FR2937186A1 - DEPLOYABLE STRUCTURE AND MEMBRANE ANTENNA SYSTEM INCLUDING SUCH STRUCTURE. - Google Patents

Abstract

The invention relates to a deployable structure comprising: a plurality of membranes (M) supporting at least one printed element having the antenna function; a plurality of pantographs (20) for deploying the membranes; characterized in that a membrane (M) is supported by two pantographs facing each other, the pantographs being identical and arranged on either side of the membrane.

Description

GENERAL TECHNICAL FIELD The invention relates to a deployable structure supporting at least one membrane and more particularly its use in an antenna system whose membranes constitute the main radiating structure and in particular those that can be embedded on a satellite system.

STATE OF THE ART Deployable structures are frequently used on the satellites in order to meet the congestion constraints under the hood during launch. Deployable is a structure whose stored volume is less than the volume after deployment. This is a foldable structure when the stored volume is equal to the volume in operation. Deployable structures are particularly suitable for the mechanical design of antennas, whose area projected in a given direction expressed in wavelengths strongly conditions the radiation performance. Thus when a high directivity is required or when the operating frequency is relatively low, large antennas are required. Beyond two to three meters, foldable solutions can not generally meet the constraints of development under headdress. Among the known deployable antenna solutions, many embodiments rely on membrane technologies. Associated with a carrier structure and a deployment system, the membrane antennas have the advantage of being of a small footprint when they are in storage configuration. These antennas also generally have a substantially lower weight than rigid antennas of equivalent size.

When a large antenna is needed, several problems constraining the design must be considered. First of all, the storage volume must be compatible with under-the-head layout constraints.

In addition, the carrier structure and the associated deployment mechanism must provide sufficient rigidity to obtain a good surface condition, the latter feature having a direct impact on the electromagnetic performance of the antenna. More precisely, the gain of the antenna is degraded when the surface state is not in conformity. Unwanted radiation (side lobes, backward radiation, cross polarization) can also be accentuated. The nonconformity of the surface condition may be due to the accuracy of the carrier structure itself or the mechanical forces and vibrations experienced. In particular, for large antennas, beat phenomena in the direction orthogonal to the plane of the antenna can substantially affect the surface state. In addition, when multiple membranes are required to perform the antenna function (typically two or more parallel membranes), the relative positioning accuracy is particularly important to ensure good matching and radiation performance. The quality of the surface condition and any relative positioning of the membranes is generally defined in proportion to the wavelength. Typically, a precision of the order of one twentieth of the wavelength is necessary. The choice of the supporting structure is therefore particularly important so as not to lead to mechanical oversizing, with consequent increased mass and bulk.

Thus, a deployable membrane antenna must satisfy several constraints: a small bulk in storage configuration, a large size in deployed configuration, a precise holding structure and which is more capable of withstanding mechanical forces, and a reduced mass compared to its equivalent in rigid technologies.

PRESENTATION OF THE INVENTION The invention relates to a deployable structure for obtaining a membrane antenna with a large radiating aperture while maintaining a low storage volume. The structure of the invention offers additional rigidity compared to deployable antennas of known type, in particular to minimize the effects of flapping in the direction orthogonal to the plane of the antenna. In addition, the structure of the invention makes it possible to ensure a good surface state of the deployed membranes by the addition of transverse bars on which the membrane or membranes rest. Thus, according to a first aspect, the invention relates to a deployable structure comprising: a plurality of membranes supporting at least one printed element having the antenna function; a plurality of pantographs for deploying the membranes. The structure of the invention is characterized in that a membrane is supported by two pantographs facing each other, the pantographs being identical and arranged on either side of the membrane. The deployment of the membrane takes place in a general direction which is vertical to the base of the structure and more precisely in a direction which corresponds to that given by the shape of the pantographs used. Thus, the shape of the deployed structure is given by the profile of the pantographs: straight, parabolic or such that the deployed structure has a hexagonal or trapezoidal shape.

In deployed configuration, such a structure can have a height of two meters and more depending on the mechanical constraints, weight and flatness required specific to the targeted application, and more particularly to the operating frequency.

According to a second aspect, the invention relates to an antenna system comprising a deployable structure according to the first aspect of the invention. According to a third aspect, the invention relates to a satellite system comprising at least one antenna system according to the second aspect of the invention.

PRESENTATION OF THE FIGURES Other features and advantages of the invention will become apparent from the description which follows which is purely illustrative and non-limiting and should be read with reference to the appended figures in which: FIG. 1 schematically illustrates a satellite; FIG. 2 illustrates a deployable structure according to the invention used in a antennasystem of the direct radiation network type; FIG. 3 illustrates a deployable structure according to the invention used in an antennasystem of the reflector or transmitter network type powered by a radiating element in vis-à-vis; FIG. 4 illustrates two deployable structures according to the invention used in an antennasystem of the direct radiation network type; FIG. 5 illustrates a deployable structure according to the invention used in an antenna system comprising a plurality of reflector networks or transmitters in a so-called pallet arrangement with a radiating element facing each other by means of a network; FIGS. 6a, 6b and 6c illustrate several configurations of deployed membranes with different profiles for the pantographs facing each other; FIG. 7 illustrates a profile view of a deployable structure allowing a surface other than flat; Figures 8a, 8b illustrate the deployment principle of a pantograph implemented to deploy the carrier structure; FIG. 9 illustrates a pantograph extending in a direction with a parabolic profile; Figures 10a, 10b, 10c illustrate different phases of the deployment of the carrier structure.

DETAILED DESCRIPTION Figure 1 schematically illustrates a satellite 10 comprising two deployable structures 11. In storage configuration, the deployable structures are folded over the central portion 12 of the satellite. FIG. 2 illustrates a deployed structure 11 comprising a membrane M used in an antennasystem of the direct radiation network type. The printed components R (for illustrative purposes shown here all identical) on the membrane M directly emit the energy which is transmitted to them by the appropriate supply circuit, usually also printed. The structure deployed in this example has a parallelepipedal shape. The pantographs 20 are arranged in parallel manner, on either side of the membranes M to be deployed. In order to increase the rigidity of the deployed structure, transverse bars 21 may be provided to connect the pantographs in particular to the ends of the structure. Thanks to these crossbars the mechanical strength of the structure is guaranteed.

These transverse bars 21 also contribute to the flatness of the membranes. The entire bearing structure, including pantograph 20 and transverse bars 21, can be made with standard materials in space applications of aluminum or carbon type. It should be noted that the structure naturally offers a controllable dimension in the direction orthogonal to the main plane of the antenna. This dimension is controllable in that it depends directly on the dimensioning of the pantograph.

This aspect makes it possible to ensure a good relative positioning of the different necessary membranes. The membranes M make it possible to include all radio-frequency functions of known type and necessary for the use of this structure in an antennasystem of the direct radiation network type, reflector network or transmitting network, also called lens. In particular, a membrane M can act as a ground plane, while another comprises the radiating elements. The ground plane makes it possible in particular to minimize the backward radiation, which is usually undesired for operating modes of the direct radiation network or reflector network type. In the case of a lens-like mode of operation, the printed elements do not require a ground plane. The supply circuit or additional stacked type radiators may optionally be printed on one or more additional membranes. The advantage of printing the supply circuit on a separate membrane is to reduce the coupling with the radiating elements and thus to improve the overall performance of the antenna, whereas the stacked type of radiating structures usually make it possible to enlarge The frequency band.

By membrane is meant a flexible material of relatively thin thickness radially electrically on which it is possible to make a metallization deposit (copper for example) in order to achieve patterns corresponding to radio-frequency functions mentioned above. The material used for the membrane may be Kapton. FIG. 3 illustrates a deployed structure 11 similar to that of FIG. 2 used in an antennal system of the reflector or lens network type further comprising a plurality of printed patterns R disposed on the membrane M and a source S placed opposite. The electromagnetic energy is radiated by the source S and is reflected or transmitted by the network of printed elements. The interest of reflector networks (in English, reflect array) and transmitters or lenses networks (in English, transmit array or lens) is to allow radiation performance with a flat surface comparable to that of a shape reflector antenna. parabolic known to focus the energy and thus ensure in theory a maximum antenna directivity. The reflector arrays and lenses as described above are advantageous in that a planar surface is generally simpler to achieve than a surface formed for a given surface-state accuracy. The reflector or transmitter network consists of a plurality of elementary patterns whose shape changes the phase of the reflection or transmission coefficient respectively. To ensure optimum operation of the reflector or transmitter array, the phase of the reflection or transmission coefficient respectively must compensate for the phase shift induced by the difference in electrical paths between a planar surface and the parabolic surface having its focus at the source. S.

In order to increase the radiation surface in the case of a structure in direct radiation, it is possible to position two structures 11 deployable on either side of the center 12 of a satellite as shown in FIG. 4.

FIG. 5 illustrates a deployable structure comprising a membrane M on which several reflectors R1, R2, R3, R4 are printed in a so-called pallet arrangement. Each of the sources S1, S2, S3, S4 is respectively associated with a reflector R1, R2, R3, R4 and is pointed in its direction.

Figures 6a, 6b, 6c illustrate different possible orientations for the two pantographs for deploying the structure. FIG. 6a makes it possible to obtain a parallelepiped-shaped expanded structure already described above. This arrangement has the advantage of having rigid transverse bars, as opposed to the other orientations envisaged. From an electromagnetic point of view, this orientation allows forms of highly rectangular antennas, allowing a significant directivity along an axis only. This mode of radiation is regularly used in radar and radiometer applications.

The type of antenna associated is usually a direct radiation network, but a reflector or transmitter network mode of operation can also be envisaged for certain specific applications. Figure 6b provides a deployed hexagon-shaped structure. This form of structure is interesting for increasing the directivity of the antenna while having a geometric similarity between the two main axes defining the plane of the antenna. This last feature allows very similar far-field radiant cross-sectional diagrams in the two main orthogonal planes of the antenna, a property of interest for certain applications such as telecommunications for example. This shape may have an interest in direct or indirect radiation mode (reflector network or lens).

Figure 6c provides an expanded trapezoidal structure. This form of structure is interesting for a pallet type antenna implantation as described above (see FIG. 5). Indeed, in this type of configuration, the most remote reflectors or lenses generally need to have a larger diameter in order to compensate for certain phenomena of radio frequency losses (overflow losses or degraded surface efficiency). For each of these orientations, the deployment is always carried out in a direction perpendicular to the base of the structure.

For the configurations illustrated in FIGS. 6b and 6c, the deployment sequence requires extensible transverse bars. It will be preferred to use known technologies of extensible bars with stopping point or blocking at the end of deployment to ensure better rigidity of the entire structure.

Figure 7 illustrates a side view of a deployed structure with pantographs 20 with a parabolic or circular profile. Such profiles make it possible to improve the radio-frequency performance of the antenna in reflector network configuration. More precisely, they make it possible to widen the bandwidth of the antenna by reducing the electrical path differences between the actual shape of the antenna and the equivalent parabola. As a result, the phase shift required at the level of the radiating elements that reflect the electromagnetic energy emitted by the source is less important. Figures 8a, 8b illustrate the deployment of a pantograph 20.

A pantograph consists of a plurality of rigid strands 200, 201 arranged in scissors and such that a tightening of the base produces an elongation of the pantograph. To illustrate this point, Fig. 8a shows a pantograph 20 in stored configuration, while Fig. 8b shows the same pantograph 20 in deployed configuration. The pantograph in question is said to be regular in that all the constituent strands have the same length. By judiciously defining the respective lengths of each strand, it is possible to obtain the parabolic or circular profiles mentioned above. Figure 9 illustrates a pantograph with a parabolic profile. Due to its nature, the pantograph has a greater rigidity in the plane containing it. It may, however, be subject to beat phenomena in the direction orthogonal to the plane containing it. For this reason, the proposed structure has a good arrangement of these pantographs ensuring better mechanical strength of the assembly. In particular, the pantographs minimize the beat phenomena in the direction orthogonal to the plane containing the membrane or membranes, while the assembly consisting of the opposite arrangement and the transverse bars ensures a good mechanical strength in the plane. For a detailed geometric description of the pantographs, see A. Kaveh, A. Davaran, Analysis of pantograph foldable structures, August 1994. Figures 10a, 10b, 10c illustrate the deployment of the complete supporting structure, including the two pantographs 20 and the cross bars 21. The carrier structure changes from the stored state to the fully deployed state.

This deployment can be carried out in known manner either by a motor in rotation associated with a mechanism based on son whose winding produces a voltage to extend the pantograph or by a motor producing a linear displacement of one of the ends pantograph base. In both cases, the other end at the base of the pantograph is attached to the interface with the satellite via a pivot link. Depending on the flatness constraints, directly related to the operating frequency of the antenna, different modes of attachment of the membranes can be envisaged. The membranes M may for example be attached to the pantographs 20 by tensioning systems. They can also be attached at the cross bars. Depending on the method of attachment chosen, the membrane in the storage position can either be left free or folded back along the carrier structure or be wrapped around a suitable structure at the base of the pantograph. In this latter configuration, the attachment points of the membrane would be limited. But in return, the roll storage 20 avoids the appearance of folds on the membrane can degrade the surface condition for operations at higher frequencies. In the case where the membrane is just folded, a tensioning system is necessary to ensure the flatness of the membranes and the disappearance of the previously mentioned folds.

Claims (10)

1. Deployable structure comprising: a plurality of membranes (M) supporting at least one printed element having the antenna function; a plurality of pantographs (20) for deploying the membranes; characterized in that a membrane (M) is supported by two pantographs facing each other, the pantographs being identical and disposed on either side of the membrane. 2. Structure according to claim 1, characterized in that the pantographs are regular so that the structure is deployed in a direction (D) perpendicular to the base (B) of the structure. 3. Structure according to one of claims 1 to 2, characterized in that the pantographs are parallel so that the deployed structure forms a parallelepiped. 20 4. Structure according to one of claims 1 to 2, characterized in that the pantographs are configured so that the deployed structure forms a trapezium. 5. Structure according to one of claims 1 to 2, characterized in that the pantographs are configured so that the deployed structure forms a hexagon. 6. Structure according to claim 1, characterized in that the pantographs have a parabolic or circular profile. 15 30 7. Structure according to one of the preceding claims, characterized in that the pantographs are connected by at least one transverse bar for ensuring the rigidity of the deployed structure. 8. Antenna membrane system, characterized in that it comprises at least one deployable structure according to one of the preceding claims. 9. Antenna system according to the preceding claim 10 characterized in that its mode of operation is selected from the following group: direct radiation network type, reflector array or lens. 10. Satellite system comprising at least one antennal membrane system according to the preceding claim.