Abstract:
The disclosure concerns an antenna with open loops and multipath current distribution to achieve ultra wideband characteristics and antenna miniaturization, while simultaneously keeping high performance for a more reliable WAN communication, with higher data transfer, less dropping connections and improved sensitivity. To further reduce spatial requirements, the antenna may be incorporated on a flex substrate for bending with the contour of a device housing or the like.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of priority with U.S. Provisional Application Ser. No. 61/930,143, filed Jan. 22, 2014; the contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The claimed invention relates to antennas; and more particularly, to such antennas having open loop conductors with multi-path current distributions for achieving multiple wideband resonances for use in WAN communications. 
         [0004]    2. Description of the Related Art 
         [0005]    New methodologies and techniques for antenna miniaturization, and further widening the response across multiple frequencies are in present high demand. The wide area network (WAN) main spectrum is allocated from 698 MHz to 3000 MHz, including most of the cellular bands around the World. 
         [0006]    This demand drives a present need for novel and differentiated antenna configurations and topologies which provide useful wide band operation. 
         [0007]    Moreover, those with skill in the art recognize that it is very difficult to design an antenna with stable radiation performance across the ultra-wide bandwidth. Conventional antenna topologies and configurations look for one or two paths to obtain lower and upper resonances (around 800 MHz and 1900 MHz), with other techniques to widen the resonances, getting more bandwidth. However, this conventional technique generally results in more space per each element, and such space is not something that is available with modern device constraints. 
         [0008]    There is a need for an alternative solution for providing ultra-wide band resonances with reduced spatial requirements. 
       SUMMARY  
       [0009]    An antenna is disclosed which provides open loops and multipath current distribution to achieve ultra wideband characteristics and antenna miniaturization, while simultaneously keeping high performance for a more reliable WAN communication, with higher data transfer, less dropping connections and improved sensitivity. To further reduce spatial requirements, the antenna may be incorporated on a flex substrate for bending with the contour of a device housing or the like. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1A  shows an isometric view of a multipath open loop antenna in accordance with an illustrated embodiment; 
           [0011]      FIG. 1B  details the conductor portions of the multipath open loop antenna of  FIG. 1A ; 
           [0012]      FIG. 2A  shows the multipath open loop antenna and certain associated current distribution pathways; 
           [0013]      FIG. 2B  shows the multipath open loop antenna and certain other associated current distribution pathways; 
           [0014]      FIG. 2C  shows the multipath open loop antenna and certain other associated current distribution pathways; 
           [0015]      FIG. 3  shows a multipath open loop antenna in accordance with a Multi-input multi-output (MIMO) 2×2 configuration embodiment, including an optional band pass filter and a current distribution concentrators; 
           [0016]      FIG. 4  shows measured and simulated return loss of the antenna of  FIG. 3 ; 
           [0017]      FIG. 5  shows measured isolation of the antenna of  FIG. 3 ; 
           [0018]      FIG. 6  shows measured efficiency of the antenna of  FIG. 3 ; and 
           [0019]      FIG. 7  shows measured peak gain of the antenna of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    In the following description, for purpose of illustration and not limitation, detailed descriptions are provided in an effort to enable those having skill in the art to make and use the inventive embodiments. It will be understood by those with skill in the art that various modifications and alterations may be practiced, with only limited experimentation, in order to achieve the substantial result of the invention as set forth in the claims. 
         [0021]    Now turning to the drawings,  FIG. 1A  shows an isometric view of a multipath open loop antenna in accordance with an illustrated embodiment. The antenna comprises a flexible substrate sheet  11  having an open-loop ground conductor portion  13  and an open-loop radiating portion  12 . The ground conductor  13  comprises a ground solder pad  14   b  disposed adjacent to each of: a peripheral edge  111  of the substrate, and the centerline (C′) thereof. The radiating portion  12  comprises a feed solder pad  14   a  disposed adjacent to each of: a peripheral edge  111  of the substrate, and the centerline (C′) thereof. 
         [0022]      FIG. 1B  further details the antenna of  FIG. 1A . The substrate  11  comprises a length longer than a width of the substrate, and a thickness much less than the length and width, forming a flexible substrate sheet. The length of the substrate is bisected at the centerline (C′). The open-loop ground conductor  13  is disposed on the substrate at a first side with respect to the center line (shown as the left side in  FIG. 1B ), and the open-loop radiating portion  12  is disposed on the substrate at a second side opposite of the first side with respect to the centerline (shown as the right side in  FIG. 1B ). 
         [0023]    The open-loop ground conductor  13 , comprises, in series, a first vertical ground conductor portion  131 , a first horizontal ground conductor portion  132 , a second vertical ground conductor portion  133 , a second horizontal ground conductor portion  134 , a third vertical ground conductor portion  135 , and a third horizontal ground conductor portion  136 . The first through third horizontal ground conductor portions are each disposed parallel to one another and at least partially overlapping with one another. 
         [0024]    The first vertical ground conductor portion  131  extends parallel to the centerline of the substrate from the first peripheral edge  111  to a second peripheral edge  112  opposite of the first peripheral edge. 
         [0025]    The first horizontal ground conductor portion  132  extends parallel with the second peripheral edge of the substrate from the first vertical ground conductor portion  131  to a corner of the substrate defined at the intersection of the second peripheral edge  112  and the terminal edge  113  of the substrate. 
         [0026]    The second vertical ground conductor portion  133  extends parallel with the centerline along the terminal edge  113  of the substrate from the first horizontal ground conductor portion  132  to the second horizontal ground conductor portion  134 . 
         [0027]    The third vertical ground conductor portion  135  extends parallel with the centerline from the second horizontal ground conductor portion  134  to the third horizontal ground conductor portion  136 . 
         [0028]    Each of the ground conductor portions  131 - 136  forms a ground conductor having an open-loop configuration with three regions of overlap; i.e. a first region of overlap between the first and third vertical ground conductors  131  and  135 ; the first and second horizontal ground conductors  132  and  134 ; and the second and third horizontal ground conductors  134  and  136 , respectively. As will be identified herein, the open-loop ground conductor provides multiple ground paths for achieving multiple resonances. 
         [0029]    The open-loop radiating portion comprises: a first conductor section and a second conductor section, each conductor section extending from a point of feed (feed solder pad  14   a ). 
         [0030]    The first conductor section includes: a first vertical element  121 , a first horizontal element  122 , a second vertical element  123 , and at least a second horizontal element  125 . The first conductor section is configured to overlap with itself for providing a first loop region. 
         [0031]    The second conductor section comprises a first horizontal element  126 , a first vertical element  127 , and at least a second horizontal element  128 . The second conductor section is configured with one or more overlapping elements forming at least a second loop region, and optionally a third loop region  129 . The multiple loop regions provide a plurality of distinct current paths and associated resonances. 
         [0032]      FIG. 2A  shows the multipath open loop antenna and certain associated current distribution pathways. The ground conductor portion  13  is configured to provide a first current distribution path  21  and a second current distribution path  22 . The radiating conductor portion  12  is configured to provide a third current distribution path  23 . 
         [0033]      FIG. 2B  shows the multipath open loop antenna and certain other associated current distribution pathways. The radiating conductor portion  12  is further configured to provide a fourth current distribution path  24  and a fifth current distribution path  25 . 
         [0034]      FIG. 2C  shows the multipath open loop antenna and certain other associated current distribution pathways. The radiating conductor portion  12  is further configured to provide a sixth current distribution path  26  and a seventh current distribution path  27 . 
         [0035]    Thus, the antenna as-illustrated is configured with seven unique current distribution paths, each producing a distinct resonance for ultra-wide band response. 
         [0036]    In another embodiment, as shown in  FIG. 3 , a multipath open loop antenna is arranged in accordance with a multi-input multi-output (MIMO) 2×2 configuration. In the embodiment of  FIG. 3 , the antenna can be configured with an optional band pass filter  34  and current distribution concentrators  33   a;    33   b.  Here, the flexible substrate sheet comprises a pair of current distribution concentrators  33   a;    33   b,  respectively, being coupled by a band-pass filter  34  extending therebetween. Each of the current distribution concentrators comprises a solder pad  36   a;    36   b,  respectively, for connecting a transceiver to ground. On either side of the current distribution concentrators is a distinct radiating conductor portion  32   a;    32   b  as described in the embodiment of  FIGS. 1-2 , wherein a first of the two radiating conductor portions  32   a  is a mirror image of the second radiating conductor portion  32   b.  Each of the radiating conductor portions  32   a;    32   b  comprises a feed solder pad  35   a;    35   b  as described above. 
         [0037]    The disclosed antenna, having a MIMO 2×2 configuration as shown in  FIG. 3 , was reduced to a functional prototype and tested. The prototype antenna substrate had a size of 96 mm×21mm×0.1 mm, having copper conductors on a flexible substrate (polyimide). The prototype antenna achieved the following resonances: 700, 850, 900, 1575, 1700, 1800, 1900, 2100, 2400 and 2600 MHz. Such an antenna can be useful with LTE-Advanced and Diversity Systems, among others. 
         [0038]      FIG. 4  shows measured and simulated return loss of the antenna of  FIG. 3 ; 
         [0039]      FIG. 5  shows measured isolation of the antenna of  FIG. 3 ; 
         [0040]      FIG. 6  shows measured efficiency of the antenna of  FIG. 3 ; and 
         [0041]      FIG. 7  shows measured peak gain of the antenna of  FIG. 3 . 
         [0042]    Depending on design requirements, the antenna can be fabricated with a flexible or rigid body that can be installed as peel and stick easy process, simplifying the assembly process while manufacturing the device in which the antenna is allocated. 
         [0043]    Coaxial cables can be used to connect the antenna feed and ground to a transceiver. 
         [0044]    Thus, a multipath current distribution is used to create different resonances in a limited space, and with open loops intrinsic in the design the antenna is configured to achieve wide resonance performance. Using conventional antenna design methodologies, an antenna size of 180mm×25mm will be required to obtain resonances down to 700 MHz band and ultra wide band characteristics. Accordingly, by using multipath current distribution the antenna size was decreased in half, providing a significant improvement in the state of the art. 
         [0045]    Moreover, providing the antenna on a flexible substrate body allows for conforming with the shape of the surface where the antenna is to be mounted, or alternatively bending the antenna one or multiple times to fit in a tight volume. 
         [0046]    The disclosed antenna has several current distribution paths based in open loop structures formulating multipath resonances. A MIMO arrangement of 2×2, with an isolator gap was incorporated to increase the correlation coefficient and isolation. In the MIMO 2×2 configuration a near field concentrator was added to boost isolation.