The present application is based on Japanese Patent Application No. 2009-049765 filed on Mar. 3, 2009, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a dual-polarized antenna and an antenna block, more particularly, to a mobile communication base station antenna for realizing a Space Division Multiple Access (SDMA).
2. Related Art
In general, conventional mobile communication base station antenna has a sharp vertical plane directivity as shown in
In the mobile communications, particularly, in portable phone communications, MIMO (Multiple Input Multiple Output) communication becomes popular. In the MIMO communication, data transmission efficiency can be enhanced by employing plural antenna as transmitting antenna and receiving antenna, respectively. In comparison with communication speed in the case of using one transmitting antenna and one receiving antenna, communication speed in the case of using two transmitting antennas and two receiving antennas is theoretically double, and communication speed in the case of using four transmitting antennas and four receiving antennas is theoretically four times.
In the MIMO communication, correlation of signals from respective transmitting antennas to respective receiving antennas becomes important. In particular, a channel capacity of the transmitting antenna is influenced by a correlation coefficient between the respective transmitting antennas, and a channel capacity of the receiving antenna is influenced by a correlation coefficient between the respective receiving antennas. For example, in the 4×4 MIMO communication using four transmitting antennas and four receiving antennas, when there is “no correlation”, namely, the correlation coefficient is substantially zero (0), between the respective antennas, the communication speed is close to 4 times which is theoretically established. On the other hand, when the correlation coefficient is substantially 1, the effect of the MIMO communication cannot be expected. In practical use, it is preferable that the correlation coefficient between the antennas is 0.7 or less.
For example, Japanese Patent Laid-Open No. 2005-203841 (JP-A 2005-203841) discloses a conventional polarization diversity antenna element used in a mobile phone base station antenna.
So as to decrease the correlation coefficient, it is sufficient to spatially or electrically divide (separate) the antenna. By way of example only, the conventional polarization diversity antenna element used in the mobile phone base station antenna disclosed by JP-A 2005-203841 is a two-system antenna which is divided by polarization. Therefore, if such an antenna is used for an antenna block, it can be converted into a base station antenna for 2×2 MIMO communication.
By way of example only, for the case of 4×4 MIMO communication, if a distance between two antennas is increased, namely, the two antennas are distant from each other, the correlation coefficient will be decreased in accordance with the increase in distance. Therefore, referring to
Therefore, an object of the present invention is to provide a mobile communication base station antenna, in which the correlation coefficient between respective antenna blocks is decreased by changing a tilt angle in the vertical plane of the antenna block.
According to a feature of the invention, a mobile communication base station antenna comprises:
a plurality of polarization diversity antenna blocks, each of the polarization diversity antenna blocks comprising a plurality of polarization diversity antenna elements, each of the polarization diversity antenna elements comprising antenna elements that are disposed to be orthogonal to each other,
wherein the polarization diversity antenna elements of one of the polarization diversity polarization diversity antenna blocks are interposed between the polarization diversity antenna elements of another one of the polarization diversity polarization diversity antenna blocks, and tilt angles in the vertical plane of the respective polarization diversity polarization diversity antenna blocks are different from each other.
In the mobile communication base station antenna, the polarization diversity antenna blocks may be vertically arranged in the vertical plane, and the tilt angles in the vertical plane of the respective polarization diversity antenna blocks may be determined such that a correlation coefficient between the respective polarization diversity antenna blocks is 0.7 or less.
In the mobile communication base station antenna, the tilt angles in the vertical plane of the respective polarization diversity antenna blocks may be arbitrarily set by mechanically changing a direction of each of the polarization diversity antenna blocks.
In the mobile communication base station antenna, the tilt angles in the vertical plane of the respective polarization diversity antenna blocks may be arbitrarily set by shifting a signal phase by a phase shifter.
In the mobile communication base station antenna, the phase shifter may be a fixed phase shifter in which a shift amount of the signal phase is fixed.
Alternatively, in the mobile communication base station antenna, the phase shifter may be a variable phase shifter in which a shift amount of the signal phase is freely determined.
The present invention provides following excellent effects.
(1) The correlation coefficient between the respective antenna blocks can be decreased.
(2) The increase in volume (space) required for antenna installation can be suppressed.
Next, the mobile communication base station antenna in embodiments according to the invention will be explained in conjunction with appended drawings, wherein:
Next, the embodiments according to the present invention will be explained below in more detail in conjunction with appended drawings.
(Points of the Invention)
In the present invention, polarization diversity antenna elements in one polarization diversity antenna block are disposed alternately in overlap arrangement for plural stages between polarization diversity antenna elements in another polarization diversity antenna block. According to this structure, a dimension in a longitudinal direction can be decreased and an increase in volume required for antenna installation can be suppressed.
As described above, in the antenna block having a configuration in which the polarization diversity antenna elements provided in different antenna blocks (i.e. different polarization diversity antenna blocks) are partially overlapped, it is expected that the antenna correlation coefficient between the respective antenna blocks can be reduced by changing a tilt angle in the vertical plane of each of the antenna blocks. In other words, the tilts angle in the vertical plane of the respective antenna blocks, each of which comprises a plurality of antenna elements disposed to be orthogonal to each other, are set to be different from each other in the mobile communication base station antenna having a sharp directivity in the vertical plane, in order to provide a difference in the directivities of the respective antenna blocks. As a result, the antenna correlation coefficient between the respective antenna blocks can be reduced.
In the present invention, the tilt angle in the vertical plane may be fixed or variable. The tilt angle in the vertical plane of the antenna element included in the antenna block can be mechanically changed by changing a direction of the antenna block. In addition, the tilt angle in the vertical plane of the antenna element included in the antenna block can be arbitrarily changed by changing a phase of an electric power fed to the antenna element. When the phase shifter is used for changing the phase, the phase shifter may be a fixed phase shifter in which a shift amount of signal phase is fixed to a constant value. The phase shifter may be a variable (tunable) phase shifter in which the shift amount of the signal phase can be set freely.
Next, a mobile communication base station antenna in the embodiments according to the invention will be explained below in conjunction with appended drawings.
Referring to
In
In the mobile communication base station antenna 100 of
The polarization diversity antenna elements (the ±45 degree polarization diversity elements 113, 114) are disposed with a predetermined distance in the vertical direction in each of the polarization diversity antenna blocks (the first polarization diversity antenna block 111 and the second polarization diversity antenna block 112). In an overlapped portion, the ±45 degree polarization diversity elements 114 of the second polarization diversity antenna block 112 are interposed between each interval between the respective ±45 degree polarization diversity elements 113 of the first polarization diversity antenna block 111.
In the mobile communication base station antenna 100 of
Referring to
As shown in
According to the present invention, positions of the antenna elements may be changed, and a combination of antenna elements in the polarization diversity antenna element may be changed.
Referring to
Referring to
Referring to
In
Referring to
(Adjustment of the Tilt Angle in the Vertical Plane)
In the mobile communication base station antenna 100 of
Referring to
By way of example only, a tilt angle in the vertical plane of the first antenna block 451 comprising the antenna elements connected to the first port is set as 3 degrees and a tilt angle in the vertical plane of the second antenna block 452 comprising the antenna elements connected to the third port is set as 6 degrees. Herein, the antenna block comprising antenna elements connected to the second port and the antenna block comprising antenna elements connected to the fourth port are not shown in
Referring to
As shown in
As described above, since the mobile communication base station antenna has the sharp directivity in the vertical plane, when the tilt angle in the vertical plane is changed, a three-dimensional directivity, particularly a directivity of the main beam varies greatly. Therefore, overlap of the directivities of the respective antenna blocks can be reduced by providing a difference in the tilt angles in the vertical plane, thereby decreasing the correlation coefficient.
This operation of decreasing the correlation coefficient can be conducted in the antenna block comprising the antenna element connected to the second port (the antenna element of the first polarization diversity antenna block 111) and the antenna block comprising the antenna element connected to the fourth port (the antenna element of the second polarization diversity antenna block 112) that have the same polarization characteristics, by providing a difference between the tilt angles in the vertical plane. In addition, this operation of decreasing the correlation coefficient can be also conducted between the respective antenna blocks comprising the antenna elements having different polarization characteristics.
Functions and effects of the present invention will be established below by simulation calculation.
As shown in
In the antenna block in which the tilt angle in the vertical plane is set as 3 degrees, the main beam is directed to a cell edge (i.e. edge of the cell radius, wherein the cell radius is a radius of an arrival range of the signals). In the other antenna blocks, the tilt angle in the vertical plane is set as 6 degrees which is greater than 3 degrees, so as to suppress the interference with the other cells. In
As described above, the correlation coefficient between the antenna blocks can be reduced by adjusting the tilt angle in the vertical plane of the beam such that the directivities will be orthogonal to each other (i.e. the beams will not interfere with each other). Since any null point does not exist in directivities of all ports, enhancement in performance can be expected.
Further,
As described above, an overall length of the mobile communication base station antenna 100 can be shortened by overlapping the antenna elements 11, 12 of the first and second polarization diversity antenna blocks 111, 112 in a middle part of the mobile communication base station antenna in the present invention. It is possible to improve the correlation coefficient between the antenna blocks comprising the antenna element connected to the respective ports by changing the beam tilt angle in the vertical plane (the tilt angle in the vertical plane) between the upper and lower polarization diversity antenna blocks 111, 112.
The directivity can be changed by changing the beam tilt angle in the vertical plane (the tilt angle in the vertical plane) between the upper and lower polarization diversity antenna blocks 111, 112, thereby reducing the correlation coefficient between the polarization diversity antenna blocks 111, 112. Further, a space multiplexing effect of MIMO can be enhanced by decreasing the correlation coefficient between the respective antenna blocks, thereby enhancing the data transmission efficiency.
In
In other words, an overall length of the mobile communication base station antenna 200 can be shortened by overlapping the antenna elements of the first and second polarization diversity antenna blocks 211, 212 in a middle part of the mobile communication base station antenna 200. It is possible to improve the correlation coefficient between the antenna blocks 211, 212 comprising the antenna element connected to the respective ports by changing the beam tilt angle in the vertical plane (the tilt angle in the vertical plane) between the upper and lower polarization diversity antenna blocks 211, 212.
The directivity can be changed by changing the beam tilt angle in the vertical plane (the tilt angle in the vertical plane) between the upper and lower polarization diversity antenna blocks 211, 212, thereby reducing the correlation coefficient between the polarization diversity antenna blocks 211, 212. Further, a space multiplexing effect of MIMO can be enhanced by decreasing the correlation coefficient between the respective antenna blocks, thereby enhancing the data transmission efficiency.
Similarly, an overall length of the mobile communication base station antenna 300 can be shortened by overlapping the antenna elements of the first and second polarization diversity antenna blocks 311, 312 in a middle part of the mobile communication base station antenna 300. It is possible to improve the correlation coefficient between the antenna blocks 311, 312 comprising the antenna element connected to the respective ports by changing the beam tilt angle in the vertical plane (the tilt angle in the vertical plane) between the upper and lower polarization diversity antenna blocks 311, 312.
The directivity can be changed by changing the beam tilt angle in the vertical plane (the tilt angle in the vertical plane) between the upper and lower polarization diversity antenna blocks 311, 312, thereby reducing the correlation coefficient between the polarization diversity antenna blocks 311, 312. Further, a space multiplexing effect of MIMO can be enhanced by decreasing the correlation coefficient between the respective antenna blocks, thereby enhancing the data transmission efficiency.
Although the invention has been described, the invention according to claims is not to be limited by the above-mentioned embodiments and examples. Further, please note that not all combinations of the features described in the embodiments and the examples are not necessary to solve the problem of the invention.
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