Machined core antenna reflector and methods of assembling machined core antenna reflector

Abstract

To provide an antenna reflector for reflecting a radio frequency (RF) signal, and a method of assembling the antenna reflector for reflecting a radio frequency (RF) signal.SOLUTION: The antenna reflector includes a first face, a second face, and a core. The first face includes a reflective material for reflecting the RF signal. The first face is mounted on the core and opposes the second face mounted on the core. The first face and the second face together provide a monocoque structure to the antenna reflector. The core has: a honeycomb structure, including a plurality of cells disposed between the first face and the second face for separating the first face and the second face; and integral support ribs for stiffening the antenna reflector. The antenna reflector is shaped to reflect the RF signal. The antenna reflector includes mounting points for attachment to a spacecraft.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates generally to antenna reflectors, and more particularly to antenna reflectors with machined cores. [Background technology]

[0002] Conventional antenna reflectors are often unable to achieve both overall and local curvature, and in particular are often unable to achieve both concave and convex local curvature (i.e., both a concave local curvature in at least a first portion of the antenna reflector and a convex local curvature in at least a second portion of the antenna reflector).

[0003] The assembly of conventional antenna reflectors involves assembling multiple parts to achieve the desired curvature for transmitting and receiving RF signals, the desired stiffness to maintain the desired curvature during use, a compact configuration to fit onto a launch vehicle, a required effective thermoelastic coefficient to minimize thermoelastic deformation, and the desired robustness to withstand launch and on-orbit operations. The greater the complexity, e.g., the number of parts, in an antenna reflector, the greater the likelihood of errors during assembly or failure during use. Summary of the Invention [Problem to be solved by the invention]

[0004] Therefore, there is a need for an improved machined core antenna reflector and an improved method of assembling a machined core antenna reflector that overcomes at least some of the aforementioned drawbacks.

[0005] Other aspects and features will become apparent to those skilled in the art upon reading the following description of several exemplary embodiments.

[0006] The drawings included herein are intended to illustrate various examples of the articles, methods and apparatus herein. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is an exploded perspective view of a machined core antenna reflector according to one embodiment. [Figure 2] 2 is a top perspective view of a portion of the core of FIG. 1 showing the internal honeycomb structure (specifically the cells) according to one embodiment. [Figure 3] 1 is a flow diagram of a method for assembling a machined core antenna reflector according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Various devices or processes are described below to illustrate examples of each claimed embodiment. None of the embodiments described below limit the claimed embodiments, and any claimed embodiment may encompass processes or devices different from those described below. The claimed embodiments are not limited to devices or processes having all the features of any one device or process described below, or to features common to multiple or all of the devices described below.

[0009] Furthermore, although process steps, method steps, algorithms, or the like may be described (in this disclosure and / or claims) sequentially, such processes, methods, and algorithms may be configured to operate in different orders. In other words, any permutation or order of steps described does not necessarily dictate a requirement that the steps be performed in that order. Steps of processes described herein may be performed in any order practical. Additionally, some steps may be performed simultaneously.

[0010] Where a single device or article is described herein, it will be readily understood that two or more devices / articles (whether or not they cooperate) may be used in place of the single device / article. Similarly, where two or more devices or articles (whether or not they cooperate) are described herein, it will be readily understood that a single device / article may be used in place of the two or more devices or articles.

[0011] The following description relates generally to deployable antenna reflectors, and more particularly to machined core antenna reflectors.

[0012] In particular, the present disclosure provides a machined core antenna reflector shaped to enable accurate transmission and / or reception of RF signals. Such shaping may include curved surfaces. Such curved surfaces may include machining or shaping the entire antenna reflector ("global curved surface") to include, for example, concave and / or convex surfaces or concave and / or convex curves. Furthermore, such curved surfaces may include machining or shaping specific portions of the antenna reflector ("local curved surfaces") to include, for example, concave and / or convex surfaces or concave and / or convex curves. A single antenna reflector may be shaped or machined with a concave global curve and further shaped or machined with concave and convex local curves, for example, to discriminate or reflect only a specific RF signal range. A single antenna reflector may be shaped or machined with a convex global curve and further shaped or machined with concave and convex local curves, for example, to discriminate or reflect only a specific RF signal range.

[0013] In one embodiment, the machined core antenna reflector includes a first surface, a second surface, and a core. The first surface includes a reflector for reflecting RF signals. The first surface is attached to the core and is located opposite the second surface attached to the core. The first and second surfaces together provide a monocoque structure for the antenna reflector. The core has a honeycomb structure with multiple cells within the core. The honeycomb structure is disposed between the first and second surfaces, separating the first and second surfaces. The reflector includes an integral support rib for stiffening the antenna reflector. The core includes attachment points for the first and second surfaces. The antenna reflector is shaped to reflect RF signals.

[0014] Depending on the shape of the antenna reflector, machining of the core may be performed on the back surface only (if the overall shape is relatively flat and does not include local shaping) or on the back and front surfaces (if the overall shape is relatively bowl-shaped and / or includes local shaping).

[0015] Referring now to FIG. 1, an exploded perspective view of a machined core antenna reflector 10 according to one embodiment is shown.

[0016] The reflector 10 may be part of a larger antenna system mounted on an antenna platform (not shown), such as a spacecraft, satellite, or satellite bus. The reflector 10 may have a parabolic surface.

[0017] The reflector 10 comprises a first surface 12 for reflecting an RF signal. The first surface 12 may be understood to be a skin. The first surface 12 may be locally or globally shaped or contoured to improve, optimize, maintain, or minimize degradation or loss of fidelity of the signal retransmission. In particular, the first surface 12 may be shaped to retransmit the signal as a beam.

[0018] The first surface 12 of the reflector 10 may be adapted to be shaped to precisely select or reflect only a particular desired signal or band of signals (eg, C-band, Ku-band, Ka-band, etc.).

[0019] The first surface 12 is formed from an RF reflective material for reflecting RF signals. Such an RF reflective material may be or include carbon or resin.

[0020] In a preferred embodiment, first surface 12 comprises or is formed from an ultra-high modulus carbon fiber reinforced polymer (CFRP) prepreg fiber skin, such as, for example, a polymer resin prepreg graphite skin.

[0021] In another embodiment, the first surface 12 is, includes, or is formed from a reinforced fiber skin. In one embodiment, the fiber skin includes aramid fiber. If the fiber skin includes aramid, the fiber skin further includes a metal grid or strips or has metalized features to reflect RF signals.

[0022] The first surface 12 has a thickness that is locally configured and optimized to meet design, structural, thermal, manufacturing, and RF performance requirements.

[0023] The reflector 10 further comprises a second surface 30. The second surface 30 may be understood to be a skin. In one embodiment, the second surface 30 is non-reflective. For example, the second surface 30 may be made of a different material than the first surface 12.

[0024] In another embodiment, the second surface 30 is, includes, or is formed from a reinforced fiber skin. In one embodiment, the fiber skin includes aramid fibers.

[0025] The second surface 30 has a thickness that is locally configured and optimized to meet design, structural, thermal, manufacturing, and RF performance requirements.

[0026] The second surface 30 further comprises an outer non-raised portion 34 .

[0027] The second surface 30 further comprises a raised portion 36 for forming an integral rib 28 as discussed hereinafter, and an inner non-raised portion 38. The raised portion 36 of the reflector 10 is discussed further below.

[0028] The reflector 10 further includes a core 24 for separating the first surface 12 and the second surface 30. The first surface 12 and the second surface 30 are respectively attached to each side of the core 24. Attachment may be achieved using any suitable attachment mechanism. The surfaces 12, 30 may completely cover the core 24, for example, such that all portions of the core 24 are invisible (except for the edges of the core) after attachment of the surfaces 12, 30. The surfaces 12, 30 may not completely cover the core, for example, such that only portions of the core 24 are visible (except for the edges of the core) after attachment of the surfaces 12, 30.

[0029] The faces 12, 30 attached to or around the core 24 form a monocoque structure.

[0030] The core 24 has a honeycomb structure. The honeycomb structure includes a plurality of cells 26 (shown in FIG. 2). The cells 26 may be hexagonal, as shown in FIG. 2. The cells 26 may also have a flex-core cell shape (e.g., when only the back surface of the core 24 is machined).

[0031] The core 24 includes a plurality of ribs 28a, 28b, 28c, 28d, 28e, 28f, 28g, and 28h (collectively referred to as ribs 28 and generally referred to as ribs 28) disposed therein. The ribs 28 are integral with the core 24. The ribs 28 may be considered to be integrally machined support ribs. The ribs 28 may form flat or raised sections for attachment to the surfaces 12, 30. The ribs 28 increase the rigidity of the reflector 10. The rib shape may span the entire footprint of the reflector 10.

[0032] Ribs 28 may be created by machining core 24 to a particular thickness, level, or height. Such machining may include machining the overall and / or local curvature of core 24. Support ribs 28 may be tapered; for example, support rib 28f may include tapered side portions 29a, 29b and top portion 29c. Top portion 29c may be flat, have an offset RF shape, or any other desired shape. It will be understood that such tapered side portions 29a, 29b and top portion 29c may be present on some or all of support rib 28. For clarity, such tapered side portions 29a, 29b and top portion 29c are shown only with respect to support rib 28f. The aforementioned tapering may provide a smooth transition for layups of prepreg graphite material (e.g., having variable thicknesses).

[0033] The core 24 may include thousands of cells 26. The height of the cells 26 is structurally optimized.

[0034] The ribs 28 of the core 24 correspond to the thicker portions 36 of the second face 30 as previously described.

[0035] Core 24 may be of variable thickness, including thicker and thinner sections (thicker sections being, for example, ribs 28). Core 24, or each instance thereof, may be customized according to specific needs, for example, with one or more thicker sections at specific locations on core 24 and one or more thinner sections at other specific locations on core 24. Core 24 may be up to 4 inches thick at its thickest point. Core 24 may be as thin as 0.25 inches thick at its thinnest point.

[0036] In one embodiment, the thickness of the core 24 varies from 0.25 inches at its thinnest point to 4 inches at its thickest point.

[0037] In one embodiment, core 24 has a uniform thickness. The thickness may be between 0.25 inches and 4 inches. It may be advantageous to manufacture or machine core 24 to be as thin as possible where possible.

[0038] In one embodiment, the honeycomb structure (eg, the walls of the cells 26) may be made from aluminum.

[0039] The ribs 28 are thin relative to the volume of the cells 26. Those skilled in the art will appreciate that a variety of honeycomb structures may be suitable for the core 24 according to the present disclosure, however, any honeycomb structure suitable for the present disclosure will include an array of cells 26 or a plurality of cells 26. In one embodiment, the cells 26 may have a columnar and hexagonal shape.

[0040] Advantageously, such a honeycomb structure for or within the core 24 may provide a material with minimal density and relatively high out-of-plane compression and shear properties.

[0041] The honeycomb structure may be fabricated, manufactured, or assembled by stacking honeycomb material (such as aluminum honeycomb material) that provides tensile strength between surfaces 12 and 30 to form a plate-like assembly.

[0042] In one embodiment, core 24 can be, comprise, or be formed from foam.

[0043] The core 24 may be machined. The core 24 may be pre-machined before the faces 12, 30 are attached. Machining the core 24 includes machining one or both faces of the core 24 to set the relative heights of the cells 26. The machining of one face, facing the first face 12, is set by an RF engineer or by RF requirements for the RF reflective surface of the first face 12. The machining of the second face of the core 24, facing the second face 30, is set by a structural engineer or by structural requirements to structurally reinforce the reflector 10, specifically to maintain a stable reflective surface profile of the first face 12. The aforementioned machining includes setting or machining the local levels or relative heights of the cells 26, which may be hexagonal.

[0044] Machining the core 24 includes machining the core 24 to have a ribbed profile to provide structural support for the reflector 10 .

[0045] The machined core 24 has various sections with different local levels, tapering from a height of, for example, 0.25 inches to a height of, for example, 4 inches at 29a / 29b.

[0046] The core 24 may be manufactured by additive manufacturing methods such as 3D printing.

[0047] The core 24 may be an assembly of multiple honeycomb material pieces. Such multiple honeycomb material pieces may be assembled together using a bonding material (e.g., foam adhesive, sewing thread, etc.) or a bonding method (e.g., nesting of open core edges). Such multiple honeycomb material pieces may be assembled together without using a bonding material (e.g., foam adhesive, sewing thread) or a bonding method (e.g., nesting of open core edges). Bonding between multiple honeycomb material pieces may be at the skin level.

[0048] In one preferred embodiment, the core 24 comprises aluminum in a 3D honeycomb structure as previously described.

[0049] Core 24 may be adhered to faces 12, 30 using a film adhesive having a glass transition temperature of 180° C. or greater. Ribs 28 may be adhered to one another to form core 24 using a foam adhesive having a glass transition temperature of 180° C. or greater.

[0050] The core 24 may be bonded to the faces 12,30 via resin in the prepreg fiber material of the faces 12,30.

[0051] In one embodiment, the core 24 comprises core pieces bonded together with a foam adhesive, and the so-bonded core 24 is further bonded to the faces 12,30.

[0052] In one embodiment, the core 24 does not use or include a separate adhesive. If the faces 12, 30 are prepregged as described herein, it is possible to use resin from the prepregged faces 12, 30 themselves to bond to the core.

[0053] In other embodiments, core 24 comprises any of an aramid, carbon, aluminum, or glass compound.

[0054] Advantageously, core 24 is not plastically deformed. Core 24 may be curved, machined, or otherwise three-dimensionally shaped. Such bending, machining, or further shaping may include providing core 24 with concave and / or convex surfaces. Core 24 may have concave, convex, and / or flat surfaces. Core 24 and / or the entire reflector 10 may have a concave, convex, or both profile. Such three-dimensional machining may eliminate all or substantially all material stresses in all dimensions.

[0055] In one embodiment, the core 24 is machined on both sides. The side facing the first side 12 is machined to be flat or curved, i.e., to match the shape requirements of the RF surface. The other side facing the second side 30 is machined according to structural engineering specifications (e.g., to define ribs 28).

[0056] In one embodiment, second surface 30 is a mold of core 24 .

[0057] The faces 12, 30 are attached to the core 24 in a uniform manner on each machined surface of the core 24.

[0058] Different portions of the same core 24 may be manufactured in different ways. For example, some portions of the core 24 may be constructed entirely from flat stock sheets, other portions may be manufactured in three dimensions (e.g., by machining, additive manufacturing, etc.), and still other portions may be manufactured in two dimensions (e.g., by machining, additive manufacturing, etc.). Any combination of core 24 components that achieves the objectives of this disclosure is expressly included herein. Thus, the core may have different and multiple densities, e.g., multiple different densities.

[0059] The core 24, and therefore the entire reflector 10, may have any suitable shape, diameter, or footprint.

[0060] The core 24 forms a reinforcing structure in or for the reflector 10 by acting as an integral rib that provides a defined spacing between the faces 12,30.

[0061] The aforementioned properties of the core 24 allow for non-zero curvatures of the reflector 10, including both convex and concave local curvatures.

[0062] Advantageously, the core 24 may have very high thermal conductivity. For example, if the core 24 is aluminum and the faces 12, 30 are graphite, the thermal conductivity of the aluminum core 24 will provide a thermal bridge between the front face 12 and the back face 30. Advantageously, the graphite faces 12, 30 have a CTE (coefficient of thermal expansion) value that is near zero, which advantageously provides thermoelastic stability to the reflector 10.

[0063] Core 24 is a pre-machined core to which a resin carbon fiber reflective surface is applied to form a stress-free sandwich reflector 10. This resin carbon fiber reflective surface serves as or substantially forms first surface 12. Second surface 30 may be similarly fabricated.

[0064] Advantageously, the reflector 10 may comprise a minimum number of parts. Advantageously, the reflector 10 may have both concave and convex local and / or global curvatures.

[0065] If the core 24 is machined to the exact shape, no stresses are induced. The first and second faces 12, 30 conform to the machined core.

[0066] Advantageously, the material of reflector 10, particularly the material of faces 12 and 30, may be very thermally stable, and advantageously, core 24 has high thermal conductivity. First face 12 and second face 30 may be exposed to different temperatures. If core 24 is aluminum, the thermal gradient between first face 12 and second face 30 is minimized as a result of the high thermal conductivity of aluminum core 24, minimizing deformation of the reflector. Advantageously, a thermal protective cover may not be necessary when using reflector 10.

[0067] Additionally, reflector 10 includes attachment or mounting points 40a, 40b, 40c, and 40d (collectively referred to as attachment points 40 and generally referred to as attachment points 40). These attachment points 40 may be substantially flat and / or raised. These attachment points 40 allow reflector 10 to be attached to a spacecraft (not shown). Attachment points 40 may be disposed on first face 12, core 24, and / or second face 30, or any combination thereof. Attachment points 40 may be disposed on or consist of portions other than corners of first face 12, core 24, and / or second face 30, as shown in the square embodiment of FIG. 1 . In particular, attachment points 40 may be located at or consist of any one or more vertices of reflector 10 (e.g., on first face 12, core 24, and / or second face 30) when reflector 10 has a shape such as a triangle, hexagon, octagon, or other polygon. Attachment points 40 may consist of points located at the center and along the periphery of a polygon, such as points along the circumference of a circular reflector 10. Attachment points 40 can vary in type and / or shape.

[0068] The attachment point 40 may include additional structures (e.g., 3D printed structures) to aid in attachment to the spacecraft.

[0069] Referring now to FIG. 2, there is shown a top perspective view of region 44 of core 24 showing the internal honeycomb structure (specifically cells 26) according to one embodiment.

[0070] Cells 26 separate faces 12, 30.

[0071] 3, a flow diagram of a method 200 for assembling a machined core antenna reflector according to one embodiment is shown. The machined core antenna reflector assembled by this method 200 may be reflector 10 of FIG.

[0072] At 202, method 200 includes machining at least one face of a core. The core machined at 202 may be core 24 of FIG. 1. Preferably, this machining includes three-dimensional machining. Either the front or back face of core 24 may be machined. In a preferred embodiment, both the front and back faces of the core are machined.

[0073] In one embodiment, the front surface of the core 24 is machined with a global and / or local curvature.

[0074] At 204, the method 200 includes attaching a front skin and a back skin to each side of the core. The front skin and back skin may be the first side 12 and the second side 30 of FIG. 1, respectively.

[0075] These skins may be or include resin carbon fiber. These skins may be the same or different materials. Preferably, the skins are, include, or are formed from carbon fiber reinforced polymer (CFRP) prepreg fiber skins. The skins may be made using polymer resins or cyanate esters. The CFRP may be ultra-high modulus CFRP.

[0076] In another embodiment, the skins are, include, or are formed from reinforced fiber skins. In one embodiment, the fiber skins include aramid fibers. If the fiber skins include aramid, the fiber skins further include metal grids or strips or have metalized features to reflect RF signals.

[0077] At 206, method 200 includes curing the front and back skins against the core on each side. The curing may be performed substantially simultaneously ("co-curing"). The curing may be performed sequentially. The curing may be performed at different times.

[0078] The front and back skins are cured in the mold to create stress-free skins. The core may be machined on both sides to create a stress-free core. At 206, the reflector is cured using the stress-free skins and stress-free core to produce a stress-free reflector for optimal RF performance in the environment. Because the reflector and its components are stress-free, the reflector maintains its shape after removal from the mold, so method 200 may not include further shaping after the reflector is removed from the mold.

[0079] The method 200 may further include precisely machining a mold to a desired shape to achieve the foregoing. The method 200 may include providing or using a mold that has been precisely pre-machined to a desired shape to achieve the foregoing.

[0080] Those skilled in the art will appreciate that the skins may be pre-cured at 204 before being attached to the different faces of the core.

[0081] Those skilled in the art will appreciate that the core may be fully or partially additively manufactured at 202.

[0082] Preferably, the core is a honeycomb core as described with respect to core 24 in Figure 1. The core may also be a molded foam core.

[0083] Advantageously, reflector 10 of FIG. 1 and / or a reflector assembled by method 200 of FIG. 3 have a monocoque construction to allow for shaping of larger surfaces (convex surfaces, concave surfaces) without compromising structural integrity or signal transmission fidelity.

[0084] Each of the skins 10, 32 may be or be made from fibers that can be spread over a mold and cured. Such fibers may be infused with resin. A core 24, with at least one side machined as described above, may be placed over the mold, and fibers for the skins 10, 32 may be applied to each side of the core 24. Curing may include sandwiching the core 24 with the fibers disposed thereon in a vacuum bag and curing at 350°F. After curing, the reflector 10 may be separated from the mold as a rigid shaped structure.

[0085] In one embodiment where only the back surface of the core is machined, the core may be preloaded on the mold.

[0086] The objective of this disclosure is to minimize the preload applied to the core on the mold. If the front RF surface is bowl-shaped globally or locally, both the front and back surfaces are preferably machined. If the front RF surface is globally flat and not locally shaped, only the back surface may be machined.

[0087] Although the above description presents one or more example devices, methods, or systems, it will be understood that other devices, methods, or systems may also fall within the scope of the claims as interpreted by one of ordinary skill in the art.

Claims

1. 1. An antenna reflector for reflecting radio frequency (RF) signals, comprising: the antenna reflector comprises a first surface, a second surface, and a core; the first surface comprises a reflector for reflecting the radio frequency (RF) signal, the first surface being attached to the core and facing the second surface attached to the core, the first surface and the second surface together providing the antenna reflector with a monocoque structure; the core comprises a honeycomb structure having a plurality of cells disposed between the first surface and the second surface to separate the first surface and the second surface, and an integral support rib for stiffening the antenna reflector; the antenna reflector is shaped to reflect the radio frequency (RF) signal; The antenna reflector includes an attachment point for mounting to a spacecraft.

2. 2. The antenna reflector of claim 1, wherein the reflector is a carbon fiber reinforced polymer (CFRP) resin prepreg fabric skin.

3. The antenna reflector of claim 1 , wherein the first surface and the second surface are formed from a resin carbon fiber.

4. 10. The antenna reflector of claim 1, wherein the core has a variable thickness between 0.25 inches and 4 inches and a plurality of different densities.

5. 10. The antenna reflector of claim 1, wherein a generally curved surface of the antenna reflector is shaped to reflect the radio frequency (RF) signal, the generally curved surface including a concave surface and / or a convex surface.

6. 10. The antenna reflector of claim 1, wherein a localized curvature of the antenna reflector is shaped to reflect the radio frequency (RF) signal, the localized curvature including a concave surface and / or a convex surface.

7. 2. The antenna reflector of claim 1, wherein the honeycomb structure is an aluminum honeycomb structure and the plurality of cells have a columnar, hexagonal shape.

8. The antenna reflector of claim 1 , wherein the core is three-dimensionally pre-machined.

9. 2. The antenna reflector of claim 1, wherein the first surface and the second surface are attached to the core using a film adhesive having a glass transition temperature of 180°C or greater.

10. 10. The antenna reflector of claim 1, wherein the integral support ribs are provided by machining the core to one or more particular thicknesses, and the integral support ribs are tapered.

11. 1. A method of assembling a machined core antenna reflector, comprising: machining at least one face of the core; attaching a front surface and a back surface to each face of the core, the front surface comprising a reflective material for reflecting radio frequency (RF) signals; and stiffening the front and back surfaces for each face of the core to provide a monocoque structure for the antenna reflector.

12. The method of claim 11 , wherein machining at least one face of the core comprises machining both faces of the core.

13. The method of claim 11 , wherein the front and back surfaces are cured to the core simultaneously.

14. 12. The method of claim 11, wherein the core has a variable thickness varying between 0.25 inches and 4 inches and a plurality of different densities.

15. 12. The method of claim 11, wherein a globally curved surface and / or a locally curved surface of the antenna reflector is machined to reflect the radio frequency (RF) signal, and the machined globally curved surface and / or the locally curved surface includes concave and convex surfaces.

16. The method of claim 11 , wherein the reflective material is a carbon fiber reinforced polymer (CFRP) resin prepreg fabric skin.

17. 12. The method of claim 11, wherein the core has an aluminum honeycomb structure, the aluminum honeycomb structure comprising a plurality of prismatic hexagonal cells within the core and disposed between and separating the front and back surfaces, the core comprising integral support ribs for stiffening the machined core antenna reflector, and the machined core antenna reflector comprising attachment points for mounting to a spacecraft.

18. 16. The method of claim 15, wherein machining at least one face of the core comprises machining the core to one or more specified thicknesses to form integral support ribs.

19. 20. The method of claim 18, wherein machining the core to one or more specified thicknesses to form the integral support ribs comprises machining the global and / or local curved surfaces.

20. The method of claim 19 , wherein the integral support rib is tapered.

Images