Patent Publication Number: US-2023155297-A1

Title: Automatic beam steering system for a reflector antenna

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
     The present application claims benefit from IL288183 filed on Nov. 17, 2021. 
     TECHNICAL FIELD 
     The presently disclosed subject matter relates to antennas. In particular, it relates to new systems and methods for a reflector antenna, such as a dish antenna. 
     BACKGROUND 
     Dish antennas are antennas which include a dish and a feed. The antenna may be subject to vibrations, which alter the beam direction transmitted or received by the antenna and therefore degrade performance of the antenna. 
     Documents which constitute background to the presently disclosed subject matter include:
         U.S. Pat. No. 8,963,790B2;   U.S. Pat. No. 2,956,248A;   U.S. Pat. No. 4,786,913A;   U.S. Pat. No. 6,943,750B2;   EP1408581A2;   US20190341671A1;   www.mweda.com/cst/cst2013/mergedProjects/Examples_Overview_E MS/examplesoverview % tutorials/linear_motor.htm; and   Carpino, Francesca &amp; Moore, Lee &amp; Chalmers. Jeffrey &amp; Zborowski, Maciej &amp; Williams, Philip. (2005), “ Quadrulxole magnetic field - flow fractionation for the analysis of magnetic nanoparticles ”. Journal of Physics: Conference Series. 17. 174. 10.1088/1742-6596/17/1/024.       

     Acknowledgement of the above references herein is not to be inferred as meaning that these references are in any way relevant to the patentability of the presently disclosed subject matter. 
     There is now a need to propose new solutions for improving the structure and operation of antenna(s), and in particular of dish antennas. 
     GENERAL DESCRIPTION 
     In accordance with certain aspects of the presently disclosed subject matter, there is provided an antenna, comprising a main reflector, a waveguide, wherein at least part of the waveguide protrudes towards a region external to the antenna, wherein the antenna is operative to transmit electromagnetic radiations between the waveguide and the main reflector, and a mechanism which enables displacement of at least part of the waveguide with respect to the main reflector, and an actuator operative to displace the at least part of the waveguide. 
     In addition to the above features, the antenna according to this aspect of the presently disclosed subject matter can optionally comprise one or more of features (i) to (xix) below, in any technically possible combination or permutation:
         i. at least part of the waveguide protrudes from the main reflector, or the waveguide is coupled to a first waveguide, wherein at least part of the first waveguide protrudes from the main reflector;   ii. a position of the mechanism matches a position of a vertex of the main reflector according to a proximity criterion;   iii. the mechanism is located at an interface between the first waveguide and the waveguide;   iv. the mechanism enables at least one of a displacement in azimuth of the at least part of the waveguide, or a displacement in elevation of the at least part of the waveguide;   v. the mechanism includes a ball joint;   vi. the antenna comprises a sensor generating data usable to determine data D motion  informative of a displacement of the antenna, and a controller operative to obtain data D beam  informative of a required beam direction of electromagnetic radiations to be received or transmitted by the antenna, and determine a displacement D corrective  for the at least part of the waveguide using D motion  and D beam ;   vii. the controller is operative to determine a displacement D corrective  for the at least part of the waveguide using D motion  and D beam , for which a beam direction of electromagnetic radiations received or transmitted by the antenna, after said displacement D corrective  of said at least part of the waveguide, matches the required beam direction according to a matching criterion;   viii. the antenna comprises a first sensor generating data usable to determine data informative of a displacement of the antenna in a first range of frequencies, and a second sensor generating data usable to determine data informative of a displacement of the antenna in a second range of frequencies, wherein an average frequency of the first range is below an average frequency of the second range;   ix. the controller is operative to control an actuator of the antenna to move the at least part of the waveguide according to said displacement D corrective ;   x. the mechanism comprises a first element operatively coupled to a second element, wherein a gap between the first element and the second element has a dimension which is below a tenth of a wavelength informative of a range of wavelengths in which the antenna operates;   xi. the antenna comprises a magnet coupled to the at least part of the waveguide;   xii. the antenna comprises a first ferromagnetic element, a first inductor associated with the first ferromagnetic element, and a second ferromagnetic element, wherein an electric current generated in the first inductor enables displacement of the magnet and of the at least part of the waveguide;   xiii. the antenna comprises a first ferromagnetic element, a first inductor associated with the first ferromagnetic element, a second ferromagnetic element, and a second inductor with the second ferromagnetic element, wherein an electric current generated in at least one of the first inductor or the second inductor enables displacement of the magnet and of the at least part of the waveguide;   xiv. the first ferromagnetic element is a U-shaped ferromagnetic element;   xv. the first ferromagnetic element includes a first arm located at least partially above the magnet, a second arm located at least partially below the magnet, and a third arm joining the first portion to the second portion;   xvi. the electric current enables generation of a magnetic force operative to attract or repel the magnet, thereby moving the at least part of the waveguide;   xvii. the antenna is configured to generate a first current in the first inductor, and a second current in the second inductor, wherein the second current has a sign opposite to the first current;   xviii. the antenna comprise a magnet coupled to the waveguide, a first ferromagnetic element, a first inductor associated with the first ferromagnetic element, a second ferromagnetic element, a third ferromagnetic element, a second inductor associated with the third ferromagnetic element, and a fourth ferromagnetic element, wherein an electric current generated in the first inductor enables displacement of the magnet and of the at least part of the waveguide along a first direction, and an electric current generated in the second inductor enables displacement of the magnet and of the at least part of the waveguide along a second direction, different from the first direction; and   xix. the antenna comprises a third inductor associated with the second ferromagnetic element, a fourth inductor associated with the fourth ferromagnetic element, wherein electric currents generated in the first and third inductors with an opposite sign enable displacement of the magnet and of the at least part of the waveguide along the first direction, and wherein electric currents generated in the second and fourth inductors with an opposite sign enable displacement of the magnet and of the at least part of the waveguide along the second direction, different from the first direction.       

     In accordance with certain aspects of the presently disclosed subject matter, there is provided an antenna, comprising a main reflector, a waveguide, wherein at least part of the waveguide protrudes towards a region external to the antenna, wherein the antenna is operative to transmit electromagnetic radiations between the waveguide and the main reflector, and an actuator operative to displace at least part of the waveguide, the actuator comprising a magnet coupled to the at least part of the waveguide, a first ferromagnetic element, a second ferromagnetic element, and an inductor associated with the first ferromagnetic element or with the second ferromagnetic element. 
     In addition to the above features, the antenna according to this aspect of the presently disclosed subject matter can optionally comprise one or more of features (xx) to (xxix) below, in any technically possible combination or permutation:
         xx. the antenna comprises a mechanism which enables displacement of the at least part of the waveguide with respect to the main reflector,   xxi. the antenna comprises a magnet coupled to the at least part of the waveguide:   xxii. the antenna comprises a first ferromagnetic element, a first inductor associated with the first ferromagnetic element, and a second ferromagnetic element, wherein an electric current generated in the first inductor enables displacement of the magnet and of the at least part of the waveguide;   xxiii. the antenna comprises a first ferromagnetic element, a first inductor associated with the first ferromagnetic element, a second ferromagnetic element, and a second inductor with the second ferromagnetic element, wherein an electric current generated in at least one of the first inductor or the second inductor enables displacement of the magnet and of the at least part of the waveguide;   xxiv. the first ferromagnetic element is a U-shaped ferromagnetic element;   xxv. the first ferromagnetic element includes a first arm located at least partially above the magnet, a second arm located at least partially below the magnet, and a third arm joining the first arm to the second arm;   xxvi. the electric current enables generation of a magnetic force operative to attract or repel the magnet, thereby moving the at least part of the waveguide;   xxvii. the antenna is configured to generate a first current in the first inductor, and a second current in the second inductor, wherein the second current has a sign opposite to the first current;   xxviii. the antenna comprises a magnet coupled to the at least part of the waveguide, a first ferromagnetic element, a first inductor associated with the first ferromagnetic element, a second ferromagnetic element, a third ferromagnetic element, a second inductor associated with the third ferromagnetic element, and a fourth ferromagnetic element, wherein an electric current generated in the first inductor enables displacement of the magnet and of the at least part of the waveguide along a first direction, and an electric current generated in the second inductor enable displacement of the magnet and of the at least part of the waveguide along a second direction, different from the first direction; and   xxix. the antenna comprises a third inductor associated with the second ferromagnetic element, a fourth inductor associated with the fourth ferromagnetic element, wherein electric currents generated in the first and third inductors with an opposite sign enable displacement of the magnet and of the at least part of the waveguide along the first direction, and wherein electric currents generated in the second and fourth inductors with an opposite sign enable displacement of the magnet and of the at least part of the waveguide along the second direction, different from the first direction.       

     In accordance with certain aspects of the presently disclosed subject matter, there is provided a method of controlling an antenna comprising a main reflector and a waveguide, the method comprising, by a processor and memory circuitry, obtaining data D beam , informative of a required beam direction of electromagnetic radiations to be received or transmitted by the antenna, obtaining data D motion  informative of a displacement of the antenna, and determining a displacement D corrective  for at least part of the waveguide using D motion  and D beam , for which a beam direction of electromagnetic radiations received or transmitted by the antenna, after said displacement D corrective  of said at least part of the waveguide, matches the required beam direction according to a matching criterion. 
     In addition to the above features, the method according to this aspect of the presently disclosed subject matter can optionally comprise one or more of features (xxx) to (xxxi) below, in any technically possible combination or permutation:
         xxx. the method comprises controlling an actuator of the antenna to move the at least part of the waveguide according to said displacement D corrective ; and   xxxi. the method comprises (1) obtaining data D beam  informative of a required beam direction of electromagnetic radiations to be received or transmitted by the antenna, repeatedly performing over time (2) to (4): (2) obtaining data D motion  informative of a displacement of the antenna, (3) determining a displacement D corrective  for the at least part of the waveguide using D motion  and D beam  for which a beam direction of electromagnetic radiations received or transmitted by the antenna, after said displacement D corrective  of said at least part of the waveguide, matches the required beam direction according to a matching criterion, and (4) controlling an actuator of the antenna to move the at least part of the waveguide according to said displacement D corrective .       

     According to some embodiments, the method can include controlling an antenna as described in the various embodiments above (optionally including one or more of the features (i) to (xxix) above, in any technically possible combination or permutation). 
     According to some embodiments, the proposed solution provides an antenna which can be controlled to compensate vibrations affecting the beam direction of the antenna. 
     According to some embodiments, the proposed solution provides an accurate and efficient solution to compensate vibrations present in an antenna, such a reflector antenna (e.g. dish antenna). 
     According to some embodiments, the proposed solution enables real time or quasi real time control of an antenna subject to vibrations, such a reflector antenna (e.g. dish antenna). 
     According to some embodiments, the proposed solution improves the accuracy of control of the direction of the beam transmitted and/or received by an antenna, such as a reflector antenna (e.g. dish antenna). 
     According to some embodiments, the proposed solution enables efficient and accurate control of the direction of a narrow beam. 
     According to some embodiments, the proposed solution enables compensating vibrations present in an antenna by moving only a fraction of the antenna. As a consequence, it is possible to use smaller and less costly actuators. 
     According to some embodiments, the proposed solution provides a robust approach to compensate vibrations present in an antenna. 
     According to some embodiments, the proposed solution improves performance of antennas, such as reflector antenna (e.g. dish antennas). In particular, it improves performance of large dish antennas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to understand the invention and to see how it can be carried out in practice, embodiments will be described, by way of non-limiting examples, with reference to the accompanying drawings, in which: 
         FIG.  1 A  illustrates an embodiment of an antenna without vibrations; 
         FIG.  1 B  illustrates an example of an effect of vibrations on an antenna which operates in transmission; 
         FIG.  1 C  illustrates an example of an effect of vibrations on an antenna which operates in reception; 
         FIG.  1 D  illustrates an embodiment of an antenna including a mechanism enabling motion of at least part of a waveguide of the antenna; 
         FIG.  1 E  illustrates another embodiment of an antenna including a mechanism enabling motion of at least part of a waveguide of the antenna; 
         FIG.  1 F  illustrates another embodiment of an antenna including a mechanism enabling motion of at least part of a waveguide of the antenna; 
         FIG.  1 G  illustrates an example of a compensation of the effect of vibrations on an antenna which operates in transmission; 
         FIG.  1 H  illustrates an example of a compensation of the effect of vibrations on an antenna which operates in reception: 
         FIGS.  2 A to  2 C  illustrate an embodiment of a mechanism enabling motion of at least part of a waveguide of the antenna: 
         FIG.  3    illustrates an embodiment of an antenna including mechanical and electronic elements enabling control of the motion of the waveguide to compensate vibrations: 
         FIG.  4    illustrates a flow chart of a method of compensating the effect of vibrations on an antenna: 
         FIG.  5 A  illustrates an embodiment of an actuator to control motion of at least part of a waveguide of the antenna; 
         FIG.  5 B  illustrates a cross-sectional view of the actuator of  FIG.  5 A : 
         FIG.  5 C  illustrates a cross-sectional view of a ferromagnetic element usable in the actuator of  FIG.  5 A ; 
         FIG.  5 D  illustrates a cross-sectional view of another ferromagnetic element usable in the actuator of  FIG.  5 A ; 
         FIG.  6 A  illustrates a flow chart of a method of compensating the effect of vibrations on an antenna, using an actuator including elements depicted in  FIG.  6 B ; and 
         FIG.  6 C  illustrates a flow chart of a method of compensating the effect of vibrations on an antenna, using an actuator including elements depicted in  FIG.  6 D . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the presently disclosed subject matter may be practiced without these specific details. In other instances, well-known methods have not been described in detail so as not to obscure the presently disclosed subject matter. 
     The term “processor and memory circuitry” (PMC) as disclosed herein should be broadly construed to include any kind of electronic device with data processing circuitry, which includes for example a computer processing device operatively connected to a computer memory (e.g. digital signal processor (DSP), a microcontroller, a field programmable gate array (FPGA), and an application specific integrated circuit (ASIC), etc.) capable of executing various data processing operations. 
     It can encompass a single processor or multiple processors, which may be located in the same geographical zone, or may, at least partially, be located in different zones and may be able to communicate together. 
     Unless specifically stated otherwise, as apparent from the following discussions, it is appreciated that throughout the specification discussions utilizing terms such as “obtaining”. “determining”, “controlling”, “performing” or the like, refer to the action(s) and/or process(es) of a processor and memory circuitry that manipulates and/or transforms data into other data, said data represented as physical, such as electronic, quantities and/or said data representing the physical objects. 
       FIG.  1 A  illustrates an antenna  100 . As visible in  FIG.  1 A , the antenna  100  includes a main reflector  101  (also called dish). The antenna  100  is therefore a reflector antenna. 
     The main reflector  101  includes a curved surface  116  which is operative to reflect electromagnetic radiations (electromagnetic waves) when the antenna  100  operates in reception and/or in transmission. 
     In the non-limitative example of  FIG.  1 A , the main reflector  101  is a parabolic reflector which has a curved surface  116  with the cross-sectional shape of a parabola, to direct the electromagnetic waves. 
     The antenna  100  includes a waveguide  120 . The waveguide  120  can be designated as a feed waveguide  120  of the antenna  100 . This term is not to be construed as limitative and used only for simplifying its designation. 
     At least part of the waveguide  120  protrudes towards a region  130  (space  130 ) external to the antenna  100 . 
     Electromagnetic radiations are transmitted by the antenna  100  towards at least part of the space  130 , or electromagnetic radiations are received by the antenna  100  from at least part of the space  130 . 
     In some embodiments, the waveguide  120  can protrude from the main reflector  101  (see  FIG.  1 A , in which the waveguide  120  protrudes out of the main reflector  101  towards the space  130 ). 
     In some embodiments, the waveguide  120  is coupled to a first waveguide, wherein at least part of the first waveguide protrudes out of the main reflector  101  towards the space  130  (as explained with reference to  FIG.  1 E ). 
     In some embodiments, only part of the waveguide  120  protrudes from the main reflector  101  towards the space  130  (as explained with reference to  FIG.  1 F , in which only part of the waveguide  120  protrudes out of the main reflector  101  towards the space  130 ). 
     An end  121  (distal end which faces the space  130 ) of the waveguide  120  can be connected to a reflector  122  (also called a sub-reflector  122 ). 
     The antenna  100  includes a first waveguide  115  (only partially represented in  FIG.  1 A ). The first waveguide  115  and the waveguide  120  are operatively coupled. In particular, the antenna  100  can transmit electromagnetic radiations between the first waveguide  115  and the waveguide  120 . 
     In some embodiments, the electromagnetic radiations are in the radio-frequency (RF) range. This is however not limitative. 
     In the example of  FIG.  1 A , the first waveguide  115  protrudes inwardly from the main reflector  101  towards an inner portion  131  of the antenna  100 . The inner portion  131  includes various elements of the antenna  100  such as transceivers, low band port and/or high band port (not represented in  FIG.  1 A ), etc. 
     The first waveguide  115  is connected, directly or indirectly, to one or more transceivers (not represented) of the antenna  100 . The transceivers can be used to generate electromagnetic radiations transmitted by the antenna  100  and/or to process electromagnetic radiations received by the antenna  100 . 
     When the antenna  100  operates in transmission, electromagnetic radiations are transmitted from the first waveguide  115  to the waveguide  120 . The waveguide  120  transmits the electromagnetic radiations (via the sub-reflector  122 ) to the main reflector  101  (see arrow  150 ). In the absence of vibrations in the antenna  100 , the main reflector  101  transmits the electromagnetic radiations as a beam along the required direction (see arrow  151  in  FIG.  1 A ). 
     When the antenna  100  operates in reception, electromagnetic waves are received by the main reflector  101  and reflected by the main reflector  101  towards the waveguide  120  (via the sub-reflector  122 ). The waveguide  120  transmits the electromagnetic radiations to the first waveguide  115  (in order to be eventually processed by the transceivers). 
     As explained hereinafter, one or more elements can be present on the path of transmission between the first waveguide  115  and the waveguide  120 , such as a mechanism  165  described e.g. in  FIGS.  1 D,  1 E  and IF. 
     Attention is now drawn to  FIG.  1 B . 
     During operation of the antenna  100 , the antenna  100  is generally submitted to vibrations. The vibrations can be caused e.g. by wind, by the platform (e.g. mast or pole) on which the antenna  100  is mounted, by human activities, by other sources of vibrations, etc. This is however not limitative. 
     Due to these vibrations, at least part of the structure of the antenna  100  undergoes a displacement, along one or more axes. Such displacement can include in particular a displacement (such as a rotation or tilt) in azimuth and/or in elevation (also called pitch and/or yaw rotation). 
       FIG.  1 B  illustrates an example of an effect of the vibrations on the structure of the antenna  100 , when the effect of these vibrations is not compensated. 
     Assume for example that it is desired to transmit a beam of electromagnetic radiations along the required direction depicted by arrow  151  of  FIG.  1 A . 
     In the non-limitative example of  FIG.  1 B , the antenna  100  is tilted about one axis (depending on the definition of the axes this can correspond to a motion in azimuth or in elevation) due to the vibrations. 
     As a consequence, the beam  160  transmitted by the antenna  100  to the space  130  has a direction which differs from the required direction  151 . 
     Note that this problem arises also when the antenna  100  operates in reception, as visible in  FIG.  1 C , when the effect of the vibrations is not compensated. Assume that the antenna  100  receives electromagnetic rays (beam)  161  which are parallel to the required direction  151  (depicted in  FIG.  1 A ). Due to the vibrations, the antenna  100  is therefore not able to collect the desired electromagnetic rays/beam (or with a poor performance). 
     As can be understood from the example of  FIGS.  1 B and  1 C , if the effect of the vibrations is not compensated, the performance of the antenna is altered. 
     This problem is even more critical in large dish antennas, which produce a narrow beam width. The table illustrates non-limitative values of the beam width with respect to the diameter of the dish, at a frequency of 80 GHz. 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Dish diameter [feet] 
                 Beam width [deg] 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 0.5 
                 1.6 
               
               
                   
                 1 
                 0.8 
               
               
                   
                 2 
                 0.4 
               
               
                   
                 4 
                 0.2 
               
               
                   
                   
               
            
           
         
       
     
     Therefore, an error in the direction of transmission (respectively in reception) of the beam transmitted (respectively received) by the antenna strongly impacts performance of the antenna. 
     Attention is now drawn to  FIG.  1 D . 
     In order to compensate, at least partially, for vibrations of the antenna  100 , the antenna  100  includes a mechanism  165 . As explained hereinafter, the mechanism  165  can include one or more mechanical elements enabling motion of at least part of the waveguide  120  with respect to the main reflector  101  and/or the first waveguide  115 . In particular, it can enable a displacement in azimuth (see arrow  166 ) and/or elevation (see arrow  167 ) of at least part of (or of all of) the waveguide  120  (and of the sub-reflector  122  located at its proximal end). The displacement is e.g. a rotation or tilt in azimuth and/or elevation. 
     According to some embodiments, the mechanism  165  is located at an interface between the first waveguide  115  and the waveguide  120 . 
     In a parabolic antenna (dish antenna), the vertex  164  of the main reflector  101  (parabolic reflector) is the innermost point at the centre of the parabolic reflector. According to some embodiments, the position of the mechanism  165  matches a position of the vertex of the main reflector  101  according to a proximity criterion. The mechanism  165  is generally located on an axis of revolution of the waveguide  120  (main axis Z of the waveguide  120  oriented towards the space  130 ), at the same level of vertex  164  of the main reflector  101 , above the vertex  164  of the main reflector  101  (see  FIG.  1 E ) or below the vertex  164  of the main reflector  101  (see  FIG.  1 F ). 
     The proximity criterion can define e.g. that the distance (height) along axis Z (noted  168  in  FIGS.  1 E and  1 F ) between the mechanism  165  and the vertex  164  of the main reflector  101  is smaller than 100% of the diameter  169  of the main reflector  101 . This value is however not limitative. 
     When the mechanism  165  is located at the vertex  164  of the main reflector  101 , the whole waveguide  120  (or most of it) which protrudes from the main reflector  101  is tilted with respect to the main reflector  101 , as visible in  FIG.  1 E . In other words, the whole waveguide (or most of it) of the antenna  100  is tilted. 
       FIG.  1 E  shows a configuration in which the waveguide  120  is coupled to the first waveguide  115 , wherein at least part of the first waveguide  115  protrudes from the main reflector  101  towards the space  130 . In this case, the first waveguide  115  extends within the inner portion  131  of the antenna  100  and part of the first waveguide  115  protrudes out of the main reflector  101  towards the space  130 . 
     The mechanism  165  is located at the interface between the first waveguide  115  and the waveguide  120 . As visible in  FIG.  1 E , the mechanism  165  enables motion (rotation in azimuth and/or elevation) of the waveguide  120  with respect to the main reflector  101 . 
       FIG.  1 F  shows another configuration, in which the waveguide  120  includes a part which is located below the vertex  164  of the main reflector  100  (along axis Z). In other words, the waveguide  120  extends within the inner portion  131  of the antenna  100  and part of the waveguide  120  protrudes out of the main reflector  101  towards the space  130 . 
     The waveguide  120  is coupled to the first waveguide  115  which is located in the inner portion  131  of the antenna  100 . 
     The mechanism  165  is located at the interface between the first waveguide  115  and the waveguide  120 . In this embodiment, the mechanism  165  is located in the inner portion  131  of the antenna  100 . As visible in  FIG.  1 F , the mechanism  165  enables motion (rotation in azimuth and/or elevation) of the waveguide  120  with respect to the main reflector  101 . The main reflector  101  can include an opening at its vertex  164  which enables this motion. 
     Attention is now drawn to  FIG.  1 G . 
     As already explained with reference to  FIG.  1 B , the vibrations induce a displacement of the antenna  100 , which, in turn, cause the beam  160  transmitted by the antenna  100  to the space  130  to have a direction which differs from the required direction  151 . 
     As explained with reference to  FIGS.  1 D  to IF, the mechanism  165  enables a displacement of the waveguide  120 . The waveguide  120  is therefore controlled to be moved (e.g. rotated/tilted) about at least one axis, in order to compensate, at least partially, for the effect of the vibrations. 
     As shown in  FIG.  1 G , the waveguide  120  is moved from its original position  171 , to a new position  172 . At its new position  172 , the waveguide  120  transmits (via the sub-reflector  122 ) the beam  173  to the main reflector  101 , which, in turn, transmits the beam  174 . The beam  174  is transmitted along the required direction (the required direction is depicted as arrow  151  in  FIG.  1 A ). Note that the beam  174  includes a plurality of electromagnetic rays which are transmitted by the main reflector  101  as parallel to the required direction  151 . 
     In other words, the effect of the vibrations on the antenna  100  is compensated (at least partially) by moving at least part of the waveguide  120 . 
     Note that it is not necessary to move the whole antenna  100  (for example, it is not necessary to move the main reflector  101 ), but only part (or all) of the waveguide  120  (elements which are affixed to the waveguide  120  also move, such as the sub-reflector  122 ). 
     By virtue of the reciprocity effect, the same principles as described in the transmission mode can be used when then antenna operates in reception, as illustrated in  FIG.  1 H . 
     When the vibrations are not compensated, the vibrations induce a displacement of the antenna  100 , which, in turn, cause the antenna  100  to fail (partially or totally) to collect the beam  174   1  received from the required direction  151 . To the contrary, the antenna  100  may collect beam  160   1  (note that arrow  160   1  can also correspond to an electromagnetic ray) which is not of interest (since it comes from a direction which differs from the required direction  151 ). 
     By using the mechanism  165 , the waveguide  120  is therefore controlled to be moved (e.g. rotated/tilted) about at least one axis, in order to compensate, at least partially, for the effect of the vibrations. 
     As shown in  FIG.  1 H , the waveguide  120  is moved from its original position  171   1 , to a new position  172   1 . The main reflector  101  reflects the desired beam  174   1  into beam  1731  towards the sub-reflector  122  affixed to the waveguide  120  located at its new position  172   1 . Therefore, the beam received along the required direction is received by the antenna  100 . Note that by virtue of the shape of the main reflector, any electromagnetic ray (see e.g. reference  177 ) which is parallel to the required direction  151  is transmitted to the sub-reflector  122  and to the waveguide  120  located at its new position  172   1 . 
     Note that the examples of  FIG.  1 G  and  FIG.  1 H  are depicted with reference to the configuration of the antenna  100  as depicted in  FIG.  1 D . This is not limitative and the configuration of the antenna  100  as depicted in  FIG.  1 E  or  FIG.  1 F  can be used. 
     Attention is now drawn to  FIGS.  2 A and  2 B . 
       FIG.  2 A  depicts an embodiment of the mechanism  165  (noted  265  in  FIG.  2 A ). This embodiment is however not limitative. 
     In this embodiment, the mechanism  265  includes a socket  200  (e.g. a spherical socket) and a protrusion  210  (e.g. a spherical protrusion). Therefore, the protrusion  210  can rotate within the socket  200 . In particular, the waveguide  120  can rotate around the center of the protrusion  210 . This mechanism  265  is also called a ball joint. 
     This mechanism  265  enables a rotation of the waveguide  120  around at least two axes: azimuth axis and elevation axis. Note that in this specific example, the mechanism  265  enables also rotation around the Z axis (however, in order to compensate vibrations, it is not required to move the waveguide  120  about this axis). 
     In some embodiments, it is possible to use a mechanism  265  which enables motion along only one axis (azimuth or elevation). This can include e.g. a waveguide rotary joint or a waveguide rotating joint. This is not limitative. 
     In the example of  FIG.  2 A , the mechanism  265  is located at the interface between the first waveguide  115  and the waveguide  120 . As a consequence, the socket  200  is located at an end  205  of the first waveguide  115  (this corresponds to the end  205  of the first waveguide  115  which is coupled to the waveguide  120 ) and the protrusion  210  is located at an end  220  of the waveguide  120  (this corresponds to the end  220  of the waveguide  120  which is coupled to the first waveguide  115 ). 
     Note that the mechanism  265  is only an example, and other mechanisms can be used, such as a waveguide rotary joint, a waveguide rotating joint, a flexible waveguide, etc. This list is not limitative. 
     As can be understood from the examples above, the mechanism (see e.g.  165  or  265 ) is located between two waveguides (e.g. between the first waveguide  115  and the waveguide  120 ). During operation of the antenna  100 , electromagnetic radiations must be transmitted between the two waveguides. Assume that the mechanism includes at least a first mechanical element and a second mechanical element (mechanical pieces) which cooperate to enable the desired motion. In order to optimize performance of the antenna  100 , the gap (air gap) between the first element and the second element has a dimension (e.g. a thickness) which is below a tenth (10 percent) of a wavelength λ mean  informative of a range of wavelengths [λ min λ max ] at which the antenna  100  operates. In some embodiments, λ mean , corresponds to λ min  (minimal wavelength of operation) or λ max  (maximal wavelength of operation) or to the average of λ min  and λ max . Since the first element and the second element are located in close proximity one to the other, the leakage of electromagnetic radiations out of the antenna  100  (antenna loss) is limited or even prevented. 
     In the example of  FIGS.  2 A and  2 B , the first mechanical element corresponds to the socket  200  and the second mechanical element corresponds to the protrusion  210 . The gap between the socket  200  and the protrusion  210  is noted  250  (as visible in  FIG.  2 C ). 
     Attention is now drawn to  FIG.  3   . 
     In order to induce motion of the waveguide  120 , the antenna  100  can include (or be operatively coupled to) an actuator  170 , such as a motor. The actuator  170  can be used to control motion of at least part of the waveguide  120 , in cooperation with the mechanism  165 . 
     In some embodiments (such as in  FIG.  3   ), the actuator  170  is operatively coupled to the waveguide  120  and induces a displacement of the waveguide  120 . This displacement is guided by the mechanism  165 , which enables at least one degree of freedom for displacement of the waveguide  120  with respect to the main reflector  101 . 
     The antenna  100  can further include (or is operatively coupled to) at least one sensor  175  (or a plurality of sensors  175 ). The sensor  175  generates data (e.g. inertial data) usable to determine data D motion  informative of a displacement of the antenna  100  over time (and/or of at least part of the antenna  100 , such as of the main reflector  101 ). Note that the sensor  175  can be placed at various locations of the antenna  100 . The sensor  175  can include e.g. a gyroscope, which measures angular velocity along the azimuth axis and/or the elevation axis, and an accelerometer which measures the gravitation direction. Integration of the angular velocity (by a processor and memory circuitry, such as controller  180 ) provides the position of the antenna over time. In some embodiments, the sensor  175  can include an inertial measurement unit (IMU). In some embodiments, the sensor  175  can include a position sensor. 
     In some embodiments, the antenna  100  includes a first sensor generating data usable to determine data informative of a displacement of the antenna  100  in a first range of frequencies (low frequencies), and a second sensor generating data usable to determine data informative of a displacement of the antenna in a second range of frequencies (high frequencies), wherein the average frequency of the first range is below the average frequency of the second range. 
     For example, the first sensor can be an accelerometer which measures the gravitation direction. This enables to determine the elevation angle. In particular, it can detect variations of the elevation angle at frequencies below 1 Hz. These variations can be due e.g. to the sun, which warms the platform (mast or pole) on which the antenna  100  is mounted. These variations occur at low frequencies (below 1 Hz). 
     The second sensor can be a gyroscope which measures vibrations at higher frequencies (e.g. up to 30 Hz). These vibrations are caused e.g. by wind. 
     Note that the source of vibrations and the frequency values as described above are not limitative. 
     The antenna  100  can further include (or is operatively coupled to) at least one controller  180 . The controller  180  can include a processor and memory circuitry (not represented). The controller  180  can receive data from the sensor  175 . The data can correspond to D motion  or can be used to generate D beam . The controller  180  can use the data of the sensor  175  to generate a command for the actuator  170 , in order to control the motion of the waveguide  120 , to compensate for the vibrations undergone by the antenna  100 . 
     Attention is now drawn to  FIG.  4   , which describes a method of controlling the antenna  100 . 
     The method includes obtaining (operation  400 ) data D beam  informative of a required beam direction of electromagnetic radiations to be received or transmitted by the antenna  100 . Data D beam  can be obtained by the controller  180 . In the example of  FIGS.  1 G and  1 H , data D beam  defines the direction  151  as the required direction. D beam  can include e.g. a 2D or a 3D vector defining the required beam direction. 
     In some embodiments, D beam  can be e.g. known in advance (because it is known that the antenna  100  needs to transmit electromagnetic radiations to a second antenna, and the position and orientation of the second antenna is known). In some embodiments, D beam  can be measured (e.g. by obtaining position and orientation data of the second antenna). 
     D beam  can be provided to the controller  180  by e.g. an operator of the antenna  100  (using a computerized interface), and/or by a system which communicates with the antenna  100 . 
     In the example of  FIG.  1 A . D beam , defines the required direction  151  as a zero angle tilt (with respect to the Z axis). Note that this is not limitative, and in some embodiments, the tilt angle of the required beam direction can be non-zero (in reception and/or in transmission). 
     The method further includes obtaining (e.g. by controller  180 ) data D motion  informative of a displacement of the antenna  100  (operation  410 ). As mentioned above, D motion  can be provided by the sensor  175 , or can be generated using data provided by the sensor  175 . D motion  can include e.g. the displacement (e.g. angular displacement) of the antenna  100  (or at least of the main reflector  101 ) about the azimuth axis and/or elevation axis.  FIG.  3    illustrates an angular displacement (rotation) in azimuth (see arrow  166  which illustrates a rotation about axis X) and an angular displacement (rotation) in elevation (see arrow  167  which illustrates a rotation about axis Y). Note that the definition of the azimuth axis and of the elevation axis is a matter of convention. Therefore, in another convention, a rotation in azimuth can correspond to arrow  167  and a rotation in elevation can correspond to arrow  166 . 
     In some embodiments, operation  410  can include measuring angular velocities along the azimuth axis and/or elevation axis and integrating the velocity along the azimuth axis and/or elevation axis to get the angular displacement along the azimuth axis and/or elevation axis. 
     The method further includes (operation  420 ) determining a displacement (corrective displacement) D corrective  for the waveguide  120  (or for at least part of it) using D motion  and D beam . 
     When the antenna  100  operates in transmission, D corrective  is determined such that, when the waveguide  120  moves according to D corrective , the direction of the beam transmitted by the antenna  100  corresponds to the required beam direction obtained at operation  400 . 
     When the antenna  100  operates in reception, D corrective  is determined such that, when the waveguide  120  moves according to D corrective , an incoming electromagnetic beam (or incoming electromagnetic ray) which has the required beam direction, is reflected by the main reflector  101  towards the sub-reflector  122 , and then to the waveguide  120 . 
     Note that in some embodiments, the antenna  100  can operate simultaneously (or quasi simultaneously) both in reception and transmission. If the required beam direction is the same for reception and transmission, the waveguide  120  is moved to ensure both reception and transmission according to this required beam direction. 
     Operation  420  can be performed by the controller  180 . Based on this displacement D corrective , the controller  180  can generate the command (e.g. electrical signal) to be transmitted to the actuator  170 , in order to command the actuator  170  to move at least part of the waveguide  120  according to the displacement D corrective . In some embodiments, the controller  180  determines D corrective  which is transmitted to a motor driver, which converts D corrective  into electrical signals to be transmitted to the actuator  170 . In particular, as explained hereinafter, the electrical signals can correspond to electrical currents to be applied to inductors of the actuator  170 . 
     In some embodiments, the displacement is determined along one axis (e.g. angular rotation in azimuth or angular rotation in elevation). In some embodiments, the displacement is determined along two axes (e.g. rotation in both azimuth and elevation). 
     Assume for example that the angular displacement of the antenna  100  (due to the vibrations) in elevation is noted θ (see  FIG.  1 G ). 
     The corrective displacement D corrective  can be calculated as follows: a 1 θ+a 2 θ 3 , wherein a 1  and a 2  are coefficients which depend on the shape and dimensions of the main reflector  101 . For example, for a typical dish antenna, which has a “f over D ratio” (corresponding to the ratio between the focal length of the antenna  100  and the diameter  169  of the main reflector  101 ) equal to 0.4, a 1 =1.1 and a 2 =0. This is not limitative. If the f over D ratio is different, the values of a 1  and a 2  can be tuned accordingly, using an electromagnetic simulation software (the dimensions and shape of the antenna are provided to the electromagnetic simulation software which provide direction of the beam depending on the tilt of the waveguide  120 ). 
     In other words, at least part of the waveguide  120  must be rotated in elevation with an angular rotation equal to a 1 θ+a 2 θ 3 . 
     Similarly, if the displacement of the antenna  100  along the azimuth axis is noted φ (not represented), the corrective displacement D corrective  can be calculated as follows: a 1 φ+a 2 φ 3 . The values for at and a 2  used for the azimuth motion can be used for the elevation motion. 
     Note that these formulas are not limitative and other formulas can be used. 
     The method further includes transmitting (e.g. by the controller  180 ) the command signal(s) (as determined at operation  420 ) to the actuator  170  (operation  430 ). At least part of the waveguide  120  (together with the sub-reflector  122 ) is moved by the actuator  170  (as mentioned above, the mechanism  165  enables a motion of the waveguide  120 ) to reach its new position (see position  172  in  FIG.  1 G  and position  172   1  in  FIG.  1 H ). 
     The method further includes transmitting (operation  440 ) electromagnetic radiations using the antenna  100  in which the waveguide  120  has reached its new position. In the example of  FIG.  1 G , the direction of the beam  174  transmitted by the antenna  100  matches the required beam direction  151  according to a matching criterion. The matching criterion can define e.g. the maximal angular error (between the required beam direction and the actual beam direction). In some embodiments, the matching criterion defines that the maximal angular error is less than quarter of the beam width (the beam width defines the angular opening of the beam transmitted or received by the antenna). 
     Similarly, operation  440  can include receiving (operation  440 ) electromagnetic radiations using the antenna  100  in which the waveguide  120  has reached its new position. 
     When the antenna  100  operates in reception, the antenna  100  receives an electromagnetic beam which matches the required beam direction  151  according to a matching criterion. The matching criterion can define that any electromagnetic beam which has a direction which differs from the required beam direction by a value which is equal to or below the maximal angular error, is received by the antenna (whereas an electromagnetic beam which has a direction which differs from the required beam direction by a value which is above the maximal angular error is not received by the antenna, or received with an amplitude below a threshold, such as 1 dB—this value being not limitative). In some embodiments, the maximal angular error is less than quarter of the beam width to be received by the antenna  100 . 
     In the example of  FIG.  1 H , the beam  174   1  received by the antenna  100  matches the required beam direction  151  according to the matching criterion and is therefore collected by the waveguide  120 . To the contrary, beam  160   1  (note that arrow  160   1  can also correspond to an electromagnetic ray) does not match the required beam direction  151  according to the matching criterion, since its angular deviation Δ with respect to the required beam direction is above the maximal angular error. Therefore, beam  160   1  is not received by the waveguide  120 . 
     As visible in  FIG.  4    (see reference  450 ), the method of  FIG.  4    can be repeated over time. If the required beam direction does not change, then operations  410  to  440  can be repeated, since the vibrations applied to the antenna  100  can change over time, and it is therefore needed to update the corrective displacement to compensate for these vibrations. 
     If the required beam direction changes, then operations  400  to  440  can be repeated. 
     A real time (or quasi real time) compensation of the vibrations can be obtained. The frequency at which the method of  FIG.  4    is repeated can be set e.g. by an operator depending on the frequency of vibrations which need to be compensated. If necessary, this frequency can be changed over time. In some embodiments, the frequency of the vibrations is measured and the frequency at which the method of  FIG.  4    is repeated is dynamically adjusted depending on the frequency of the vibrations. 
     Attention is now drawn to  FIG.  5 A  and  FIG.  5 B , which depicts an embodiment of the actuator  170  (in  FIG.  5 A , the actuator is noted  570 ). Note that this embodiment is not limitative and other actuators can be used. 
     The actuator  570  includes a magnet  510  (e.g. a permanent magnet) coupled (e.g. affixed) to the waveguide  120 . In the non-limitative example of  FIG.  5 A , the magnet  510  has a through hole at its center. The waveguide  120  expands through this through hole. This is however not limitative and other methods can be used to affix the magnet  510  to the waveguide  120 . 
     The actuator  570  further includes a first ferromagnetic element  525   1  and a second ferromagnetic element  5252 . The first ferromagnetic element  525   1  is located opposite to the second ferromagnetic element  5252  with respect to the waveguide  120 . Examples of ferromagnetic elements include e.g. iron and/or steel (this is not limitative). 
     The actuator  570  includes at least one inductor, which can be associated with the first ferromagnetic element  525   1  and/or with the second ferromagnetic element  5252 . The inductor can include an insulated wire wound into a coil. The inductor can be therefore be wrapped around the first ferromagnetic element  525   1  and/or the second ferromagnetic element  525  (in order to be able to magnetize the corresponding ferromagnetic element). Note that the inductor does not need to be in direct contact with the corresponding ferromagnetic element (an insulating layer can be present on the ferromagnetic element). 
     As explained hereinafter, a inductor associated with one of the two opposite ferromagnetic elements enables displacement of the waveguide  120  along one axis (see arrow  580 —this corresponds e.g. to an azimuth or elevation rotation depending on the convention). In particular, a rotation about an axis orthogonal to an axis joining the two opposite ferromagnetic elements can be obtained. It is however possible (as in the non-limitative embodiment of  FIG.  5 A ) to use two inductors (or more), each inductor being associated with a ferromagnetic element. 
     In the absence of electrical currents applied to the inductor, the two opposite ferromagnetic elements maintain the magnet  510  at its equilibrium position (with a tilt of zero degrees). 
     In  FIG.  5 A , the actuator  570  includes a first inductor  5201  associated with the first ferromagnetic element  525   1  and a second inductor  5202  associated with the second ferromagnetic element  5252 . 
     In the embodiment of  FIG.  5 A , the first pair of elements (which includes the first inductor  5201  and the first ferromagnetic element  525   i ) is located opposite to the second pair of elements (which includes the second inductor  5202  and the second ferromagnetic element  5252 ) with respect to the waveguide  120 . In particular, the first pair of elements faces a first side of the magnet  510  and the second pair of element faces a second side of the magnet  510 , which is opposite to the first side. 
     The first pair and the second pair of elements enable controlling motion of the waveguide  120  along direction  580 . 
     In some embodiments, the actuator  570  can include additional elements. 
     The actuator  570  can include a third ferromagnetic element  525   3  and a fourth ferromagnetic element  525   4 . The third ferromagnetic element  525   3  is located opposite to the fourth ferromagnetic element  525  with respect to the waveguide  120 . 
     The actuator  570  can include at least one additional inductor, which can be associated with the third ferromagnetic element  525   3  and/or with the fourth ferromagnetic element  525   4 . The additional inductor is therefore located in the vicinity of the third ferromagnetic element  525   3  and/or of the fourth ferromagnetic element  525   4  (in order to be able to magnetize the corresponding ferromagnetic element). 
     An inductor associated with one of the two opposite ferromagnetic elements  525   3 ,  525   4  enables displacement of the waveguide  120  along an additional axis (see arrow  581 —this corresponds e.g. to an azimuth or elevation rotation depending on the convention). It is however possible (as in the non-limitative embodiment of  FIG.  5 A ) to use two inductors (or more), each inductor being associated with a ferromagnetic element. 
     In  FIG.  5 A , the actuator  570  includes a third inductor  520   3  associated with the third ferromagnetic element  525   3  and a fourth inductor  520   4  associated with the fourth ferromagnetic element  525 . 
     In the embodiment of  FIG.  5 A , the third pair of elements (which includes the third inductor  520   3  coupled to the third ferromagnetic element  525   3 ) is located opposite to the fourth pair of elements (which includes the fourth inductor  520   4  and the fourth ferromagnetic element  525   4 ) with respect to the waveguide  120 . In particular, the third pair of elements faces a second side of the magnet  510  and the fourth pair of elements faces a side of the magnet  510 , which is opposite to the second side. 
     If four ferromagnetic elements are used (and at least two inductors, one per axis), each ferromagnetic element can be located (in a plane X-Y orthogonal to the main axis Z of the waveguide  120 ) at a 90-degree angle to its adjacent ferromagnetic element. 
     In the non-limitative example of  FIG.  5 A  in which four pairs of elements are used, each pair of elements is located (in a plane X-Y orthogonal to the main axis Z of the waveguide  120 ) at a 90-degree angle to its adjacent pair of elements. 
     Note that another number of elements can be used: for each axis along which the motion of the waveguide  120  has to be controlled, two ferromagnetic elements (located opposite one to the other with respect to the waveguide  120 ) and at least one inductor coupled to one of the two ferromagnetic elements can be used. 
     Note that the ferromagnetic elements can be connected to the body of the antenna  100  using appropriate mechanical connections. 
     Attention is now drawn to  FIGS.  5 B to  5 D .  FIG.  5 B  illustrates a cross section of the actuator  570  (therefore, only three pairs of elements are visible in  FIG.  5 B ). 
     In the non-limitative example of  FIG.  5 B , the cross-section of each ferromagnetic element has a shape which is similar to a U (“U-shaped” ferromagnetic elements). The magnet  510  can extend at least partially within a cavity  595  defined by the interior portion of the shape of each ferromagnetic element. 
     In some embodiments, each ferromagnetic element can act as a yoke which surrounds the magnet  510 . 
     Assume that a Z-axis (oriented towards the outer space of the antenna  100 ) corresponds to the axis of revolution of the waveguide  120 . 
     Each ferromagnetic element (or at least one of the ferromagnetic elements) can include two portions (corresponding to the two “arms” of the “U”): a first arm  585  is located at least partially above the magnet  510  (along axis Z), and a second arm  586  is located at least partially below the magnet  510  (along axis Z). A third arm  587  joins the first arm  585  to the second arm  586 . In  FIG.  5 B , at least part of the first arm  585  surrounds the magnet  510 . This is not limitative, and the lengths of the first arm  585  and/or of the second arm  586  can be selected such that the first arm  585  and/or of the second arm  586  does not surround the magnet  510 . 
     The first arm  585  and the second arm 5% can be substantially parallel. In some embodiments, the first arm  585  and the second arm 5% can have a curved profile (see  FIG.  5 C ). 
     Note that the first arm  585  and the second arm  586  can have different lengths. This is illustrated in  FIG.  5 C . In other embodiments (see  FIG.  5 D ), the first arm  585  and the second arm  586  can have the same length. 
     Attention is now drawn to  FIGS.  6 A and  6 B , which describe a method of controlling the motion of the waveguide  120 , using an actuator including at least two opposite ferromagnetic elements and at least one inductor associated with one of the ferromagnetic elements. 
     The method includes generating (operation  600 ) an electric current in the inductor (e.g. inductor  520   4 ). An electrical generator (controlled e.g. by the controller  180 ) can be used to generate the electrical current applied to the inductor(s). The electrical generator is not represented in the drawings. 
     The magnet  510  has a magnetic dipole moment with North Pole  606  and South Pole  607 . 
     Since an electric current  609  is present in the inductor  520   4 , it acts as a magnet (operation  601 ) which is associated with a magnetic dipole moment  610  (magnetic flux). The magnetic dipole moment  610  has a north pole  611  and a south pole  612 . It expands through the shape (in particular through the first portion, the second portion and the third portion) of the ferromagnetic element  525   4 . Due to the presence of the ferromagnetic element  525   4 , the magnetization induced by the inductor  520   4  flows through the ferromagnetic element  525   4 . The ferromagnetic element  525   4  enables to transfer the magnetic field induced by the inductor  520   4  in the vicinity of the magnet  510 . 
     According to the laws of Physics, there is attraction between south and north poles and repulsion between two south poles and between two north poles. 
     In the configuration of  FIG.  6 B , the south pole Sm  607  is attracted by the north pole N 2   611 . The north pole Nm  606  is attracted by the south pole S 2   612 . 
     In other words, the electric current  609  enables to generate an attraction force (magnetic force) in the direction  650 . The magnet  510  is therefore moved in the direction  650 . Since the magnet  510  is coupled to the waveguide  120 , the waveguide  120  is moved in the direction  650 . Motion of the waveguide  120  is guided by the mechanism  165 . 
     If it is desired to move the waveguide  120  in a direction  651  which is opposite to the direction  650 , an electrical current which has an opposite direction (that is to say opposite sign) to the electrical current  609 , is applied to the inductor  520   4 . 
       FIGS.  6 C and  6 D  describe a variant of the method of  FIGS.  6 A and  6 B . In  FIG.  6 D , two opposite pairs of elements (each pair including a ferromagnetic element and an inductor) are used to control motion of the waveguide  120  along one axis. 
     The magnet  510  has a magnetic dipole moment  605  with north pole  606  and south pole  607 . 
     An electric current  609  is applied (operation  660 ) to an inductor (e.g. coil  520   4 ). Since an electric current  609  is present in the inductor  520   4 , it acts as a magnet which is associated with a magnetic dipole moment  610 . The magnetic dipole moment  610  has a north pole  611  and a south pole  612 . It expands through the shape (in particular through the first arm, the second arm and the third arm) of the ferromagnetic element  525   4 . Due to the presence of the ferromagnetic element  525   4 , the magnetization induced by the inductor  520   4  flows through the ferromagnetic element  525   4 . 
     An electric current  615  is applied (operation  661 ) to another inductor (e.g. inductor  520   3 ). The electric current  615  flows in the inductor  520   3  in a direction which is opposite to the direction in which the electric current  609  flows in the inductor  520   4  (current of opposite sign). Due to the presence of the ferromagnetic element  525   4 , the magnetization induced by the inductor  520   4  flows through the ferromagnetic element  525 . 
     Since an electric current  615  is present in the inductor  520   3 , it acts as a magnet which is associated with a magnetic dipole moment  625 . The magnetic dipole moment  625  has a north pole  626  and a south pole  627 . It expands through the shape (in particular through the first portion, the second portion and the third portion) of the ferromagnetic element  525   3 . Due to the presence of the ferromagnetic element  525   3 , the magnetization induced by the inductor  520   3  flows through the ferromagnetic element  520   3 . 
     In some embodiments, the amplitude of the electric current  609  is equal to the amplitude of the electric current  615 . This is however not mandatory. 
     In the configuration of  FIG.  6 D , the south pole Sm  607  is attracted by the north pole N 2   611  and is repelled from the south pole S 1   627 . 
     The north pole Nm  606  is attracted by the south pole S 2   612  and is repelled from the north pole N 1   626 . 
     In other words, the electric currents  609 ,  615  enable to generate an attraction force in the direction  650 . The magnet  510  is therefore moved in the direction  650  (operation  662 ). Note that the attraction force generated in  FIG.  6 D  is of larger amplitude than in  FIG.  6 B , because two inductors are used. Since the magnet  510  is coupled to the waveguide  120 , the waveguide  120  is moved in the direction  650  (as mentioned above, the mechanism  165  enables motion of the waveguide  120 ). 
     If it is desired to move the waveguide  120  in a direction  651  which is opposite to the direction  650 , an electrical current which has an opposite direction (opposite sign) to the electrical current  609  is applied to the inductor  520   4 , and an electrical current which has an opposite direction (opposite sign) to the electrical current  615  is applied to the inductor  520   3 . 
     The actuator as described above is not limitative and, in some embodiments, or actuators or motors can be used (e.g. an electrical motor mechanically coupled to the waveguide  120 ). 
     It is to be noted that the various features described in the various embodiments may be combined according to all possible technical combinations. 
     It is to be understood that the invention is not limited in its application to the details set forth in the description contained herein or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Hence, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the presently disclosed subject matter. 
     Those skilled in the art will readily appreciate that various modifications and changes can be applied to the embodiments of the invention as hereinbefore described without departing from its scope, defined in and by the appended claims.