WO2019067474A1

WO2019067474A1 - Low profile beam steering antenna with integrated divergent lens

Info

Publication number: WO2019067474A1
Application number: PCT/US2018/052725
Authority: WO
Inventors: James Allan WILKERSON JR.; Scott Robert KEMPSHALL; Shawn Kalen O'BRIEN
Original assignee: Trak Microwave Corporation
Priority date: 2017-09-26
Filing date: 2018-09-25
Publication date: 2019-04-04

Abstract

Methods and systems for transmitting or receiving communication signals. The system includes a planar antenna array located on a surface and configured to transmit or receive communication signals. The system also includes a divergent lens located above the antenna array and surrounding the antenna array, the divergent lens having a base portion on or near the surface and a top portion located above the antenna array, a thickness of the divergent lens being greater at the base portion compared to the top portion to enable the antenna array to transmit or receive communication signals that are substantially parallel to the surface.

Description

LOW PROFILE BEAM STEERING ANTENNA

WITH INTEGRATED DIVERGENT LENS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and the priority of U.S. Provisional

Application No. 62/563,550 filed on September 26, 2017 entitled "Low Profile Beam

Steering Antenna with Integrated Divergent Lens," the entirety of which is herein incorporated by reference.

BACKGROUND

[0002] 1. Field

[0003] This specification relates to a system and a method for transmitting and receiving communication signals.

[0004] 2. Description of the Related Art

[0005] An electronically scanned array having a computer-controlled array of antennas may be used to transmit signals in a particular direction without moving the antennas. The phases of the signals emitted from the antennas may be adjusted and coordinated. In doing so, certain portions of the signals from the antennas may be summed and cancelled, creating a directed signal transmission in a particular direction.

[0006] However, a key limitation of these beam steerable antennas is a total pointing angle range. When a substantially planar array of antennas is used, regardless of the beam steering methods employed, performance at the directions of plus or minus 90 degrees of the axis normal to the antennas deteriorates sharply. That is, signals are unable to be sent in a direction parallel or substantially parallel to the array of antennas.

[0007] Conventionally, non-flat arrays of antennas have been used to compensate for this limitation in pointing angle range. Other solutions include using negative index meta- material and active lenses. However, existing systems have drawbacks such as undesirably add to the height profile of the antenna system and/or are costly and complex to manufacture. Thus, there is a need for improved antenna systems.

SUMMARY

[0008] What is described is a system for transmitting or receiving communication signals. The system includes a planar antenna array located on a surface and configured to transmit or receive communication signals. The system also includes a divergent lens located above the antenna array and surrounding the antenna array. The divergent lens has a base portion on or near the surface and a top portion located above the antenna array. A thickness of the divergent lens is greater at the base portion compared to the top portion to enable the antenna array to transmit or receive communication signals that are substantially parallel to the surface.

[0009] Also described is a divergent lens located above a planar antenna array located on a surface and configured to transmit or receive communication signals. The divergent lens includes a base portion on or near the surface and a top portion located above the antenna array. A thickness of the divergent lens is greater at the base portion compared to the top portion to enable the antenna array to transmit or receive communication signals that are substantially parallel to the surface.

[0010] Also described is an airborne device or vehicle. The airborne device or vehicle includes an exterior surface. The airborne device or vehicle includes a planar antenna array located on the exterior surface and configured to transmit or receive communication signals. The airborne device includes a divergent lens located above the antenna array and surrounding the antenna array. The divergent lens has a base portion contacting the exterior surface and a top portion located above the antenna array. A thickness of the divergent lens is greater at the base portion compared to the top portion to enable the antenna array to transmit or receive communication signals that are substantially parallel to the exterior surface.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other systems, methods, features, and advantages of the present invention will be apparent to one skilled in the art upon examination of the following figures and detailed description. Component parts shown in the drawings are not necessarily to scale, and may be exaggerated to better illustrate the important features of the present invention.

[0012] FIG. 1 illustrates a perspective view of the low profile beam steering antenna with integrated divergent lens, according to various embodiments of the invention.

[0013] FIG. 2A illustrates a side cross-sectional view of the low profile beam steering antenna with integrated divergent lens, according to various embodiments of the invention.

[0014] FIG. 2B illustrates a detailed view of the cross-section of the divergent lens, according to various embodiments of the invention.

[0015] FIG. 3A illustrates a side cross-sectional view of the low profile beam steering antenna with integrated divergent lens, according to various embodiments of the invention.

[0016] FIG. 3B illustrates a detailed view of a signal transmitted from the antenna array, according to various embodiments of the invention.

[0017] FIG. 3C illustrates a detailed view of the signal transmitted from the antenna array after passing through the divergent lens, according to various embodiments of the invention.

[0018] FIG. 4 illustrates a side cross-sectional view of the low profile beam steering antenna with integrated divergent lens also having a tilting device, according to various embodiments of the invention.

[0019] FIG. 5 illustrates a perspective view of the low profile beam steering antenna with integrated divergent lens of FIG. 4, according to various embodiments of the invention. DETAILED DESCRIPTION

[0020] Disclosed herein are systems, devices, and methods for transmitting and receiving communication signals (e.g., radio frequency signals) using an antenna array. The systems, devices, and methods described herein enable transmission and reception of communication signals that are substantially parallel to the antenna array, while achieving a relatively low height profile. The relatively low height profile is important in reducing drag when the antenna array is located on an aircraft. The systems, devices, and methods described herein have a reduced complexity as compared to other systems, increasing the reliability and efficiency of the system as a whole, as well as reducing costs.

[0021] The systems and methods described herein use a divergent lens over a beam steerable antenna array to provide pointing angle coverage near plus or minus 90 degrees from the axis normal to the antenna aperture. As used herein, "pointing angle" refers to the direction in which the beam steerable antenna array communicates signals. Use of the divergent lens synthesizes an array with a larger projected area at pointing angles close to (e.g., within 10 degrees of) plus or minus 90 degrees from the axis normal to the antenna aperture. For example, a curved aperture (the lens surface) is synthesized from a flat array of antennas located inside the lens, as shown herein.

[0022] The divergent lens described herein has no known restrictions, and the source beam steerable flat panel containing the antenna array can be implemented with an unrestricted design. In addition, the divergent lens described herein makes efficient use of the lens area, as compared to other systems which may only illuminate a small fraction of the lens at any given pointing angle.

[0023] The low profile beam steering antenna with divergent lens described herein may be used in airborne satellite communications because of its wide pointing angle range capabilities and reduced height profile. The low profile beam steering antenna with divergent lens may also be used with other radio frequency antenna applications, such as data link, identification friend or foe (IFF), or radar, for example. The frequency range of the low profile beam steering antenna with divergent lens may be shifted lower or higher as needed, limited by the practical size of the divergent lens in the low frequency direction.

[0024] The low profile beam steering antenna with divergent lens retains most of the low profile of flat panel beam steerable antenna arrays, while mitigating its performance issues at extreme pointing angles.

[0025] FIG. 1 illustrates a perspective view of the system 100, which includes an antenna array 102 and a divergent lens 104. The antenna array 102 and the divergent lens 104 are located on a surface 106. The antenna array 102 includes a plurality of antennas 1 12, which are controlled by a controller 1 14. The controller 1 14 is configured to coordinate the transmission of the communication signals from the antennas 112 of the antenna array 102 to achieve the desired beam steering. In some embodiments, the antenna array 102 is an electronically scanned array (ESA) that is capable of controlling the phase and the amplitude of individual antenna elements at a given pointing angle. This provides control over the phase and the amplitude on an element-by-element basis, thus allowing compensation of the beam shape to compensate for the divergent lens 104.

[0026] The antenna array 102 may have antennas 1 12 arranged in any shape, such as a rectangle, a square, or a circle, for example. The antenna array 102 may be substantially flat and substantially parallel with the surface 106. The surface 106 may be an exterior surface of an aircraft or other airborne device, such as a drone or a satellite. The antenna array 102 may transmit signals (shown by arrow 108) or receive signals (shown by arrow 1 10).

[0027] The divergent lens 104 is located above the antenna array 102 and surrounds the antenna array 102. That is, the divergent lens 104 makes contact with the surface 106 in a circular shape, and the antenna array 102 is located within the circular shape formed by the connection of the divergent lens 104 with the surface 106. As will be shown in FIG. 2A, the divergent lens 104 is generally dome-shaped, but is not spherical in shape. Instead, the divergent lens 104 is more similar to a top half of an oblate spheroid than a half of a sphere.

[0028] FIG. 2A illustrates a side cross-sectional view of the divergent lens 104 and the antenna array 102. The divergent lens 104 has a base portion 218 and a top portion 220. The divergent lens 104 makes contact with the surface 106 at the base portion 218. The antenna array 102 may be located in an embedded manner within the surface 106 such that a top side of the antenna array 102 is coplanar with the surface 106.

[0029] The divergent lens 104 has a diameter 230 and a height 210 from the top side of the antenna array 102. The antenna array 102 has a diameter 212. In some embodiments, when the antenna array 102 is rectangular in shape, the diameter 212 may be a length connecting any two corners of the antenna array 102 (i.e., a diagonal or any side of the rectangle). In other embodiments, when the antenna array 102 is circular in shape, the diameter 212 is the diameter of the antenna array 102.

[0030] To achieve a low profile, the ratio of the height 210 of the divergent lens 104 to the diameter 212 of the antenna array 102 may be less than 0.5. That is, in these embodiments, the height 210 is less than half of the diameter 212. In some embodiments, the ratio of the height 210 of the divergent lens 104 to the diameter 212 of the antenna array 102 is less than 0.334. That is, in these embodiments, the height 210 is less than a third of the diameter 212. Thus, while the divergent lens 104 is generally dome-shaped, it has a relatively low height and thus not spherical in shape.

[0031] The divergent lens 104 has a base thickness 206. The base thickness 206 is the thickness of the divergent lens 104 where the divergent lens 104 contacts the surface 106. The divergent lens 104 also has a top thickness 208. The top thickness 208 is the thickness of the divergent lens 104 where the divergent lens 104 is farthest from the antenna array 102 or the surface 106. The base thickness 206 of the divergent lens 104 is many times larger (e.g., lOx to 50x) than the top thickness 208.

[0032] The divergent lens 104 has an inner surface 214 and an outer surface 216. The inner surface 214 may have an inner curvature or shape, and the outer surface 216 may have an outer curvature or shape. Toward the top portion 220, there may be little to no distance between the inner curvature and the outer curvature. However, toward the base portion 218, there may be a substantial distance between the inner curvature and the outer curvature. The difference between the inner curvature and the outer curvature allows the signal that passes through the divergent lens 104 to be bent or curved, as will be shown in more detail in FIGS. 3A-3C.

[0033] The divergent lens 104 may be a dielectric lens, as shown in FIG. 2B. The divergent lens 104 may be made of a dielectric material 204. The dielectric material 204 may have a dielectric constant of between 2 and 4, inclusive. For example, the dielectric material 204 may be a plastic, such as polytetrafluoroethylene (PTFE), polypropylene, polyethylene, polystyrene, acrylonitrile butadiene styrene (ABS), polycarbonate, or polyethylene terephthalate (PET). In some embodiments, the dielectric material 204 is a glass or ceramic filled plastic. In some embodiments, materials commonly used for printed circuit board (PCB) substrates may be used.

[0034] The divergent lens 104 may include matching layers made of a matching layer material 202. The matching layer material 202 may be applied as a coating on both sides of the dielectric material 204. The matching layer material 202 may reduce reflections at the lens surfaces in a manner similar to optical anti-reflection coatings. The thickness 232 of the matching layer material 202 may be thin (e.g., ¼ wavelength at the operating frequency). The matching layer material 202 may have a dielectric constant that is lower than that of the dielectric material 204. The thicknesses of the layers of matching layer material 202 may be the same or may be different. That is, the exterior matching layer thickness 232A may be the same as the interior matching layer thickness 232B, or the exterior matching layer thickness 232A may be greater than or less than the interior matching layer thickness 232B.

[0035] Instead of or in addition to the matching layers, the divergent lens 104 may have a fine texture on one or more of the inside surface or the outside surface of the divergent lens 104, in order to reduce reflections. The texture may be fine relative to the wavelength of the operating frequency. A material may be deposited onto the divergent lens 104 to form the texture, or the divergent lens 104 may be treated by a chemical or mechanical process to form the texture.

[0036] While the figures in all embodiments herein illustrate the divergent lens as being a smooth lens, a stepped thickness Fresnel lens design may also be used to reduce lens weight.

[0037] FIG. 3 A illustrates a side cross-sectional view of the divergent lens 104 and the antenna array 102. The antenna array 102 is transmitting a signal 316. The signal 316 is directed in a particular direction using beam steering techniques. The signal 316 has a curved wave front shape while in the interior area 312 between the divergent lens 104 and the antenna array 102. However, as the signal 316 travels through the divergent lens 104, the signal 316 transitions to a planar wave front shape. The signal 316 is in the planar wave front shape in the exterior area 314 outside of the divergent lens 104. A curved wave front shape has a particular focus point associated with it, limiting the distance it can be reliably transmitted to. The planar wave front shape allows the signal 316 to essentially have a focus point at infinite distance and travel farther toward a remote location 302 than if the signal 316 remained in the curved wave front shape.

[0038] The focus of the antenna array 102 may be adjusted to compensate for the divergent lens 104, and in order to form the planar wave shape by a certain point after passing through the divergent lens 104. In some embodiments, a controller (e.g., controller 114) is configured to determine a virtual image point to focus the antenna array on in order to form the planar wave shape by a certain point after the signal 316 passes through the divergent lens 104. The determination of the virtual image point may be based on the dimensions of the divergent lens 104 as well as the pointing angle. The controller 114 may then adjust the phase and the amplitude of one or more antenna elements in the antenna array 102 such that the antenna array 102 focuses on the virtual image point.

[0039] The signal 316 transitions from the curved wave front shape to the planar wave front shape due to the shape of the divergent lens 104 as well as the dielectric material 204. One of skill in the art would recognize the properties of the divergent lens allowing the wave front shape of the signal 316 to transition from the curved wave front shape to the planar wave front shape.

[0040] As shown in FIG. 3B, the signal 316 is emitted from the antenna array 102 in a first direction 310 at a transmission angle 304. Since the antenna array 102 is substantially flat and planar, the signal 316 is unable to be emitted in a direction parallel or substantially parallel with the surface 106. However, the shape of the divergent lens 104 bends the signal 316 to be substantially parallel with the surface 106. In particular, the shape of the inner surface of the divergent lens 104 as compared to the shape of the outer surface of the divergent lens 104 provides for the bending of the signal 316. As shown in FIG. 3C, the signal 316, after passing through the divergent lens 104, travels in a second direction 306 that is substantially parallel with the surface 106. As used herein, "substantially parallel" may mean within +/- 10 degrees. For example, when the signal 316 and the surface 106 form an angle of +/- 10 degrees or less, the signal 316 is substantially parallel with the surface 106. [0041] While FIGS. 3A-3C illustrate a transmission of a signal 316 from the antenna array 102 to the remote location 302, the system 100 may be used to receive, at the antenna array 102, a signal from a signal source (e.g., remote location 302). In addition, FIGS. 3A- 3C illustrate an exaggerated curved signal 316 for illustrative purposes only.

[0042] As described herein, the shape and the properties of the divergent lens 104 allows for receiving and transmitting of communication signals by the antenna array 102 in a full 180 degree range 320. The antenna array 102 may compensate for the divergent lens 104 by adapting the shape of the beam dependent upon the pointing angle.

[0043] The exact dimensions of the divergent lens 104, such as the base thickness 206, the top thickness 208, the height 210, the lens diameter 230, the dielectric material 204, the matching layer material 202, and the matching layer thickness 232 may be determined and optimized based on the dimensions of the antenna array 102, application of the system 100, and environmental constraints.

[0044] In some embodiments, in order to further increase the range and the strength of signal transmission and reception, the antenna array may be tilted and rotated. FIG. 4 illustrates a system 400 similar to the system 100, but capable of angling the antenna array in various directions.

[0045] The system 400 includes a divergent lens 404 similar to the divergent lens 104. The system 400 includes an antenna array 402 similar to the antenna array 102. However, the system 400 also includes a tilting device 407 to additionally tilt the antenna array 102 by a tilting angle 405. The tilting device 407 may be adjustable in height 408 such that a variety of different tilting angles 405 may be achieved. By tilting the antenna array 402, signals received and communicated that are substantially parallel to the surface 406 may be received and communicated with greater strength and integrity than non-tilting systems. [0046] A signal 416 similar to the signal 316, but illustrated as a line for simplicity, may be communicated by the antenna array 402. The transmission angle 414 may be greater than the transmission angle 304 of a non-tilting system. As will be appreciated by one skilled in the art, beam steered signals at extreme angles, such as the transmission angle 304 may have lower signal strength and/or integrity as compared to beam steered signals at less extreme angles, such as the transmission angle 414. As used herein, "extreme angles" may refer to angles within 10 degrees of the horizon. The tilting of the antenna array 402 allows for the transmission angle 414 to be outside of the extreme angle range, and allows for improved signal transmission.

[0047] As is the case with the divergent lens 104, the divergent lens 404 bends the signal 416 to be substantially parallel with the surface 406. The divergent lens 404 and the tilted antenna array 402 also allows for signal range to be greater than 180 degrees, assuming the surface 406 does not interfere with the signal 416.

[0048] FIG. 5 illustrates a perspective view of the system 400. The system 400 includes a divergent lens 404 surrounding the antenna array 402. The antenna array 402 may be tilted by the tilting device 407, as described above. The antenna array 402 may be located on a rotating platform 420 configured to rotate the antenna array 402 in any direction 422 in 360 degrees, so that the antenna array 402 may communicate and receive signals in any direction.

[0049] The system 400 allows for azimuth pointing by rotating the rotating platform 420, and elevation pointing and beam shaping by phase shifting at each antenna element in the antenna array 402. The system 400 may be slightly taller than the system 100, but may reduce the number of antenna phase shifter elements in the antenna array 402, as the beam may only have to be steered in one direction, and the rotating platform 420 can orient the steered beam in the azimuth direction. For example, a 32 by 32 antenna array 402 may use 32 phase shifter elements to steer the beam in one direction, but may use 1024 phase shifter elements to steer the beam in two dimensions.

[0050] In yet another embodiment, a curved antenna array may be used instead of the flat antenna array 102 or the tiltable and rotatable antenna array 402.

[0051] In some or all embodiments, the divergent lens (e.g., divergent lens 104 or 404) may be integrated with a radome to minimize overall height and weight, and to optimize performance of the radome and lens unit.

[0052] The useful projected area and performance at maximum pointing angles may be based on the height of the divergent lens (e.g., height 210). A balance may be achieved between the divergent lens height, desired pointing angle coverage, and performance at the maximum pointing angles (i.e., the pointing angles where signal performance begins to be diminished).

[0053] Exemplary embodiments of the methods/systems have been disclosed in an illustrative style. Accordingly, the terminology employed throughout should be read in a non-limiting manner. Although minor modifications to the teachings herein will occur to those well versed in the art, it shall be understood that what is intended to be circumscribed within the scope of the patent warranted hereon are all such embodiments that reasonably fall within the scope of the advancement to the art hereby contributed, and that that scope shall not be restricted, except in light of the appended claims and their equivalents.

Claims

CLAIMS What is claimed is:

1. A system for transmitting or receiving communication signals, the system comprising:

a planar antenna array located on a surface and configured to transmit or receive communication signals; and

a divergent lens located above the antenna array and surrounding the antenna array, the divergent lens having a base portion on or near the surface and a top portion located above the antenna array, a thickness of the divergent lens being greater at the base portion compared to the top portion to enable the antenna array to transmit or receive communication signals that are substantially parallel to the surface.

2. The system of claim 1, wherein the surface is an exterior surface of an airborne device or vehicle.

3. The system of claim 1, wherein a ratio of a height of the divergent lens to a diameter of the antenna array is less than 0.5.

4. The system of claim 1, wherein a ratio of a height of the divergent lens to a diameter of the antenna array is less than 0.334.

5. The system of claim 1, wherein the divergent lens is made of a dielectric material having a dielectric constant between 2 and 4, inclusive.

6. The system of claim 5, wherein the divergent lens has an inner surface having an inner curvature and an outer surface having an outer curvature, and at the base portion of the divergent lens, the inner curvature and the outer curvature are different, such that communication signals passing through the divergent lens are bent.

7. The system of claim 6, further comprising a matching layer material disposed on the inner surface and/or the outer surface, the matching layer material having a dielectric constant lower than that of the dielectric material the divergent lens is made of, and the matching layer material being configured to reduce reflections of communication signals.

8. The system of claim 6, wherein the inner surface and/or the outer surface have a texture such that reflections of communication signals are reduced.

9. The system of claim 1, wherein a communication signal having a curved wave front shape between the antenna array and the divergent lens has a planar wave front shape outside of the divergent lens, the planar wave front shape having a focus at an infinite distance.

10. The system of claim 1, further comprising a tilting device located beneath the antenna array and configured to tilt the antenna array at a tilting angle to improve signal strength.

1 1. The system of claim 10, further comprising a rotating platform located beneath the tilting device and the antenna array and configured to rotate the antenna array.

12. A divergent lens located above a planar antenna array located on a surface and configured to transmit or receive communication signals, the divergent lens comprising: a base portion on or near the surface and a top portion located above the antenna array, a thickness of the divergent lens being greater at the base portion compared to the top portion to enable the antenna array to transmit or receive communication signals that are substantially parallel to the surface.

13. The divergent lens of claim 12, wherein a ratio of a height of the divergent lens to a diameter of the antenna array is less than 0.5.

14. The divergent lens of claim 12, wherein a ratio of a height of the divergent lens to a diameter of the antenna array is less than 0.334.

15. The divergent lens of claim 12, wherein the divergent lens is made of a dielectric material having a dielectric constant between 2 and 4, inclusive.

16. The divergent lens of claim 15, further comprising an inner surface having an inner curvature and an outer surface having an outer curvature, wherein the inner curvature and the outer curvature are different at the base portion of the divergent lens, such that communication signals passing through the divergent lens are bent.

17. The divergent lens of claim 16, further comprising a matching layer material disposed on the inner surface and/or the outer surface, the matching layer material having a dielectric constant lower than that of the dielectric material the divergent lens is made of, and the matching layer material being configured to reduce reflections of communication signals.

18. The divergent lens of claim 16, wherein the inner surface and/or the outer surface have a texture such that reflections of communication signals are reduced.

19. An airborne device or vehicle comprising:

an exterior surface;

a planar antenna array located on the exterior surface and configured to transmit or receive communication signals; and

a divergent lens located above the antenna array and surrounding the antenna array, the divergent lens having a base portion on or near the exterior surface and a top portion located above the antenna array, a thickness of the divergent lens being greater at the base portion compared to the top portion to enable the antenna array to transmit or receive communication signals that are substantially parallel to the exterior surface.

20. The airborne device or vehicle of claim 19, wherein the divergent lens is made of a dielectric material having a dielectric constant between 2 and 4, inclusive.