KR20140050684A

KR20140050684A - Antenna isolation using metamaterial

Info

Publication number: KR20140050684A
Application number: KR1020147004604A
Authority: KR
Inventors: 마크 하퍼
Original assignee: 마이크로소프트 코포레이션
Priority date: 2011-08-24
Filing date: 2012-08-16
Publication date: 2014-04-29
Also published as: EP2748893B1; GB201214655D0; CN103999286B; WO2013027029A1; EP2748893A1; JP2014527366A; GB2495365A; CN103999286A; TW201320467A; KR101944568B1; TWI590523B; GB201114625D0

Abstract

A meta-material comprising an array of unit cells each formed by one or more conductive tracks is disclosed. One or more conductive tracks of one or more unit cells have a length, width, or thickness that is different from the one or more conductive tracks of another unit cell. The meta-material may be disposed between two or more antennas to improve isolation between the antennas.

Description

[0001] ANTENNA ISOLATION USING METAMATERIAL [0002]

The present invention relates to a technique for improving the isolation between antennas by using a meta material, a meta material itself, and an antenna device including such a meta material.

Metamaterials are artificial materials engineered to have characteristics not found in nature. The naturally occurring material exhibits the electromagnetic behavior determined by its atomic and molecular structure. The electromagnetic behavior is modified by introducing into the naturally occurring material a structural feature smaller than the wavelength propagated through the material using a metamaterial. Typically, these features will have a size of? / 10 to? / 20. In its simplest form, these structural features are distributed capacitive and inductive elements fabricated on a dielectric substrate, such as, for example, FR4 (commonly used in printed circuit boards (PCBs)). More complex structures are possible, for example, the use of discrete components such as commercial capacitors has also been studied.

From the perspective of the antenna designer, one of the potentially most useful properties of metamaterials is the engineering of structures with negative refractive indices. Negative refractive index materials do not occur naturally because all natural materials have positive values for both permittivity () and permeability (). There are many interesting properties of negative refractive index materials including changes to conventional geometric diffraction law, inversion of Doppler shift, and the like. However, the characteristics that are most often of interest to wireless and antenna technicians are that materials with negative epsilon or negative [mu] (but not both) are impermeable to electromagnetic radiation. The electromagnetic properties of the permeable material are generally specified by the parameters [epsilon] and [mu]

N &lt; / RTI > When n becomes negative, conventional dielectric substrate materials such as, for example, FR4 (naturally semitransparent at microwave radio frequencies) may be impermeable to radio waves. This may have applications to improve isolation between the antennas and to protect the antenna from adjacent conductive surfaces.

Negative index of refraction metamaterials can be configured at microwave frequencies using an array of electrically conductive elements that are engineered to have an appropriate capacitance C and an inductance L. [ One of the earliest and most commonly used elements is a split ring resonator (SRR) (Pendry, JB .; AJ Holden, DJ Robbins, and WJ Stewart. Magnetism from Conductors and Enhanced Nonlinear Phenomena " IEEE Trans . Microwave Theory Tech 47 (11): 2075-2084, 1999). Each SRR element includes two or more concentric rings each having a split. The capacitance of each element is generated from the close spacing between the concentric rings, and the inductance is generated from the thin print trace used to form the ring.

This is known to provide dual L-type resonator inclusions to left-handed metamaterials (JH Lv, XW Hu, MH Liu, BR Yan and LH Kong .: "Negative refraction of a double L- shaped metamaterial ", J. Opt. A: Pure Appl. Opt. 11085101, 2009). Here, the L-type resonator is formed of copper wiring on the FR4 substrate, and each unit cell includes a pair of L-type resonators arranged such that one L-type resonator is rotated by 180 degrees with respect to the other resonator do.

This is also to provide a back-to-back L-shaped conductive member surrounded by the surrounding tracks to the metamaterial, as described by Hsu, CC et al. ("Design of MIMO Antennas with Strong Isolation for Portable Applications IEEE Antennas and Propagation Society International Symposium, 2009, pp 1-4). Metamaterials can be placed between pairs of MIMO antennas to improve isolation.

Other metamaterials include, for example, those described in Moser, HO et al., &Quot; Electromagnetic metamaterials over the whole THz range - achievements and perspectives ", ELECTROMAGNETIC MATERIALS Proceedings of the Symposium, ICMAT 2005 (World Scientific Publishing Co.) Ring resonator unit cell as described in U.S. Pat.

A commonly used microwave radio frequency is 2.4 GHz, which is used in the case of a Bluetooth (TM) link, a wireless local area network (WLAN), and the like. At 2.4 GHz the wavelength is approximately 120 mm, so that each LC element in the array is typically expected to have a size of approximately 6 mm to 12 mm.

Modern wireless communication systems typically use antenna diversity or MIMO (multiple input, multiple output) antenna technology. Both the diversity and MIMO systems require more than one antenna operating at the same time and at the same frequency, so that good isolation between the antennas becomes important. Poor isolation results in loss of antenna efficiency, because power from one antenna is dissipated at the other antenna instead of radiated. In addition, poor coupling results in loss of diversity and MIMO performance, since coupling between antennas implies that they do not receive sufficiently independent samples of the wireless multipath environment.

Viewed from a first aspect, there is provided a meta-material comprising an array of unit cells each formed by one or more conductive tracks, wherein one or more conductive tracks of the one or more unit cells have a length or length different from the one or more conductive tracks of the other unit cells Width or thickness.

The metamaterial may comprise a 2D array of unit cells formed in or on the dielectric substrate.

In some embodiments, the meta-material may comprise a stack of 2D arrays of unit cells and each 2D array of unit cells is formed in or on a respective dielectric substrate. One or more dielectric substrates in the stack may be made of a material having a dielectric constant different from one or more of the other dielectric substrates in the stack. This can help improve bandwidth and over this bandwidth the meta-material provides isolation between two or more antennas.

The meta-material may include a first 2D array of unit cells on a first surface of the dielectric substrate, and a second 2D array of unit cells on a second facing surface of the dielectric substrate. One or more additional 2D arrays of unit cells may be formed in the intervening layers in the dielectric substrate between the first 2D array and the second 2D array.

The unit cells of one or more 2D arrays may be formed by one or more conductive tracks each having a length or width or thickness different from the one or more conductive tracks of a unit cell in one or more other 2D arrays. This can help improve bandwidth and over this bandwidth the meta-material provides isolation between two or more antennas.

One or more and typically each unit cell may include one or more conductive tracks configured as split-ring resonators. The split-ring resonator may be symmetric about the mirror plane, or it may be asymmetric. In the present document, asymmetry refers to that the split-ring resonator does not have a mirror symmetry plane perpendicular to the plane of the conductive track. Asymmetric arrays can provide isolation over a wider bandwidth than symmetric arrays.

The one or more unit cells may include first and second L-shaped conductive members, the conductive members being successively disposed in a plane with spacing therebetween and having both of the L-shaped conductive members in a plane And are connected to each other by a peripheral conductive track leading from the arm of the first L-shaped conductive member to the arm of the second L-shaped conductive member so as to substantially surround it.

Preferably, the L-shaped conductive member, the split-ring resonator and / or the surrounding conductive tracks are mounted on a dielectric substrate, for example a printed circuit board (PCB) substrate such as Duroid® or FR4, Is formed on the same flexible plastic substrate as used for the circuit. In some embodiments, the L-shaped conductive member, split-ring resonator, and / or peripheral conductive tracks may be printed or formed on the dielectric substrate in the form of an adhesive tape that may be applied to the PCB substrate thereafter if desired.

In some embodiments, the circumferential conductive track is generally rectangular in outline. Alternatively, generally circular, oval, oval or other polygonal contours may be used.

A gap may be formed in the peripheral conductive track corresponding to the distance between successive L-shaped conductive members. That is, the peripheral conductive track can be divided between two L-shaped members.

Alternatively, the peripheral conductive track is not divided between the two L-shaped members but forms a continuous periphery.

The array of elements can generally be configured as an n x m array with a 2-D configuration. Alternatively, the array of elements may generally be configured as an l x n x m array with a 3-D configuration. In a further embodiment, several layers of meta-material may be laminated together, and each layer has a 2-D array of identical or different elements formed thereon.

Devices within any given array may generally have the same shape and size. Alternatively, one or more elements in any given array may have somewhat different sizes or shapes such that the elements resonate at somewhat different frequencies. Alternatively or additionally, the L-shaped conductive member of one of the L-shaped conductive members in the one or more elements may have a different size than the other L-shaped conductive member or may be molded differently. These arrangements can help improve bandwidth.

Each array of elements need not be a filled array. In addition, it has been found that more than one element can be removed from the array, which improves the isolation over a wider bandwidth. Moreover, since the array is not charged, it can provide a degree of regulation by changing the location of one or more elements where space may be acceptable. For example, an incompletely filled array may include a left column of two elements, a right column of two elements, and an intermediate column with only one element. By moving the device above or below the column in the middle column, the bandwidth of the meta material can be finely tuned as needed.

The meta-material may be used to improve isolation between two or more antennas. This is particularly preferred in antenna systems using antenna diversity or MIMO techniques because they use several antennas operating simultaneously within a small space.

Viewed from a second aspect, the present invention provides an antenna system comprising a portion of a meta-material of a first aspect disposed between two or more antennas and two or more antennas disposed on the substrate.

It is also possible to use a meta-material including a dielectric substrate with first and second opposing surfaces, wherein a first pattern of elements is formed on the first surface and a second pattern of elements is formed on the second surface . The first and second patterns of elements can be tuned to different frequencies or frequency bands, and when dual surface metamaterials are placed between a pair of dual-band antennas this can improve antenna isolation in both bands.

Forming a first meta-material including a dielectric substrate having a first pattern of elements, forming a second meta-material including a dielectric substrate having a second pattern of elements, Similar results can be achieved by placing a second metamaterial on top of the material.

This principle can be extended to multiple meta-material layers or surfaces to improve isolation between two antennas in some bands.

The meta-material may also be used to improve the isolation between some (more than two) antennas, including some antennas arranged in a co-planar and non-co-planar geometry.

In some embodiments, the conductive structure of the metamaterial is printed or otherwise formed on one or both surfaces of a dielectric substrate material, such as, for example, FR4. In another embodiment, the conductive structure is printed or otherwise formed on an intervening layer of a dielectric substrate material, such as, for example, FR4. It will be appreciated that other conventional PCB substrate materials including Duroid® may also be used. Multiple layers of a dielectric substrate having the same or different dielectric constants may be used.

Other low or high dielectric constant materials (typically in the range of 1 to 90) may be used as the substrate for the metamaterial.

The novel meta-material structures of certain embodiments may be used to increase the isolation between a pair of closely spaced antennas. The metamaterial structure of some embodiments may be inexpensive enough that the structure can be printed on a layer of FR4, and low cost substrate materials are typically used in the radio wave industry. Some embodiments have the additional advantage that, in the case of dual band antennas and antenna arrays, the meta-material can be engineered to improve isolation between both bands. This can be achieved by introducing an additional layer of dielectric substrate printed in a different array of LC elements above or below the first layer. In addition, isolation between more bands is possible by introducing more layers.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention are further described below with reference to the accompanying drawings:
BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a prior art arrangement including a pair of closely spaced dual-band WLAN antennas on a PCB;
Figure 2 is a diagram illustrating isolation between two WLAN antennas in the arrangement of Figure 1;
Figure 3 shows a first embodiment comprising a meta material on a PCB;
Figure 4 shows a second embodiment comprising a meta material on a PCB;
Figure 5 illustrates a third embodiment comprising a dual-band composite meta-material comprising a second layer of the embodiment of Figure 4 and a first layer of the embodiment of Figure 3;
FIG. 6 is a diagram illustrating the meta-material of FIG. 5 disposed between a pair of WLAN antennas similar to those shown in FIG. 1;
Figure 7 is a diagram illustrating isolation between two WLAN antennas of the arrangement of Figure 6;
Figure 8 illustrates how the meta-material of the embodiment of Figure 5 can be adjusted by moving the intermediate element on one layer of meta-material;
FIG. 9 is a diagram illustrating isolation between two WLAN antennas of the arrangement of FIG. 6 when an intermediate element is moved over one layer of meta-material;
Figure 10 shows a meta-material comprising a 2D array of split-ring resonators on a dielectric substrate, wherein the at least one split-ring resonator has a different size than another resonator;
Figure 11 shows a meta-material comprising a 2D array of split-ring resonators on a dielectric substrate, wherein the at least one split-ring resonator has a different shape than another resonator;
Figure 12 shows a schematic diagram of a meta-material comprising a 2D array of split-ring resonators having a first configuration on one surface of a dielectric substrate and a 2D array of split-ring resonators having a second different configuration on the other surface of the dielectric substrate A drawing;
Figure 13 shows a 2D array of split-ring resonators having a first configuration on one surface of a dielectric substrate, a 2D array of split-ring resonators having a second different configuration on the other surface of the dielectric substrate, Lt; RTI ID = 0.0 > 2D < / RTI > arrays of split-ring resonators having a third different configuration between them.

In Figure 1 there are shown two coplanar 2.4 / 5 GHz dual-band 1/4-paramopole antennas 1 and 2 which are provided with a conductive ground plane 5 across a portion of the dielectric substrate 4 Are closely spaced in a generally parallel arrangement on the PCB 3 including the dielectric substrate 4 and the area 6 without the ground plane 5 on which the antennas 1 and 2 are disposed ). It will be appreciated that this is only an exemplary arrangement and that other types of antennas and other frequency bands may be used in conjunction with the presently disclosed embodiments where appropriate adjustment of the metamaterial design is presented. In Fig. 1, the PCB 3 is 20 mm wide and the antenna area 6 without the ground plane 5 is 15 mm long. The long lower portion 7 of the antenna is typically responsible for 2.4 GHz radiation and the upper portion 1, 2 is responsible for 5 GHz radiation. The height of the antenna is 3.2 mm in the longest part of the antenna.

In the WLAN bands of 2.40 GHz to 2.48 GHz, the monopole antennas 1,2 are only about lambda / 6 apart, so that the isolation between them is poor at about -6 dB (see Fig. 2). In the WLAN band of 4.9 GHz to 5.9 GHz, the monopole antennas 1 and 2 are electrically further spaced apart, but at worst, the isolation remains poor at approximately -8 dB.

A meta-material structure of an embodiment of the present application is shown in Fig. A plurality of conductive LC (inductive capacitive) elements 8 are printed on a single surface of the FR4 substrate 9 and do not require any vias to the ground (used in some metamaterial constructions). In the embodiment shown, the elements 8 are not conductively connected to each other. The inductance of each element 8 is generated from the conductive narrow trap 10 and the capacitance is generated mainly from the back-to-back L-type element 11 arranged closely spaced. The use of dual L-type meta-materials is described in JH Lv, XW Hu, MH Liu, BR Yan and LH Kong .: Negative refraction of a double L-shaped metamaterial, J. Opt. A: Pure Appl. Opt. 11085101, 2009, wherein one L-shape is inverted for another L-shape and is not continuous as described in the present application. It has been found that it is preferred to use an unfilled array of elements 8, as shown in Fig. 3, where the elements 8 are not at position 12. Removal of the element has been found to improve bandwidth and it may be used to move the remaining central element 13 (in this embodiment) up and down to adjust the bandwidth to a particular application. The metamaterial structure of Figure 3 provides good electromagnetic isolation at approximately 2.4 GHz.

An alternative meta-material design is shown in Figure 4 and is tuned to the 5 GHz band. According to the embodiment of FIG. 3, a plurality of conductive LC elements 8 'are printed on a single surface of the FR4 substrate 9, whereas in the embodiment of FIG. 4 the elements 8' are conductively linked to one another, Arranged in close proximity to each other. Other arrangements are possible.

To implement a suitable dual-band device, two different meta-material surfaces may be combined. For example, a 5 GHz surface of the embodiment of FIG. 4 may be mounted on top of the 2.4 GHz surface of the embodiment of FIG. 3 as shown in FIG. 5 to provide dual-band meta-material 14, May be suitably resisted or aligned.

6 shows the complete structure of a pair of monopole antennas 1, 2 on PCB 3, where the dual-band combined metamaterial 14 of FIG. 5 is disposed between monopole antennas 1, Respectively.

As shown in Fig. 7, with the dual-band meta-material 14 in place, isolation between the antennas 1,2 is improved in both bands. In the lower 2.4 GHz band, isolation has a very deep null, even at the band edge, which is approximately -12 dB. This can be improved by careful adjustment of the meta-material 14 to accurately position the nulls at the center of the band. In the high frequency band, the isolation at approximately 5 GHz is -20 dB. This notch can be moved to any portion of 4.9 GHz to 5.9 GHz by reconditioning the meta-material 14.

The lower layer of the dual-band meta-material 14 is an unfilled array and has one element deviated from the center column (see FIG. 3). Moving the position of the device within the column (see FIG. 8) can be used to vary the isolation bandwidth in the 5 GHz band without significantly affecting the 2.4 GHz isolation frequency. This effect is shown in Fig.

In this exemplary arrangement, a 2.4 GHz metamaterial is shown as a 3x2 element array, while a 5 GHz metamaterial is shown as a 2x3 array. It will be appreciated that other array configurations are possible with more or fewer devices. It will also be appreciated that more than one array element can be removed to control the bandwidth of the isolation effect.

In the above-described exemplary arrangement, FR4 is used as the substrate material. Many different types of substrate materials can be used including low and high dielectric materials. In general, the beneficial properties of the metamaterial are enhanced as the number of elements in the array increases. For a given platform size, the use of a high dielectric substrate can be used to reduce the size of the device and allow more devices to be used in the array.

The exemplary arrangement describes a dual-band meta-material comprising two layers. Generally, an n-band meta-material may be formed using an n-layer substrate.

Although isolation between two antennas is described in this exemplary arrangement, isolation between more numbers is possible by properly positioning the metamaterial elements between all pairs.

Although the exemplary arrangement describes two coplanar antennas, the described metamaterial may also be used to improve isolation between antennas arranged using different geometric shapes.

In FIG. 10, a meta-material is shown in which at least one of the split-ring resonators 8 has a different size than the other resonators and includes a 2D array of split-ring resonators 8 on a dielectric substrate 9. This can help provide isolation over a wider bandwidth.

FIG. 11 shows a meta-material in which at least one of the split-ring resonators 8 has a different shape than the other resonators and includes a 2D array of split-ring resonators 8 on a dielectric substrate 9. This can help provide isolation over a wider bandwidth.

12 shows a 2D array of split-ring resonators 8 having a first configuration on one surface of a dielectric substrate 9 and a split-ring resonator 8 having a second different configuration on the other surface of the dielectric substrate 9, A meta-material including a 2D array of resonators 8 ' is shown. This can help provide isolation over a wider bandwidth.

13 shows a 2D array of split-ring resonators 8 having a first configuration on one surface of a dielectric substrate 9, a split-ring resonator 8 having a second different configuration on the other surface of the dielectric substrate 9, There is shown a meta-material comprising a 2D array of split-ring resonators 8 'with a third different configuration between the surfaces of the dielectric substrate 9 and a 2D array of the split-ring resonators 8' It can help provide isolation across bandwidth.

Throughout the description and claims of this specification, the expressions "comprising" and "comprising" and variations thereof mean "including but not limited to ", excluding the presence of other parts, It is not intended to (but does not exclude). Throughout the description and claims of this specification, the singular forms "a", "an" and "the" include plural unless the context otherwise requires. In particular, where indefinite articles are used, the specification should be understood to encompass not only singular but also plural, unless the context requires otherwise.

Any feature, integer, feature, compound, chemical moiety or group described in connection with any particular aspect, embodiment, or embodiment of the invention is not to be considered as incompatible with any other aspect, embodiment, or embodiment And the like. All features disclosed herein (including the appended claims, abstract and drawings), and / or any steps or steps of any method or process disclosed herein, are intended to encompass all such features and / or steps when at least some of these features and / or steps are mutually exclusive combinations May be combined in any combination. The present invention is not limited to the details of any of the above embodiments. The present invention extends to any novel feature or any novel combination of features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel method One step, or any new combination.

The reader should pay attention to all papers and documents filed concurrently with this specification or filed prior to this specification and which are publicly disclosed for review by the present specification, / RTI >

Claims

An array of unit cells each formed by one or more conductive tracks,
One or more conductive tracks of one or more unit cells have a length or width or thickness different from the one or more conductive tracks of another unit cell
Metamaterial.

The method according to claim 1,
Comprising a 2D array of unit cells formed in or on a dielectric substrate
Metamaterial.

The method according to claim 1,
A stack of 2D arrays of unit cells, each 2D array of unit cells being formed in or on a respective dielectric substrate
Metamaterial.

The method of claim 3,
Wherein at least one of the dielectric substrates in the stack is made of a material having a dielectric constant different from one or more of the other dielectric substrates in the stack
Metamaterial.

The method according to claim 1,
Comprising a first 2D array of unit cells on a first surface of a dielectric substrate and a second 2D array of unit cells on a second facing surface of the dielectric substrate
Metamaterial.

6. The method of claim 5,
Further comprising one or more additional 2D arrays of unit cells formed in the intervening layers in the dielectric substrate between the first 2D array and the second 2D array
Metamaterial.

7. The method according to any one of claims 3 to 6,
The unit cells of the one or more 2D arrays are each formed by one or more conductive tracks having a length, width, or thickness different from the one or more conductive tracks of the unit cells in one or more other 2D arrays
Metamaterial.

8. The method according to any one of claims 1 to 7,
Wherein the at least one unit cell comprises at least one conductive track configured as a split-ring resonator
Metamaterial.

9. The method according to any one of claims 1 to 8,
Wherein each unit cell comprises at least one conductive track configured as a split-ring resonator
Metamaterial.

10. The method according to any one of claims 1 to 9,
Wherein the at least one unit cell comprises first and second L-shaped conductive members, wherein the conductive members are successively disposed in a plane with a gap between the members and both of the L-shaped conductive members in the plane Shaped conductive member from the arm of the first L-shaped conductive member to the arms of the second L-shaped conductive member to substantially surround the first L-shaped conductive member
Metamaterial.

11. The method of claim 10,
The peripheral conductive tracks of the one or more unit cells generally have a rectangular outline
Metamaterial.

11. The method of claim 10,
The peripheral conductive tracks of the one or more unit cells are generally circular, oval, oval or polygonal in outline
Metamaterial.

13. The method according to any one of claims 10 to 12,
For one or more unit cells, a gap is formed in the peripheral conductive track corresponding to the distance between the back-to-back conductive members
Metamaterial.

14. The method according to any one of claims 10 to 13,
For one or more elements, the peripheral conductive track is not divided between the two L-shaped members but forms a continuous perimeter
Metamaterial.

15. The method according to any one of claims 10 to 14,
In the one or more unit cells, the first and second L-shaped conductive members are formed to be different in size from each other and /
Metamaterial.

10. The method according to claim 8 or 9,
A meta-material in which at least one split-ring resonator is constructed in an asymmetric structure.

17. The method according to any one of claims 1 to 16,
Wherein the one or more unit cells have different sizes or shapes such that the unit cells resonate at different frequencies
Metamaterial.

18. The method according to any one of claims 1 to 17,
The array of unit cells is not a filled array and one or more elements are removed therefrom
Metamaterial.

Comprising a portion of a meta-material as claimed in any one of claims 1 to 18 disposed between two or more antennas and two or more antennas disposed on the substrate
Antenna system.

Substantially as shown in Figures 3 to 13 of the accompanying drawings,
Metamaterial.

Substantially as shown in Figures 3 to 13 of the accompanying drawings,
Antenna system.