Patent Publication Number: US-11038252-B1

Title: Deployable loop antenna

Description:
GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of antennas, and more particularly, to deployable antennas for space vehicles. 
     BACKGROUND OF THE INVENTION 
     Antennas are used in a number of terrestrial and orbital applications. With larger apertures being attractive for their higher gain, it is desirable to deploy space-based antennas from a small storage volume. This allows large antennas to fit within the confines of the launch vehicle and more easily survive the dynamic loading of the launch vehicle. 
     For example, U.S. Pat. No. 5,969,695 to Bassily et al., entitled “Mesh Tensioning, Retention and Management Systems for Large Deployable Reflectors,” relates to systems for controlling and retaining tension in a mesh reflector in the deployed condition, as well as for managing the mesh during launch and transport in the stowed condition. 
     U.S. Pat. No. 5,313,221 to Denton entitled “Self-deployable Phased Array Radar Antenna,” is directed to a phased array monopole antenna that has a single layer membrane upon which a plurality of antenna units are attached. Each antenna unit has a flexible curved antenna blade which bends over or springs up when the membrane is rolled or unrolled on a drum. 
     Also, U.S. Patent Application No. 2012/0167943 to Blanchard et al., entitled “Unwindable Flat Solar Generator,” is directed to a solar generator deployment device that includes an assembly having a plurality of tape-springs supporting a windable membrane on a face of which is arranged a plurality of elements capable of converting the solar energy into electrical energy. The tape-springs and membrane are co-wound around a unique radius of curvature equal to the natural radius of curvature of folding of the tape-spring in the wound state. 
     Tape-springs are known as being tapes capable of changing from the wound state to the unwound state essentially by virtue of their own elastic energy. In the unwound state, tape-springs normally have a rigidity which is capable of maintaining them in that state. Conventional tape-springs are generally metallic, and it may be difficult to control their unfolding. 
     However, conventional tape-springs made of composite material have also been developed and make it possible to better control their winding radius. They also have a high rigidity/weight ratio and a low expansion coefficient. 
     Various studies indicate that it is possible to render a composite tape-spring bistable. Such studies include “Carbon Fibre Reinforced Plastic First antenna structure s”, J. C. H. Yee et al., AIAA 2004-1819, and “Analytical models for bistable cylindrical shells”, S. D. Guest et al. Such bistable tape-springs are mechanically stable both in the unwound state and in the wound state. The bistable tape-springs remain stable in the wound state around their natural radius of curvature, without external force. All that is needed is to unfold one end thereof, with a force of low intensity, exerted by a motor-drive system for example, to trigger the unwinding. 
     However, there may be a need for a space loop antenna that is self-deployable from a compact storage size without the use of motors or actuators. 
     This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding description constitutes prior art against the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     With the above in mind, embodiments of the present invention are related to a loop antenna for use in space that is self-deployable from a compact storage space without the use of motors or actuators. 
     Advantages may be provided by an embodiment that is directed to an antenna including a base, at least one spool, and an antenna structure coupled to the spool or spools having ends that are affixed at the base, the antenna structure being configured to actuate between a stowed state and a deployed state. The stowed state is defined by the antenna structure being wound or coiled about the spool(s). The deployed state is defined by the antenna structure being unwound from the spool(s) to form a loop. 
     The antenna structure may be a bistable composite tape having one or more antenna conductors embedded therein. The bistable composite tape has a cross-sectional curvature. The bistable composite tape may be a bistable fiber-reinforced composite tape including first and second forty-five degree (45°) biased woven layers and a unidirectional lamina layer sandwiched therebetween. Additionally, multiple loop antenna connectors may be embedded in the bistable composite tape. The connectors may lie in parallel. 
     The ends of the antenna structure are affixed to the base such that in the stowed state, the antenna structure generates and stores a strain force applied to the spool(s) which is biased toward the deployed state. A storage containment device is configured to hold the antenna structure in the stowed state, and a release mechanism configured to release the antenna structure so that, without external assistance, the coiled antenna structure unwinds into the deployed state. 
     The antenna structure is comprised of two connected sections, with each having a curved cross section with a radius of curvature. The respective curved cross sections form concave surfaces facing in opposite directions when the antenna structure is in the deployed state. The cross sections are flattened when the sections are wound around the spool in the stored state. 
     Advantages may be provided by another embodiment of an antenna including a base, first and second spools, an antenna structure coupled to each of the spools and having ends affixed to the base, the antenna structure being configured to actuate between a stowed state and a deployed state. The stowed state is defined by respective portions of the first antenna structure being wound or coiled about the first and second spools, and the deployed state is defined by the antenna structure being unwound from about the first and second spools to form a first loop. 
     Additionally, or alternatively, the antenna may include third and fourth spools, and a second antenna structure coupled to each of the third and fourth spools and having ends that are affixed at the base, with the second antenna structure being configured to actuate between the stowed state and the deployed state. The stowed state is also defined by respective portions of the second antenna structure being wound about the third and fourth spools, and the deployed state is also defined by the second antenna structure being unwound from about the third and fourth spools to form a second loop. The first and second loops would lie in respective intersecting planes. The planes could intersect orthogonally. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of a deployable loop antenna using one spool, according to features of the present invention. 
         FIG. 2  is a flow diagram illustrating the transition of antenna embodiment of  FIG. 1  from the deployed state into the stowed state. 
         FIG. 3  is a flow diagram illustrating an embodiment of a deployable loop antenna having two spools, and showing the transition of the antenna from the deployed state into the stowed state. 
         FIG. 4  is a flow diagram illustrating an embodiment of a deployable antenna having four spools and two antenna loop structures lying in intersecting planes, and showing the transition of the antenna from the deployed state into the stowed state. 
         FIG. 5  is a schematic diagram illustrating a portion of an antenna structure comprised of multiple antenna conductors on a flexible substrate. 
         FIG. 6  is a partial cut-away view of a bistable composite tape of the antenna loop structure having a cross-sectional curvature. 
         FIG. 7  is a perspective view of a portion of an antenna structure showing its two sections, with each having a curved cross section and the respective radii of curvature pointing in opposite directions. 
         FIG. 8  illustrates a space vehicle with deployment of a deployable loop antenna of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Those of ordinary skill in the art realize that the following descriptions of the embodiments of the present invention are illustrative and are not intended to be limiting in any way. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Like numbers refer to like elements throughout. 
     Although the following detailed description contains many specifics for the purposes of illustration, anyone of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the invention. Accordingly, the following embodiments of the invention are set forth without any loss of generality to, and without imposing limitations upon, the claimed invention. 
     In this detailed description of the present invention, a person skilled in the art should note that directional terms, such as “above,” “below,” “upper,” “lower,” and other like terms are used for the convenience of the reader in reference to the drawings. Also, a person skilled in the art should notice this description may contain other terminology to convey position, orientation, and direction without departing from the principles of the present invention. 
     Furthermore, in this detailed description, a person skilled in the art should note that quantitative qualifying terms such as “generally,” “substantially,” “mostly,” and other terms are used, in general, to mean that the referred to object, characteristic, or quality constitutes a majority of the subject of the reference. The meaning of any of these terms is dependent upon the context within which it is used, and the meaning may be expressly modified. 
     The present embodiments may provide a loop antenna that is remotely deployable from a small storage size, yet that presents a larger aperture when deployed so as to deliver high gain. Such a storage and deployment approach enables larger loop antennas to fit within the confines of a space-limited launch vehicle and more easily survive the dynamic loading of the launch vehicle, and then to deploy to a pre-determined, operable shape upon demand. 
     The features that deliver these advantages may be found in the rolling of the loop antenna structure around a single or double spool that is deployed in a loop (e.g. in either a diamond or circular loop configuration), and the use of thin flexible and bistable composite tape elements with electrical antenna conductors embedded therein. 
     A notable use of the deployable loop antenna is for a radio frequency (RF) receive antenna, either for communications or for passive measurement of RF fields or returns from an ionosphere sounding device in terrestrial and orbital applications. 
     Turning to the drawings,  FIG. 1  is a perspective view of a deployable loop antenna  10  according to features of the present invention. Loop antenna  10  includes base  12 , rotatable spool  14 , and antenna structure  16  coupled to spool  14  and having ends that are affixed at base  12 . End  17  is shown, while the other end is not. Antenna structure  16  is configured to actuate between a stowed state and the illustrated deployed state. The stowed state is defined by antenna structure  16  being wound about spool  14 , as will be described below. The deployed state is defined by antenna structure  16  being unwound from around spool  14  to form a loop antenna. 
     Storage containment device  20  is configured to hold antenna structure  16  in the stowed state, and release mechanism  22  is configured to release antenna structure  16  to allow it to transition into the deployed state. As shown, the storage containment device  20  is a frame with a hinged door defining the release mechanism  22 . Other embodiments are contemplated, for example, a tensioned strap could be severed to release antenna structure  16  into the deployed state, or a removeable pin could be inserted into spool  14  adjacent base  12  to hold antenna structure  16  in the stowed state, and withdrawn to allow its deployment. Also, a limiter  24 , such as a cable or cord, may be coupled between the spool  14  and the base  12  to limit the travel of spool  14  and, concomitantly, the deployment of antenna structure  16 , and aid in defining its resulting shape in the deployed state (e.g., the diamond loop in  FIG. 1 ). 
       FIGS. 2-4  illustrate that the common elements of the concept that can be applied to loop antennas in several different configurations.  FIG. 2  is a flow diagram illustrating the single spool antenna embodiment of  FIG. 1  being rolled up into the stowed state.  FIG. 3  is a flow diagram illustrating another embodiment the present invention comprising deployable loop antenna  30 , including spool  34  and spool  35 . Loop antenna  30  is shown transitioning from the deployed state into the stowed state. 
       FIG. 4  is a flow diagram illustrating deployable loop antenna  40 , another embodiment of the present invention, comprised of antenna structures  42  and  43  using first through fourth spools  44 - 47 . Loop antenna  40  is shown transitioning from its deployed state to its stowed state. In its deployed state, spools  44  and  45  lie in a plane orthogonal to a plane including spools  46  and  47 .  FIG. 4  shows a benefit of the two spool approach in that two orthogonal loops are coupled at the distal extent  49  of the antenna  40  and stowed together. 
     Referring to  FIG. 5 , antenna structure  16  may be a bistable composite tape  50  having one or more antenna conductors  52  embedded therein. The antenna conductors  52  may be embedded in parallel in the bistable composite tape  50 . The antenna conductors  52  are electrically coupled at or near the base  12  and may include the use of an antenna tuner, a matchbox, antenna tuning unit (ATU), antenna coupler, or feedline coupler coupled between a radio transmitter or receiver and the antenna conductors to improve power transfer between them by matching the impedance of the radio to the antenna&#39;s feedline (such features are not shown), as would be appreciated by those skilled in the art. A basic form of antenna  10  includes a single conductor  52  embedded in tape  50 , but multiple parallel conductors  52  can be embedded therein to provide additional antenna gain by wiring them to produce a system of several loops, as would be appreciated by those skilled in the antenna art. 
     As shown in  FIG. 6 , bistable composite tape  50  has a cross-sectional curvature, and is composed of bistable fiber-reinforced composite tape. The bistable fiber-reinforced composite tape is composed of first and second forty-five degree (45°) biased woven layers  53  and  54  and a unidirectional lamina layer  56  sandwiched therebetween. The utilization of bistable composite tape  50  for antenna structure  16  allows the antenna  10  to roll around the spool  14  in a way that controls the deployment of loop antenna  10 . More particularly, the bistability enables linear controlled unrolling of tape  50  along a pre-determined kinematic path without random billowing. The bistability is imparted through the composite layup as well as the curved cross-section. 
     Referring to  FIG. 7 , tape  50  is composed of sections  58  and  60  having respective radii of curvature represented by vectors R 58  and R 60  drawn from their centers to their curved surfaces, respectively. The vectors thus point towards the concavity in each section. In reference to antenna  10  shown in its deployed state in  FIG. 1 , sections  58  and  60  would lie on the two sides of spool  14  and base  20 , respectively. The concave surface of section  58  thus faces inwards toward the geometric center of the loop of antenna  10 , while the concavity of section  60  faces outwardly, away from the geometric center. The orientation of the concavities defined by the directions of R 58  and R 60  are shown for the clockwise rotation of spool  14  shown In  FIG. 2 . If spool  14  were to rotate in a counterclockwise direction, the orientations of R 58  and R 60  would be reversed so that the respective concave surfaces would face in the opposite direction as shown. As will be discussed below, tape  50  is flattened when rolled into the stored state. 
     In reference to antenna  30  in  FIG. 3 , section  58  could be considered as that section of tape  50  coupling spools  34  and  35 , with section  60  being further divided into two sub-sections, sub-section  62  coupling base  12  and spool  34 , and sub-section  64  coupling base  12  and spool  35 . The underlying principle remains as outlined with respect to antenna  10 ; that is, the concave surface for section  58  would face toward the geometric center of the loop of antenna  30  when in its deployed state, while the concavities for the two sub-sections  62  and  64  of section  60  would face outwards, away from the geometric center. 
     Referring to antenna  40  in  FIG. 4 , antenna structure  42  is comprised of section  58  of tape  50  coupling spools  44  and  45 , sub-section  62  coupling base  12  and spool  44 , and sub-section  64  coupling base  12  and spool  45 . For antenna  40  and antenna structure  42  in the deployed state, the concave surface for section  58  would face inward, toward the geometric center of the loop of antenna structure  42 , while the concave surfaces of sub-sections  62  and  64  would face outward, away from the geometric center. For antenna structure  43 , section  66  couples spools  46  and  47 , with sub-section  68  coupling base  12  and spool  46 , and sub-section  70  coupling base  12  and spool  47 . The concave surface for section  66  would face inward, toward the geometric center of the loop of antenna structure  43 , while the concave surfaces of sub-sections  68  and  70  would face outward, away from the geometric center. 
     Strain energy is used to actuate the deployment of the antennas  10 ,  30  and  40 . This strain energy is generated and stored by rolling and flattening curved cross sections of the respective antenna structures in the stored state. This means that the loop antennas  10 ,  30  and  40  can deploy via their own strain energy without any external motors or actuators. A simple release mechanism  22  is used to initiate deployment by releasing the antenna structure from its coiled storage in storage containment device  20 . As such, the end  17  and the other end (not shown) of antenna structure  16  are fixed to the base  12  such that in the stowed state, antenna structure  16  stores a strain energy imparted thereto and is configured to be biased toward the deployed state. Without the clamped ends, the bi-stability might actually keep antennas  10 ,  30  and  40  in their respective stowed states without having the strain energy necessary to deploy them. 
     Turning to  FIG. 8 , Antenna  10  (or antennas  30  and  40 ) are preferably for use with a space vehicle  72 , which may be a spacecraft, space capsule, space station and/or satellite, for example. Other spacecraft are also contemplated. Space vehicle  72  may typically include a body  74  housing various electronic components, solar arrays  76  and deployable antenna  10 . 
     The above description provides specific details, such as material types and processing conditions to provide a thorough description of example embodiments. However, a person of ordinary skill in the art would understand that the embodiments may be practiced without using these specific details. 
     Some of the illustrative aspects of the present invention may be advantageous in solving the problems herein described and other problems not discussed which are discoverable by a skilled artisan. While the above description contains much specificity, these should not be construed as limitations on the scope of any embodiment, but as exemplifications of the presented embodiments thereof. Many other ramifications and variations are possible within the teachings of the various embodiments. While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best or only mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Also, in the drawings and the description, there have been disclosed exemplary embodiments of the invention and, although specific terms may have been employed, they are unless otherwise stated used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention therefore not being so limited. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another. Furthermore, the use of the terms a, an, etc. do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, and not by the examples given.