Patent Publication Number: US-10320091-B2

Title: Array antenna for satellite communications and antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Japanese Patent Application No. 2014-114983, filed on Jun. 3, 2014, and Japanese Patent Application No. 2015-106054, filed on May 26, 2015, the entire disclosures of which are incorporated by reference herein. 
     FIELD 
     This application relates to an array antenna for satellite communications and an antenna, each including two-dimensionally arrayed antenna elements. 
     BACKGROUND 
     In general in array antennas for satellite communications, a side-lobe level indicating the relative level, that is, relative signal strength, of a side lobe with respect to the main lobe is required to be low so as not to cause radio interference between satellite communication systems. Patent Literature 1 (Unexamined Japanese Patent Application Kokai Publication No. H9-214241) discloses an array antenna in which sub-arrays, each constituted by a plurality of antenna elements, are arrayed densely in a satellite orbital direction so that the side-lobe level is low. 
     SUMMARY 
     In the array antenna disclosed in Patent Literature 1, some power-supply lines, each being from a power-supply part to a respective antenna element, are required to be routed with redundant windings so as to equalize the line length among all of the power-supply lines, to align excitation phases. Thus, power-supply loss may be high. 
     The present disclosure is made in consideration of such circumstances, and an objective of the present disclosure is to provide an array antenna for satellite communications and an antenna, in which the side-lobe level and power-supply loss are low. 
     An array antenna for satellite communications according to the present disclosure includes a first sub-array and a second sub-array, each including antenna elements arrayed in a matrix with a regular pitch, the first sub-array and the second sub-array being shifted relative to each other in a satellite orbital direction. 
     Furthermore, an antenna according to the present disclosure includes a substrate, a first sub-array comprising a plurality of antenna elements arrayed in a matrix on the substrate, and a second sub-array comprising a plurality of antenna elements arrayed in a matrix on the substrate, the first sub-array and the second sub-array being arranged to be adjacent to each other in the short-side direction and to be shifted relative to each other in a long-side direction. 
     According to the present disclosure, an array antenna for satellite communications and an antenna, in which the side-lobe level and power-supply loss are low, can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of this application can be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
         FIG. 1  is a diagram illustrating an arrangement of sub-arrays of an array antenna for satellite communications according to Embodiment 1 of the present disclosure; 
         FIG. 2  is a diagram illustrating a coupling state of power-supply lines for antenna elements in a section AA shown in  FIG. 1 ; 
         FIG. 3A  is a diagram illustrating a radiation pattern of the array antenna for satellite communications according to Embodiment 1; 
         FIG. 3B  is an explanatory diagram of an angle θ shown in  FIG. 3A ; 
         FIG. 4  is a diagram illustrating a relationship between an interval and a side-lobe-level maximum value, the interval being between a phase center of each antenna element included in a first sub-array and a phase center of each antenna element included in a second sub-array; 
         FIG. 5  is a diagram illustrating a modification of the array antenna for satellite communications according to Embodiment 1; 
         FIG. 6  is a diagram illustrating another modification of the array antenna for satellite communications according to Embodiment 1; and 
         FIG. 7  is a diagram illustrating an arrangement of sub-arrays of an array antenna for satellite communication according to Embodiment 2 of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiment 1 
     An array antenna for satellite communications according to Embodiment 1 of the present disclosure is described below, with reference to  FIGS. 1 to 4 . 
       FIG. 1  is a diagram illustrating an arrangement of sub-arrays of an array antenna for satellite communications according to Embodiment 1 of the present disclosure. As shown in  FIG. 1 , an array antenna for satellite communications  100  (hereinafter referred to as “array antenna  100 ”) according to Embodiment 1 of the present disclosure includes an insulating substrate  30  and antenna elements  1  disposed on a main surface of the insulating substrate  30 . To facilitate distinguishing between the antenna elements  1  and the insulating substrate  30 , the antenna elements  1  are hatched. 
     To facilitate understanding, an xyz orthogonal coordinate system is used. In  FIG. 1 , the short-side direction of the main surface of the array antenna  100  is defined as an x-axis direction, and the long-side direction of the main surface of the array antenna  100 , that is, a direction orthogonal to the x-axis direction, is defined as a y-axis direction. Also, a direction orthogonal to each of the x and y axes is defined as a z-axis direction. While the array antenna  100  communicates with a satellite using the array antenna  100 , the main surface of the array antenna  100  is directed to the satellite. That is, the z-axis direction that is the normal direction of the main surface of the array antenna  100  is directed to the satellite. And, the y-axis direction of the main surface of the array antenna  100  is arranged so that the satellite orbital plane of a satellite for communication with the array antenna  100  is parallel to the yz plane that includes the y and z axes. A satellite orbital direction  60  is parallel to the intersection line of the satellite orbital plane and the main surface of the array antenna  100 , and is parallel to the y-axis direction. 
     As shown in  FIG. 1 , the array antenna  100  includes a first sub-array  10  and a second sub-array  20 , each including antenna elements  1  arrayed in a matrix of m rows and n columns, with a regular pitch d. In other words, the first sub-array  10  and the second sub-array  20  each include antenna elements  1  arrayed in two rows and 12 columns, with the pitch d. The row direction and the column direction of the matrix of the antenna elements  1  are set to be in the y-direction, that is, the long-side direction and the x-direction, that is, the short-side direction, respectively. The pitch d is a distance between phase centers  2  of adjacent antenna elements  1 . 
     The first sub-array  10  and the second sub-array  20  are arranged to be adjacent to each other in the x-axis direction, that is, a direction orthogonal to the satellite orbital direction  60 , and to be shifted relative to each other in the y-axis direction, that is, the long-side direction, by one half of the pitch d. Arranging sub-arrays so that positions of sub-arrays are shifted relative to each other in a direction can also be said that sub-arrays are arranged with an offset in the direction. An interval Δd 1  between a projection point  2   a , obtained when projecting the phase center  2  of each antenna element  1  included in the first sub-array  10  perpendicularly onto the satellite orbital plane, and projection point  2   b , obtained when projecting the phase center  2  of each antenna element  1  included in the second sub-array  20  perpendicularly onto the satellite orbital plane, is equal to the positional difference between the first sub-array  10  and the second sub-array  20 , that is, one half of the pitch d. The positional difference, that is, an intended position-shifting can also be said as an offset. 
       FIG. 2  is a diagram illustrating a coupling state of power-supply lines for antenna elements  1  in a section AA shown in  FIG. 1 . As shown in  FIG. 2 , the antenna elements  1  arrayed in a matrix in the section AA are each coupled via the same length of power-supply line  90  to a branch point na, from which each power-supply line  90  extends. This configuration also applies to the sections BB through FF shown in  FIG. 1 . The respective branch points na provided in the sections AA through FF are coupled to the same power-supply part via the same length of respective power-supply lines  90 . Hence, in the sections AA through FF, the same length of power-supply line  90  is used to couple the power-supply part to each antenna element, without forming a redundant wiring. 
     With reference to  FIGS. 3A and 3B , the side-lobe level of the array antenna  100  are described below. The horizontal axis of  FIG. 3A  indicates an angle θ [deg] between the boresight direction of the array antenna  100 , that is, the z-axis direction, which is used as a reference direction, and an observation direction in the yz plane and, as shown in  FIG. 3B . The vertical axis of  FIG. 3A  indicates the side-lobe level [dB] at each angle θ, using the main lobe at the θ angle of 0 as a reference level. A radiation pattern  8  indicates a radiation pattern of the array antenna  100 . A radiation pattern  9  indicates a radiation pattern of an array antenna for satellite communications including two sub-arrays that are not shifted in the satellite orbital direction  60 . A standard value example  12  indicates an acceptable side-lobe level defined by recommendations by the International Telecommunication Union Radiocommunications Sector (ITU-R) or the like. The standard value example  12  is set to be −34 dB or less in angle ranges of −90 to −48 [deg] and of 48 to 90 [deg]. 
     As shown in  FIG. 3A , the radiation pattern  9  of the array antenna for satellite communications including two sub-arrays that are not shifted, that is, without an offset in the satellite orbital direction  60 , exceeds the standard value example  12 . In contrast, the radiation pattern  8  of the array antenna  100  having a structure in which two sub-arrays are shifted, that is, with an offset in the satellite orbital direction  60 , falls below the standard value example  12 . Thus, the array antenna  100  generates a lower level of side lobes in the satellite orbital plane than an array antenna including two sub-arrays that are not shifted in the satellite orbital direction  60  does. 
     With reference to  FIG. 4 , the relationship between the interval Δd 1  and the side lobes is described below.  FIG. 4  is a diagram illustrating the relationship between the interval Δd 1  and a side-lobe-level maximum value  13 . The side-lobe-level maximum value  13  indicated in  FIG. 4  is a maximum value of side lobes in the angle ranges of −90 to −48 [deg] and of 48 to 90 [deg], for which the standard value example  12  is set in  FIG. 3A . 
     As shown in  FIG. 4 , the side-lobe-level maximum value  13  is greatest when the interval Δd 1  is zero or d. In contrast, the side-lobe-level maximum value  13  is least when the interval Δd 1  is one half of d. Hence, when the interval Δd 1  is one half of the pitch d, the side-lobe level in the satellite orbital plane is lowest. 
     The array antenna  100  is designed such that the interval Δd 1  is equal to the positional difference, that is, the offset between the two sub-arrays and is one half of the pitch d, and thus the side-lobe level in the satellite orbital plane is extremely low. 
     According to the array antenna  100  of Embodiment 1 as described above, the two sub-arrays, each including antenna elements  1  arrayed in a matrix, are shifted relative to each other in the satellite orbital direction  60 . This arrangement enables an extremely low side-lobe level in the satellite orbital plane. Furthermore, because the antenna elements  1  are arrayed in a matrix, the same length of power-supply line  90  can be used for each antenna element  1  without routing any power-supply line in a winding manner for adjustment of the line length. Thus, power-supply loss is low. 
     Furthermore, the array antenna  100  according to Embodiment 1 is designed such that the positional difference between the two sub-arrays is one half of the pitch d, and thus the side-lobe level in the satellite orbital plane is extremely low. 
     In the foregoing present embodiment, the shape of each antenna element  1  is a square as shown in  FIG. 1 , by way of an example. However, any shape may be employed. The shape of each antenna element  1  may be, for example, a rectangle, a circle, an ellipse, a triangle, or the like. 
     Furthermore, in the present embodiment, the sub-arrays, each having antenna elements  1  arrayed in a matrix of m rows and n columns, are arranged in two rows as shown in  FIG. 1 . This disclosure is not limited to this arrangement, and such sub-arrays may be arranged in three or greater rows. For example, in the example shown in  FIG. 5 , a first sub-array  15  is disposed on the main surface of the insulating substrate  30 , and a second sub-array  21  and a third sub-array  22  are disposed with the first sub-array  15  therebetween in the vertical direction. The first sub-array  15  is shifted relative to each of the second sub-array  21  and the third sub-array  22  in the long-side direction, that is, the satellite orbital direction  60 , by one half of the pitch d. The number of antenna elements  1  included in the first sub-array  15  and the total number of antenna elements  1  included in the second sub-array  21  and the third sub-array  22  are preferably set to be the same. Moreover, the structure of the sub-arrays shown in  FIG. 5  is equivalent to an example where a sub-array of four rows and 12 columns is divided into two divided sub-arrays, the divided sub-arrays being disposed with the first sub-array  15  of four rows and 12 columns therebetween in the vertical direction. 
     In the present embodiment, an example where the antenna elements  1  are arrayed with the pitch d, both in the row direction and in the column direction, is described. However, as exemplified in  FIG. 6 , the pitch dr in the row direction, that is, the satellite orbital direction  60 , and the pitch dc in the column direction, that is, a direction orthogonal to the satellite orbital direction  60 , may be different from each other. Also, the number of antenna elements  1  included in each sub-array is not limited to the number of the antenna elements  1  included in each of the array antenna  101  and the array antenna  102  shown in  FIGS. 5 and 6 , respectively, and any number of antenna elements  1  may be used. 
     Embodiment 2 
       FIG. 7  is a diagram illustrating an arrangement of sub-arrays of an array antenna for satellite communications  200  (hereinafter referred to as “array antenna  200 ”) according to Embodiment 2 of the present disclosure. Similar to the array antenna  100  according to Embodiment 1, the array antenna  200  includes an insulating substrate  30  and antenna elements  1  disposed on a main surface of the insulating substrate  30 . To facilitate distinguishing between the antenna elements  1  and the insulating substrate  30 , the antenna elements  1  are hatched. The relationship between each coordinate axis of the xyz orthogonal coordinate system shown in  FIG. 7  and the array antenna  200  or the like is similar to that of Embodiment 1, and thus such relationship is not described herein. 
     As shown in  FIG. 7 , the array antenna  200  according to Embodiment 2 is designed such that a first sub-array  10  and a second sub-array  20  are shifted relative to each other in a satellite orbital direction  60  as described in Embodiment 1 above. Additionally, the first sub-array  10  and the second sub-array  20  are each divided by a plane orthogonal to a satellite orbital direction  60 , and the divided sub arrays are shifted relative to each other in a direction  70  orthogonal to the satellite orbital direction  60 . Specifically, the first sub-array  10  and the second sub-array  20  are divided into a first divided sub-array  10 A and a second divided sub-array  10 B, and a third divided sub-array  20 A and a fourth divided sub-array  20 B, respectively, by the plane orthogonal to the satellite orbital direction  60 . The first divided sub-array  10 A and the second divided sub-array  10 B are shifted relative to each other by one half of the pitch d in the x-axis direction, and the third divided sub-array  20 A and the fourth divided sub-array  20 B are shifted relative to each other by one half of the pitch d in the x-axis direction. Due to this arrangement, an interval Δd 2  between a projection point  2   c , obtained when projecting the phase center  2  of each antenna element  1  included in the first divided sub-array  10 A perpendicularly onto a plane orthogonal to a satellite orbital plane, and a projection point  2   d , obtained when projecting the phase center  2  of each antenna element  1  included in the second divided sub-array  10 B perpendicularly onto the plane orthogonal to the satellite orbital plane, is one half of the pitch d. Similarly, an interval Δd 3  between a projection point  2   e , obtained when projecting the phase center  2  of each antenna element  1  included in the third divided sub-array  20 A perpendicularly onto the plane orthogonal to the satellite orbital plane, and a projection point  2   f , obtained when projecting the phase center  2  of each antenna element  1  included in the fourth divided sub-array  20 B perpendicularly onto the plane orthogonal to the satellite orbital plane, is one half of the pitch d. Thus, the projection points of the phase centers  2  of the antenna elements  1  in the array antenna  200  according to Embodiment 2 are positioned densely in the direction  70  orthogonal to the satellite orbital direction  60 , as compared with those in an array antenna including sub-arrays that are not shifted relative to each other. Thus, the side-lobe level in the plane orthogonal to the satellite orbital direction  60  is low. 
     As described above, the array antenna  200  according to Embodiment 2 is designed such that the first sub-array  10  and the second sub-array  20  are shifted relative to each other in the satellite orbital direction  60 , and also such that the first divided sub-array  10 A and the second divided sub-array  10 B are shifted relative to each other in the direction  70  orthogonal to the satellite orbital direction  60 , and the third divided sub-array  20 A and the fourth divided sub-array  20 B are shifted relative to each other in the direction  70  orthogonal to the satellite orbital direction  60 . This arrangement offers the effect of a low side-lobe level in the plane orthogonal to the satellite orbital direction  60 , in addition to the effect provided by the array antenna  100  according to Embodiment 1. 
     Moreover, the array antenna  200  according to Embodiment 2 is designed such that the positional difference between the divided sub-arrays, divided from the same sub-array, is set to be one half of the pitch d. This arrangement enables an extremely low side-lobe level in the plane orthogonal to the satellite orbital direction  60 . 
     The array antenna  200  according to Embodiment 2 can be recognized as an array antenna having two sub-arrays that are arranged to be adjacent to each other in a short-side direction and to be shifted relative to each other in a long-side direction, and also having additional two sub-arrays. Under such recognition, the first divided sub-array  10 A, for example, is a first sub-array, and the third divided sub-array  20 A is a second sub-array. And, the second divided sub-array  10 B is a third sub-array, and the fourth divided sub-array  20 B is a fourth sub-array. As shown in  FIG. 7 , the third sub-array, that is, the second divided sub-array  10 B, and the fourth sub-array, that is, the fourth divided sub-array  20 B, are arranged to be adjacent to each other in a short-side direction and to be shifted relative to each other in a long-side direction. The third sub-array, that is, the second divided sub-array  10 B, is arranged to be adjacent to the first sub-array, that is, the first divided sub-array  10 A, in the long-side direction and to be shifted relative to the first sub-array in the short-side direction. The fourth sub-array, that is, the fourth divided sub-array  20 B, is arranged to be adjacent to the second sub-array, that is, the third divided sub-array  20 A, in the long-side direction and to be shifted relative to the second sub-array in the short-side direction. 
     In the foregoing Embodiment 1, it is indicated that the side-lobe level in the satellite orbital plane is extremely low when the positional difference between the first sub-array  10  and the second sub-array  20  is one half of the pitch d. Furthermore, in the foregoing Embodiment 2, it is indicated that the side-lobe level in the plane orthogonal to the satellite orbital direction  60  is extremely low because the positional difference between the divided sub-arrays, divided from the same sub-array, is set to be one half of the pitch d. However, the positional difference between the sub-arrays may be substantially one half of the pitch d; for example, the positional difference may be 80 to 120% of one half of the pitch d, so long as similar effects can be obtained. 
     In the foregoing embodiments, transmission properties of the array antenna  100  according to Embodiment 1 and the array antenna  200  according to Embodiment 2 are mainly discussed. These array antennas also exhibit excellent properties in receiving operations. 
     The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the disclosure. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the disclosure is defined only by the included claims, along with the full range of equivalents to which such claims are entitled.