Array antenna for satellite communications and antenna

An array antenna for satellite communications includes a first sub-array and a second sub-array, each including a plurality of 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.

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.

DETAILED DESCRIPTION

An array antenna for satellite communications according to Embodiment 1 of the present disclosure is described below, with reference toFIGS. 1 to 4.

FIG. 1is 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 inFIG. 1, an array antenna for satellite communications100(hereinafter referred to as “array antenna100”) according to Embodiment 1 of the present disclosure includes an insulating substrate30and antenna elements1disposed on a main surface of the insulating substrate30. To facilitate distinguishing between the antenna elements1and the insulating substrate30, the antenna elements1are hatched.

To facilitate understanding, an xyz orthogonal coordinate system is used. InFIG. 1, the short-side direction of the main surface of the array antenna100is defined as an x-axis direction, and the long-side direction of the main surface of the array antenna100, 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 antenna100communicates with a satellite using the array antenna100, the main surface of the array antenna100is directed to the satellite. That is, the z-axis direction that is the normal direction of the main surface of the array antenna100is directed to the satellite. And, the y-axis direction of the main surface of the array antenna100is arranged so that the satellite orbital plane of a satellite for communication with the array antenna100is parallel to the yz plane that includes the y and z axes. A satellite orbital direction60is parallel to the intersection line of the satellite orbital plane and the main surface of the array antenna100, and is parallel to the y-axis direction.

As shown inFIG. 1, the array antenna100includes a first sub-array10and a second sub-array20, each including antenna elements1arrayed in a matrix of m rows and n columns, with a regular pitch d. In other words, the first sub-array10and the second sub-array20each include antenna elements1arrayed in two rows and 12 columns, with the pitch d. The row direction and the column direction of the matrix of the antenna elements1are 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 centers2of adjacent antenna elements1.

The first sub-array10and the second sub-array20are arranged to be adjacent to each other in the x-axis direction, that is, a direction orthogonal to the satellite orbital direction60, 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 Δd1between a projection point2a, obtained when projecting the phase center2of each antenna element1included in the first sub-array10perpendicularly onto the satellite orbital plane, and projection point2b, obtained when projecting the phase center2of each antenna element1included in the second sub-array20perpendicularly onto the satellite orbital plane, is equal to the positional difference between the first sub-array10and the second sub-array20, 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. 2is a diagram illustrating a coupling state of power-supply lines for antenna elements1in a section AA shown inFIG. 1. As shown inFIG. 2, the antenna elements1arrayed in a matrix in the section AA are each coupled via the same length of power-supply line90to a branch point na, from which each power-supply line90extends. This configuration also applies to the sections BB through FF shown inFIG. 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 lines90. Hence, in the sections AA through FF, the same length of power-supply line90is used to couple the power-supply part to each antenna element, without forming a redundant wiring.

With reference toFIGS. 3A and 3B, the side-lobe level of the array antenna100are described below. The horizontal axis ofFIG. 3Aindicates an angle θ [deg] between the boresight direction of the array antenna100, that is, the z-axis direction, which is used as a reference direction, and an observation direction in the yz plane and, as shown inFIG. 3B. The vertical axis ofFIG. 3Aindicates 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 pattern8indicates a radiation pattern of the array antenna100. A radiation pattern9indicates a radiation pattern of an array antenna for satellite communications including two sub-arrays that are not shifted in the satellite orbital direction60. A standard value example12indicates an acceptable side-lobe level defined by recommendations by the International Telecommunication Union Radiocommunications Sector (ITU-R) or the like. The standard value example12is set to be −34 dB or less in angle ranges of −90 to −48 [deg] and of 48 to 90 [deg].

As shown inFIG. 3A, the radiation pattern9of the array antenna for satellite communications including two sub-arrays that are not shifted, that is, without an offset in the satellite orbital direction60, exceeds the standard value example12. In contrast, the radiation pattern8of the array antenna100having a structure in which two sub-arrays are shifted, that is, with an offset in the satellite orbital direction60, falls below the standard value example12. Thus, the array antenna100generates 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 direction60does.

With reference toFIG. 4, the relationship between the interval Δd1and the side lobes is described below.FIG. 4is a diagram illustrating the relationship between the interval Δd1and a side-lobe-level maximum value13. The side-lobe-level maximum value13indicated inFIG. 4is 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 example12is set inFIG. 3A.

As shown inFIG. 4, the side-lobe-level maximum value13is greatest when the interval Δd1is zero or d. In contrast, the side-lobe-level maximum value13is least when the interval Δd1is one half of d. Hence, when the interval Δd1is one half of the pitch d, the side-lobe level in the satellite orbital plane is lowest.

The array antenna100is designed such that the interval Δd1is 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 antenna100of Embodiment 1 as described above, the two sub-arrays, each including antenna elements1arrayed in a matrix, are shifted relative to each other in the satellite orbital direction60. This arrangement enables an extremely low side-lobe level in the satellite orbital plane. Furthermore, because the antenna elements1are arrayed in a matrix, the same length of power-supply line90can be used for each antenna element1without routing any power-supply line in a winding manner for adjustment of the line length. Thus, power-supply loss is low.

Furthermore, the array antenna100according 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 element1is a square as shown inFIG. 1, by way of an example. However, any shape may be employed. The shape of each antenna element1may 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 elements1arrayed in a matrix of m rows and n columns, are arranged in two rows as shown inFIG. 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 inFIG. 5, a first sub-array15is disposed on the main surface of the insulating substrate30, and a second sub-array21and a third sub-array22are disposed with the first sub-array15therebetween in the vertical direction. The first sub-array15is shifted relative to each of the second sub-array21and the third sub-array22in the long-side direction, that is, the satellite orbital direction60, by one half of the pitch d. The number of antenna elements1included in the first sub-array15and the total number of antenna elements1included in the second sub-array21and the third sub-array22are preferably set to be the same. Moreover, the structure of the sub-arrays shown inFIG. 5is 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-array15of four rows and 12 columns therebetween in the vertical direction.

In the present embodiment, an example where the antenna elements1are arrayed with the pitch d, both in the row direction and in the column direction, is described. However, as exemplified inFIG. 6, the pitch dr in the row direction, that is, the satellite orbital direction60, and the pitch dc in the column direction, that is, a direction orthogonal to the satellite orbital direction60, may be different from each other. Also, the number of antenna elements1included in each sub-array is not limited to the number of the antenna elements1included in each of the array antenna101and the array antenna102shown inFIGS. 5 and 6, respectively, and any number of antenna elements1may be used.

FIG. 7is a diagram illustrating an arrangement of sub-arrays of an array antenna for satellite communications200(hereinafter referred to as “array antenna200”) according to Embodiment 2 of the present disclosure. Similar to the array antenna100according to Embodiment 1, the array antenna200includes an insulating substrate30and antenna elements1disposed on a main surface of the insulating substrate30. To facilitate distinguishing between the antenna elements1and the insulating substrate30, the antenna elements1are hatched. The relationship between each coordinate axis of the xyz orthogonal coordinate system shown inFIG. 7and the array antenna200or the like is similar to that of Embodiment 1, and thus such relationship is not described herein.

As shown inFIG. 7, the array antenna200according to Embodiment 2 is designed such that a first sub-array10and a second sub-array20are shifted relative to each other in a satellite orbital direction60as described in Embodiment 1 above. Additionally, the first sub-array10and the second sub-array20are each divided by a plane orthogonal to a satellite orbital direction60, and the divided sub arrays are shifted relative to each other in a direction70orthogonal to the satellite orbital direction60. Specifically, the first sub-array10and the second sub-array20are divided into a first divided sub-array10A and a second divided sub-array10B, and a third divided sub-array20A and a fourth divided sub-array20B, respectively, by the plane orthogonal to the satellite orbital direction60. The first divided sub-array10A and the second divided sub-array10B are shifted relative to each other by one half of the pitch d in the x-axis direction, and the third divided sub-array20A and the fourth divided sub-array20B are shifted relative to each other by one half of the pitch d in the x-axis direction. Due to this arrangement, an interval Δd2between a projection point2c, obtained when projecting the phase center2of each antenna element1included in the first divided sub-array10A perpendicularly onto a plane orthogonal to a satellite orbital plane, and a projection point2d, obtained when projecting the phase center2of each antenna element1included in the second divided sub-array10B perpendicularly onto the plane orthogonal to the satellite orbital plane, is one half of the pitch d. Similarly, an interval Δd3between a projection point2e, obtained when projecting the phase center2of each antenna element1included in the third divided sub-array20A perpendicularly onto the plane orthogonal to the satellite orbital plane, and a projection point2f, obtained when projecting the phase center2of each antenna element1included in the fourth divided sub-array20B perpendicularly onto the plane orthogonal to the satellite orbital plane, is one half of the pitch d. Thus, the projection points of the phase centers2of the antenna elements1in the array antenna200according to Embodiment 2 are positioned densely in the direction70orthogonal to the satellite orbital direction60, 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 direction60is low.

As described above, the array antenna200according to Embodiment 2 is designed such that the first sub-array10and the second sub-array20are shifted relative to each other in the satellite orbital direction60, and also such that the first divided sub-array10A and the second divided sub-array10B are shifted relative to each other in the direction70orthogonal to the satellite orbital direction60, and the third divided sub-array20A and the fourth divided sub-array20B are shifted relative to each other in the direction70orthogonal to the satellite orbital direction60. This arrangement offers the effect of a low side-lobe level in the plane orthogonal to the satellite orbital direction60, in addition to the effect provided by the array antenna100according to Embodiment 1.

Moreover, the array antenna200according 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 direction60.

The array antenna200according 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-array10A, for example, is a first sub-array, and the third divided sub-array20A is a second sub-array. And, the second divided sub-array10B is a third sub-array, and the fourth divided sub-array20B is a fourth sub-array. As shown inFIG. 7, the third sub-array, that is, the second divided sub-array10B, and the fourth sub-array, that is, the fourth divided sub-array20B, 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-array10B, is arranged to be adjacent to the first sub-array, that is, the first divided sub-array10A, 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-array20B, is arranged to be adjacent to the second sub-array, that is, the third divided sub-array20A, 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-array10and the second sub-array20is 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 direction60is 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 antenna100according to Embodiment 1 and the array antenna200according to Embodiment 2 are mainly discussed. These array antennas also exhibit excellent properties in receiving operations.