EP2446504A1

EP2446504A1 - Antenna system having a balanced positioner

Info

Publication number: EP2446504A1
Application number: EP10725757A
Authority: EP
Inventors: Thierry Lucidarme; Marc Touret
Original assignee: Thales SA
Current assignee: Thales SA
Priority date: 2009-06-26
Filing date: 2010-06-21
Publication date: 2012-05-02
Also published as: FR2947387B1; FR2947387A1; WO2010149619A1; US8963788B2; US20120268333A1; IL217180A0; IL217180A

Abstract

The invention relates to an antenna system including at least one antenna and an X-Y positioner, said positioner consisting of at least three mechanical elements, the first element being a plinth (105), the second element being a so-called bottom box (104), the third element being a so-called top box (103), the antenna (100, 101, 102) of the system being attached to the top box (103). The components of the down lead are distributed among the various elements that comprise the X-Y positioner; an OMT junction (111) included in the top box (103) is suitable for separating the components of the down lead into two separate paths, i.e. a first path (125) referred to as the rising path and including components for amplifying and processing the signals to be transmitted by the antenna, and a second path (126) referred to as the descending path and including components for processing and amplifying the signals received by the antenna, the components (118, 115, 113, 121, 120, 114) associated with said paths are placed on either side of the various elements of the X-Y positioner.

Description

ANTENNA SYSTEM WITH BALANCED POSITIONER

The invention relates to an antenna system with balanced positioner and applies in particular to the fields of electronics and telecommunications, for example by satellites.

It can also be used in related fields such as radars or radio-relay systems.

In space communications in the band C, X, Ku, Ka, etc., with one or more satellites, some transmitting / receiving stations are equipped with antenna systems comprising a positioner, said positioner allowing the antenna to automatically point to a traffic satellite, regardless of the position of it in the sky. In other words, the positioner makes it possible to adapt the direction of transmission and / or reception of the antenna of the system. This adaptation is useful when, for example, a ground antenna has to follow the position of satellites in non-geostationary orbit. This feature is also useful when the antenna is embedded on a mobile vehicle to maintain a communication link with a given satellite. The equipment on which the antenna is fixed, that is to say the positioner, must allow dynamic positioning thereof.

Several types of positioner exist in the prior art. For example, an elevation positioner on azimuth may be used. This allows a movement of the antenna along two axes, the first being the azimuth axis and the second the axis of elevation. Its use is inappropriate in the context of satellite telecommunications applications, especially when said satellites are at high elevation. Indeed, a singular point at the zenith is inherent to elevation positioners on azimuth. When the antenna is being raised, that is to say when it moves along the elevation axis, and that it reaches the zenith of its trajectory, the positioner must rotate fast 180 ° along the azimuth axis for the antenna to continue its movement. This rotation results in rapid wear of the positioner. Moreover, if said rotation is not fast enough, the current communication can be interrupted. A second family of positioners also exists. These are the three-axis positioners. The latter do not have a singular point, but are bulky and relatively expensive. In addition, their significant weight makes it difficult to consider a use embedded on small aircraft, especially on unmanned aircraft, also called "drones".

It is also possible to use a scanning antenna so as to overcome the use of a positioner, but this solution nevertheless faces difficulties related to its cost and lack of precision.

A suitable compromise for satellite communications is obtained by the use of X-Y positioners. These allow in particular to avoid the appearance of the singular point vertically and minimize the weight and size of said positioner. The singular point is not vertical, as is the case for positioners elevation on azimuth, but horizontally, which is less problematic in the context of satellite applications, especially when they are positioned at high altitude (high elevation satellites). This type of positioner is compared to elevation-azimuth positioners in the article by AJ Rolinski, DJ Carlson and RJ Croats titled Satellite-tracking characteristics of the XY mount for data acquisition antennas, NASA technical note D-1697, Washington, DC C, June 1964.

In the following description, the movement of the antenna induced by the positioner of the system according to the invention can be described in a three-dimensional reference orthonormal reference. The x and y axes are included in the plane on which the base of the positioner is fixed. By definition, the third axis z is perpendicular to this plane. When an XY positioner is used, the movement of the antenna is the consequence of two rotational movements along two axes / rotation shafts X and Y, denoted in capital letters, with the differences of the x, y, z axes of the orthonormal coordinate system. reference. The axes of rotation X and Y are represented and their links with the various mechanical elements composing the positioner X-Y are highlighted in the following description.

Due to the mechanical structure of the XY positioners, the balancing of the different elements composing them is then a crucial point that must be kept account during the design and also to avoid having moments of inertia too large and significant wear and fast, especially when the antenna is embedded on an aircraft. Thus, it is important to balance the different elements of the antenna descent included in the positioner.

An object of the invention is in particular to overcome the aforementioned drawbacks.

For this purpose the subject of the invention is an antenna system comprising at least one antenna and an XY positioner, said positioner being composed of at least three mechanical elements, the first element being a base, the second element being a so-called lower, the third element being a so-called upper box, the antenna of the system being fixed to the upper box. The components of the antenna descent are distributed in the various elements composing the XY positioner, an OMT-type junction included in the upper box making it possible to separate the components of the descent by following two distinct paths, a first path called a rising path comprising components for amplifying and processing the signals to be transmitted by the antenna, a second path called a descending path comprising components for processing and amplifying the signals received by the antenna, the components associated with these paths being placed on either side different elements of the XY positioner.

According to one embodiment, the OMT junction is of the turnstile type, said junction being composed of a central part, of four coplanar arms arranged in a cross around the central part, two of the coplanar arms being used for the implementation. short circuits, the other two coplanar arms being respectively connected to the ascending path and the descending path of the antenna descent, and a circular arm corresponding to the horn of the antenna of the system. For example, the two short circuit arms are removable and interchangeable.

The short circuit arms may be of the same length, at least one electrically controlled PIN diode being placed in both arms at a selected distance from the base of the arm so as to adjust the length of the short circuit depending on whether the diode is open or closed. . According to one mode of implementation, the lower box is connected to the base by a first rotation shaft along an axis X, the upper box being connected to the lower box by a second rotation shaft along a Y axis, the X and Y being chosen as they are without intersection. According to another mode of implementation, the lower box is connected to the base by a first rotation shaft along an axis X, the upper box being connected to the lower box by a second rotation shaft along a Y axis, the X axes. and Y being chosen as belonging to the same plane.

For the paths of the antenna descent, the conductivity between the components of the same path is ensured from one element to the other of the positioner, for example, by the use of rotating joints microwaves simple.

The base comprises, for example, a cold box containing at least one power amplifier associated with the rising path, said box being cooled by the use of a cold plate fixed to the base.

According to another aspect of the invention, at least one hydraulic jack is fixed to the cold plate and the support on which the antenna system rests, said jack being electrically or mechanically controlled so as to introduce a static angle of inclination between the antenna system and the support.

According to another aspect of the invention, at least one linear electric motor is fixed to the cold plate and to the support on which the antenna system rests, said motor being electrically controlled so as to introduce a static inclination angle between the antenna system and support.

Other features and advantages of the invention will become apparent with the aid of the following description given by way of non-limiting illustration, with reference to the appended drawings in which:

FIG. 1a represents in the plane yz an example of an antenna system according to the invention with two offset axes of rotation; Figure 1b corresponds to the same antenna system as that of Figure 1a, but shown in the plane xz; FIG. 2a gives an example of an antenna associated with a positioning system according to the invention whose axes of rotation are concurrent, represented in the plane yz; Figure 2b shows the same example as Figure 2a but shown in the plane xz; Figure 2c shows a top view (in the xy plane) of the antenna system of the example of Figures 2a and 2b; FIG. 3 gives an example of a turnstile junction that can be used by the antenna system according to the invention; FIG. 4 gives an example of a turnstile junction including a mechanism for reconfiguring short circuits.

FIG. 1a represents in the plane yz an example of an antenna system according to the invention with two offset axes of rotation. The antenna is for example Cassegrain type. In this case, it is composed of a primary reflector 100, for example of parabolic shape, a secondary reflector 101 and a horn 102 used as a source and for illuminating the primary reflector. The horn can be corrugated so that the side lobe power of the transmitted and received signals is minimized. This type of antenna has very good performance for circular polarization signals.

The positioner associated with this antenna is composed of three main elements. The first element is called upper box 103 and on which the antenna is fixed. The second element is called the lower box 104, said element being connected to the upper box 103 by a mechanical rotation shaft. This shaft is associated with one or more motors 106, 107 located at its ends and allows a rotational movement of the upper box 103 relative to a Y axis of rotation aligned with the mechanical shaft. The third element is the base of the positioner 105 and is connected to the lower box 104 by a second mechanical rotation shaft, the lower box being set in motion, for example, by two motors 109, 1 10 located on either side said tree. This second shaft allows a rotational movement of the lower box 104 relative to an axis X of rotation aligned with the second mechanical shaft. The antenna descent, included in the various elements of the positioner, comprises several electronic and mechanical components for processing the analog signals transmitted and received by the antenna. When designing the XY positioner, it is important to balance the set of system components. If the elements of the antenna descent are judiciously distributed in the positioner, the overall balancing of the system is improved. The antenna system according to the invention allows an almost symmetrical distribution of the components of the antenna descendant within the upper box 103, the lower box 104 and the base 105 of the positioner. This symmetry is made possible by the use of a microwave circulator type OMT 1 1 1, acronym from the English expression "Orthomode Transducer" whose French translation is transducer orthomode. This OMT 1 1 1 is placed in the upper box 103 and is connected to the horn 102 of the antenna. It aims to separate the processing and routing within the positioner signals transmitted and signals received by the antenna. Electromagnetic signals are usually polarized differently depending on whether they are transmitted or received by the antenna system. For example, the transmitted signals may be in right circular polarization and the received signals in left circular polarization. The OMT is a polarization duplexer and thus allows to separate reception remission so that their treatments are performed independently at the level of the antenna descent.

In this case, these transmitted and received signals use, for example, the same horn 102 at the antenna. At the positioner, the signals are processed and transmitted differently after separation by the OMT 11 1. Thus the received signals will be routed from the antenna to the outside of the positioner using a path, called descending path 126 in the following. the description, said path being implemented between an output of the OMT and an output of the positioner, the output for example at the base 105.

The second path 125, called rising path in the following description, is used for the processing and transmission to the antenna of the signals to be transmitted. This dissociation between the upstream path 125 and the downward path 126 makes it possible to distribute the components associated with them on each side of the positioner and thus to improve its balancing. The uplink used for the transmission includes a cold box 1 12. This cold box contains, for example, a power amplifier followed by a BUC converter, acronym from the English expression "Block Up Converter". If the amplifier is of high power and a sufficiently efficient ventilation system can not be implemented, the use of a liquid-cooled plate 122, called a cold plate, can be envisaged fixed to the base 105 of the positioner . This solution is adapted in particular when the antenna is embarked on an unmanned aircraft. Indeed amplifiers with a power of the order of 300 W can be used. In addition, at high altitude, air is scarce, which makes ventilation of electronic equipment particularly difficult.

In addition, the cold plate 122 attached to the base 105 of the positioner may be in motion relative to the surface 134 on which the antenna system is fixed. Cylinders 130, 131, 132, 133 fixed to the ends of said plate allow, for example, to adjust the overall orientation of the system. Such a mechanism gives the possibility of using the antenna system according to the invention to follow a low elevation satellite by configuring a static angle of inclination of the system relative to its support (134).

The cylinders are, for example, hydraulic cylinders, and these can be controlled electronically by an antenna calculator, or mechanically.

An alternative solution to hydraulic cylinders is to use electric motors of the linear motor type. Thus variable reluctance motors can be used. It is also possible to use conventional rotary reducing motors and converting circular movement into translational movement, that is to say of the "worm" type, this embodiment having the advantage of being cheap. The antenna system according to the invention can use at least one jack or a pedestal motor and advantageously four. When four cylinders or motors are implemented, they can be positioned for example at the ends of the cold plate 122, two being positioned along the X axis 132, 133 and the other two along the Y axis 130, 131. The BUC converter included in the cold box January 12 aims to convert a signal occupying a given frequency band into a signal occupying a higher frequency band. In applications for which the signals to be transmitted are satellite signals, the conversion is usually from the intermediate band L to one of the Ku, C or Ka bands. In the remainder of the description, an antenna system using an L-band intermediate band and a Ka-band transmitting / receiving band is taken as an example. The BUC converters can be made using a phase-locked loop using an external reference frequency, of the order of 10 MHz for example. The signal is then routed through the lower box 104 using a waveguide 1 13 to reach the upper box 103 and a transmission filter 1 15 used in particular to effectively decouple the transmission channel of the reception channel and the image frequencies. The waveguides used in particular in the positioner may be rigid or flexible, and are for example of the coaxial cable type.

A waveguide section 1 16 then allows the signal to reach the OMT junction 1 1 1 and be emitted by the horn of the antenna, the OMT junction being common to both upstream and downstream paths. This junction may be chosen, for example, of the "turnstile" type, as illustrated later in the description with the aid of FIG. 3. Simple rotating joints 14, 124 operating optimized for Ka-band operation are used to maintain connectivity between the waveguide sections during rotational movements of the different elements of the positioner relative to each other.

The downward path 126 used for the processing and routing out of the antenna system of the signals received by the antenna is composed, for the part contained in the upper box 103, of a section of microwave line 1 17 connected to an output of the OMT junction, an LNB low noise amplification block, acronym from the English expression Low Noise Block, followed by a frequency converter 1 18 allowing, for example, passing from the band Ka to L band. After amplification and conversion 1 18, the signal is transmitted to the lower box 104 with the aid of another waveguide section 1 19. A seal single turn 120 makes it possible to make the junction between said waveguide section 1 19 included in the upper box 103 and another waveguide section 121 included in the lower box 104, while supporting the rotational movement of the upper box 103 relative to the lower box 104, that is to say by maintaining the conductivity between the two sections of waveguide. The section 121 of the lower box has the function of transmitting the signal to the base 105 of the positioning system. The junction between the lower box and the base is also achieved by means of a simple rotary joint 123. The two joints of the descending path therefore operate in an intermediate frequency band, ie in an L-band in the context of this example.

Regarding the descent of the descending path antenna, it is therefore possible to place the low noise amplifier 1 18 as close as possible to the antenna in the upper box and advantageously use coaxial cables to lower the signal to the lower box. .

In an alternative implementation mode, the low noise amplifier can be located in the lower box and the descent of the reception signals can be done, for example, rigid waveguide low loss in the reception band. The positioner comprises in this case four single seals operating in the reception band.

The use of an OMT junction to separate the two paths has the particular advantage of avoiding the use of double rotating microwave seals whose cost is high. In addition, power losses due to leakage currents are greater than when single seals are used.

Figure 1b corresponds to the same antenna system as that of Figure 1a, but shown in the plane xz.

The representation in the xz plane corresponds to a 90 ° rotation of the representation of FIG. 1a. The upper box 103 therefore appears on the side and the OMT junction, the transmit and receive filters are not shown for the sake of clarity because they are located behind one of the motors 106 of the Y axis of rotation.

The base 105 is represented in its length. The mechanical rotation shaft X 108 and passing through said base 105 is shown with and other said axis, a motor 109, 1 10 for rotating the lower box. The upstream 125 and down 126 paths appear dissociated at the two feet of the base 105. Two single seals 123, 124 operating in L-band for the upstream path and in Ka-band for the downstream path are used to enable the transmission of signals transiting on the paths 125 rising and descending 126 at the junction of the waveguides of the base 105 and the lower box 104. The rotating joints forming the junction of the waveguide sections of the lower box 104 and the upper box 103 do not are not shown in Figure 1b but appear in Figure 1a.

FIG. 2a gives an example of an antenna associated with a positioning system according to the invention whose axes of rotation are concurrent, represented in the plane yz. Figure 2b shows the same example as Figure 2a but shown in the xz plane.

The orientation of the antenna 200, composed of two reflectors and a horn 210 is controlled by the positioner. The antenna descent, contained in said positioner, follows the same principle as in the example of FIGS. 1a and 1b, that is to say that the upstream and downstream paths 209 are separated using a micro circulator. UNT type 219.

The two rotation shafts along the X and Y axes are perpendicular and on the same plane. A side box 202 and an inner box 201 represent respectively correspond to the upper box 103 and the lower box 104 of the positioner with offset axes of rotation described above. The base 203 contains the cold box 212 containing the power amplifier and the BUC converter.

For example, two motors 204, 205 transmit a rotational movement to the inner box according to the shaft 21 1 of the Y axis. For rotation along the X axis, two other motors 206, 207 may be used. The X and Y axes belong to the same plane. Therefore, the four motors are also positioned on the same plane, which contributes to the balancing of the antenna and the positioner. A block 218 containing the low noise amplifier and the reception filter is located in the inner box 201 on the downward path 209. The emission filter 217 is located in the internal box 201 on the upstream path 208. The OMT junction 219 between the two paths is also implemented in the internal box 201.

The positioner includes four single seals. A first simple rotating joint 214 in L-band makes it possible to join the waveguide portions of the inner box 201 and the outer box 202 for the downward path.

A second simple rotating joint 213 in the L-band makes it possible to join the waveguide portions of the outer box 202 and the base 203 for the downward path.

A third simple rotary joint 216 in the Ka-band makes it possible to join the waveguide portions of the inner box 201 and the outer box 202 for the upstream path.

A fourth simple rotating joint 151 in the Ka-band makes it possible to join the waveguide portions of the outer box 202 and the base 203 for the upstream path.

Figure 2c shows a top view in the xy plane of the antenna system whose axes of rotation are concurrent. The reflectors of the antenna are not represented to keep a clear representation. The horn 210 is apparent in the center of the figure. At the junction of the inner box 202 and the outer box 203 appear the single strip seals L 213, 214 associated with the downward path and the single seals in the band Ka 215, 216 associated with the rising path.

FIG. 3 gives an example of a turnstile junction, an English expression meaning in French turnstile junction, which can be used by the antenna system according to the invention. The article by MA Meyer and HB Goldberg titled Applications of the Turnstile Junction, IRE Transactions on Micro wave theory and techniques, December 1955, describes the properties and applications that can be envisaged for such a device. In the antennas used for satellite communications, it is usual for a "septum" type polarizer to be used, this being placed for example in the horn of the antenna. It allows to receive a signal with circular polarization and to obtain at the output a rectilinear polarization. Conversely, the rectilinear-circular conversion is obtained in the other direction, for the emission.

A turnstile junction is equivalent to a polarizer and a duplexer. Therefore, when this is used, the use of a septum polarizer is not required. This generally avoids the losses associated with the use of a rectangular / circular guide transition and, moreover, allows flexibility in the polarization switching.

Moreover, the use of the turnstile junction is adapted for the symmetrical distribution of the channels of the antenna system according to the invention, whereas it is difficult to find rectilinear compact OMTs which exhibit this type of symmetry.

A turnstile junction is composed of a central portion 305, four coplanar arms 301, 302, 303, 304 arranged in a cross around the central portion and a circular arm 300. The circular arm corresponds to the horn of the antenna system and is used both as an input and as an output for signals received and transmitted by the system, said signals being circularly polarized.

Two of the aligned coplanar arms 301, 302 are respectively used as input and output signals polarized linearly pointed by the junction and correspond to the input points of the upstream path and the descending path described above.

The other two coplanar arms 303, 304, also aligned, are used as short circuits. If a linearly polarized signal is introduced into the input arm 301, a power signal substantially equal to half of the incident power is transmitted in the horn 300, the remaining half will separate equally in both arms in short circuits 303, 304. The signal resulting from reflection within these arms 303, 304 and the central portion of the junction 305 will also be transmitted at the outlet of the junction by the horn. The resulting signal output of the horn is then circularly polarized.

Following the same principle, a circularly polarized signal received at the horn can be converted to a rectilinearly polarized signal at the output 302 of the junction. The use of a turnstile junction thus makes it possible, as a duplexer, to separate within the positioner the upstream path and the downstream path respectively corresponding to the transmitted signals and to the signals received by the same antenna, as previously described in the description.

For this separation to be effective, the choice of short circuit length must follow certain rules. Indeed, the lengths L1 and L2 of the two short circuit arms 303, 304 must respect the following relations:

L1 = ^ (l + 4n) (1) δ

L2 = ^ (3 + 4n) (2) δ

in which: λ is the wavelength of the signal propagating in the waveguide; n is any positive integer.

It appears therefore that the length L2 is greater than λ / 4 with respect to the length L1.

The two short circuit arms 303, 304 may be removable. It is then possible to interchange them. In this case, the input 306 and the output 307 of the turnstile junction corresponding respectively to the upstream path and the downstream path are inverted. Thus, the antenna system can be manually reconfigured and support different polarization patterns of the incoming and outgoing signals at the horn 300 of the antenna.

Figure 4 gives a symbolic example of a turnstile junction including a mechanism for reconfiguring short circuits. The first arm 401 and the second arm 402 used for the implementation of the short circuit are of the same length L. Each arm comprises at least one circuit comprising at least one PIN diode 403, 404 behaving as a switch and located at a length L 'of the origin of the arm.

An example of using PIN diodes in the waveguide antenna frame is presented in the article by G. Craven and R. R. Thomas entitled Waveguide Antenna Switches Using p-i-n Diodes, Electronics Letter, August 18, 1977, Vol. 13, No. 17.

These diodes make it possible to adjust the lengths of the short circuits L1 and

L2 of each arm and are electrically controlled, these two lengths must meet the constraints expressed by equations (1) and (2) previously explained. For example, two short circuit configurations can be implemented:

Configuration 1: L1 = L; L2 = L ';

Configuration 2: L1 = L '; L2 = L.

For the configuration 1, for example, if for the first arm 401, L1 = L = 7λ / 8 and for the second arm 402, L2 = L '= 5λ / 8. In this case, the diode 403 of the first arm 401 must be open and the diode 404 of the second arm 402 must be closed. The choice of L and L 'must in particular ensure that the two short circuits have a difference in length equal to λ / 4.

Claims

CLAIMS - An antenna system comprising at least one antenna and an XY positioner, said positioner being composed of at least three mechanical elements, the first element being a base (105), the second element being a so-called lower box (104), the third element being a so-called upper box (103), the antenna (100, 101, 102) of the system being fixed to the upper box (103), the system being characterized in that the components of the antenna descent are distributed in the different elements composing the positioner

XY, an OMT type junction (11 1) included in the upper box (103) for separating the components of the descent by following two distinct paths, a first path (125) called a rising path comprising components for amplifying and processing the signals to be transmitted by the antenna, a second path (126) called a descending path comprising components for processing and amplifying the signals received by the antenna, the components (1 18, 1 15, 113, 121, 120, 1 14) associated with these paths being placed on either side of the different elements of the XY positioner. - System according to claim 1 characterized in that the OMT junction is turnstile type, said junction being composed of a central portion (305), four coplanar arms (301, 302, 303, 304) arranged in a cross around the central part, two of the coplanar arms (303, 304) being used for the implementation of short circuits, the two other coplanar arms (306, 307) being respectively connected to the upstream path and the descending path of the antenna descent, and a circular arm (300) corresponding to the horn of the system antenna. - System according to claim 2 characterized in that the two short circuit arm (303, 304) are removable and interchangeable. System according to any one of claims 2 or 3 characterized in that the short circuit arms (401, 402) are likewise length (L), at least one electrically controlled PIN diode (403, 404) being placed in these two arms at a selected distance (L ') from the base of the arm so as to adjust the length of the short circuit according to whether the diode is open or closed.

5. System according to any one of the preceding claims, characterized in that the lower box (104) is connected to the base by a first rotation shaft (108) along an axis X, the upper box being connected to the lower box by a second rotation shaft (127) along a Y axis, the X and Y axes being chosen such that they are without intersection.

6. System according to any one of claims 1 to 4 characterized in that the lower box (104) is connected to the base by a first rotating shaft (108) along an axis X, the upper box being connected to the lower box by a second rotation shaft (127) along an axis Y, the X and Y axes being chosen as belonging to the same plane.

7- System according to any one of the preceding claims characterized in that for the paths (125, 126) of the antenna descent, the conductivity between the components of the same path is ensured from one element to another the positioner (103, 104, 105) by the use of single microwave rotary joints (114, 120, 123, 124).

8- System according to any one of the preceding claims characterized in that the base (105) comprises a cold box (1 12) containing at least one power amplifier associated with the rising path (125), said box being cooled by the using a cold plate (122) attached to the base (105).

9- System according to claim 8 characterized in that at least one hydraulic cylinder is attached to the cold plate (122) and the support (134) on which the antenna system rests, said cylinder being controlled electrically or mechanically so as to introduce a static inclination angle between the antenna system and the support (134). - System according to claim 8 characterized in that at least one linear electric motor is fixed to the cold plate (122) and the support (134) on which the antenna system rests, said motor being electrically controlled so as to introduce a static inclination angle between the antenna system and the support (134).