Abstract:
The present invention relates to an antenna arrangement with a printed circuit board, which has an upper side and a lower side, and an antenna supported by the printed circuit board, in particular ring antenna, which comprises at least one electrically conductive antenna section which is arranged on a narrow side of the printed circuit board adjoining the upper side and/or the lower side. The invention also relates to a process for producing an antenna arrangement which comprises a printed circuit board with an upper side and a lower side and an antenna supported by the printed circuit board, in which process for forming at least one antenna section, an electrically conductive material is attached to a narrow side of the printed circuit board which adjoins the upper side and/or the lower side.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an antenna arrangement with a substrate/printed circuit board and an antenna supported by the substrate/printed circuit board. 
       BACKGROUND OF THE INVENTION 
       [0002]    Such antenna arrangements are known in principle and are used, for example as transmitting antennae in-hand transmitters or electronic keys with which, for example motor vehicles may be locked and unlocked by remote control or garage doors may be opened and closed. 
         [0003]    The known antennae arrangements prove to be disadvantageous inasmuch as they have a comparatively low antenna efficiency. That is, the transmission power broadcast by the antenna which can be used is relatively low compared to the power input of the antenna which is necessary therefor. 
         [0004]    In the known antenna arrangements this generally leads to a low range and to a high energy requirement of the antenna or to a correspondingly low battery service life. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the present invention is therefore to provide an antenna arrangement of the type mentioned in the introduction which has an increased antenna efficiency. 
         [0006]    To achieve this object, an antenna arrangement having the features of the claims is provided. 
         [0007]    The antenna arrangement of the invention comprises a substrate such as a printed circuit board, which has an upper side and a lower side, and an antenna supported by the printed circuit board, in particular ring antenna, which comprises at least one electrically conductive antenna section, which is arranged on a narrow side of the printed circuit board adjoining the upper side and/or the lower side. 
         [0008]    According to the invention it has been recognised that the efficiency of the antenna arrangement is impaired in particular by power losses in the conductive track of the antenna and by dielectric losses in the dielectric material of the printed circuit board. Due to the arrangement of an antenna section on the narrow side, the power losses occurring during operation of the antenna can be reduced and the antenna efficiency thus increased. 
         [0009]    The cause of the problems of high power losses is not least the skin effect, which is particularly pronounced at frequencies which are suitable for operation of the antenna arrangement. The skin effect designates the phenomenon that eddy currents counteract an alternating current flowing in the interior of a conductor increasingly at high frequencies and which are induced by the alternating current in the interior of the conductor and thus reduce the net current flow so that the current flow is displaced from the centre of the conductor to the edge of the conductor. Consequently, at high frequencies essentially only the edge of the conductor contributes to the current power, and the effective resistance of the conductor is increased. 
         [0010]    In addition there is the fact that a conductor arranged on the upper side or lower side of the printed circuit board conducts the current only less efficiently in that edge region in which it is in contact with the upper side or lower side, because the surface of the printed circuit board and hence also that of the conductor in this edge region conventionally have a high roughness and the current path in this region is extended accordingly. 
         [0011]    The dielectric losses are produced in the printed circuit board supporting the antenna and thus depend on the dielectric loss properties of the materials forming the printed circuit board. Within the framework of the invention, the printed circuit board supporting the antenna preferably consists completely of electrically non-conductive, dielectric material. The printed circuit board may be laminated, for example from several dielectric layers. 
         [0012]    The design according to the invention of a conductive antenna section on a narrow side of the printed circuit board provides an electric current path with good current-conduction properties and thus reduces the power losses of the antenna which occur. 
         [0013]    One advantage of a conductive antenna section attached to a narrow side is thus that the antenna section itself does not require any space on the upper side and or the lower side. Hence, a relatively large electrically conductive antenna section may also be realised with low space supply on the upper side and lower side of the printed circuit board and hence increased conductivity of the antenna may be achieved. 
         [0014]    A narrow-sided antenna section is particularly advantageous when the antenna is a ring antenna and has a current path which runs at least essentially annularly in the plane of the printed circuit board. A narrow-sided antenna section has here at least approximately the shape of a jacket segment, which leads to a particularly good emission characteristic and contributes to increased antenna efficiency. 
         [0015]    As a result the antenna arrangement of the invention thus has an improved antenna efficiency, as a result of which in the end not only the antenna range is increased, but also the energy requirement is reduced. 
         [0016]    Advantageous embodiments of the invention are described in the sub-claims, the description and the drawings. 
         [0017]    The conductive antenna section arranged on the narrow side preferably has a metallic material, in particular copper or gold. The conductive narrow-sided antenna section is preferably a metallic layer arranged on the narrow side and having essentially constant thickness, which is for example several 10 μm. 
         [0018]    According to one embodiment, the narrow side of the printed circuit board adjoins the upper side and/or the lower side of the printed circuit board. The narrow side may thus extend essentially vertically to the upper side or lower side of the printed circuit board. It is preferred if the narrow side extends from the upper side to the lower side of the printed circuit board and hence thus through the printed circuit board. In this case the narrow side makes available a particularly large surface for the antenna section arranged on the narrow side. 
         [0019]    The narrow side may define a hole of the printed circuit board extending through the printed circuit board and which is preferably designed to be elongated. Alternatively, the narrow side may form an outer side of the printed circuit board. If the narrow-sided antenna section adjoins a hole or an outer side of the printed circuit board, less dielectric printed circuit board material is present in the immediate surroundings of the narrow-sided antenna section, as a result of which the dielectric losses of the electromagnetic field generated by a current flowing in the narrow-sided antenna section are reduced. In addition, such narrow sides can be formed particularly simply, for example by holes being formed in the printed circuit board by a milling process or by the outer contour of the printed circuit board being cut to size accordingly by a milling process. 
         [0020]    According to a further embodiment, the narrow-sided antenna section does not form a closed electrically conductive ring. If the narrow side, to which the antenna section is attached, defines a hole of the printed circuit board, the antenna section is preferably attached only to one part region of the narrow side defining the hole without forming a closed ring in the hole. Such a narrow-sided antenna section may be generated in simple manner by complete coating of a narrow side defining a hole with electrically conductive material and subsequent removal of undesirable electrically conductive material. 
         [0021]    Although within the framework of the invention, an antenna arrangement can be conceived which has exclusively a narrow-sided antenna section and no upper-side or lower-side antenna sections, the antenna section arranged on the narrow side according to a preferred embodiment is connected to an antenna section running on the upper side and/or to an antenna section running on the lower side. By providing the narrow-sided antenna section in addition to an antenna section connected to the narrow-sided antenna section and running on the upper side and/or lower side, the conductivity of the entire arrangement is significantly increased. The narrow-sided antenna section may be connected along its at least approximately entire length to the antenna section running on the upper side or lower side. 
         [0022]    According to a further embodiment, two narrow-sided antenna sections on opposite side of an antenna section running on the upper side or of an antenna section running on the lower side are connected to the latter. The two narrow-sided antenna sections and the upper-side or lower-side antenna section thus form two angles, in the apices of which higher currents may flow, as a result of which the conductivity of the antenna section as a whole is increased still further. 
         [0023]    According to a further embodiment, the antenna section arranged on the narrow side extends through the printed circuit board and connects an antenna section arranged on the upper side of the printed circuit board to an antenna section arranged on the lower side of the printed circuit board. Due to this arrangement, likewise two antenna section angles are formed, in the apices of which higher currents may flow and which contribute to an increased antenna efficiency. 
         [0024]    An upper-side and a lower-side antenna section are advantageously connected to one another by two opposing narrow-sided antenna sections. Four antenna section angles are formed in this manner and an even higher current flow and antenna efficiency achieved. 
         [0025]    According to a further embodiment provision is made in that the antenna section arranged on the narrow side electrically bridges an interruption of a first antenna section running on the upper side or on the lower side of the printed circuit board. The narrow-sided antenna section may thus connect the first antenna section additionally to a second antenna section running on the lower side or upper side. 
         [0026]    An interruption of the antenna section of the upper side or lower side of the printed circuit board may thus serve to accommodate other circuit parts attached to the upper side or lower side of the printed circuit board, such as for example a conductor track running through the interruption to connect various circuit parts or components. 
         [0027]    Hence, the printed circuit board may support, apart from the antenna, still further circuit parts, which are produced for example in common process steps with the antenna, for example connection leads and connection surfaces for further circuit parts arranged on the printed circuit board. 
         [0028]    Antenna sections arranged on the upper side and/or lower side of the printed circuit board may be formed in this case in a common process step with the further circuit parts, such as for example connection leads and connection surfaces. Such further circuit parts may belong, for example to an activation circuit which exposes the antenna attached to the printed circuit board to an activation signal, or, in the case of a receiving antenna, to a receiving and evaluation circuit. In the case of a transmitting antenna, the antenna is preferably activated at frequencies in the range between 300 and 1,000 MHz. 
         [0029]    A further object of the invention is a process having the features of the process claims. The process of the invention may serve in particular for the production of an antenna arrangement of the type described above. The advantages illustrated above thus apply accordingly. 
         [0030]    In the process of the invention, to form at least one antenna section, an electrically conductive material is attached to a narrow side of the printed circuit board, which adjoins the upper side and/or the lower side of the printed circuit board. 
         [0031]    According to one embodiment, the narrow side of the printed circuit board is generated by removing printed circuit board material, in particular by forming an, in particular elongated, hole in the printed circuit board, for example by a drilling or milling process. Drilling and milling processes for printed circuit boards are known per se and may be effected in simple manner with available tools and machines. 
         [0032]    Several holes along the required antenna conductor track for several narrow-sided antenna sections are advantageously generated in the printed circuit board. Known drilling or milling machines may generate such a plurality of holes with high precision and at high speed using an electronic layout, for example a CAD layout. 
         [0033]    It is particularly preferred if the removal of printed circuit board material for generating the narrow side is effected in a common process step with the formation of holes for interconnections between circuit parts on the upper side and circuit parts on the lower side of the printed circuit board, so-called vias. 
         [0034]    Due to the common generation of via holes and narrow side(s), the production process for the antenna arrangement is simplified by there being no need to carry out a separate process step for removing printed circuit board material for generating the narrow side(s). The via holes and the narrow side(s) may thus be produced in particular in one and the same tool machine without the printed circuit board having to be removed in between from the working region of the machine. The geometric data for drilling and/or milling for generating the narrow side(s) may thus be added simply to the layout data file for generating the via holes. 
         [0035]    According to an advantageous embodiment, the electrically conductive material is attached to the narrow side by a deposition process, in particular by means of a galvanic process. By galvanic deposition processes, layers of electrically conductive material may be generated on a narrow side which have high quality, high electric conductivity and good adhesion to the printed circuit board material. Copper and/or gold is preferably deposited and particularly preferably a layer having at least approximately constant thickness is deposited, which may be for example between 30 and 100 μm. 
         [0036]    It is particularly preferred if the narrow sides and the side walls, which define the via holes, are coated with electrically conductive material at the same time in a common deposition process, since a separate deposition process is thus not necessary on the narrow sides for generating the antenna sections. 
         [0037]    Electrically conductive material attached to the narrow sides and/or printed circuit board material which is adjoined thereto is preferably subsequently removed in some regions, for example by a milling process. 
         [0038]    Electrically conductive material not required can be eliminated in this manner, for example electrically conductive material which is facing away from the antenna section, or the weight and the space requirement of the printed circuit board can be reduced. In addition, dielectric losses can be reduced by the removal of printed circuit board material. 
         [0039]    For example the narrow side may be generated by the formation of a hole in the printed circuit board and after metallisation of the narrow side, printed circuit board material may be removed which extends between the hole and an outer side of the printed circuit board so that the narrow side itself becomes the outer side of the printed circuit board. The outer contour of the printed circuit board is thus reduced by cutting to size until the narrow side becomes the outer side of the printed circuit board. This cutting-to-size of the printed circuit board towards the narrow side reduces the space requirement of the printed circuit board and the dielectric losses which occur. Since the narrow-sided antenna section extends at least in some regions along the outer contour of the printed circuit board, for preset size, in addition a maximum antenna length or a maximum antenna diameter is achieved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]    The present invention is described below purely by way of example using an advantageous embodiment with reference to the attached drawings. 
           [0041]      FIG. 1   a  shows a printed circuit board arrangement after drilling via holes; 
           [0042]      FIG. 1   b  shows a cross-sectional view along the line A-A′ of  FIG. 1   a  on an enlarged scale; 
           [0043]      FIG. 2   a  shows the arrangement of  FIG. 1  after milling elongated holes; 
           [0044]      FIG. 2   b  shows a cross-sectional view along the line A-A′ of  FIG. 2   a  on an enlarged scale; 
           [0045]      FIG. 3   a  shows the arrangement of  FIG. 2  after coating of the holes with conductive material; 
           [0046]      FIG. 3   b  shows a cross-sectional view along the line A-A′ of  FIG. 3   a  on an enlarged scale; 
           [0047]      FIG. 4   a  shows the arrangement of  FIG. 3  after structuring of conductor tracks; 
           [0048]      FIG. 4   b  shows a cross-sectional view along the line A-A′ of  FIG. 4   a  on an enlarged scale; 
           [0049]      FIG. 4   c  shows a rear-side view of the arrangement of  FIG. 4   a;    
           [0050]      FIG. 5  shows a cut-to-size trajectory, along which the printed circuit board arrangement of  FIG. 4  is cut to size on a reduced scale; 
           [0051]      FIG. 6   a  shows an antenna arrangement of the invention which has been produced by the process of  FIGS. 1-5 ; 
           [0052]      FIG. 6   b  shows a cross-sectional view of the antenna arrangement of  FIG. 6   a  along the line A-A′ of  FIG. 6   a  on an enlarged scale. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0053]      FIGS. 1 to 6  show an antenna arrangement of the invention in different stages of its production. 
         [0054]      FIG. 1   a  shows a plan view of the upper side of a printed circuit board  10 , which comprises an upper side and a lower side, on which in each case a copper layer  14 ,  14 ′ has been applied.  FIG. 1   a  shows holes  12  for interconnections  22  (vias) between circuit parts on the upper side and circuit parts on the lower side of the printed circuit board  10 . The via holes  12  may be produced, for example by a drilling or milling process. Side walls  11  of the printed circuit board  10  define the via holes  12 . 
         [0055]      FIG. 1   b  shows the printed circuit board  10  of  FIG. 1   a  in a cross-section along the line A-A′ of  FIG. 1   a . In addition to a via hole  12 , the copper layers  14 ,  14 ′ can also be seen, which are applied in each case to the upper side and the lower side of the printed circuit board  10 . In  FIG. 1   b  and also in the remaining cross-sectional representations, the thickness s of the copper layers  14 ,  14 ′ is shown to be excessively large compared to the thickness d of the printed circuit board  10 . The thickness d of the printed circuit board  10  may be, for example about 1.5 mm and the thickness s of the copper layers  14 ,  14 ′ in each case about 50 μm. 
         [0056]      FIG. 2   a  shows the printed circuit board  10  of  FIG. 1  after elongated holes  16  have been generated in the printed circuit board  10 . The elongated holes  16  run along required antenna conductor tracks and are defined in each case in annular manner by a narrow side  18  of the printed circuit board  10 . In some sections in each case two elongated holes  16  run parallel to one another on opposite sides of an antenna conductor track so that in each case an elongated self-supporting bar  19  of the printed circuit board  10  is defined by two adjacent elongated holes  16 , which printed circuit board  10  may support an upper-side and lower-side antenna section  24 ,  24 ′. 
         [0057]    In the present exemplary embodiment, the elongated holes  16  are generated by a milling process. The elongated holes  16  are milled vertically to the upper side and lower side of the printed circuit board  10  so that the narrow sides  18  defining the elongated holes  16  and the upper side or lower side of the printed circuit board  10  form essentially a right-angle. The drilling process for the via holes  12  and the milling process for the elongated holes  16  may be carried out in a common process step in the same machine. 
         [0058]    After generating the via holes  12  and the elongated holes  16 , the side walls  11  of the via holes  12  and the narrow sides  18  defined by the elongated holes  16  are coated with a conductive material, in the present exemplary embodiment with copper, by a deposition process. 
         [0059]      FIG. 3   a  shows a plan view of the arrangement of  FIG. 2   a  after deposition, which may be effected in a manner known per se by galvanisation in a galvanic bath. The thickness of the deposited copper material may be, for example several 10 μm. 
         [0060]    The copper material deposited on the narrow sides  18  forms firstly narrow-sided antenna sections  20  and secondly undesirable or not required copper material  20 ′, namely in the regions of the narrow sides  18  defining the elongated holes  16  and which are facing away from the required narrow-sided antenna section  20 . In addition, the copper deposited in the via holes  12  forms the interconnections  22  (vias). 
         [0061]      FIG. 3   b  shows that the cross-section of a self-supporting printed circuit board bar  19  is surrounded all around by conductive material, namely by the copper layers  14 ,  14 ′ and the narrow-sided antenna sections  20 . The conductive material  14 ,  14 ′,  20  surrounding the self-supporting bar  19  forms due to its geometry an antenna current path with increased conductivity. 
         [0062]    After deposition of the conductive material, the copper layer  14  is structured in suitable manner on the upper side and the copper layer  14 ′ on the lower side of the printed circuit board  10 , for example by an etching process known per se in order to provide electrically conductive antenna sections  24 ,  24 ′ on the upper side and the lower side of the printed circuit board  10  and electrical connection leads  28  and electrical connection surfaces  26  for circuit parts to be produced in addition to the antenna on the printed circuit board  10  ( FIG. 4 ). 
         [0063]      FIGS. 4   a, b, c  show the printed circuit board  10  after structuring of the copper layers  14 ,  14 ′. For better orientation, the view of the lower side of the printed circuit board  10  is shown in  FIG. 4   c  from the perspective from the top, that is, from the upper side observed through the printed circuit board  10 , so that it can be seen in simplified manner which elements on the upper side of the printed circuit board  10  are opposite which elements on the lower side of the printed circuit board  10  without the observer having to take into account the mirror-inverted perspective which is produced if the printed circuit board  10  is observed once from the top and once from the bottom. 
         [0064]    As  FIG. 4   a  shows, an approximately annular antenna section  24  is formed on the upper side of the printed circuit board  10  and which runs in some regions along the narrow sides  18  of the elongated holes  16  and thus is in electrical contact with the conductive material of the narrow-sided antenna sections  20  deposited on the narrow sides  18 . An essentially identically designed antenna section  24 ′, which is likewise connected to the conductive material of the narrow-sided antenna section  20 , is formed opposite the antenna section  24  on the lower side of the printed circuit board  10 . The two antenna sections  24 ,  24 ′ on the upper side and the lower side are connected to one another via the narrow-sided antenna sections  20 , as shown in  FIG. 4   b.    
         [0065]    The antenna conductor tracks  24 ,  24 ′ on the upper side and lower side of the printed circuit board  10 , together with the narrow-sided antenna sections  20 , form an essentially annular antenna, which, in particular in the region of the self-supporting bars  19 , has an increased conductivity due to the conductive material deposited on the narrow sides  18  and reduced dielectric losses due to the formation of the elongated holes  16  in the dielectric material of the printed circuit board  10 . 
         [0066]      FIG. 4   a  shows several electrical connection surfaces  26  generated in the structuring step and electrical connection leads  28 . These connection surfaces  26  and connection leads  28  permit attachment of electronic components for the formation of an activation circuit for activation of the antenna on the printed circuit board  10 . The antenna is connected to the activation circuit via the connection surface  26   a  and via a connection surface  26   b  located on the rear side of the printed circuit board  10  and which serves the circuit as a reference potential. 
         [0067]    To form the activation circuit, electronic components, for example SMD components, may be attached in a manner known per se to the connection surfaces  26  and connected to one another via the electrical connection leads  28 . As  FIGS. 4   a, b  and  c  show, circuit parts are thus connected to one another on the upper side of the printed circuit board  10  by the interconnections  22  produced before the structuring process. Assembly of the components to form the activation circuit may be effected before or after a cut-to-size step following the structuring step or even between two part steps of the cut-to-size step. The cut-to-size step is illustrated below. 
         [0068]    After structuring, the printed circuit board  10  is cut to the required size of the antenna arrangement.  FIG. 5  shows schematically the cutting lines  30   a, b , along which the printed circuit board  10  is cut to size. Due to the cutting line  30   a , the outer contour of the printed circuit board  10  is defined so that the narrow-sided antenna sections  20  adjacent the cutting line  30   a  of the elongated holes  16  placed on the outside now form outer sides of the printed circuit board  10  and regions of the antenna sections  24 ,  24 ′ on the upper side and lower side directly adjoin the outer side of the printed circuit board  10 . Electrically conductive material  20 ′ which is not necessary and excess printed circuit board material is thus removed. 
         [0069]    Instead of cutting to size all around the outer contour of the printed circuit board  10 , that is, according to a closed cutting line, such as the cutting line  30   a , the outer contour of the printed circuit board  10  may also be cut to size in that printed circuit board material, which extends between an elongated hole  16  placed on the outside and an outer side of the printed circuit board  10 , is cut out by two cuts guided between the outer side of the printed circuit board  10  and the elongated hole  16 . In this case, the printed circuit board  10  may preferably be cut to size coarsely to an outer contour even before the structuring of the copper layers  14 ,  14 ′ and which is somewhat greater than its final dimension, so that thin bars of the printed circuit board  10  remain which extend between the outer elongated holes  16  and the outer side of the printed circuit board  10 . They are then cut out in a further cut-to-size step following structuring. 
         [0070]    Undesirable deposited electrically conductive material  20 ′ is also removed at the elongated holes  16  lying on the inside by the cutting lines  30   b . Printed circuit board material placed around the undesirable electrically conductive material  20 ′ is thus optionally also removed. 
         [0071]      FIGS. 6   a  and  b  show the finished antenna arrangement after cutting-to-size. In this antenna arrangement, the electrical conductivity of the antenna is increased by the narrow-sided antenna sections  20 , and the dielectric losses are reduced by the removal of dielectric material. By using outer narrow sides  18  of the printed circuit board  10  for narrow-sided sections  20  of the antenna, in addition a maximum antenna diameter is achieved with minimum space requirement of the antenna arrangement.