Patent Publication Number: US-2018052227-A1

Title: Beam pattern diversity-based target location estimation

Description:
FIELD OF THE INVENTION 
     The subject invention relates to beam pattern diversity-based target location estimation. 
     BACKGROUND 
     In many radar applications, one or more transmit antenna elements is used to transmit radiation, and the resulting reflections, which are received by one or more receive antenna elements, indicate information about one or more targets. One such system is a multi-input multi-output (MIMO) radar system. Each receive antenna element receives reflections resulting from every transmit antenna element, and the number of transmit and receive antenna elements need not be equal. Each antenna element likely does not exhibit the same gain in all directions. For example, each receive antenna element in the array does not receive radiation with the same gain at every angle in the azimuthal plane. The beam pattern of a given antenna element indicates the directional (angular) dependence of the gain. When the beam patterns in a given dimension (e.g., azimuthal dimension when the array is a horizontal linear array of antenna elements) are identical among receive antenna elements, then any phase difference among reflections received by the receive antenna elements relates to the angle of arrival, and the position of the target is easily resolved. However, manufacturing antenna elements to have identical beam patterns can present a challenge. Further, information in another dimension (e.g., elevation when the array is a horizontal linear array of antenna elements) is not provided by an array that exhibits identical beam patterns. Accordingly, it is desirable to perform beam pattern diversity-based target location estimation. 
     SUMMARY OF THE INVENTION 
     In one exemplary embodiment of the invention, a method of estimating location of a target using a radar system includes obtaining a beam pattern for each of one or more transmit antenna elements and a plurality of receive antenna elements; transmitting from at least one of the one or more transmit antenna elements; and estimating the location based on comparing a gain indicated by the beam pattern associated with each of the plurality of receive antenna elements and comparing gains of reflections resulting from the transmitting. 
     In another exemplary embodiment, a system to estimate a location of a target includes a radar system including one or more transmit antenna elements and a plurality of receive antenna elements; a memory device configured to store a beam pattern exhibited by each of the one or more transmit antenna elements and the plurality of receive antenna elements; and a processor configured to estimate the location based on comparing a gain indicated by the beam pattern associated with each of the plurality of receive antenna elements and comparing gains of reflections resulting from the transmitting. 
     The above features and advantages and other features and advantages of the invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features, advantages and details appear, by way of example only, in the following detailed description of embodiments, the detailed description referring to the drawings in which: 
         FIG. 1  illustrates beam pattern diversity of receive antenna elements in the azimuthal dimension according to an embodiment; 
         FIG. 2  illustrates beam pattern diversity of transmit antenna elements in the azimuthal dimension according to an embodiment; 
         FIG. 3  shows beam patterns associated with transmit antenna elements according to an embodiment; and 
         FIG. 4  shows beam patterns associated with receive antenna elements according to an embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     As previously noted, for a given transmission, when the receive antenna elements are arranged in a linear array (e.g., in the azimuthal plane) and have identical beam patterns, then angle of arrival of a target reflection (e.g., determination of target position in the azimuthal plane) can be determined based on the phase difference among the reflections received by the different antenna elements. The beam pattern refers to the directional (angular) dependence of transmitted or received signal strength. For example, one transmit element may have a peak gain of 6.8 decibels-isotropic (dBi) at an azimuth angle of +15 degrees, while another transmit element may have a peak gain of 7.3 dBi at an azimuth angle of +5 degrees and a gain of only 4.5 dBi at +15 degrees. Rather than assuming identical beam patterns or trying to achieve identical beam patterns among all the antenna elements, embodiments of the systems and methods detailed herein take advantage of differences in the beam patterns of each antenna element. 
     This beam pattern diversity-based direction of arrival estimation, according to one embodiment, involves using beam pattern diversity rather than phase differences to determine direction of arrival in a single dimension. According to another embodiment, minimal beam pattern diversity is assumed in the dimension in which antenna elements are arranged (e.g., in azimuth), and beam pattern diversity in another dimension (e.g., elevation) is used to determine target position in that dimension. According to yet another embodiment, beam pattern diversity alone is used to determine the position of the target, and phase difference is not used in any dimension. The beam patterns of both transmit and receive elements are known and used according to embodiments discussed herein. That is, the beam pattern diversity among receive antenna elements is relevant to discerning direction of arrival for reflections associated with a given transmit element. When there is more than one transmit element (e.g., in a MIMO system), the beam pattern diversity among transmit antenna elements is relevant to comparing the direction of arrival that is determined based on the two or more different transmissions. 
       FIG. 1  illustrates beam pattern diversity of receive antenna elements  122  in the azimuthal dimension according to an embodiment. A platform  100  including a radar system  120  is shown. The platform  100  is an automobile  110  in the exemplary embodiment shown in  FIG. 1 . In alternate embodiments, the platform  100  may be a different vehicle or even a stationary support. The radar system  120  is well-known and is not detailed herein. The radar system  120  includes one or more transmit antenna elements  121  and a plurality of receive antenna elements  122 . Four receive antenna elements  122  are in the exemplary radar system  120  of  FIG. 1 . The radar system  120  may also include other known components such as a controller  123 . The controller  123  may be specific to the radar system  120  or may additionally perform other functions in the automobile  110  such as collision avoidance or steering control. The controller  123  generally includes processing circuitry that may include an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide functionality such as generation of transmitted signals and processing of received signals. When more than one transmit antenna element  121  is part of the radar system  120 , the transmission of each transmit antenna element  121  is distinguished based on a time division multiple access (TDMA) scheme or based on each transmit antenna element  121  transmitting a different code, for example. The transmission may be a linear frequency modulated continuous wave (LFM-CW), for example. 
     Four different beam patterns  130   a  through  130   d  (generally,  130 ) are shown corresponding with the four exemplary receive antenna elements  122 . While the beam patterns  130  show the regions with relatively stronger gain, other regions are not intended to be conveyed as regions with no return. For example, given the beam pattern  130   a , the associated receive antenna elements  122  still receives a reflection (albeit one with very low gain) from the target  140 - 1 , which is outside the illustrated beam pattern  130   a . The exemplary receive antenna elements  122  are arranged in a linear array along the azimuthal plane, and a cross section of the beam patterns  130  (which are three-dimensional) in the azimuthal plane is shown. This exemplary arrangement is shown only for explanatory purposes. The receive antenna elements  122  may instead be arranged in a linear array in another plane (e.g., the elevation plane), and the beam patterns  130  may instead be in that other plane (e.g., elevation plane). 
     As noted, an exemplary target  140 - 1  is shown, and  FIG. 1  indicates the reflection  135   a  through  135   d  associated with each receive antenna element  122  which corresponds with each of the illustrated beam patterns  130   a  through  130   d .  FIG. 1  also indicates the relative radiation gain  150  associated with each receive antenna element  122  at the location of the target  140 - 1  based on the corresponding beam pattern  130 . For example, the reflection  135   a  associated with the receive antenna element  122  corresponding with beam pattern  130   a  exhibits the lowest gain at the location of the target  140 - 1 , as compared with all the reflections  135   a  through  135   d . As another example, the reflection  135   b  associated with the receive antenna element  122  corresponding with beam pattern  130   b  exhibits the highest gain at the location of the target  140 - 1 . 
     Knowledge of the beam patterns  130  facilitates resolution of angular estimates based on each of the receive antenna elements  122 . For example, when the reflection  135   a  received at the receive antenna element  122  that is associated with beam pattern  130   a  exhibits the highest gain among the reflections  135   a  through  135   d , then the corresponding target must be in region  145 , for which the beam pattern  130   a  exhibits the highest gain (relative to the other beam patterns  130 ). 
       FIG. 2  illustrates beam pattern diversity of transmit antenna elements  121  in the azimuthal dimension according to an embodiment. As noted with reference to  FIG. 1 , the transmit antenna elements  121  are assumed to be in a linear array in the azimuthal plane for explanatory purposes, and an azimuthal cross-section of the beam patterns  230   a  and  230   b  (generally,  230 ) is shown. However, the arrangement of the transmit antenna elements  121  and the plane in which the beam patterns  230  are shown could be different.  FIG. 2  shows two exemplary beam patterns  230   a  and  230   b  associated with two exemplary transmit antenna elements  121 . The exemplary target  140 - 1  from  FIG. 1  is shown in  FIG. 2 , as well. The relative gains  150  of the transmissions  235   a  and  235   b  associated with the transmit antenna elements  121  corresponding with the beam patterns  230   a  and  230   b  are shown at the location of the target  140 - 1 . These indicate that the relative gain  150  associated with beam pattern  230   b  is higher than the relative gain  150  associated with beam pattern  230   a  at the location of target  140 - 1 . 
     This means that the reflections  135  received by the receive antenna elements  122  will have a lower gain when those reflections  135  result from transmission by the transmit antenna element  121  associated with beam pattern  230   a  (rather than with beam pattern  230   b ). Based on the location of the target  140 - 1 , the relative gain  150  distribution among the reflections  135   a  through  135   d  (shown in  FIG. 1 ) will remain unchanged, but the gain values will be lower when the reflections  135   a  through  135   d  result from transmissions by the transmit antenna element  121  associated with beam pattern  230   a . Thus, when the radar system  120  includes more than one transmit antenna element  121 , knowing the beam pattern  230  of each of the transmit antenna elements  121  provides another layer of information in resolving the location of any detected target  140 . 
     A second target  140 - 2  is shown in  FIG. 2 . Again, the relative gain  150  distribution among the receive antenna elements  122  will not change with respect to the target  140 - 2  regardless of which transmit antenna element  121  caused the received reflections  135 . However, the gain values will be higher for reflections  135  received as a result of transmission by the transmit antenna element  121  associated with beam pattern  230   a.    
     According to another embodiment, the beam patterns  130 ,  230  can be assumed to have minimal diversity in the same plane in which the antenna elements ( 121 ,  122 ) are arranged (e.g., in the azimuthal plane). In this case, phase differences in reflections  135  received among the receive antenna elements  122  may still be used to determine angle of arrival of the reflections  135  in that plane (e.g., azimuthal plane). Then, according to this embodiment, the diversity of the beam patterns  130 ,  230  in another plane (e.g., elevation) could be used to determine the angle of arrival of reflections  135  in that plane. Thus, even though an array of antenna elements ( 121 ,  122 ) is arranged only in the azimuthal plane, for example, determination of the location of the target  140  in another plane, such as in elevation, is facilitated. The process for determining the location of the target  140  in the other plane (e.g., in elevation) would be similar to the process discussed with reference to  FIGS. 1 and 2 . 
       FIG. 3  shows beam patterns  230   m ,  230   n  associated with transmit antenna elements  121   m ,  121   n  according to an embodiment. A cross-section of each beam pattern  230   m ,  230   n  is shown in the elevation plane (X/Z plane, as indicated).  FIG. 4  shows beam patterns  130   x ,  130   y ,  130   z  associated with receive antenna elements  122  according to an embodiment. The beam patterns  130   x ,  130   y ,  130   z  are cross-sections shown in the elevation plane (X/Z plane). At any given elevation angle, the beam patterns  130 ,  230  are designed to maintain a constant differential with the other beam patterns  130 ,  230  over azimuth. That is, for example, at an elevation angle of five degrees, the difference in gain between beam patterns  230   m  and  230   n  is 5 dBi. This difference is maintained at each azimuth angle at that elevation angle. 
     According to the current embodiment, the angle of arrival in the azimuthal plane is determined based on a phase difference among the reflections  135  received by the different receive antenna elements  122 . With respect to the angle of arrival in the elevation plane, however, the different gains exhibited by the beam patterns  230   m ,  230   n  and  130   x ,  130   y ,  130   z  of each of the transmit antenna elements  121  and receive antenna elements  122 , respectively, are used. The procedure is similar to the way that direction of arrival of reflections in the azimuth plane is determined according to the discussion of  FIGS. 1 and 2 . Specifically, the relative gain  150  is used in conjunction with the known beam patterns  130 ,  230 . 
     According to yet another embodiment, known beam patterns  130 ,  230  may be used to determine the location of a target  140  in every dimension. That is, minimal diversity need not be assumed in the azimuthal plane or another plane such that phase differences are not used to determine direction of arrival at all. In every embodiment, knowing the beam pattern  130 ,  230  of each antenna element ( 121 ,  122 ) has the technical effect of facilitating determination of direction of arrival of reflections (location of a target  140 ) without using phase difference among received reflections. 
     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the application.