Abstract:
A diversity antenna arrangement, in particular a diversity radio antenna arrangement, for WLAN can have two or more antenna elements. In at least one implementation, the antenna elements are arranged in a manner spatially separate from one another on a printed circuit board.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present invention claims the benefit of priority to German Patent Application No. 20 2014 103 657.1 filed Aug. 6, 2014 entitled “Diversity antenna arrangement for WLAN, and WLAN communication unit having such a diversity antenna arrangement, and device having such a WLAN communication unit,” the entire content of which is incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. The Field of the Invention 
         [0003]    The invention relates to a diversity antenna arrangement, in particular a diversity radio antenna arrangement for WLAN (Wireless Local Area Network). The invention also relates to a WLAN communication unit having such a diversity antenna arrangement and to a device having a communication device, in particular a vehicle terminal, comprising such a WLAN communication unit. 
         [0004]    2. Background and Relevant Art 
         [0005]    Two frequency bands are currently available for WLAN: 2.4 GHz to 2.5 GHz (2.4 GHz ISM band) and 5.15 GHz to 5.725 GHz (5 GHz ISM band). 
         [0006]    Diversity antenna systems are used to ensure a good transmission and reception power in radio networks. These antenna systems have two or more antennas for transmitting and/or receiving radio signals. This reduces interference, for example interference effects during radio transmission, caused by reflection of the radio waves. 
         [0007]    There is generally the requirement for devices for wireless communication to become smaller and smaller. Therefore, it is known practice to arrange the antenna elements on a printed circuit board. However, there is the risk of wave coupling with such a design. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    The present invention is therefore based on the object of specifying a new antenna arrangement which has a high degree of decoupling. The intention is also to specify a WLAN communication unit having such a diversity antenna arrangement and a device having such a WLAN communication unit, in particular a vehicle terminal. 
         [0009]    This object is achieved, with respect to the diversity antenna arrangement, by the features of claim  1 , with respect to the WLAN communication unit, by the features of claim  12 , and, with respect to the device, by the features of claim  18 . Advantageous configurations and developments are specified in the respective dependent claims. 
         [0010]    The diversity antenna arrangement according to the invention, in particular the diversity radio antenna arrangement, for WLAN has two or more antenna elements. The latter are arranged in a manner spatially separate from one another on a printed circuit board. 
         [0011]    Arranging two or more antenna elements on a printed circuit board in such a manner that the antenna elements are spatially separate from one another makes it possible to achieve a particularly high degree of decoupling between the individual antennas. The advantages of the invention therefore lie, in particular, in the compact dimensions and a simultaneous high degree of decoupling of the individual antennas. It is also advantageous that such an arrangement can be produced in a comparatively cost-effective manner. 
         [0012]    One development of the invention provides for the antenna elements to be formed on a substantially planar surface of the printed circuit board as a metal coating, in particular as a flat metal coating, of the surface, the metal coating preferably being formed by a single-layer copper structure. 
         [0013]    Provision may also be made for the antenna elements to be arranged on the printed circuit board at an intended distance from one another, in particular a distance of ⅝ of the wavelength in the 2.4 GHz range or a distance of ¼ of the wavelength in the 5.8 GHz range, preferably a distance of 33 mm. This achieves a high degree of decoupling between the antenna elements. 
         [0014]    One configuration provides for a copper structure to be provided between the antenna elements on the printed circuit board, with the result that a high degree of decoupling between the antenna elements is achieved. 
         [0015]    One development of the invention provides for the copper structure to be in the form of a T structure and, in order to short-circuit the field lines, to preferably be connected to a retaining bracket which forms a ground, in particular a ground plane, the retaining bracket resting on the copper structure and therefore forming part of the antenna and/or part of the ground plane. 
         [0016]    Provision may also be made for the antenna elements to be formed from monopole antennas and F antennas, in particular inverted F antennas. 
         [0017]    One embodiment variant of the invention provides for the antenna elements to be in the form of F antennas, a further connection being provided between the two vanes of the F antenna, with the result that a rectangular area enclosed by the antenna structure is produced between the vanes of the F antenna, a recess being provided in the printed circuit board in the region of the rectangular area in order to increase the antenna gain or the efficiency of the antenna. 
         [0018]    Another configuration provides for the antenna elements to be in the form of mutual mirror images during reflection at a central axis between them. 
         [0019]    According to one development of the invention, the antenna elements are formed and/or tuned in such a manner that they cover all WLAN frequency bands, in particular the frequency ranges of 2.4 GHz to 2.5 GHz and 5.15 GHz to 5.725 GHz or frequency ranges up to 5.805 GHz. A diversity antenna arrangement for WLAN is therefore proposed which, as a result of two or more antenna elements being arranged on a common printed circuit board and as a result of the antenna elements being tuned to at least two different WLAN frequency ranges, covers a plurality of frequency ranges in a very small space. 
         [0020]    One configuration of the invention provides for the antenna elements to have cable connections for cables, preferably coaxial cables. 
         [0021]    The invention also relates to a WLAN communication unit comprising a diversity antenna arrangement according to the invention. Provision may be made for the WLAN communication unit to comprise the printed circuit board and a retaining bracket, the printed circuit board being arranged on the retaining bracket, in particular being retained by the retaining bracket. 
         [0022]    Provision may also be made for the retaining bracket to be provided as ground, in particular as a ground plane, for the antenna elements, the retaining bracket resting on the copper structure and therefore forming part of the antenna and/or part of the ground plane. 
         [0023]    The ground connection of the retaining bracket or of the retaining bracket together with a housing and the bandwidth of the antenna (preferably in a range of 500 MHz to 1500 MHz) make the antenna unsusceptible to coverage, for example coverage by the hand of a user or other objects. 
         [0024]    Provision may also be made for the retaining bracket to consist of a metal, in particular a sheet metal. 
         [0025]    One development of the invention provides for the printed circuit board and the retaining bracket to be provided with a radome (or, covering), preferably a radome made of plastic, the radome enclosing the printed circuit board and the retaining bracket. The antenna is preferably matched to the radome without this resulting in a shift of the resonant frequency. 
         [0026]    The invention also relates to a device having a WLAN communication unit according to the invention, as described above. The device may be a vehicle terminal, in particular. 
         [0027]    According to one development, the device may comprise a housing, the housing being connected to the retaining bracket and/or the radome of the WLAN communication device. 
         [0028]    Provision may also be made for the WLAN communication device to be arranged on the outside of the device in order to achieve a high efficiency, in particular an efficiency in the range of 80% to 97.8%. Antennas inside a device or terminal generally cannot achieve this efficiency. The high efficiency is needed for fast-roaming (rapid change between the access points on a vehicle up to 30 km/h). 
         [0029]    Additional features and advantages of exemplary implementations of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of such exemplary implementations. The features and advantages of such implementations may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features will become more fully apparent from the following description and appended claims, or may be learned by the practice of such exemplary implementations as set forth hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0030]    In order to describe the manner in which the above-recited and other advantages and features of the invention can be obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
           [0031]      FIG. 1  shows a schematic illustration of an exemplary embodiment of a diversity antenna arrangement for WLAN according to the invention; 
           [0032]      FIG. 2  shows a WLAN communication device having such a diversity antenna arrangement; and 
           [0033]      FIG. 3  shows a vehicle terminal having a WLAN communication unit. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]      FIG. 1  shows a diversity antenna arrangement  10  for WLAN having two antenna elements  21 ,  22 . The antenna elements  21 ,  22  are arranged in a manner spatially separate from one another on a printed circuit board and are formed on a substantially planar surface of the printed circuit board  30  as a flat metal coating of the surface. The metal coating is formed by a single-layer copper structure. The antenna elements  21 ,  22  are also in the form of mutual minor images during reflection at a central axis between them. 
         [0035]    In order to achieve a high degree of decoupling, the antenna elements  21 ,  22  are arranged on the printed circuit board  30  at an intended distance from one another, in particular a distance of ⅝ of the wavelength in the 2.4 GHz range or a distance of ¼ of the wavelength in the 5.8 GHz range, preferably at a distance of 33 mm. A copper structure  40  is also provided between the antenna elements  21 ,  22  on the printed circuit board  30 , with the result that a high degree of decoupling between the antenna elements  21 ,  22  is achieved. 
         [0036]    The copper structure  40  is in the form of a T structure for this purpose and, in order to short-circuit the field lines, is preferably connected to a retaining bracket  80  which forms a ground, in particular a ground plane. The retaining bracket  80  rests on the copper structure and therefore forms part of the antenna. 
         [0037]    The antenna elements  21 ,  22  are formed from monopole antennas and inverted F antennas and have cable connections  51 ,  52  for coaxial cables  61 ,  62 . 
         [0038]    The antenna elements  21 ,  22  in the form of F antennas each have two vanes  23 ′,  23 ″,  24 ′,  24 ″, a further connection  25 ,  26  being provided between the two vanes  23 ′,  23 ″,  24 ′,  24 ″ of the F antenna, with the result that a rectangular area  27 ,  28  enclosed by the antenna structure is produced between the vanes  23 ′,  23 ″,  24 ′,  24 ″ of the F antenna, a recess being provided in the printed circuit board  30  in the region of the rectangular area  27 ,  28  in order to increase the antenna gain or the efficiency of the antenna. 
         [0039]    The antenna elements  21 ,  22  have an omnidirectional radiation? characteristic and are formed and/or tuned in such a manner that they cover the frequency ranges of 2.4 GHz to 2.5 GHz and 5.15 GHz to 5.725 GHz. 
         [0040]      FIG. 2  shows a WLAN communication unit  70  comprising a diversity antenna arrangement as described above. The WLAN communication unit  70  comprises the printed circuit board  30  and the retaining bracket  80 , the printed circuit board  30  being retained by the retaining bracket  80 . The retaining bracket  80  consists of a sheet metal and is provided as a ground plane for the antenna elements  21 ,  22 . The printed circuit board  30  and the retaining bracket  80  are provided with a radome (or, covering)  90  made of plastic, the radome  90  enclosing the printed circuit board  30  and the retaining bracket  80 . 
         [0041]      FIG. 3  shows a vehicle terminal  100  comprising a WLAN communication unit  70 . The device  100  comprises a housing  110 , the housing  110  being connected to the retaining bracket  80  and the radome  90  of the WLAN communication device  70 . 
         [0042]    The WLAN communication device  70  is arranged on the outside of the housing  110  in order to achieve a high efficiency, in particular an efficiency in the range of 80% to 97.8%. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
         
           
               10  Diversity antenna arrangement 
               21  Antenna element 
               22  Antenna element 
               23 ′ Vane 
               23 ″ Vane 
               24 ′ Vane 
               24 ″ Vane 
               25  Connection 
               26  Connection 
               27  Area 
               28  Area 
               30  Printed circuit board 
               40  Copper structure 
               51  Cable connection 
               52  Cable connection 
               61  Cable 
               62  Cable 
               70  WLAN communication unit 
               80  Retaining bracket 
               90  Covering 
               100  Device 
               110  Housing