Patent Publication Number: US-2022231428-A1

Title: Circular polarization array antenna device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of International Patent Application No. PCT/JP2020/031597, filed Aug. 21, 2020, which claims priority to Japanese Patent Application No. 2019-192023, filed Oct. 21, 2019, the entire contents of each of which being incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a circular polarization array antenna device. 
     BACKGROUND ART 
     The circular polarization array antenna is realized by arranging a plurality of radiation elements each radiating a circularly polarized wave in proximity to each other. In an ideal circularly polarized wave, a magnitude of a rotating electric field is constant, but in reality, the magnitude of the rotating electric field may not be constant and may be distorted into an elliptical shape. A ratio of a minor axis to a major axis of the elliptical shape of the circularly polarized wave is referred to as an “axial ratio”. In order to make a circularly polarized wave an ideal circularly polarized wave, it is required to improve axial ratio characteristics. 
     As a technique for improving the axial ratio characteristics of the circular polarization array antenna, there is a technique called a sequential array. In the sequential array, a plurality of circularly polarized radiation elements are arranged while each of which is rotated at an arbitrary angle. It is known that such an arrangement may improve the axial ratio characteristics of the entire circular polarization array antenna even when the axial ratio characteristics or a single radiation element are not preferable. 
     Japanese Unexamined Patent Application Publication No. 6-140835 discloses a circular polarization array antenna device in which a plurality of circularly polarized radiation elements are arranged in a matrix. In this circular polarization array antenna, 16 circularly polarized radiation elements are sequentially arranged in a matrix of four rows and four columns (even-numbered rows and even-numbered columns) such that a positional relationship between adjacent radiation elements comes into a positional relationship in which the radiation elements are rotated by a predetermined angle with each other and translated. 
     CITATION LIST 
     Patent Document 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. 6-140835 
       
    
     SUMMARY 
     Technical Problem 
     In a case that a plurality of circularly polarized radiation elements are arranged in a matrix, arranging the plurality of circularly polarized radiation elements in a matrix of even-numbered rows and even-numbered columns as in the circular polarization array antenna disclosed in Japanese Unexamined Patent Application Publication No. 6-140835 may more effectively improve the axial ratio characteristics. 
     However, the size of the circular polarization array antenna may be restricted depending on the size of a device to which the circular polarization array antenna is attached, and there may be a case that the number of rows of the arrangement has to be an odd number instead of an even number (that is, the number of radiation elements in a single column has to be an odd number). In this case, it is considered that improving the axial ratio characteristics is hard. 
     The present disclosure has been made in order to solve the problem above, and an object of the present disclosure is to make it simple to improve axial ratio characteristics even in the case that the number of rows of the arrangement is an odd number in a circular polarization array antenna device in which a plurality of radiation elements each capable of radiating a circularly polarized wave are arranged in a matrix. 
     Solution to Problem 
     A circular polarization array antenna device according to the present disclosure is a circular polarization array antenna device that is formed by arranging a plurality of elements each capable of radiating a circularly polarized wave in a matrix. When N is an odd number of three or more and M is an odd number of one or more, the plurality of elements are included in a first element group in which elements are arranged in a matrix of N rows and M columns in one end portion side of a region in which the plurality of elements are arranged, and a second element group in which elements are arranged in a matrix of N rows and M columns in the other end portion side of the region in which the plurality of elements are arranged. The plurality of elements include a plurality of types of elements having a positional relationship rotationally symmetric with each other. A first center element disposed at the center of the first element group is an element of a type obtained by rotating a second center element disposed at the center of the second element group by 180 degrees. 
     In the element unit described above, the first center element disposed at the center of the first element group arranged in a matrix of N rows and M columns (odd-numbered rows and odd-numbered columns) in one end portion side, and the second center element disposed at the center of the second element group arranged in a matrix of N rows and M columns (odd-numbered rows and odd-numbered columns) in the other end portion side are radiation elements of a type obtained by rotating one another by 190 degrees. With this, the first center element and the second center element may cancel out directivity distortion with each other. Consequently, an entire element group configured of a pair of the first element group and the second element group may be brought close to a sequential arrangement. Further, even when the number of rows of an arrangement, is an odd number, it may be made simple to improve the axial ratio characteristics. 
     Advantageous Effects 
     According to the present disclosure, in a circular polarization array antenna device in which a plurality of radiation elements each capable of radiating a circularly polarized wave are arranged in a matrix, it may be made simple to improve the axial ratio characteristics even when the number of rows of the arrangement is an odd number. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an example of a block diagram of a communication device to which an antenna device is applied. 
         FIG. 2  is a transparent perspective view of the communication device illustrating the inside thereof. 
         FIG. 3  is a diagram illustrating an arrangement of a plurality of radiation elements in the antenna device. 
         FIG. 4  is a partially enlarged view illustrating an arrangement of the radiation elements in a third element group disposed in a center portion of the antenna device. 
         FIG. 5  is a partially enlarged view illustrating an arrangement of the radiation elements in a first element group and a second element group respectively disposed in a left end portion and a right end portion or the antenna device. 
         FIG. 6  is a partially enlarged view illustrating an arrangement of the radiation elements in a first element group in the left end portion and a second element group in the right end portion of an antenna device according to Modification 1. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference signs, and description thereof will not be repeated. 
     (Basic Configuration of Communication Device) 
       FIG. 1  is an example of a block diagram of a communication device  10  to which an antenna device  120  according to the present embodiment is applied. The communication device  10  is configured to be capable of transmitting a circularly polarized wave from the antenna device  120 . The communication device  10  may be, for example, a terminal transmitting data to a wearable terminal (such as a head-mounted display, for example) whose relative position to the communication device  10  may change. In addition, the communication device  10  may be a communication terminal supporting “WiGig” which is a wireless communication standard mainly using 60 GHz band radio, for example. 
     The communication device  10  includes an antenna module  100  including the antenna device  120  and a BBIC  200  constituting a baseband signal processing circuit. The antenna module  100  includes an RFIC  110  that is an example of a power feeding component in addition to the antenna device  120 . The communication device  10  up-converts a signal transferred from the BBIC  200  to the antenna module  100  into a radio frequency signal and radiates the radio frequency signal from the antenna device  120 . The communication device  10  down-converts a radio frequency signal received by the antenna device  120  and processes the signal in the BBIC  200 . 
     The antenna device  120  includes a plurality of radiation elements  121  each configured to be capable of radiating a circularly polarized wave. In  FIG. 1 , for ease of explanation, only a configuration corresponding to four radiation elements  121  among the plurality of radiation elements  121  included in the antenna device  120  is illustrated, and configurations corresponding to other radiation elements  121  having the same configuration are omitted. In the present embodiment, the radiation element  121  is a patch antenna having a substantially square flat plate shape. 
     The RFIC  110  includes switches  111 A to  111 D,  113 A to  113 D, and  117 , power amplifiers  112 AT to  112 DT, low noise amplifiers  112 AR to  112 DR, attenuators  114 A to  114 D, phase shifters  115 A to  115 D, a signal multiplexer/demultiplexer  116 , a mixer  118 , and an amplifier circuit  119 . 
     When transmitting a radio frequency signal, the switches  111 A to HID and  113 A to  113 D are switched to the power amplifiers  112 AT to  112 DT side, and the switch  117  is switched to a transmission-side amplifier in the amplifier circuit  119 . When a radio frequency signal is received, the switches  111 A to  111 D and  113 A to  113 D are switched to the low noise amplifiers  112 AR to  112 DR side, and the switch  117  is switched to a reception-side amplifier in the amplifier circuit  119 . 
     A signal transferred from the BBIC  200  is amplified by the amplifier circuit  119 , and is up-converted by the mixer  118 . The transmission signal, which is an up-converted radio frequency signal, is divided into four waves by the signal multiplexer/demultiplexer  116 . The waves pass through four signal paths and are fed to the respective different radiation elements  121 . At this time, by individually adjusting phase shift degrees in the phase shifters  115 A to  115 D disposed in respective signal paths, circularly polarized waves having the same phase are radiated from the antenna device  120 . 
     Reception signals, which are radio frequency signals received by the radiation elements  121 , pass through respective four different signal paths and are combined by the signal multiplexer/demultiplexer  116 . The combined received signal is down-converted by the mixer  118 , amplified by the amplifier circuit  119 , and transferred to the BBIC  200 . 
     The RFIC  110  is formed as a single chip integrated circuit component including the circuit configuration described above, for example. Alternatively, the devices (switches, power amplifiers, low noise amplifiers, attenuators, and phase shifters) corresponding to each radiation element  121  in the RFIC  110  may be formed as a single chip integrated circuit component for each corresponding radiation element  121 . 
     (Antenna Device and Arrangement of Radiation Elements) 
       FIG. 2  is a transparent perspective view of the communication device  10  illustrating the inside thereof. The communication device  10  is covered with a housing  11 . The housing  11  accommodates the antenna device  120 , the RFIC  110 , a mounting substrate  20 , and the like. 
     The antenna device  120  includes a plate-shaped dielectric substrate  131  having a multilayer structure, and the plurality of radiation elements  121  disposed inside the dielectric substrate  131 . The dielectric substrate  131  is disposed on a side surface  22  of the mounting substrate  20  with the RFIC  110  interposed therebetween. Hereinafter, as illustrated in  FIG. 2 , a normal direction of the side surface  22  of the mounting substrate  20  is referred to as a “Z axis direction”, a normal direction of a main surface  21  of the mounting substrate  20  is referred to as an “X axis direction”, and a direction perpendicular to the Z axis direction and the X axis direction is referred to as a “Y axis direction”. 
     The dielectric substrate  131  is provided with an antenna layer having an arrangement region in which the plurality of radiation elements  121  are arranged. In the arrangement region of the antenna layer, the plurality of radiation elements  121  are arranged in a matrix along the X axis direction and the Y axis direction. Specifically, 30 radiation elements  121  are arranged in a matrix of three rows and ten columns with the X axis direction being a “row” and the Y axis direction being a “column”. 
     In general, in a case that a plurality of circularly polarized radiation elements are arranged in a matrix, arranging the plurality of circularly polarized radiation elements in a matrix of even-numbered rows and even-numbered columns, such as in the circular polarization array antenna disclosed in Japanese Unexamined Patent Application Publication No. 6-140835, may more effectively improve the axial ratio characteristics. 
     However, in the antenna device  120  according to the present embodiment, a length of the dielectric substrate  131  in the X axis direction is limited by a thickness (length in the X axis direction) T of the housing  11 . Because of this limitation, in the antenna device  120  according to the present embodiment, the number of rows at which the plurality of radiation elements  121  are arranged is three rows (odd-numbered rows). Accordingly, without any countermeasures, it may be hard to improve the axial ratio characteristics as compared with the case that the plurality of radiation elements  121  are arranged in a matrix of even-numbered rows and even-numbered columns. 
     Then, in the antenna device  120  according to the present embodiment, arranging the plurality of radiation elements  121  in the following manner makes it simple to improve the axial ratio characteristics even in the case that the number of rows at which the plurality of radiation elements  121  are arranged is three rows (odd-numbered rows). 
       FIG. 3  is a diagram illustrating an arrangement of the plurality of radiation elements  121  in the antenna device  320  according to the present embodiment. In the present embodiment, the 30 radiation elements  121  are arranged in a matrix of three rows and ten columns, as described above. Each radiation element  121  has two feed points. Two radio frequency signals having a phase difference of 90° relatively to each other are supplied from a hybrid circuit which is not illustrated, for example, to the two feed points of each radiation element  121 . With this, a circularly polarized wave is radiated from each radiation element  121 . 
     The 30 radiation elements  121  include radiation elements of four types having a positional relationship rotationally symmetric with each other. That is, the 30 radiation elements  121  include a plurality of first type radiation elements  121   a , a plurality of second type radiation elements  121   b , a plurality of third type radiation elements  121   c , and a plurality of fourth type radiation elements  121   d.    
     The first type radiation element  121   a  includes a feed point disposed at a negative direction side of the Y axis relative to a surface center, and a feed point disposed at a positive direction side of the X axis relative to the surface center. The second type radiation element  121   b  is obtained by rotating the first type radiation element  121   a  clockwise by 90 degrees and translating the rotated first type radiation element  121   a . The third type radiation element  121   c  is obtained by rotating the first type radiation element  121   a  clockwise by 270 degrees and translating the rotated first type radiation element  121   a . The fourth type radiation element  121   d  is obtained by rotating the first type radiation element  121   a  clockwise by 130 degrees with the surface center being a rotational axis, and translating the rotated first type radiation element  121   a.    
     With the rotation position (rotation angle) of the first type radiation element  121   a  being “reference (0 degrees)”, the clockwise rotation position of each radiation element  121  is expressed as follows. The rotation position of the second type radiation element  121   b  is “90 degrees”, the rotation position of the third type radiation element  121   c  is “270 degrees”, and the rotation position of the fourth type radiation element  121   d  is “180 degrees”. In light of the above, the phase shift degrees of the phase shifters  115 A to  115 D are individually adjusted as follows when the phase of a signal supplied to the first type radiation element  121   a  is expressed as a “reference phase”. The phase of a signal supplied to the second type radiation element  121   b  is “reference phase minus 90 degrees”, the phase of a signal supplied to the third type radiation element  121   c  is “reference phase minus 270 degrees”, and the phase of a signal supplied to the fourth type radiation element  121   d  is “reference phase minus 180 degrees”. With this, circularly polarized waves of the same phase are radiated from the respective radiation elements  121  of the antenna device  120 . 
     Hereinafter, among the 30 radiation elements  121 , the nine radiation elements  121  arranged in first to third columns in a left end portion are also referred to as a “first element group U 1 ”, the nine radiation elements  121  arranged in eighth to tenth columns in a right end portion are also referred to as a “second element group U 2 ”, and the 12 radiation elements  121  arranged in fourth to seventh columns in a center portion are also referred to as a “third element group U 3 ”. Further, in the following description, any integer from 1 to 3 is denoted by n, any integer from 1 to 4 is denoted by m, and a position of the n-th row and the m-th column in a matrix is denoted by (n×m). 
       FIG. 4  is a partially enlarged view illustrating an arrangement of the radiation elements  121  in the third element group U 3  disposed in the center portion of the antenna device  120 . The 12 radiation elements  121  included in the third element group U 3  include three sets of the radiation elements  121   a  to  121   d  of four types. 
     The first type radiation element  121   a  is disposed at (1×1), (2×3), and (3×1) of the third element group U 3 . The second type radiation element  121   b  is disposed at (1×2), (2×4), and (3×2) of the third element group U 3 . The third type radiation element  121   c  is disposed at (1×3), (2×1), and (3×3) of the third element group U 3 . The fourth type radiation element  121   d  is disposed at (1×4), (2×2), and (3×4) of the third element group U 3 . First to fourth columns of the third element group U 3  are the fourth to seventh columns of the entire antenna device  120 . 
     With the arrangement above, in the third element group U 3 , any one radiation element  121  and the radiation elements  121  disposed around (vertically, horizontally, and obliquely) the one radiation element  121  are of different types from each other. With this, in the third element group U 3 , the radiation elements  121   a  to  121   d  of four types are uniformly and sequentially arranged in the same number (three each), and overall balance is achieved. 
     Consequently, it may be made simple to improve the axial ratio characteristics. 
     However, the first element group U 1  in the left end portion and the second element group U 2  in the right end portion are both arranged in a matrix of three rows and three columns (odd-numbered rows and odd-numbered columns) and include the nine (odd number) radiation elements  121 . In the first element group U 1  and the second element group U 2 , therefore, the radiation elements  121   a  to  121   d  of four types cannot be uniformly arranged in the same number as in the third element group U 3 . This generates a portion in which radiation elements of the same type are adjacent to each other. Thus, each of the first element group U 1  and the second element group U 2  alone cannot form a sequential arrangement as in the third element group U 3 . 
     Then, in the present embodiment, the first element group U 1  in the left end portion and the second element group U 2  in the right end portion are regarded as a pair of element groups, and the radiation element  121  at the center of the first element group U 1  and the radiation element  121  at the center of the second element group U 2  are rotated one another by 180 degrees. That is, the radiation element  121  disposed at the center of the first element group U 1  (hereinafter also referred to as a “first center element”) is the radiation element  121  of a type obtained by rotating the radiation element  121  disposed at the center of the second element group U 2  (hereinafter also referred to as a “second center element”) by 180 degrees. With this, the first center element and the second center element may cancel out the directivity distortion with each other, with the same number (two) of radiation elements  121   a  to  121   d  of four types being disposed at positions other than the center in each of the first element group U 1  and the second element group U 2 . Consequently, the entire element group configured of the pair of the first element group U 1  and the second element group U 2  may be brought close to the sequential arrangement, and therefore, the axial ratio characteristics may be improved. 
       FIG. 5  is a partially enlarged view illustrating an arrangement of the radiation elements  121  in the first element group U 1  and the second element group U 2  respectively disposed in the left end portion and the right end portion of the antenna device  120 . 
     The first type radiation element  121   a  is disposed at (1×1), and (3×3) of the first element group U 1 . The second type radiation element  121   b  is disposed at (1×2), and (3×2) of the first element group U 1 . The third type radiation element  121   c  is disposed at (2×1), and (2×3) of the first, element group U 1 . The fourth type radiation element  121   d  is disposed at (1×3), and 3×1 of the first element group U 1 . 
     Similarly, the first type radiation element  121   a  is disposed at (1×1), and (3×3) of the second element group U 2 . The second type radiation element  121   b  is disposed at (1×2), and (3×2) of the second element group U 2 . The third type radiation element  121   c  is disposed at (2×1), and (2×3) of the second element group U 2 . The fourth type radiation element  121   d  is disposed at (1×3), and (3×1) of the second element group U 2 . Note that, first to third columns of the second element group U 2  are the eighth to tenth columns of the entire antenna device  120 . 
     With the arrangement above, in each of the first element group U 1  and the second element group U 2 , the same number (two) of the radiation elements  121   a  to  121   d  of four types are disposed at positions other than the center (2×2), and adjacent, radiation elements are of different types. 
     Further, in the center (2×2) of the first element group U 1 , the second type radiation element  121   b  is arranged as the first center element. In the center (2×2) of the second element group U 2 , the third type radiation element  121   c  obtained by rotating the second type radiation element.  121   b , which is the first center element, by 180 degrees is disposed as the second center element. With the arrangement above, the first center element is the same type as the second type radiation elements  121   b  adjacent in the upper and lower side in the first element group U 1 , and the second center element is the same type as the third type radiation element  121   c  adjacent in the right and left side in the second element group U 2 . However, since the first center element and the second center element are the radiation elements  121  of a type obtained by rotating one another by 180 degrees, the first center element and the second center element may cancel out the directivity distortion with each other. Consequently, the entire element group configured of the pair of the first element group U 1  and the second element group U 2  may be brought close to the sequential arrangement, and therefore, the axial ratio characteristics may be improved. 
     As described above, the antenna device  120  according to the present embodiment is formed by arranging the plurality of radiation elements  121  each radiating a circularly polarized wave in a matrix of three rows and ten columns. The plurality of radiation elements  121  include the radiation elements  121   a  to  121   d  of four types having a positional relationship rotationally symmetric with each other. 
     The plurality of radiation elements  121  are included in the first element group U 1  arranged in a matrix of three rows and three columns in one end portion side, the second element group U 2  arranged in a matrix of three rows and three columns in the other end portion side, and the third element group U 3  arranged in a matrix of three rows and four columns in the center portion between the first element group U 1  and the second element group U 2 . 
     In the third element group U 3  in the center portion, the radiation elements  121   a  to  121   d  of four types are uniformly and sequentially arranged in the same number (three each). With this, the overall balance is achieved in the third element, group U 3 , and it may be made simple to improve the axial ratio characteristics. 
     Whereas, each of the first element, group U 1  and the second element group U 2  does not form the sequential arrangement alone. Considering this, the first element group U 1  and the second element group U 2  are regarded as a pair of element groups, and the first center element and the second center element are made to be the radiation element  121  of a type obtained by rotating one another by 180 degrees. With this, the first center element and the second center element may cancel out the directivity distortion with each other, with the same number (two) of the radiation elements  121   a  to  121   d  of four types being disposed at positions other than the center in each of the first element group U 1  and the second element group U 2 . Consequently, the entire element group configured of the pair of the first element group U 1  and the second element group U 2  may be brought close to the sequential arrangement, and therefore, the axial ratio characteristics may be improved. 
     Consequently, in the antenna device  120  in which the plurality of radiation elements  121  each capable of radiating a circularly polarized wave are arranged in a matrix, even when the number of rows of the arrangement is three rows (odd number), it may be made simple to improve the axial ratio characteristics. 
     The “antenna device  120 ” and the “plurality of radiation elements  121 ” according to the present embodiment may correspond to the “circular polarization array antenna device” and the “plurality of elements” of the present disclosure, respectively. The “first element group U 1 ”, the “second element group U 2 ”, and the “third element group U 3 ” according to the present embodiment may correspond to the “first element group”, the “second element group”, and the “third element group” of the present disclosure, respectively. The “second type radiation element  121   b ” disposed at the center (2×2) of the first element group U 1  and the “third type radiation element  121   c ” disposed at the center (2×2) of the second element group U 2  according to the present embodiment may correspond to the “first center element” and the “second center element” of the present disclosure, respectively. Further, the “first type radiation element  121   a ”, the “second type radiation element  121   b ”, the “third type radiation element  121   c ”, and the “fourth type radiation element.  121   d ” according to the present embodiment may correspond to the “first type element”, the “second type element”, the “third type element”, and the “fourth type element” of the present disclosure, respectively. 
     &lt;Modification 1&gt; 
     In the embodiment described above, there has been described an example in which each of the first element group U 1  and the second element group U 2  is arranged in a matrix of three rows and three columns. However, it is sufficient that the first element group U 1  and the second element group U 2  are arranged Ln a matrix of N rows and M columns with which N is an odd number of three or more and M is an odd number of one or more, and the first element group U 1  and the second element group U 2  are not necessarily limited to three rows and three columns. 
       FIG. 6  is a partially enlarged view illustrating an arrangement of radiation elements  121  in a first element group U 1 A in a left end portion and a second element group U 2 A of a right end portion of an antenna device  120 A according to Modification 1. 
     Each of the first element group U 1 A and the second element group U 2 A is arranged in a matrix of three rows and one column. The third type radiation element  121   c  is disposed at (1×1) of the first element group U 1 A. The fourth type radiation element  121   d  is disposed at (3×1) of the first element group U 1 A. The first type radiation element  121   a  is disposed at (1×1) of the second element group U 2 A. The second type radiation element  121   b  is disposed at (3×1) of the second element, group U 2 A. With the arrangement above, the same number (one) of the radiation elements  121   a  to  121   d  of four types are arranged at four corners of the pair of element groups of the first element group U 1  and the second element group U 2 . 
     Further, in the center (2×1) of the first element group U 1 A, the second type radiation element  121   b  is disposed as the first center element. In the center (2×1) of the second element group U 2 A, the third type radiation element  121   c  obtained by rotating the second type radiation element  121   b , which is the first center element, by 180 degrees is disposed as the second center element. With the arrangement above, the first center element and the second center element may cancel out the directivity distortion with each other. Consequently, the entire element group configured of the pair of the first element group U 1  and the second element group U 2  may be brought close to the sequential arrangement, and therefore, the axial ratio characteristics may be improved. 
     The “first element group U 1 A” and the “second element group U 2 A” according to Modification 1 may correspond to the “first element group” and the “second element group” of the present disclosure, respectively. 
     &lt;Modification 2&gt; 
     In the embodiment described above, an example has been described in which the third element group U 3  arranged in a matrix of three rows and four columns is disposed between the first element group U 1  and the second element group U 2 . However, it is sufficient that the third element group U 3  is arranged in a matrix of odd-numbered rows and even-numbered columns, and the number of rows and the number of columns of the third element group U 3  are not necessarily limited to “three rows” and “four columns” described above. 
     Further, only the first element group U 1  and the second element group U 2  may be included without including the third element group U 3 . 
     &lt;Modification 3&gt; 
     In the embodiment described above, there has been described the radiation element  121  of the two-point feed system as the circularly polarized radiation element. However, a radiation element of a single point feed system, which uses degeneracy obtained by making the shape of the radiation element, asymmetric, nay be used as a circularly polarized radiation element. 
     &lt;Modification 4&gt; 
     In the embodiment described above, there has been described an example in which the radiation element  121  is a patch antenna. However, it is sufficient that the radiation element  121  is an antenna capable of radiating a circularly polarized wave, and the radiation element  121  is not necessarily limited to a patch antenna. For example, the radiation element  121  may be a slot antenna. 
     It should be understood that the embodiment disclosed herein is exemplary and non-restrictive in every respect. The scope of the present disclosure is indicated by the scope of claims rather than the description of the embodiment described above, and it is intended to include all modifications within the meaning and range of equivalency of the scope of claims.