Electromagnetic window

• US 20030034933A1
• Filed: 08/13/2002
• Published: 02/20/2003
• Est. Priority Date: 08/17/2001
• Status: Active Grant

• Current Assignee: Anafa-Electromagnetic Solutions Limited
• Original Assignee: Anafa-Electromagnetic Solutions Limited
• Inventors: Frenkel, Avraham
• Granted Patent: US 6,897,820 B2
• Time in Patent Office: Days
• US Class Current: 343/872
• 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 17/00 Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems

Abstract

A device substantially transparent to electromagnetic radiation of a certain frequency band is presented. The device comprises at least one dielectric structure of a predetermined thickness defined by the central frequency of the operational frequency band of the device, and comprises a predetermined substantially periodic inner pattern inside the dielectric structure composed of a two-dimensional array of substantially identical sub-resonant capacitive elements made of an electrically conducting material and capable of scattering said electromagnetic radiation arranged in a disconnected from each other spaced-apart relationship.

Claims

1. A device substantially transparent to electromagnetic radiation of a certain frequency band, the device comprising at least one dielectric structure of a predetermined thickness defined by the central frequency of said certain frequency band, and a predetermined substantially periodic pattern inside said at least one dielectric structure, the inner pattern being formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements, which are disconnected from each other and are made of an electrically conducting material capable of scattering the electromagnetic radiation.

2. The device according to claim 1, wherein the periodicity of said inner pattern is such that average density of the elements is approximately the same all along a patterned area.

3. The device according to claim 1, wherein dimensions of the radiation scattering elements and spaces between them are selected such that the scattering from said elements substantially compensates for reflection effects from dielectric discontinuities at and inside the device.

4. The device according to claim 1, wherein the array of said elements is positioned in a plane located at the middle of the dielectric structure parallel to planes defined by upper and lower surfaces of the dielectric structure.

5. The device according to claim 1, wherein the size of the electrically conductive element is such that the fundamental resonance frequency of the element is above said certain frequency band.

6. The device according to claim 1, wherein the thickness of the dielectric structure is such that the dielectric structure without the inner pattern has first and second reflection minima, the center of said certain frequency band of the device being approximately a mid point between said first and second reflection minima.

7. The device according to claim 1, wherein the dielectric structure comprises a single dielectric layer formed with said inner pattern.

8. The device according to claim 7, wherein the electrically conductive element has the size smaller than the half-wavelength of propagation of said electromagnetic radiation in said dielectric structure.

9. The device according to claim 7, wherein the thickness of the dielectric layer is about 0.75_λ

, wherein _λ

is the wavelength of propagation of said radiation in the dielectric layer.

10. The device according to claim 1, wherein said at least one structure is a substantially symmetrical structure formed by a stack of dielectric layers, wherein the central dielectric layer is formed with said inner pattern.

11. The device according to claim 10, wherein the dielectric layers are made of different dielectric materials characterized by different wavelengths of propagation of said electromagnetic radiation.

12. The device according to claim 11, wherein the electrically conductive element has the size smaller than the half of at least maximal wavelength of propagation of said electromagnetic radiation in said dielectric structure.

13. The device according to claim 11, wherein the thickness of the device is in the range from three quarters of the shortest wavelength and three quarters of the longest wavelength of radiation propagation in the different dielectric layers at the central frequency of said frequency band.

14. The device according to claim 1, wherein said elements are made of a metal-containing material.

15. The device according to claim 1, wherein said elements are formed by coating conductive elements with one or more dielectric layers.

16. The device according to claim 1, wherein said elements are formed by coating dielectric elements by at least one conducting layer.

17. The device according to claim 1, wherein said elements are formed by selective coating of through-holes or honeycomb cores.

18. The device according to claim 1, having a constant thickness all along the device.

19. The device according to claim 1, having a varying thickness all along the device.

20. The device according to claim 1, wherein said elements have circular or polygonal cross-section.

21. The device according to claim 20, wherein said elements are voluminous.

22. The device according to claim 1, and also comprising electrically conductive strips arranged in a spaced-apart parallel relationship on opposite surfaces of said at least one dielectric structure.

23. The device according to claim 1, and also comprising at least two layers made of a ferroelectric material at opposite sides of said at least one dielectric structure.

24. The device according to claim 23, wherein said ferroelectric layers are formed with electrically conductive strips arranged in a spaced-apart parallel relationship to be charged and grounded during an application of an electric field to the ferroelectric layers.

25. The device according to claim 1, capable of transmitting the electromagnetic radiation impinging thereon at an angle of incidence up to 60 degrees.

26. The device according to claim 1, and also comprising at least one additional dielectric structure with a predetermined substantially periodic inner pattern formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements made of an electrically conducting material and capable of scattering said electromagnetic radiation, and arranged in a disconnected from each other spaced-apart relationship, the at least two structures being located one above the other.

29. A radiation source for generating electromagnetic radiation of a certain frequency band, the radiation source comprising the device constructed according to claim 1, accommodated adjacent to an emitter of the electromagnetic radiation.

30. A frequency-selective multi-reflector device comprising a sub-reflector element substantially transparent for certain frequencies and totally reflective for other frequencies, wherein said sub-reflector is the device of claim 10.

27. A device substantially transparent to electromagnetic radiation of a certain frequency band, the device comprising at least one dielectric structure of a thickness of about 0.75_λ

, wherein _λ

is the wavelength of propagation of said radiation in the dielectric structure; and

a predetermined substantially periodic pattern inside said at least one dielectric structure, the inner pattern being formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements, which are disconnected from each other and are made of an electrically conducting material capable of scattering the electromagnetic radiation.

28. A device substantially transparent to electromagnetic radiation of a certain frequency band, the device comprising a dielectric layer of a thickness of about 0.75_λ

, wherein _λ

is the wavelength of propagation of said radiation in the dielectric layer, and a predetermined substantially periodic pattern inside said at least one dielectric structure, the inner pattern being formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements, which are disconnected from each other and are made of an electrically conducting material capable of scattering the electromagnetic radiation, each of the elements having the size smaller than the _λ

/2.

31. A radiation source for generating electromagnetic radiation of a certain frequency band, the radiation source comprising an emitter of the electromagnetic radiation, and a window device accommodated adjacent to said emitter and being substantially transparent with respect to said certain frequency band of the electromagnetic radiation, the window device comprising at least one dielectric structure of a predetermined thickness defined by the central frequency of said certain frequency band, and comprising a predetermined substantially periodic pattern inside said at least one dielectric structure, the inner pattern being formed by a two-dimensional array of spaced-apart substantially identical sub-resonant capacitive elements, which are disconnected from each other and are made of an electrically conducting material capable of scattering the electromagnetic radiation.

32. A controllable device for transmitting electromagnetic radiation of a certain frequency band, the device comprising:

at least one dielectric structure of a predetermined thickness defined by the central frequency of said certain frequency band;

an inner pattern formed by inclusions inside said at least one dielectric structure, the pattern being in the form of a two-dimensional array of substantially identical electrically conductive sub-resonant capacitive elements capable of scattering said electromagnetic radiation, said elements being arranged in a disconnected from each other spaced-apart relationship; and

at least two ferroelectric layers located at opposite sides of said at least one dielectric structure, the application of an electric field to said ferroelectric layer effecting a change in a dielectric constant of said ferroelectric layer.

33. A method for constructing the above-described window device to be substantially transparent to electromagnetic radiation of the certain frequency band, the method comprising:

fabricating at least one dielectric structure made from at least one dielectric material of a predetermined dielectric constant and having a predetermined thickness defined by the central frequency of the window device and, fabricating an inner pattern inside said at least one dielectric structure in the form of a two-dimensional array of substantially identical sub-resonant capacitive electrically conductive scattering elements arranged in a disconnected spaced-apart relationship, the dimensions of the electrically conductive scattering elements and the spaces between them being selected so as to ensure that the scattering from said elements compensates for reflection effects from the dielectric discontinuities.