The present invention relates to a MIMO antenna device which can be formed in small size.
Recently, Multiple-Input Multiple-Output (hereinafter, abbreviated as MIMO) systems have become popular in wireless communication. A MIMO system is a space division multiplexing (SDM) transmission system. Multiple antennas on the transmitting side transmit information streams different from each other and multiple antennas on the receiving side receive them. Therefore, the MIMO system can greatly increase a channel capacity in comparison with conventional wireless communication.
A wireless communication device used for the MIMO system includes multiple antenna elements having the same resonant frequency. A mutual coupling occurs between antenna ports of the multiple antenna elements. However, there is a problem that the mutual coupling between antenna ports cause degrades communication characteristics. As a means to solve this problem, there is MIMO SYSTEM disclosed in FIG. 3 of PTL 1. In PTL 1, a mutual coupling which occurs between antenna ports of a MIMO antenna is eliminated by bridging between two monopole antennas with a metal wire.
[PTL 1] US Patent Application Publication No. 2011/0267245
However, in MIMO ANTENNA SYSTEM disclosed in PTL 1, it is certainly necessary that two monopole antennas are spaced apart with a certain interval via a metal wire. Accordingly, in MIMO ANTENNA SYSTEM disclosed in PTL 1, miniaturization of an entire antenna is a problem.
The present invention is made in view of the above problem. An object of the present invention is to provide a MIMO antenna device which is small in size and capable of securing isolation between antenna ports.
A MIMO antenna device according to the present invention includes a first conductor layer having a first opening portion and a first feed line and a second feed line. Each of the first feed line and the second feed line crosses the first opening portion, has a connection point with a first opening edge of the first opening portion, and feeds power to the first conductor layer at the connection points. The first conductor layer includes a first split portion and a second split portion at the first opening edge. The first split portion and a second split portion are cut up to a conductor edge of the first conductor layer.
According to the present invention, a MIMO antenna device which is small in size and securing isolation between antenna ports can be provided.
Hereinafter, with reference to the drawings, exemplary embodiments of the present invention will be explained in detail. Technically preferred limitations are imposed on exemplary embodiments described below in order to implement the present invention. However the scope of the invention is not limited to following exemplary embodiments.
According to the present exemplary embodiment, the MIMO antenna device 11 which is small in size and securing isolation between antenna ports is realized.
The MIMO antenna device 1 of the second exemplary embodiment includes a conductor layer 2 having a first conductor layer 2a and a second conductor layer 2b on the front side and the back side of a dielectric layer 10. The MIMO antenna device 1 includes a plurality of metal vias 8 for electrically connecting the first conductor layer 2a and the second conductor layer 2b through the dielectric layer 10. The first conductor layer 2a includes a first dual-split ring 3a. The first dual-split ring 3a includes a first opening portion 4a. Similarly, the second conductor layer 2b includes a second dual-split ring 3b. The second dual-split ring 3b includes a second opening portion 4b. A first opening edge 5a of the first opening portion 4a includes a first split portion 6a and a second split portion 6b which are cut up to a conductor edge which is an outer periphery of the first conductor layer 2a. Similarly, a second opening edge 5b of the second opening portion 4b includes a third split portion 6c and a fourth split portion 6d which are cut up to a conductor edge which is an outer periphery of the second conductor layer 2b.
Furthermore, in the front side of the first conductor layer 2a, a first feed line 7a and a second feed line 7b are arranged across the first opening portion 4a. An end of each of the first feed line 7a and the second feed line 7b is respectively connected to the first opening edge 5a. A first clearance 11a and a second clearance 11b are formed from the first opening portion 4a toward the inside of the first conductor layer 2a. The first feed line 7a is arranged along the first clearance 11a. The second feed line 7b is arranged along the second clearance 11b. Power is fed to the first conductor layer 2a and the second conductor layer 2b from the first feed line 7a and the second feed line 7b.
Inside the first opening portion 4a of the first dual-split ring 3a, a bridge line 9 which bridges between the first feed line 7a and the second feed line 7b is arranged. When the first feed line 7a or the second feed line 7b feeds power, the bridge line 9 suppresses a current from being mixed into the other feed line. In other words, the MIMO antenna device 1 of the present exemplary embodiment can secure isolation between antenna ports by the bridge line 9. Note that the bridge line 9 is linear in the present exemplary embodiment but obviously its structure is not limited to this. For example, the bridge line 9 may be a meandering shape.
L-shaped matching circuits which are formed using lumped constants X1 to X4 are connected to the first feed line 7a and the second feed line 7b. The L-shaped matching circuits are matching with an input impedance of the dual-split ring 3 viewed from each of the first feed line 7a and the second feed line 7b.
A resonant frequency of an antenna is determined by a capacitance and an inductance. A capacitance of the MIMO antenna device 1 arises from the first split portion 6a and the second split portion 6b and from the third split portion 6c and the fourth split portion 6d. An inductance of the MIMO antenna device 1 arises from path lengths of the first opening edge 5a and the second opening edge 5b. The resonant frequency becomes lower as the capacitance and/or the inductance becomes larger. For example, when lengths of the first split portion 6a and the second split portion 6b and the third split portion 6c and the fourth split portion 6d are increased, the capacitance of the MIMO antenna device 1 becomes large. In other words, since the resonant frequency of the MIMO antenna device 1 becomes low, the MIMO antenna device 1 is miniaturized without changing an occupied area of the entire antenna.
Furthermore, the dual-split ring 3 plays a role of two antennas by itself. The dual-split ring 3 does not need to space the two antennas apart with a certain interval unlike the MIMO antenna of PTL 1. Accordingly, the dual-split ring 3 facilitates miniaturization of the MIMO antenna device 1.
It is assumed that a dimension of each portion of the MIMO antenna device 1 is that the width of the conductor layer 2: L1=106.7 mm, the depth of the conductor layer 2: L2=58.1 mm, the thickness of the conductor layer 2: L3=1 mm, the width of the opening portion 4: L4=28.9 mm, and the depth of the opening portion 4: L5=5 mm. It is also assumed that lumped constants of the matching circuits are X1=X3=3 pF and X2=X4=1.5 pF. The antennas are designed such that the operating band becomes a 2.4 to 2.5 GHz range. Referring to
According to
According to the MIMO antenna device 1 of the present exemplary embodiment, a MIMO antenna device can be provided which is small in size and secures isolation between antenna ports by using the dual-split ring 3.
In the present exemplary embodiment, the MIMO antenna device 1 is configured as a three-layered structure of the first conductor layer 2a/the dielectric layer 10/the second conductor layer 2b. But it is possible to be configured as a single layer of a conductor layer or to be configured as a multi-layered structure such as a conductor layer/a dielectric layer/a conductor layer/a dielectric layer/a conductor layer. The multi-layered structure is realized by electrically connecting each conductor layer through a plurality of metal vias 8. Since a split portion is formed in each conductor layer, a number of split portions can be increased by multi-layering. By increasing a number of split portions, a capacitance value of the MIMO antenna device 1 can be increased. As the capacitance value becomes large, an inductance value required for obtaining a desired antenna resonant frequency can be reduced. In other words, a path length of the opening edge 5 which determines the value of the inductance can be shortened. This means that it is possible to be small the size of the dual-split ring 3. In other words, multi-layering of the MIMO antenna device 1 contributes to miniaturization of the antennas.
Each layer of the conductor layer 202 with six layers includes a split portion 206a and a split portion 206b. By the split portion 206a and the split portion 206b being stacked in six layers, the MIMO antenna device with six-layered the split portion 206a and the split portion 206b can obtain a capacitance value larger than the MIMO antenna device with single layered the split portion 206a and the split portion 206b. In other words, the MIMO antenna device is miniaturized since a path length of the opening edge 205 can be shortened.
In the present exemplary embodiment, a number of split portions formed in the first conductor layer 2a is assumed to be two from the first split portion 6a and the second split portion 6b. However, a number of split portions of each layer may be more than two. But, since increasing a number of split portions results in increasing a serial capacitance component, it does not result in increasing an entire capacitance of the antenna. In other words, from a viewpoint of miniaturization of antennas, it brings about an adverse effect. Furthermore, a number of split portions of each layer may be one. However, when a number of split portions of each layer is one, the operation as an antenna becomes unstable. Therefore, two split portions in each layer are suitable.
In the MIMO antenna device of the present exemplary embodiment, 2×2 MIMO communication is assumed. However, for example, by arranging four of the present MIMO antenna devices in a printed circuit board, the MIMO antenna device easily realizes 8×8 MIMO communication.
As described above, according to the present exemplary embodiment, the MIMO antenna device 1 which is small in size and securing isolation between antenna ports is realized.
The MIMO antenna device 71 of the present exemplary embodiment includes a conductor layer 72 having a first conductor layer 72a and a second conductor layer 72b on the front side and back side of a dielectric layer 710. The MIMO antenna device 71 includes a plurality of metal vias 8 for electrically connecting the first conductor layer 72a and the second conductor layer 72b through the dielectric layer 710. The first conductor layer 72a includes a first dual-split ring 73a. The first dual-split ring 73a includes a first opening portion 74a. A first opening edge 75a of the first opening portion 74a includes a first split portion 76a and a second split portion 76b which are cut up to a conductor edge which is an outer periphery of the first conductor layer 72a. Similarly, the second conductor layer 72b includes a second dual-split ring 73b. The second dual-split ring 73b includes a second opening portion 74b. A second opening edge 75b of the second opening portion 74b includes a third split portion 76c and a fourth split portion 76d which are cut up to a conductor edge which is an outer periphery of the second conductor layer 72b.
The dual-split ring 73 of the present exemplary embodiment is formed in a corner common to the first conductor layer 72a and the second conductor layer 72b unlike the dual-split ring 3 of the second exemplary embodiment. In each of the first conductor layer 72a and the second conductor layer 72b, an opening portion 74 of the dual-split ring 73 is formed in a right angle shape along the shape of the corner.
In addition, in the front side of the first conductor layer 72a, ends of a first feed line 77a and a second feed line 77b which are arranged across the first opening portion 74a are respectively connected to the first opening edge 75a. Two clearances (not illustrated in
Inside the first opening portion 74a of the first dual-split ring 73a, a bridge line 79 which bridges between the first feed line 77a and the second feed line 77b is arranged. When the first feed line 77a or the second feed line 77b feeds power, the bridge line 79 suppresses a current from being mixed into the other feed line. The MIMO antenna device 71 can secure isolation between antenna ports of the bridge line 79.
L-shaped matching circuits which are formed using lumped constants are connected to the first feed line 77a and the second feed line 77b in order to achieve matching with an input impedance of the dual-split ring 73 viewed from each of them (not illustrated in
A resonant frequency of the antenna is determined by a capacitance arisen from the first split portion 76a and the second split portion 76b and the third split portion 76c and the fourth split portion 76d and an inductance arisen from path lengths of the first opening edge 75a and the second opening edge 75b. The resonant frequency becomes lower as magnitudes of the capacitance and the inductance become larger. Accordingly, a capacitance value can be increased by increasing lengths of the first split portion 76a and the second split portion 76b and the third split portion 76c and the fourth split portion 76d. This means that an antenna can be miniaturized without changing an occupied area of the entire antenna.
Furthermore, the dual-split ring 73 plays a role of two antennas by itself. Since the dual-split ring 73 does not need to space the two antennas apart with a certain interval unlike the MIMO antenna of PTL 1, it facilitates miniaturization of the entire MIMO antenna device 1.
As described above, according to the present exemplary embodiment, the MIMO antenna device 71 which is small in size and capable of securing isolation between antenna ports is realized.
A difference between the MIMO antenna device 91 of the fourth exemplary embodiment and the MIMO antenna device 1 of the second exemplary embodiment is that the MIMO antenna device 91 of the fourth exemplary embodiment is not provided with the bridge line 9 of the MIMO antenna device 1 (
An opening side 98 of the MIMO antenna device 91 has an effect that it also serves as the bridge line 9 of the MIMO antenna device 1 of the second exemplary embodiment. Therefore, the MIMO antenna device 91 can secure isolation between antenna ports without providing a bridge line. However, since the effect of the opening side 98 is inferior to the effect of the bridge line, isolation between antenna ports of the present exemplary embodiment is inferior to the second exemplary embodiment.
As described above, according to the present exemplary embodiment, the MIMO antenna device 91 which is small in size and capable of securing isolation between antenna ports is realized.
A difference between the MIMO antenna device 101 of the fifth exemplary embodiment and the MIMO antenna device 1 of the second exemplary embodiment is that, in the MIMO antenna device 101 of the fifth exemplary embodiment, the bridge line 9 of the MIMO antenna device 1 (refer to
As described above, according to the present exemplary embodiment, the MIMO antenna device 101 which is small in size and of securing isolation between antenna ports is realized.
A difference between the MIMO antenna device 111 of the sixth exemplary embodiment and the MIMO antenna device 1 of the second exemplary embodiment is that, in the MIMO antenna device 111 of the sixth exemplary embodiment, a separation line 1112 is provided in between a feed line 117a and a feed line 117b. The separation line 1112 crosses an opening portion 114 of the dual-split ring 113. Both ends of the separation line 1112 are connected to an opening edge 115. The separation line 1112 separates the dual-split ring 113 into two single-split rings. In this case, the bridge line 119 connects the feed line 117a and the feed line 117b sterically crossing the separation line 1112 so as not to contact with the separation line 1112. Other configurations are the same as the MIMO antenna device 1 of the second exemplary embodiment.
Almost no current flows in the separation line 1112 of
As described above, according to the present exemplary embodiment, the MIMO antenna device 111 or 121 which is small in size and securing isolation between antenna ports is realized.
Differences between the MIMO antenna device 131 of the seventh exemplary embodiment and the MIMO antenna device 1 of the second exemplary embodiment are as follows. The MIMO antenna device 131 of the seventh exemplary embodiment includes a first opening portion 134a in a first conductor layer 132a. The first opening portion 134a includes a first opening edge 135a. The first opening edge 135a includes a first split portion 136a and a second split portion 136b. The first split portion 136a and the second split portion 136b are respectively at the ends of the first opening portion 134a. Similarly, the MIMO antenna device 131 includes a second opening portion 134b in a second conductor layer 132b. The second opening portion 134b includes a second opening edge 135b. The second opening edge 135b includes a third split portion 136c and a fourth split portion 136d. The third split portion 136c and the fourth split portion 136d are respectively at the ends of the second opening portion 134b. The opening edge 135a and the first split portion 136a and the second split portion 136b form pairs. The opening edge 135b and the third split portion 136c and the fourth split portion 136d form pairs. The MIMO antenna device 131 includes a first dual-split ring 133a and a second dual-split ring 133b which form a capacitance due to this structure.
The MIMO antenna device 131 of the seventh exemplary embodiment can obtain a radiation pattern different from the MIMO antenna device 1 of the second exemplary embodiment by providing the split portions at both ends of the opening portions.
As described above, according to the present exemplary embodiment, the MIMO antenna device 131 which is small in size and securing isolation between antenna ports is realized.
A differences between the MIMO antenna device of the eighth exemplary embodiment and the MIMO antenna device 1 of the second exemplary embodiment is that, in the MIMO antenna device of the eighth exemplary embodiment, split portions 166a and 166b and split portions 166c and 166d are respectively arranged in an opening edge 165a and an opening edge 165b of a region sandwiched by a first feed line 167a and a second feed line 167b. Other configurations are the same as the MIMO antenna device 1 of the second exemplary embodiment. Characteristics of the MIMO antenna device of the present exemplary embodiment are equivalent to the MIMO antenna device 1 of the second exemplary embodiment.
As modified examples of the eighth exemplary embodiment, structures illustrated, for example, in
The two positions of the split portions 166a and 166b of the first conductor layer 162a are preferably not located in one side of the opening edge 165a which is outside of a region sandwiched by the first feed line 167a and the second feed line 167b as the structures illustrated in
When each split portion 166 is independently provided as illustrated in
As described above, according to the present exemplary embodiment, the MIMO antenna device which is small in size and securing isolation between antenna ports is realized.
The present invention is not limited to the first to eighth exemplary embodiments described above and various modifications are possible within the scope of the invention described in the claims. In addition, modifications of the invention should be included in the scope of the present invention.
This application claims priority based on Japanese Patent Application No. 2013-111867, filed on May 28, 2013, the entire disclosure of which is incorporated herein.
The present invention can be utilized as an antenna for a wireless communication device used in a MIMO system in wireless communication.
Number | Date | Country | Kind |
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2013-111867 | May 2013 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2014/002722 | 5/23/2014 | WO | 00 |