DEPLOYABLE ANTENNA DEVICE WITH LATCH INFLATING MECHANISM.

Abstract

An 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 flexible conductors, 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 flexible conductors electrically connects one of the conductive patches to the base surface. A latching mechanism is disposed between the base layer and the FSS layer. An inflatable reservoir system between the base layer and the FSS layer is configured to receive a gas inlet during deployment of the antenna apparatus and inflate to produce sufficient force to cause the latching mechanism to transition from an unlatched state to a latched state, in which the conductive base surface separates from the FSS layer by a predetermined distance.

Description

DEPLOYABLE ANTENNA DEVICE WITH LATCH INFLATION MECHANISM Cross Reference to Related Request This application claims priority to U.S. Provisional Application No. 63 / 091.909, 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 refers to storage and deployment techniques for ground plane antennas; and 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-based 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 comprising at least one antenna element above the ground plane. The ground plane includes a conductive base surface, a plurality of flexible conductors, and a frequency-selective surface (FSS) layer over the base surface, wherein the FSS layer comprises a plurality of conductive patches separated from each other. Each of the flexible conductors electrically connects one of the conductive patches to the base surface. A latching mechanism is disposed between the base layer and the FSS layer.An unreliable depot system is positioned between the base layer and the FSS layer and is configured to receive an influx of gas during the deployment of the antenna apparatus and inflate to produce sufficient force to cause the latching mechanism to transition from an unlatched state to a latched state in which the conductive base surface separates from the FSS layer to a predetermined distance. - 2 The AMC antenna apparatus may further include a retention structure configured to retain, when the AMC antenna apparatus is stored: (i) the antenna element layer; (ii) the ground plane with the FSS layer folded towards the base surface; and (iii) the inflatable reservoir system. The retention structure may retain the antenna element layer, the ground plane, and the inflatable reservoir system in a rolled-up state. The AMC antenna apparatus may further include at least one actuator configured to remove the antenna element layer, ground plane, and inflatable reservoir system 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 flexible conductors that electrically and mechanically couple the conductive base surface to the FSS layer. The method involves, during deployment of the AMC antenna: removing the AMC antenna from the retaining structure by using an actuator; and inflating the inflatable reservoir to produce sufficient force to cause the latching mechanism to transition from an unlatched state to an engaged state. In the engaged state, the conductive base surface is separated from the FSS layer by a predetermined distance. 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. Several 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 simply 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 have 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 apparatus in an operational configuration, according to one embodiment. Figure 2 is a cross-section perspective view showing an example structure of a 30 portion of the AMC antenna apparatus from Figure 1. Figure 3 is a perspective view showing an AMC antenna apparatus retention structure that retains the AMC antenna of Figure 1 in a coiled configuration during storage. Figure 4 is a perspective view showing the AMC antenna apparatus of Figure 1 35 immediately after removing the AMC antenna from the holding structure during deployment. Figure 5 is a cross-sectional view of a portion of the AMC antenna apparatus of Figure 1, illustrating various structures of it in a folded state during storage. -3Figure 6 is a plan view of an example flexible printed circuit board (PCB) included inside the AMC antenna apparatus of Figure 1. Figure 7 is a cross-sectional view taken along lines 7-7 of Figure 6, illustrating an example layered structure of the flexible PCB. Figure 8 is a cross-sectional view taken along lines 8-8 of Figure 1, depicting an interlayer structure of the AMC antenna apparatus. Figure 9 is a schematic diagram illustrating an example antenna feed connected to antenna elements of the AMC antenna apparatus of Figure 1. Figure 10 is a perspective view of a central portion of a top part of the AMC antenna in Figure 1, illustrating a portion of the example antenna feed. Figure 11 is a cross-sectional view taken along lines 11-11 of Figure 10, depicting an integration of the example antenna feed within the AMC antenna. Figure 12A is a partial end view of the AMC antenna from Figure 1, illustrating an example latch in a folded state of the AMC antenna. Figure 12B is a partial end view of the AMC antenna from Figure 1, illustrating an example latch in an engaged state during an operational state of the AMC antenna after deployment. Figure 13 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 apparatus, 100, in an operational configuration, according to one embodiment. The AMC antenna apparatus 100 may include an AMC antenna 10 and a retention structure 20 for retaining the AMC antenna 10 during storage. (Note that the AMC antenna 100 may also sometimes be referred to interchangeably as an AMC antenna apparatus.) Figure 1 depicts the AMC antenna 10 in a configuration after removal from the retention structure 20 and following operations that transform its structure from a folded configuration to an expanded operational configuration, which are described hereafter. Figure 2 is a cross-section perspective view showing an example structure of a portion of the AMC antenna apparatus of Figure 1. With collective reference to Figures 1 and 2, the AMC antenna 10 may include a ground plane 105, a layer of antenna elements 130 with at least one -4 antenna element 135, and an antenna feed (e.g., 300 of Figure 11, omitted from Figures 1 and 2 for clarity). 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 flexible conductors 115 electrically connecting the FSS layer 120 to the conductive base surface. A conductor 115 may comprise an electrically conductive material such as a metal. A conductor 115 may have any of a variety of possible shapes. For example, a conductor 115 may be a wire, a column, a spring, a trace, or the like. The 105 ground plane with a textured surface configuration of this type of conductive feature 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.) The 105 ground plane can also be understood as an in-phase reflector with suppressed surface waves. The textured structure of the 105 ground plane allows the AMC 10 antenna to be substantially thinner than traditional ground plane antennas—that is, non-AMC antennas with a radiating element spaced λ / 4 on a ground plane. The AMC 10 antenna also includes a latch mechanism L (e.g., comprising individual latches Li to Ln) between the 110 base layer and the 120 FSS layer. The L latch mechanism is configured to transition from an unlatched state to a latched state when the AMC 10 antenna is deployed from a stored configuration. In the latched state, illustrated in Figures 1 and 2, the 110 base layer is fixedly separated from the 120 FSS layer by a predetermined distance. The AMC 10 antenna also includes an unreliable depot system, for example, with a first depot 103a (portion of first depot) and a second depot 103b (portion of second depot) between the base layer 110 and the FSS 120 layer. As described later, when the unreliable depot system is deflated and the latch mechanism L is disengaged, the FSS 120 layer can be folded against the base layer 110, making the AMC 10 antenna structure very thin.This allows the AMC 10 antenna to be stored in a wound configuration within the retention structure 20. When the AMC 10 antenna is removed from the retention structure 20 on a carrier surface 285, such as an orbiting satellite, the depot system receives a gas inlet to configure the AMC 10 antenna into its operational configuration. To this end, the depot system inflates to produce sufficient force to cause the latch mechanism L to transition from the disengaged to the engaged state, whereby the FSS 120 layer is properly separated from the base layer 110 by the desired predetermined distance. A plurality of flexible printed circuit boards (PCBs) 107 can each be arranged between the base layer 110 and the FSS layer 120, wherein each PCB 107 includes a group of the flexible conductors 115. As illustrated in Figure 2, each PCB 107 can be oriented substantially orthogonal to the base layer 110 and the FSS layer 120 when the latching mechanism is in the latched state. As illustrated in Figure 5, discussed later, each PCB 107 can be folded at least - 5 partially with respect to base layer 110 and FSS layer 120 when the latch mechanism L is disengaged. In this state, a main surface of each PCB 107 can be tilted towards base layer 110, closing the air gap between base layer 110 and FSS layer 120 to provide a compact configuration for storage. Note here that, in other embodiments, flexible conductors 115 are provided between FSS layer 120 and base layer 110 as separate conductors not integrated within the PCB 107 (the PCB 107 are omitted). The FSS 120 layer includes a plurality of conductive patches 1211 to 121_n separated from each other by narrow insulating regions (streets) 123. Each conductive patch 121 may include a conductive surface printed on a thin dielectric foil such as a polyimide film (e.g., Kapton®), and the insulating regions 123 may be areas of the dielectric foil without a printed conductor. Thus, the conductive patches 1211 to 121_n together with the dielectric foil (and in some cases, an additional dielectric foil 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 conductor 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 (reinforced with the dielectric of the PCBs 107) 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. By appropriately designing the quantity, geometry, and arrangement of the conductive patches 121; the at least one antenna element of the antenna layer 130; the lengths of the conductors 115; and the separation between the antenna element layer 130 and the FSS 120, an AMC phenomenon can be achieved. As mentioned, the AMC phenomenon allows the AMC antenna 10 to be significantly thinner than a traditional antenna with a radiating element spaced λ / 4 above 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 range of λ / 40 to λ / 10. Such efficiency can be achieved due to in-phase reflection and surface wave suppression.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 120 layer and the base layer 110 of Figure 1. In other -6 examples, the antenna element layer 130 is coextensive in the xy plane with each of the FSS layer 120 and the base layer 110. An example construction of the ground plane 105 may include 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 conductors 115. For example, the ribs 117 may be arranged in a lattice pattern comprising rows (for example, oriented along or substantially parallel to the x-axis in Figure 2) of multiple ribs and columns (for example, oriented along or substantially parallel to the y-axis in Figure 2) of multiple ribs. As another example, as illustrated in Figure 2, each rib 117 can extend substantially along (e.g., oriented along or substantially parallel to the y-axis of Figure 2) the base layer 110.As another example, the base layer 110 may comprise one or more continuous ribs 117. Alternatively, the base layer 110 may not include ribs 117. Each of the conductive patches 121_1 to 121_n may be arranged in a lattice and have identical geometries, for example, all rectangular or all square as depicted, or alternatively all hexagonal, all circular, or some other suitable shape. The conductive patches 121_1 to 121_n may also be configured with identical or substantially identical dimensions (for example, within manufacturing tolerances) in some embodiments. Each conductive patch 121 may be electrically connected to a respective conductor 115 via a connection 128 at a central location thereon. Figure 3 is a perspective view showing the AMC 100 antenna apparatus's retention structure 20, which holds the AMC 10 antenna in a coiled configuration during storage. All AMC 10 antenna elements illustrated in Figures 1 and 2 can be retained coiled within the retention structure 20. In addition, other AMC 10 antenna elements described hereafter, such as an antenna feed and baluns, can also be stored coiled within the retention structure 20. The baluns can be connected via flexible cables to an RF front end located outside the retention structure 20. These flexible cables have a section coiled inside the retention structure 20 and uncoiled when the AMC 10 antenna is removed from the structure. Figure 4 is a perspective view depicting the AMC 10 antenna immediately after its removal from the retention structure 20 during deployment. Figure 4 also illustrates an example arrangement of the AMC 10 antenna with respect to the retention structure 20 before its insertion. Under these conditions, tanks 103a and 103b are deflated, allowing the FSS 120 layer to fold against the base layer 110 (the latch mechanism L disengages and can lie flat between the FSS 120 layer and the base layer 110 during the deflated state of the tank system). The resulting AMC 10 antenna structure is flattened so that it can be easily inserted and rolled up within the retention structure 20 during initial stowage and subsequently unrolled for removal during deployment.The 103a tank may include a gas insertion port 102a connected to a gas line 104a. The 103b tank may include a gas insertion port 102b connected to a gas line 104b. After removal. - 7 of the retention structure 20, gas can be inserted into each of the gas lines 104a and 104b to inflate the tanks 103a and 103b to inflated states as illustrated in Figure 1. It is noted here that at least one additional tank portion of the reservoir system can be provided within the AMC antenna 10, for example, an oblong tank arranged longitudinally between the peripheral portions 110a and 120a. The additional tank can have its own insertion port and gas line or can be coupled to each of the tanks 103a and 103b to provide a continuous reservoir system arranged along three sides of the AMC antenna 10. In the latter case, only one gas port and one gas line, for example, 102a and 104a, can be included in the reservoir system. The illustrated reservoir system is an example. The storage system can have different configurations and tank layouts. With continued reference to Figures 1-4, it is exemplified that the latch mechanism L comprises a plurality of latches Li to Ln (e.g., N=6 as depicted) distributed along opposite peripheral portions of the AMC 10 antenna. For example, the FSS 120 layer may include first to fourth oblong peripheral portions (strips) 120a, 120b, 120c, and 120d, which may overlap corresponding peripheral portions 110a, 110b, 110c, and 110d, respectively, when the depot system is inflated. A first group of latches, Li, L2, and Ln, may be distributed between peripheral portions 110b and 120b, and a second group of latches, L3, L4, and Ls, may be distributed between peripheral portions 110a and 120a. Deposit 103a is located between peripheral portions 110c and 120c; deposit 103b is located between peripheral portions 120d and 110d.In other embodiments, one or more additional latches may be arranged adjacent to the reservoir 103a between the peripheral portions 110c and 120c, and one or more additional latches may be arranged adjacent to the reservoir 103b between the peripheral portions 110d and 120d. The retention structure 20 in this embodiment is generally a cylindrical structure with opposing first and second end walls 216 and 218, a spindle 225 between the opposing end walls 216 and 218, and support rods 228 coupling the opposing end walls 216 and 218 together. Each of the end walls 216, 218 may have a spiral groove 214 on an inner surface 212 thereof to facilitate guiding and retaining the AMC antenna 10 in a wound configuration. Opposing peripheral portions of at least the ground plane 105 are retained wound within the pair of spiral grooves 214 during storage. If the antenna layer 130 is configured coextensive with the ground plane 105, the opposite peripheral portions of the antenna layer 130 can also be retained within the spiral slots 214. The spindle 225 may have a mechanical link 272 (shown schematically) to the peripheral portion 110a of the base layer 110. To initially retain the AMC antenna 10 within the retention structure 20, the AMC antenna 10 may be placed in a folded state as shown in Figure 4. In the folded state, conductors 115 are bent 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 slots 214. Note that, in the folded state, the FSS layer 120 may be folded toward the base layer 110 in the +x direction such that the FSS layer 120 is tilted -8 with respect to base layer 110. Because the two layers are tilted in the folded condition, the peripheral portion 110a of base layer 110 no longer overlaps with the corresponding peripheral portion 120a of FSS layer 120. The spindle 225 can be rotated (e.g., clockwise) to draw the AMC 10 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 rotational force to draw the AMC 10 antenna into the retention structure 210. Once the AMC 10 antenna is thus retained, the AMC 100 antenna apparatus can be carried to a carrier, such as an orbital satellite prior to launch, and attached to a surface 285 of the carrier.Since the retention structure 20 is more resistant to environmental conditions and movement than the AMC 10 antenna itself (if otherwise mounted on surface 285 without protection), securing the retention structure 20 to surface 285 before deploying the AMC 10 antenna on surface 285 can improve the chances of a successful deployment. As another example, surface 285 is a planetary surface or the surface of an artificial structure on a planet. In this case, the retention structure 20 with the AMC 10 antenna attached to it can be transported by drone and released onto surface 285 for subsequent unmanned deployment. To deploy the AMC 10 antenna from the retention structure 20, a spindle 225 can be rotated (e.g., counterclockwise) by means of an actuator 275, whereby the AMC 10 antenna can be slid outwards in a dish-like configuration while in its folded state in the +x direction. Alternatively or additionally, another actuator 260 arranged on surface 285 can automatically extract the AMC 10 antenna from the retention structure 20. For this purpose, the AMC 10 antenna can have an opening 129 in the peripheral portion 120b, through which a link 262 of the actuator 260 can be coupled to the AMC 10 antenna. Note that actuator 260 and / or actuator 275 can be a robotic arm fixed to surface 285. Figure 5 is a cross-sectional view of a portion of the AMC 10 antenna, illustrating various structures of the antenna in a folded state during storage. It can be seen that, in the folded state, each PCB 107 is tilted with respect to the FSS layer 120 and the base layer 110, such that, in the cross-sectional view, each PCB 107 forms an acute angle with the base layer 110. Each conductor 115 may include a lower end 116b and an upper end 116a, which are discussed later. Figure 6 is a plan view of an example flexible PCB 107. Figure 7 is a cross-sectional view taken along lines 7-7 in Figure 6, illustrating an example layered structure of a flexible PCB 107. The PCB 107 may have a generally rectangular profile. Each PCB 107 may have a group of integrated conductors 115 extending across its width from edge to edge. Each conductor 115 may include an upper end 116a and a lower end 116b, each in the form of a rectangular or square tab. The conductors 115 may be sandwiched between a first dielectric film 111 and a second dielectric film 112, for example, Kapton® or FR4. Figure 8 is a cross-sectional view taken along lines 8-8 of Figure 1, depicting an interlayer structure of the AMC 10 antenna during an operational (deployed) state. Figure 8 represents an example connection structure with respect to a single conductor 115 of an underlying antenna element layer 130 of PCB 107; the same connection structure can be applied with respect to all conductors 115 of the underlying antenna element layer 130 of the AMC 10 antenna. For those conductors 115 outside the antenna element layer 130 region, the top structure may differ (discussed later). (Note also that in Figure 8 and other cross-sectional views herein, features located behind those illustrated may be omitted for clarity.)The base layer 110 may include a conductive base surface 119 bonded or printed on a lower surface of a flexible dielectric foil 144 for structural integrity and to facilitate electrical and mechanical connections to the conductors 115. A dielectric rib 117 may be bonded to a top surface of the dielectric foil 144 and allow a connection of a conductor 115 to the base surface 119. A silver through-hole 158 may have been formed through the rib 117 and the base layer 110. A lower end 116b of the conductor 115 may have been inserted into the through-hole 158 and electrically connected to the conductive base surface 119 with an adherent conductor 157 surrounding the end 116b within the through-hole 158, for example, by molten and cooled soldering. 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 the upper portion of the conductor 115 and the FSS 120 layer may comprise a silver through-hole 168, an upper end 116a, and a conductive adherent 167 within a through-hole 168. Figure 8 depicts a single connection 128 between a conductor 115 and a given conductive patch 121J, which is separated by respective insulation regions 123 from the adjacent conductive patches 121_(j-1) 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 10 can be provided at a distance above the dielectric foil 144 (with latch mechanism L in the engaged state). In this way, the FSS layer 120 is supported with its lower surface uniformly separated by a fixed distance from the base layer 110. An air gap 191 can be present in the regions surrounding the conductors 115. The antenna element layer 130 may include at least one antenna element 132 printed on 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 upper end 116a of the conductor - IO115 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 adherent 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 adherent 177. All or most of the conductors 115 underlying the antenna element layer 130 may also include an extension 176 adhered to the dielectric foil 174 in this manner. As a result, the antenna element layer 130 may be fully supported by the conductors 115 and uniformly separated at a close distance from the top surface of the FSS layer 120.It is observed 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 conductors 115 located outside the region of the antenna layer 130 can omit the extensions 176. These conductors 115 can be designed entirely to the same or substantially the same length (e.g., within manufacturing tolerances), and their upper ends can be flush with the top surface of the dielectric foil 164. Similarly, each of the conductors 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 layer 120 and the antenna element layer 130, a narrow air gap 171 can exist between the layers 120 and 130.In an alternative configuration, the extensions 176 on the conductors 115 are omitted throughout the AMC antenna 100; 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 layer 120 and the antenna element layer 130. Figure 9 is a schematic diagram illustrating an example of an antenna feed, 300, that can be connected to antenna element 135 of the AMC 10 antenna. Antenna feed 300 may include a pair of baluns 350; a first flexible coaxial cable 310 having one end connected to the baluns 350 and having an outer conductor 313 and an inner conductor 311; a second flexible coaxial cable 320 having one end connected to the baluns 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. The first dipole element 132 includes dipole arms 132a and 132b; the second dipole element 134 includes 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 10 is a perspective view depicting a sample center portion of an AMC 10 antenna top, illustrating a portion of the sample antenna feed 300. A center portion of the crossed dipole antenna element 135 can be superimposed on an intersection region of adjacent centralized conductive patches 121J, 121_(i+1), 121_(i+2), and -11 121_(i+3). An opening 375 may form in the FSS 120 layer in the centralized region by removing a corner piece from each of the conductive patches 121_i to 121(i+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 10 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 conductive extension. The funnel-shaped metal section is soldered or otherwise electrically connected to the respective external conductors 313 or 323, and the conductive 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 11 is a cross-sectional view taken along lines 11-11 of Figure 10, depicting an example integration of antenna feed 300 within the AMC 10 antenna. This view shows that baluns 350 can be arranged adjacent to the lower surface of the AMC 10 antenna, and the lower ends of coaxial cables 310 and 320 can penetrate opening 365 in base layer 100 and connect to baluns 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 sheet 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 fold in a manner similar to conductors 115 (the folded state illustrated in Figure 5). Figure 12A is a partial end view of the AMC 10 antenna, illustrating an example latch, Li, in an unlatched and folded state of the AMC 10 antenna. Figure 12B is the same partial end view of the AMC 10 antenna in an operational latched state after deployment. Any of the AMC 10 antenna Li-Ln latches may have the Li latch structure, which may include an upper rod 405, a lower rod 403, and a center latch coupler 401 that couples the upper and lower rods 405 and 403. An upper end bracket 407 may be attached to the FSS layer 120 and form a movable joint with an upper portion of the upper rod 405. An upper end bracket 409 may be attached to the base layer 110 and form a movable joint with the lower rod 403.Therefore, in the unlocked state, the upper rod 405 forms an acute angle with the FSS 120 layer and the lower rod 403 forms an acute angle with the base layer 110, such that the FSS 120 layer and the base layer 110 are closely separated for optimal storage of the AMC 10 antenna. In the locked state, the upper rod 405 and the lower rod 403 are vertically aligned, thus providing a fixed predetermined separation between the base layer 110 and the FSS 120 layer. Figure 13 is a flowchart depicting the operations of an example method 1300 for deploying an AMC 10 antenna on an unmanned carrier according to one embodiment. With method 1300, the AMC 10 antenna is first stored in its folded state in a holding structure, for example, the holding structure 20 described above (S1310). The holding structure can then be transported with an AMC 10 antenna stored on it to an unmanned carrier (S1320). As mentioned earlier, examples of an 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 then be deployed (S1330) by removing it from the retaining structure using an actuator (e.g., 275 and / or 260) as described above, and inflating the reservoir system (e.g., reservoirs 103a and 103b) sufficiently to cause the latching mechanism (e.g., L) to transition from the disengaged to the engaged state. As a result of the locking, the FSS 120 layer is properly separated from the base layer 110, and the AMC antenna 10 is configured to operate, for example, in the configuration described above and shown in Figure 1. With the AMC antenna in an operational configuration, a robotic arm or similar device (e.g., actuator 260 with link 262) can secure the AMC antenna to the carrier surface 285. In one embodiment, the balun 350 is already connected by cables to an RF front end of a communication system, for example, via a flexible cable (not shown) that has a section wound inside the retention structure 20 during storage and unwound when the AMC antenna 10 is removed. If the balun 350 is not connected by cables, a robotic arm or similar device can electrically connect the balun 350 to the RF front end. In either case, active signal communication via the AMC antenna can be initiated once the RF front end connection to the balun 350 is secured. Although the technology described herein has been 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 object as defined by the following claims and their equivalents.

Claims

1. An artificial magnetic conductor (AMC) antenna apparatus (100) comprising: a ground plane (105) comprising: a base layer (110) comprising a conductive base surface (119); a frequency selective surface (FSS) layer (120) on the base layer, wherein the FSS layer comprises a plurality of conductive patches (121) separated from each other; and a plurality of flexible conductors (115), each electrically connecting one of the conductive patches to the conductive base surface; a flexible antenna element layer (130) on the FSS layer, comprising at least one antenna element (135).a latching mechanism (L) between the base layer and the FSS layer, configured to transition from an unlatched state to a latched state, wherein in the latched state, the conductive base surface is separated from the FSS layer by a predetermined distance; and an unreliable depot system (103a, 103b) between the base layer and the FSS layer, configured to receive a gas inlet during deployment of the AMC antenna apparatus and inflate to produce sufficient force to cause the latching mechanism to transition from the unlatched state to the latched state.

2. The AMC antenna apparatus (100) according to claim 1, wherein the inflatable reservoir system comprises: a first inflatable reservoir portion (103a) extending longitudinally between a first peripheral portion of the base layer (110c) and a first peripheral portion of the FSS layer (120c); and a second inflatable reservoir portion (103b) extending longitudinally between a second peripheral portion of the base layer (110d) and a second peripheral portion of the FSS layer (120d), wherein the second peripheral portion of the base layer is opposite the first peripheral portion of the base layer and the second peripheral portion of the FSS layer is opposite the first peripheral portion of the FSS layer.

3. The AMC antenna apparatus (100) according to claim 1 or 2, further comprising a retention structure (20) configured to retain, when the AMC antenna apparatus is stored: (i) the antenna element layer; (ii) the ground plane with the FSS layer folded towards the base surface; and (iii) the inflatable reservoir system.

4. The AMC antenna apparatus (100) according to claim 3, further comprising at least one actuator (275, 260) configured to remove the antenna element layer, ground plane, and inflatable reservoir system from the retaining structure.

5. The AMC antenna apparatus (100) according to claim 4, wherein the retaining structure retains the antenna element layer, the ground plane, and the inflatable reservoir system in a rolled-up state.

6. The AMC antenna apparatus (100) according to claim 5, wherein the retention structure is a cylindrical structure comprising a pair of spiral grooves (214) at the respective opposite ends (216, 218), wherein the opposite peripheral portions of the ground plane are retained wound within the pair of spiral grooves.

7. The AMC antenna apparatus (100) according to any of claims 1-6, wherein: the FSS layer comprises a first dielectric sheet (154) and the plurality of conductive patches are conductive patches printed on the first dielectric sheet; and the at least one antenna element is at least one conductive element printed (132, 134) on a second dielectric sheet (174); wherein each of the first and second dielectric sheets is flexible.

8. The AMC antenna apparatus (100) according to any of claims 1-7, further comprising a flexible antenna feed (310, 320) having a first end electrically connected to the at least one antenna element, an opposite end beneath the base layer, and a central portion extending between the base surface and the at least one antenna element through at least one opening (375) in the FSS layer.

9. The AMC antenna apparatus (100) according to claim 8, further comprising a balun (350) disposed under the base layer and connected to the opposite end of the antenna feed.

10. The AMC antenna apparatus (100) according to any of claims 1-9, wherein the at least one antenna element comprises at least one crossed dipole antenna element (135).

11. The AMC antenna apparatus (100) according to any of claims II10, wherein the base layer further comprises a flexible dielectric substrate (144), and the conductive base surface is conductive material printed on the flexible dielectric substrate.

12. The AMC antenna apparatus (100) according to any one of claim 111, further comprising a plurality of flexible printed circuit boards (PCBs) (107), each disposed between the base layer and the FSS layer and each including a group of the plurality of flexible conductors (115), wherein each of said flexible PCBs is oriented substantially orthogonally to the base layer and the FSS layer when the latching mechanism is in the latched state, and is oriented non-orthogonally to adjacent portions of each of the base layer and the FSS layer when the latching mechanism is disengaged.

13. The AMC antenna apparatus (100) according to any of claim 112, wherein the latching mechanism comprises a plurality of individual latches (Li to Ln) distributed between at least two peripheral portions of the FSS layer (120a, 120b) and at least two corresponding peripheral portions of the base layer (110a, 110b).

14. A method (1300) for stowing and deploying an artificial magnetic conductor (AMC) antenna (10) on an unmanned carrier (285), wherein the method comprises: stowing the AMC antenna in a retention structure (S1310), wherein the AMC antenna comprises: (i) a layer of antenna elements; (ii) a ground plane comprising a frequency-selective surface (FSS) layer, a base layer beneath the FSS layer and including a conductive base surface; (iii) a latching mechanism between the base layer and the FSS layer; and (iv) an inflatable depot system between the base layer and the FSS layer; during deployment of the AMC antenna: withdrawing the AMC antenna from the retention structure by using an actuator (S1330);and inflating the inflatable reservoir to produce a force sufficient to cause the latching mechanism to transition from an unlatched state to a latched state (S1330), wherein in the latched state, the conductive base surface separates from the FSS by a predetermined distance.

15. The method (1300) according to claim 14, wherein the unmanned carrier is an orbital satellite.

16. The method (1300) according to claim 14 or 15, wherein the retaining structure retains the AMC antenna in a coiled state, and the actuator causes the AMC antenna to uncoil from the retaining structure in a dish-like manner.

17. The method (1300) according to any of claims 14-16, wherein the AMC antenna further comprises a flexible antenna feed (132, 134) stored in a spiral form within the retention structure, wherein the flexible antenna feed unwinds during removal of the AMC antenna.

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