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US-12620721-B2 - Low-profile, low-observable, wide-band, azimuthally-omni-directional monopole antenna

US12620721B2US 12620721 B2US12620721 B2US 12620721B2US-12620721-B2

Abstract

A low-profile antenna comprising a ground plane, a center hub, a plurality of arms, and a conductive ring. The center is hub disposed above the ground plane. The plurality of arms extend radially from the center hub. Each arm of the plurality of arms is conductive, has a uniform thickness, and has an upper and a lower surface. Each lower surface has an exponential taper that flares away from the ground plane such that any given arm and a corresponding image of the given arm below the ground plane form a tapered-slot antenna element. The plurality of arms are shaped such that the upper surfaces conform to contours of a bowl shape. The conductive ring is disposed parallel to the ground plane and is electrically connected to distal ends of each of the plurality of arms at a rim of the bowl shape.

Inventors

  • David Walker Brock

Assignees

  • THE UNITED STATES OF AMERICA, AS REPRESENTED BY THE SECRETARY OF THE NAVY

Dates

Publication Date
20260505
Application Date
20240507

Claims (20)

  1. 1 . A low-profile antenna comprising: a ground plane; a center hub disposed above the ground plane; a plurality of arms extending radially from the center hub, wherein each arm of the plurality of arms is conductive, has a uniform thickness, and has an upper and a lower surface, wherein each lower surface has an exponential taper that flares away from the ground plane such that any given arm of the plurality of arms forms half of a tapered-slot antenna element, wherein the plurality of arms are shaped such that the upper surfaces conform to contours of a bowl shape; and a conductive ring disposed parallel to the ground plane and electrically connected to distal ends of each of the plurality of arms at a rim of the bowl shape.
  2. 2 . The low-profile antenna of claim 1 , further comprising a center absorber made of RF-absorbing material and disposed to substantially fill the bowl shape without touching the conductive ring.
  3. 3 . The low-profile antenna of claim 1 , wherein the plurality of arms consists of seven arms.
  4. 4 . The low-profile antenna of claim 1 , further comprising a conductive feed cone having a base that is connected to a bottom of the center hub and having a vertex that is connected to a center conductor of a coaxial feed line such that the plurality of arms are electrically connected in parallel to the center conductor, wherein the vertex is separated from the ground plane by a distance D.
  5. 5 . The low-profile antenna of claim 4 , wherein the distance D is no greater than 0.127 mm and a height H from the ground plane to a top surface of the ring is no greater than 33.5 mm.
  6. 6 . The low-profile antenna of claim 2 , wherein a top of the center absorber is separated from a bottom of the conductive ring by a distance of 2.54 mm.
  7. 7 . The low-profile antenna of claim 2 , further comprising interstitial absorbers made of RF-absorbing material that fill spaces between the plurality of arms without physically touching the plurality of arms.
  8. 8 . The low-profile antenna of claim 7 , wherein each interstitial absorber between two given arms further comprises an outer projection of RF-absorbing material that is equidistantly spaced between the two given arms, has a rectangular cross section and extends beyond the bowl shape and the given space.
  9. 9 . The low-profile antenna of claim 6 , wherein the ring has a thickness of 0.127 mm.
  10. 10 . The low-profile antenna of claim 1 , wherein the center hub, the plurality of arms, and the ring are made of metal-coated 3D-printed material.
  11. 11 . A low-profile antenna comprising: a ground plane; a plurality of arms equidistantly-spaced from each other and extending radially from a center axis, wherein proximal ends of the arms are electrically connected in parallel to a center hub, which is in turn connected to a feed line, wherein each arm of the plurality of arms is conductive, has a uniform thickness, and has an upper and a lower surface, wherein each lower surface substantially conforms to an exponential curve that flares away from the ground plane such that any given arm of the plurality of arms forms half of a tapered-slot antenna element, and wherein the upper surfaces of the arms conform to a contour of a bowl shape; and a conductive ring disposed parallel to the ground plane and electrically connected to distal ends of each of the plurality of arms, wherein the conductive ring is disposed above the bowl shape.
  12. 12 . The low-profile antenna of claim 11 , wherein the contour of the bowl shape is a surface of a first prolate ellipsoid dome defined by rotating an elliptical curve around the center axis.
  13. 13 . The low-profile antenna of claim 12 , further comprising a center absorber made of RF-absorbing material and disposed to substantially fill the first prolate ellipsoid dome without touching the conductive ring.
  14. 14 . The low-profile antenna of claim 13 , wherein the plurality of arms consists of seven arms.
  15. 15 . The low-profile antenna of claim 14 , further comprising seven interstitial absorbers made of the RF-absorbing material, wherein each interstitial absorber substantially fills a space between two given arms without physically touching the two given arms.
  16. 16 . The low-profile antenna of claim 15 , further comprising seven equidistantly-spaced outer projections made of the RF-absorbing material, wherein each outer projection protrudes from a corresponding interstitial absorber, has a rectangular cross section with a thickness that is double a thickness of each of the arms, and has an outer surface bounded by a second prolate ellipsoid dome that is larger than the first prolate ellipsoid dome.
  17. 17 . The low-profile antenna of claim 16 , wherein a distance from the ground plane to a feed line connection point is 0.127 mm, a distance between the ground plane and a top surface of the ring is 33.5 mm, the ring has a thickness of 0.127 mm, and each arm has a thickness of 4.67 mm and an impedance of 350 ohms.
  18. 18 . The low-profile antenna of claim 17 , further comprising a non-conductive housing configured to cover and support the plurality of arms, the ring, the center absorber, the interstitial absorbers, and the outer projections over the ground plane.
  19. 19 . The low-profile antenna of claim 18 , wherein the RF-absorbing material is made of dielectric foam.
  20. 20 . The low-profile antenna of claim 19 , further comprising a feed cone, a base of which is connected to each of the seven arms so as to yield a combined impedance of 50 ohms, wherein a vertex of the feed cone is connected to a center conductor of a coaxial cable, and wherein the ground plane is connected to an outer conductor of the coaxial cable.

Description

FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT The United States Government has ownership rights in the invention claimed herein. Licensing and technical inquiries may be directed to the Office of Research and Technical Applications, Naval Information Warfare Center Pacific, Code 72110, San Diego, CA, 92152; voice (619) 553-5118; NIWC_Pacific_T2@us.navy.mil. Reference Navy Case Number 210272. BACKGROUND OF THE INVENTION The invention claimed herein relates to radio frequency (RF) antennas. Large antennas, while effective/efficient in many instances, can be unsightly and result in unwanted reflections of incident RF radiation. There is a need for a low-profile antenna that can operate over a wide bandwidth. SUMMARY Disclosed herein is a low-profile antenna comprising a ground plane, a center hub, a plurality of arms, and a conductive ring. The center is hub disposed above the ground plane. The plurality of arms extend radially from the center hub. Each arm of the plurality of arms is conductive, has a uniform thickness, and has an upper and a lower surface. Each lower surface has an exponential taper that flares away from the ground plane such that any given arm and a corresponding image of the given arm below the ground plane form a tapered-slot antenna element. The plurality of arms are shaped such that the upper surfaces conform to contours of a bowl shape. The conductive ring is disposed parallel to the ground plane and is electrically connected to distal ends of each of the plurality of arms at a rim of the bowl shape. Another embodiment of the low profile antenna is disclosed herein as comprising a ground plane, a plurality of arms, and a conductive ring. The arms are equidistantly-spaced from each other and extend radially from a center axis. Proximal ends of the arms are electrically connected in parallel to a center hub, which is in turn connected to a feed line. Each arm of the plurality of arms is conductive, has a uniform thickness, and has an upper and a lower surface. Each lower surface substantially conforms to an exponential curve that flares away from the ground plane such that any given arm of the plurality of arms and a corresponding image of the given arm below the ground plane form a tapered-slot antenna element. The upper surfaces of the arms conform to a contour of a hypothetical bowl shape. The conductive ring is disposed parallel to the ground plane and is electrically connected to distal ends of each of the plurality of arms. The conductive ring represents a rim of the hypothetical bowl shape and a base of the hypothetical prolate ellipsoid dome. BRIEF DESCRIPTION OF THE DRAWINGS Throughout the several views, like elements are referenced using like references. The elements in the figures are not drawn to scale and some dimensions are exaggerated for clarity. FIGS. 1A and 1B are perspective-view illustrations of an embodiment of a low-profile antenna. FIG. 2 is a cross-sectional side-view of the embodiment of the low-profile antenna shown in FIGS. 1A and 1B. FIGS. 3A and 3B are partial cross-sectional views of the embodiment of the low-profile antenna shown in FIGS. 1A, 1B, and 2. FIG. 4 is a plot of points defining a profile of an embodiment of a conductive arm of a low-profile antenna. FIG. 5A is a cross-sectional, side-view of another embodiment of a low-profile antenna. FIG. 5B is a cross-sectional, side-view of RF-absorbing components of an embodiment of a low-profile antenna. FIGS. 6A and 6B are respectively top and bottom perspective views of the embodiment of the low-profile antenna shown in FIG. 5A. FIGS. 7A and 7B are perspective views of the embodiment of the low-profile antenna shown in FIGS. 5A, 6A, and 6B. FIG. 8 is a bottom-view illustration of the embodiment of the low-profile antenna shown in FIGS. 5A, 6A, and 6B. FIGS. 9A and 9B are respectively a cross-sectional, perspective view and a top view of another embodiment of a low-profile antenna. DETAILED DESCRIPTION OF EMBODIMENTS The disclosed antenna below may be described generally, as well as in terms of specific examples and/or specific embodiments. For instances where references are made to detailed examples and/or embodiments, it should be appreciated that any of the underlying principles described are not to be limited to a single embodiment, but may be expanded for use with any of the other methods and systems described herein as will be understood by one of ordinary skill in the art unless otherwise stated specifically. References in the present disclosure to “one embodiment,” “an embodiment,” or any variation thereof, means that a particular element, feature, structure, or characteristic described in connection with the embodiments is included in at least one embodiment. The appearances of the phrases “in one embodiment,” “in some embodiments,” and “in other embodiments” in various places in the present disclosure are not necessarily all referring to the same embodiment or the same set of embodiments. As used