Decoherence plate for use in a communications system

• US 20050237259A1
• Filed: 04/11/2005
• Published: 10/27/2005
• Est. Priority Date: 07/03/2003
• Status: Active Grant

• Current Assignee: Deere & Company
• Original Assignee: Navcom Technology, Inc. (Deere & Company)
• Inventors: Stephens, Scott Adam
• Granted Patent: US 7,450,080 B2
• Time in Patent Office: Days
• US Class Current: 343/841
• CPC Class Codes: H01Q 1/521 reducing the coupling between adjacent antennas

Abstract

A decoherence plate provides reduced field coupling or improved isolation between two or more antennas. An antenna module includes a first antenna, a second antenna and a decoherence plate having a surface. The first antenna transmits one or more electromagnetic signals. The surface of the decoherence plate is positioned in a plane perpendicular to a line connecting the first antenna and the second antenna. For each first path from the first antenna to the plane to the second antenna, in a plurality of paths having a range of path lengths, there is a corresponding second path, from the first antenna to the plane to the second antenna, that is substantially 180° out of phase for a respective wavelength in the one or more electromagnetic signals transmitted by the first antenna. In this way, the decoherence plate reduces the field coupling between the first antenna and the second antenna.

Claims

1. An antenna module, comprising:

a first antenna;

a second antenna; and

a decoherence plate having a surface positioned substantially in a plane that is substantially perpendicular to a line connecting the first antenna and the second antenna, wherein for each first path from the first antenna to the plane to the second antenna in a plurality of paths having a predefined range of path lengths there is a corresponding second path, from the first antenna to the plane to the second antenna, that is substantially 180°

out of phase with the first path for a respective wavelength in one or more electromagnetic signals transmitted by the first antenna, thereby reducing a field coupling between the first antenna and the second antenna.

2. The antenna module of claim 1, wherein the surface of the decoherence plate is intercepted by the line connecting the first antenna and the second antenna.

3. The antenna module of claim 1, wherein the field coupling between the first antenna and the second antenna at the respective wavelength is at least 30 dB less than a field coupling corresponding to free space path loss between the first antenna and the second antenna.

4. The antenna module of claim 1, wherein the field coupling between the first antenna and the second antenna at the respective wavelength is between 40 and 70 dB less than a field coupling corresponding to free space path loss between the first antenna and the second antenna.

5. The antenna module of claim 1, wherein the decoherence plate includes a metal layer.

6. The antenna module of claim 5, wherein the metal layer is thicker than a skin depth of the metal, the skin depth corresponding to a minimum frequency of the one or more electromagnetic signals transmitted by the first antenna.

7. The antenna module of claim 5, wherein the metal layer is patterned into a predetermined shape.

8. The antenna module of claim 7, wherein the predetermined shape has a maximum lateral extent that is no larger than a distance separating a dipole moment of the first antenna from a dipole moment of the second antenna.

9. The antenna module of claim 7, wherein the predetermined shape has a maximum lateral extent that is no larger than half a distance separating a dipole moment of the first antenna from a dipole moment of the second antenna.

10. The antenna module of claim 5, wherein the metal layer is selected from the group consisting of copper, aluminum, gold, silver and their related alloys and oxides.

11. The antenna module of claim 5, the decoherence plate further including a substrate, wherein the metal layer is deposited in a layer located above a surface of the substrate.

12. The antenna module of claim 11, wherein the substrate is a circuit board.

13. A communications system, comprising:

a device configurable to transmit and receive one or more electromagnetic signals; and

an antenna module, including;

a first antenna, wherein the first antenna transmits the one or more electromagnetic signals;

a second antenna; and

a decoherence plate having a surface positioned substantially in a plane that is substantially perpendicular to a line connecting the first antenna and the second antenna, wherein for each first path from the first antenna to the plane to the second antenna in a plurality of paths having a predefined range of path lengths there is a corresponding second path, from the first antenna to the plane to the second antenna, that is substantially 180°

out of phase with the first path for a respective wavelength in the one or more electromagnetic signals, thereby reducing a field coupling between the first antenna and the second antenna.

14. The communications system of claim 13, wherein the surface of the decoherence plate is intercepted by the line connecting the first antenna and the second antenna.

15. The communications system of claim 13, wherein the field coupling between the first antenna and the second antenna at the respective wavelength is at least 30 dB less than a field coupling corresponding to free space path loss between the first antenna and the second antenna.

16. The communications system of claim 13, wherein the field coupling between the first antenna and the second antenna at the respective wavelength is between 40 and 70 dB less than a field coupling corresponding to free space path loss between the first antenna and the second antenna.

17. The communications system of claim 13, wherein the decoherence plate includes a metal layer.

18. The communications system of claim 17, wherein the metal layer is thicker than a skin depth of the metal, the skin depth corresponding to a minimum frequency of the one or more electromagnetic signals transmitted by the first antenna.

19. The communications system of claim 17, wherein the metal layer is patterned into a predetermined shape.

20. The communications system of claim 19, wherein the predetermined shape has a maximum lateral extent that is no larger than a distance separating a dipole moment of the first antenna from a dipole moment of the second antenna.

21. The communications system of claim 19, wherein the predetermined shape has a maximum lateral extent that is no larger than half a distance separating a dipole moment of the first antenna from a dipole moment of the second antenna.

22. The communications system of claim 17, wherein the metal layer is selected from the group consisting of copper, aluminum, gold, silver and their related alloys and oxides.

23. The communications system of claim 17, the decoherence plate further including a substrate, wherein the metal layer is deposited in a layer located above a surface of the substrate.

24. The communications system of claim 23, wherein the substrate is a circuit board.

25. A method of determining a shape of a decoherence plate for a respective geometry having a first antenna and a second antenna, comprising:

selecting a shape of the decoherence plate in a plane substantially perpendicular to a line connecting the first antenna and the second antenna;

determining a field coupling between the first antenna and the second antenna for a respective wavelength of an electromagnetic signal;

selecting a next shape for the decoherence plate in accordance with a result from the determining; and

repeating the determining and selecting a next shape until the field coupling between the first antenna and the second antenna is less than a threshold.

26. The method of claim 25, wherein the determining includes:

summing a Kirchoff diffraction kernel in the plane of the decoherence plate at least over a surface area comprising the shape of the decoherence plate, wherein the Kirchoff diffraction kernel includes a product of a weighting component, a spherical wave Green'"'"'s function and an obliquity component that includes a near-field expression.

27. The method of claim 26, wherein the summing is performed in the plane of the decoherence plate over a surface area extending beyond that defined by the shape of the decoherence plate.

28. The method of claim 26, wherein the weighting component includes a real portion and an imaginary portion.

29. The method of claim 25, wherein the determining is performed for two or more wavelengths in the electromagnetic signal.

30. The method of claim 25, wherein the threshold is at least 30 dB less than a field coupling corresponding to free space path loss between the first antenna and the second antenna

31. The method of claim 25, wherein the threshold is between 40 and 70 dB less than a field coupling corresponding to free space path loss between the first antenna and the second antenna.

32. The method of claim 25, wherein the decoherence plate includes two or more separate segments.