Abstract:
A low passive intermodulation (PIM) RF rotary switch comprises a plurality of center conductors connected to stationary pads, at least two rotatable pads being connected by a rotatable pad bridge. Depending on the switching state of the switch, at least two stationary pads are in close proximity to at least two rotatable pads, at a distance sufficient to generate/form a RF signal connection between the center conductors via the stationary and rotatable pads.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation from pending International Application No. PCT/EP2016/051025 filed on Jan. 19 2016, which designates the United States and claims priority from the European Application No. 15152379.2 filed on Jan. 23, 2015. The disclosure of each of the above-identified applications is incorporated herein by reference. 
     
    
     BACKGROUND 
     1. Field of the Invention 
       [0002]    The invention relates to a low passive intermodulation radio frequency rotary switch for use in switching coaxial lines. Such switches may be used in test equipment, which preferably is used for intermodulation measurement. 
       2. Description of Relevant Art 
       [0003]    For performing tests and measurements in RF (radio frequency) equipment, it is often required to switch individual coaxial lines. 
         [0004]    U.S. Pat. No. 4,967,174 A discloses a rotating coaxial switch. This switch operates by lifting the switching circuitry before rotating. Such performance allows for increase of the contact force after the switching has been performed. In such switches, the passive intermodulation decreases with increasing contact force. However, there exist mechanical limits imposed on the contact force and therefore the reduction of passive intermodulation is limited as well. Furthermore, with wear of the contacts, the intermodulation increases. Accordingly, the described in U.S. Pat. No. 4,967,174A switch has a limited lifetime. 
       SUMMARY 
       [0005]    The embodiments address a goal of providing an RF (Radio Frequency) switch for switching coaxial lines, which offers a very low passive intermodulation (PIM). Furthermore, the disclosed switch requires low maintenance and has an extended lifetime as compared to those of related art. 
         [0006]    In an embodiment, a low passive intermodulation (PIM) switch includes four ports, which may be connected by switching elements in a predetermined manner. The switching elements are rotated about a rotation axis and interact with stationary coupling elements, thereby forming a capacitively coupled switch. The resulting capacitively coupled switch does not have any mechanical or galvanic contacts and, therefore, does not generate any passive intermodulation of RF signals. In an alternate embodiment, the switching elements may be moved between alternate positions, preferably with a linear movement. The basic switching function of such embodiment remains independent of the specific movement. Therefore, embodiments of switches may be based on a linear or any other kind of displacement of the pads. In the description of such embodiments provide below, all terms which are related to “rotation” or “rotatable” are intended to mean and should be more generally understood as meaning “movement” or “movable”. 
         [0007]    In one embodiment, the switch is a rotatable switch for alternatingly connecting four ports. The ports have RF connectors which, in operation, are preferably connected to any kind of test equipment, such as for example a network analyzer, a load, or any other device. It is further preferred, if the coaxial connectors are chosen to also be low PIM connectors. The coaxial connectors are connected via coaxial center conductors to at least one stationary pad for capacitively coupling an RF signal. Preferably, the center conductors comprise solid or hollow metal tubes or rods. In another embodiment, the center conductors may also be structures like striplines on a dielectric carrier (such as a printed circuit board, for example). Preferably, there are two pads connected to each center conductor. At the rotatable part, there is at least one rotatable pad interfacing with at least one stationary pad. It is further preferred to have two stationary pads, most preferably one stationary pad above a rotatable pad and the second stationary pad below or under a rotatable pad. It is further preferred, if two rotatable pads are connected by a bridge. The bridge preferably provides an electrical and mechanical connection between these pads, and most preferably is mechanically connected to a shaft to guide or rotate the bridge together with the pads. An RF signal coming from a first coaxial connector is coupled via a first center conductor to at least a first stationary pad. From the stationary pad, the signal is coupled to a rotatable pad, from which it is further guided by the bridge to a second rotatable pad to be coupled to at least one second stationary pad, and via a second center conductor to a second coaxial connector. In a first embodiment, there are four ports, each port having a coaxial connector, a center conductor, and at least one, preferably two stationary pads. A rotor has two sets of rotatable pads, whereas a first rotatable pad is coupled to a second rotatable pad via a first bridge, and a third rotatable pad is coupled to a fourth rotatable pad via a second bridge. 
         [0008]    Although the rotatable pads may rotate continuously, there are certain positions where at least one rotatable pad overlaps with at least one stationary pad, and preferably overlaps in a centered manner, such that the overlapping surface/area is maximized. At maximum degree of overlap, there is the highest coupling capacitance, and therefore the best coupling between the stationary and the rotatable pads. In the above embodiment (having four ports with four stationary pads and four rotatable pads) there are four discrete positions with maximum overlap of the pads. In a preferred embodiment, the stationary pads and the rotatable pads are arranged under angles of 90° centered around the rotation axis of the rotor. Accordingly, the four discrete positions for maximum coupling are 90° distant from each other. 
         [0009]    In a related embodiment, at least one movable pad and/or at least one pad bridge is movable and/or displaceable. Most preferably, at least one movable pad and/or at least one pad bridge is a) displaceable parallel to a plane defined by the pad and/or b) tiltable from (with respect to) a plane defined by the pad. Preferably, a pad bridge has two ends, each end holding a movable pad. 
         [0010]    With the use of such displacement and/or tilt, mechanical tolerances of the stationary pads may be compensated. This allows the stationary pads to be constructed from a stiff (and not elastic or springy) material forming the pad sections. A stiff material with a predefined distance of the stationary pad sections results in a precisely defined coupling capacitance between the rotatable pads and the stationary pads, further resulting in more reproducible and improved coupling characteristics. Furthermore, the gap (distance) between the stationary pad sections can be minimized, such that the movable parts fit in between precisely, resulting in a significantly improved coupling capacitance. The remaining gap between two stationary pad sections and a movable pad in between may be in a range of 0.5 mm to 0.005 most preferably between 0.05 mm and 0.1 mm. 
         [0011]    It is further preferred to have a symmetrical arrangement of the stationary pads and to have symmetrical arrangement of the two sets of rotatable pads, as each set has two pads connected by a bridge. The switch of this specific embodiment has the following states: 
         [0000]    
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 state 
                 port 1 
                 port 2 
                 port 3 
                 port 4 
               
               
                   
               
             
             
               
                 1 
                 X 
                 X 
                 Y 
                 Y 
               
               
                 2 
                 Y 
                 X 
                 X 
                 Y 
               
               
                 3 
                 Y 
                 Y 
                 X 
                 X 
               
               
                 4 
                 X 
                 Y 
                 Y 
                 X 
               
               
                   
               
             
          
         
       
     
         [0012]    The marks X in this table refer to a connection of the ports by means of the first set of rotatable pads, while the marks Y relate to connection of the ports by the second set of rotatable pads. 
         [0013]    In a preferred embodiment, there is at least one ridge of conductive material between adjacent stationary pads. Such a ridge may be at the bottom and/or at the top of the housing. The ridge increases isolation between the stationary pads and therefore between the ports. 
         [0014]    Preferably, the movable pads have an arcuately shaped outer contour, which may be limited by a common circle for all movable pads. This way, the movable pads are configured to rotate in close proximity (that is, at a separation distance sufficient to cause a capacitive coupling between the corresponding components and/or to form an RF signal connection between them) to an inner contour (which may be straight or arc shaped) of the stationary pads, which further increases coupling capacitance. 
         [0015]    In a further embodiment, at least one movable pad bridge (which may be the first and/or second pad bridge) is narrower than the least one movable pad. This may result in lower capacitance to ground as the ridges are closer to the bridge than the sidewalls. 
         [0016]    Although a described-above embodiment may be preferred, there may be any other number of ports and/or pads at the rotatable part. 
         [0017]    It is further preferred to have a drive means which may be a motor, preferably a stepping motor or a solenoid, which may further be coupled by means of a gear to the rotatable part. It is further preferred to have a position sensor to indicate the region of certain discrete coupling positions and/or to indicate which coupling position has been reached. There may also be a position indicator which indicates either the individual positions and/or the switching state of the switch. Basically, a switch as mentioned above having four ports has two switching states, as the states 1 and 3 as well as 2 and 4, as shown in the table above, connect the same ports. 
         [0018]    In a further preferred embodiment, the shaft is made of plastic material, although it may also be made of any other non-conductive material, like ceramics. It is further preferred, if a plurality stationary pads form a gap such that the rotatable pads fit in-between with a very low air gap to obtain a maximum coupling capacity. In an alternate embodiment, a plurality of rotatable pads form a gap such that stationary pads fit in-between. In another embodiment there may be any number of rotating or stationary pads which are geared together. To avoid/prevent a galvanic contact between the rotatable and stationary pads, it is preferred to coat the pads with a specific, galvanic-contact-preventing paint (referred to as non-contacting paint), which may for example be an epoxy material. Furthermore, the pads may have an anodized isolating layer, or there may be any plastic material, like a sheet of PTFE in-between the pads. 
         [0019]    In a preferred embodiment, each or at least one pad is in a plane orthogonal to the rotation axis. The planes of different pads may be displaced to each other for allowing the pads to move as described herein. In another embodiment, each pad may be on a circular cylinder surface centered to the rotation axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    In the following, the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment and with reference to the drawings. 
           [0021]      FIG. 1  shows a perspective view of a preferred embodiment. 
           [0022]      FIG. 2  shows a top view. 
           [0023]      FIG. 3  shows a sectional view from the top. 
           [0024]      FIG. 4  shows a sectional side view. 
           [0025]      FIG. 5  shows details of the electrical components. 
           [0026]      FIG. 6  shows further details of the electrical components. 
           [0027]      FIG. 7  shows details of connected rotatable pads. 
           [0028]      FIG. 8  shows further details of connected rotatable pads. 
           [0029]      FIG. 9  shows a full assembly of a preferred embodiment. 
           [0030]      FIG. 10  shows an embodiment with tiltable pads. 
           [0031]      FIG. 11  shows an embodiment with tilted pads. 
           [0032]      FIG. 12  shows an embodiment with tiltable pads in a top view. 
           [0033]      FIG. 13  shows a section of the pads. 
       
    
    
       [0034]    Various modifications and alternative forms can be introduced to the embodiments without the deviation from the scope of the invention. Specific embodiments are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0035]    In  FIG. 1 , a perspective view of a preferred embodiment of a rotary switch is shown. The basic switching function is independent of the specific movement. Therefore, switches may be based on a linear or any other kind of displacement of the pads. A rotary switch  100  comprises a housing  110  for holding and enclosing the electrical components. At the housing, there are a first coaxial connector  121 , a second coaxial connector  122 , a third coaxial connector  123 , and a fourth coaxial connector  124 . For contacting, the coaxial connectors have center conductors. The first coaxial connector has a center conductor  131  (which will be shown later), the second coaxial connector has a center conductor  132 , the third coaxial connector has a center conductor  133 , and the fourth coaxial connector has a center conductor  134  (which will be shown later). The center conductors of the coaxial connectors are connected to respective center conductors of the switch ( 141 ,  142 ,  143 , and  144 ). At the end of the switch center conductors, there are stationary pads, whereas always one primary stationary pad section is combined with a secondary stationary pad section, forming a contact fork. A first primary stationary pad section  151  and a first secondary stationary pad section  161  are connected to the first center conductor  141 . The other stationary pads ( 152 ,  162 ;  153 ,  163 ;  154 ,  164 ) are connected in the same way to their respectively center conductors  141 ,  142 ,  143 ,  144 . For switching, rotatable pads, which will be shown in more detail later, are provided in-between the stationary pads, thus forming a coupling capacitance between the stationary and the rotatable pads. Details of the rotor will be shown and explained in the following Figures. 
         [0036]    In  FIG. 2 , a top view of a first embodiment is shown. Basically, here the same components as in the previous Figure may be seen. Due to the different viewing angle, a first ridge  111 , a second ridge  112 , a third ridge  113 , and a fourth ridge  114 , all at the housing and preferably at the bottom of the housing, supporting a shaft  211  for driving the rotatable pads, are shown. Furthermore or alternatingly, the ridges may increase isolation between the stationary pads, therefore increasing isolation between the ports. There may be a recess  118  and threaded holes  119  for holding and fixing a cover and a drive motor to the unit. 
         [0037]    In  FIG. 3 , a sectional view of the first embodiment is shown. It shows a cut through a plane defined by the rotatable pads. Accordingly, the rotatable pads  221 ,  222 ,  223 ,  224  can be seen clearly. The first rotatable pad  221  and the second rotatable pad  222  are electrically and mechanically connected by a first rotatable pad bridge  225 . The third rotatable pad  223  and the fourth rotatable pad  224  are electrically and mechanically connected by the second rotatable pad bridge  226 . This Figure shows further details of the coaxial connectors and the center conductors of the switch, which previously were mentioned. The center conductors are held by isolators  171 ,  172 ,  173 ,  174 , which preferably comprise a dielectric material, like a plastic material, and most preferably like PTFE or polyethylene. 
         [0038]    In  FIG. 4 , a sectional side view in a plane going through the center of the first center conductor and the third center conductor is shown. Here, the fork-shaped arrangement of the primary stationary pad sections and secondary stationary pad sections can be seen by way of the examples of the primary stationary pad section  151  and first secondary stationary pad section  161  enclosing first rotatable pads  221 . The rotatable parts are driven by a drive shaft  211 , to which a first bridge holder  212  and second bridge holder  213  are attached. There may be at least one bearing, preferably a first bearing  215  at the bottom of the drive shaft, and a second bearing  216  at the top of the drive shaft. To allow easy disassembly of the unit, the drive shaft may comprise several parts. For example, there may be a drive shaft receptacle  214  comprising the lower section of the drive shaft, which is holding the bridge holders and into which an upper section of the drive shaft may be plugged or connected. Furthermore, the drive shaft may be operated by a drive lever  217 . 
         [0039]    In  FIG. 5 , details of the electrical components are shown. Here, the stationary and the rotatable pads can be seen in detail. The rotatable pads may be moved by rotating the drive shaft  211 , as shown by arrow  218 . Although the drive shaft  211  together with the rotatable pads may be continuously rotated about 360°, it is preferred that there are discrete positions in which the rotation is stopped. Such a position is shown in this Figure, where the rotatable pads completely or almost completely overlap with the stationary pads, as this results in a maximum coupling capacitance between the rotatable and stationary pads. The drive shaft defines a rotation axis  219 . The position of the drive shaft and the rotatable pads shown in here is a first switching position. In this first switching position, the first center conductor  141  is connected to the second center conductor  142  via first stationary pads  151 ,  161  coupled to first rotatable pad  221 , further connected via first bridge holder  212  to the second rotatable pad  222 , which is further capacitively coupled to second primary stationary pad section  152  and second secondary stationary pad section  162 . Furthermore, third center conductor  143  is connected to fourth center conductor  144  in a similar way. When rotating the drive shaft  211  for example 90° clockwise, the second center conductor  142  is connected to third center conductor  143 , and fourth center conductor  144  is connected to first center conductor  141 . If the drive shaft and the rotatable pads are further rotated by 90°, again as in the first position first center conductor  141  is connected to second center conductor  142  and third center conductor  143  is connected to fourth center conductor  144 . Here, only the rotatable pads and the corresponding bridges are exchanged, but the function is basically the same. The same applies if the drive shaft rotates for further 90°, which results in a connection scheme of this fourth position, which is the same as in the second position. Rotating the drive shaft by further 90° will result in the first position. 
         [0040]    In  FIG. 6 , further details of the electrical components can be seen, as the stationary parts, like the stationary pads  151  and  152  are removed in this Figure. 
         [0041]    In  FIG. 7 , details of connected rotatable pads are shown. The pads are connected by a second rotatable pad bridge  226 , which may have some holes for fixing the bridge  226  to the second bridge holder  213 . 
         [0042]    In  FIG. 8 , further details of connected rotatable pads are shown. 
         [0043]    In  FIG. 9 , a full assembly of a preferred embodiment is shown. In addition to the previously shown switch components, a drive unit  300  is mounted to the top of the switch. It comprises of a motor housing  310 , which preferably has a position indicator  311 , showing the basic position of the switch, which is either at a first position mark  312  or at a second position mark  313 . There may be a bottom shell  319  which is further mounted to the switch housing and a drive control connector  320  which may provide drive control and position feedback signals to and from the drive unit. 
         [0044]    In  FIG. 10 , an embodiment with tiltable pads is shown. A bridge holder comprises a top section  232  and a bottom section  231 , preferably further connected to the drive shaft receptacle  214 . Both sections hold pad bridge  226  which further holds and connects the third pad  223  and fourth pad  224 . The gap between the top section and bottom section is larger than the thickness of the pad bridge, such that the pad bridge may be displaced and/or tilted. 
         [0045]      FIG. 11  shows the same embodiment as above in a tilted state (dashed lines). There may be elastic spacers  235  between the top section and the pad bridge as well as between the pad bridge and the bottom section. Preferably, the displacement and/or tilt angle are limited. A preferred range of displacement is in a range between 0.05 mm and 0.5 mm, most preferably 0.15 mm in either direction. A preferred angle of tilt is in a range between 0.5° and 5°, most preferably 1.5°. 
         [0046]    In  FIG. 12  a reference drawing is shown. Its indicated section A-A is shown in  FIGS. 10 and 11 . 
         [0047]    In  FIG. 13 , a section of the pads is shown. Movable pad  221  has an arc shaped outer contour  291  matching to the inner contour  191  (which may be straight or arc shaped) of stationary pad  191 . Preferably, there is only a small gap between the movable pad and the stationary pad which results in an increased coupling capacitance. Almost hidden from view below the movable pad  221  is the stationary pad  161 . 
         [0048]    It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide a low PIM switch. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           100  rotary switch 
           110  housing 
           111  first ridge 
           112  second ridge 
           113  third ridge 
           114  fourth ridge 
           118  recess 
           119  threaded hole 
           121  first coaxial connector 
           122  second coaxial connector 
           123  third coaxial connector 
           124  fourth coaxial connector 
           131  first coaxial connector center conductor 
           132  second coaxial connector center conductor 
           133  third coaxial connector center conductor 
           134  fourth coaxial connector center conductor 
           141  first center conductor 
           142  second center conductor 
           143  third center conductor 
           144  fourth center conductor 
           151  first primary stationary pad section 
           152  second primary stationary pad section 
           153  third primary stationary pad section 
           154  fourth primary stationary pad section 
           161  first secondary stationary pad section 
           162  second secondary stationary pad section 
           163  third secondary stationary pad section 
           164  fourth secondary stationary pad section 
           171  first insulator 
           172  second insulator 
           173  second insulator 
           174  second insulator 
           191  arc shaped inner contour 
           211  drive shaft 
           212  first bridge holder 
           213  second bridge holder 
           214  drive shaft receptacle 
           215  first bearing 
           216  second bearing 
           217  drive lever 
           218  rotation of drive shaft 
           219  rotation, center axis 
           221  first rotatable pad 
           222  second rotatable pad 
           223  third rotatable pad 
           224  fourth rotatable pad 
           225  first rotatable pad bridge 
           226  second rotatable pad bridge 
           231  bridge holder top section 
           232  bridge holder bottom section 
           235  spacers 
           291  arc shaped outer contour 
           300  drive unit 
           310  motor housing 
           311  position indicator 
           312  first position mark 
           313  second position mark 
           319  bottom shell 
           320  drive control connector