Abstract:
An inflatable structure usable as a satellite terminal. An inflatable structure may include an inflatable membrane for forming the structure and two integral RF reflective portions. When the membrane is inflated, the two RF reflective portions oppose each other to form an antenna. One RF reflective portion may be a main reflector and the other RF reflective portion may be a subreflector, both reflectors curvatures that face each other to form a Gregorian antenna or a Cassegrain antenna. In another embodiment, an inflatable antenna may include an inflatable dish including a RF reflective main reflector and an opposing RF transparent dish wall. An inflatable RF transparent support member and an RF reflective subreflector extend from the dish wall. Again, when the antenna is inflated, the main reflector and the subreflector oppose each other to reflect RF energy toward each other to form an antenna.

Description:
FIELD 
       [0001]    The present disclosure relates to satellite terminals, and more particularly to satellite terminals including antennas that are inflatable and may be portable with relatively low weight and small storage requirements. 
       BACKGROUND 
       [0002]    High capability satellite terminals for communications are, in general, relatively very large, heavy, and expensive. While the physical characteristics of such terminals are not as critical for vehicle-mounted terminals, it is desirable in some circumstances for the terminals to be manually transported by a person, i.e., man-portable. In some cases, weight may be decreased by making the units smaller or using lighter materials, but certain antenna aperture sizes are needed to achieve useful data rates. When the antenna is made smaller, the combination of amplifier and up-converter , such as a Block Up-Converter (BUC), associated with the terminal needs to be made larger for transmission to be adequate. A larger BUC requires additional batteries, which increases weight, contradicting the purpose of reducing the size of the antenna. With respect to lighter materials, 1.2 meter dishes can be made to disassemble and can be made of lightweight plastic, but the precision of manufacturing involved has made this type of production expensive, and to an extent cost-prohibitive. 
         [0003]    The laws of radio frequency (RF) transmission physics pose a strategic design dilemma for achieving increased digital transmission speed. Increased transmission speed requires any or all of increased dish size, increased transmission power, decreased transmission losses, or decreased system-wide link noise. Accordingly, apparatus is needed that provides adequate transmission speed, factoring in the above criteria, combined with the ability for the apparatus to be man-portable. 
       SUMMARY 
       [0004]    In accordance with an embodiment, an inflatable structure is provided. The inflatable structure includes an inflatable membrane for forming the structure, a first RF reflective portion integral to the inflatable membrane, and a second RF reflective portion integral to the inflatable membrane. When the membrane is inflated, the first RF reflective portion and the second RF reflective portion oppose each other to form an antenna. 
         [0005]    In some embodiments, the inflatable membrane is made or assembled to be in one piece. In some embodiments, the first RF reflective portion comprises a main reflector and the second RF reflective portion comprises a subreflector, and the main reflector includes a first concave surface and the subreflector includes a second concave surface. The first concave surface and the second concave surface are spaced from and oppose each other to form a Gregorian antenna. In other embodiments, the first RF reflective portion comprises a main reflector and the second RF reflective portion comprises a subreflector, and the main reflector includes a concave surface and the subreflector includes a convex surface. The concave surface and the convex surface are spaced from and oppose each other to form a Cassegrain antenna. 
         [0006]    In some embodiments, the inflatable membrane can be compressed and compacted and subsequently inflated one or more times without substantially altering the original inflated shape of the membrane or the reflective efficiency of the first RF reflective portion and the second RF reflective portion. 
         [0007]    In accordance with another embodiment, an inflatable antenna may include an inflatable dish including a radio frequency (RF) reflective main reflector and an opposing RF transparent dish wall. An RF transparent support member extends from the RF transparent dish wall away from the main reflector and has a free end. An RF reflective subreflector is proximate and attached to the free end of the RF transparent support member, and the support member and the subreflector are inflatable. When the antenna is inflated, the main reflector and the subreflector oppose each other to reflect RF energy toward each other to form an antenna. In some embodiments, the main reflector and the RF transparent dish wall define a dish interior volume, the subreflector and the RF transparent support member define a support member interior volume, and the dish interior volume and the support member interior volume are in fluid communication. 
         [0008]    In accordance with another embodiment, a method of making an inflatable antenna may include providing material for forming an inflatable structure. A first portion and a second portion of the material are caused to be RF reflective. The material is assembled to form an inflatable membrane. When the membrane is inflated, the first portion and the second portion oppose each other to form an antenna. 
         [0009]    Other aspects and features of the present disclosure, as defined solely by the claims, will become apparent to those ordinarily skilled in the art upon review of the following non-limited detailed description of the disclosure in conjunction with the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0010]    The following detailed description of embodiments refers to the accompanying drawings, which illustrate specific embodiments of the disclosure. Other embodiments having different structures and operations do not depart from the scope of the present disclosure. 
           [0011]      FIG. 1  is a rear perspective view of an embodiment of a communications terminal including a first embodiment of an inflatable antenna assembly with a base in accordance with the present disclosure. 
           [0012]      FIG. 2  is an exploded view of the inflatable antenna assembly of  FIG. 1 . 
           [0013]      FIG. 3  is a perspective view of an example of a mounting frame of the inflatable antenna assembly of  FIG. 1 . 
           [0014]      FIG. 4  is a side view of the exemplary mounting frame of  FIG. 3  assembled to an exemplary assembly of a horn, orthomode transducer (OMT), and waveguide, referred to herein as a horn/OMT/waveguide, of  FIG. 1 . 
           [0015]      FIG. 5  is a perspective view of an example of a gimbal of the support of  FIG. 1 . 
           [0016]      FIG. 6  is a partially exploded rear perspective view of the horn/OMT/waveguide of the inflatable antenna assembly of  FIG. 1 , showing a portion of the exemplary gimbal of  FIG. 5 . 
           [0017]      FIG. 7  is a partially exploded side view of the exemplary horn/OMT/waveguide and the portion of the exemplary gimbal as shown in  FIG. 6 . 
           [0018]      FIG. 8  is an exploded perspective view of a second embodiment of an inflatable antenna assembly. 
           [0019]      FIG. 9  is a perspective view of an example of a mounting frame of the inflatable antenna assembly of  FIG. 8 . 
       
    
    
     DESCRIPTION 
       [0020]    The following detailed description of embodiments refers to the accompanying drawings, which illustrate specific embodiments of the disclosure. Other embodiments having different structures and operations do not depart from the scope of the present disclosure. Like reference numerals may refer to the same element or component in the different drawings. 
         [0021]    Certain terminology is used herein for convenience only and is not to be taken as a limitation on the embodiments described. For example, words such as “front,” “rear,” “top,” “bottom,” “upper,” “lower,” “left,” “right,” “horizontal,” “vertical,” “upward,” and “downward” merely describe the configuration shown in the figures or relative positions. The referenced components may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise. 
         [0022]    Referring now to the drawings, wherein like reference numerals designate corresponding or similar elements throughout the several views,  FIG. 1  shows an embodiment of an inflatable antenna assembly  30  including an antenna  40  with an inflatable dish  42  that substantially rectangular in one plane to provide higher gain in the horizontal axis than in the vertical axis of that plane, and an inflatable support member  44 . The antenna assembly  30  also includes transmission and reception elements including a horn/OMT/waveguide  46 , a transmitter  48 , and a receiver  50 . The antenna assembly  30  is shown disassembled from its tripod base  56  and modem  58 , and in  FIG. 2  the antenna assembly  30  is shown with its components separated. The inflatable antenna dish  42  includes at least an RF reflective membrane at the rear that is the main reflector  60 , and an RF transparent membrane  62  at the front. There may also be RF transparent sides  64  as necessary to realize the desired shape of the main reflector  60 . When the term “RF reflective” is used herein, it should be understood that the membrane is in actuality substantially RF reflective, reflecting RF energy in an amount that is adequate for the successful performance of the antenna, as opposed to being perfectly reflective. Likewise, when the term “RF transparent” is used herein, it should be understood that the membrane is in actuality substantially RF transparent, allowing RF energy to pass through in an amount that is adequate for the successful performance of the antenna, as opposed to being perfectly transparent. 
         [0023]    The inflatable dish  42  defines an interior volume. The main reflector  60  is concave frontward. In addition to the main reflector  60 , the inflatable support member  44  supports a subreflector  70   a  that is RF reflective and may be an RF reflective membrane is provided at the end of the inflatable support member  44 . The support member  44  may also be a membrane, and with the subreflector  70   a  defines an interior volume that is in fluid communication with the interior volume of the dish  42 , which occurs in the example shown through an opening  76  between the two interior volumes to effectively create a larger interior volume. The support member  44  in this embodiment may have a substantially rectangular front  78  and rear  80 , and may have four sides  82  that taper from back to front. The sides  82  of the support member  44  are RF transparent. The subreflector  70   a  may be at the front end of the support member  44  and may also be rectangular. The subreflector  70   a  may be concave toward the dish  42 , resulting in a dish  42  and subreflector  70   a  that are concave toward each other to form a Gregorian antenna. Alternatively, the subreflector may take the shape shown as the second subreflector  70   b  in  FIG. 2 , which is convex toward the dish  42 , while the dish  42  remains concave toward the subreflector  70   b.  This results in a dish  42  and subreflector  70   b  that form a Cassegrain antenna. 
         [0024]    The antenna  40  may be made of any flexible material for forming a membrane that will contain a gas and includes, but is not limited to, such materials, for example, as Mylar, fiber reinforced material with a weave, thin film doped or vapor deposited, or aluminized rubber fabric. In addition, the material will preferably (a) hold its shape after being folded, rolled, compressed, or compacted, (b) be capable of being coated with a smooth, highly RF reflective substance to make it suitable as an antenna, (c) be RF transparent when without RF reflective coating, and (d) when RF reflective coating is applied, be capable of being compressed and compacted and subsequently being uncompressed and uncompacted one or more times without affecting its original and desired inflated shape or ability to efficiently reflect RF energy. The RF reflective main reflector  60  and the RF reflective subreflector  70   a  are both integral to the membrane and may be made by the application of RF reflective coating to the membrane, which when fabricated may all be one piece of material. The subreflector  70   a,    70   b  may be made of RF reflective-coated solid material that holds its shape when the antenna  40  is not inflated, including but not limited to a plastic. This is particularly relevant to the convex subreflector  70   b,  which as a membrane would not hold a convex shape when the antenna  40  is inflated. The relatively small size of the subreflector  70   a,    70   b  may provide the ability for a solid subreflector not to damage the membrane when the antenna  40  is compressed and expanded, which in some embodiments may happen repeatedly. Rounded corners and edges on a rectangular solid subreflector  70   a,    70   b  may be desirable. 
         [0025]    In one method of fabrication, the antenna  40  may be constructed out of multiple flexible elements and bonded together after RF reflective coating has been applied to the inner surface of the main reflector  60  and the inner surface of the subreflector  70   a,    70   b.  The dish  42  and support member  44  may be, as one method vacuum form molded with high precision and relatively low cost, and may be filled with, for example, a dry gas or two-part, hardening, RF transparent foam. If two part hardening foam is used, it is understood that the inflatable antenna will not be collapsible and compactable after inflation, however, the other attributes of the antenna will still apply, such as light weight and high gain. If used, the hardening foam will supply an additional benefit of stiffness of the antenna structure in windy conditions. Bonding must be airtight to allow inflation of the antenna  40  with any dry gas or foam. A gas could be discharged, for example, from a CO 2  cartridge into the antenna  40 . Alternatively, the two part foam could be discharged into the antenna  40  from two small, pressurized canisters. 
         [0026]    With respect to the transmission and reception elements, in this example a transmitter  48  and receiver  50  are mounted to the horn/OMT/waveguide  46 , which in turn is mounted to the tripod base  56 , as will be discussed in greater detail below. A mounting frame  90  is provided that may be attached to the back of the main reflector  60  at a central position with a permanent, airtight bond. In this embodiment, the mounting frame  90  is rectangular. The area of the main reflector  60  that is within the limits of the mounting frame  90  has no RF reflective material applied to it and accordingly is an RF transparent region  92 , as may be accomplished by masking this area when the RF reflective material is applied to the rest of the main reflector  60 . Therefore, the RF transparent region  92  allows RF energy to pass in and out of the horn/OMT/waveguide  46 . 
         [0027]    As shown in  FIG. 3 , the mounting frame  90  provides an airtight pressure window  94  (not shown in  FIG. 2 ) and a valve  96  (also not shown in  FIG. 2 ) that communicates with the front side of the window  94 . The valve  96  may be a Schrader valve or any airtight check valve of suitable size for admission of dry gas or two part foam. With the mounting frame  90  bonded in place, a source of dry gas or two part foam may be connected to the valve  96 . The gas or foam may pass through the valve  96 , to the front side of the window  94 , through an opening in the main reflector  60  in the RF transparent region  92  to inflate the dish  42 , and also through the opening  76  between the front, RF transparent membrane  62  of the dish  42  and the back  80  of the support member  44  to inflate the support member  44 . Thus, the entire antenna  40  may be inflated from one valve  96 . It should be understood that alternative port locations for a valve could be provided, such as, for example, a port directly into a horn/OMT/waveguide with a flow path for gas or two part foam to get into the antenna. In such an alternative configuration, an opening could be provided in the mounting frame in place of the pressure window to allow entry of the gas or foam into the dish  42  and an airtight seal would be needed between the mounting frame  90  and the horn/OMT/waveguide  46 . Additional airtight pressure windows would then be needed on the horn/OMT/waveguide&#39;s  46  receiver port and transmitter port. 
         [0028]    In  FIG. 4 , the mounting frame  90  is shown mounted to the horn/OMT/waveguide  46 . The opening of the horn  100  is rectangular and accommodates the mounting frame  90 . While omitted from other figures, an example of apparatus for mounting the mounting frame  90  to the horn/OMT/waveguide  46  is shown in  FIG. 4 . Clips  102  that may be loops may be pivotally attached with hinges  104  to the top and bottom of the mounting frame  90 . Latches  106  that also pivot at hinges  108  may be attached to the horn  100 . The clips  102  may be positioned over the latches  106 , and the latches  106  may be pivoted rearward to secure the clips  102  and pull the mounting frame  90  to a tight fit with the horn  100 . Other means, such as captured thumbscrews, may be used. Preferably the mounting means used provides components that do not detach from the mounting frame  90  or horn  100 , which avoids the possibility of loss of those parts or searching for them when dropped. 
         [0029]      FIG. 5  shows the gimbal  120  of the tripod base  56 . In one embodiment, the gimbal  120  is motorized, but the gimbal  120  could alternatively be manually controlled, in which case degree markings on the azimuth, elevation and polarity axis and a level, such as a two axis bubble level, could be provided. The gimbal  120  provides three axis control of azimuth, elevation, and polarity. Azimuth adjustment may be provided by relative rotation of horizontal plates  122 ,  124 . Elevation adjustment may be provided by pivoting at a hinge  126 . Polarity adjustment may be provided by rotation of a front, polarity rotation plate  128  relative to a back plate  130 . 
         [0030]      FIGS. 6 and 7  show the mounting of the horn/OMT/waveguide  46  to the tripod base  56 . Specifically, the horn/OMT/waveguide  46  is mounted to the front, polarity rotation plate  128  of the tripod base  56 . In the embodiment shown, a bracket  132  is provided on the back of and may be integral to the horn/OMT/waveguide  46  (shown only in  FIGS. 6 and 7 ). The bracket  132  includes two holes  136  on spaced arms at the top, and a downward facing hook  140  at the bottom. The holes  136  are spaced to receive bolts  144  extending from the polarity rotation plate  128 . Captured thumb nuts  146  ( FIG. 7 ) are provided on the bracket  132  for tightening the horn/OMT/waveguide  46  to the polarity rotation plate  128 . At the bottom of the polarity rotation plate  128  is an upward facing hook  150 . The downward facing hook  140  of the horn/OMT/waveguide  46  is received in the upward facing hook  150  of the polarity rotation plate  128  to secure the bottom of the horn/OMT/waveguide  46  to the bottom of the polarity rotation plate  128 . A gasket may be used to provide and airtight connection if an alternative configuration is used in which inflation gas is provided through the horn/OMT/waveguide  46 . The horn/OMT/waveguide  46 , transmitter  48 , and receiver  50  are located close to the mounting point of the antenna  40  (the mounting frame  90 , right behind the main reflector  60 ) to reduce the required torque the gimbal  120  must apply to maintain the position of the antenna  40 , and this allows decreasing the size and weight of the gimbal  120 , particularly if the antenna  40  is to be used as a motorized steerable unit. 
         [0031]    The horn/OMT/waveguide  46  in some embodiments may be made of a lightweight material, such as but not limited to, for example, a composite, aluminized plastic or styrene, carbon fiber reinforced epoxy, other materials that can have a reflective surface applied to them, or metal. The horn/OMT/waveguide  46  may be coated on the inside with an RF reflective substance, such as, but not limited to, vaporized aluminum. 
         [0032]    The antenna shape is not limited to rectangular, but may be other shapes as well. For example,  FIG. 8  shows an embodiment of an inflatable antenna assembly  160  including an antenna  170  that is substantially circular in one plane, with an inflatable dish  172  and support member  174 . The antenna assembly  160  also includes a horn/OMT/waveguide  176 , transmitter  178 , and receiver  180 . Again, the antenna dish includes at least an RF reflective membrane at the rear that is the main reflector  180 , and an RF transparent membrane  182  at the front. 
         [0033]    The dish  172  defines an interior volume. The main reflector  180  is concave frontward. In addition to the main reflector  180 , the inflatable support member  174  supports a subreflector  184   a  that is, once again, RF reflective and may be an RF reflective membrane provided at the end of the support member  174 . The support member  174  may also be a membrane, and with the subreflector  184   a  defines an interior volume that is in fluid communication with the interior volume of the dish, which occurs in the example shown through an opening  186  between the two interior volumes to effectively create a larger interior volume. The support member  174  in this embodiment has a substantially frustoconical shape, as it tapers from back to front, with substantially circular front  188  and rear  190 . The support member  174  is RF transparent. The subreflector  184   a  is at the front end  188  of the support member  174  and may be substantially circular as well. The subreflector  184   a  may be concave toward the dish  172 , resulting in a dish  172  and subreflector  184   a  that are concave toward each other to form a Gregorian antenna. Alternatively, the subreflector may take the shape shown as the second subreflector  184   b  in  FIG. 2 , which is convex toward the dish  42 , while the dish  42  remains concave toward the subreflector  184   b.  As discussed with respect to the previous convex subreflector  70   b,  this results in a dish  42  and subreflector  184   b  that form a Cassegrain antenna. The materials may be selected and the antenna  170  may be fabricated as previously described for the rectangular antenna  40 . 
         [0034]    The transmission and reception elements, in this example a transmitter  48  and receiver  50 , respectively, are mounted to the horn/OMT/waveguide  176 , which includes a horn  192  with a circular opening. A mounting frame  194  may be provided that is attached to the back of the main reflector  180  at a central position with a permanent, airtight bond. In this embodiment, the mounting frame  194  is circular. An RF transparent region  196  on the main reflector  180  may also be circular. 
         [0035]    As shown in  FIG. 9 , the mounting frame  194  provides an airtight pressure window  198  and a valve  96  (not shown in  FIG. 8 ) that communicates with the front side of the window. With the mounting frame  194  bonded in place, a source of dry gas or two part foam may be connected to the valve  96 . The gas or foam may pass through the valve  96 , to the front side of the window, through an opening  200  in the main reflector  180  to inflate the dish  172 , and also through the opening  186  between the front, RF transparent membrane  182  of the dish  172  and the back  190  of the support member  174  to inflate the support member  174 . The entire antenna  170  may be inflated from one valve  96 . 
         [0036]    Operation, horn/OMT/waveguide  176  material selection and design, mounting of the mounting frame  194  to the horn/OMT/waveguide  176 , and mounting to the horn/OMT/waveguide  176  to the gimbal  120  may be done similarly to that of the rectangular antenna assembly  30  embodiment previously described. 
         [0037]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
         [0038]    Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art appreciate that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown and that the embodiments herein have other applications in other environments. This application is intended to cover any adaptations or variations of the present disclosure. The following claims are in no way intended to limit the scope of the disclosure to the specific embodiments described herein.