Abstract:
A satellite antenna for transmitting and receiving an electromagnetic signal has at least one parabolic reflector, a source arm, and a high-power amplifier, in which antenna the high-power amplifier includes a traveling wave tube on the source arm and a high-voltage power supply off the source arm and adapted to supply power to the tube. A satellite mobile telecommunications station includes such a satellite antenna and a storage structure into which the antenna is folded and in which the high-voltage power supply sits.

Description:
RELATED APPLICATIONS 
     This application is a National Phase Application of PCT/FR2008/001240, filed on Sep. 5, 2008, which in turn claims the benefit of priority from French Patent Application No. 07 06215, filed on Sep. 5, 2007, the entirety of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field of the Invention 
     The invention relates to the field of satellite transmission antennas, possibly provided with receiving capacity. Such antennas are used in satellite broadcasting systems and they comprise a primary reflector and a source arm generally both connected to a support. The source arm may also be equipped with a secondary reflector. 
     The invention also relates to a satellite mobile telecommunications station. Satellite mobile telecommunications stations suitable for remote news gathering have recently become available, either transported in flight cases (Swe-Dish Fly-Away terminals, for example) or mounted on a vehicle (Swe-Dish Drive-Away terminals, for example). Such stations also have receiving capacities providing a bidirectional link. 
     2. Description of the Related Art 
     The uplink connection from a sender station to the satellite requires a high radiated power level in order for the signal rebroadcast by the satellite to be received and used correctly. To satisfy the required transmission power, in particular under extreme conditions (edge of satellite coverage, poor propagation channel), the sender station transmission system is provided with high-power amplifiers (HPA). Note that receive-only satellite antennas do not suffer from this power problem. 
     In satellite mobile telecommunications stations, these HPAs are in the form of a single unit combining one or more amplifier components (called active components, for example power transistors or traveling wave tubes (TWT)) and an appropriate power supply to provide the necessary and appropriate electrical power to the active components. These components are bulky and heavy if a power of tens or hundreds of watts is required, the resulting HPA weighing more than ten kilograms. This weight imposes high structural stresses on the elements supporting these components. 
     The invention also relates to the use of high-power amplifiers (HPA) based on traveling wave tubes (TWT) with a transmission power of at least 100 watts (W). A TWT-based HPA consists of a TWT subsystem and a high-voltage power supply subsystem producing voltages of several kilovolts. Generally designed as a one-piece unit, a TWT-based HPA incorporates a switch-mode power supply unit accepting direct current (DC) voltages (generally in the range 12 volts (V) to 48 V) or alternating current (AC) voltages (generally in the range 90 V to 265 V at 50 hertz (Hz) to 60 Hz) and supplying the high voltage necessary for the TWT to operate correctly. 
     It is known in the art to use fixed satellite antennas in which the HPAs are installed on the source arm of the antenna. The source arm is then sized appropriately to ensure the stiffness of the assembly and to maintain the centering of the secondary reflector or horn, such sizing sometimes being associated with the use of retaining rods or cables that relieve the source arm of the forces that are applied to it. These satellite antennas quickly become bulky and too heavy for mobile applications, in particular to conform to transportation standards such as those of the International Air Transport Association (IATA). 
     OBJECTS AND SUMMARY 
     An object of the invention is to propose an antenna in particular a source arm, of simplified mechanical design. 
     Given this background, another approach to satellite mobile telecommunications stations has been adopted. Documents EP-1 465 288, U.S. Pat. Nos. 4,771,293, and 6,573,871 disclose satellite mobile telecommunications stations each comprising a satellite antenna for transmitting an electromagnetic signal, and comprising at least:
         a parabolic primary reflector;   a source arm; and   high-power amplifier means.       

     The primary reflector is the main reflecting surface, which for reception concentrates waves broadcast by a satellite towards a source antenna mounted on the source arm, and for transmission broadcasts by reflection waves emitted by this source antenna towards the satellite. The primary reflector may be formed of one or more reflector portions (also known as petals) that, in use, are held in contact with one another to form the primary reflecting surface. The expression “parabolic reflector” means any reflector of a satellite antenna or any portion of a reflector made up of one or more portions in contact with one another forming a reflecting surface having substantially parabolic curvature, whatever the outline (external shape) of the reflector: circular, substantially lozenge-shaped, ellipse-shaped, etc. 
     The source arm defines the mechanical part responsible for holding the components that illuminate the primary reflector, notably the secondary reflector, when present, the radiating source (horn, patches, array of such elements), and the systems and components associated with the source of radiation (filters, orthomode feed, HPA, LNA (low-noise amplifier), LNB (low-noise block downconverter), etc.). In many configurations the source arm extends from a fastening point (usually at the periphery of the primary reflector) towards the focal point of the primary reflector (at the free end of the source arm). This focal point (situated approximately 500 millimeters (mm) from the center of the primary reflector for example) constitutes the primary focus of the antenna, at which the source antenna is placed, either in the form of a source of radiation or in the form of a secondary reflector reflecting radiation from or towards a source that is farther away. The source arm may be cantilevered from its fastening point, which is why attempts are made to limit the load applied to it. 
     In vehicle-mounted satellite mobile telecommunications stations (known as drive-away stations) with an HPA mounted on the source arm, the source arm is strengthened to support these components. If there is a mechanism for driving the source arm, it is also strengthened and bulky. 
     In contrast, the source arms of most transportable (fly-away) satellite mobile telecommunications stations known in the art are provided with respective horn antennas (source antenna), possibly with respective secondary reflectors. The HPA is positioned externally to the reflector elements and the source arm of the antenna and is connected to the horn antenna by a waveguide. In this configuration, the source arm is less heavily loaded and may therefore be less bulky. The drawbacks of this configuration are, firstly, deterioration of the signal and loss of power before transmission caused by ohmic losses within the waveguide and, secondly, increased bulk of the support part of the antenna (excluding the source arm and reflector). This loss of power must be compensated by a more powerful HPA and therefore by an additional load and an additional volume, compromising transportability. A more powerful HPA is also more costly. 
     Another object of the invention is therefore to improve the transmission performance of these antennas using the same HPA and without larger source arms, i.e. retaining a simple mechanical design of the source arm conducive to transportation and its motor-driven pointing towards the satellite. 
     This simple mechanical design of the source arm is also advantageous in itself: if a motorized mechanism for driving the antenna is provided, the smaller the load to be motorized, the smaller this mechanism, and the less energy it consumes. The mechanism may be a two-axis or a three-axis positioner for adjusting the azimuth, polarization, and elevation of the antenna, an actuator for deploying/folding the antenna, or possibly a module combining the capabilities of an actuator and a 2-axis or 3-axis positioner. 
     Using a waveguide to connect the antenna to the HPA is also undesirable for several reasons. 
     Firstly, rotary joints or waveguides must be used between the horn antenna and the waveguide to provide effective wave guidance when the source arm is rotated to adjust the elevation of the antenna, for example. Such rotary joints or waveguides are costly and, when integrated into the system, represent an additional weight load on the source arm. 
     Another object of the invention is to dispense with such rotary joints or waveguides in order to propose steerable antennas of low cost. 
     Secondly, if there is to be no risk of degrading the transmission of guided waves, the waveguide must not be too curved. Consequently, the waveguide that extends from the source arm towards the external HPA forms a bend at the base of the source arm, causing a problem during manipulation operations, for example when folding the antenna. The volume occupied by this bend and its movement also compromise the aim of producing a compact system conforming to transportation standards such as IATA standards. Furthermore, the stiffness of the guide generates resisting forces on a mechanism for driving the antenna (azimuth, polarization, or elevation adjustment, or folding). A more powerful and more robust motorized mechanism must then be used, to the detriment of the weight and the volume of the system. 
     Thus another object of the invention is to dispense with the waveguide at the connections between the source arm and the support in order to limit the inconvenience and resisting forces caused by the waveguide. This results in a simplified drive mechanism and a saving in volume and weight. 
     At least one of the above objects is achieved by the present invention by separating the high-voltage power supply and the TWT of the HPA, the TWT being placed on the source arm whereas the high-voltage power supply is preferably placed on the support of the source arm and the reflector. A configuration of this kind enables the use of flexible electrical cables between the high-voltage power supply and the TWT and the use of a flexible coaxial cable (rather than a rigid waveguide) to feed the low-power signal to the TWT, the coaxial connection being compatible with the transmission of a low-power signal. Consequently, the TWT of the HPA is kept as close as possible to the primary focus (source) of the antenna, generating minimum power loss and limiting the additional load imposed on the source arm. A TWT rated at 200 W weighs approximately 2 kilograms (kg). Consequently, the source arm and the mechanisms for adjusting the arm and the antenna can have reasonable dimensions compared to a source arm having to support the weight of the TWT and its high-voltage power supply (around 10 kg). 
     To this end, the invention provides firstly a satellite antenna for transmitting an electromagnetic signal, and comprising at least:
         a parabolic primary reflector;   a source arm; and   high-power amplifier means including at least one traveling wave tube with a transmission power of at least 100 watts on said source arm and a high-voltage power supply off said source arm and adapted to supply power to said traveling wave tube.       

     TWT amplifiers routinely offer a transmission power of several hundred watts. A transmission power of 200 W is compatible with a satellite link that is effective under difficult conditions, for example if the antenna is situated at the edge of the coverage of the satellite, if the target satellite is old and of low sensitivity or if meteorological conditions are unfavorable. 
     According to the invention, the TWT is carried by the source arm as close as possible to the source antenna (horn antenna, patch antenna, or any other device consisting of an assembly of radiating elements (RE), for example an array of REs), where applicable coupled to a secondary reflector. A TWT weight of approximately 1 kg to 2 kg does not require a significant increase in the dimensions of the source arm, since the length of such an arm is generally of the order of 50 centimeters (cm) for a 70 cm diameter reflector. 
     The high-voltage power supply, weighing of the order of 5 kg to 10 kg, is not carried either by the source arm or by any mobile component of the antenna (for example the primary reflector). The high-voltage power supply is preferably secured to a support adapted to receive the mobile source arm and the mobile primary reflector. A bundle of electrical cables runs along the source arm and the means connecting the source arm/primary reflector and the support and connects the high-voltage power supply to the TWT. The mobile means connecting the source arm and the primary reflector to the support are of the 2-axis or 3-axis positioner type (elevation, azimuth, and where applicable, polarization). 
     In one embodiment of the invention said parabolic primary reflector and the source arm are mounted to move relative to a support between a position of use and a storage position. The storage position may for example be such that the primary reflector and the source arm are folded into a storage structure that acts as the support on which the mobile reflector and the mobile source arm are mounted. 
     In one embodiment of the invention, the primary reflector is formed of a plurality of removable portions known as petals and said storage structure is adapted to house said portions when removed when the antenna is in the storage position. 
     To minimize the resulting overall size of the antenna in the folded storage position, the TWT is arranged on said source arm so that, in the storage position, it occupies at least part of the space defined by the parabolic curvature of the primary reflector. The space defined by the curvature of the reflector is to be understood as the space contained between the curved reflecting surface of the reflector (or central petal if the reflector consists of a plurality of removable petals, only the central petal generally remaining in place in the storage position) and the plane bearing on the edge of the reflector, given that the reflector may be of a non-circular outline. 
     In prior art systems the source antenna (horn antenna and/or secondary reflector) come up against the primary reflector in the folded storage position. This prevents use of the space between these two components, notably the hollow space formed by the curved primary reflector. The invention uses this space formed by the primary reflector to store the TWT. 
     In particular, said TWT is positioned on said source arm substantially on the side facing the primary reflector in the storage position. 
     In particular, said TWT is arranged on said source arm so as substantially to face the central part of said primary reflector in the storage position. 
     In one embodiment of the invention, said TWT is positioned on one side of said source arm and is inclined so as to follow the inclination of the facing primary reflector. The lateral position of the TWT leaves the center of the source arm free for the horn antenna and secondary reflector components. Inclining the TWT to follow the inclination of the primary reflector at the same location optimizes use of the storage space. 
     The source arm and the primary reflector may have multiple capacities for rotation, notably in elevation (both components rotating about the same horizontal axis), in azimuth (both components rotating about the same vertical axis), and/or in polarization (rotation of the radiating element [patch, horn, array] with its orthomode feed, if it has one). 
     In particular, said source arm is mounted to rotate via cam means secured to said primary reflector. The cam effect is produced firstly by the rotation axis of the primary reflector (and the cam means) and secondly by the parallel and separate rotation axes of the source arm and the cam means. The source arm is freely rotatable relative to the cam means. 
     In particular, said cam means are arranged so that said source arm moves in translation between said position of use and said storage position when said primary reflector is folded. If this movement in translation moves the source arm towards the folding mechanism (the reflector rotation axis), then the folded system is more compact. 
     Furthermore, the cam means are arranged so that the source arm rotates relative to said support when adjusting the elevation of said primary reflector. 
     To provide both the movement in translation in the folding phase and the rotation movement in use, the cam means comprise means for driving said source arm in rotation when said primary reflector is rotated relative to said support. In particular, said drive means include an abutment provided on the cam and a corresponding abutment provided on the source arm so that when the cam is driven in rotation at the same time as the primary reflector, the two abutments come into contact and drive the source arm. 
     To prevent loss of contact between the two abutments and/or tilting of the source arm in the presence of wind, retaining means are provided to maintain the contact between said abutments. In particular, said retaining means include a catch on the source arm and a corresponding opening on the cam means, the catch being engaged in the opening when the station is in use. Accordingly, these retaining means hold the source arm and said cam means in the same relative position when said antenna is in use. Maintaining the same relative position preserves the stiffness of the cam plus source arm assembly and thus ensures efficacious rotation of the source arm. 
     In an advanced embodiment of the invention, the antenna further includes a secondary reflector rotatably mounted on said source arm. In the prior art, the secondary reflector is substantially perpendicular to the source arm. When the antenna is folded by rotation of the primary reflector, the second reflector is immediately substantially perpendicular to the primary reflector, leading either to a collision between the two reflectors or to a limitation on the movement of the source arm towards the primary reflector. According to the present invention, said support includes guide means adapted to guide rotation of said secondary reflector during said movement in translation of the source arm. Because the movement in translation of the source arm is coupled to the secondary reflector guide means, said means are progressively inclined as the antenna is folded towards its storage position. In this position, the secondary reflector is no longer perpendicular to the primary reflector. The primary reflector may therefore be closer to the source arm. The antenna in the storage position thus gains in terms of compactness. 
     Where appropriate, said guide means formed on said support, for example a rail, have a curved profile, said second reflector being adapted to come into contact with said profile during unfolding/folding of the antenna. 
     In satellite mobile telecommunications stations it is necessary to retain the various components securely during transportation in order to prevent them being damaged by shock and vibration. To this end, the satellite antenna further includes means for fastening/immobilizing said source arm in the storage position. In particular, said fastener means include a first fastener member disposed on said source arm and a second fastener member secured to said support, said first and second fastener members being adapted to cooperate with each other during said movement in translation of the source arm. 
     In particular, said first fastener member is a finger secured to said source arm and said second fastener member is an opening in said support adapted to receive said finger during the movement in translation. During folding, a first phase of rotation of the cam brings the source arm and the finger onto the axis of the opening formed in the support. During the movement in translation of the source arm, the finger is engaged in the opening and prevents the source arm from moving. This increases the resistance of the antenna to shock and vibration by preventing the source arm from moving relative to the support. 
     The invention further provides a satellite mobile telecommunications station including an antenna as defined above and a cover removably engaged with said support, said support and said cover being adapted to form a structure for storing said antenna in the storage position. 
     The use of high-strength materials such as carbon fiber for the storage structure imparts a shock protection function to the structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood in the light of the following detailed description and the appended figures, in which: 
         FIG. 1  shows a satellite mobile telecommunications station of the present invention in its folded storage and transport position; 
         FIG. 2  is a view in elevation of the same satellite mobile telecommunications station when deployed, having the sighting directions azimuth=0° and elevation=20°; 
         FIG. 3  is a more detailed view of the folded satellite mobile telecommunications station from  FIG. 1 , the protective cover being shown as if transparent; 
         FIG. 4  represents a cross-section of the rear of the satellite mobile telecommunications station in the folded position, showing details of the integration of the TWT and the sighting adjustment mechanisms; 
         FIG. 5  is a view of the rear of the satellite mobile telecommunications station in the folded position, showing the inclination of the TWT of the present invention; 
         FIG. 6  is a view of a rear lateral corner showing the integration of the cam mechanism and the TWT from  FIG. 5 ; 
         FIG. 7  is a lateral view of the satellite mobile telecommunications station from  FIG. 2  in the operating position; 
         FIGS. 8 to 12  show the satellite mobile telecommunications station at various stages of folding it from its operating position to its storage position; 
         FIGS. 7   a  to  12   a  show the position and the rotation of the secondary reflector in the corresponding positions from  FIGS. 7 to 12 ; 
         FIGS. 8   b  and  9   b  are lateral views to a larger scale of the cam means in the corresponding positions from  FIGS. 8 and 9 ; 
         FIG. 13  is a view to a larger scale of the source arm fastening portion of the satellite mobile telecommunications station; and 
         FIG. 14  shows in the folded position and with its primary reflector petals a satellite mobile telecommunications station adapted to be placed directly on the roof-rack of a motor vehicle. 
     
    
    
     DETAILED DESCRIPTION 
     The same reference numbers are used to refer to the same items in the various figures and the following text. 
     The example described here relates to a satellite mobile telecommunications station conforming to the IATA international transport standard (weight less than 32 kg, combined width, length, and height less than 1580 mm). In this example the station  1  sends and receives on satellite links in the Ku frequency band (it is equally possible to use other frequency bands: X, Ka, C, etc.). 
     Referring to  FIG. 1 , the folded station  1  has a substantially rectangular base  2  having an interface  3  consisting of electrical and/or electronic connectors  4  for connecting the station to external equipment, for example an electrical power supply (mains) or a laptop computer. 
     The station  1  also has a lid  5  of complementary shape to the base  2 . The base  2  and the lid  5  are of carbon composite material and form the lower and upper shells of a structure for protecting internal electronic and mechanical components in a folded position of the station. A closure system (not shown) is provided for closing the protective structure. 
     A satellite mobile telecommunications (send and receive) station includes two separate systems that are distinguished as follows in the remainder of the description:
         the antenna system, which includes the antenna, power amplifier components (transmission), and low-noise amplifier components (reception);   the base-band system, which includes components for processing the signals transmitted and received. These components include modulation and demodulation components, encryption components (if necessary), multiplexing and demultiplexing components (if necessary), other routers (for data signals), and finally upconverters for uplink transmission (to the satellite) and downconverters for downlink transmission (from the satellite). This base-band system is not described in more detail below since the invention relates to the antenna system. It can be incorporated in the support of the antenna system or housed in a flight case separate from the antenna system.       

     In  FIG. 2 , the station  1  is in the unfolded operating position with the following parameters: azimuth=0° and elevation=20°. 
     The base  2  can include (concealed inside it and not shown) a miniature PC and components of the antenna system such as a high-voltage power supply unit for an HPA, a power supply unit for the electronics, a dedicated electronic circuit card, a KU to L band converter, an L band to KU band converter, a beacon receiver, a microwave switching card, a 2-axis inclinometer, and a compass. 
     A carbon fiber parabolic primary reflector  10  is articulated to the base  2  on two pivots  11 ′ to rotate about a horizontal axis  11 . The primary reflector  10  consists of a central petal  10 ′ secured to the pivots  11 ′ that articulate it about the horizontal axis  11  and three removable petals  10 ″ that are attached to it by attachment means that are not shown, for example by hooks. The focal length of the primary reflector  10  is approximately 500 mm. 
       FIG. 3  shows the satellite mobile telecommunications station in the folded configuration without the lid  5  and shows how the removable petals  10 ″ are stowed when they are not attached to the folded central petal  10 ′. 
     A source arm  12  is also articulated about the axis  11  by the same two pivots  11 ′ as the primary reflector  10 . The source arm  12  is formed of a continuous hollow carbon fiber structure  120  comprising two parallel rectilinear arms  120 ′ connected together by a bridge at one end to provide stiffness, and connected at their other end by cams  13  to rotate about the axis  11 . The cams  13  are described in more detail below. The source arm  12  has a length of approximately 700 mm and supports part of the antenna system. In particular, the source arm  12  supports at its end opposite the elevation rotation axis  11  an elliptical or quasi-elliptical secondary reflector  121  articulated about a horizontal axis  122  parallel to the axis  11 . The source arm  12  also supports a radiating element (here a horn  123  adapted to receive electromagnetic waves from or to emit electromagnetic waves towards the secondary reflector  121 ), the power amplifier/low-noise amplifier components  124  of the send/receive system and in particular the TWT  125  rated at 200 W and having dimensions of 290×70×45 mm excluding its cooling components (fan and heatsink). Other components of the send and receive systems are also supported by the source arm  12  but are not described in detail here: polarization axis drive system (motor, coder, limit switches), orthomode feed, RX filter, LNA, polarization rotary joint, harmonic filter, TX filter, coupler, isolator, connection guides, guide support structures, etc. 
     The TWT  125  is connected to a high-voltage power supply unit (not shown) inside the base  2  by a flexible electrical cable (not shown) running along the rectilinear arms  120 ′ of the source arm and past the articulations  11 ′. This power supply unit is screwed to cylindrical mounting blocks providing vibration and shock resistance in the bottom of the base  2 . 
     The power amplifier/low-noise amplifier components  124  are connected to the base-band components by a coaxial cable (not shown) near the pivots  11 ′ for rotation about the axis  11 . Using a coaxial cable, which is more flexible than a waveguide, reduces the resisting forces to which the pivots  11 ′ are subjected. 
     Thus the signal generated by the base-band system is applied to the satellite mobile telecommunications station, which changes its frequency band (from band L to band KU) and then sends it to the TWT  125  via the coaxial cable, is amplified by said TWT  125  (which is supplied with power by the high-voltage power supply unit in the base), is then sent in the form of electromagnetic waves via a waveguide  126  to the horn  123 , and is then reflected towards the target satellite by the secondary reflector  121  and the primary reflector  10  in succession. The reverse path for the received signal is identical except that the received signal is processed conventionally by the low-noise amplifier  124  (not by the HPA) and transposed into the L band by the KU band to L band converter inside the case before being sent to the base-band system outside the case via a coaxial cable. 
     The turntable  141  constitutes a positioner with azimuth axis AZ and elevation axis EL:
         the turntable  141  turns horizontally about the axis AZ (see  FIG. 4 );   the EL axis (coinciding with the rotation axis  11 , see  FIG. 3 ) and movement about this axis is driven by the gear motor  14  is on the turntable  141 .       

     Movement about the axis  11  is driven by the gear motor  14 . There is no structural correlation between the source arm and the primary reflector. The AZ/EL positioner  141  serves as the interface between these two components. The cams  13  and the primary reflector  10  are secured to the axis  11  so that the angle α (see  FIG. 7 ) formed by the cams  13  and the primary reflector  10  does not vary. The positioner  14  modifies the elevation of the antenna  10  (and the source arm  12 ) by rotation about the axis  11  by means of a system of gears  143  and a lead screw  143 ′ (see  FIG. 8   ter ). 
     The primary reflector  10 , the source arm  12 , and the EL axis drive system  14  are mounted on the horizontal turntable  141  that is turned about a vertical axis by the AZ axis drive system (not shown) to adjust the azimuth of the antenna  10 . The turntable  141  is mounted on the base  2  via a ball bearing  142  ( FIG. 4 ). The AZ axis drive system drives the turntable  141  in rotation via a system of toothed wheels (not shown). 
     An automatic pointing system can be provided for controlling the AZ, EL and POL axes so that the satellite mobile telecommunications station automatically points towards a preselected satellite. 
     The POL axis of an ad hoc positioner (not shown) mounted on the source arm enables the polarization of the antenna to be adjusted by turning the horn  123  about its revolution axis. 
     Because the high-voltage power supply unit for the TWT  125  is in the base  2 , the forces to which the positioner  141  is subjected are lower than if this unit were on the source arm  12  and the positioner  141  and its AZ and EL axis drive systems can therefore be made smaller. 
     Referring to  FIGS. 4 to 6 , the TWT  125  is of substantially rectangular shape. It is positioned laterally on the source arm  12  on one of the two rectilinear arms  120 ′ and extending towards the exterior of the source arm and is slightly inclined to the plane formed by the two arms  120 ′ extending from the axis  11 . This inclination allows the TWT  125  to fit optimally against the curvature of the primary reflector  10  in the folded position. This inclination β is of the order of 0 to 15°, preferably 5° to 10°. As shown in  FIGS. 4 to 6 , the position of the TWT  125  and its inclination enable it to occupy part of the space defined by the curvature of the primary reflector  10 , making the station  1  more compact in the storage position. 
     The inclination of the TWT  125  is obtained by giving the arm  120 ′ supporting the TWT  125  a right-angle trapezium profile (see  FIG. 4 ), the inclined side of which (inclined at an angle β) corresponds to the upper surface of the arm  12  to which the TWT  125  is fixed. The TWT  125  is glued or screwed to the arm  120 ′. 
     The cams  13  and the resulting movement are described in more detail below with reference to  FIGS. 7 to 12 . 
     A cam  13  is fixed to each end of the arms  120 ′ of the source arm  12  at the level of the pivots  11 ′. The cam  13  has:
         two separate rotation axes: the first axis  11  coinciding with the rotation axis of the primary reflector  10  to enable packaging of the structure in the storage position and adjustment of elevation in use, and the second axis  130  for rotation of the source arm  12  relative to the cam  13 ;   an abutment area  131  which, in the position of use, is in permanent contact with a corresponding abutment  132  on the arm  120 ′ to enable the drive system for the elevation axis  11  to drive the source arm  12  in rotation. In use, the source arm  12  is held cantilever fashion by the cams  13 . In the examples shown in the figures, the abutments are provided on the side opposite the axis  11  relative to the axis  130 ; the abutment  132  on the arm  12  is above the abutment  131  on the cam  13  to counterbalance the weight of the source arm  12 . Abutments can be provided between the two axes, the abutment  132  on the arm  120 ′ then being below the abutment  131  on the cam  13 ;   retaining means  133  of the type with an oblong housing that accommodates a catch mechanism  134  provided at the end of the source arm  12 . When the source arm  12  and the cam  13  are aligned (in the position of use), the catch mechanism  134 , secured to the source arm  12 , is engaged and gripped in the oblong housing  133  of the cam  13 . Because of the oblong shape of the housing  133 , the catch  134  does not prevent slight rotation of the source arm  12  relative to the cam  13 . The force generated by a spring in the catch mechanism  134  defines the force with which the source arm  12  is retained by the cam  13 . The catch mechanism  134  therefore has a retaining force greater than the weight of the source arm  12  when equipped and less than the force applied by an actuating mechanism for folding the antenna system. Accordingly, the cam can be folded again relative to the arm (by applying a force greater than the predefined value of the spring force) to reach the folded position of the system.       

     Typically, for high antenna elevations (large rotation about the axis  11 , of the order of 85 to 90°, the source arm  12  can be quasi-vertical and the primary reflector  10  can be quasi-horizontal. The catch mechanism  124  therefore enables prevention of tilting of the source arm  12  towards the rear (towards the primary reflector) by wind or shock. 
     The role of the cam  13  is to allow packaging of the equipped source arm  12  in the stored position. 
       FIGS. 7 to 11  show the folding of the satellite mobile telecommunications station from the position of use ( FIG. 7 ) to the packaging/storage position ( FIG. 12 ). 
     Just before the cam  13  begins to function, the source arm  12  is at an acute angle to the horizontal ( FIGS. 7-8 ) and rests on an abutment  15  secured to the base  2 . This abutment  15  stops rotation of the source arm  12 , whereas rotation about the axis  11  continues. When further rotation about the axis  11  starts folding of the satellite mobile telecommunications station, the abutment  15  prevents rotation of the arm  12 , the force applied by the EL axis gear motor  14  about the axis  11  extracts the catch  134  from the corresponding oblong housing  133  and contact between the abutments  131  and  132  is immediately lost (see  FIGS. 9 and 9   ter ). As soon as the cam  13  begins to function, it imparts to the source arm  12  a two-fold movement in vertical translation relative to the tilting/rotation point of the abutment  150 , i.e. in the position of use:
         upward movement on the side of the secondary mirror  121  (arrow F 1 ,  FIG. 9   bis ) for the portion of the source to the left of the abutment, because of the tilting/rotation about the abutment  150  (there being minimal front to rear movement); and   downward movement on the side of the came  13  (arrow F 2 ,  FIG. 9   ter );   thus imposing on the source arm a horizontal orientation (synonymous with a small overall size in the heightwise direction) by slight tilting of the arm  12  about the bearing point (or abutment)  15 .       

     The cam  13  continues its rotation (arrow F 3 ,  FIG. 9   ter ) about the axis  11  and (the downward movement becoming minimal) imparts to the source arm  12  a front-to-rear movement (arrow F 4 ,  FIG. 10 ) by virtue of the arm  12  sliding on the abutment  15 . This movement enables the arm  12  to end up under the mechanism of the positioner  14  to reduce the space required for storing the front end of the source arm  12 . This makes the station more compact in the storage position. 
     The primarily horizontal movement in translation continues ( FIG. 11 ), the cam  13  ending up in a vertical position ( FIG. 12 ) corresponding to a horizontal folded arm  12  and a primary reflector  10  folded on top of the arm  12 . 
     Fastener means are also provided for fastening the source arm  12  to the base  2  in the storage position to increase the resistance of the station to shock or vibration to which it may be subjected during transportation and handling. To this end, as shown in  FIG. 7 , a finger  16  is provided on the source arm  12 , the end of the finger extending in the lengthwise direction of the arm  12  towards the cam  13 . A housing  17  complementary to the finger  16  is provided on the base  2 . As shown in  FIG. 7 , this housing  17  is formed in the bearing abutment  15  provided on the base  2 . 
     As shown in  FIGS. 10   bis  and  11   bis , during the primarily horizontal movement in translation imparted to the source arm  12  by the cam  13 , the finger  16  approaches the housing  17  and then engages in the housing  17  to cooperate in fastening the arm  12  in the storage position ( FIG. 13 ). 
     The fastener system ( 16 ,  17 ) is provided for both arms  120 ′ of the source arm  12  to enable retention and immobilization of the source arm  12 , which is a fundamental function when the satellite mobile telecommunications station is being transported or when it is mounted on a vehicle (drive-away). 
     As indicated above, the secondary reflector  121  is articulated about the horizontal axis  122  ( FIG. 7 ) which, in combination with the primarily horizontal movement in translation imparted to the source arm  12  by the cam  13 , enables efficient storage of the reflector  121  in a housing  20  provided in the base  2  (see  FIG. 7   bis ). The reflector  121  can thus be retracted into part of the space defined by the curvature of the primary reflector  10 , making the satellite mobile telecommunications station more compact. 
     The housing  20  has a curved profile  21  between an upper point  210  substantially at the top of the base  2  and a lower point  211  substantially at the bottom of the base  2 . 
     The mechanism for folding the secondary reflector  121  is described below with reference to  FIGS. 7   bis  to  12   bis , which are views in section to a larger scale of the area of the secondary reflector during the same folding steps as  FIGS. 7 to 12 . 
     When use of the station  1  ends, it is returned to the azimuth=0° and elevation=20° position shown in  FIG. 7 . In this position, the secondary reflector  121  is not in contact with the profile  21  (see  FIG. 7   bis ). 
     The start of the folding phase, effected by rotation about the axis  11 , brings the lower area of the secondary reflector  121  into contact with the upper point  210  of the profile  21  in the housing  20  (see  FIG. 8   bis ). 
     During successive movements in translation in the downward direction ( FIG. 9 ) and the rearward direction ( FIGS. 10-11 ), the secondary reflector  121  slides along the guiding profile  21 , turning about the axis  122 . The effect of the horizontal movement in translation (see  FIG. 10 ) is to bring the axis  122  towards the rear of the station  1  (on the same side as the axis  11 ), driving greater rotation of the secondary reflector  121  (see  FIGS. 10   bis  and  11   bis ). 
     In the completely folded storage position ( FIG. 12 ), the secondary reflector  121  is inclined at approximately 35°, the bottom of this reflector  121  being substantially level with the lower point  211  of the profile  21  (see  FIG. 12   bis ). 
     This inclination can be modified by appropriately modifying the profile  21 . An inclination is required that limits the horizontal extent of the secondary reflector  121  in the folded position and that tends to render the secondary reflector  121  parallel with the portion of the primary reflector  10  facing it in the storage position. 
     Although the above description is given with reference to folding the station  1 , its unfolding can be deduced by taking the steps of  FIGS. 7 to 12  in reverse order, from the last  FIG. 12  to the first  FIG. 7 . 
     Thus the primarily horizontal movement in translation disengages the finger  16  from the housing  17 . 
     When the cam  13  and the reflector  10  rotate about the axis  11 , the catch  134  is engaged in the oblong housing  133  whereas the abutments  131  and  132  are not yet in contact. By means of the oblong shape of the housing  133 , the rotation of the cam  13  continues to bring the two abutments into contact, by virtue of the rotation about the axis  11  and the positioner  14 , the source arm  12  still resting on the bearing point  15 . Once contact between the abutments has been established, the axis  11  drives the source arm  12  in rotation. 
     During the primarily horizontal movement in translation of the source arm  12 , the secondary reflector  121  is rotated in the opposite direction by a return force produced by a spring provided at the level of the rotation axis  122 , for example. An abutment (not shown) can equally be provided at the level of the secondary reflector  121  and the source arm  12  to define the position of use of the secondary reflector  121 . The spring applies a contact force between the secondary reflector and the abutment to limit movement of the secondary reflector  121  in the presence of shock or vibration. 
     The above station  1  can be mounted on a vehicle (see  FIG. 14 ), with the base  2  fixed to a roof rack on the vehicle with no top lid  5 . The aerodynamic shape of the primary reflector  10  fitted with its petals  10 ′ and  10 ″ in the folded storage position of the station  1  enables such use without serious risk of the station being damaged. The station is then unfolded into the position of use when the vehicle is stationary at the site of use.