b  of the spacer section  42 . The transmission thickness  48  will refer to the total. 
     The term angular transmission thickness as used herein will indicate the total thickness of material, at an angle not perpendicular to the surface of the material, through which radar energy, represented by non-perpendicular radar beams  46   a,    46   c  must propagate. 
     As above, the angular transmission thickness, for which thickness  50  is one example, can include a distance through both the bumper section  40  and through the spacer section  42  where the spacer section  42  is provided as piece distinct from the bumper section  40 . 
     In addition to radar energy, represented by three radar beams  46   a - 46   c,  that propagates outward from the radar system  36 , some of the radar energy  46  can reflect back from the bumper section  40 , and in the alternative embodiment where the spacer section  42  is provided as piece distinct from the bumper section  40 , radar energy  46  can reflect back from the spacer section  42 . Hereafter such multiple reflections are collectively called reflection. 
     It will be recognized by one of ordinary skill in the art that if the dielectric constant along the transmission thickness is a uniform value, and if the transmission thickness is made to be equal to one half of the wavelength of the transmitted radar energy, refection is minimized and the radar energy propagating outward in a direction away from the radar system  36  through the bumper section  40  is maximized. Thus, if the spacer section  42  is composed of a material that has the same dielectric constant as the bumper section  40 , the spacer section  42  can be used to provide a transmission thickness that is one half wavelength, where such wavelength is the wavelength in the bumper section  40  and spacer section  42 . Alternatively, a transmission thickness corresponding to other multiples one half wavelength can be used with similar effect. 
     It will also be recognized by one of ordinary skill in the art that in an alternate embodiment, the spacer section  42  can be composed of a material that has a different and dielectric constant than that of the bumper section  40 , so as to form a two layer radome, also known as a sandwich radome. In this embodiment, the spacer section  42  is provided to have a spacer thickness  48   b  that is one half wavelength and the bumper section  40  is provided to have a bumper thickness  48   a  that is one half wavelength, where the wavelength is that in the respective material. It should further be recognized that, whereas alternative embodiments shown in subsequent figures indicate spacer sections provided with a dielectric constant equal to that of the respective bumper sections, the two layer radome applies equally well to these embodiments as well. 
     It is desirable to space the antenna of the radar system  36  relative to the vehicle structure  40 ,  42  such that the vehicle structure  40 ,  42  appears in the far field of the antenna radiation pattern. 
     In one exemplary embodiment, the radar system  36  transmits continuous wave (CW) radar energy that is repetitively swept in frequency from a minimum CW frequency to a maximum CW frequency and the return echo is simultaneously received. At any time, the frequency difference between the transmitting frequency and the receiving frequency of an echo produced by an echoing object represents the distance between the radar antenna and the echoing object. 
     It should be recognized that where the radar transmitting frequency of radar system  36  changes, as in the exemplary implementation described above, then the corresponding wavelength of the radar energy also changes. Thus, where there is no one particular wavelength, then there is no one particular transmission thickness  48  that would correspond to a multiple of one-half wavelength. In this case, one optimal transmission thickness is chosen, for example a transmission thickness that corresponds to a multiple of one-half wavelength of a frequency which is generally near or in the center of the swept frequency range. The transmission thickness is then optimized at this one transmission frequency. 
     In one exemplary embodiment, the radar system  36  transmits and receives signals having a frequency in the range of 24.0125 GHz to 24.2375 GHz respectively, as described in the aforementioned patent applications. It will be recognized to one of ordinary skill in the art that, assuming a propagation velocity of 3×10 8  m/sec, the corresponding maximum and minimum wavelengths in air are 1.249 cm and 1.238 cm respectively. 
     The dielectric constant of bumper section material, conventionally made of plastic, is approximately 4.0. Whereas the propagation of radar energy through a material is related to the square root of the dielectric constant, the propagation velocity though the bumper section  40  is known to be approximately one half that of propagation in air. Thus, the wavelength in the bumper section  40  is about half that of the wavelengths in air. Thus, the wavelength range is 0.625 cm to 0.619 cm. It will be noticed that the wavelength, when swept in the above range, does not depart greatly from the median of the maximum and minimum wavelengths. The transmission efficiency is enhanced throughout the swept band of frequencies by selecting a single transmission thickness corresponding to one-half of the median of the wavelength range, or 0.361 cm. Alternatively, a transmission thickness that corresponds to one-half of any of the transmitted wavelengths can be used. Use of the spacer section  42  facilitates a design that incorporates a desired transmission spacing. 
     The exemplary radar system  36  produces multiple transmit and receive beams, where three such beams are designated  46   a - 46   c.  The beams may be electronically scanned in azimuth via the radar system  36 . In one embodiment, the exemplary radar system  36  provides seven such transmit and receive beams, each with beamwidths of approximately fifteen degrees, and with a steer angle in azimuth that can cover in excess of one hundred fifty degrees. It will be recognized by one of ordinary skill in the art that other azimuth scan angles, other beam patterns, and other beam widths are possible with this invention. 
     It should be recognized that for radar energy that propagates though a material at an angular direction, i.e. along the angular transmission thickness such as angular transmission thickness  50 , it is desirable to provide an angular transmission thickness that is one half wavelength or a multiple thereof along the angular direction. Because of the wide steer angle in of the exemplary radar system  36 , it should be recognized that a constant angular transmission thickness at the angular direction of all beam steering angles in azimuth, though one hundred fifty degrees, is not achieved with a flat bumper section  40  and a flat spacer section  42 . It will be recognized that a shaped spacer section  42 , that is not flat on its inner surface  54  can provide a more uniform angular transmission thickness throughout the beam steering range. For example, a spacer section  42  having a surface  54  with a semi-spherical or generally rounded shape could be used with the flat bumper section  40 . Alternate embodiments to achieve constant angular transmission thickness will be shown in FIGS. 4 and 4A and FIGS. 5 and 5A 
     It will be recognized by one of ordinary skill in the art, that conventional pulsed and other types of radar systems can also be used with this invention. It will be further recognized by one of ordinary skill in the art that this invention applies to any system that transmits radar energy, and it is not limited to a CW radar system or to a pulsed radar system. It will be further recognized by one of ordinary skill in the art, that this invention can be utilized with a radar system having any number of beams and that transmits and/or receives signals at any frequency. It will be further recognized by one of ordinary skill in the art, that this invention applies to any number of radar systems so mounted to a vehicle. 
     The position of the radar system  36  on the automobile is selected in accordance with a variety of factors including but not limited to the type and position of an intended detection object, and the overall system with which the radar system is associated. Such systems can include active collision systems, intelligent speed and traffic spacing systems, and passive indication systems. For many such systems, it is desirable to provide one or more radar beams oriented generally forward or rearward of the vehicle. For these systems, the radar system  36  can be mounted behind the front or rear bumper as described. For other such systems, it is desirable to provide radar beams oriented to the side of the vehicle. For side oriented systems, the radar system  36  can be mounted at the comers of the bumper as was indicated in FIG.  1 . Alternatively, it may be desirable to mount the radar system  36  behind door or body panels rather than a bumper. The techniques described herein are not limited to mounting of the radar system  36  behind a bumper. Rather, by using a spacer section similar to spacer section  42 , on a section of any automobile body part that allows radar energy to pass through, so as to maintain a desired transmission thickness, or more preferably a desired angular transmission thickness, that is a multiple of a half wavelength, transmission efficiency can be optimized. 
     In one embodiment, the system is attached to the body of an automobile. It will, however, be recognized by one of ordinary skill in the art that the mounting system for radar applies to any vehicle and is not limited to automobiles. 
     With the radar system  36  mounted behind the automobile bumper or behind some other automobile body part, the original aerodynamics associated with the automobile are maintained, resulting in no loss of fuel economy while maintaining the original aesthetics of the design shape of the automobile. 
     Referring now to FIG. 3A, it will be recognized that all of the aforementioned techniques can be employed to provide a bumper section  56  having a spacer section  58  thereof removed which acts as the spacer section in the sense that the remaining transmission thickness  60  corresponds to one-half wavelength. Removal material to provide the spacer section  58  can provide not only an optimal transmission thickness but can, in some applications, place the bumper section  56  far enough away from the radar system  36  so that the bumper section  56  is in the far field of the radiating pattern. Also, it should be recognized that the removed spacer section  58  can be shaped to provide a constant angular transmission thickness as similarly described above. The removed spacer section  58  can be associated with either surface of the bumper section  56 , though it is shown in association with the inner surface. 
     Referring now to FIG. 4 shown from top view, another embodiment is shown that provides a generally uniform angular transmission thickness for all transmission beam angles. In this embodiment, the bumper section  62  is curved and a curved spacer section  64  can be optionally used to provide an angular transmission thickness  66  that is one half wavelength or a multiple thereof. Using curved sections  62 ,  64 , a uniform angular transmission thickness, for example thickness  66 , is achieved throughout the range of beam steer angles. Thus, transmission efficiency can be achieved throughout the range. 
     Referring now to FIG. 4A shown also from top view, this embodiment can be compared to that of FIG. 3A, The bumper section  68  incorporates a spacer section  70 , that is formed by the removal of material rather than addition of material. Again, using a curved bumper section  68 , a uniform angular transmission thickness can be achieved throughout the beam steer angle range. 
     Referring now to FIG. 5 again shown from top view, in some applications it may be desirable or necessary to use a spacer section  72  having one curved surface  72   a  and one non-curved surface  72   b.  The shapes of the two surfaces can be selected to match or conform to physical structure of the bumper section  74  while improving performance of the radar system. By selection of the curvature of the curved surface  72   a,  the spacer section  72  can provide a uniform angular transmission thickness  76  over the range of beam steer angles. 
     Referring now to FIG. 5A again shown from top view, in some applications it may be desirable or necessary to use a spacer section  78  having two curved surfaces  78   a,    78   b.  As shown in FIG. 5A, the spacer section  78  can be disposed on a curved surface of the bumper section  80 . As above, by selection of the curvature of the curved surfaces  78   a,    78   b  the spacer section  78  can provide a uniform angular transmission thickness  82  over the range of beam steer angles. It is also possible to provide the spacer section  78  having a shape which can accommodate an irregularly shaped bumper section or vehicle structure. 
     All references cited herein are hereby incorporated herein by reference in their entirety. 
     Having described preferred embodiments of the invention, it will now become apparent to one of ordinary skill in the art that other embodiments incorporating their concepts may be used. It is felt therefore that these embodiments should not be limited to disclosed embodiments, but rather should be limited only by the spirit and scope of the appended claims.