Abstract:
The invention is an inflatable antenna system. The antenna system includes an inflatable lenticular dish. The dish is enclosed in an inflatable radome. The inflatable radome stabilizes the orientation of the dish and protects it from environment conditions such as wind.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates generally to an antenna. More specifically, the present invention relates to an inflatable antenna that is stabilized with a radome.  
           [0003]    2. Background Art  
           [0004]    Antennas tend to be very sensitive elements of communications or radar systems. Correct alignment of the dish portion of the antenna is critical to proper operation. However, a large antenna dish can become unstable when exposed to environmental conditions such as wind. Typical solutions involve bracing and reinforcing the antenna system with a heavy support structure. While this approach works for fixed location antennas, it is difficult to implement for portable antennas. FIG. 1 shows an example of a prior art deployable satellite communications antenna  10 . The satellite dish  12  is braced by heavy beams  14  in order to keep the entire antenna properly aligned. The amount of weight and storage space required by such an antenna system is an impediment to quick and easy movement and assembly in locations that need satellite communications. Other solutions include using an antenna with a smaller dish size. While smaller antennas are more portable, their performance is not as good as that of larger antennas. Antenna performance characteristics such as the signal-to-noise ratio are dependent on the size and parabolic curvature of the antenna dish. Typically, a larger dish has better performance.  
           [0005]    Light weight inflatable antennas have been demonstrated for use on orbital satellites. These inflatable antennas are large in size and have excellent performance characteristics. Since they are used in space, they are not subject to environmental conditions such as wind that can affect their alignment. However, because of the structural weakness resulting from their light weight, they are typically unsuitable for atmospheric use. Consequently, a need exists for a ground based inflatable antenna that is both stable and portable.  
         SUMMARY OF INVENTION  
         [0006]    In some aspects, the invention relates to an antenna, comprising:  
           [0007]    an inflatable dish; and an inflatable radome that surrounds the dish, where the radome stabilizes the orientation of the dish.  
           [0008]    In other aspects, the invention relates to a phased-array antenna, comprising: at least one array of multiple radiator panels, where the panels are folded with off-set, self-aligning hinges; and an inflatable radome that surrounds the array, where the radome stabilizes the orientation of the array.  
           [0009]    In other aspects, the invention relates to a phased-array antenna, comprising: an array of multiple radiator panels; an inflatable, cylindrical-shaped radome that surrounds the array, where the radome stabilizes the orientation of the array; and where the radiator panels are attached to the interior of the radome with multiple catenaries.  
           [0010]    In other aspects, the invention relates to a phased-array antenna, comprising: an array of multiple radiator panels, where the panels are folded with off-set, self-aligning hinges; and a support frame that stabilizes the orientation of the array.  
           [0011]    In other aspects, the invention relates to an antenna, comprising: a log periodic array antenna; and an inflatable radome that surrounds the log periodic array antenna, where the radome stabilizes the orientation of the log periodic array antenna.  
           [0012]    In other aspects, the invention relates to an antenna, comprising: means for transmitting and receiving signals; and means for stabilizing the means for transmitting and receiving signals.  
           [0013]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]    It should be noted that identical features in different drawings are shown with the same reference numeral.  
         [0015]    [0015]FIG. 1 shows a view of a prior art deployable satellite communications antenna.  
         [0016]    [0016]FIG. 2 a  shows a cross-section view of a ground based inflatable antenna accordance with one embodiment of the present invention.  
         [0017]    [0017]FIG. 2 b  shows an alternative cross-section view of a ground based inflatable antenna in accordance with one embodiment of the present invention.  
         [0018]    [0018]FIG. 2 c  shows a view of catenary connections for a lenticular dish in accordance with one embodiment of the present invention.  
         [0019]    [0019]FIGS. 3 a  and  3   b  show an overhead and side view of a support cradle for the antenna shown in FIG. 2 in accordance with one embodiment of the present invention.  
         [0020]    [0020]FIG. 4 a  shows a view of a standard feed horn used in accordance with one embodiment of the present invention.  
         [0021]    [0021]FIG. 4 b  shows a view of an array feed used in accordance with an alternative embodiment of the present invention.  
         [0022]    [0022]FIG. 5 shows a view of a vehicle with a fully deployed inflatable antenna and radome in accordance with one embodiment of the present invention.  
         [0023]    [0023]FIGS. 6 a ,  6   b , and  6   c  show progressive steps of deploying an inflatable antenna in accordance with one embodiment of the present invention.  
         [0024]    [0024]FIGS. 7 a  and  7   b  show an inflatable torus and lenticular used with an antenna in accordance with one embodiment of the present invention.  
         [0025]    [0025]FIG. 8 shows a deployed phased-array radar panel used in accordance with one embodiment of the present invention.  
         [0026]    [0026]FIG. 9 shows a deploying phased-array radar panel with radome in accordance with one embodiment of the present invention.  
         [0027]    [0027]FIG. 10 shows a deployable phased-array radar panel used in accordance with one embodiment of the present invention.  
         [0028]    [0028]FIG. 11 shows two panels of a deployed phased-array antenna with self-aligning offset hinges in accordance with one embodiment of the present invention.  
         [0029]    [0029]FIGS. 12 a  and  12   b  show two partially unfolded panels of a phased-array antenna with self-aligning offset hinges in accordance with one embodiment of the resent invention.  
         [0030]    [0030]FIG. 13 a  shows a cut away view of a vehicle with a single phased-array radar panel and radome in accordance with one embodiment of the present invention.  
         [0031]    [0031]FIG. 13 b  shows a cut away view of a vehicle with triple phased-array radar panels and radome in accordance with one embodiment of the present invention.  
         [0032]    [0032]FIGS. 14 a  and  14   b  show an alternative embodiment of a single phased-array antenna panel and radome.  
         [0033]    [0033]FIGS. 15 a ,  15   b , and  15   c  show an alternative embodiment single panel phased-radar panel being extended on top of a vehicle.  
         [0034]    [0034]FIG. 16 shows a man-portable antenna in accordance with one embodiment of the present invention.  
         [0035]    [0035]FIGS. 17 a ,  17   b , and  17   c  show an alternative embodiment of the present invention that uses a log-periodic antenna and a radome. 
     
    
     DETAILED DESCRIPTION  
       [0036]    A ground-based inflatable antenna that may be used as part of a portable satellite communications system has been developed. The antenna may also be used for other applications such as radar or line-of-sight communications. FIG. 2 a  shows a cross-section view of an example of an antenna  16  in accordance with one embodiment of the present invention. The antenna includes an inflatable lenticular or “dish”  18  that is oriented towards a target such as a satellite. The dish  18  is surrounded by an inflatable radome  20 . The radome  20  is a spherical-shaped cover that provides protection for the dish  18  from environmental elements such as wind, etc. This allows the dish  18  to maintain proper alignment towards its target. The radome  20  is constructed of a flexible material or a membrane that is stable in ultraviolet light. A membrane is a thin, pliable sheet of natural or synthetic material that is supported by either mechanical tension or a pressure differential. The material should not interfere with the signals being generated or received by the antenna. Observation windows (not shown) made of clear material such as vinyl may be included on the surface of the radome  20  to allow visual inspection of the internal area of the antenna.  
         [0037]    The radome  20  is supported by a cradle  22  that holds the antenna in position. The cradle  22  may attached to additional base structures such as a vehicle top or trailer. FIGS. 3 a  and  3   b  show respectively an overhead view and a side view of an example of a cradle  22 . The inter-connections from the antenna  16  to the other components of the system are made through an opening  30  in the bottom of cradle  22 .  
         [0038]    Returning to FIG. 2 a , access to the interior of the radome  20  is available through a port  26 . In this embodiment, the port is sealed with a zipper. The inflation and deflation of the antenna is controlled with an inflation tube  24  and an egress valve  25  respectively. A feed horn  28  for the dish  18  is located on the exterior of the radome  20 . It is supported entirely by the surface of the inflated radome without any additional structure. The dimensions of the radome are configured such that the feed horn is located at the focal point of the dish  18 . This configuration of the feed horn  28  with the dish  18  is called an “on-axis” or “prime focus” alignment. In alternative embodiments, other configurations of the feed and dish may be used such as: an offset alignment; a folded alignment (including both Gregorian and Cassegrain arrangements); and a hybrid of the offset and folded alignments.  
         [0039]    The dish  18  may be constructed of two complementary, doubly-curved membranes. In FIG. 2 b , the dish  18  is shown with a parabolic curved reflector membrane  21  and an RF-transparent parabolic canopy  23 . The concave sides of the membranes are joined at a bond band  27  to form a convex-shaped structure that is called the lenticular dish  18 . As shown in FIG. 2 c , the lenticular dish  18  is held in place when the radome  20  is inflated by a series of catenaries  29  that are connected to the bond band  27  with grommets  31 .  
         [0040]    [0040]FIGS. 4 a  and  4   b  show two examples of types of feeds that may be used with the present invention. FIG. 4 a  shows a radio frequency (RF) feed horn with a 90° bend  32 . Other embodiments may use different configurations and angles for a feed horn. The feed horn is mounted on the radome so that the opening  34  in the pyramid-shaped base faces down towards the dish of the antenna. FIG. 4 b  shows an array feed  36  that also may be mounted on the radome. The array feed  36  contains a series of identical elements  37  which can be used to form multiple signal beams or to electrically steer the antenna.  
         [0041]    [0041]FIG. 5 shows an example of an inflatable antenna mounted on the top of a vehicle  38 . A cradle  42  is used to connect the radome  40  to the top of the vehicle. The antenna is inflated through a connection  44  in the side of the cradle  42 . A blower (not shown) is attached to the connection to provide a continuous flow of air to the antenna. In this example, the air flow from the blower should be continuous to the antenna in order to compensate for leakage of air from the radome through the material, zipper, observation panels, etc. The remaining components of the communication system are located in the vehicle and are connected to the antenna through the cradle  42 .  
         [0042]    [0042]FIGS. 6 a ,  6   b , and  6   c  show an example of how the antenna is carried and inflated. FIG. 6 a  shows a deflated antenna that is stowed away for easy transportation. The cradle  42  is attached to the top of a vehicle as previously shown in FIG. 5. The cradle  42  and its cover  46  contain the collapsed deflated antenna. As shown FIG. 6 b , once the vehicle arrives at its destination, a blower (not shown) is attached to the connection  44  on the side of the cradle  42  and the cover  46  is opened. As shown in FIG. 6 c , once the blower is turned on, the antenna  48  begins to inflate. The inflation continues until the antenna is fully deployed. Once inflated, the air pressure inside the radome should be maintained to ensure mechanical stability of the antenna over vibration, wind gusts, gravity, etc.  
         [0043]    The internal air pressure is typically maintained by a continuous air flow from the attached blower to compensate for leakage. However, if the radome is less prone to leakage, intermittent use of the blower could be used to periodically re-pressurize the antenna. The amount of internal air pressure is dependent on the expected amount of force to be exerted on the antenna. Such forces primarily include wind but also may include the weight of the horn that is supported by the radome. For example, an internal air pressure of about 0.1 pounds per square inch, gauge (PSIG) is sufficient to withstand the load of winds of 30 miles per hour (MPH) on a 5-meter diameter radome. Higher internal pressures may be used to withstand loads from higher winds. Additionally, the antenna may be secured by supplemental guy lines called “tethers” that attach to the exterior of the radome and are tied to a stable structure such as the vehicle or an in-ground stake. In an alternative embodiment, the exterior of the radome could be coated with a resin that would harden and cure when exposed to sunlight. This embodiment would typically not be re-stowed once it had been initially deployed and consequently would become a semi-permanent antenna.  
         [0044]    [0044]FIGS. 7 a  and  7   b  show a perspective and frontal view respectively of an example of an inflatable torus  50  and lenticular or “dish”  52  used with the antenna. The torus  50  is an inflatable ring that fits within and is attached to the interior of the radome of the antenna. In alternative embodiments, the antenna could be used without the radome by securing it with separate support struts such as ground tethers, etc. When it is fully inflated and expanded, the torus  50  holds the dish  52  in place with a series of catenaries  54 . These catenaries are attached to both the torus  50  and the dish  52  with grommets. The size and parabolic arc of the dish is designed so that its focal point should be on the surface of the radome. The focal point will be where the feed is located. It is important to note that the dimensions of antennas will vary widely in different embodiments. However in the present example, the antenna has a diameter of 196 inches. The internal dish has a diameter of 189 inches (4.8 meters) with a focal length of about 120 inches and is supported from the spherical radome by a series of elastic retainers.  
         [0045]    The lenticular dish may be formed by seaming two parabolic membranes together. One membrane is microwave-reflective and the other is non-reflective. The membranes may be made of light weight, thin polymers. The microwave-reflective composition of the dish of the antenna may be either a heterogeneous material or a homogenous material. The reflective membrane may be rendered reflective by coating it with metallizing paint. In one embodiment, metallizing paint is a heterogeneous material that includes silver metallic flake in an epoxy binder. In other embodiments, other conductive materials such as a homogeneous thin layer of aluminum or other microwave reflective materials could be used as a reflective coating. The non-reflective membrane is uncoated and transparent to RF signals. The membranes that make up the dish are about 1.00-1.25 mils thick. The heterogeneous reflective metallic coating for one of the membranes is about 100,000 Angstroms thick. Homogenous reflective coatings for the reflective membrane may be between 1,000-2,000 Angstroms thick.  
         [0046]    [0046]FIG. 8 shows cross-section view of an alternative embodiment of the present invention that uses a phased array antenna  56 . A phased array antenna uses an array of identical radiators with the capability of altering the phase of the power fed to each of them. This allows the shape and direction of the radiation pattern to be altered without mechanical adjustment of the antenna. In FIG. 8, the phased array antenna  56  has sixteen separate antenna panels  62 . Each panel  62  contains an array of smaller antennas or radiators. The antenna panels  62  are surrounded by a radome  58  in a similar manner as described in previous examples.  
         [0047]    The antenna is supported by a cradle  60  that may be attached to a supporting structure (not shown). Each panel  62  has a connection  64  with the other components of the system (not shown) through the interior of the cradle  60 .  
         [0048]    The panels  62  are made of a light weight, rigid material and they are connected with each other with a series of off-set, self-aligning hinges. This configuration allows for the panels to fold up when being stowed away. FIG. 9 shows a cut-away view of the antenna panels  66  being folded up inside the deflated radome  68 . As shown in FIG. 10, the antenna panels are arranged in four separate columns  70 ,  72 ,  74 , and  76  and four rows in each column  78 ,  80 ,  82  and  84 . When the antenna is stowed, the columns and rows all fold simultaneously with each other. The twelve panels on the exterior edge of the antenna are connected to the interior of the radome by flexible cords. As the radome inflates, these cords pull the panels apart from their folded configuration. Once the radome is fully deployed, the panels are fully extended into a single panel. The off-set, self-aligning hinges are used to compensate for the thickness of the individual panels.  
         [0049]    [0049]FIG. 11 shows two panels  71  of a deployed phased-array antenna with an off-set, self-aligning hinge  73 . The hinge allows the panels of the antenna to fold in an “Origami-style” technique. This means that the panels  71  fold and unfold simultaneously when force is applied instead of being able to fold or unfold one column or row at a time. The origami folding technique ensures that all of the panels of the antenna will fully deploy when the antenna is unfolded. Likewise, all of the panels of the antenna will fully fold up when the antenna is packed up.  
         [0050]    [0050]FIGS. 12 a  and  12   b  show two partially folded panels of a phased-array antenna with off-set, self-aligning hinges. An electrical connector (not shown) is located on the edges of the body of the panels  71 . It is used to make an electrical connection between the panels  71 . The connector may be a spring contact connector for direct current (DC) connections or a capacitive coupled co-axial connector for radio frequency (RF) connections. Other types of connectors that are known in the art could be used in alternative embodiments. The self-aligning hinge  73  is shown with a cross member  79  that spans across the seam  75  of the two panels  71 . The cross member  79  connects to each panel by cantilever struts  81  with a pivoting or flexing-membrane hinge. Each folding connector  81  is attached to its respective panel  71 . When the panels are fully deployed, the cantilever struts  81  fold underneath the cross member  79  and the entire hinge  73  seats flush across the seam  75  of the panels  71  in a recessed slot. When the panels are unfolded, the cantilever struts  81  fold out from under the cross member  79  and allow the panels  71  to move.  
         [0051]    [0051]FIGS. 13 a  and  13   b  show cut away views of alternative embodiments of deployed phased array antennas. FIG. 13 a  shows a fully deployed single plane phased array antenna  86  that is mounted on the top of a vehicle. FIG. 13 b  shows a fully deployed triple plane phased array antenna  88  that is also mounted on top of a vehicle. In this embodiment, three identical phased array antennas are configured at an angle of 120° with respect to each other. This arrangement provides full 360° coverage without having to re-orient the antenna&#39;s direction. Alternative embodiments could use varying numbers of panels that are equidistantly angled for 360° coverage. For example, four panels could be used that are arranged at a 90° angle with respect to each other.  
         [0052]    [0052]FIGS. 14 a  and  14   b  show cross sectional views of another embodiment of a deployed phased array antenna. In this embodiment, the antenna  89  is cylindrically shaped. The radome  93  is an inflatable elongated cylinder with dome-shaped cap on each end. The antenna panels  91  are suspended in the radome  93  with multiple flexible centenaries  95 . This embodiment of an inflatable antenna may be deployed on the back of a trailer or fixed on the ground with guy lines to hold it in position.  
         [0053]    [0053]FIGS. 15 a ,  15   b  and  15   c  show an alternative embodiment of a phased array antenna being deployed. In this embodiment, the phased array antenna panels are not surrounded by a radome, but instead they are held in place with a support frame. The antenna may use the off-set, self-aligning hinges described previously. FIG. 15 a  shows the phased array antenna in a stowed configuration  90  on top of a vehicle. As shown in FIG. 15 b , once the vehicle arrives on station, the panels of the antenna  96  are deployed by extending the support frame  98 . FIG. 15 b  shows the antenna  94  fully extended and braced by the support frame  98 . The antenna may also be retracted and stowed in a similar manner. In alternative embodiments, the antenna could be mounted on a rotating base so that the orientation may be changed without moving the vehicle. In other embodiments, the antenna could have multiple phased array panels to provide 360° coverage as previous shown and described in FIG. 13 b.    
         [0054]    In alternative embodiments, the present invention could be deployed in a man-portable configuration. FIG. 16 shows a man-portable antenna  99  that is carried in a backpack  100  and tethered to the ground  101  when deployed. In this embodiment, the antenna is supported on an inflatable torus  102  and uses an array feed  103  with the inflatable lenticular  104  inside a spherical radome  105 . Alternatively, the radome of the antenna could be filled with helium, etc. and lifted in the air. Ground tethers would be used to secure the antenna to the ground. In other embodiments, the present invention could be used on aeronautical vehicles such as blimps or other types of aircraft as well as orbital satellites.  
         [0055]    [0055]FIGS. 17 a - 17   c  show an alternative embodiment of the present invention that uses a log-periodic antenna. FIGS. 17 a  and  17   b  show a top view and a front view of the antenna respectively. FIG. 17 c  shows a perspective view of the embodiment. This antenna contains a cross-polarized, log periodic array (LPA) antenna  110  that is inside an inflatable radome  112 . The LPA  110  could be printed elements on membranes  114  as shown. In alternative embodiments, the LPA  110  could be wire antennas that are held in place and supported by non-conducting catenaries. In other embodiments, multiple LPA  110  could be mounted inside one radome  112 .  
         [0056]    The present invention has the advantages of being a light weight, transportable antenna for ground based use. Both the inflatable reflector and foldable phased array antennas offer significant improvements in weight and stowage space used over conventional antennas. While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed here. Accordingly, the scope of the invention should be limited only by the attached claims.