Patent Publication Number: US-2017365935-A1

Title: Array antenna

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to array antennas that irradiate radio waves. 
     2. Description of the Related Art 
     Known array antennas of related art include the array antenna discussed in Japanese Unexamined Patent Application Publication No. 4-37204.  FIG. 14  illustrates the configuration of the array antenna disclosed in Japanese Unexamined Patent Application Publication No. 4-37204. 
     The array antenna illustrated in  FIG. 14  is a microstrip array antenna where patch antennas and strip conductors are formed on a dielectric substrate  2  with the back face on which a conductor ground plate  1  is formed. The power input from a feeding portion  3  is radiated from each of radiating elements  5  through microstrip lines  4  arranged on the dielectric substrate  2 . 
     In the array antenna illustrated in Japanese Unexamined Patent Application Publication No. 4-37204, as illustrated in  FIG. 14 , columns A, B, and C are different in number of elements in the Y direction and the number of elements in column A in an end portion of the substrate is smaller than the number of elements in column C in a central portion of the substrate. This configuration enables the gain of a column in an end portion of the substrate to be lower than the gain of a column in a central portion of the substrate and can inhibit unwanted radiation (the side lobe level). 
     Since in the related-art techniques of Japanese Unexamined Patent Application Publication No. 4-37204 described above, however, the numbers of elements differ among columns and besides, coupling conditions between adjacent elements differ among columns, feeding lines need to be designed for individual columns and this hinders designing of an array antenna. 
     SUMMARY 
     One non-limiting and exemplary embodiment facilitates providing an array antenna where side lobes of radiated radio waves can be controlled with a simple feeding line configuration. 
     In one general aspect, the techniques disclosed here feature an array antenna that includes a dielectric substrate, and a plurality of radiating elements being arranged linearly and provided on a first face of the dielectric substrate, each of the plurality of radiating elements having linear polarization and a rotation reference point, wherein one or more radiating elements included in the plurality of radiating elements are rotated differently with respect to the corresponding rotation reference positions each other. 
     The present disclosure contributes to control of side lobes of radiated radio waves with a simple feeding line configuration. 
     Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view that illustrates an array antenna according to a first embodiment; 
         FIG. 2  is a II-II cross-sectional view of the array antenna according to the first embodiment; 
         FIG. 3  illustrates a change calculation model of gain with respect to a rotation angle of a radiating element; 
         FIG. 4  illustrates change characteristics of the gain with respect to the rotation angle of the radiating element; 
         FIG. 5  illustrates gain distribution of columns according to the first embodiment; 
         FIG. 6  illustrates an XZ-plane radiation pattern according to the first embodiment; 
         FIG. 7  is a front view that illustrates an array antenna according to a second embodiment; 
         FIG. 8  is a front view that illustrates an array antenna according to a third embodiment; 
         FIG. 9  is a front view that illustrates an array antenna according to a fourth embodiment; 
         FIG. 10  illustrates an example of a configuration of a loop array antenna according to the fourth embodiment; 
         FIG. 11  illustrates an example of a configuration of a microstrip comb-line antenna according to the fourth embodiment; 
         FIG. 12  illustrates an example of a configuration of a slot array antenna according to the fourth embodiment; 
         FIG. 13  is a front view that illustrates an array antenna according to a fifth embodiment; and 
         FIG. 14  is a perspective view that illustrates an array antenna of related art. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments 
     A radar device employing an array antenna and installed in a vehicle is described below. 
     Radio waves radiated from directional antennas of a typical array antenna, for example, include side lobes oriented in directions shifted from a desired direction in addition to the main lobe oriented in the desired direction. 
     A radar device installed in a vehicle causes the main lobe to be oriented in a desired direction so as to detect an object in the desired direction. When the radar device radiates radio waves that include large side lobes, however, false detection is caused under the influence of the side lobes as if there would be an object in the desired direction even without any object in the desired direction. 
     An array antenna radiating radio waves whose side lobes can be controlled by changing the polarization directions of a plurality of arrayed radiating elements on a column-by-column basis is described below. 
     Embodiments of the present disclosure are described below with reference to the drawings. In each embodiment, identical references are given to the constituents having identical functions and the overlapping descriptions are omitted. All the figures mentioned below schematically illustrate configurations and the dimensions of each element are exaggerated in the illustrations for simplification of descriptions while some elements are omitted in the illustrations where appropriate. The embodiments described below are examples and are not intended to limit the present disclosure. 
     First Embodiment 
       FIG. 1  is a plan view that illustrates a configuration of a planar array antenna  100  according to a first embodiment of the present disclosure.  FIG. 2  is a cross-sectional view along II-II in  FIG. 1 . In the description below, the lateral direction in  FIG. 1  is referred to as the X direction and specifically, the rightward direction is referred to as the +X direction while the leftward direction is referred to as the −X direction. Further, the orthogonal direction to the X direction in  FIG. 1  is referred to as the Y direction and specifically, the upward direction is referred to as the +Y direction while the downward direction is referred to as the −Y direction. Also in the description below, the spatial depth direction in  FIG. 1  is referred to as the Z direction and specifically, the spatially forward direction is referred to as the +Z direction while the spatially backward direction is referred to as the −Z direction. 
     As illustrated in  FIG. 1 , the planar array antenna  100  is a patch array antenna for example, which includes radiating elements  101   a  to  101   h , a dielectric substrate  102 , feeding vias  103 , feeding lines  104   a  to  104   h , a ground plate  105 , and a radio unit  106 . 
     As illustrated in  FIGS. 1 and 2 , the radiating elements  101   a  to  101   h  are arranged so that, on the dielectric substrate  102  shaped like a flat plate, the central positions of the radiating elements  101   a  to  101   h  agree in the Y direction and are aligned at regular intervals in the X direction. That is, the radiating elements  101   a  to  101   h  are arranged so that the centers of the radiating elements  101   a  to  101   h  are linearly located by performing rotation by predetermined angles while the central positions of the radiating elements  101   a  to  101   h  serve as the centers of the rotation. The radiating elements  101   a  to  101   h  are square patch antennas and radiate radio waves of linear polarization. 
     The radiating elements  101   a ,  101   b ,  101   c ,  101   d ,  101   e ,  101   f ,  101   g , and  101   h  are positioned sequentially from the negative direction of the X axis to the positive direction of the X axis. Also, the radiating element  101   a  is positioned in column A, the radiating element  101   b  is positioned in column B, the radiating element  101   c  is positioned in column C, the radiating element  101   d  is positioned in column D, the radiating element  101   e  is positioned in column E, the radiating element  101   f  is positioned in column F, the radiating element  101   g  is positioned in column G, and the radiating element  101   h  is positioned in column H. 
     In  FIG. 1 , the alternate long and short dashed lines indicated by Q-Q denote the straight line that connects the central positions of the radiating elements  101   a  to  101   h  in the Y direction. Because of such an arrangement, the positions of feeding ports of the feeding vias  103  through which power is fed to the radiating elements  101   a  to  101   h  are different from each other in the Y direction and are spaced from each other at non-regular intervals in the X direction. 
     The distance between the feeding via  103  of the radiating element  101   a  and the feeding via  103  of the radiating element  101   b  is L 1 , the distance between the feeding via  103  of the radiating element  101   b  and the feeding via  103  of the radiating element  101   c  is L 2 , the distance between the feeding via  103  of the radiating element  101   c  and the feeding via  103  of the radiating element  101   d  is L 3 , the distance between the feeding via  103  of the radiating element  101   d  and the feeding via  103  of the radiating element  101   e  is L 4 , the distance between the feeding via  103  of the radiating element  101   e  and the feeding via  103  of the radiating element  101   f  is L 5 , the distance between the feeding via  103  of the radiating element  101   f  and the feeding via  103  of the radiating element  101   g  is L 6 , and the distance between the feeding via  103  of the radiating element  101   g  and the feeding via  103  of the radiating element  101   h  is L 7 . The distances L 1  to L 7  have values different from each other for example. 
     As illustrated in  FIG. 2 , the outside of each feeding via  103  is metal for example, and the feeding vias  103  are provided so as to correspond to the respective radiating elements  101   a  to  101   h  and pass through the dielectric substrate  102  in the Z direction. End portions of the feeding vias  103  in the +Z direction are coupled to the corresponding radiating elements  101   a  to  101   h  and the other end portions of the feeding vias  103  in the −Z direction are coupled to the corresponding feeding lines  104   a  to  104   h . Each feeding via  103  may be hollow or be filled with a filling material. 
     As illustrated in  FIGS. 1 and 2 , in the dielectric substrate  102 , the feeding lines  104   a  to  104   h  are arranged on the back face, which is opposite the face where the radiating elements  101   a  to  101   h  are arranged. The radio unit  106  is mounted on the same face as that where the feeding lines  104   a  to  104   h  are arranged. The feeding lines  104   a  to  104   h  are configured as a copper foil pattern formed by etching for example. The feeding lines  104   a  to  104   h  are each coupled to the radio unit  106 . The output power from the radio unit  106  is fed to the radiating elements  101   a  to  101   h  through the feeding lines  104   a  to  104   h  and the feeding vias  103 . 
     As illustrated in  FIG. 2 , the ground plate  105  is arranged in the dielectric substrate  102  lying in the −Z direction relative to the radiating elements  101   a  to  101   h  and functions as a reflector. In  FIG. 2 , the ground plate  105  is separated but coupled in other portions. 
     The radiating elements  101   a  to  101   h  function as an array antenna and form beams. Thus, by regulating the phase of the output power from the radio unit  106  to the feeding lines  104   a  to  104   h  by known techniques, the direction of the directivity can be regulated. In the present embodiment, the main polarization direction of the radio system that uses the planar array antenna  100  is in the +Y direction. 
     In the present embodiment, as illustrated in  FIG. 1 , when a represents the rotation angle for each of the radiating elements  101   a  to  101   h  in the +X direction relative to the +Y direction, the rotation angles α for the radiating elements  101   d  and  101   e  in columns D and E are each 0 degrees, the rotation angles α for the radiating elements  101   c  and  101   f  in columns C and F are each 15 degrees, the rotation angles α for the radiating elements  101   b  and  101   g  in columns B and G are each 30 degrees, and the rotation angles α for the radiating elements  101   a  and  101   h  in columns A and H are each 45 degrees. 
     That is, the deviation of the polarization direction of the radiating element  101   c  with the rotation angle α of 15 degrees from the +Y direction is larger than the deviation of the radiating element  101   d  with the rotation angle α of 0 degrees, which is adjacent to the radiating element  101   c  in a portion dose to the center of the planar array antenna  100 , from the +Y direction. 
     Similarly, the deviation of the polarization direction of the radiating element  101   b  with the rotation angle α of 30 degrees from the +Y direction is larger than the deviation of the radiating element  101   c  with the rotation angle α of 15 degrees from the +Y direction. Further, the deviation of the polarization direction of the radiating element  101   a  with the rotation angle α of 45 degrees from the +Y direction is larger than the deviation of the radiating element  101   b  with the rotation angle α of 30 degrees from the +Y direction. 
     Moreover, the deviation of the polarization direction of the radiating element  101   f  with the rotation angle α of 15 degrees from the +Y direction is larger than the deviation of the radiating element  101   e  with the rotation angle α of 0 degrees, which is adjacent to the radiating element  101   f  in a portion close to the center of the planar array antenna  100 , from the +Y direction. 
     Similarly, the deviation of the polarization direction of the radiating element  101   g  with the rotation angle α of 30 degrees from the +Y direction is larger than the deviation of the radiating element  101   f  with the rotation angle α of 15 degrees from the +Y direction. Further, the deviation of the polarization direction of the radiating element  101   h  with the rotation angle α of 45 degrees from the +Y direction is larger than the deviation of the radiating element  101   g  with the rotation angle α of 30 degrees from the +Y direction. 
     By changing the rotation angles of radiating elements on a column-by-column basis in this manner, the main polarization direction of each radiating element is changed and the planar array antenna  100  attains two or more polarization directions. 
     Described below using an example of a model of a single patch antenna illustrated in  FIG. 3  is the relation between the rotation angle α of a radiating element based on the central position of the radiating element and gain in the +Z direction. 
     The example of the single patch antenna model illustrated in  FIG. 3  includes a radiating element  201 , a dielectric substrate  202 , and a feeding port  203 . The dielectric substrate  202  has a dielectric constant of 3.4 and a thickness of 0.25 mm. 
       FIG. 4  illustrates gain of Y-direction polarization in a case where, in the single patch antenna model depicted in  FIG. 3 , the radiating element  201  is rotated by the angle α in the +X direction from the +Y direction on the basis of the center of the radiating element  201 . The horizontal axis in  FIG. 4  indicates the rotation angle α of the radiating element  201  and the vertical axis in  FIG. 4  indicates relative gain of the Y-direction polarization. 
     In  FIG. 4 , the vertical axis indicates the relative gain obtained by standardizing the gain at the rotation angle α of 0 degrees as 0 dB. As illustrated in  FIG. 4 , the gain of the Y-direction polarization is highest when the rotation angle α is 0 degrees, and as the rotation angle α changes from 0 degrees toward 90 degrees, the polarization loss increases and the gain decreases accordingly. 
       FIG. 5  illustrates gain distribution of the Y-direction polarization in the planar array antenna  100  where the rotation angles α for the radiating elements  101   a  to  101   h  are changed on the basis of the columns illustrated in  FIG. 1  by utilizing the change in the Y-direction polarization with respect to the rotation angle α of a radiating element, such as that demonstrated in  FIG. 4 . In  FIG. 5 , the horizontal axis indicates columns A to H and the vertical axis indicates absolute gain of the Y-direction polarization. Since the gain distribution illustrated in  FIG. 5  exhibits the Taylor distribution, side lobes in an XZ-plane radiation pattern of the planar array antenna  100  can be reduced. 
       FIG. 6  illustrates XZ-plane radiation patterns of planar array antennas. In  FIG. 6 , the horizontal axis indicates an angle. In  FIG. 6 , the vertical axis indicates relative gain obtained by standardizing the maximum gain of a planar array antenna as 0 dB. A radiation pattern  301 , which is indicated by a solid line in  FIG. 6 , is a radiation pattern of the planar array antenna  100  according to the present embodiment. For comparison, a radiation pattern  302  of a planar array antenna where the rotation angles α for the radiating elements in all columns are 0 degrees is indicated by a broken line. In both the radiation patterns  301  and  302 , all the radiating elements are excited in phase. 
     As illustrated in  FIG. 6 , it can be observed that in the radiation pattern  301  using the techniques of the present disclosure, all the side lobes other than the main lobe are reduced more successfully than in the radiation pattern  302 . Particularly, it can be observed that the side lobes close to the main lobe, which become one of the causes of false detection in a radar device that employs a planar array antenna, are largely reduced. 
     Thus, according to the present disclosure, by rotating the polarization directions of the radiating elements  101   a ,  101   b ,  101   c ,  101   f ,  101   g , and  101   h , which are arrayed in array end portions of the planar array antenna  100 , relative to the polarization directions of the radiating elements  101   d  and  101   e , which agree with the main polarization direction of the radio system that uses the planar array antenna  100 , the Taylor distribution illustrated in  FIG. 5  can be achieved and the side lobes can be reduced. In addition, as illustrated in  FIG. 1 , the pattern shapes of the feeding lines  104   a  to  104   h  in the respective columns can be simplified and feeding lines can be therefore formed with a simple configuration. 
     Although in the present embodiment illustrated in  FIG. 1 , the radiating elements with the polarization directions that agree with the main polarization direction of the radio system that uses the planar array antenna  100  (i.e. the +Y direction) are arrayed in two columns dose to an array central portion, which are columns D and E, the arrangement is not limited thereto. For example, the radiating elements with the polarization directions that are in the +Y direction may be arranged in two columns that are columns C and D or may be arranged in two columns that are columns A and B. 
     Although in the present embodiment illustrated in  FIG. 1 , the radiating elements  101   a  to  101   h  are arranged so that the central positions of the radiating elements  101   a  to  101   h  are spaced at regular intervals in the X direction, the arrangement is not limited thereto. For example, adjacent radiating elements may be arranged so that the central positions of the radiating elements are spaced at non-regular intervals in the X direction. 
     Although in the present embodiment illustrated in  FIG. 1 , the polarization directions of the radiating elements  101   d  and  101   e  agree with the main polarization direction of the radio system (i.e. the +Y direction), the arrangement is not limited thereto. As long as the polarization directions of the radiating elements  101   d  and  101   e  are close to the +Y direction, similar advantages can be obtained. 
     Although in the present embodiment illustrated in  FIG. 1 , the rotation angles α are increased as the distance from the radiating elements  101   d  and  101   e  becomes larger by setting the rotation angle α for the radiating elements  101   c  and  101   f  to 15 degrees, the rotation angle α for the radiating elements  101   b  and  101   g  to 30 degrees, and the rotation angle α for the radiating elements  101   a  and  101   h  to 45 degrees, the rotation angle α for each radiating element is not limited thereto. 
     The rotation angles α for a plurality of adjacent radiating elements may be identical or the rotation angles for all the radiating elements other than the radiating elements with the polarization directions that are in the +Y direction may be identical predetermined angles larger than 0 degrees. Side lobes can be reduced by changing the rotation angles for the radiating elements other than the radiating elements with the polarization directions that are in the +Y direction. 
     Among adjacent radiating elements, the rotation angles for the radiating elements arranged closer to array end portions may be larger than the rotation angles for the radiating elements arranged closer to an array central portion. Accordingly, the Taylor distribution can be achieved as the gain distribution of columns and side lobes can be reduced more suitably. 
     Second Embodiment 
       FIG. 7  is a plan view that illustrates a configuration of a planar array antenna  400  according to a second embodiment of the present disclosure. As illustrated in  FIG. 7 , the planar array antenna  400  includes radiating elements  401   a  to  401   h  arranged on a dielectric substrate  402 , feeding vias  403  that pass through the dielectric substrate  402  in the Z direction, feeding lines  404   a  to  404   h  and a radio unit  406  arranged on the back face of the dielectric substrate  402 , and a ground plate  405 . Since the basic configuration of the planar array antenna  400  is similar to the configuration of the planar array antenna  100  according to the first embodiment, the description thereof may be omitted. 
     In the planar array antenna  100  according to the first embodiment, the rotation angle for the radiating element  101   f  is set to 15 degrees, which is equal to the rotation angle for the radiating element  101   c , the rotation angle for the radiating element  101   g  is set to 30 degrees, which is equal to the rotation angle for the radiating element  101   b , and the rotation angle for the radiating element  101   h  is set to 45 degrees, which is equal to the rotation angle for the radiating element  101   a . In contrast, in the planar array antenna  400  according to the second embodiment, the direction in which the radiating elements  401   f ,  401   g , and  401   h  are rotated is caused to be opposite the direction in which the radiating elements  401   c ,  401   b , and  401   a  are rotated while the rotation angle for the radiating element  401   f  is set to −15 degrees, the rotation angle for the radiating element  401   g  is set to −30 degrees, and the rotation angle for the radiating element  401   h  is set to −45 degrees. 
     According to the second embodiment, the polarization directions of columns A and H, the polarization directions of columns B and G, and the polarization directions of columns C and F can each be mirror symmetric and it is thus facilitated to equalize the degrees of reduction in the side lobes that appear on both sides of the main lobe in an XZ-plane radiation pattern (see  FIG. 6 ). 
     Third Embodiment 
       FIG. 8  is a plan view that illustrates a configuration of a planar array antenna  500  according to a third embodiment of the present disclosure. As illustrated in  FIG. 8 , the planar array antenna  500  includes radiating elements  501   a  to  501   h  arranged on a dielectric substrate  502 , feeding vias  503  that pass through the dielectric substrate  502  in the Z direction, feeding lines  504   a  to  504   h  and a radio unit  506  arranged on the back face of the dielectric substrate  502 , and a ground plate  505 . As illustrated in  FIG. 8 , the feeding vias of adjacent radiating elements are each spaced by a distance L. Since the basic configuration of the planar array antenna  500  is similar to the configuration of the planar array antenna  100  according to the first embodiment, the description thereof may be omitted. 
     In the planar array antenna  100  according to the first embodiment, the radiating elements  101   a  to  101   h  are arranged so that the central positions of the radiating elements  101   a  to  101   h  agree in the Y direction and are aligned at regular intervals in the X direction. 
     In contrast, in the planar array antenna  500  according to the third embodiment, as illustrated in  FIG. 8 , the radiating elements  501   a  to  501   h  are arranged so that the positions of the feeding ports of the feeding vias  503  through which power is fed to the radiating elements  501   a  to  501   h  agree in the Y direction and are aligned at regular intervals in the X direction. That is, the radiating elements  501   a  to  501   h  are arranged so that the feeding positions for the radiating elements  501   a  to  501   h  are linearly located. Specifically, by being rotated by predetermined angles while the feeding ports each serve as the center of the rotation, the radiating elements  501   a  to  501   h  can be arranged so that the respective feeding vias of the radiating elements  501   a  to  501   h  are positioned linearly and the radiating elements  501   a  to  501   h  adjacent to each other are each spaced by an identical distance. 
     According to the third embodiment, since the radiating elements are arranged so that the positions of the feeding ports of the feeding vias through which power is fed to the radiating elements agree in the Y direction and are aligned at regular intervals in the X direction, side lobes that appear on both sides of the main lobe in an XZ-plane radiation pattern (see  FIG. 6 ) can be reduced. 
     Although in the description of the example above, the feeding ports of the radiating elements  501   a  to  501   h  are positioned so as to be aligned at regular intervals in the X direction, the arrangement is not limited thereto. The feeding ports for part of the adjacent radiating elements may be positioned so as to be arranged at non-regular intervals in the X direction. For example, at least one radiating element  501  may undergo horizontal displacement in the X-axis direction in addition to predetermined rotation. 
     Fourth Embodiment 
       FIG. 9  is a plan view that illustrates a configuration of a planar array antenna  700  according to a fourth embodiment of the present disclosure. While the planar array antenna  100  according to the first embodiment is an array antenna where a plurality of radiating elements are arrayed in the X direction, the planar array antenna  700  according to the fourth embodiment is an array antenna where a plurality of radiating element groups in each of which a plurality of radiating elements are arrayed in the X direction are arrayed in the Y direction. 
     As illustrated in  FIG. 9 , the planar array antenna  700  includes radiating elements  701   aa  to  701   dh  arranged on a dielectric substrate  702 , feeding vias  703  that pass through the dielectric substrate  702  in the Z direction, feeding lines  704   a  to  704   h  and a radio unit  706  arranged on the back face of the dielectric substrate  702 , and a ground plate  705 . Since the basic configuration of the planar array antenna  700  is similar to the configuration of the planar array antenna  100  according to the first embodiment, the description thereof may be omitted. 
     The feeding line  704   a  illustrated in  FIG. 9  couples the radio unit  706  arranged near an end portion in the −Y direction on the back face of the dielectric substrate  702  and the radiating element  701   aa  arranged near an end portion in the +Y direction on the back face of the dielectric substrate  702 , and is also coupled to the radiating elements  701   ba ,  701   ca , and  701   da  by branching midway. 
     The radiating elements  701   aa  to  701   ah  ( 701   ba  to  701   bh ,  701   ca  to  701   ch , and  701   da  to  701   dh ) are arranged so that the respective central positions of the radiating elements agree in the Y direction and are aligned at regular intervals in the X direction. 
     Further, the radiating elements  701   aa  to  701   da  are arranged so that the respective central positions of the radiating elements agree in the X direction and are aligned at regular intervals in the Y direction. 
     When in the planar array antenna  700 , the wavelength of a radio wave radiated from the radiating elements  701   aa  to  701   da  is an effective wavelength λe that takes reduction in the wavelength of the dielectric substrate  702  into account, the radiating elements  701   aa  to  701   da  can be excited in phase by setting each interval between the radiating elements  701   aa  to  701   da  to λe. 
     Moreover, also in columns B to F, all the radiating elements arranged on the dielectric substrate  702  can be excited in phase by causing the shapes of the feeding lines to be identical. Accordingly, high gain can be obtained while reducing side lobes on an XZ-plane. 
     In addition, when a plurality of radiating elements are arrayed in the X direction and the Y direction, it is unnecessary to change the number of elements in the Y direction on a column-by-column basis and thus, variation in coupling conditions between adjacent radiating elements in each column in the array antenna can be inhibited and the configuration can be simplified. 
     Although in the description of the example illustrated in  FIG. 9 , the radiating elements arrayed in the Y direction are excited in phase, it is also possible to cause a phase difference between the radiating elements arrayed in the Y direction and tilt beams in the Y direction, and even in such a case, the advantages brought in the other embodiments can be obtained. 
     Moreover, although in the example illustrated in  FIG. 9 , the radiating elements arranged so as to be aligned in the X direction are arranged so that the respective central positions of the radiating elements agree in the Y direction and are spaced at regular intervals in the X direction, the arrangement is not limited thereto. For example, the radiating elements arranged so as to be aligned in the X direction may be arranged so that the positions of the respective feeding ports of the radiating elements agree in the Y direction and are spaced at regular intervals in the X direction. 
     Variations of Fourth Embodiment 
       FIGS. 10 to 12  illustrates examples in which the radiating elements in the planar array antenna  700  according to the fourth embodiment of the present disclosure are implemented with radiating elements having other shapes. Since in each variation, the basic configuration is similar to the configuration of the planar array antenna  700  according to the fourth embodiment, the description thereof may be omitted. 
       FIG. 10  illustrates an example of a planar array antenna  800 , where the radiating elements are configured using loop antennas. As illustrated in  FIG. 10 , a plurality of loop array antennas  801   a  to  801   h  where a plurality of loop elements  803  are arrayed in the Y direction are arrayed in the X direction on a dielectric substrate  802 . 
     The loop array antennas  801   a  to  801   h  are constituted using the loop elements  803 , which each have an element length of λe, and feeding lines  804   a  to  804   h , and the loop elements  803  are fed with power from a radio unit  806  through the feeding lines  804   a  to  804   h  by electromagnetic coupling. Reference  805  indicates a ground plate. 
     The loop elements  803  arranged so as to be aligned in the X direction are arranged so that the respective central positions of the loop elements  803  agree in the Y direction and are aligned at regular intervals in the X direction. For example, in  FIG. 10 , the alternate long and short dashed lines indicated by S-S denote the straight line that connects the central positions of the radiating elements  801   a  to  801   h  in the Y direction. The loop elements may be arranged so that the central positions thereof are spaced at non-regular intervals in the X direction. 
     In part of each loop element  803 , a cut portion  803   a  is formed and the position of the cut portion  803   a  determines the polarization direction. For example, since in the example illustrated in  FIG. 10 , the positions of the cut portions of the loop array antennas  801   d  and  801   e  in columns D and E are each in the +Y direction, the polarization directions thereof are each in the +Y direction. 
     In contrast, as for the loop array antennas  801   a  to  801   c  in columns A to C and the loop array antennas  801   f  to  801   h  in columns F to H, the positions of the cut portions are in the directions resulting from rotation from the +Y direction by the rotation angles α, and the polarization directions are also in the direction resulting from the rotation from the +Y direction by the rotation angles α. 
     Thus, according to the planar array antenna  800  illustrated in  FIG. 10 , side lobes in a radiation pattern of an XZ plane can be reduced by forming the cut portions  803   a  of the loop elements arrayed on end portion sides of the array antenna so that the cut portions  803   a  are in the directions resulting from the rotation from the main polarization direction of the radio system that uses the planar array antenna  800 . 
       FIG. 11  illustrates an example of a planar array antenna  900 , which employs a microstrip comb-line antenna for the configuration of the present disclosure. As illustrated in  FIG. 11 , on a dielectric substrate  902 , a plurality of array antennas  901   a  to  901   h  where a plurality of radiating elements  903  are arrayed in the Y direction are arrayed in the X direction. On the back face of the dielectric substrate  902 , a ground plate  905  is provided. 
     Each radiating element  903  is coupled to a radio unit  906  through corresponding one of feeding lines  904   a  to  904   h . The shape of each radiating element  903  is rectangular and all the radiating elements  903  are excited in phase by setting the length of each radiating element  903  in the long-length direction to 0.5 λe. The long-length direction of each radiating element  903  matches the polarization direction of the radiating element  903 . Thus, as illustrated in  FIG. 11 , similar advantages to those brought in the example illustrated in  FIG. 9  can be obtained by causing the rotation angles α for the radiating elements  903  in the long-length direction to be similar to the rotation angles in the example illustrated in  FIG. 9 . 
     Also, in the example illustrated in  FIG. 11 , the radiating elements arranged so as to be aligned in the X direction are arranged so that the positions of the coupling points to the feeding lines agree in the Y direction and are aligned at regular intervals in the X direction. In addition, the radiating elements arranged so as to be aligned in the X direction are arranged so that the respective central positions of the radiating elements in the X direction and the Y direction agree in the Y direction and are aligned at regular intervals in the X direction. The radiating elements may be arranged so that the central positions thereof in the X direction or the Y direction are spaced at non-regular intervals in the X direction. 
       FIG. 12  illustrates an example of a planar array antenna  1000 , where a configuration according to the present disclosure is implemented with a slot array antenna. In the planar array antenna  1000 , array antennas  1001   a  to  1001   h  in respective columns are arrayed in the X direction and part of a metal plate  1003  is provided with slots  1002  that function as radiating elements. 
     The radiating elements are electrically coupled to a radio unit  1006  through waveguides  1004   a  to  1004   h . When λg represents each intra-pipe wavelength of the waveguides  1004   a  to  1004   h , all the radiating elements are excited in phase by setting the length of each slot  1002  in the long-length direction to λg. Further, the short-length direction of each slot  1002  matches the polarization direction of each radiating element. Thus, as illustrated in  FIG. 12 , similar advantages to those brought in the example illustrated in  FIG. 9  can be obtained by causing the rotation angles α for the slots  1002  in the short-length direction to be similar to the rotation angles in the example illustrated in  FIG. 9 . 
     Moreover, although in the example illustrated in  FIG. 12 , the radiating elements arranged so as to be aligned in the X direction are arranged so that the respective central positions of the radiating elements in the X direction and the Y direction agree in the Y direction and are spaced at regular intervals in the X direction. The respective central positions of the radiating elements in the X direction or the Y direction may be arranged at non-regular intervals in the X direction. 
     Fifth Embodiment 
       FIG. 13  is a plan view that illustrates a configuration of a planar array antenna  1100  according to a fifth embodiment of the present disclosure. Since the basic configuration of the planar array antenna  1100  according to the fifth embodiment is similar to the configuration of the planar array antenna  700  according to the fourth embodiment, the description thereof may be omitted. 
     In the planar array antenna  700  according to the fourth embodiment, the rotation angles of the radiating elements are changed on a column-by-column basis. That is, the rotation angles α for the radiating elements in columns A and H are each set to 45 degrees, the rotation angles α for the radiating elements in columns B and G are each set to 30 degrees, and the rotation angles α for the radiating elements in columns C and F are each set to 15 degrees. 
     In contrast, in the fifth embodiment illustrated in  FIG. 13 , among the radiating elements in respective columns, the rotation angles α for radiating elements  1101   ba  to  1101   bh  and  1101   ca  to  1101   ch , which are positioned closer to a central portion in the Y direction, are each set to 0 degrees and the rotation angles α for radiating elements  1101   aa  to  1101   ah , which are positioned on an end portion side in the +Y direction, and for radiating elements  1101   da  to  1101   dh , which are positioned on an end portion side in the −Y direction, are each set to 30 degrees. 
     Such an arrangement enables side lobes in a YZ-plane radiation pattern of the planar array antenna  1100  to be reduced. 
     Although each embodiment of the present disclosure is described above, the present disclosure is not limited to the descriptions of the embodiments. It is also possible to combine the embodiments as appropriate. 
     The array antenna according to the present disclosure is applicable to a radar device installed in a vehicle for example.