Abstract:
A cable plug for a coaxial cable, in particular comprising an external corrugated conductor, comprises an electrically conductive housing, which concentrically surrounds an insulated internal conductor, in addition to fixing elements which are used to connect the external conductor of the coaxial cable electrically and mechanically to the housing of the cable plug. The cable plug permits a particularly simple configuration and assembly. To achieve this, the fixing elements ensure a fixed and sealed connection between the external conductor of the coaxial cable and the housing of the cable plug.

Description:
BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The present invention relates to the field of plug-in connector technology for coaxial cables and to a method for fitting such a cable plug. 
   2) Description of Related Art 
   Coaxial cables, as are used nowadays, for example, in the sector of base stations of mobile radio networks, have, in a concentric arrangement, an inner conductor and an outer conductor, which are insulated from one another by a dielectric lying therebetween. The outer conductor is generally surrounded by a protective outer sheath consisting of plastic. The outer conductor of a coaxial cable can be in the form of metallic braiding (at frequencies which are not too high). However, it can also be in the form of a continuous tube. If an increased flexibility of the cable is not required, the tube of the outer conductor may have smooth walls. In order to achieve increased flexibility, corrugated tubes or hoses consisting of metal are generally used as the outer conductor, it being possible for the corrugations to either be separated annularly or continuously helical. 
   In many cases it is desirable to provide detachable connections for such coaxial cables in order to simplify fitting and maintenance. For this purpose, a large number of cable plugs have been developed and proposed in the past which differ from one another in terms of cable type and fixing concept. In principle, such a cable plug needs to fulfill the following requirements:
         The cable plug needs to produce good electrical contact between the plug housing, which generally forms the outer conductor within the plug, and the outer conductor of the cable.   The cable plug needs to ensure a mechanical connection having a high tensile strength between the plug housing and the outer conductor of the cable in order to ensure that the plug-in connection can be subjected to a sufficient mechanical load.   The cable plug, in particular if the plug-in connection—as in the case of base stations—is subjected to weathering influences, needs to adjoin the outer sheath of the coaxial cable in a sealing manner in order to prevent the ingress of moisture, dirt and other influences on the interior of the cable.   Other, constant requirements relate to a simple design, fitting which is as simple as possible and cost-effective manufacture and storage.       

   A known cable plug which is suitable in particular for coaxial cables having an outer conductor with annular corrugations is illustrated in longitudinal section in  FIG. 1 . The cable plug  10  has a housing  18 , which acts as the outer conductor and in which an inner conductor  16  is held concentrically and in electrically insulated fashion by means of an insulator  15 . A union nut  11  is fitted such that it can be rotated on the plug-in side end on the housing  18  by means of a snap ring  13 , with which union nut the cable plug  10 , once it has been inserted into a corresponding female connector, can be screwed to the female connector. For guidance purposes during the insertion, an annular insert  14  is provided around which a seal  12  is arranged. On the cable side of the cable plug  10 , the inner conductor  16  merges with a seal  21 , which rests in an inner conductor  19  and produces the electrical contact with the inner conductor of the coaxial cable (not illustrated). The cable-side screw connection, which is used for contact-making, retaining and sealing purposes, comprises a large number of different parts: in order to make contact with and retain the outer conductor of the coaxial cable, a contact sleeve  24  is provided which is split into individual, radially sprung tongues by axially running slits  23  arranged distributed over the circumference. The contact sleeve  24  has, on the plug-in side, an edge which thickens in the form of a bead inwards and with which the contact sleeve  24  bears against a circumferential projection  22  shaped in the interior of the housing  18 . A flanged edge of the outer conductor of the cable is clamped in between the bead-shaped edge of the contact sleeve  24  and the projection  22  during fitting in order to produce the electrical contact between the housing  18  and the outer conductor and to mechanically fix the cable. The fixing of the outer conductor is illustrated in detail, for example, in the figures of EP-A2-0 901 200. 
   The contact ring  24  is pressed in clamping fashion against the projection  22  by means of a first hollow screw  20 , which can be screwed into the housing  18 . At the same time, in order to provide sealing between the first hollow screw  20  and the housing  18 , an inner seal  17  is compressed. In order to provide sealing between the first hollow screw  20  and the outer conductor of the cable, a further seal  25  is provided which surrounds the outer conductor and is pressed radially inwards against the outer conductor by being compressed axially by means of a further hollow screw  26 . Finally, a further seal  17 ′ is provided in the second hollow screw  26 , which further seal  17 ′ provides sealing with respect to the outer sheath of the cable. 
   Owing to the various screw connections and seals, the design and fitting of the known cable plug shown in  FIG. 1  are complicated and laborious. One of the reasons for these disadvantages can be found in the contact sleeve  24 : the contact sleeve  24  could in principle, if it were to be in the form of a sleeve without slits, press the flanged edge of the cable outer conductor against the projection  22  uniformly over the entire circumference and therefore not only produce the necessary electrical and mechanical contact but at the same time also take on the sealing function for the outer conductor with respect to the housing. Further seals may therefore not be required and it would be possible to implement a significantly simplified cable plug which can be fitted more easily. However, the contact sleeve  24  has slits, since it is necessary for the contact sleeve  24 , in the case of a cable having an outer conductor with annular corrugations, to be capable of being pushed onto the outer conductor, on the one hand, despite the corrugation and, on the other hand, to dip into the first corrugation trough with the beaded edge behind the flanged conductor edge in order to press the conductor edge safely against the projection  22 . Such configurations are not only known from EP-A2-0 901 200, but also from U.S. Pat. No. 4,046,451 or EP-A1-0 938 165. 
   A slightly different situation results if the coaxial cable has a corrugated outer conductor with a helical corrugation, as is the case in documents EP-A1-0 599 602 or U.S. Pat. No. 5,518,420 or U.S. Pat. No. 6,032,358. Here, in principle a closed sleeve, i.e. one without slits, can be used as the contact sleeve and has a thread structure, which matches the helical corrugation of the outer conductor, on the inner side and can be screwed onto the outer conductor like a nut. Even in this case, sealing is not obviously considered at the flanged edge of the outer conductor since, in all cases, additional sealing means such as O rings or the like are provided in order to seal the cable plug off towards the outside. 
   SUMMARY OF THE INVENTION 
   The object of the invention is therefore to provide a cable plug for a coaxial cable, in particular having an outer conductor with annular corrugations, which avoids the disadvantages of known cable plugs and is characterized in particular by a simplified, cost-effective design and simplified fitting, as well as to specify a method for fitting said cable plug. 
   The essence of the invention consists in designing the fixing means for fixing the cable outer conductor to the cable plug such that, with the fixing, at the same time a sealing connection is produced between the outer conductor of the coaxial cable and the housing of the cable plug. As a result, it is possible to dispense with further sealing means and additional screw connections, and a particularly simple cable plug which can be fitted easily and is also suitable in principle for all types of cable outer conductors results. 
   One preferred configuration of the invention is characterized by the fact that the fixing means comprise a sealing and clamping ring, which is pushed over the end of the outer conductor of the coaxial cable and, with an annular, first sealing face, presses an edge at the end of the outer conductor in a sealing manner against a continuous and annular, second sealing face, which is arranged in the housing of the cable plug, and that the sealing and clamping ring is arranged and guided axially within the housing. 
   In order to actuate the sealing and clamping ring, provision is advantageously made for the fixing means to further comprise a screw element, which can be screwed to the housing of the cable plug and, when it is screwed to the housing, exerts an axial force on the sealing and clamping ring. The screw element is in particular in the form of a nut or hollow screw, which has a pressure ring on the inside, with which it dips into the housing when screwed and presses onto the sealing and clamping ring in the axial direction. 
   In order that the sealing and clamping ring can be used without any problems in all types of corrugated and uncorrugated outer conductors, it is advantageous that the sealing and clamping ring is designed to be closed annularly, that the sealing and clamping ring has a conically tapering ring section towards the sealing side, that a corresponding conical guide face is arranged in the housing, on which guide face the sealing and clamping ring is guided with its conical ring section towards the axis, that the first sealing face is designed to be continuous, and that the two sealing faces are oriented essentially at right angles to the conical guide face. 
   The deformation of the sealing and clamping ring during screwing is facilitated if the sealing and clamping ring is cylindrical on the side facing away from the sealing side and has a ring section with a reduced wall thickness in the cylindrical part, adjacent to the conical ring section. 
   The sealing and clamping ring may consist of a metallic material, in particular of stainless steel. However, it may also consist of a plastic or a composite material. 
   The production of the cable plug is simplified if the second sealing face and possibly the conical guide face are formed on a metallic adjusting ring, which is inserted into the housing of the cable plug and is in electrical contact with the housing. 
   A configuration of the cable plug in accordance with the invention which is an alternative to the closed sealing and clamping ring is characterized by the fact that the sealing and clamping ring is designed as an open ring provided with a split or designed to comprise a plurality of ring segments. It can therefore be pushed over the corrugations of the outer conductor without any difficulties in the slightly open state and, after closing, can be fixed axially in a simple manner in a corrugation trough. Owing to the opening split, much less severe forces are required for the clamping and sealing in order to press the end of the outer conductor with a radial component against the corresponding sealing face. 
   Preferably, the fixing means further comprise a screw element, which can be screwed to the housing of the cable plug and, when screwed to the housing, exerts an axial force on the sealing and clamping ring, means for guidance being provided on the sealing and clamping ring and on the screw element and preventing the sealing and clamping ring from tipping. 
   In particular, the guide means comprise a v-shaped guide groove in the front face of the screw element and a v-shaped edge contour, which matches said guide groove, on the sealing and clamping ring. 
   The sealing and clamping ring may be essentially cylindrical. In this case, it preferably has a circumferential annular bead on the inside, with which annular bead it presses the outer conductor against the second sealing face. The use of the sealing and clamping ring is further simplified if it is designed to be mirror-symmetrical with respect to a central plane passing through the annular bead. 
   However, the sealing and clamping ring may also be conical. 
   In the method according to the invention, the flanged edge can be clamped in in particular by means of a screw connection. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail below with reference to exemplary embodiments in connection with the drawing, in which: 
       FIG. 1  shows a longitudinal section through a cable plug for cables with a corrugated outer conductor in accordance with the prior art; 
       FIG. 2  shows a longitudinal section through a cable plug in accordance with a preferred exemplary embodiment of the invention; 
       FIG. 3  shows, partially sectioned, the adjusting ring of the cable plug from  FIG. 2 ; 
       FIG. 4  shows, partially sectioned, the sealing and clamping ring of the cable plug from  FIG. 2 ; 
       FIG. 5  shows the cable plug from  FIG. 2  with a cable having an outer conductor with annular corrugations, shortly before the screwing process; 
       FIG. 6  shows a simplified longitudinal section through another preferred exemplary embodiment of the invention with an open (split) sealing and clamping ring of the type illustrated in  FIG. 7 ; 
       FIG. 7  shows, in various subfigures  7 ( a )-( c ), the sealing and clamping ring from  FIG. 6 , in section ( FIG. 7   a ), in a front view ( FIG. 7   b ) and in the fitted state on the end of the outer conductor ( FIG. 7   c ); and 
       FIG. 8  shows a simplified longitudinal section through a further preferred exemplary embodiment of the invention with an open (split) sealing and clamping ring, which is conical. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference to  FIG. 2 , a preferred exemplary embodiment of a cable plug according to the invention is reproduced. The cable plug  30  comprises a housing  33 , which concentrically surrounds an inner conductor  31 , which is held in insulated fashion e housing by means of an insulator  32 . In turn, a union nut  27  is fixed with the aid of a snap ring  29  such that it can be rotated at the plug-in side end of the housing  33 . For sealing purposes in interaction with the female connector, a seal  28  is provided. In order to fix, make contact with and seal the outer conductor of the coaxial cable, a screw connection is provided which comprises three elements, namely an adjusting ring  34  consisting of metal, for example brass, which is inserted into the housing  33  and is supported on a shoulder at the level of the insulator  32 , a sealing and clamping ring  35  and a nut  36 . The nut  36  can be screwed onto the housing  33  at the cable-side end, the cable being guided through a central through-hole in the nut  36 . A pressure ring  37  is formed in the interior of the nut  36 , dips into the central hole in the housing  33  when the nut  36  is screwed onto the housing  33  and presses on the cable-side ring face of the sealing and clamping ring  35 . 
   The adjusting ring  34  and the sealing and clamping ring  35 , which are illustrated individually in  FIGS. 3 and 4 , form, with their mutually assigned sealing faces  39  and  42 , a clamping mechanism, which clamps the flanged edge  52  on the outer conductor  50  of an introduced coaxial cable  47  in when the cable plug  30  is screwed (see  FIG. 5 ). In order that the sealing and clamping ring  35  can be pushed over the corrugations of an outer conductor  50  with annular corrugations without any problems (as is shown in  FIG. 5 ), but at the same time can also engage safely behind the flanged edge  52  when screwed together, it comprises a plurality of ring sections  43 ,  44  and  45 , of which the plug-in side ring section  43  tapers conically in the plug-in direction and the two other ring sections  44  and  45  are cylindrical. A corresponding conical guide face  41  on the adjusting ring  34  lies opposite the conical ring section  43  and causes the conical ring section  43  to be increasingly narrowed when the cable plug  30  is screwed and therefore when the sealing and clamping ring  35  is inserted into the housing  33 . This narrowing results in the sealing and clamping ring pressing an edge of the outer conductor  50  of sufficient width against the sealing face  39  on the adjusting ring  34  and therefore ensuring reliable sealing. 
   In order to make safe clamping possible in the case of a conically widened flanged edge  52  and the inwardly directed narrowing movement of the sealing and clamping ring  35 , the two sealing faces  39  and  42  on the adjusting ring  34  and the sealing and clamping ring  35 , respectively, are oriented essentially at right angles to the conical guide face  41 . Since the two sealing faces  39 ,  42  form closed, uniform rings, the flanged edge  52 , which is clamped in between the two sealing faces  39 ,  42 , acts as a metallic sealing ring. 
   The sealing and clamping ring  35 , as a closed ring (without any slits), is subjected to considerable mechanical loads during screwing owing to the narrowing associated therewith. It therefore needs to be produced from a suitable material in order to withstand these loads. In particular, the material of the sealing and clamping ring  35  should also be selected such that as few intermodulations as possible occur within the cable plug  30  on signal transmission. A metallic material such as, for example, aluminum or in particular stainless steel (V2A, material No. 4301) has proven successful. However, it should be nonmagnetic in order not to negatively influence the conduction properties in the cable plug. However, other materials such as plastics or composite materials can also be used. Such a suitable composite material is, for example, a PTFE filled with small metal particles. The sealing and clamping ring  35  can additionally be coated in order to make it subject to as little friction as possible. 
   When fitting the cable plug  30  shown in  FIG. 5 , first the nut  36  is pushed over the coaxial cable  47 . Then, the sealing and clamping ring  35  is pushed over an exposed end of the outer conductor  50  of the coaxial cable  47 . 
   Subsequently, the edge at the end of the outer conductor  50  is flanged on the outside to form a flanged edge  52 . Then, the cable is inserted with the exposed inner conductor  48  into the female connector part, which has slits, of the inner conductor  31  in the cable plug  30 . Finally, the nut  36  is screwed onto the housing  33  until the flanged edge is clamped in uniformly around the circumference between the two sealing faces  39 ,  42  in a sealing and retaining manner and in a manner providing electrical contact. An exposed section of the dielectric  49  of the cable is in this case accommodated by the adjusting ring  34 . Towards the rear out, the coaxial cable  47  can additionally be sealed by a sealing ring, which is introduced into a corresponding annular groove  38  in the nut  36 . 
   The sealing clamping of the flanged edge  52  in the cable plug  30  shown in  FIG. 5  is not restricted to coaxial cables having an outer conductor with annular corrugations, but can also be used in cables having an outer conductor with helical corrugations or in cables having a straight, tubular outer conductor, with the result that, on top of the advantageous simple design and simple fitting, a single plug type can be used for many types of cable. Even in the case of cables with a braided outer conductor, corresponding clamping can be achieved with the novel cable plug without, however, it being possible for sufficient simultaneous sealing to be ensured. 
   The previously explained exemplary embodiment shown in  FIGS. 2-5  was based on a closed sealing and clamping ring, which, owing to its constant inner diameter is not only subject to restrictions when pushed onto the outer conductor of the coaxial cable but also requires considerable forces during the clamping and sealing. 
   An improvement in this respect can be achieved if, in the context of the invention, a sealing and clamping ring is used which is not completely closed but is open, i.e. is provided with a slit or a split at least at one point, or overall comprises a plurality of independent ring segments. Owing to the design as an open ring, the inner diameter of the sealing and clamping ring can be enlarged by being bent up temporarily so as to facilitate the procedure for pushing it onto the outer conductor, with the result that the sealing and clamping ring can then be pushed over the corrugations of the outer conductor without any effort. Once it has been pushed on, the inner diameter can be reduced in size again by being bent together. The sealing and clamping ring then assumes, for example, a position between two adjacent corrugations which is secured against being axially displaced. 
   A first exemplary embodiment for a cable plug with an open sealing and clamping ring is reproduced in  FIGS. 6 and 7 , in which case no hatching of the sectioned parts has been provided. The cable plug  60  in  FIG. 6  has a similar design to the cable plug  30  from  FIG. 5 . A housing  56  coaxially surrounds an inner conductor  53 , which is retained in insulated fashion in the housing  56 . A union nut  55  is provided for the plug-in connection, and an annular seal  54  is used for sealing the plug-in connection. From the opposite side, the end of a coaxial cable  65  having a corrugated outer conductor  61  and a surrounding outer sheath  64  is inserted into the cable plug  60 . The connection of the inner conductor of the coaxial cable  65  to the inner conductor  53  of the cable plug  60  is not illustrated in  FIG. 6 . 
   For the sealing clamping of the outer conductor  61  in the housing  56 , an open sealing and clamping ring  58  (with slits or splits) is provided which is illustrated individually in  FIG. 7 . The metallic sealing and clamping ring  58  is essentially cylindrical. It is mirror-symmetrical with respect to a central plane  74  at right angles to the ring axis. In the central plane  74 , an inwardly protruding, circumferential annular bead  68  is integrally formed on the inner side of the sealing and clamping ring  58 , which annular bead, when the screw connection  59 ,  63  is tightened, presses the outer conductor  61  in sealing and clamping fashion against a sealing face  57 , which is formed slightly conically on the housing  56 . Since the sealing and clamping ring  58  is provided with a radial split  69  ( FIG. 7   b ), it can be compressed comparatively easily when the cable plug  60  is screwed whilst reducing the size of the inner diameter and therefore produces the required contact pressure for the outer conductor  61 . 
   The screw connection comprises a hollow screw  63  (with an inner sealing groove  62 ) and a corresponding thread arrangement  59 . The hollow screw  63  has a v-shaped guide groove  73  on the front end facing the sealing and clamping ring  58 , which guide groove accommodates a corresponding v-shaped edge contour  66 ,  67  on the sealing and clamping ring and thus guides the sealing and clamping ring  58  during the screwing and prevents it from tipping. The sealing and clamping ring  58  enters axially into a corresponding bore in the housing  56 , which is delimited towards the inside by the conical sealing face  57 . The annular bead  68 , which fixes the sealing and clamping ring  58  at the same time in a corrugation trough of the outer conductor  61  (see also  FIG. 7   c ), presses the outer conductor  61  in sealing and clamping fashion inwards against the sealing face  57 . 
   A slightly different configuration of the open sealing and clamping ring is implemented in the cable plug  70  from  FIG. 8 . The sealing and clamping ring  72  in this case has a conical shape, with which the ring, with its front end, presses the outer conductor  61  in sealing and clamping fashion against a corresponding sealing face  71 . 
   The open sealing and clamping ring has the following features and advantages:
         The sealing and clamping ring has splits and makes sealing possible owing to the guidance in the housing of the cable plug.   With the open sealing and clamping ring, the sealing is brought about virtually without any complexity in terms of deformation. The force used is conducted directly and without losses to the sealing faces from the outer conductor.   Owing to the reduced expenditure of force, a reduction in the physical length of the cable plug of up to 25% is possible.   The sealing and clamping ring can be reused up to 30 times, since it does not become plastically deformed.   The sealing and clamping ring is so far open that it can be pushed over the corrugations of the outer conductor without any problems.   Even during the insertion into the housing, the ring is so far closed that it can no longer slide out of the corrugation of the outer conductor.   The v-shaped guide on the nut prevents the ring from tipping.