STRETCHED FOAMLESS MULTI-LAYER SUBSTRATE POLARIZER AND METHODS FOR FABRICATING SAME

Abstract

A radio frequency (RF) polarizer includes a frame having a first side and a second side spaced apart from and opposite the first side, a first polarizer substrate attached to the first side and including a plurality of conductor patterns formed on a surface of the first polarizer substrate, and a second polarizer substrate attached to the second side. The first polarizer substrate and the second polarizer substrate are attached to the first side and the second side, respectively, under tension.

Claims

1. A radio frequency (RF) polarizer, comprising: a frame having a first side and a second side spaced apart from and opposite the first side; a first polarizer substrate attached to the first side and including a plurality of conductor patterns formed on a surface of the first polarizer substrate; and a second polarizer substrate attached to the second side, wherein the first polarizer substrate and the second polarizer substrate are attached to the first side and the second side, respectively, under tension.

2. A radio frequency (RF) polarizer, comprising: a frame having a first side and a second side spaced apart from and opposite the first side; a first polarizer substrate attached to the first side and including a plurality of conductor patterns formed on a surface of the first polarizer substrate; and a second polarizer substrate attached to the second side, wherein an inner-most planar surface of the first polarizer substrate and an inner-most planar surface of the second polarizer substrate face each other, and exposed portions of the respective inner-most planar surfaces are structurally independent of each other.

3. The RF polarizer according to claim 1, wherein the conductor patterns are formed on an outer-most surface of at least the first polarizer substrate.

4. The RF polarizer according to claim 1, wherein the plurality of conductor patterns comprise at least one of meanderline geometries or gridline geometries.

5. The RF polarizer according to claim 1, wherein the first polarizer substrate is fixed to the first side of the frame at a first tension, and the second polarizer substrate is fixed to the second side of the frame at a second tension, the first tension substantially the same as the second tension.

6. The RF polarizer according to claim 5, wherein the first and second tension are about 2000 psi.

7. The RF polarizer according to claim 1, wherein an air gap is formed between the first polarizer substrate and the second polarizer substrate.

8. The RF polarizer according to claim 7, wherein the air gap is devoid of any structural elements connecting the first polarizer substrate to the second polarizer substrate.

9. The RF polarizer according to claim 1, wherein the frame comprises an attaching portion for attaching the first and second polarizer substrates to the frame, and part of an inner planar surface of the first polarizer substrate and part of an inner planar surface of the second polarizer substrate are attached to the attaching portion, wherein portions of the respective inner planar surfaces disposed between the attaching portion are adhesive-free.

10. The RF polarizer according to claim 1, wherein the frame comprises an attaching portion for attaching the first and second polarizer substrates to the frame, and part of an inner planar surface of the first polarizer substrate and part of an inner planar surface of the second polarizer substrate are attached to the attaching portion, wherein portions of the respective inner planar surfaces disposed between the attaching portion are mechanically independent of each other.

11. The polarizer according to claim 1, further comprising the planar antenna disposed adjacent to the RF polarizer.

12. The polarizer according to claim 1, wherein the polarizer comprises a circular form factor.

13. The polarizer according to claim 1, wherein the substrate comprises one of polyimide, polycarbonate, polyethylene terephthalate, or polyetherimide.

14. An antenna system, comprising: a plurality of the RF polarizers according to claim 1; and a scanning antenna including an aperture and feed, wherein the scanning antenna is arranged relative to the plurality of polarizers to communicate RF signals between the aperture and the plurality of polarizers.

15. The antenna system according to claim 14, wherein the scanning antenna comprises a variable inclination continuous transverse stub (VICTS) antenna.

16. A method for forming a radio frequency (RF) polarizer, comprising: providing a frame having a first side and a second side spaced apart from and opposite the first side; attaching to the first side of the frame a first polarizer substrate including a plurality of conductor patterns; and attaching to the second side of the frame a second polarizer substrate, wherein attaching the first and second polarizer substrates includes placing the first and second polarizer substrates under tension.

17. The method according to claim 16, wherein placing the first and second polarizer substrates under tension includes applying substantially the same tension to both the first and second polarizer substrates.

18. The method according to claim 17, wherein applying substantially the same tension comprises applying a tension of about 2000 psi.

19. The method according to claim 16, wherein attaching includes attaching part of inner planar surfaces of the first and second polarizer substrates to an attaching portion of the frame, and maintaining portions of the respective inner planar surfaces disposed between the attaching portion adhesive-free.

20. The method according to claim 16, wherein attaching includes attaching part of inner planar surfaces of the first and second polarizer substrates to an attaching portion of the frame, and maintaining portions of the respective inner planar surfaces disposed between the attaching portion mechanically independent of each other.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] In the annexed drawings, like references indicate like parts or features.

[0033] FIG. 1 illustrates an exploded view of an antenna system that utilizes conventional polarizers with a VICTS antenna.

[0034] FIG. 2 is a side view of the antenna system of FIG. 1.

[0035] FIG. 3 is a detailed side view of a conventional polarizer showing the foam and adhesive layers between polarizer substrates.

[0036] FIG. 4A is a top view of an exemplary polarizer in accordance with the invention.

[0037] FIG. 4B is a side view of the polarizer of FIG. 4A.

[0038] FIG. 4C is a detailed partial side view of the polarizer of FIGS. 4A and 4B.

[0039] FIG. 5 is a cross section of a conventional polarizer showing plane wave control.

[0040] FIG. 6 is a cross section of a polarizer in accordance with the invention showing plane wave control.

[0041] FIGS. 7A and 7B are sectional views of an exemplary antenna system using polarizers in accordance with the invention.

DETAILED DESCRIPTION OF INVENTION

[0042] Embodiments of the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It will be understood that the figures are not necessarily to scale. \

[0043] The word “about” when immediately preceding a numerical value means a range of plus or minus 10% of that value, e.g., “about 50” means 45 to 55, “about 25,000” means 22,500 to 27,500, etc., unless the context of the disclosure indicates otherwise, or is inconsistent with such an interpretation. For example, in a list of numerical values such as “about 49, about 50, about 55, “about 50” means a range extending to less than half the interval(s) between the preceding and subsequent values, e.g., more than 49.5 to less than 52.5. Furthermore, the phrases “less than about” a value or “greater than about” a value should be understood in view of the definition of the term “about” provided herein.

[0044] The present invention finds utility in Variable Inclination Continuous Transverse Stub (VICTS) antenna systems and therefore will be described chiefly in this context. However, aspects of the invention are also applicable to other scanning planar antenna systems, including but not limited to electronically-scanned slotted planar arrays, printed patch arrays, open-ended waveguide arrays, or the like.

[0045] A VICTS antenna, in its simplest form, includes two components, namely an aperture and a feed. Antenna main beam scanning in θ (elevation) is achieved via rotation of the aperture with respect to the feed. This type of rotation also scans the antenna main beam over a small range of ϕ (azimuth), while additional desired scanning in ϕ is achieved by rotating the aperture and feed simultaneously, leading to near hemispherical scan coverage.

[0046] With reference to FIGS. 1 and 2, illustrated is an exploded view (FIG. 1) and a side view (FIG. 2) of a conventional stack of polarizers 10 and a planar scanning antenna 12 including an aperture and feed (e.g., a VICTS antenna), the scanning antenna 12 arranged relative to the polarizers 10 to communicate RF signals between the aperture and the polarizers. As shown, the antenna 12 and polarizers 10, which may be mounted to a spindle or other device that enables relative rotation between the respective polarizers about a common axis, each have a circular form factor and are concentric with each other. While other form factors are possible, due to the relative-rotation capability of the polarizers 10 with respect to each other and to the antenna 12, a circular form factor is best suited for minimizing the overall size of the system while at the same time providing optimal performance.

[0047] The antenna 12, which in the illustrated embodiment is a VICTS antenna, includes an antenna port 14 for receiving/outputting an RF signal, and lower and upper conducting plates 16 and 18 as is conventional. The upper conducting plate 18 includes a plurality of stubs 18a that define an aperture 18b of the VICTS antenna 12. It is noted that the embodiment illustrated in FIGS. 1 and 2 is merely exemplary, and other embodiments are envisioned. For example, embodiments with a different number of polarizers 10 and/or a different scanning antenna 12 are possible and may be used in place of those shown in FIGS. 1 and 2.

[0048] With additional reference to FIG. 3, each polarizer 10 includes an upper substrate 20a and a lower substrate 20b, the upper substrate 20a including, for example, metal meanderline or gridline geometries 22. The upper and lower substrates are approximately 0.001 to 0.003 inches thick and are formed from a thin film material. For example, the substrates can be formed from one of polyimide (Kapton®), polycarbonate (Lexan®), polyethylene terephthalate (Mylar®), or polyetherimide (Ultem™). Arranged between the upper and lower substrates 20a, 20b is a foam spacer 24 having a thickness of about 0.1 inches, the foam spacer bonded to the upper and lower substrates 20a, 20b with an adhesive 26 that is approximately 0.003 inches thick. An air gap 28 is formed between adjacent polarizers 10.

[0049] As discussed above, the adhesive 26 and foam spacer 24 can reduce efficiency of the polarizer and thus of the antenna system. A device and method in accordance with the invention provide a design and construction of polarizers, such as gridline and meanderline polarizers, for CTS and VICTS antennas that improve antenna performance and utilize fewer materials. In accordance with the invention, dielectric substrate layers that are either blank or support the gridline and meanderline geometries are stretched adequately during assembly such that they remain under tension and thus remain entirely flat under all operational conditions. This is particularly important in harsh ground and airborne operational environments where the antennas are required to operate over wide temperature ranges and high humidity conditions. By maintaining flat dielectric layers under all operational conditions, predictable and consistent polarization performance is achieved.

[0050] Adequate stretch of the of the polarizer substrate is achieved by the following steps: 1) determining the substrate variation in tension that will occur over operational temperature extremes, which is a function of the coefficient of thermal expansion (CTE) of the ring frame, CTE of the substrate, maximum & minimum temperature that the polarizer is intended to operate, and overall dimension of both parts, 2) determining the substrate variation in tension that will occur over operational humidity extremes, which is a function of the humidity expansion coefficient of the substrate, absolute humidity of the environment at each extreme (dry & humid), and overall dimension of the substrate, 3) combining the temperature and humidity variations in tension at each extreme to determine the maximum variation in tension of the substrate, and 4) selecting an initial room condition tension of the substrate that will i) ensure there is still residual tension in the substrate at one end of variation range (to prevent sag of the substrate between the minimum and maximum temperatures of operation), and ii) ensure the tension at the other end of the variation range does not exceed the substrate tensile strength (to prevent structural failure of the substrate between the minimum and maximum temperatures of operation).

[0051] A benefit and improvement relative to the conventional polarizer designs is that the intermediate supporting foam spacer 24 and adhesive layers 26 of are eliminated, as the essential dielectric substrate layers are stretched and attached directly to a support frame or ring. The elimination of the foam spacer and adhesive layers directly improves the antenna performance by reducing the dielectric losses internal to the polarizer and obviates any concerns with respect to moisture entrapment or outgassing as associated with traditional “bonded foam” embodiments.

[0052] The support frame/ring with stretched dielectric substrate layer(s) can then be attached to each other to achieve a multilayer design or can be attached directly to another part of the antenna structure. In addition, the laminated “dual-substrate” structure provides superior surface wave suppression and control, particularly at larger angles of incidence (larger scan angles) where this novel “paired” boundary structure enables superior transmission and polarization properties, as compared to conventional construction methods. Further, the absence of the conventional adhesive layers (typically 3-4 mils in thickness each, and present at both substrate-to-foam and foam-to-substrate interfaces in the conventional embodiment) provides for superior performance at higher frequencies (30 GHz and above) where the presence of the adhesive layers in conventional polarizer embodiments can further degrade the overall electrical properties (transmission loss and polarization purity) at these higher operating frequencies.

[0053] A stretched polarizer in accordance with the invention, in its simplest form, includes two dielectric substrate membranes bonded to opposite faces of a thin metal ring, where the thickness of the ring is sized to satisfy the separation distance requirement based on RF electrical performance considerations (polarization purity, transmission loss, and surface wave control.) More complex designs can consist of stacked stretched polarizers.

[0054] The polarizer design in accordance with the invention relies on the membrane tension and the flatness of the perimeter ring to maintain the flat shape of the polarizer. More particularly, the flatness of the novel stretched polarizer is dictated and maintained by the flatness of the perimeter ring and/or the flatness of the structure to which it is attached. The effects of differential expansion do not affect the flatness of the polarizer as long as there is sufficient tension in the dielectric substrate layers. This is achieved by pre-tensioning the dielectric substrate layers during manufacturing to a level that is sufficient to accommodate a partial loss of tension due to differential expansion effects. A “partial loss of tension” means that the tension in the substrate has decreased from a nominal tension, but the substrate is still under tension. Additionally, the foam spacer and adhesive layers are eliminated in the stretched polarizer design, which improves RF performance.

[0055] Referring to FIGS. 4A-4C, illustrated are top, side, and detailed section views of an exemplary polarizer 30 in accordance with the invention. The polarizer 30 includes a frame 32 having a first side 32a and a second side 32b spaced apart from and opposite the first side 32a. In the illustrated embodiment the frame 32 is formed as a circular ring, although other shapes, such as rectangular, elliptical etc., are possible. A circular ring is preferred as it provides the minimum footprint as the polarizer is rotated about its axis. The frame may be formed from any number of different materials of sufficient strength but is typically formed from metal such as aluminum or steel.

[0056] A first polarizer substrate 20a that includes a plurality of conductor patterns, such as meanderline conductor patterns or gridline conductor patterns, is attached to the first side 32a of the frame 32. A second polarizer substrate 20b that is blank or includes a plurality of conductor patterns (e.g., meanderline conductor patterns or gridline conductor patterns) is attached to the second side 32b of the frame 32. In attaching the first and second substrates, according to one embodiment the frame may include attaching portions, e.g., grip sections and/or clamping means, for fixedly holding the respective substrates on the frame 32. According to another embodiment, an adhesive may be used to bond the substrate to the ring frame to mitigate any reduction in the pre-tensioning that may occur over time. A combination of grip/clamping sections and adhesive also may be used.

[0057] Both the first polarizer substrate 20a and the second polarizer substrate 20b are stretched across and attached to the frame 32 under tension. More specifically, the first polarizer substrate 20a is fixed to the first side 32a of the frame 32 at a first tension, and the second polarizer substrate 20b is fixed to the second side 32b of the frame 32 at a second tension. Preferably, the first tension is substantially the same as the second tension such that the stress applied by the respective substrates on the frame is effectively canceled. The actual tension depends on the application of the polarizer. For example, the tension can be based on one or more of an expected temperature range of operation, the substrate material of the polarizer, the frame material, the size of the frame, etc. Preferably, the tension at room temperature during bonding is at least 2000 psi for each substrate.

[0058] By attaching the substrates 20a, 20b to the frame 32 under tension, a foam spacer, and thus the corresponding adhesive that attaches the foam spacer to the substrates 20a, 20b, is not needed. Thus, an inner-most planar surface 34a of the first polarizer substrate 20a and an inner-most planar surface 34b of the second polarizer substrate 20b face each other such that exposed portions of the respective inner-most planar surfaces (i.e., portions of the respective substrates that are not attached to the frame 30) are adhesive-free, structurally independent of each other, mechanically independent of each other, and are separated by a gap, e.g., an air gap, between the entire exposed portions. Further, by attaching the two substrates 20a, 20b on opposite sides of the frame at about the same tension, the force applied to the frame 32 by the first (top) polarizer substrate 20a and the force applied to the frame 32 by the second (bottom) polarizer substrate 20b effectively cancel each other. Therefore, the frame does not tend to bend one way or the other.

[0059] The polarizer in accordance with the invention provides improved performance relative to a conventional polarizer. More particularly, and with reference to FIG. 5, illustrated is a cross section of a plane wave 40 passing through a conventional polarizer having a foam layer 24 bonded to upper and lower substrates 20a, 20b with an adhesive 26. As illustrated, a plane wave 40 is incident on a first (bottom) surface of polarizer 10 produces a resultant plane wave 42 that exits a second (top) surface of the polarizer 10. Due to the dielectric refraction and guiding properties created by the foam layer 24 and adhesive 26, undesired surface waves 44 couple with the structure. Further, the relatively strong surface waves 44 produce magnetic and electric fields 46 about the polarizer 10 that are relatively large (i.e., they extend a substantial distance away from the surface of the top and bottom substrates in a direction normal to those surfaces), which may result in undesirable coupling with other metal structures in the vicinity of the polarizer 10.

[0060] In contrast to the polarizer of FIG. 5, a polarizer 30 in accordance with the invention provides significantly improved performance. More specifically, and with reference to FIG. 6, the absence of a foam layer and corresponding adhesive produces significantly lower surface waves 44′, which in turn produces a tighter boundary for the magnetic and electric fields 46′ (, i.e., the magnetic and electric fields do not extend as far away from the surface of the respective substrates and thus there is less chance of undesirable coupling with nearby objects).

[0061] To form the polarizer in accordance with the invention, a frame 32 is provided that has a first side 32a and a second side 32b spaced apart from and opposite the first side. A first polarizer substrate 20a including one of a plurality of meanderline conductor patterns or a plurality of gridline conductor patterns is attached to the first side 32a of the frame 32. In this regard, the polarizer substrate is stretched across the frame 32 equally in all directions, and portions of the substrate are fixed to the frame 32 while the substrate is in the stretched state. The substrate 20a may be fixed to the frame 32 using a fastening means, such as a clamping device, an adhesive, a threaded fastener, or a combination of such fastening means. Once the substrate 20a is fixed to the frame in the stretched state, the substrate 20a remains under tension. After the first substrate 20a is attached to the frame 32, a second substrate 20b then is attached to the second side 32b of the frame 32 in the same manner. That is, the second substrate 20b is stretched across the second side 32b of the frame 32 and fixed to the frame using the fastening means. In attaching the second substrate 20b, the tension of the second substrate should be the same or approximately the same (e.g., within 10%) of the tension of the first substrate.

[0062] Referring to FIGS. 7A and 7B, illustrated is a sectional view of an exemplary antenna system 48 utilizing a polarizer 30 in accordance with the invention. The antenna system 48 includes a VICTS antenna 50 having a first (upper) conductive plate 52 having continuous transverse stubs 52a, and a second (lower) conductive plate 54 spaced apart from the first conductive plate 52.

[0063] Mounted on the first conductive plate 52 on top of the continuous transverse stubs 52a is a first polarizer assembly 53 constructed via conventional means. Mounted above the first polarizer assembly 53 is a second polarizer assembly 56 that includes a support structure 58 having a polarizer 30 according to the invention attached thereto and a clamp 61 that is used to affix the polarizer 30 to the support structure 58 using fasteners (not shown). A bearing 60a is arranged in races of the first conductive plate 52 and the support structure 58, the bearing enabling relative rotation between the second polarizer assembly 56 and the first polarizer assembly 53 and upper conductive plate 52.

[0064] Mounted on the second polarizer assembly 56 is a third polarizer assembly 62 that includes a support structure 64 having a polarizer 30 according to the invention attached thereto and a clamp 61 that is used to affix the polarizer 30 to the support structure 58 using fasteners (not shown). Another bearing 60b is arranged in races of the second polarizer assembly 56 and the third polarizer assembly 62, the bearing enabling relative rotation between the second polarizer assembly 56 and the third polarizer assembly 62. The VICTS antenna 50, the second polarizer assembly 56 and the third polarizer assembly 62 are mounted within a housing 66.

[0065] Accordingly, a polarizer in accordance with the invention not only provides enhanced performance, but also requires less components. In particular, the polarizer in accordance with the invention does not include a foam spacer and the corresponding adhesive layers, which reduces losses through the polarizer.

[0066] Although the invention has been shown and described with respect to a certain embodiment or embodiments, equivalent alterations and modifications may occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.