Electromagnetic-field polarization twister
View Patent ↗An apparatus and method to twist the field polarization of an electromagnetic wave over a desired frequency band is described. In one embodiment, a transmission twister rotates the polarization of a linearly-polarized incident field to produce a transmitted field. In one embodiment, the transmission twister includes a resonant polarization-twisting array between two linearly-polarized arrays. In one embodiment, the transmission twister rotates the polarization by 90 degrees. In one embodiment, the transmission twister produces low reflection of a desired incident polarization. In one embodiment, the transmission twister has a transmission coefficient (with respect to the desired incident field polarization and a correspondingly rotated transmitted field polarization) close to unity.
1. An electromagnetic field polarization twister comprising:
a first frequency selective surface comprising first resonant linearly-polarized elements;
a second frequency selective surface comprising resonant, polarization-twisting, elements; and
a third frequency selective surface comprising second resonant linearly-polarized elements, said first resonant linearly-polarized elements cross-polarized with respect to said second resonant linearly-polarized elements.
2. The electromagnetic field polarization twister of claim 1 , wherein said first resonant linearly-polarized elements comprise dipole elements.
3. The electromagnetic field polarization twister of claim 1 , wherein said first resonant linearly-polarized elements comprise slot elements.
4. The electromagnetic field polarization twister of claim 1 , wherein said first resonant linearly-polarized elements comprise dipole elements, and wherein said second resonant linearly-polarized elements comprise dipole elements.
5. The electromagnetic field polarization twister of claim 1 , wherein said polarization-twisting elements comprise dipoles loaded by dipoles.
6. An electromagnetic field polarization twister comprising:
a first frequency selective surface comprising elements that reflect electromagnetic fields having a first polarization and transmit electromagnetic fields having a second polarization;
a second frequency selective surface comprising elements that receive electromagnetic fields having said second polarization and scatter electromagnetic fields having said first polarization; and
a third frequency selective surface comprising elements that reflect electromagnetic fields having said second polarization and transmit electromagnetic fields having said first polarization.
7. The electromagnetic field polarization twister of claim 6 , wherein said first polarization is a first linear polarization and said second polarization is a second linear polarization.
8. The electromagnetic field polarization twister of claim 6 , wherein said first polarization is a first linear polarization and said second polarization is a second linear polarization orthogonal to said first linear polarization.
9. The electromagnetic field polarization twister of claim 6 , wherein said first frequency selective surface comprises dipole elements.
10. The electromagnetic field polarization twister of claim 6 , wherein said first frequency selective surface comprises slot elements.
11. The electromagnetic field polarization twister of claim 6 , wherein said first frequency selective surface comprises first dipole elements, and wherein said second frequency selective surface comprises second dipole elements.
12. The electromagnetic field polarization twister of claim 6 , wherein said second frequency selective surface comprises dipole elements with dipole loads.
13. The electromagnetic field polarization twister of claim 6 , wherein said first frequency selective surface comprises dipole elements and said third frequency selective surface comprises slot elements.
14. The electromagnetic field polarization twister of claim 6 , wherein said third frequency selective surface comprises non-resonant wire elements.
15. The electromagnetic field polarization twister of claim 6 , wherein said third frequency selective surface comprises non-resonant slot elements.
16. A method for converting a first electromagnetic wave having a first polarization into a second electromagnetic wave having a second polarization, comprising:
producing a scattered field having first components corresponding to said first polarization and second components corresponding to said second polarization, said scattered field produced in response to said first electromagnetic wave, said first electromagnetic wave propagating in a forward direction;
reflecting at least a portion of said second components that do not propagate in said forward direction; and
reflecting at least a portion of said first components that propagate in said forward direction.
17. An apparatus for converting a first electromagnetic wave having a first polarization into a second electromagnetic wave having a second polarization, comprising:
means for producing a scattered field having first components corresponding to said first polarization and second components corresponding to said second polarization, said scattered field produced in response to said first electromagnetic wave, said first electromagnetic wave propagating in a forward direction;
means for reflecting at least a portion of said second components that do not propagate in said forward direction; and
means for reflecting at least a portion of said first components that propagate in said forward direction.
18. A reflection twister comprising:
a frequency selective surface comprising resonant, polarization-twisting, elements; and
a ground plane disposed a distance behind said frequency selective surface.
19. The reflection twister of claim 18 , wherein said distance is approximately one-quarter wavelength at a desired frequency in a desired frequency band.
20. The electromagnetic field polarization twister of claim 18 , wherein said polarization-twisting elements comprise first dipoles loaded by second dipoles, said second dipoles orthogonal to said first dipoles.
21. An electromagnetic field polarization twister comprising:
a first frequency selective surface comprising first resonant elements that are orthogonal to a first polarization;
a second frequency selective surface comprising polarization-twisting, elements; and
a third frequency selective surface comprising second resonant elements that are orthogonal to a second polarization, said second frequency selective surface disposed between said first frequency selective surface and said third frequency selective surface, said first frequency selective surface and said second frequency selective surface separated by a first distance, said second frequency selective surface and said third frequency selective surface separated by a second distance.
22. The electromagnetic field polarization twister of claim 21 , wherein said first polarization is orthogonal to said second polarization.
23. The electromagnetic field polarization twister of claim 21 , wherein said first polarization is linear and said second polarization is linear.
24. The electromagnetic field polarization twister of claim 21 , wherein said first distance is at least approximately equal to said second distance.
25. The electromagnetic field polarization twister of claim 21 , wherein said first resonant elements comprise first dipole elements, and wherein said second resonant elements comprise second dipole elements.
26. The electromagnetic field polarization twister of claim 21 , wherein said polarization-twisting elements comprise dipoles loaded by dipoles.
27. The electromagnetic field polarization twister of claim 21 , further comprising a dielectric spacer between said first frequency selective surface and said second frequency selective surface.
28. The electromagnetic field polarization twister of claim 21 , further comprising a dielectric spacer between said third frequency selective surface and said second frequency selective surface.
29. The electromagnetic field polarization twister of claim 21 , wherein said first resonant elements comprise first slot elements, and wherein said second resonant elements comprise second slot elements.