Patent Publication Number: US-6664939-B1

Title: Foam-filled antenna and method of manufacturing same

Description:
RELATED APPLICATIONS 
     This application is related to, and claims the benefit of priority from, U.S. Provisional Patent Application Ser. No. 60/279,349, filed Mar. 28, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to parabolic antennas, such as are employed to receive and/or transmit carrier signals, and a method of forming such antennas and other metal or alloy parts where precise tolerances are required in the finished product. More particularly, the present invention relates to a parabolic antenna comprising a backing section and reflector made of deformable material, for instance metal or alloy, the backing section and reflector being mated to define a hollow interior cavity that is filled with a rigid support structure comprising a closed-cell foam. The present invention also particularly relates to a method of forming accurately dimensioned parts having close tolerances, such as transmission antennas, wherein a deformable material skin, for instance an antenna reflector of metal, is maintained in exact conformance with a vacuum buck, the vacuum buck having a configuration corresponding to the close tolerances of the preferred configuration of the completed part, and wherein a closed-cell foam slurry is provided, the cured foam forming a rigid support structure adequate to maintain the deformable material skin in the preferred configuration thereof following removal of the product from the vacuum buck. 
     BACKGROUND 
     Parabolic antennas generally have been around for a number of years and have, in the past several decades, become more and more widely used residentially and commercially for wireless television services, as well as other signal-communications applications. For instance, the advent of direct satellite television service, and the comparative “miniaturization” of the receiving and transmitting antennas have driven, and promise to continue driving, consumer demand for these goods and services. Recent advances in communications technology in particular have led to the development of earth-bound antennas with diameters on the order of tens of centimeters, rather than tens of feet, that are capable of receiving and transmitting signals. 
     One important consideration in the manufacture and design of such antennas is the fact that, necessarily, antennas are employed in all variety of climates. While parabolic antennas are relatively simple in their design, the fact that signal reception and transmission is dependent upon the shape of the reflector face, or “dish”, renders their precise manufacture difficult and, sometimes, expensive. The importance of dish tolerances is especially pronounced in transmission antennas, where variations in the surface of the dish too far from a desired curvature will significantly degrade transmission performance. 
     Conventional antennas, for instance of the type used for residential satellite reception, are typically composed of a metal skin, manufactured, for example, by stamping. Antenna formed in this fashion do not, by reason of shape “memory” properties of the commonly used materials, retain their preferred curvatures. These drawbacks make such antennas prone to performance degradation, and render them particularly ill-suited to use as transmitting antennas. 
     In the past, one of the named inventors of this application developed an improved method for forming an antenna having sufficiently close tolerances in the reflector, the method comprising placing one of two panels for an antenna on a vacuum die, and connecting to both panels a structural means such as a plurality of undulating strips to interlock the panels. This methodology is more particularly described in U.S. Pat. No. 4,791,432, issued to Piper et al., the disclosure of which is incorporated herein by reference in its entirety. However, the method of this patent is complicated, requires considerable parts fabrication relative to the structural means, and so is not suited to the inexpensive mass-production of antenna. 
     Consequently, there is a need for a parabolic antenna that is simple but robust in construction, economical to manufacture, while at the same time able to retain a reflector curvature of high tolerances even through variations in ambient temperatures, wind loading, and other environmental influences. 
     SUMMARY OF THE DISCLOSURE 
     The present invention addresses and solves the problems discussed above, and encompasses other features and advantages, by providing a parabolic, or dish-type, antenna comprising a backing section and a reflector of deformable material, such as polymer, metal, alloy, etc., the backing section and reflector being mated to define a hollow interior cavity that is filled with a rigid support structure comprising a closed-cell foam. Advantageously, the rigid support foam provides accurate shape retention for the preferred parabolic curvature of the antenna reflector, even through variations in temperature, wind loading, and other environmental influences. 
     The present invention also provides an economical and efficient method for forming accurately dimensioned parts having close tolerances, including parabolic antenna of the type of the inventive apparatus, the method comprising the steps of: 
     (a) providing a backing section and a reflector made of deformable material, the backing section and reflector being mateable to define a hollow interior cavity, and at least the reflector having a first curvature; 
     (b) providing a forming die including a male portion comprising a vacuum buck having a curved surface of predetermined tolerances exactly corresponding to a second, preferred curvature of the reflector, and a female portion dimensioned to receive the backing section therein; 
     (c) positioning and maintaining the reflector on the vacuum buck under vacuum pressure in conformance with the curved surface corresponding to the second, preferred curvature of the reflector; 
     (d) mating the backing section to the reflector; 
     (e) capturing the backing section and reflector in the mated condition thereof between the male and female portions of the forming die; 
     (f) injecting an expandable, closed-cell foam slurry into the hollow interior cavity defined between the mated backing section and reflector; 
     (g) while maintaining the reflector on the vacuum buck in conformance with the curved surface corresponding to the second, preferred curvature the curved surface corresponding to the second, preferred curvature of the reflector, curing the closed-cell foam slurry to form a rigid support structure; and 
     (h) releasing the vacuum pressure at the vacuum buck to thereby form an antenna wherein the reflector has a curvature corresponding to the second, preferred curvature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects, features, and advantages of the present invention will become apparent upon reference to the following description and drawings, in which: 
     FIG. 1 comprises a cross-sectional view of one embodiment of the parabolic antenna of the present invention; 
     FIG. 1A comprises a detailed view of the parabolic antenna shown in FIG. 1; 
     FIG. 1B comprises a detailed view of the mounting system of the parabolic antenna of FIG. 1; 
     FIG. 2 is a perspective view of the backing section of the parabolic antenna of FIG. 1; 
     FIG. 3 is a perspective view of the mounting plate employed in the antenna of the embodiment of FIG. 1; 
     FIG. 4 comprises a cross-sectional view of a second embodiment of the parabolic antenna of the present invention; and 
     FIGS. 5 through 8 depict the steps of the methodology of this invention. 
    
    
     DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
     Referring now to the drawings, wherein like numerals indicate like or corresponding parts, the present inventive apparatus will be seen to generally comprise a parabolic antenna comprising at least a reflector of deformable material, the reflector having a parabolic shape of predetermined close tolerances, and a rigid structural substrate provided on one side of and coextensive with the reflector, the rigid structural substrate comprising a closed-cell foam sufficient to accurately maintain the close tolerances of the reflector&#39;s parabolic shape. 
     According to a first embodiment of this invention, shown in FIG. 1, the antenna  10  preferably includes a backing section  15  and a reflector  30 , the backing section and reflector being mateable to define a hollow interior cavity filled with a closed-cell foam  40  forming a rigid support structure for maintaining the close tolerances of the reflector against distortion. The backing section  15  and reflector  30  comprise components formed of suitable material or materials, for instance metal, such as steel, an alloy, or other material or materials known to those of skill in the art to be suited to the purposes of antennas of the type referenced herein. According to the material or materials from which they are fashioned, the backing section  15  and reflector  30  may be formed by any conventional means. In the illustrated embodiments, the backing section  15  and reflector  30  are preferably stamped from metal, such as steel, according to conventional means, all as known to those of skill in the art. It will be appreciated from the remainder of this disclosure that the instant invention is particularly well suited to the economic manufacture of low-cost transmission antenna of precise tolerances that are fashioned from deformable materials such as steel and the like. 
     By virtue of the present invention, the backing section  15  and reflector  30  are able to be—and preferably are—formed from relatively thin material, being thereby characterized by deformability in their unassembled condition. It will be particularly appreciated with respect to the detailed description of the method of this invention that the reflector section  30  is ideally at least characterized by sufficiently deformability so as to be readily conforming to the preferred curvature for the reflector in the assembled antenna. In accordance with the illustrated embodiments, the reflector  30  and backing section  15  are each stamped from sheet metal having a thickness of from anywhere between approximately 0.010 to approximately 0.030 inches. Of course, these dimensions are exemplary only, and are not intended to be limiting of the present invention. Likewise, it will be appreciated by those of skill in the art that the shape and dimensions of the antennas of this disclosure are subject to variation according to the desired application. For instance, the antennas of this invention may be larger or smaller, may be characterized by various preferred curvatures, etc. It will also be understood that while the reflector  30  is preferably characterized by a curvature suitable to a given application, the backing section  15 , if employed in an antenna according to this invention, need not necessarily have a complimentary curvature to the reflector  30 , nor any curvature at all, the purpose of the backing section  15  in the illustrated embodiment being generally to facilitate mounting of the assembled antenna to a suitable support structure or surface, and to partially define a cavity for the closed-cell foam adjacent to the reflector. 
     Referring now to FIGS. 1 through 3, the backing section  15  according to a first embodiment of the inventive antenna is shown to define a generally convex shape, and includes an annular bead  16  defined by an inwardly curving, radiused lip portion  17  of the backing section  15 . The center, or apex, of the backing section  15  is preferably adapted for mounting the antenna to a support structure or surface, such as a mast (not shown), tripod, etc. The backing section  15  has formed therein a recess  19  dimensioned to receive a similarly dimensioned mounting plate  25 . The mounting plate  25  is preferably manufactured from a suitably strong material. In the embodiment of this disclosure, the mounting plate  25  is formed from steel having a thickness of approximately 0.18 inches, although these characteristics are not intended to be limiting of the present invention. The recess  19  includes a plurality of bores  20  therethrough, each adapted to receive one of a plurality of threaded bolts  26  projecting from a surface of the mounting plate  25 . As shown particularly in FIGS. 1 and 1B, these bolts  26  extend through the bores  20  and outwardly away from the backing section  15 , thereby providing a means for the antenna  10  to be bolted to a support structure or surface (not shown), as mentioned above. Of course, the particular mounting means disclosed herein are only exemplary, the mounting plate or other mounting means for the antenna of this disclosure not forming part of the present invention. 
     A foam injection port  21 , the employment of which is described in more detail below, is provided on at least one of the backing section  15  and/or the reflector  30 . In the illustrated embodiment, the injection port  21  is provided on the backing section  15 , positioned centrally in the recess  19 . According to this first embodiment, the mounting plate  25  also includes a bore  27  therethrough, the bore  27  being arranged coaxially with the foam injection port  21  so as to permit the communication of the foam slurry into the cavity defined between the backing section  15  and reflector  30 , all as described more fully below. Of course, it will be understood from this disclosure that the foam injection port  21  or ports may be provided elsewhere on the backing section  15  and/or reflector  30 , consistent with maintaining acceptable antenna performance for a given application. 
     Still referring to FIGS. 1 and 2, the reflector  30  of the first embodiment will be seen to define a generally convex, “dish”-shape having an outside diameter less than the outside diameter of the backing section  15 , but larger than the inside diameter of the backing section  15  as defined by the inside of the lip  17  proximate the bead  16 . According to this design, the reflector  30  can be captured by, and is prohibited from axial separation relative to, the backing section  15  in the assembled antenna  10 . As indicated, the precise curvature and size of the reflector  30  is determined by user desire and need, according to known methods, and may be altered without departing from the broader aspects of the present invention. 
     The closed-cell foam  40  comprising the rigid structure of the antenna  10  is of a commercially available type known in the art, being available, for instance, from the BASF corporation. This preferred foam is a thermal-set material which, when cured, forms a rigid structure the dimensions of which are not measurably influenced by temperatures of the kind likely to be encountered in environments where antennas such as of the type described are typically employed. The foam  40  is available as a liquid slurry that expands as it cures to form a rigid foam-like material. The injectable foam  40  expands in volume in proportion to the amount of slurry injected to occupy any cavity into which it is introduced. The cured foam is rigid but light-weight, and further characterized by a limited resiliency. Foams of the preferred type may be formed in varying densities, for instance 2 lbs., 4 lbs., 6 lbs., etc., these values referring to the weight of a cubic foot of foam upon curing. In practice, it has been discovered in connection with the present inventive antenna and method of manufacture that foam having a cured density of 2 lbs. per cubic foot in the cavity defined between the reflector and backing section is satisfactory to act as a rigid support structure sufficient to maintain the reflector in a predetermined parabolic shape of close tolerances in an antenna having an overall thickness in the range of approximately ¾ of an inch to approximately 1½ inches. Closed-cell foams are most preferred as they are not susceptible to environmental degradation such as can effect open-cell foams, for instance as may be caused by the migration of water into the foam. Of course, comparable materials may be substituted for the preferred material as described. 
     Given that the preferred foam expands while curing to occupy a known volume corresponding to the amount of slurry injected, it will be appreciated from this disclosure that the amount of foam slurry injected into the cavity is measured by suitable means to ensure that, upon curing, the foam provides a rigid structure to the antenna without altering the desired tolerances of the reflector. In the preferred method of this invention, described in more detail below, the amount of foam slurry injected into a cavity of a given size is regulated by injection time. 
     Referring now to FIG. 4, a second embodiment of the antenna of this invention is shown to comprise mateable backing section  15 ′ and reflector  30 ′ characterized in that each of the backing section and reflector includes an outwardly radiating, annular rim  24 ,  34 , respectively. The annular rims  24 ,  34  define axially confronting surfaces that abut when the backing section  15 ′ and reflector  30 ′ are mated. In this mated condition, shown in the FIG. 4, the backing section  15 ′ and reflector  30 ′ define a hollow interior cavity filled with closed-cell foam  40 ′, such as described above. An injection port  21 ′ is provided through the backing section  15 ′ for injecting the foam slurry into the hollow interior cavity, as previously set forth. Further according to this embodiment, the foam  40 ′ adheres to and forms a laminate of the backing section  15 ′ and reflector  30 ′, the backing section and reflector including no interrelating elements such as provided in the first embodiment of the inventive antenna. 
     It will be appreciated from the foregoing disclosure that the antenna of this invention may be manufactured by a variety of processes. However, it is also envisioned in this disclosure that the inventive antenna, or indeed any product where it is desired to maintain close tolerances, may be mass produced with the aid of a forming die designed to securely maintain the reflector curvature in a predetermined curvature of close tolerances until the closed-cell foam has cured to form a rigid support structure sufficient to accurately maintain the reflector in the close tolerances of the predetermined curvature. 
     More particular to the application of forming parabolic antennas, and especially transmitting antennas, the inventive method comprises the steps of: 
     (a) providing a backing section and a reflector made of deformable material, the backing section and reflector being mateable to define a hollow interior cavity, and at least the reflector having a first curvature; 
     (b) providing a forming die including a male portion comprising a vacuum buck having a curved surface of predetermined tolerances exactly corresponding to a second, preferred curvature of the reflector, and a female portion dimensioned to receive the backing section therein; 
     (c) positioning and maintaining the reflector on the vacuum buck under vacuum pressure in conformance with the curved surface corresponding to the second, preferred curvature of the reflector; 
     (d) mating the backing section to the reflector; 
     (e) capturing the backing section and reflector in the mated condition thereof between the male and female portions of the forming die; 
     (f) injecting an expandable, closed-cell foam slurry into the hollow interior cavity defined between the mated backing section and reflector; 
     (g) while maintaining the reflector on the vacuum buck in conformance with the curved surface corresponding to the second, preferred curvature of the reflector, curing the closed-cell foam slurry to form a rigid support structure; and 
     (h) releasing the vacuum pressure at the vacuum buck to thereby form an antenna wherein the reflector has a curvature corresponding to the second, preferred curvature. 
     Referring now to FIGS. 5 through 8, the foregoing steps are explained in more detail with respect to the exemplary application of forming a parabolic antenna, by which example the inventive method, and its application to the manufacture of other products, will be thereby better understood. 
     A forming die is provided including a male part comprising a vacuum buck  50  having a convex portion  51  the surface tolerances of which exactly correspond to the preferred close tolerances for the preferred curvature of the reflector  30  of the finished antenna, and a female part  55  having a concave portion  56  dimensioned to receive therein the backing section  15  of the antenna. (FIG. 5.) In the illustrated embodiment, the close tolerances of the convex portion  51  are achieved by the computer-aided miling of a suitable material, for instance a manufacturing-grade resin or aluminum, according to a computer-generated model of the optimum parabolic curvature for the finished antenna reflector. However, myriad other materials may be employed for the male and female parts of the forming die, including wood, steel, etc., the particular material of the forming die not comprising part of this invention. 
     According to the shape and dimensions of the backing section  15  as described in connection with the antenna of this invention, it will be seen with reference to the drawings that the female part  55  includes a bore  57  therethrough coaxially aligned with and communicating the injection port  16  with a regulatable source of the preferred closed-cell foam slurry (not shown). 
     Since shape “memory” and other material considerations make perfect fidelity to the preferred close tolerances of antennas practically impossible to achieve on a commercial scale in prior art forming methods for metal and polymer antennas especially, the reflector  30  is most preferably preformed from a deformable material to have a first curvature as closely corresponding to the surface tolerances of the convex portion  51  and so as closely corresponding to the preferred curvature of the reflector B as possible. Alternatively, it is also envisioned that the curvature of the reflector  30  may be formed on the male part  50  coincident with the remainder of the inventive method as described hereinafter. For purposes of this example, discussion will be made with reference to a reflector  30  preformed, for instance by stamping, with a first curvature approaching the close tolerances of the preferred curvature of the convex portion  51 . 
     As discussed below, the male part  50  is adapted to securely maintain the reflector  15  thereon in exact or nearly exact conformance with the curvature of the convex portion  51 . While this may be accomplished by a variety of means, it is most preferred that the male part  50  comprise a vacuum buck, whereby the reflector  30  is securely positioned on the convex portion  51  in exact or nearly exact conformance therewith by means of vacuum pressure. According to this most preferred method, the male part  50  includes a vacuum chamber  52  communicating with both a plurality of openings  53  provided through the convex portion  51 , as well as, via a suitable connection  54 , a regulatable vacuum source (not shown). Ideally, the openings  53  on the surface of the convex portion  51  are interconnected by superficial, recessed channels (not shown) that will communicate the vacuum pressure between the openings  53  so as to ensure the exertion of a sufficient vacuum force against the surface of reflector  30  to hold the reflector in exact or nearly exact conformance with the curvature of the convex portion  51 . 
     In operation of the inventive method, the reflector  30 ′ of an antenna is provided, having been formed from a desired material and having desired dimensions and a first curvature approaching the close tolerances of the second, preferred curvature of the convex portion  51 . The reflector  30 ′ is then positioned on the convex portion  51  of the male part  50  and secured against movement in relation thereto, ideally by the application of vacuum pressure communicated to the surface of the convex portion  51  via the openings  53 . (FIG. 6.) A backing section  15 ′ formed from a desired material and having desired dimensions is provided, the backing section  15 ′ being next aligned relative to the reflector  30 . (FIG. 7.) Thereafter, the male  50  and female  55  parts are positioned relative to each other such that the backing section  15 ′ is received in the concave portion  56 , and the backing section  15 ′ and reflector  30 ′ are captured between the male  50  and female  55  parts in precise radial and axial alignment. It is important that the backing section  15  and reflector  30  be securely mated so as to ensure against the unwanted migration of foam slurry outside of the cavity. It is also important that the female part  55  define an opposing surface coextensive with and closely confronting the backing section  15 , to thereby ensure that the closed-cell foam does not, during expansion thereof, deform the backing section. The closed-cell foam slurry is next injected through the bore  57  and injection port  21 ′ and into the hollow cavity defined between the reflector  30 ′ and backing section  15 ′ of the antenna. (FIG. 8.) The amount of slurry injected into the cavity is measured to ensure that, upon curing, the foam provides a rigid structure to accurately maintain the curvature of the reflector  30 ′ in the close tolerances of the second, preferred curvature. Upon complete curing of the closed-cell foam, the vacuum source (not shown) is extinguished and the male  50  and female  55  parts of the forming die are separated so that the completed antenna can be removed and the process repeated as desired in the formation of subsequent antennas. 
     By securely maintaining the deformable reflector on the vacuum die during curing of the foam slurry, it will be appreciated that the reflector of the resulting antenna is fixed in a curvature corresponding to the close tolerances of the preferred curvature. 
     It will also be appreciated from the above disclosure that the present invention improves upon the prior art by providing a parabolic antenna, and method of forming the same, that at once combines a robust design with a simple and economical means of manufacture. 
     Of course, the foregoing is merely illustrative of the present invention; those of ordinary skill in the art will appreciate that many additions and modifications to the present invention, as set out in this disclosure, are possible without departing from the spirit and broader aspects of this invention as defined in the appended claims.