Abstract:
An improved HF coupler or HF power splitter comprises four connection lines arranged on the same side of the substrate. Two coupling zones are formed on the substrate on two opposite sides; the second coupling zone is connected to the associated connection lines arranged on the side of the substrate opposing the coupling zone, by means of two via holes in an electroplated manner. The capacitors provided at the beginning and at each end of each coupling zone are respectively embodied as interdigital capacitors; and the capacitors are respectively coupled to earth.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. national phase of International Application No. PCT/EP2006/002189, filed 9 Mar. 2006, which designated the U.S. and claims priority to German Patent Application No. 10 2005 016 054.9, filed 7 Apr. 2005, the entire contents of each of which are hereby incorporated by reference. 
     
    
     FIELD 
       [0002]    The technology herein relates to an HF coupler or HF power splitter, especially a narrow-band HF coupler or HF power splitter. 
       BACKGROUND AND SUMMARY 
       [0003]    In high-frequency technical systems it is often necessary for a signal, for example with a power P, to be split into two signals with a power of P/2 each. To do this, ring couplers are frequently used. Such ring couplers are known, for example, from Zinke Brunswig, “High-frequency Technology”, Springer-Verlag, 6 th  Edition, 2000, and specifically page 192. 
         [0004]    These ring couplers are frequently designed in microstrip conductor technology. 
         [0005]    In addition to this, however, high-frequency couplers are also known with which the earth of the coupling is, as a rule, adjusted by way of lines coupled via the face side or the longitudinal side. 
         [0006]    For higher degrees of coupling, such as are needed for a power splitter, these distance intervals are often very small or even too small to be capable of being manufactured economically. 
         [0007]    Thus, for example, a directional coupler is also known from EP 1 291 959 A1, which is based, for example, on suspended-substrate technology. In other words, a coupling zone in stripline technology is provided on a substrate on the one side, which is in connection with two, first and second, connections on the substrate, likewise designed in stripline technology. A second coupling zone is then arranged on the opposite side, which leads to a third and fourth output or connection. In a plan view, the two coupling zones are arranged at least partially overlapping. 
         [0008]    According to the previous publication referred to heretofore, EP 1 291 959 A1, it is also possible for capacitors to be connected to the two opposed ends of the two coupling zones in each case, the second connection point of which is in each case in contact with an earth. 
         [0009]    From the same previous publication, however, other embodiments are also disclosed, in which the coupler is designed in coplanar technology. In this case, the two coupling leads are in each case arranged with their two connection points on a common side of the substrate, wherein the coupling zones run parallel to one another with the smallest possible distance interval between them. 
         [0010]    Finally, however, a directional coupler is also known from EP 1 014 472 B1, which in turn is likewise formed in suspended-substrate technology. This previously known directional coupler is a broadband directional coupler with at least two coupler sections connected in cascade, of different coupler loss, in which the coupler sections with loose coupling consist of face-coupled bus strips and the coupler sections with fixed coupling consist of broad-side-coupled bus strips. 
         [0011]    In order to create the corresponding coupling zone with a fixed coupling, in this embodiment electroplated-through holes are provided in the substrate. All feed leads, however, are arranged on one side of the substrate. 
         [0012]    With regard to the couplers previously known from the prior art, it can therefore be determined that these are frequently designed in microstrip conductor technology. As a result of the relatively high attenuation of the microstrip conduction and its sensitivity to fluctuations in the dielectric constants, the disadvantages of these couplers lie in the high space requirement and the relatively great electrical losses and the high costs of high-quality PCB material. 
         [0013]    The disadvantages of the directional coupler in suspended-substrate technology are, on the one hand, high demands on the positioning of the substrate between the two earthing surfaces (problems arise here with the correct positioning in the horizontal but also with regard to the exact consideration of the distance intervals between the cover and the base). These requirements for correct or optimum positioning incur high costs for the mechanical processing and assembly. On the other hand, when a coupler is being designed the geometry of the housing is already determined as a result. This is often disadvantageous with regard to the possibility of reuse or the attainment of adequate flexibility with regard to the realisation and implementation of a selected concept for a coupler, as well as for its use for further applications. 
         [0014]    In addition to this, from the electrical point of view, with this technology it is only possible with difficulty to compensate for the different phase velocities of the common-mode and differential-mode waves. 
         [0015]    In the final analysis, the main disadvantages of directional couplers in coplanar technology lie in the minimum distance intervals required between the conductor paths coupled on the longitudinal side and the coupling factor which is also to this extent limited. In addition, the coupling factor is highly tolerance-dependent (etch tolerances and fluctuations in the dielectric constants of the substrate material exert a disadvantageous influence). A coupler in coplanar technology is also not optimum with regard to electrical losses. 
         [0016]    A disadvantage with all three types of couplers, as explained heretofore, in particular with their use in a modern technical communications system, is that they do not have the properties of a high-frequency coupler required for this purpose, such as, for example, an adequate and suitable coupling factor, directional focus, or symmetry or cannot be produced or only with substantial development effort and expenditure. 
         [0017]    From GB 2 218 853 A, a high-frequency coupler or power splitter is in addition known which comprises two coupling zones formed on one substrate on one side. Both coupling zones are provided in each case at the beginning and end with connection lines which lead to offset connections. Also, provided and formed between the two coupling zones are capacitors for the coupling of both coupling zones. 
         [0018]    A directional coupler is also known from EP 1 014 472 B1. As a departure from the generic prior art, this directional coupler is formed on a substrate in such a way that the one coupling zone on the one substrate, and the second coupling zone coupled to it, is located on the opposite substrate side. In this situation, in each case a through connection through the substrate is provided on one side of the coupling zone, in order to create an electrical-galvanic connection of a connection line to an opposite coupling surface. 
         [0019]    A microwave coupler is further known from U.S. Pat. No. 4,376,921, which likewise has four connections and two coupling zones, wherein, between the two coupling zones, which are kept comparatively short, capacitors are provided from the beginning to the end to provide coupling between the coupling zones. 
         [0020]    Disadvantageous to all the coupler types referred to heretofore is that, in particular for use in a modern communications system, they do not have the necessary properties of a high-frequency coupler required for this, e.g. with a sufficient coupling factor, adequate directional focus, or symmetry, or cannot be produced or only with substantial development effort and expenditure. A generic coupler or power splitter has become known from US 2005/0017821 A1. Two connection lines are provided on the substrate, which lead to a beginning and an end of a first coupling zone. In addition, a second coupling zone, which is connected to the first coupling zone, is provided, two further connection lines leading to the beginning and end of the second coupling zone. 
         [0021]    The two coupling zones referred to are formed on the substrate on two opposing sides, in which the entire arrangement with the lower coupling zone bears on a lower substrate. 
         [0022]    Another coupler is known from US 2004/0113717 A1, which comprises, for example, earthed inter-digital capacitors which serve to improve the electrical properties. 
         [0023]    The object of the technology herein is, therefore, taking the generic prior art as the starting point, to provide an improved coupler or power splitter, especially a narrow-band, preferably a 3 dB coupler, which is optimized in comparison with conventional solutions with regard to costs, construction size, losses and manufacturing tolerances. 
         [0024]    The exemplary illustrative non-limiting HF coupler or power splitter has a series of positive advantages which set it apart from conventional solutions. The exemplary illustrative non-limiting high-frequency coupler is designed as narrow-band. 
         [0025]    The coupling zone itself is formed on two opposite sides of a substrate, wherein at the two opposed ends of the coupling zone or at the two opposed ends in each case of one of the two coupling zones, an electroplated via hole is provided as in the prior art. As a result, it becomes possible, in the final effect, for all four external connection lines (even when one is closed off) to be arranged on one side of the substrate. This opens up the possibility that on one side on the substrate, should this become necessary, further electrical structural parts and components in conventional solder technology can be provided and connected. 
         [0026]    In addition to this, the exemplary illustrative non-limiting coupler or power splitter has capacitors at the opposed end areas or connection areas to the individual coupling zones in each case, such as they are known in principle from EP 1 291 959 A1. As a departure from this, however, no discrete reactances or capacitors are used but instead what are referred to as inter-digital capacitors. These have not hitherto been used with such power splitters or couplers in this manner; inter-digital capacitors are in principle known from Rainee Simons Coplanar Waveguide Circuits, Components and Systems, first edition, New York, Chichester, Weinheim etc.; John Wiley &amp; Sons, 2001. The use of such inter-digital capacitors in a coupler is, as a basic principle, known from the abovementioned US 2004/0113717 A1. 
         [0027]    By way of an exemplary illustrative non-limiting solution, a power splitter or coupler can be produced with extremely low space requirement, of which the electrical parameters are within broad limits comparatively freely adjustable or pre-selectable. In particular, it has low electrical losses. In addition to this, the exemplary illustrative non-limiting power splitter or coupler is also characterized by its high directional focus. It is above all characterized by the fact that the exemplary illustrative non-limiting coupler or power splitter—which is generally built into a housing—also has a distance interval from the housing in the region of the lower coupling zone, i.e., a housing wall, thus no fixed dielectric is provided immediately adjacent and a lower ∈ is realized and attained which has a positive effect on the electrical properties of the coupler or power splitter. As a result, the exemplary coupler or power splitter has further advantages compared to the generic prior art. 
         [0028]    The exemplary illustrative non-limiting coupler or power splitter is also comparatively robust in respect of housing tolerances. This is shown in particular in the selection of different cover distance intervals. This robustness in respect of housing tolerances also opens the possibility of individual designs being re-used in further application situations. In addition to this, the exemplary coupler is also comparatively robust with regard to etching tolerances as well as towards fluctuations in the dielectric constants of the substrate material. Further, in principle no further wiring arrangements or concentrated component elements are necessary, although basically they can be used if required. Finally, all feed lines are provided on the same side of the substrate, which is to be regarded as advantageous. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    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: 
           [0030]      FIG. 1  is a schematic plan view of an exemplary illustrative non-limiting coupler; 
           [0031]      FIG. 2  is a rear view of the exemplary illustrative non-limiting coupler; 
           [0032]      FIG. 3  is a section along the line III-III in  FIG. 1 ; 
           [0033]      FIG. 4  is a representation corresponding to  FIG. 1  in respect of an exemplary illustrative non-limiting implementation slightly modified in relation to  FIG. 1 ; and 
           [0034]      FIG. 5  is a rearwards view of the exemplary illustrative non-limiting implementation according to  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0035]      FIG. 1  shows a plan view of a first exemplary illustrative non-limiting coupler or power splitter  1  which is formed on a substrate  3  in the form of a printed circuit board. 
         [0036]    Visible on the substrate  3  are four surface areas  5 , on the upper side  3   a  of the substrate visible in  FIG. 1 , which are electrically-galvanically separated from one another by cut-outs  7 . This surface area  5  involves earthing surfaces  5 . 
         [0037]    Formed in the cut-outs  7  is a first coupling zone  9  in stripline technology, which runs in a first direction or longitudinal direction on the substrate  3 . 
         [0038]    Provided at the beginning  11   a  and end  11   b  of this coupling zone  9 , running transversely, are a first and second connection line  13   a  and  13   b , which lead to connections  15   a  and  15   b  on the one substrate edge  3 ′. 
         [0039]    The non-conductive cut-out area  7  shown in the plan view of the exemplary illustrative non-limiting implementation according to  FIG. 1  is formed as H-shaped. In the immediate extension of the connection line  13   a  and  13   b , however, separated from these, two further connection lines  17   a  and  17   b  are to be seen, which lead to the opposite substrate edge  3 ″ and there form connections  19   a  and  19   b.    
         [0040]    At the ends of the connection lines  17   a ,  17   b  opposite the connections  19   a  and  19   b , these are provided with electroplated via holes  21 , adjacent to the first coupling zone  9 , which run through holes  21 ′ through the substrate  3 . 
         [0041]    As can be seen in particular from the view from below from  FIG. 2 , a second coupling zone  25  is provided on the underside  3   b  reproduced there, which runs parallel to the first coupling zone  9 , and in plan view, preferably, overlaps this in whole or at least in part. The length and/or width of the two coupling zones is also at least approximately the same in the exemplary implementation shown. 
         [0042]    As can be seen from the view from below of the underside  3   b  of the substrate  3  according to  FIG. 2 , at the beginning  27   a  and at the end  27   b  of the second coupling zone  25 , and corresponding to the second coupling zone, there are provided two electrically connected line extensions  25 , formed in stripline technology, in the middle of which the holes  21 ′ of the electroplated via hole  21  end. Due to this, the second connection lines  17   a  and  17   b  are electrically-galvanically connected by way of the two electroplated via holes mentioned to the second coupling zone  25 . 
         [0043]    The length of the coupling zones corresponds to approximately lambda/4. The four feed or connection lines  13   a ,  13   b  and  17   a ,  17   b  are designed in coplanar conductor technology and connect the coupler  1  with other high-frequency modules not shown individually in this embodiment. 
         [0044]    To improve the electrical properties, in the embodiment shown there are provided in addition a total of twelve capacitors C, which are located in each case in the input and output areas, i.e. at the beginning  11   a  and at the end  12   b  in each case of the first coupling zone  9 , or at the beginning  11 ′ a  and at the end  12 ′ b  of the second coupling zone  25  respectively. In this situation, therefore, the capacitors C- 9   a  and C- 9   b  are arranged at one end of the first coupling zone  9  and the corresponding capacitors C- 9   c  and C- 9   d  at the other end. Corresponding capacitors are also provided at the beginning and end of the second coupling zone  25 , namely the capacitors C- 25   a  and C- 25   b , as well as, at the opposite end of the coupling zone  25 , the capacitors C- 25   c  and C- 25   d . These capacitors are not formed by the use of discrete components but in the form of inter-digital capacitors. 
         [0045]    From  FIGS. 1 and 2 , however, it can be seen that in the exemplary illustrative non-limiting implementation shown, preferably provision is also made in the middle area, i.e. at half the length of the individual coupling zones  9  and  25  respectively, for a further pair of capacitors C, which in the embodiment shown is designated as C- 9   e  and C- 9   f  and C- 25   e  and C- 25   f.    
         [0046]    With regard to the capacitors, in each case the one capacitor surface or capacitor half is conductively connected to the individual coupling zones  9  and  25  respectively and the electrically-galvanically separated capacitor surface or capacitor half interacting with these, is connected to the pertinent earthing surface. 
         [0047]    For this purpose, the substrate  3  is also provided on the underside according to  FIG. 2  with a circumferentially enclosed earthing surface  31 , in the middle area of which a non-conductive cut-out  33  is provided, within the longitudinal direction of which runs the second coupling zone  2 , galvanically separated from the cut-out  33 . 
         [0048]    The dimensioning of the inter-digital capacitors can be effected in such a way that specific coupling properties can be adjusted or preselected by means of this. The earthing surfaces referred to are necessary, however, in order to provide, on the one hand, defined earthing conditions and, on the other, to form an earth potential for the inter-digital capacitors. The actual coupling accordingly takes place by way of the lines  9  and  25  formed on both sides of the substrate  3  (suspended substrate). 
         [0049]    As can be seen from the cross-sectional representation according to  FIG. 3 , preferably an indentation  37  in a housing  29  is formed below the coupling zone, that is, a distance interval  37  from a corresponding housing wall  29  is provided. The dimension of the indentation, that is, the dimension of the distance interval between the substrate and the housing and housing wall  29  respectively, as well as the distance interval between the substrate and the cover  41  pertaining to it can be freely selected within certain limits. 
         [0050]    Departing from the exemplary implementation shown, it is also possible for the capacitors provided preferably in the center of the coupling zones to be provided, instead of in the center, between the condensers at the beginning and end of the individual coupling zone. If appropriate, it is also possible for further additional capacitors to be provided between the capacitors located at the beginning and end areas of the individual coupling zone, i.e. more than in the exemplary implementations shown. 
         [0051]    Related to the entire coupling length from the beginning area  11   a  to  12   b , and from the beginning area  11 ′ a to the end area  12 ′ b , the capacitors C- 9   a , C- 9   b  and C- 9   c , C- 9   d  respectively on the input and output sides, and on the opposite side the capacitors C- 25   a , C- 25   b  and C- 25   c , C- 25   d  respectively, can also be offset towards the center. The distance interval between the beginning and end areas can in this situation be, for example, up to 30% of the total length of the coupling zone, but preferably is less, in particular less than 25%, 20%, 15% or 10% respectively of the total length of the coupling zone. In this situation, account must be taken of the fact that the positioning of the capacitors at the beginning and end of the coupler develop the greatest effect. 
         [0052]    The exemplary illustrative non-limiting implementation according to  FIGS. 4 and 5  corresponds largely to that according to  FIGS. 1 to 3 . 
         [0053]    The only difference is that, for example, in the plan view of the substrate, in a manner comparable to the embodiment according to  FIG. 1 , the coupling zone  9  located on the one side of the substrate is not provided with two connection lines leading to the same peripheral boundary  3 ′ of the substrate but the connection line  15   b , located on the right in  FIG. 4 , which is electrically-galvanically connected to the coupling zone  9 , leads to the opposite side  3 ″ of the substrate, to the connection  17   b  formed there. Correspondingly, the right-hand connection line  17   b , located at the top in  FIG. 4 , is provided with an electroplated via hole  21 , so that the connection  19   b  located at the top right in  FIG. 4  is electrically-galvanically connected to the connection  19   a  located in the bottom left in  FIG. 4 . 
         [0054]    It therefore follows from the exemplary implementations explained that the earthing surfaces on both sides of the substrate in the area of the connection lines, as well as of the coupling zones  9  and  25 , have cut-outs  7 . The distance interval between the coupling paths  9  and  25  and the earthing surfaces amounts preferably to 1.5 to 4 times the width of the line. Likewise, the distance between the connection lines and the adjacent earthing surfaces amounts to about 1.5 to 4 times the width of these connection lines. 
         [0055]    As has likewise been mentioned, the coplanar coupling lines  9  and  25  are arranged in a suitable manner for attaining the desired coupling. In a plan view of the substrate, i.e. perpendicular to the substrate plane, both coupling lines  9 ,  25 , should therefore either lie above one another or have a lateral offset, which preferably is less than the width of the coupling line. Accordingly, the coupling lines in a plan view do not lie next to one another but overlap. Preferably, the lateral offset is greater than half the width of the coupling conductoripath  9  and  25  respectively, so that both lines, with the preferred width, overlap by fifty percent. In other words, the coverage should preferably be more than 0%, in particular more than 10%, more than 20%, more than 30% and preferably more than 50%, in particular related to the width of the coupling paths  9  and  25 . 
         [0056]    From the structure of the coupler or the power splitter described, it follows that the four connection lines  13   a ,  13   b , and  17   a ,  17   b , are formed in coplanar technology. It likewise results from the description of the embodiments of the invention that the two coupling zones  9  and  25  are formed in suspended-substrate technology. 
         [0057]    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.