RF device with isolated antennas

1. An RF device comprising:

a first antenna set comprising a first antenna and a second antenna, the first and second antennas being planar in shape and both lying in a common first plane, the first antenna being arranged to operate in a first frequency band and the second antenna being arranged to operate in a second frequency band;

a first isolator, the first isolator being planar in shape and lying in the first plane between the first and second antennas, the first isolator having at least one branch that is electrically conductive, the first isolator being electrically floating, the first isolator being arranged to reduce first coupling by electromagnetic radiation between the first and second antennas in the first frequency band and/or in the second frequency band;

at least one second isolator having at least one electrically conductive branch, the second isolator being electrically floating, the second isolator being positioned on one side of a particular antenna selected from the first and second antennas, said side of the particular antenna being remote from the first isolator, the second isolator being arranged to correct a modification to the directivity of the particular antenna as caused by the presence of the first isolator.

2. The RF device according to claim 1 , wherein the first and second frequency bands are separated by a frequency gap lying in the range approximately 0 MHz to approximately 1 GHz.

3. The RF device according to claim 1 , wherein the first antenna set and the first isolator are positioned on a support made out of a dielectric material, the support lying in the first plane.

4. The RF device according to claim 1 , wherein the first isolator has first and second branches that are both electrically conductive, the second branch are substantially perpendicular to the first branch and projecting from a central portion of the first branch, a free end of the second branch is open circuit, the first isolator thus is T-shaped.

5. The RF device according to claim 4 , wherein the first and second antennas are planar dipole antennas, each is rectangular in shape, the first antenna is arranged to generate a first maximum electric field along a first axis, the second antenna is arranged to generate a second maximum electric field along a second axis, and the first and second axes are substantially parallel to each other.

6. The RF device according to claim 5 , wherein the first and second axes are oriented at substantially 45° relative to the second branch.

7. The RF device according to claim 5 , wherein the first and second axes are substantially perpendicular to the second branch.

8. The RF device according to claim 5 , wherein the first maximum electric field is greater than the second maximum electric field, one end of the first branch of the first isolator is spaced apart from the first axis (E 2a ) by a distance lying in the range 5 mm to 1.5 cm.

9. The RF device according to claim 4 , wherein the first isolator is arranged to reduce the first coupling by electromagnetic radiation to a greater extent in the first frequency band, the first branch of the first isolator has a predefined length that is substantially equal to at least one quarter of a first wavelength λ A , the first wavelength λ A being such that:

λ

A

=

c

v

1

×

ε

⁢

r

wherein ν 1 is a first center frequency centered between the maximum frequency and the minimum frequency of the first frequency band, and wherein εr is the dielectric permittivity of the medium in which the first isolator lies, the medium being a dielectric support or air.

10. The RF device according to claim 4 , wherein the first isolator is arranged to reduce the first coupling by electromagnetic radiation in equal manner in the first and second frequency bands, the first branch of the first isolator has a predefined length that is substantially equal to at least one quarter of a first wavelength λ A , the first wavelength λ A being such that:

λ

A

=

c

v

1

+

v

2

2

×

ε

⁢

r

wherein ν 1 is a first center frequency centered between the maximum frequency and the minimum frequency of the first frequency band, wherein ν 2 is a second center frequency centered between the maximum frequency and the minimum frequency of the second frequency band, and wherein εr is the dielectric permittivity of the medium in which the first isolator lies, the medium being a dielectric support or air.

11. The RF device according to claim 9 , wherein the second branch of the first isolator has a predefined length that is substantially equal to one quarter of the first wavelength λ A .

12. The RF device according to claim 4 , wherein the first branch of the first isolator has a width that is predefined so that the characteristic impedance of said first branch is substantially equal to the characteristic impedance of one antenna selected from the first and second antennas, the second branch of the first isolator has a width that is predefined so that the characteristic impedance of said second branch is substantially equal to the characteristic impedance of the antenna selected from the first and second antennas.

13. The RF device according to claim 4 , wherein the first branch of the first isolator has a width that is predefined so that the characteristic impedance of said first branch lies substantially in the range 75Ω to 120Ω, the second branch of the first isolator has a width that is predefined so that the characteristic impedance of said second branch lies substantially in the range 75Ω to 120 Ω.

14. The RF device according to claim 1 , wherein the first isolator has three branches that are all electrically conductive and that are arranged in such a manner that said first isolator is Y-shaped.

15. The RF device according to claim 1 , wherein the second isolator has a single electrically conductive branch, said isolator thus having a shape that is longitudinal.

16. The RF device according to claim 1 , comprising a third antenna extending in a second plane, wherein the second isolator also is arranged to reduce second coupling by electromagnetic radiation between the third antenna and the particular antenna over a particular frequency band in which the particular antenna operates and over a third frequency band in which the third antenna operates.

17. The RF device according to claim 1 , wherein the second isolator is arranged to reduce the second coupling by electromagnetic radiation to a greater extent in the particular frequency band, the single branch of the second isolator has a predefined length that is substantially equal to half a second wavelength λ B , the second wavelength λ B being such that:

λ

B

=

c

v

#

×

ε

⁢

r

wherein ν # is a particular center frequency centered between the maximum frequency and the minimum frequency of the particular frequency band, and wherein εr is the dielectric permittivity of the medium in which the second isolator lies, the medium being a dielectric support or air.

18. The RF device according to claim 15 , wherein the second isolator is arranged to reduce the second coupling by electromagnetic radiation in equal manner in the particular frequency band and in the third frequency band, the single branch of the second isolator has a predefined length that is substantially equal to half a second wavelength λ B , the second wavelength λ B being such that:

λ

B

=

c

v

#

+

v

3

2

×

ε

⁢

r

wherein ν # is a particular center frequency centered between the maximum frequency and the minimum frequency of the particular frequency band, wherein ν 3 is a third center frequency centered between the maximum frequency and the minimum frequency of the third frequency band, and wherein εr is the dielectric permittivity of the medium in which the second isolator lies, the medium being a dielectric support or air.

19. The RF device according to claim 15 , wherein the branch of the second isolator has a width that is predefined so that the characteristic impedance of said branch is substantially equal to the characteristic impedance of an antenna selected from the particular antenna and the third antenna.

20. The RF device according to claim 15 , wherein the branch of the first isolator has a width that is predefined so that the characteristic impedance of said branch lies substantially in the range 75Ω to 120 Ω.

21. The RF device according to claim 16 , wherein the second isolator is situated in the proximity of an intersection between the first and second planes.

22. The RF device according to claim 21 , wherein the second isolator is positioned in an intersecting plane that intersects the first and second planes.

23. The RF device according to claim 21 , wherein the second isolator forming a rounded corner between the first and second planes.

24. The RF device according to claim 16 , wherein the first and second planes being perpendicular.

25. The RF device according to claim 16 , comprising a second antenna set comprising the third antenna and a fourth antenna, wherein the second antenna set being similar to the first antenna set, and also including a third isolator similar to the first isolator and positioned between the third and fourth antennas.

26. The RF device according to claim 25 , comprising a support having four faces comprising two mutually parallel first faces and two mutually parallel second faces, two first antenna sets each positioned on a distinct first face, and two second antenna sets each positioned on a distinct second face, wherein the RF device further comprising two first isolators each positioned between the first and second antennas of a distinct first antenna set, two third isolators each positioned between a third antenna and a fourth antenna of a distinct second antenna set, and four second isolators each positioned in a distinct corner of the support.

27. A MIMO system including the RF device according to claim 25 together with an RF transmitter and an RF receiver both connected to the first and second antenna sets of said RF device.

28. Electronic equipment including a MIMO system according to claim 27 .

29. Electronic equipment according to claim 28 , wherein the electronic equipment is a residential gateway.