Patent Grant
10741929
The present invention relates to an antenna including a split ring resonator that operates in a plurality of frequency bands and a wireless communication device using the antenna. This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-248169, filed on Nov. 12, 2012, the entire contents of which are incorporated herein.
Various techniques have been developed for antennas and structures used in wireless communication devices. For example, PTL 1 discloses an antenna device whose resonant frequency is tunable with a high degree of precision. PTL 2 (which is equivalent to WO98/44590) discloses a feed network for antenna. PTL 3 discloses an electromagnetic wave propagation medium that has broadband phase response. PTL 4 discloses an antenna device using a microwave resonator device. PTL 5 (which is equivalent to WO2006/023195) discloses metamaterials, including lenses having negative refractive indices in a wide band, diffractive optical devices, and gradient index optical devices. PTL 6 discloses a microwave transmission line. NPL 1 and NPL 2 disclose split ring resonator antennas.
Metamaterials in which a conductor pattern having a certain structure is periodically arranged to artificially control propagation characteristics of electromagnetic waves propagating through the structure have been developed in recent years. Among known basic components of the metamaterials are resonators that use a C-shaped split ring which is a ring conductor one circumferential portion of which is cut. The split ring resonators can interact with magnetic fields to control an effective magnetic permeability.
On the other hand, there is demand for reduction of the whole size of electronic devices that have communication functionality (for example wireless communication devices) and accordingly antennas need to be reduced in size. Therefore, the use of split ring resonators to reduce the size of antennas has been proposed. For example, NPL 1 discloses a technique in which a split ring resonator is disposed near a monopole antenna to increase the effective magnetic permeability and reduce the size of the monopole antenna. NPL 2 discloses a technique in which split ring resonators are periodically disposed in a region between a patch and a ground plane of a patch antenna to increase the effective magnetic permeability and reduce the size of the patch antenna.
In relation to the techniques described above, PTL 1 discloses an antenna device in which a slot is formed in a conductor plate provided on a surface of a dielectric substrate and a stub is formed on the other surface of the dielectric substrate through a via in such a manner that the stub extends across the slot, thereby enabling precise tuning of resonant frequency.
The antennas using split ring resonators disclosed in NPL 1 and NPL 2 operate in only one frequency band and therefore it is difficult for these antennas to conform to wireless communication standards that use multiple frequency bands as in wireless LANs. Furthermore, electronic devices that equipped with GPS and wireless LAN functionality need to operate on a plurality of frequency bands. However, conventional techniques are difficult to conform to a plurality of wireless communication standards.
The present invention has been made in order to solve the problem described above and an object of the present invention is to provide an antenna configured by combining a plurality of split ring resonators so as to operate in a plurality of frequency bands and a wireless communication device using the antenna.
A first mode of the present invention is an antenna including a first conductor plane in which a first split ring resonator and a second split ring resonator that have different resonant frequencies are formed and a feed line including a first branch line, a second branch line and a branch portion. The first split ring resonator includes a first conductor region along an opening edge of a first opening formed in the first conductor plane and a first split portion cutting through a portion of the first conductor region. The second split ring resonator includes a second conductor region along an opening edge of a second opening formed in the first conductor plane and a second split portion cutting through a portion of the second conductor region. One end of the first branch line is connected to the first split ring resonator and the other end extends to the branch portion across the first conductor region; one end of the second branch line is connected to the second split ring resonator and the other end extends to the branch portion across the second conductor region.
A second mode of the present invention is a wireless communication device that uses electromagnetic waves including two or more frequencies to transmit and receive wireless signals. The wireless communication device includes an antenna having the configuration described above.
The present invention provides a small antenna in which a plurality of split ring resonators having different resonant frequencies are compactly arranged. The use of the antenna in a wireless communication device enables transmission and reception of wireless signals in conformity with a plurality of communication standards without increasing the whole size of the wireless communication device.
Antennas and wireless communication devices according to the present invention will be described in detail with exemplary embodiments with reference to the accompanying drawings. Note that the same or like components are given the same or like reference numerals throughout the drawings and repeated description thereof will be omitted as appropriate.
The first split ring resonator 2 includes a first conductor region 12 along an opening edge of a first opening 11 formed in the first conductor plane 1 and a first split portion 13 formed by cutting a portion of the first conductor region 12. The second split ring resonator 3 includes a second conductor region 15 along an opening edge of a second opening 14 formed in the first conductor plane 1 and a second split portion 16 formed by cutting a portion of the second conductor region 15. Specifically, the first split ring resonator 2 is a particular conductor region that occupies a portion of the first conductor plane 1 and is a C-shaped conductor region made up of the first conductor region 12 which is a frame-like region around the opening edge of the first opening 11 and the first split portion 13 that cuts through a portion of the first conductor region 12. However, the first split ring resonator 2 does not have a defined border with the other region of the first conductor plane 1. The second split ring resonator 3 is a particular conductor region that occupies a portion of the first conductor plane 1 and is a C-shaped conductor region made up of the second conductor region 15 which is a frame-like region around the opening edge of the second opening 14 and the second split portion 16 that cuts through a portion of the second conductor region 15. In order to set desired resonance characteristics in the antenna 10, the first opening 11 and the second opening 14 are preferably formed close to the edge of the first conductor plane 1 as illustrated in
The first conductor plane 1 is rectangular shaped in plan view and the first split portion 13 and the second split portion 16 are formed on the same side of the first conductor plane 1, but not so limited. It should be that at least a portion of the periphery of the first conductor plane 1 form a linear side and the first split portion 13 and the second split portion 16 be formed on the same side.
As illustrated in
One end of the first branch line 5a of the feed line 5 is connected to the first split ring resonator 2 and the other end extends to the branch line 5c across the first conductor region 12. One end of the second branch line 5b of the feed line 5 is connected to the second split ring resonator 3 and the other end extends to the branch portion 5c across the second conductor region 15.
The first conductor plane 1 includes a clearance 8 which communicates with the first opening 11 and the second opening 14. In particular, the clearance 8 includes a first branch clearance 8a that communicates with the first opening 11 and a second branch clearance 8b that communicates with the second opening 14. The branch clearances 8a and 8b are formed so that they extend, join together and then extend in one direction. The feed line 5 is formed in the same plane as the components given above in the first conductor plane 1 and extends inside the clearance 8 while keeping a predetermined distance to the first conductor plane 1 at both sides. Specifically, one end of the first branch line 5a connects to the first right arm portion 12b provided closer to the second split ring resonator 3 with respect to the first split portion 13. The other end passes through the first opening 11, extends inside the first clearance 8a across the first conductor region 12 at the opposite side, and connects to the branch portion 5c. One end of the second branch line 5b connects to the second left arm portion 15a provided closer to the first split ring resonator 2 with respect to the second split portion 16. The other end passes through the second opening 14, extends inside the second clearance 8b across the second conductor region 15 at the opposite side, and connects to the branch portion 5c.
The first branch line 5a and the second branch line 5b of the feed line 5 extend and connect to the branch portion 5c and the feed line 5 extends inside the clearance 8 in one direction. Then, the end of the feed line 5 connects to a radio frequency circuit (RF circuit, not depicted). Note that “the first branch line 5a (or the second branch line 5b) extends across the first conductor region 12 (or the second conductor region 15)” means that the first branch line 5a (or the second branch line 5b) extends inside the first branch clearance 8a (or the second branch clearance 8b) which is a portion where the conductor in the first conductor region 12 (or the second conductor region 15) is partially missing.
The feed line 5 electrically couples to the first conductor plane 1 disposed at both sides of the feed line 5 with the clearance 8 between them to form a transmission line. The characteristic impedance of the transmission line can be set by adjusting the line width of the first branch line 5a and the second branch line 5b of the feed line 5 or the distance between each of the first branch line 5a and the second branch line 5b and the first conductor plane 1 as appropriate. Accordingly, the characteristic impedance of the transmission line can be matched to the impedance of the RF circuit to provide a signal from the RF circuit to the antenna without reflection. However, whether the characteristic impedance of the transmission line matches to the impedance of the RF circuit or not does not affect the operation of this exemplary embodiment.
In the antenna 10, the first branch line 5a connects to the first right arm portion 12b of the first split ring resonator 2 whereas the second branch line 5b connects to the second left arm portion 15a of the second split ring resonator 3. This enables good impedance matching to the split ring resonators 2 and 3 at a resonant frequency. Furthermore, in the antenna 10, impedance matching between the first branch line 5a and the first split ring resonator 2 can be adjusted by adjusting the position of connection between the first branch line 5a and the first right arm portion 12b without inserting an impedance matching circuit. Moreover, in the antenna 10, impedance matching between the second branch line 5b and the second split ring resonator 3 can be adjusted by adjusting the position of connection between the second branch line 5b and the second left arm portion 15a without inserting an impedance matching circuit.
Typically, the first conductor plane 1 and the feed line 5 are made of copper foil in any of the layer in a multilayer printed circuit board and a dielectric substrate (not depicted) supports the first conductor plane 1 and the feed line 5. However, the antenna 10 according to the first exemplary embodiment does not necessarily need to be formed in a multilayer printed circuit board. For example, the antenna 10 may be formed on a metal sheet. Furthermore, the first conductor plane 1 and the feed line 5 may be made of any conductive material other than copper foil and may be made of the same material or different materials.
A specific operation of the antenna 10 according to the first exemplary embodiment will be described next. The resonant frequency of the first split ring resonator 2 in the antenna 10 is denoted by f1 and the resonant frequency of the second split ring resonator 3 is denoted by f2. It is assumed that the characteristic impedance of the transmission line made up of the feed line 5, the clearance 8 and the first conductor plane 1 has been appropriately adjusted so that reflection of a radio frequency signal (RF signal) does not occur.
First, the RF circuit (not depicted) as an RF source (or a feeding point) connected to the feed line 5 provides an RF signal of the frequency f1 to the feed line 5. The feed line 5 propagates the RF signal of the frequency f1 input from the RF circuit without reflection, thereby providing radio frequency power (RF power) to the first split ring resonator 2. Note that impedance matching for the frequency f1 is not done in the transmission line made up of the second split ring resonator 3 and the branch line 5b and therefore the feed line 5 does not transmit the RF signal of the frequency f1 to the second split ring resonator 3.
The first split ring resonator 2 into which the RF signal of the frequency f1 has been input functions as an LC series resonance circuit made up of an inductance formed by the first conductor region 12 along the opening edge of the first opening 11 and a capacitance formed by the first left arm portion 12a and the first right arm portion 12b disposed in parallel across the first split portion 13 to resonate the input RF signal. Then the antenna 10 emits an electromagnetic signal of the frequency f1 into the air on the basis of resonance that occurs in the first split ring resonator 2.
An operation by the RF circuit to transmit an RF signal of the frequency f2 to the feed line 5 will be described next. The feed line 5 propagates an RF signal of the frequency f2 input from the RF circuit without reflection, thereby providing RF power to the second split ring resonator 3. Note that impedance matching for the frequency f2 is not done in the transmission line made up of the first split ring resonator 2 and the branch line 5a and therefore the feed line 5 does not transmit the RF signal of the frequency f2 to the first split ring resonator 2.
The second split ring resonator 3 into which the RF signal of the frequency f2 has been input functions as an LC series resonance circuit made up of an inductance formed by the second conductor region 15 along the opening edge of the second opening 14 and a capacitance formed by the second left arm portion 15a and the second right arm portion 15b disposed in parallel across the second split portion 16 to resonate the input RF signal. Then the antenna 10 emits an electromagnetic signal of the frequency f2 into the air on the basis of resonance that occurs in the second split ring resonator 3.
While the RF circuit outputs the RF signals of the frequencies f1 and f2 in different periods in the foregoing description, the RF circuit may concurrently outputs the RF signals of the frequencies f1 and f2. Furthermore, while the antenna 10 reflects electromagnetic waves as the sender of radio signals in the foregoing description, the antenna 10 is not so limited. The antenna 10 can receive electromagnetic waves as the receiver of radio signals. Specifically, the antenna can receive an electromagnetic wave (for example an RF signal) of the frequency f1 or f2 that has transmitted from an external device and propagated through the air and can send the RF signal to the RF circuit (or a receiving circuit). In this case, the antenna 10 performs the operation procedure that is the reverse of the procedure described above.
In the split ring resonators 2, 3, the openings 11, 14 can be enlarged to elongate the ring-like current path, thereby increasing the inductance to decrease the resonant frequency. Furthermore, reducing the distance between the conductors arranged in parallel across the split portion 13 (or the split portion 16) in the antenna 10, i.e. the first left arm portion 12a and the first right arm portion 12b (or the second left arm portion 15a and the second right arm portion 15b), can increase the capacitance to decrease the resonant frequency. Alternatively, increasing the width of the conductors arranged in parallel across the split portion 13, 16 in the antenna 10 can increase the capacitance to decrease the resonant frequency.
Especially, the method that increases the capacitance formed across the split portion 13, 16 can decrease the resonant frequency without increasing the whole size of the antenna 10 and therefore can reduce the antenna 10 in size in comparison with the wavelengths of electromagnetic waves. Furthermore, settings can be made to allow the split ring resonators 2 and 3 to have different resonance frequencies, thereby enabling the antenna 10 to function as a multiband antenna. In this way, in the antenna 10 according to the first exemplary embodiment, the split ring resonators 2 and 3 can be reduced in size in comparison with the wavelengths of electromagnetic waves and an impedance matching circuit does not need to be included in order to achieve impedance matching to a particular frequency. Accordingly, the antenna 10 according to the first exemplary embodiment is smaller than an antenna in which a plurality of combinations of one split ring resonator, one transmission line and one RF circuit are provided, and yet is capable of operating in a plurality of frequency bands. Consequently, provision of at least one antenna 10 according to the first exemplary embodiment in a wireless communication device can reduce the whole size of the wireless communication device.
The structure of the antenna 10 according to the first exemplary embodiment is not limited to the structure illustrated in
By adjusting the position of connection between the first branch line 5a and the first left arm portion 12a in the antenna 10 in
Note that the mode of connections between the branch lines 5a, 5b and the split ring resonators 2, 3 is not limited to the connection modes illustrated in
While components or wiring lines are not provided in the region of the first conductor plane 1 in
Typically, the feed line 5 is made of copper foil in a layer different from the layer of the first conductor plane 1 in a multilayer printed circuit board and a dielectric substrate (not depicted) is inserted between the first conductor plane 1 and the feed line 5 and supports them. However, the antenna 20 of the second exemplary embodiment does not necessarily need to be formed in a multilayer printed circuit board. For example, components made from a metal sheet may be partially supported by dielectric supports. In that case, the part other than the dielectric supports is hollow and therefore dielectric loss can be reduced and the radiation efficiency of the antenna can be improved. While typically the first feed conductor via 21 and the second feed conductor via 22 are formed by plating through-holes drilled in the dielectric substrate, the formation of the vias 21 and 22 is not limited to this. The feed conductor vias 21 and 22 may be any structures that can electrically interconnect the layer of the first conductor plane 1 and the layer of the plane that face the first conductor plane 1.
While the mode of connections between branch lines 5a, 5b and the split ring resonators 2, 3 in the antenna 20 in
In the antenna 30 in
Since the first split ring resonator 2 and the third split ring resonator 35 in the antenna 30 of the third exemplary embodiment are interconnected through the plurality of conductor vias 37, the first split ring resonator 2 and the third split ring resonator 35 operate as a single split ring resonator. In the split ring resonators 2 and 35, capacitances formed by split portions (i.e. a first split portion 13 and a third split portion 13X) are connected in parallel. Accordingly, the split ring resonators can achieve a lower resonant frequency than that achieved by the antenna 10 of the first exemplary embodiment. Furthermore, since the second split ring resonator 3 and the fourth split ring resonator 36 are interconnected through the plurality of conductor vias 38, the second split ring resonator 3 and the forth split ring resonator 36 operate as a single split ring resonator. In the split ring resonators 3, 36, capacitances formed by split portions (i.e. a second split portion 16 and a fourth split portion 16X) are connected in parallel. Accordingly, the split ring resonators can achieve a lower resonant frequency than that achieved by the antenna 10 of the first exemplary embodiment.
Typically, the second conductor plane 31 is made of copper foil in a layer in a multilayer printed circuit board that is different from the layer of the first conductor plane 1 and a dielectric substrate (not depicted) is provided between the first conductor plane 1 and the second conductor plane 31 and supports the first conductor plane 1 and the second conductor plane 31. However, the antenna 30 of the third exemplary embodiment does not necessarily need to be formed in a multilayer printed circuit board. For example, a component made from a metal sheet may be partially supported by dielectric supports. In that case, the part other than the dielectric supports is hollow and therefore dielectric loss can be reduced and the radiation efficiency of the antenna can be improved. While typically the conductor vias 37, 38 are formed by plating through-holes drilled in the dielectric substrate, the formation of the vias 37 and 38 is not limited to this. The conductor vias 37, 38 may be any structures that can electrically interconnect the layer of the first conductor plane 1 and the layer of the second conductor plane 31.
While the mode of connections between branch lines 5a, 5b and the split ring resonators 2, 3 in the antenna 30 in
While the second conductor plane 31 is provided in a single layer in
One end of a first branch line 5a of the feed line 5 is connected to a first split ring resonator 2 and a third split ring resonator 35 through a first feed conductor via 41. The other end extends in the plane that faces the first conductor plane 1 and the second conductor plane 31 across a first opening 11 and a first conductor region 12 and is connected to a branch portion 5c. One end of a second branch line 5b is connected to a second split ring resonator 3 and a fourth split ring resonator 36 through a second feed conductor via 42. The other end extends in the plane that faces the first conductor plane 1 and the second conductor plane 31 across a second opening 14 and a second conductor region 15 and is connected to the branch portion 5c. The first branch line 5a and the second branch line 5b of the feed line 5 extend and connect to the branch portion 5c and the feed line 5 further extends in one direction to connect to an RF circuit (not depicted).
Typically, the feed line 5 is formed from copper foil between the layer of the first conductor plane 1 and the layer of the second conductor plane 31 in a multilayer printed circuit board and a dielectric substrate (not depicted) is inserted between the first conductor plane 1 and the feed line 5 and a dielectric substrate (not depicted) is inserted between the feed line 5 and the second conductor plane 31 and the dielectric substrates support them. However, the antenna 40 of the fourth exemplary embodiment does not necessarily need to be formed in a multilayer printed circuit board. For example, components made from a metal sheet may be partially supported by dielectric supports. In that case, the part other than the dielectric supports is hollow and therefore dielectric loss can be reduced and the radiation efficiency of the antenna can be improved. While typically the first feed conductor via 41 and the second feed conductor via 42 are formed by plating through-holes drilled in the dielectric substrates, the formation of the vias 41 and 42 is not limited to this. The feed conductor vias 41, 42 may be any structures that can electrically interconnect the layer of the first conductor plane 1 and the layer of the second conductor plane 31.
While the mode of connections between branch lines 5a, 5b and the split ring resonators 2, 3 in the antenna 40 in
In the antenna 50 in
Typically, the first auxiliary conductor 51 and the second auxiliary conductor 52 are formed from copper foil in a layer in a multilayer printed circuit board that is different from the layer of the first conductor plane 1 and a dielectric substrate (not depicted) supports the first conductor plane 1 and the auxiliary conductors 51, 52. However, the antenna 50 of the fifth exemplary embodiment does not necessarily need to be formed in a multilayer printed circuit board. For example, components made from a metal sheet may be partially supported by dielectric supports. In that case, the part other than the dielectric supports is hollow and therefore dielectric loss can be reduced and the radiation efficiency of the antenna can be improved. While typically the conductor vias 37, 38 are formed by plating through-holes drilled in the dielectric substrate, the formation of the vias 37, 38 is not limited to this. The conductor vias 37, 38 may be any structures that can electrically interconnect the layer of first conductor plane 1 and the layer of the auxiliary conductors 51, 52.
In the plan view of
In this way, a capacitor is formed between the first auxiliary conductor 51 and the first right arm portion 12b, which can increase the capacitance formed across the first split portion 13. In addition, a capacitor is formed between the second auxiliary conductor 52 and the second right arm portion 15b, which can increase the capacitance formed across the second split portion 16. Alternatively, the connection portion 51a, 52a of each of the auxiliary conductors 51, 52 may be connected to the other end (i.e. the first right arm portion 12b, the second right arm portion 15b) of the conductor region 12, 15 to form a capacitance. Note that only one of the auxiliary conductors 51, 52 may be provided depending on the resonant frequency of the split ring resonators 2, 3.
While the mode of connections between branch lines 5a, 5b and the split ring resonators 2, 3 in the antenna 50 illustrated in any of
While the first antenna 62 and the second antenna 63 are oriented at right angles to one another in the wireless communication device 60 in
As illustrated in
The configuration of the single-band antenna 70 according to the seventh exemplary embodiment is not limited to the one illustrated in
Lastly, antennas and wireless communication devices according to the present invention are not limited to the exemplary embodiments described above; the present invention encompasses various design variations and modifications within the scope of the present invention defined in the appended claims.
The present invention provides an antenna in which a plurality of split ring resonators operating in a plurality of frequency bands are compactly arranged and is suitably applicable to wireless communication devices such as mobile terminals conforming to various wireless-LAN and MIMO communication methods.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-248169 | Nov 2012 | JP | national |
This is a Continuation of U.S. application Ser. No. 14/437,253, filed on Apr. 21, 2015, which claims priority from PCT/JP2013/080586 filed Nov. 12, 2013, claiming priority based on Japanese Patent Application No. 2012-248169 filed Nov. 12, 2012, the contents of all of which are incorporated herein by reference in their entirety.
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| Number | Date | Country | |
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| Parent | 14437253 | US | |
| Child | 15590317 | US |
