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Title:
SIX-PORT SIX-POLARIZED ANTENNA
Document Type and Number:
WIPO Patent Application WO/2016/093728
Kind Code:
A1
Abstract:
The present invention relates to an antenna 10 for employing multiple polarization states of radio waves. The antenna 10 includes a three-port P1, P2, P3 module 20, a single-port P4 module 30, and a two-port P5, P6 module 40. The three-port module 20 comprises an electric-type radiating element 21 and two magnetic-type radiating elements 22. The single-port module 30 comprises a magnetic-type radiating element 31. The two-port module 40 comprises two electric-type radiating elements 41, 42. The three modules 20, 30, 40 are stacked. The present invention relates further to a method for producing an antenna 10 comprising the steps of forming the three modules 20, 30, 40 separately from each other, stacking the three modules 20, 30, 40 to assemble the antenna 10, and tuning the resonance of each module 20, 30, 40 into the frequency band of the radio waves.

Inventors:
MAKAROV, Evgeny Sergeevich (Huawei Administration Building, Bantian Longgang District, Shenzhe, Guangdong 9, 518129, CN)
ZENG, Yanxing (Huawei Administration Building, Bantian Longgang District Shenzhe, Guangdong 9, 518129, CN)
SHEN, Jianqiang (Huawei Administration Building, Bantian Longgang District Shenzhe, Guangdong 9, 518129, CN)
DUDOROV, Sergey Nikolaevich (Huawei Administration Building, Bantian Longgang District, Shenzhe, Guangdong 9, 518129, CN)
KALINICHEV, Viktor Ivanovich (Huawei Administration Building, BantianLonggang Distric, Shenzhen Guangdong 9, 51812, CN)
Application Number:
RU2014/000935
Publication Date:
June 16, 2016
Filing Date:
December 12, 2014
Export Citation:
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Assignee:
HUAWEI TECHNOLOGIES CO., LTD. (Huawei Administration Building, Bantian Longgang District Shenzhe, Guangdong 9, 518129, CN)
International Classes:
H01Q21/28; H01Q21/24; H01Q25/00; H01Q1/52; H01Q7/00; H01Q9/28; H01Q9/32; H01Q13/10
Domestic Patent References:
WO2003007422A12003-01-23
Foreign References:
US20020190908A12002-12-19
US20110006960A12011-01-13
Other References:
GOSALIA K ET AL: "Increasing Wireless Channel Capacity Through MIMO Systems Employing Co-Located Antennas", IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, vol. 53, no. 6, 1 June 2005 (2005-06-01), pages 1837 - 1844, XP011134672, ISSN: 0018-9480, DOI: 10.1109/TMTT.2005.848105
DINH THANH LE ET AL: "Wideband MIMO Compact Antennas with Tri-Polarizations", IEICE TRANSACTIONS ON COMMUNICATIONS, COMMUNICATIONS SOCIETY, TOKYO, JP, vol. E94B, no. 7, 1 July 2011 (2011-07-01), pages 1982 - 1993, XP001569329, ISSN: 0916-8516, [retrieved on 20110701], DOI: 10.1587/TRANSCOM.E94.B.1982
Attorney, Agent or Firm:
LAW FIRM "GORODISSKY & PARTNERS " LTD. et al. (Mits, Alexander VladimirovichB. Spasskaya str., 25, bldg., Moscow 0, 12909, RU)
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Claims:
Claims

1. Antenna (10) for employing multiple polarization states of radio waves, comprising

a three-port (P 1 , P2, P3) module (20) comprising an electric-type radiating element (21) and two magnetic-type radiating elements (22);

a single-port (P4) module (30) comprising a magnetic-type radiating element (31); and

a two-port (P5, P6) module (40) comprising two electric-type radiating elements (41, 42);

wherein the three modules (20, 30, 40) are stacked.

2. Antenna (10) according to claim 1, wherein

each magnetic-type radiating element (22, 23) of the three-port (PI, P2, P3) module (20) comprises a slot (24, 25) provided in a first substrate (26), and

the electric -type radiating element (21) of the three-port (PI, P2, P3) module (20) comprises a monopole (27) protruding from the first substrate (26).

3. Antenna (10) according to claim 2, wherein the slots (24, 35) are orthogonal to each other.

4. Antenna (10) according to claim 2 or 3, wherein the monopole (27) protrudes orthogonally from the first substrate (26). 5. Antenna (10) according to one of the claims 1 to 4, wherein

the magnetic-type radiating element (31) of the single-port (P4) module (30) comprises a conductive loop (32) provided in a second substrate (33).

6. Antenna (10) according to claim 5, wherein

the antenna (10) is configured to maintain a uniform amplitude and phase current around the conductive loop (32).

7. Antenna (10) according to one of the claims 1 to 6, wherein each electric-type radiating element (41, 42) of the two-port (P5, P6) module (40) comprises a dipole (43, 44) provided in a third substrate (45). 8. Antenna (10) according to claim 7, wherein the dipoles (43, 44) are orthogonal to each other.

9. Antenna (10) according to one of the claims 1 to 8, wherein

the three-port (PI, P2, P3) module (20) is stacked above the one-port (P4) module (30), and the two-port (P5, P6) module (40) is stacked above the three-port (PI, P2, P3) module (20).

10. Antenna (10) according to one of the claims 1 to 9, wherein

the substrates (26, 33, 45) of the three modules (20, 30, 40) are preferably printed circuit boards, PCB, and are oriented parallel to each other.

11. Antenna (10) according to one of the claims 1 to 10, wherein

a width (w), a depth (d) and a height (h) of the stacked antenna (10) each is about half the wavelength of the radio waves.

12. Antenna (10) according to one of the claims 1 to 11 suitable for multiple-input and multiple-output, MIMO, communications.

13. Antenna (10) according to claim 12, wherein the six ports (PI, P2, P3, P4, P5,P6) of the antenna (10) are de-coupled and de-correlated and are thus suitable for six statistically independent parallel MIMO channels.

14. Antenna (10) according to one of the claims 1 to 13, wherein a port correlation for all pairs of the six ports (PI, P2, P3, P4, P5, P6) of the antenna (10) is -15 dB or less, preferably -17 dB or less, for radio waves of a frequency between about 5 and 6 GHz.

15. Method for producing an antenna according to one of the claims 1 to 14, the method comprising the steps of:

forming the three modules (20, 30, 40) separately from each other;

stacking the three modules (20, 30, 40) to assemble the antenna (10);

tuning the resonance of each module (20, 30, 40) into the frequency band of the radio waves.

Description:
SIX-PORT SIX-POLARIZED ANTENNA

TECHNICAL FIELD The present invention relates to an antenna for sending and/or receiving radio waves, the antenna employing multiple polarization states of radio waves. In particular, the antenna is a six-port six-polarization antenna, i.e. an antenna with six antenna ports and for employing six polarization states of the radio waves. The antenna is intended to use polarization diversity for enhanced communications in a scattering-rich environment in multiple input multiple output (MIMO) indoor channels.

BACKGROUND

The term diversity relates to a method for increasing the quality of wireless communications. There are five well known and different types of diversity, namely spatial diversity, temporal diversity, polarization diversity, frequency diversity, and pattern (i.e. angular) diversity. Spatial, polarization and pattern diversity are used in the prior art for practical implementations in, for example, WLAN antenna systems. In particular, polarization diversity is used in a dual-polarized antenna system, i.e. an antenna system employing two polarization states of the received and/or transmitted electromagnetic radiations, which can exhibit an up to two times better reception than a single-polarized antenna system, which employs electromagnetic radiation linearly- polarized in only one dimension. Furthermore, there exist theoretical considerations, which show that in a scattering-rich environment six degrees of freedom are in principle possible for an antenna system with the use of polarization diversity, i.e. six electromagnetic polarization states of, for example, the radio waves transmitted and/or received by the antenna system. With such six degrees of freedom, e.g. with six distinguishable electric and magnetic states of polarization at a given point, the channel capacity increased by a factor of three can be obtained relative to the conventional two degrees of freedom, which are used in free space (i.e. line-of-sight propagation between a transmitter and a receiver). For a channel with certain channel properties (particularly for a channel having a relatively narrow communication bandwidth or for a flat fading channel, in which transmitted signals are uncorrelated white Gaussian stochastic processes with equal power, and in which a signal-to-noise ratio is large), a channel matrix H has six non- zero eigenvalues in a two-reflector scattering environment. From a physical stand point, these six eigenvalues correspond to three mutually orthogonal electrical vector components and three mutually orthogonal magnetic vector components, which can all be employed for creating six independent polarization diversity branches in a scattering- rich environment.

In principle, the theoretical considerations of the six degrees of freedom were experimentally validated in a propagation channel with rich-scattering. However, the experimental validation was only demonstrated with a setup using the 377 MHz frequency band, which cannot be used in practical wireless devices. Furthermore, the experimental setup showed only very low radiation efficiency, due to use of lumped matching components, and a rather large size.

Most of the more recent approaches known in the prior art, which generally aim to increase the capacity of communications with the help of polarization diversity, focused on three-port triple-polarized antennas. This is due to complexity of the design task, which is necessary for creating a compact and efficient six-port six-polarized antenna, which could fully exploit the above-described resources of the electromagnetic polarization. Several approaches for designing tri-polarized antennas are known from the prior art. A common feature of these approaches is the proposal of a method for wireless communications, in which polarization diversity can be utilized, in order to improve fading performance or in order to increase the capacity of the communication channel in a scattering environment. The goal of the prior art approaches is to fabricate a tri- polarization antenna system, and to investigate its capacity in comparison with the capacity of a bigger-sized conventional 3x3 single-polarized antenna system. Different designs for tri-polarization antenna-systems include a combination of a circular patch and a monopole, or include a multiport antenna cube for MIMO systems based on tri-polarized antennas located on each cube side, or include three-port orthogonally polarized dipole and slot antennas, or include triple-polarized antenna systems using notch antennas.

SUMMARY

In view of the above, more advanced antenna systems are desired, which have three or more uncorrelated ports, in order to enable more independent propagation paths and accordingly more degrees of freedom to be used by the antenna system (e.g. more electromagnetic polarization states in the case of polarization diversity). Especially in scattering-rich environments, multiple polarization states would drastically improve communications. In particular, six polarization diversity branches in MIMO antenna systems would allow fully exploiting the potential of electromagnetic polarization states for enhanced communications in multipath propagation conditions. However, the technical task of creating a compact and efficient six-port six-polarized antenna for use as a MIMO antenna system is a significant challenge. Therefore, the object of the present invention is to provide an antenna, which is able to employ the maximal allowed number of polarization states of radio waves, and is both compact and efficient. In particular, the antenna should be suitable for practical applications, for example, in MIMO wireless channels. Advantageously, six statistically independent parallel MIMO channels should be usable by the antenna for increasing the capacity of the communication.

The above-mentioned object is achieved by the solution provided in the enclosed independent claims. Advantageous implementations are defined in the respective dependent claims. In particular, according to the claimed antenna and method, the capacity of communications can be increased by an antenna employing up to six polarization states of radio waves. A first aspect of the present invention provides an antenna for employing multiple polarization states of radio waves, comprising a three-port module comprising an electric-type radiating element and two magnetic-type radiating elements, a single-port module comprising a magnetic-type radiating element, and a two-port module comprising two electric-type radiating elements, wherein the three modules are stacked.

Due to the stacked antenna design, the antenna of the present invention has a very compact size in comparison with conventional spatially diverse single-port single- polarized multiple-element array antenna systems. The six radiating elements of the antenna, i.e. the three electric-type radiating elements and the three magnetic-type radiating elements, allow the use of six polarizations using three electric field vectors and three magnetic field vectors. Thereby, the capacity of communications carried out with the antenna can be tripled in comparison with dual-polarized antennas, and can be doubled in comparison with triple-polarized antennas. The present invention can be particularly applied in complicated rich-scattering-rich multipath propagation conditions.

Due to the modular approach of the antenna design, i.e. due to the stacking of the separate modules, the antenna is well suited for being assembled and being tuned. In particular, each module can be tuned independently from the other modules. A consequence of the simpler tuning is that the overall antenna cost is lower compared with densely integrated multi-port multi-polarized antennas, which require a more complex, time-consuming and expensive tuning. The modular approach further enables a more flexible design and different shapes of the modules of the antenna. Also the locations of the modules relative to each other are changeable.

In a first implementation form of the antenna according to the first aspect, each magnetic-type radiating element of the three-port module comprises a slot provided in a first substrate, and the electric-type radiating element of the three-port module comprises a monopole protruding from the first substrate.

Therefore, the three-port module may be regarded on its own as a three-port three- polarization antenna using two magnetic field components and one electric field component.

In a second implementation form of the antenna according to the first implementation form of the first aspect, the slots are orthogonal to each other.

Thus, the magnetic field components are orthogonal to each other, and allow providing two clean polarization states of the radio waves, which can be used as two independent MIMO channels.

In a third implementation form of the antenna according to the first implementation form of the first aspect or the second implementation form of the first aspect, the monopole protrudes orthogonally from the first substrate. Thus, the electric field component is orthogonal to the two magnetic field components, and allows a third clean polarization state of the radio waves, which can be used as a third independent MIMO channel.

In a fourth implementation form of the antenna according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the magnetic- type radiating element of the single-port module comprises a conductive loop provided in a second substrate.

Therefore, the single-port module may be regarded on its own as a single-port single- polarization antenna using one magnetic field component. The magnetic field component is preferably orthogonal to the magnetic field components of the three-port module, and preferably parallel to the electric field component of the three-port module. Thus, the magnetic field component provides a fourth clean polarization state of the radio waves, which can be used as a fourth independent MIMO channel.

In a fifth implementation form of the antenna according to the fourth implementation form of the first aspect, the antenna is configured to maintain a uniform amplitude and phase current around the conductive loop.

In a sixth implementation form of the antenna according to the first aspect as such or according to any of the previous implementation forms of the first aspect, each electric- type radiating element of the two-port module comprises a dipole provided in a third substrate.

Therefore, the two-port module may be regarded on its own as a two-port two- polarization antenna using two electric field components.

In a seventh implementation form of the antenna according to the fifth implementation form of the first aspect, the dipoles are orthogonal to each other.

Thus, the two electric field components are orthogonal to each other, and are orthogonal to the electric field component of the three-port modules, and thus allow a fifth and six clean polarization state of the radio waves, which can be used as a fifth and sixth third independent MIMO channel.

In an eighth implementation form of the antenna according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the three-port module is stacked above the one-port module, and the two-port module is stacked above the three-port module.

For the antenna of the present invention, radiation efficiencies and peak gain values from all antenna ports are comparable. The order of stacking of the three modules provides the optimal de-coupling and de-correlation of the individual antenna ports.

In a ninth implementation form of the antenna according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the substrates of the three modules are preferably printed circuit boards, PCB, and are oriented parallel to each other. With the use of conventional printed circuit technology a low cost antenna with a relatively simple design is possible. PCBs require only ordinary and inexpensive materials and components for fabrication. That means the whole antenna requires only conventional technologies, materials, and components for its fabrication.

In a tenth implementation form of the antenna according to the first aspect as such or according to any of the previous implementation forms of the first aspect, a width, a depth, and a height of the stacked antenna each is about half the wavelength of the radio waves.

The antenna of the present invention thus occupies only a small 3D space, of which the dimensions are of the characteristic size of around half-wavelength of the radio waves.

In an eleventh implementation form of the antenna according to the first aspect as such or according to any of the previous implementation forms of the first aspect, the antenna is suitable for multiple-input and multiple-output, MIMO, communications.

In a twelfths implementation form of the antenna according to the eleventh implementation form of the first aspect, the six ports of the antenna are de-coupled and de-correlated and are thus suitable for six statistically independent parallel MIMO channels.

In a thirteenths implementation form of the antenna according to the first aspect as such or according to any of the previous implementation forms of the first aspect, a port correlation for all pairs of the six ports of the antenna is -15 dB or less, preferably -17 dB or less, for radio waves of a frequency between about 5 and 6 GHz.

The low correlation between the six antenna ports provides the opportunity to use six statistically independent communication channels. The antenna thus increases the speed of communications, particularly in multipath propagation conditions.

A second aspect of the present invention provides a method for producing an antenna according to any one of the implementation forms of the first aspect, the method comprising the steps of forming the three modules separately from each other, stacking the three modules to assemble the antenna, tuning the resonance of each module into the frequency band of the radio waves.

The modular production scheme of the antenna of the present invention is particularly easy. The antenna can thus be fabricated in short time and low cost. In particular, the individual tuning of the modules significantly lower s the antenna costs. BRIEF DESCRIPTION OF DRAWINGS

The above aspects and implementation forms of the present invention will be explained in the following description of specific embodiments in relation to the enclosed drawings, in which

Fig. 1 shows an antenna of the present invention with three stacked modules, namely a three-port module, a single-port module, and a two-port module.

Fig. 2 shows a three-port module of the antenna of the present invention.

Fig. 3 shows a single-port module of the antenna of the present invention. Fig. 4 shows a two-port module of the antenna of the present invention. Fig. 5 shows the assembly of the antenna of the present invention.

Fig. 6 shows correlations between port pairs of the antenna of the present invention. DETAILED DESCRIPTION OF EMBODIMENTS

The antenna 10 of the present invention is designed based on the modular approach. The assembled antenna 10 of the present invention is suitable for employing multiple polarization states of radio waves, while having a compact size, due to its six-port stacked antenna design as shown in fig.l .

The antenna 10 shown in fig. 1 is composed of a plurality of stacked modules 20, 30, 40, which together form six polarization diversity branches. Preferably, as shown in fig. 1, the antenna 10 is composed of three stacked modules 20, 30, 40. The separated modules 20, 30, 40 of the antenna preferably combine polarization diversity and angle (i.e. pattern) diversity. The three modules 20, 30, 40 shown in fig.l are a three-port module 20, a single-port module 30, and a two-port module 40. The three-port module 20 is a module comprising three-ports PI, P2, P3, the two-port module 40 is a module comprising two ports P5, P6, and the single-port module 30 is a module comprising one port P4.

Preferably, the three-port module 20 is arranged between the one-port module 30 and the two-port module 40. As shown in fig. 1, the three-port module 20 is stacked above the one-port module 30, and the two-port module 40 is stacked above the three-port module 20. A total height h of the antenna 10 is defined by the thickness of each the three stacked modules 20, 30, 40 and the distances between the modules 20, 30, 40. A width w and depth d of the antenna 10 are defined by the width and depth of the modules 20, 30, 40, particularly the largest module. Preferably, the antenna 10 is designed such that it occupies a 3D space of a characteristic size of half the wavelength of the used radio waves. To this end, the height h, depth d and width w are each preferably about the size of half the wavelength of the used radio waves. As shown in the figs. 1 and 2, the three-port module 20 comprises an electric-type radiating element 21 and two magnetic-type radiating elements 22. As shown in the figs. 1 and 3 the one-port module 30 comprises a magnetic-type radiating element 31. As shown in the figs. 1 and 4 the two-port module 40 comprises two electric-type radiating elements 41, 42. Electric-type radiating elements are, for example, monopoles or dipoles. Magnetic type radiating elements are, for example, loops, apertures, holes, slots or seams. In the figures, the arrows show directions of field components in each module 20, 30, 40. Solid arrows indicate electric field components E, and dashed arrows indicate magnetic field components H.

Fig. 2 shows the three-port module 20 of the antenna 10 shown in fig. 1. The three-port module 20 has a first substrate 26 as a basis. The substrate may, for example, be a printed circuit board (PCB). Further, the three-port module 20 has three ports PI, P2, P3, which respectively connect to the three radiating elements 21, 22, 23 of the module 20. In particular, a first port PI connects a first magnetic-type radiating element 23, a second port P2 connects a second magnetic-type radiating element 22, and a third port P3 connects an electric-type radiating element 21.

Preferably, each of the two magnetic-type radiating elements 22, 23 shown in fig. 2 comprises a slot 24, 25, which is made in the first substrate 26. Preferably, the two slots 24, 25 have to each other orthogonal extension directions in the first substrate 26. Preferably, each slot 24, 25 is connected with one end to the respective port P2, PI. Preferably, each slot comprises at the other end a bend. The bend is preferably about 90°. Magnetic field components H of radio waves induced or received by the slots 24, 25 are oriented orthogonal to the extension direction of the slots 24, 25.

Furthermore, the electric-type radiating element 21 preferably comprises a monopole 27, which protrudes from the first substrate 26. On the first substrate 26 the monopole 27 is preferably connected to the port P3. The other end of the monopole 27 is free. An angle between the extension direction of the monopole 27 and the plane of the substrate is preferably about 90°. That means, the monopole 27 protrudes preferably orthogonally from the first substrate 26. As a consequence the extension direction of the monopole 27 is preferably orthogonal to the extension direction of both slots 24, 25. An electric field component E of a radio wave induced or received by the monopole 27 is oriented parallel to the extension direction of the monopole 27.

Fig. 3 shows the one-port module 30 of the antenna 10 shown in fig. 1. The one-port module 30 has a second substrate 33 as a basis. The second substrate 33 may, for example, be a PCB. The one-port module 30 has one port P4, which connects to the magnetic-type radiating element 31 of the module 30. The magnetic-type radiating element 31 shown in fig. 3 comprises a conductive loop 32 formed in the second substrate 33. Preferably, the conductive loop 32 is connected horizontally to the port P4. The port P4 can, as shown in fig. 2, protrude in-plane of the second substrate 33 to from the conductive loop 32 in direction of its center. Preferably, the conductive loop is divided into a plurality of segments 34 along its circumference, which are connected to each other by connector elements 35. A magnetic field component H of radio waves induced or received by the loop 32 is oriented orthogonal to the plane of the second substrate 33. In use of the antenna 10, the conductive loop 32 is preferably operated such that a uniform amplitude and phase current around the conductive loop 32 is maintained.

Fig. 4 shows the two-port module 40 of the antenna 10 shown in fig. 1. The two-port module 40 has a third substrate 45 as a basis. The third substrate 45 may, for example, be a PCB. The two-port module 40 has two ports P5 and P6, which respectively connect to the two electric type radiating elements 41, 42 of the module 40. In particular, a first port P5 connects to a first electric-type radiating element 41, and a second port P6 connects to a second electric-type radiating element 42.

The two electric-type radiating elements 41, 42 preferably each comprise a dipole 43, 44, which is provided in the plane of the third substrate 45. On the third substrate 45 the dipoles 43, 44 are preferably connected to the ports P5, P6, respectively. An angle between the extension directions of the two dipoles 41, 42 is preferably about 90°. That means, the two dipoles 43, 44 are preferably orthogonal to each other. Electric field components E of radio waves induced or received by the dipoles 43, 44 are oriented parallel to the extension direction of the dipoles 43, 44, i.e. parallel to the plane of the third substrate 45.

Each of the modules 20, 30, 40 shown in the figs. 2, 3 and 4 is at first designed separately from the other modules. Then, the modules 20, 30, 40 are assembled together, in order to form the stack of the antenna 10. As shown in fig. 5, in a first step the three-port module 20 and the one-port module 40 are stacked, in particular the three- port module 20 above the one port-module 40. As an intermediate product a four-port antenna 50 is formed. The four port-antenna 50 could be used as stand-alone product to employ four polarization states of radio waves (three magnetic and one electric), and thus already shows improved communication characteristics. In a second step, the two-port module 30 is stacked above the three-port module 20, i.e. above the four-port antenna 50. Thereby, the six-port antenna 10 of the present invention is formed. Preferably, the modules 20, 30, 40 are stacked such that the respective substrates 26, 33, 45 are oriented parallel to each other. The six-port antenna 10 of the present invention is able to employ six polarization states of radio waves (three magnetic and three electric).

After the modules 20, 30, 40 are assembled together, the modules 20, 30, 40 are tuned, in order to have their resonances in a given frequency band, i.e. the frequency band of the used radio waves. The tuned design of the antenna 10 of the present invention has a specified VSWR< 2 for each port P1-P6 in the frequency band of interest. For MIMO applications, low correlations between all ports P1-P6 are furthermore very important. For the design of the antenna 10 of the present invention port correlation < -17 dB for all port pairs at most examined frequencies in the 5-6 GHz frequency band are achieved. The low port correlations of the ports P1-P6 of the antenna 10 of the present invention are shown in fig. 6. The correlation is shown on the vertical axis against the frequency of the radio waves on the horizontal axis. Different curves are shown, which are labeled with e.g. "Corr 12", which denominates the correlation between port PI and port P2. Likewise "Corr 35,36" denominates the correlation between port P3 and port P5, and port P3 and port P6, respectively, and so on. It can be seen that the port correlation, particularly the envelope correlation coefficients for the proposed 6-port antenna 10, stays below 0.13 (-17 db) for all port pairs for the frequencies in the frequency range of 5.15-5.83 GHz band. In particular, the ports P1-P6 of the antenna 10 are de-coupled and de-correlated to such an extent that the antenna 10 is suitable for six statistically independent parallel MIMO channels.

The radiation characteristics of the antenna 10 of the present invention further show high radiation efficiencies and a comparable peak gain values from all ports P1-P6. In particular, the antenna 10 of the present invention further has the following peak gain values for the ports P1-P6: 7.1 dBi for PI, 7.1 dBi for P2, 5.0 dBi for P3, 5.1 dBi for P4, and 6.5 dBi for P5, 6.5 dBi for P6. The corresponding radiation efficiencies are in the range of 90- 100 %.

Therefore, in a rich-scattering environment the average received power is comparable at each port, and hence comparable for each polarization branch. The increase in capacity in a rich-scattering MIMO communication channel of the antenna 10 of the present invention is therefore 6-fold compared to a SISO single-polarized channel. The characteristics of the antenna 10 are well suited for its application in a MIMO system based on the polarization diversity.

In summary, the antenna 10 of the present invention can be applied for increasing capacity of communications in MIMO channels with complex rich-scattering multipath propagation conditions (especially indoors) In comparison with the known prior art, the size of the antenna 10 is reduced with the proposed design. Further, the capacity of the antenna 10 is larger compared with the prior art. That is, the proposed design of the antenna 10 of the present invention provides the maximal number of six polarization diversity branches, while retaining a very compact size and a rather simple structure.

The present invention has been described in conjunction with various embodiments as examples as well as implementations. However, other variations can be understood and effected by those skilled in the art in practicing the claimed invention, from the study of the drawings, the disclosure and the independent claims. In the claims as well as in the description the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several entities or items recited in the claims. The mere fact that certain measures are recited in the mutual different dependent claims does not indicate that a combination of these measures cannot be used in an advantageous implementation.