ANTENNA APPARATUS AND DEPLOYMENT METHOD EMPLOYING FOLDABLE MEMORY METAL.

Abstract

An artificial magnetic conductor (AMC) antenna apparatus includes a ground plane and a layer of flexible antenna elements above the ground plane. The ground plane includes a conductive base surface, a plurality of shape-memory metal wires, and a frequency-selective surface (FSS) layer on the base surface, where the FSS layer includes a plurality of conductive patches separated from each other. Each of the shape-memory metal wires electrically connects one of the conductive patches to the base surface. Each of the shape-memory metal wires is rigid in a shape-memory state, causing the FSS layer to be fixedly separated from the base surface during operation of the AMC antenna apparatus. Each of the shape-memory metal wires is flexible in a non-shape-memory state, allowing the FSS layer to fold back toward the base surface when the antenna apparatus is stowed.

Description

ANTENNA APPARATUS AND DEPLOYMENT METHOD EMPLOYING FOLDABLE MEMORY METAL Cross Reference to Related Request This application claims priority over U.S. Provisional Application No. 63 / 091,922, filed with the U.S. Patent and Trademark Office on October 14, 2020, the full contents of which are incorporated herein by reference. Technical Field of the Invention This disclosure generally relates to storage and deployment techniques for antennas with ground planes; already artificial magnetic conductor (AMC) antennas. Analysis of the Related Technique In a traditional antenna on a ground plane, the radiating element is separated by a quarter of a wavelength (λ / 4) from the ground plane to achieve constructive interference with the reflected signal and thus increase directivity. However, at relatively low frequencies, the λ / 4 distance can be longer than desired, resulting in a thick antenna profile (e.g., 25 cm at 300 MHz). With an artificial magnetic conductor (AMC) ground plane, the gap between the ground plane and the radiating element is significantly smaller, and comparable directivity performance can be achieved for the antenna. An AMC ground plane can include a conductive base surface and a frequency-selective surface (FSS) composed of a plurality of conductive patches separated from each other. The conductive patches can be electrically connected to the base surface via respective wires, which are typically embedded within a low-loss dielectric. The resulting structure, while thinner than traditional ground plane antennas, is rigid and cumbersome to transport, particularly for large-aperture antennas configured for frequencies below 1 GHz. BRIEF DESCRIPTION OF THE INVENTION In one aspect of this disclosure, an artificial magnetic conductor (AMC) antenna apparatus includes a ground plane and a flexible antenna element layer that includes at least one antenna element above the ground plane. The ground plane includes a conductive base surface, a plurality of shape-memory metal wires, and a frequency-selective surface (FSS) layer on the base surface, where the FSS layer includes a plurality of conductive patches separated from each other. Each of the shape-memory metal wires electrically connects one of the conductive patches to the base surface. Each of the shape-memory metal wires is rigid in a shape-memory state, causing the FSS layer to be fixedly separated from the base surface during operation of the AMC antenna apparatus.Each of the shape memory metal wires is flexible in a shape-no-memory state, allowing the FSS layer to fold back towards the base surface when the antenna apparatus is stowed. -2The AMC antenna apparatus may further include a retention structure configured to retain, when the antenna apparatus is stored, the antenna element layer and ground plane with the FSS layer folded towards the base surface. The retention structure can hold the antenna element layer and ground plane in a rolled-up state. The AMC antenna apparatus may also include at least one actuator configured to remove the antenna element layer and ground plane from the retaining structure. In another aspect, a method is provided for deploying an AMC antenna on an unmanned carrier. The AMC antenna includes: (i) a layer of antenna elements; and (ii) a ground plane with a conductive base surface, a FSS layer, and a plurality of shape-memory metal wires that electrically and mechanically couple the conductive base surface to the FSS layer. The shape-memory metal wires are folded, in a shape-no-memory state, when the AMC antenna apparatus is stowed. The method involves stowing the AMC antenna in a holding structure; and withdrawing the AMC antenna from the holding structure by means of an actuator to deploy the antenna. The shape-memory metal wires automatically transform from flexible to rigid states when the ambient temperature exceeds a threshold, causing the FSS to permanently detach from the base surface after the AMC antenna is withdrawn from the holding structure. BRIEF DESCRIPTION OF THE DRAWINGS The above aspects and features, and others, of the disclosed technology will become clearer from the following detailed description, taken in conjunction with the accompanying drawings, in which similar reference characters indicate similar elements or features. Multiple elements of the same or similar type can be distinguished by appending the reference label with an underscore / hyphen and a second label that distinguishes between identical / similar elements (e.g., _1, _2), or directly by appending the reference label with a second label. However, if a given description uses only the first reference label, it is applicable to any identical / similar elements that share the same first reference label, regardless of the second label. Elements and features may not be drawn to scale in the drawings. Figure 1 is a perspective view of an example AMC antenna in an operational configuration, according to one embodiment. Figure 2 is a cross-sectional view taken along lines 2-2 of Figure 1, representing an example of interlayer structure of the AMC antenna. Figure 3 is a schematic diagram illustrating an example of an antenna feed connected to antenna elements of the AMC antenna in Figure 1. Figure 4 is a perspective view of a central portion of a top part of the AMC antenna from Figure 1, illustrating a portion of the antenna feed example. Figure 5 is a cross-sectional view taken along lines 5-5 of Figure 4, representing an example of integrating the antenna feed within the AMC antenna. - 3 Figure 6 is a perspective view of an example of an antenna apparatus that includes a retaining structure that retains the AMC antenna of Figure 1 in a coiled configuration during storage, according to one embodiment. Figure 7 is a perspective view showing the antenna apparatus of Figure 6 after the AMC antenna was removed during deployment. Figure 8 is a cross-sectional view of the antenna apparatus of Figure 7 taken along lines 8-8, illustrating a memory metal wire in a folded state. Figure 9 illustrates the antenna apparatus of Figure 1 in a folded state for storage. Figure 10 is a perspective view depicting an AMC antenna in a partially deployed state according to another embodiment. Figure 11 is a cross-sectional view of a portion of the AMC antenna from Figure 10. Figure 12 is a flowchart depicting the operations of an example method for deploying an AMC antenna on an unmanned carrier according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION The following description, with reference to the accompanying drawings, is provided to aid in a complete understanding of certain example embodiments of the technology disclosed herein for illustrative purposes. The description includes various specific details to assist a person of average skill in understanding the technology, but these details should be considered merely illustrative. For the sake of simplicity and clarity, descriptions of well-known functions and constructions may be omitted where their inclusion might hinder an average skill in appreciating the technology. Figure 1 is a perspective view of an example artificial magnetic conductor (AMC) antenna in an operational configuration, according to one embodiment. The AMC antenna 100 (referred to interchangeably as the AMC antenna apparatus 100) may include a ground plane 105, an antenna element layer 130 with at least one antenna element, and an antenna feed (e.g., 300 in Figure 3, omitted from Figure 1 for clarity). The ground plane 105 may include: a base layer 110 having a conductive base surface; a frequency-selective surface (FSS) layer 120; and a plurality of memory metal wires 115 electrically connecting the FSS layer 120 to the conductive base surface. In some embodiments, the elements 115 may be an elongated structure other than a wire, such as a memory metal column.Ground plane 105 with this type of textured surface configuration can be understood as a high-impedance surface within a given frequency band, where the surface wave modes differ significantly from those of a smooth metal surface. (It should be noted that the term frequency-selective surface (FSS) emphasizes the frequency-sensitive nature of the high-impedance surface.) Ground plane 105 can also be understood as an in-phase reflector with suppressed surface waves. The textured structure of ground plane 105 allows the... The AMC 100 antenna is substantially thinner than traditional ground plane antennas, i.e., non-AMC antennas with a radiating element spaced λ / 4 above a ground plane. The FSS 120 layer includes a plurality of conductive patches 1211 to 121_n separated from each other by narrow insulating regions (“streets”) 123. It should be noted that each conductive patch 121 in Figure 1 may include a conductive surface printed on a thin dielectric sheet such as a polyimide film (e.g., Kapton®), and the insulating regions 123 may be regions of the dielectric sheet without an printed conductor. Therefore, the conductive patches 1211 to 121_n together with the dielectric sheet (and in some cases, an additional dielectric sheet on the opposite side of the printed conductor) may collectively form a continuous sheet-like or sandwich-like structure. The width of an insulating region 123 is small relative to the area of ​​a conductive patch 121, which generates a capacitance between adjacent conductive patches 121 that contributes to forming the high-impedance surface.Each metal memory wire 115 can be oriented in the z (vertical) direction and electrically connect one of the conductive patches 121 to the conductive base surface of the base layer 110, so that a bed of nails structure is provided between the base layer 110 and the FSS layer 120. Each of the base layer 110, the FSS layer 120, and the antenna element layer 130 can be flexible sheet-like structures having principal surfaces oriented in the xy plane. Shape memory metal cables 115 are rigid, as shown in Figure 1, in a shape memory state that can occur when the ambient temperature is above a threshold (shape memory threshold). Shape memory metal cables 115 can be composed of nickel-titanium (NiTi), also known as nitinol, or another suitable shape memory alloy such as copper-aluminum-nickel or an alloy including copper, iron, zinc, and gold. By virtue of their rigidity in the shape memory state, shape memory metal cables 115 can mechanically support the FSS 120 with respect to the base layer 110 in the operating configuration to achieve a fixed spacing between them (e.g., a uniform spacing between all regions of FSS 120 and base layer 110).Metal-memory cables 115 are flexible in a shape-memory-free state during a non-operational storage state, discussed and illustrated later, which can be initiated when the ambient temperature falls below the shape-memory threshold. For example, a nitinol-composed metal-memory cable 115 changes its state from austenite to martensite when cooled below the shape-memory threshold, allowing the metal-memory cable 115 to enter a flexible state. When the metal-memory cables 115 are flexible, the FSS layer 120 and the antenna element layer 130 can fold back toward the base layer 110, allowing the AMC antenna 100 to be stored in a smaller volume than it occupies in the operational state. This facilitates the storage and transport of the AMC antenna 100 and, in some cases, its unmanned deployment on a carrier such as an orbiting satellite.In some examples, the AMC 100 antenna is stored in a coiled or folded retention structure, as described and illustrated below. When the AMC 100 antenna is removed from the retention structure and the ambient temperature exceeds the threshold... - 5 shape memory, the 115 metal memory wires can automatically transform back into austenite, the shape memory state. With the AMC 100 antenna, the shape memory state can be a linear configuration. By appropriately designing the quantity, geometry, and arrangement of the conductive patches 121; the at least one antenna element of the antenna layer 120; the lengths of the metal memory wires 115; and the separation between the antenna element layer 130 and the FSS 120, an AMC phenomenon is achievable. As stated, the AMC phenomenon allows the AMC antenna 100 to be significantly thinner than a traditional antenna with a radiating element spaced A / 4 on a ground plane. For example, the AMC phenomenon allows for effective antenna performance with a separation between the antenna element layer 130 and the base surface 119 λ / 4, for example, in the AMO to A / 10 range. Such efficiency can be achieved due to in-phase reflection and the suppression of surface waves.Therefore, despite the narrow separation between the layers, constructive interference occurs between a signal radiated directly into free space by the antenna element layer 130 and the same signal initially propagated towards the ground plane 105 and then reflected from it. In the embodiment of Figure 1, an example antenna element is illustrated as a crossed dipole 135 comprising a first dipole element 132 and a second dipole element 134 orthogonal to the first dipole element 132. Other types of antenna elements, such as a single dipole, a loop antenna, an array of microstrip patch elements, etc., may be substituted. The crossed dipole 135 may be printed on a dielectric foil, illustrated with a hexagonal shape that occupies a smaller surface area than the FSS layer 120 and the base layer 110 of Figure 1. In other examples, the antenna element layer 130 is coextensive in the xy plane with each FSS layer 120 and base layer 110. An example construction of the ground plane 105 includes a plurality of dielectric or metallic ribs 117, each oriented longitudinally in the yox directions, for additional structural support of the lower ends of the metal memory wires 115.Each of the conductive patches 1211 to 121_n can be arranged in a network and have identical geometries, for example, all rectangular or all square as depicted, or alternatively all hexagonal, all circular, or another suitable shape. The conductive patches 1211 to 121_n can also be configured with identical or substantially identical dimensions (for example, within manufacturing tolerances) in some embodiments. Each conductive patch 121 can be electrically connected to a respective metal memory cable 115 via a connection 128 at a central location thereon. It should be noted that an entry section of the base layer 110 can include an entry fin 112 and an edge rib 184 for mechanical connection to a retention structure in some applications. Figure 2 is a cross-sectional view taken along lines 2-2 of Figure 1, and represents an example of the interlayer structure of the AMC 100 antenna during an operational (deployed) state. (In Figure 2 and other cross-sectional views herein, features located behind the illustrations may be omitted for clarity.) Base layer 110 may include a -6 A conductive base surface 119 is adhered or printed on a lower surface of a flexible dielectric foil 144 for structural integrity and to facilitate electrical and mechanical connections to the metal memory wires 115 (referred to interchangeably as memory wires 115). A dielectric rib 117 may be adhered to a top surface of the dielectric foil 144 and support a connection of a memory wire 115 to the base surface 119. A plated through-hole 158 may have been formed through the rib 117 and the base layer 110. A lower end of the memory wire 115 may have been inserted into the through-hole 158 and electrically connected to the conductive base surface 119 with a conductive adhesive 157 surrounding the memory wire 115 within the through-hole 158, for example, molten and cooled solder. The FSS 120 layer may include conductive patches 121_1 to 121_n sandwiched between a lower dielectric sheet 154 and an upper dielectric sheet 164. Alternatively, the FSS 120 layer is constructed from a single dielectric sheet 154 or 164 with conductive patches 121 printed on it. A mechanical and electrical connection 128 between an upper portion of the memory wire 115 and the FSS 120 layer may comprise a plated through-hole 168, an upper portion of the memory wire 115, and a conductive adhesive 167 within the through-hole 168. Figure 2 depicts a single connection 128 between a memory wire 115 and a given conductive patch 121J, which is separated by the respective insulation regions 123 from the adjacent conductive patches 121_(j1) and 121_(j+1).The dielectric sheet 164, which includes the insulating regions 123, may have been formed by layering dielectric material onto the conductive patches 121, following the deposition of the conductive patches 121 onto the upper surface of the dielectric sheet 154. However, if the dielectric sheet 164 is omitted, the insulating regions 123 may be air spaces or a dielectric filler. Each of the dielectric sheets 144, 154, 164, and 174 may be a polyimide film such as Kapton®. Each of the electrical connections 128 along the AMC antenna 100 can be formed at a distance d1 above the dielectric sheet 144 (with memory wires in the rigid state). In this way, the FSS layer 120 can be supported by memory wires 115 with their lower surface uniformly spaced by the distance d1 from the base layer 110. An air gap 191 can be present in the regions surrounding the memory wires 115. The antenna element layer 130 may include at least one antenna element 132 printed on top of the dielectric layer 174. An example of a mechanical connection between the antenna element layer 130 and the FSS layer 120 may include an extension portion 176 of the memory wire 115 extending above the top surface of the dielectric foil 164, a plated blind via 178 on the bottom surface of the dielectric foil 174, and an electrically conductive adhesive 177 such as solder. The upper end of the extension 176 may have been inserted into the via 178 and adhered to the dielectric foil 174 by melting and cooling the adhesive 177. All or most of the memory wires 115 underlying the antenna element layer 130 may likewise include an extension 176 adhered to the dielectric foil 174 in this manner. As a result, the antenna element layer 130 can be fully supported by memory cables 115 and -7 evenly spaced at a distance d2 (with the memory wire 115 in the rigid state) from the top surface of the FSS layer 120. Note that if the antenna layer 130 is located only at the center with respect to the FSS layer 120, as in the example in Figure 1, then the memory wires 115 located outside the region of the antenna layer 130 can omit the extensions 176. These peripheral memory wires 115 can all be designed to be the same or substantially the same length (e.g., within manufacturing tolerances), and the top ends can be flush with the top surface of the dielectric foil 164. Similarly, each of the memory wires 115 underlying the antenna layer 130 can have an identical or substantially identical design, with extensions 176 of the same or substantially the same length (e.g., within manufacturing tolerances). With the mechanical connection described above between the FSS 120 layer and the antenna element 130 layer, an air gap 171 may exist between layers 120 and 130. When the shape-memory cables 115 are in the non-metal shape-memory (flexible) state, the antenna element 130 layer may fold relative to the FSS 120 layer, thereby reducing the distance d2 in the stored state. In an alternative configuration, the extensions 176 in the shape-memory cables 115 are omitted throughout the AMC 100 antenna; the dielectric sheets 164 and 174 are fused or formed as a single dielectric sheet; and there is no air gap 171 between the FSS 120 layer and the antenna element 130 layer. Figure 3 is a schematic diagram illustrating an example of an antenna feed, 300, which can be connected to antenna elements 135 of the AMC 100 antenna. The antenna feed 300 may include a balun 350; a first flexible coaxial cable 310 having one end connected to the balun 350 and having an outer conductor 313 and an inner conductor 311; a second flexible coaxial cable 320 having one end connected to the balun 350 and having an outer conductor 323 and an inner conductor 321; and the first, second, third, and fourth interconnections 317, 319, 327, and 329, respectively. In some embodiments, there may be several baluns connected (e.g., a pair of connected baluns). The first dipole element 132 includes dipole arms 132a and 132b; The second dipole element 134 includes the dipole arms 134a and 134b.A second end of the first coaxial cable 310 is connected to the first dipole element 132, with interconnection 317 connecting the outer conductor 313 to the dipole arm 132a and interconnection 319 connecting the inner conductor 311 to the dipole arm 132b. A second end of the second coaxial cable 310 is connected to the second dipole element 134, with interconnection 327 connecting the outer conductor 323 to the dipole arm 134a and interconnection 329 connecting the inner conductor 321 to the dipole arm 134b. Figure 4 is a perspective view depicting a central portion of a top part of the AMC 100 antenna from Figure 1, which illustrates a portion of the antenna feed example 300. A central portion of the crossed dipole antenna element 135 can be superimposed on an intersection region of adjacent centralized conductive patches 121_i, 121_(i+1), 121_(i+2), and 121_(i+3). An opening 375 can be formed in the FSS 120 layer in the centralized region by removing -8 a corner piece of each of the conductive patches 121_¡ to 121(¡+3). Another opening 385 may have formed in a centralized region of the antenna element layer 130. Coaxial cables 310 and 320 may extend vertically (z direction) between the antenna element layer 130 and the base layer 110 during the deployed state of the AMC 100 antenna. During the stowed state, the coaxial cables may fold between the antenna element layer 130 and the base layer 110. The second ends of coaxial cables 310 and 320 may penetrate aperture 375 and at least partially penetrate aperture 385. Interconnections 317 and 327 may be represented as cable links. Alternatively, interconnections 317 and 327 are in the form of an integrated funnel-shaped metal section with a cable extension. The funnel-shaped metal section is soldered or otherwise electrically connected to the respective external conductors 313 or 323, and the cable extension is soldered or otherwise electrically connected to an entry point of dipole arm 132a or 134a. Interconnections 319 and 329 may be direct solder connections to the entry points of dipole arms 132b and 134b, respectively. Figure 5 is a cross-sectional view taken along lines 5-5 of Figure 4, depicting an example integration of antenna feed 300 within the AMC 100 antenna. This view shows that balun 350 can be positioned adjacent to the underside of the AMC 100 antenna, and the lower ends of coaxial cables 310 and 320 can penetrate opening 365 in base layer 110 and connect to balun 350. Coaxial cables 310 and 320 can be extended side-by-side vertically, where their upper ends penetrate opening 375 in FSS layer 120 and opening 385 in dielectric foil 174 or antenna layer 130 to facilitate electrical connection to the crossed-dipole antenna element 135. In the storage state, coaxial cables 310 and 320 can be folded in a similar manner. to the memory cables 115 (illustrated below in Figure 8). Figure 6 is a perspective view of an example antenna apparatus including a retention structure that holds an AMC antenna during storage, according to one embodiment. Figure 7 is a perspective view showing the antenna apparatus of Figure 6 after the AMC antenna has been removed during deployment. The view in Figure 7 further illustrates an example arrangement of the AMC antenna with respect to the retention structure before insertion into it. Referring to Figures 6 and 7, the AMC 200 antenna apparatus includes the AMC 100 antenna and the retention structure 210 that holds the AMC 100 antenna in a wound state during storage.The retaining structure 210 in this embodiment is generally a cylindrical structure with first and second opposite end walls 216 and 218, a spindle 225 between the opposite end walls 216 and 218, and support rods 228 coupling the opposite end walls 216 and 218 together. Each of the end walls 216, 218 may have a spiral notch 214 on an inner surface 212 thereof to facilitate guiding and retaining the AMC antenna 100 in a wound configuration. At least the opposite peripheral portions of the ground plane 105 are retained wound within the pair of spiral notches. -9214 during storage. If antenna layer 130 is configured coextensive with ground plane 105, the opposite peripheral portions of antenna layer 130 can also be retained within spiral notches 214. The spindle 225 can have a mechanical link 272 (shown schematically) to the end rib 184 of the AMC 100 antenna. To initially retain the AMC 100 antenna within the retention structure 210, the folded state of the AMC 100 antenna can be forced as in Figure 7. In the folded state, the metal memory wires 115 are flexible, and the FSS layer 120 is folded toward the base layer 110 such that the thickness of at least the peripheral portions of the folded structure is thinner than the width of the notches 214. It is noteworthy that in the folded state, the FSS 120 layer can be folded toward the base layer 110 in the +x direction such that the FSS 120 layer is tilted with respect to the base layer 110. Since the two layers are tilted in the condition folded, a corresponding portion of the FSS 120 layer no longer overlaps a peripheral portion 110a of the base layer 110.For example, the transition from the operational configuration, as seen in Figure 1, to the folded configuration, and vice versa, can be analogous to the mechanical action of a four-bar mechanism. In other words, the metal memory cables 115 can be considered analogous to a first pair of bars that transition between vertical and horizontal orientations. The plate-like geometries of the base layer 110 and the FSS layer 120 can be analogous to a second pair of bars, coupled to the first pair of bars, that switch between an aligned and an inclined condition when the first pair of bars changes between vertical and horizontal orientations. The spindle 225 can be rotated (e.g., clockwise) to draw the AMC 100 antenna into the retention structure 210. As an example, a hand crank (not shown) or actuator 275 with linkage 273 can be coupled to one end 219 of the spindle 225 to impart a turning force to draw the AMC 100 antenna into the retention structure 210. Once the AMC 100 antenna is retained within the retention structure 210, the AMC 200 antenna apparatus can be transported to a carrier, such as an orbital satellite prior to launch, and secured to a surface 285 of the carrier.Since the retention structure 210 is more robust to environmental conditions and movement than the AMC 100 antenna itself (if it is mounted on surface 285 without protection), securing retention structure 210 to surface 285 before deploying the AMC 100 antenna on surface 285 can improve the likelihood of successful deployment. As another example, surface 285 could be a planetary surface or the surface of an artificial structure on a planet. In this case, retention structure 210 with the AMC 100 antenna secured to it could be transported by drone and released onto surface 285 for subsequent unmanned deployment. To deploy the AMC 100 antenna from the retention structure 210, a spindle 225 can be rotated (e.g., counterclockwise) by means of an actuator 275, whereby the AMC 100 antenna can be slid outwards in a plate-like configuration while in its folded state in the +x direction. Alternatively or additionally, another actuator 260 arranged on the surface -10 285 can automatically extract the AMC 100 antenna from the retention structure 210. To this end, the AMC 100 antenna can have an opening 129 on the side opposite the flap 112, through which a link 262 of the actuator 260 can be coupled to the AMC 100 antenna. It is noteworthy that the actuator 260 and / or the actuator 275 can be a robotic arm secured to the surface 285. Once the AMC 100 antenna is extracted from the retention structure 210 in the folded state, if the ambient temperature is above the shape memory threshold, the shape memory metal wires 115 can automatically transition from flexible to rigid and orient themselves in the z-direction. This causes the AMC 100 antenna to transition from the folded state to the operational state, as depicted in Figure 1.In one example, if the ambient temperature is below the shape memory threshold, heat can be applied to the AMC 100 antenna to increase the localized temperature surrounding the antenna and cause the shape memory wires 115 to transition to the shape memory state. In another example, heat is applied by applying an electrical current to the electrical wires 115, whereby the resistance of the shape memory wires 115 while the current flows produces enough heat to trigger the transition. Figure 8 is a cross-sectional view of the AMC 100 antenna taken along lines 8-8 of Figure 7, illustrating an example of the AMC 100 antenna structure in a folded state. When the AMC 100 antenna is folded for storage, the flexible memory wires 115 can be folded with a generally horizontal orientation (usually oriented in the x-direction), whereby a spacer distance d3 between the base layer 110 and the FSS layer 120 is significantly smaller than the spacer distance d1, as seen in Figure 2. Furthermore, a spacer distance d4 between the FSS layer 120 and the antenna layer 130 can be reduced relative to the distance d2 (Figure 2), due to a similar folding of the extensions 176. Consequently, the overall thickness of the AMC 100 antenna can be significantly less than in the operational state, allowing for compact retention within a suitable retention structure. Figure 9 illustrates the AMC 100 antenna in a folded state for storage, which facilitates its transport. To fold the AMC 100 antenna, it is first set in the folded configuration and then folded at least once. A retention structure in the form of a retention strap 199 can hold the AMC 100 antenna in the folded state. As an example, the AMC 100 antenna in the folded state can be transported to the unmanned carrier surface 285 (shown in Figures 6 and 7) and secured to it by suitable screws (not shown) attached to the retention strap 199. For subsequent deployment of the AMC 100 antenna, a robotic arm or similar device can cut the retention straps 199 and deploy the AMC 100 antenna.From there, the AMC 100 antenna can automatically switch to the operational state, as the memory wires 115 switch to their rigid states, similarly to the above (e.g., by applying heat). Figure 10 is a perspective view depicting an AMC 100 antenna in a partially deployed state according to another embodiment. The AMC 100' antenna differs from the AMC 100 antenna described above in that it omits the support ribs 117 and employs a -11 Individual support structure for each conductive patch 121 of the FSS layer 120. Figure 11 is a cross-sectional view showing an example support structure within the centralized region of the AMC antenna 100', i.e., within the region of the antenna element layer 130. For the conductive patches 121 underlying the antenna layer region 130, a support structure may include a support 192 coupled to the base layer 110, a support 193 coupled to the FSS layer 120, and a support 194 coupled to the antenna element layer 130. Each of the supports 192, 193, and 194 may have a button-like profile, occupying a circular area at least an order of magnitude smaller than the surface area of ​​the corresponding conductive patch 121. Each of the supports 192-194 may be composed of dielectric material bonded to one of the respective dielectric sheets in layers 110, 120 or 130.Each support 192, 193, and 194 may have a central opening through which a memory cable 115 passes and is attached to the respective support. For example, a metallized bore may have been formed through the support 192 and the base layer 110 in a manner similar or identical to that described above for the rib 117 in connection with Figure 2, and the lower end of the memory cable 115 may be soldered to the support 192 and the base layer 110 by welding within the metallized bore. A similar metallized hole may have been formed in the FSS 120 layer and support 193 to adhere a central section of the memory cable 115 to support 193. Likewise, a blind path may have been formed through support 194 and the dielectric foil 174 of the antenna element layer 130 to adhere an extension 176 of the memory cable 115 to support 194 and to the antenna element layer 130.For conductive patches located on periphery 121 not underlying the antenna element layer 130, such as conductive patch 121_m, only supports 192 and 193 can be used, and extensions 176 can be omitted. Therefore, the upper ends of the memory cable 115 can be freed from the top surface of the FSS layer 120. Other aspects of the AMC 100' antenna may be the same as those described above for the AMC 100 antenna. The AMC 100' antenna may be retained and removed from a retaining structure such as 210 or 199 in a manner similar to that described above for the AMC 100 antenna. Figure 12 is a flowchart depicting the operations of an example method 1200 for deploying an AMC antenna on an unmanned carrier according to one embodiment. With method 1200, the AMC antenna, for example 100 or 100', is first stored in its folded state in a holding structure such as 210 or 199 described above (S1210). The holding structure can then be transported with an AMC antenna stored on it to an unmanned carrier (S1220). As mentioned earlier, examples of the unmanned carrier (for example, a carrier including surface 285) include an orbiting satellite, a planetary surface, or an artificial structure on a planetary surface. The AMC antenna can be deployed (S1230) by removing it from the retaining structure using an actuator (e.g., 275 and / or 260) as described above, allowing the AMC antenna's shape-memory metal wires 115 to transition from flexible to rigid states when the ambient temperature exceeds the shape-memory threshold. When the transition to the rigid state is complete, the AMC antenna is set for operation (e.g., in the configuration -12 (described above and shown in Figure 1). As previously stated, if the ambient temperature is below the shape memory threshold during deployment, heat can be applied to the AMC antenna to increase the localized temperature surrounding the AMC antenna and cause the shape memory wires 115 to transition to the shape memory state. Heat can be applied by applying electrical current to the electrical wires 115, whereby the resistance of the shape memory wires 115 while the current flows produces sufficient heat to cause the transition. With the AMC antenna in an operational configuration, a robotic arm or similar device can secure the AMC antenna to the carrier surface 285 and electrically connect the AMC antenna balun 350 to an RF front end of a communication system, whereby the AMC antenna can initiate active signal communication. Although the technology described herein was shown and described in particular with reference to exemplary embodiments thereof, persons of a mid-level trade will understand that various changes in form and detail may be made without departing from the spirit and scope of the claimed inventive object as defined by the following claims and their equivalents.

Claims

1. An artificial magnetic conductor (AMC) antenna apparatus (100, 200, 100j) comprising: a ground plane (105) comprising: a conductive base surface (119); a frequency-selective surface (FSS) layer (120) on the base surface, wherein the FSS layer comprises a plurality of conductive patches (121_1 - 121_n) separated from each other; and a plurality of shape-memory metal wires (115), each electrically connecting one of the conductive patches to the base surface and wherein each is rigid in a shape-memory state, causing the FSS layer to be fixedly separated from the base surface during operation of the AMC antenna apparatus, and wherein each is flexible in a non-shape-memory state, allowing the FSS layer to fold back towards the base surface when the antenna apparatus is stored;and a layer of flexible antenna elements (130) over the FSS layer, comprising at least one antenna element (135).; 2. The AMC antenna apparatus (100, 200, 100j according to claim 1, wherein: the plurality of conductive patches is a plurality of conductive patches printed on a first dielectric sheet (154); and the at least one antenna element is at least one conductive element printed (135) on a second dielectric sheet (174); wherein each of the first and second dielectric sheets is flexible.

3. The AMC antenna apparatus (100, 200, 100') according to claim 2, wherein; each of the memory metal wires has a substantially identical length, such that the FSS layer is uniformly separated from the base surface; and the first dielectric sheet is mechanically coupled to the second dielectric sheet such that the antenna element layer is uniformly separated from the FSS layer.

4. The AMC antenna apparatus (100, 200, 100j according to claim 3, wherein the shape memory metal wires include the respective extensions (176) extending over the FSS layer, and the first dielectric sheet is coupled to the second dielectric sheet and uniformly separated from it by the expansions when the shape memory metal wires are rigid in the shape memory state.

5. The AMC antenna apparatus (200) according to claim 1 further comprises a retention structure (210) configured to retain, when the antenna apparatus is stored, the antenna element layer and the ground plane with the FSS layer folded towards the base surface.

6. The AMC antenna apparatus (200) according to claim 5 further including at least one actuator (275, 260) configured to remove the antenna element layer and ground plane from the retaining structure.

7. The AMC antenna apparatus (200) according to claim 5, wherein the retaining structure (210) retains the antenna element layer and the ground plane in a wound state.

8. The AMC antenna apparatus (200) according to claim 7, wherein the retaining structure (210) is a cylindrical structure comprising a pair of spiral notches (214) at the respective opposite ends, wherein the opposite peripheral portions of the ground plane are retained in coiling within the pair of spiral notches.

9. The AMC antenna apparatus (100, 200, 100') according to claim 1, wherein the memory metal wires (115) are composed of nitinol.

10. The AMC antenna apparatus (100, 200, 100') according to claim 1, further comprising a flexible antenna feed (310, 320) having a first end electrically connected to the at least one antenna element, an opposite end below the base surface, and a central portion extending between the base surface and the at least one antenna element through an opening (375) in the FSS layer.

11. The AMC antenna apparatus (100, 200, 100') according to claim 10, further comprising a balun (350) disposed under the base surface and connected to the opposite end of the antenna feed.

12. The AMC antenna apparatus (100, 200, 100') according to claim 10, wherein the feed comprises at least one flexible coaxial cable (310, 320) having a linear shape when the shape memory metal cables are in the shape memory state and having a folded non-linear configuration when the shape memory metal cables are in the non-shape memory state.

13. The AMC antenna apparatus (100, 200, 100) according to claim 1, wherein the at least one antenna element comprises at least one crossed dipole antenna element (135).

14. The AMC antenna apparatus (100, 100j according to claim 1, wherein the ground plane and the antenna element layer are folded when the antenna apparatus is stored.

15. The AMC antenna apparatus (100, 200, 100) according to claim 1, wherein the base surface comprises the printed conductive material (119) on a flexible substrate (144).

16. The AMC antenna apparatus (100, 200, 100) according to claim 1, further comprising a plurality of support structures (117, 192) wherein each supports a mechanical connection between one of the memory metal wires and the base surface and / or one of the conductive patches.

17. A method (1200) of deploying an artificial magnetic conductor (AMC) antenna (100, 100j) on an unmanned carrier (285), wherein the method comprises: storing (S1210) the AMC antenna in a holding structure (210, 199), wherein the AMC antenna comprises: (i) a layer of antenna elements; and (ii) a ground plane having a conductive base surface, a frequency-selective surface (FSS) layer, and a plurality of shape-memory metal wires electrically and mechanically coupling the conductive base surface to the FSS layer, wherein the plurality of shape-memory metal wires are in a folded, shape-memory-free state when the AMC antenna is stored;and removing (S1230), by means of an actuator (260, 275), the AMC antenna from the retention structure to deploy the AMC antenna, wherein the memory metal cables automatically transform from flexible to rigid states when the ambient temperature exceeds a threshold, causing the FSS layer to permanently separate from the base surface after the AMC antenna is removed from the retention structure.

18. The method (1200) according to claim 17, wherein the unmanned carrier is an orbital satellite (285).

19. The method (1200) according to claim 17, wherein the retention structure retains the AMC antenna in a wound state, and wherein the actuator causes the AMC antenna to unfurl from the retention structure in a plate-like form.

20. The method (1200) according to claim 19, wherein the AMC antenna further comprises a flexible antenna feed stored in a coiled form within the retention structure and deployed during extraction of the AMC antenna.

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