Abstract:
An improved radio-frequency or network connection including a basic module having two or more basic signal coupling surfaces, and a network module having two or more network signal coupling surfaces. The basic module has a basic ground coupling surface, and the network module has a network ground coupling surface. In the operating state, the basic ground coupling surface is capacitively RF coupled to the network ground coupling surface, and is aligned parallel thereto.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
   Not applicable 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not applicable. 
   FIELD 
   The technology herein relates to a radio-frequency connection and to a radio-frequency distribution network. 
   BACKGROUND AND SUMMARY 
   Particularly for antenna design purposes—but not only there—difficulties in some cases occur in providing links or connections without any intermodulation. This problem occurs in particular at interfaces to which different assemblies are intended to be connected, as required. 
   Radio-frequency connections between two radio-frequency assemblies, for example between a radio-frequency board and a wire-free transmission device, for example antennas, are normally provided by means of coaxial connection techniques. However, disadvantageous and undesirable intermodulation can also occur here. Improvements to avoid or to reduce passive intermodulation when using coaxial plug connections have been proposed, by way of example, in U.S. Pat. No. 6,414,636 B1. However, if the aim, for example, is to connect a specific distribution network for a so-called smart antenna, as is known in principle from U.S. Pat. No 6,463,303 B1, in order to produce a specific polar diagram characteristic for the antenna under discussion, then the costs for a module which can be connected in such a way furthermore also rise considerably if all the connections on the input and output side are in the form of coaxial plug connections. 
   Thus, in principle, it would also be possible to provide capacitive connections instead of coaxial plug connections. 
   Capacitive RF connections have been disclosed, for example, in U.S. Pat. No. 5,812,037. These have a stripline filter coupling structure, which operates capacitively. 
   A PCMCIA signal connector, as is normally used for Notebook Computers, has in principle been disclosed in U.S. Pat. No. 5,936,841. The PCMCIA plug-in board normally has a male connector strip on one of its end faces, which interacts with a male connector strip which is integrated in the Notebook, when the corresponding PCMCIA board is inserted into a holding slot in the Notebook. A first electrically conductive layer, which represents one half of the RF coupling device, is then provided on one of the large side surfaces, parallel to this side surface. The second electrically conductive layer, which is parallel to the first, is accommodated with a lateral offset in the interior of the apparatus. There is an air gap (resulting from the lateral distance between the PCMCIA board and the adjacent inner boundary surface of the plug-in slot for the electrical apparatus, for example in the form of Notebook) and dielectric intermediate layer, which is part of the wall of the Notebook, between the two conductive layers of the RF coupling structure which are parallel to one another. 
   However, the undesirable intermodulation cannot be avoided even by means of a capacitive RF connection for a PCMCIA board such as this. 
   The object of the exemplary illustrative non-limiting technology described herein is thus to produce a radio-frequency connection and, in particular, a radio-frequency distribution network, which can be connected as required to an interface that is provided, with the aim of largely avoiding or precluding intermodulation. 
   The production of a floating radio-frequency connection at an appropriate interface allows a modular link without any intermodulation, for example between an RF network and a basic module. In this case, not only the signal lines which carry the signal but also the outer conductors or earth conductors are capacitively connected to one another at the corresponding contact devices, while avoiding any conductive contact. The nature of the interface in the form of the capacitive coupling via an interface with contacts has the major advantage of a low level of intermodulation, as is actually of major importance for mobile radio applications, such as mobile radio antennas. If very strong intermodulation products occur in the transmission frequency band, and whose frequencies extend into the reception frequency band, it would no longer be possible for mobile devices such as mobile telephones to receive weak signals at these reception frequencies. 
   The fact that a modular link between an RF network having two or more connections or connecting points to an RF device, for example a mobile radio antenna, can be achieved without any intermodulation on the basis of this principle is in this case surprising for a number of reasons. This is because it would necessarily have been presumed that, when forming corresponding coupling surfaces running parallel to one another and on which the respective RF signal is intended to be transmitted, or else for producing the floating earth connection, further influences would be noticeable which would make it impossible to produce an RF coupling connection which could always be reproduced unambiguously. This is also due to the fact that, especially when using mobile radio antennas or transmission antennas, it is absolutely essential to use a metallic housing for screening purposes. However, metallic housings fundamentally have effects on the electrical conditions and characteristics if capacitive coupling devices are used in the interior of the screened housing. This is because, in some circumstances, the distance between the coupling surfaces and the screening housing results in an additional parasitic parallel capacitance between the coupling surfaces and the electrical earth. 
   However, an exemplary illustrative non-limiting design of the RF connecting device also makes it possible to minimize these effects and influences. 
   The geometry of the coupling surfaces governs the electrical parameters for signal transmission, such as the matching to the characteristic impedance (VSWR), the insertion loss and the bandwidth of the frequency band. In order to improve fine tuning further, one preferred development of the exemplary illustrative non-limiting implementation also provides, for example, for the coupling surface on a board that is used to be provided with “small tabs” or so-called “extension surfaces”, which project at the sides. These small tabs or extension surfaces, in parallel with the coupling between the coupling surfaces, produce an additional small amount of coupling between the coupling surfaces on a board and an earth surface. 
   The exemplary illustrative non-limiting network module, which can be coupled to a basic module, furthermore has capacitively coupled earth surfaces, in addition to the coupling surfaces which provide capacitive RF coupling, in order to suppress the intermodulation-free modular link. This metal structure, which covers the board, is preferably formed on the face on which the corresponding electrical earth surfaces of the basic module are located. In this case, an insulating film with a predefined thickness is preferably used for insulation between the two electrical earth surfaces which produce the earth coupling. The coupling surfaces of the electrical earth surfaces which provide the signal transmission and which in some cases are also referred to in the following text as coupling fingers are in contrast to this preferably formed on the opposite face of the board of the network module, so that the substrate of the board acts as insulation for the corresponding signal coupling surface on the basic module. 
   The radio-frequency network on said board may, for example, be based on stripline technology (microstrip technology). 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative implementations in conjunction with the drawings of which: 
       FIG. 1  shows a schematic perspective partial view of an exemplary illustrative non-limiting mobile radio antenna with two basic module devices which can be plugged in and withdrawn on the lower face, and which are each suitable for holding one network module; 
       FIG. 2  shows a schematic illustration of an exemplary basic design of the basic module and of the network module, producing a floating RF connection; 
       FIG. 3  shows a schematic perspective illustration of an exemplary basic module and of the network module, in order to explain the floating RF coupling; 
       FIG. 4  shows a schematic plan view, in the form of an extract, of interacting coupling surfaces on the basic module and on the network module. 
       FIG. 5  shows an illustration, corresponding to  FIG. 3 , in order to explain a different connection mechanism between the two modules; 
       FIG. 6  shows a schematic perspective illustration, in the form of an extract, of an exemplary basic module and of a network module, as an exploded view; 
       FIG. 7  shows a schematic cross-sectional illustration through the exemplary implementation shown in  FIG. 5 , in the assembled state; and 
       FIG. 8  shows an enlarged detail illustration from the cross-sectional illustration shown in FIG.  6 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  shows a schematic perspective illustration, in the form of an extract, of a mobile radio antenna  1 , of a base station. This extract shows the housing cover of the antenna device, namely the so-called radon  3 . Overall, the antenna is held in position via an antenna mast  5 . A slotted opening is provided on the lower face  7  of the housing cover  3 , into which two basic modules  9  can be pushed, parallel and independently of one another, and which each interact with two interchangeable network modules  11 . 
   Specific network components and network circuits, for example based on stripline technology, are provided on the network modules  11  so that the use of an appropriately matched network module  11  results in the antenna having a specific polar diagram characteristic. The explained network modules  11  are thus used to produce a specific polar diagram characteristic for a so-called smart antenna, as is described, by way of example, in the U.S. Pat. No. 6,463,303 B1 or in the PCT publication WO 01/59 876 A1. For example, it is thus possible to use one module for transmission and reception in a first polarization direction, and the second module for reception and for transmission in a second polarization direction. However, the modules may also be used for transmission in different frequency bands. It is also possible, for example, to use two modules in such a way that one module is used for transmission and the other for reception. Depending on the requirements, two or more basic modules and associated network modules may thus also be provided in one antenna. 
     FIG. 2  shows a schematic configuration of an interacting pair of modules, to be precise with a basic module  9  and a network module  11 . Just two signal lines  13  and two earth lines  15  are in this case used to show how the respective network module  11  is coupled in a completely floating manner via an appropriate RF connection  17  to the relevant basic module  9 . 
   The respective earth potential GND 1  is in this case applied only to the basic module  9 , and the earth potential GND 2  is applied only to the network module. In this case, appropriate floating connections are provided between the basic module  9  and the network module  11  via one or more signal paths  14  and  16 . 
   FIG.  3  and  FIG. 4  will now be used to describe the schematic basic configuration of the two modules in greater detail. 
   In principle, the basic module  9  comprises an electrically screened base plate or base  21 , which is generally composed completely of metal. This electrically conductive base  21  is provided with recesses or windows  23 , in which electrically conductive basic signal coupling surfaces  25  are formed. These basic signal coupling surfaces  25  are isolated from the electrically conductive base  21  by means of in each case one circumferential gap  26 , or some other isolation, with the electrically conductive base  21  forming a basic earth coupling surface  27  adjacent to the basic signal coupling surface  25 . In the exemplary illustrative non-limiting arrangement illustrated in  FIG. 3 , three connection points  29  are shown on the base, to each of which a coaxial conductor  31  leads, with the inner conductor  31   a  of each coaxial conductor  31  being soldered to the basic signal coupling surface  25 , and the associated outer conductor  31   b  being electrically conductively connected, by means of a stripped area on the outer circumference, via a corresponding soldered joint  31   c  to the basic earth coupling surface  27 . 
   The corresponding network module  11  has a board  35  with an associated substrate  35 ′, on which connection points  129 , which correspond to the base, are formed on the network module  11  via the connection points  29 . 
   The connection points  129  on the network module  11  comprise network signal coupling surfaces  125  which, in the illustrated exemplary illustrative non-limiting arrangement, likewise have a rectangular shape, that is to say they are comparable to the respective shape of the basic signal coupling surfaces  25 . 
   The network signal coupling surface  125  is connected via a respective stripline  37  to a network  39 , which is indicated only schematically in FIG.  3  and represents an RF assembly. This is preferably provided and formed on the top face  35   a  of the board  35 , that is to say on the face of the board  35  that is opposite the base which interacts in this way. 
   Furthermore, the network module  11  also has a large-area earth coupling surface, namely a network earth coupling surface  127 , which, in the illustrated exemplary implementation, is, however, not on the same side of the board  35  on which the connection points  129  are also provided, but is formed on its lower face. In the illustrated exemplary non-limiting implementation, the electrically conductive network earth surface  127  is at least approximately rectangular in shape, and its circumferential boundary line  129 ′ extends into the immediate vicinity of the connection points  129 . During operation, the board  35  is moved towards the base as indicated by the arrows  41 , and is positioned, to be precise with the interposition of an electrically insulating intermediate layer, preferably in the form of an insulating film  43 , whose size and shape correspond to or are slightly larger than the network earth coupling surface  127 . This means that there is no possibility of the network earth coupling surface  127  making contact with the basic earth coupling surface  27 , producing an electrically conductive connection. The use of an insulating film  43  with a predetermined thickness also produces a precisely defined separation between the basic earth coupling surface  27  and the network earth coupling surface  127 , so that clearly reproducible electrical conditions can be produced. 
     FIG. 4  shows a schematic plan view corresponding to the layers of the earth coupling surfaces and of the insulating film, as well as of the network earth coupling surface  127  in relationship to the basic earth coupling surface  27  which is located underneath it. This also shows that the basic earth coupling surface  27  may, for example, be designed to be physically larger both in the longitudinal direction and in the transverse direction than that in the network earth coupling surface  127 . For fine tuning, provision is also made in this case for the network coupling surfaces  127  to have the capability to be provided with small tabs or extension sections  127 ′ which project at the sides, with this resulting, in the illustrated exemplary illustrative non-limiting implementation, in a cruciform structure, although this is not absolutely essential. These small tabs or extension sections  125 ′ provide an additional small amount of coupling between the coupling surfaces  125  on the board  35  and the basic earth coupling surface  27 , in parallel with the coupling between the coupling surfaces  25 ,  125 . The reason for this is the short distance between these small tabs or extension sections  127 ′ and the basic earth coupling surface  27  compared with the distance between the network signal coupling surface  125  and the basic earth coupling surface  27 . 
   In the assembled position, in which, as explained, the board  35  rests on the base  21 , the desired clear relationships are reproduced. This can be produced, for example, by means of a sliding mechanism which allows the network module  11  together with the board  35  to be moved to the desired clear relative position with respect to the basic module  9 , and to be held and to be fixed in this position. 
     FIG. 5  will be used only to show that, for example, a type of tilting mechanism can also be provided instead of a sliding mechanism (which, for example, has two groove holders on opposite sides, into which the board  35  can be pushed). A tilting holder  45  which, schematically, is in the form of a U-shaped recess is used in the exemplary illustrative non-limiting implementation shown in  FIG. 5 , into which one boundary edge  35 ″ of the board  35  is pushed, so that the board  35  can then be pivoted about the tilting axis formed in this way onto the base  21 , until the board  35  is resting on the base  21  with the insulating film  43  which has been mentioned being positioned between them. 
     FIGS. 6  to  8  will now be used to explain one possible configuration of the basic module  9  and of the network module  11  with further details, although the fundamental principle remains unchanged. 
   In the exemplary illustrative non-limiting arrangement shown in  FIGS. 6  to  8 , the base  21  is formed with a cross section in the form of a U-shaped electrically conductive metal sheet, which is short in height and is provided with flanges  21 ′ on opposite sides. 
   One or more coaxial cables  31  are fed to the basic module  9  from each side in the area of the flange sections  21 ′, with the individual coaxial conductor sections or coaxial conductors  31  being passed to the basic signal coupling surfaces  25 , as already explained. The outer conductor  31   b  of each coaxial conductor  31  in this case makes electrical contact with the electrically conductive base  21  on the side limbs of the U-shaped base  21 , for example by means of an electrical soldered joint, with the inner conductors  31   a  of the coaxial conductors  31  passing through these side sections  21 ″ and being soldered to the respective basic signal coupling surfaces  25  via an electrical soldered joint. 
   These basic signal coupling surfaces  25  are electrically isolated from the basic earth coupling surface  27  by means of a circumferential isolating gap  26 . In other words, the basic signal coupling surfaces  25  are formed in an appropriately physically large window  23 , so that the isolating gap  26  is formed between the basic signal coupling surfaces  25  and the basic earth coupling surfaces  27 . 
   Finally, a screening wall  49  is provided on the lower face of the base  21 , in order to produce an overall screen. A further screening wall  50  is fitted from above onto the basic module  9  formed in this way, as part of this basic module  9 , and these items can then be screwed to one another by the use of screws in holes  51 . The upper screening wall  50  in this case likewise has a U-shaped cross section with projecting flange sections  50 ′ and side limbs  50 ″, with corresponding slotted recesses  52  being incorporated in the vertical limb section  50 ′ in the area of the supplied coaxial cables and coaxial conductors  31 . 
   The basic module  9  that has been explained is thus used for holding a network module  11 , which is illustrated in exploded form in FIG.  6 . 
   In addition to the already explained board  35  and the network  39  located on it, the network module  11  also has a surrounding housing  53 , whose wall sections  53 ′ are seated on the external circumference of the board  35  and are connected to it, to be precise producing an internal area  55  in which, as explained, the appropriate assemblies and cables for producing the network  39  can be formed and provided on the board  35 . 
   The cross-sectional illustration shows that the network signal coupling surfaces  125  are located directly above the basic signal coupling surfaces  25 , with the material of the printed circuit board, that is to say the substrate  35 ′, forming the insulation between the network signal coupling surface  125  and the basic signal coupling surface  25 . The basic signal coupling surfaces  25  are in this case electrically conductively connected via a connection section  25 ′, which runs downward, to the inner conductor  31   a , which projects on it, of an associated coaxial conductor  31 , for example via a soldered joint. 
   As can also be seen from the cross-sectional illustration, an electrically insulating support  59 , which is shown in  FIGS. 7 and 8  and is in the form of a spacer, is also provided, on which on the one hand the electrical earth, that is to say the basic earth coupling surface  27 , rests, and on the other hand the basic signal coupling surface  25  also rests. Since the signal coupling surface  25  has a thinner material cross section than the basic earth coupling surface  27 , the said spacer  59  is thus designed in a stepped form. In order to ensure a unique adjustment seating, recesses or, for example, holes  61  are provided, located offset directly inwards, with respect to the boundary edge of the window-like recesses or of the isolating gap  26 , in which the spacer  59  projects into this recess or hole  61 , with a section  59 ′ which projects slightly further upwards. 
   A network module  11  formed in this way may thus be pushed into the associated basic module  9 , for example at the end, without any problems, in which case, for insertion of the network module  11  (housing cover  50 ) in the correct position, not only does the network module  11  have a projection  163  at an asymmetric point, for example on the top face, which interacts with a corresponding projection or recess  63  on the inside of the housing cover of the basic module  9  (FIG.  6 ). 
   While the technology herein has been described in connection with exemplary illustrative non-limiting implementations, the invention is not to be limited by the disclosure. The invention is intended to be defined by the claims and to cover all corresponding and equivalent arrangements whether or not specifically disclosed herein.