Low-profile and high-gain modulated metasurface antennas from gigahertz to terahertz range frequencies
A modulated MTS antenna including a metasurface fabricated from metallized cylinders on a ground plane. The antenna structure can be designed to operate in the Gigahertz or Terahertz frequency band and to have a well defined directivity. The MTS antenna may be micromachined out of a silicon wafer using deep reactive ion etching (DRIE).
1. An antenna structure, comprising:
an array of at least 1000 pillars formed on a substrate and defining unit cells, wherein:
a height of each pillar is less than 10 times a radius of the pillar, and
the height and/or orientation of the pillars varies periodically across the array with a period of at least 200 micrometers so as to realize a surface reactance at each of a plurality of the unit cells across the array needed to transform a surface-wave (SW) propagating through the array into a leaky wave (LW) that radiates from the array in a desired direction; and
a circular feed waveguide coupled to the array so as to input a transverse magnetic mode exciting the SW.
2. The antenna structure of claim 1 , wherein the pillars comprise cylinders having a circular, square, or elliptical cross-section.
3. The antenna structure of claim 1 , wherein the antenna structure does not include partially reflecting surfaces and the heights and/or the orientations vary periodically across the array so that the surface reactance of the substrate is modulated across the array and the leaky wave radiates as a beam of electromagnetic radiation.
4. The antenna structure of claim 3 , wherein the heights and/or orientations vary periodically so that a power in the beam at an angle of more than 10 degrees, from a center direction of propagation of the beam, is reduced by a factor of at least 10.
5. The antenna structure of claim 1 , wherein the pillars and the substrate comprise a semiconductor.
6. The antenna structure of claim 4 , wherein the substrate and the pillars comprise silicon.
7. The antenna structure of claim 6 , wherein the pillars comprise silicon coated with metal.
8. The antenna structure of claim 5 , wherein the pillars are etched onto a surface of the substrate.
9. The antenna structure of claim 1 , wherein the substrate and the pillars consist essentially of metal.
10. The antenna structure of claim 1 , wherein the pillars have:
a height up to 2000 micrometers,
a diameter in a range of 1 micrometer-1000 micrometers, and
a spacing between pillars in a range of 50 micrometers to 2000 micrometers or in a range such that the leaky wave radiating from the array has a frequency in a range of 2 GHz-1 THz.
11. The antenna structure of claim 10 , wherein the array has a length and width in a range of 1 mm-1 meter.
12. The antenna structure of claim 1 , wherein the heights and one or more spacings of the pillars are such that the leaky wave radiating from the array has a frequency in a range of 2 GHz-1 THz.
13. The antenna structure of claim 1 , wherein the heights and spacing of the pillars are such that the leaky wave radiating from the array has a submillimeter or millimeter wavelength.
14. The antenna structure of claim 1 , wherein the circular feed waveguide is on an aperture plane of the substrate and does not protrude a plane defined by a base of the pillars so that a z coordinate of an aperture of the feed waveguide and the base of pillars are the same.
15. A method of fabricating an antenna structure, comprising:
etching or machining an array of at least 1000 pillars onto a substrate, wherein:
the pillars define a plurality of unit cells across the array,
a height of each pillar is less than 10 times a radius of the pillar, and
a height of the pillars varies periodically across the array with a period of at least 200 micrometers, so as to realize a surface reactance at each of the plurality of the unit cells needed to transform a surface-wave (SW) propagating on the substrate into a leaky wave that radiates from the array in a desired direction; and
coupling a circular feed waveguide to the array so as to input a transverse magnetic mode exciting the SW.
16. The method of claim 15 , wherein the substrate comprises silicon.
17. The method of claim 15 , wherein the etching comprises deep reactive ion etching.
18. The method of claim 15 , wherein the circular feed waveguide comprises a hole in the substrate and metal deposited on an inner surface of the hole.
19. The antenna structure of claim 3 , wherein:
the LW comprises a (−1) indexed Floquet mode,
the heights vary periodically across the array so that the surface reactance is modulated and the (−1) indexed Floquet mode is a radiative mode.
20. The antenna structure of claim 1 , further comprising the circular feed waveguide symmetrically fed by two rectangular waveguides.
21. The antenna structure of claim 1 , wherein the pillars have an elliptical cross-section and an orientation of the pillars varies so as to further modulate the surface reactance.