Apparatus and methods for reducing mutual couplings in an antenna array

• US 10,135,133 B2
• Filed: 05/24/2017
• Issued: 11/20/2018
• Est. Priority Date: 05/26/2016
• Status: Active Grant

• Current Assignee: Chinese University of Hong Kong
• Original Assignee: Chinese University of Hong Kong
• Inventors: Wu, Ke-Li, Wei, Changning, Mei, Xide
• Primary Examiner(s): Mancuso, Huedung
• Application Number:
  US15/603,758
• Publication Number:
  US 20170346179A1
• Time in Patent Office: 545 Days
• Field of Search: 343842
• CPC Class Codes: H01Q 1/523 between antennas of an array
• CPC Class Codes: H01Q 15/0013 said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
• CPC Class Codes: H01Q 15/006 Selective devices having photonic band gap materials or materials of which the material properties are frequency dependent, e.g. perforated substrates, high-impedance surfaces
• CPC Class Codes: H01Q 19/028 for reducing the cross polarisation
• CPC Class Codes: H01Q 21/062 using dipole aerials; H01Q21/067, H01Q21/068 take precedence
• CPC Class Codes: H01Q 21/065 Patch antenna array
• CPC Class Codes: H01Q 21/22 Antenna units of the array energised non-uniformly in amplitude or phase, e.g. tapered array or binomial array
• CPC Class Codes: H01Q 25/001 Crossed polarisation dual antennas orthomode horns H01Q13/0258; cross-polarised rear feeds H01Q19/136; orthomode transducers H01P1/161
• CPC Class Codes: H01Q 9/0414 in a stacked or folded configuration
• CPC Class Codes: H04B 5/75 for isolation purposes
• CPC Class Codes: H04B 7/0413 MIMO systems

Abstract

A device is presented for improving radio frequency (RF) and microwave array antenna performance. The device sits in the near field, the reactive region, of the antenna array with a pattern of electrically isolated rectangular, cross-shaped, ell, and/or similarly-shaped patches of flat metal or other conductor in a flat plane. The patches are segmented into smaller shapes no greater than 0.3 of a shortest wavelength of the nominal operating range of the antenna and/or the height of the plane is greater than 0.25 and/or less than 0.4 of the center frequency'"'"'s wavelength. Mutual coupling S-parameters between neighboring elements are either simulated or measured, and the patch sizes or height are designed such that |S₂₁^Refl| is in a range of |S₂₁^Array|±20% of |S₂₁^Array|; and Phase(S₂₁^Refl) is in a range of Phase(S₂₁^Array)+180±30 degrees, where S₂₁^Array is an S-parameter between antenna two neighboring antenna elements measured or simulated without the device, where S₂₁^ADS is the same with the device, and S₂₁^Refl=S₂₁^ADS−S₂₁^Array.

Claims

1. A near-field apparatus for reducing mutual couplings between antenna elements in an antenna array, the antenna array having a nominal operating range of frequencies and associated wavelengths, the apparatus comprising:

a plurality of electrically conductive patches in a common plane configured to be supported above the antenna array, each electrically conductive patch being isolated from other patches and having a width of less than 50% of an underlying antenna element and a longest dimension no greater than 0.3 of a shortest wavelength of the nominal operating range; and

a standoff structure configured to hold the common plane of electrically conductive patches parallel to and at a height from a ground plane of the antenna array,

wherein at least one electrically conductive patch of the plurality of electrically conductive patches is sized to diffract a portion of an electromagnetic wave from an underlying antenna element to a neighboring antenna element such that a mutual coupling s-parameter between the underlying antenna element and the neighboring antenna element measured or simulated i) without the electrically conductive patches, S₂₁^Array, and ii) with the electrically conductive patches, S₂₁^ADS, with a difference defined as S₂₁^Refl=S₂₁^ADS−

S₂₁^Array, meets the following criteria;

|S₂₁^Refl| is in a range of |S₂₁^Array|±

20% of |S₂₁^Array|; and

Phase(S₂₁^Refl) is in a range of Phase(S₂₁^Array)+180±

30 degrees.

2. The apparatus of claim 1 wherein the height or a dimension of each electrically conductive patch is selected to minimize a difference between |S₂₁^Refl| and |S₂₁^Array|.

3. The apparatus of claim 1 wherein the height or a dimension of each electrically conductive patch is selected to minimize a difference between Phase(S₂₁^Refl) and Phase(S₂₁^Array)+180 degrees.

4. The apparatus of claim 1 wherein the height of the common plane of electrically conductive patches over the ground plane of the antenna array is between 0.25 λ

c and 0.4 λ

c, wherein λ

c is an electromagnetic wavelength corresponding to a center frequency of the antenna array.

5. The apparatus of claim 1 further comprising:

a dielectric substrate upon which the plurality of electrically conductive patches are formed.

6. The apparatus of claim 1 wherein the plurality of electrically conductive patches includes shapes having right angles and an even number of parallel sides is selected from the group consisting of a rectangle, a plus, a cross, a tee, an I, a #, an ell, a U, and a curved rectangle.

7. The apparatus of claim 1 wherein a subset of the plurality of right-angled, electrically conductive patches forms a larger, symmetric shape selected from the group consisting of a segmented rectangle, a segmented plus, a segmented frame, and a segmented ring.

8. The apparatus of claim 1 wherein each electrically conductive patch is centered over an underlying antenna element.

9. The apparatus of claim 1 wherein each electrically conductive patch is centered between two underlying antenna elements.

10. The apparatus of claim 1 further comprising:

the antenna array.

11. The apparatus of claim 10 wherein the antenna array is selected from the group consisting of a linear patch antenna array, a dual polarized linear dipole antenna array, and a patch or quadrifilar helix circularly polarized antenna array.

12. The apparatus of claim 1 wherein the plurality of electrically conductive patches is a first plurality of patches, the apparatus further comprising:

a second plurality of electrically conductive patches in the common plane, each of the second plurality of electrically conductive patches having an even number of sides, right angles at each edge, a width of less than 50% of an underlying antenna element, and a longest dimension no greater than 0.3 of a shortest wavelength of the nominal operating range,

wherein at least one electrically conductive patch of the second plurality of electrically conductive patches is sized to diffract a portion of an electromagnetic wave from an underlying antenna to a cross polarized neighboring antenna element.

13. The apparatus of claim 1, wherein the plurality of electrically conductive patches form a non-periodic or asymmetrical pattern.

24. The apparatus of claim 10 wherein the antenna array is selected from the group consisting of a linear patch antenna array, a dual polarized linear dipole antenna array, and a patch or quadrifilar helix circularly polarized antenna array.

14. A near-field apparatus for reducing mutual couplings between antenna elements in an antenna array, the antenna array having a nominal operating range of frequencies and associated wavelengths, the apparatus comprising:

a plurality of electrically conductive patches in a common plane configured to be supported above the antenna array, each electrically conductive patch being isolated from other patches; and

a standoff structure configured to hold the common plane of electrically conductive patches parallel to and at a height above a ground plane of the antenna array, wherein the height of the common plane of electrically conductive patches over the ground plane of the antenna array is between 0.25 λ

c and 0.4 λ

c, wherein λ

c is an electromagnetic wavelength corresponding to a center frequency of the antenna array,

wherein at least one electrically conductive patch of the plurality of electrically conductive patches is sized to diffract a portion of an electromagnetic wave from an underlying antenna element to a neighboring antenna element such that a mutual coupling s-parameter between the underlying antenna element and the neighboring antenna element measured or simulated i) without the electrically conductive patches, S₂₁^Array, and ii) with the electrically conductive patches, S₂₁^ADS, with a difference defined as S₂₁^Refl=S₂₁^ADS−

S₂₁^Array, meets the following criteria;

|S₂₁^Refl| is in a range of |S₂₁^Array|±

20% of |S₂₁^Array|; and

Phase(S₂₁^Refl) is in a range of Phase(S₂₁^Array)+180±

30 degrees.

15. The apparatus of claim 14 wherein the height or a dimension of each electrically conductive patch is selected to minimize a difference between |S₂₁^Refl| and |S₂₁^Array|.

16. The apparatus of claim 14 wherein the height or a dimension of each electrically conductive patch is selected to minimize a difference between Phase(S₂₁^Refl) and Phase(S₂₁^Array)+180 degrees.

17. The apparatus of claim 14 wherein each electrically conductive patch has a width of less than 50% of an underlying antenna element and a longest dimension no greater than 0.3 of a shortest wavelength of the nominal operating range.

18. The apparatus of claim 14 further comprising:

a dielectric substrate upon which the plurality of electrically conductive patches are formed.

19. The apparatus of claim 14 wherein the plurality of electrically conductive patches includes shapes having right angles and an even number of parallel sides is selected from the group consisting of a square, a rectangle, a plus, a cross, an uppercase T, an I, a #, an L, a U, and a curved rectangle.

20. The apparatus of claim 14 wherein a subset of the plurality of right-angled, electrically conductive patches forms a larger, symmetric shape selected from the group consisting of a segmented square, a segmented rectangle, a segmented plus, a segmented frame, and a segmented ring.

21. The apparatus of claim 14 wherein each electrically conductive patch is centered over an underlying antenna element.

22. The apparatus of claim 14 wherein each electrically conductive patch is centered between two underlying antenna elements.

23. The apparatus of claim 14 further comprising:

the antenna array.

25. The apparatus of claim 14 wherein the plurality of electrically conductive patches is a first plurality of patches, the apparatus further comprising:

a second plurality of electrically conductive patches in the common plane, each of the second plurality of electrically conductive patches having an even number of sides, right angles at each edge, a width of less than 50% of an underlying antenna element, and a longest dimension no greater than 0.3 of a shortest wavelength of the nominal operating range,

wherein at least one electrically conductive patch of the second plurality of electrically conductive patches is sized to diffract a portion of an electromagnetic wave from an underlying antenna to a cross polarized neighboring antenna element.

26. The apparatus of claim 14, wherein the plurality of electrically conductive patches form a non-periodic or asymmetrical pattern.

27. A method for reducing mutual couplings of antenna elements in an antenna array, the antenna array having a nominal operating range of frequencies and associated wavelengths, the method comprising:

providing a plurality of electrically conductive patches in a common plane configured to be supported above the antenna array, each electrically conductive patch being isolated from other patches;

supporting the common plane of electrically conductive patches parallel to and at a height above a ground plane of the antenna array; and

diffracting, using the plurality of electrically conductive patches, a portion of an electromagnetic wave from an underlying antenna element to a neighboring antenna element such that a mutual coupling s-parameter between the underlying antenna element and the neighboring antenna element measured or simulated i) without the electrically conductive patches, S₂₁^Array, and ii) with the electrically conductive patches, S₂₁^ADS, with a difference defined as S₂₁^Refl=S₂₁^ADS−

S₂₁^Array, meets the following criteria;

|S₂₁^Refl| is in a range of |S₂₁^Array|±

20% of |S₂₁^Array|; and

Phase(S₂₁^Refl) is in a range of Phase(S₂₁^Array)+180±

30 degrees.

28. The method of claim 27 wherein the height or a dimension of each electrically conductive patch is selected to minimize a difference between |S₂₁^Refl| and |S₂₁^Array|.

29. The method of claim 27 wherein the height or a dimension of each electrically conductive patch is selected to minimize a difference between Phase(S₂₁^Refl) and Phase(S₂₁^Array)+180 degrees.

30. The method of claim 27 wherein each electrically conductive patch has a width of less than 50% of an underlying antenna element and a longest dimension no greater than 0.3 of a shortest wavelength of the nominal operating range.

31. The method of claim 27 wherein the height of the common plane of electrically conductive patches over the ground plane of the antenna array is between 0.25 λ

c and 0.4 λ

c, wherein λ

c is an electromagnetic wavelength corresponding to a center frequency of the antenna array.