Abstract:
A quadrifilar helix antenna comprises a flexible substrate, four conductive elements with a feed network etched on a first portion of the flexible substrate, parasitic metallic lines etched on a second portion of the flexible substrate and a ground plane for the feed network. The resulting antenna structure is capable of efficiently receiving both satellite and terrestrial SDARS (Satellite digital audio radio service) signals.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a non-provisional or utility patent application corresponding to provisional application titled “Quadrifilar Antenna”, application No. 60/320,280, filed on Jun. 17, 2003 (EFS id: 42034). 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    Satellite digital audio radio service (SDARS) is a satellite broadcast service recently approved by the U.S. Federal Communications Commission (FCC) which provides satellite transmission of digital audio programs to compatible radio receivers. The radio receivers can be stationary or mobile and are generally configured to receive signals from satellites as well as terrestrial repeaters.  
           [0003]    Currently, existing SDARS automotive antenna modules are dual-arm modules: one designed to receive terrestrial (TER) signals and the other designed to receive satellite (SAT) signals. These dual-arm modules comprise two passive antenna elements, two low noise amplifiers (LNAs), and two radio frequency (RF) cables.  
           [0004]    Recently, single-arm automotive roof-mount antennas have been developed. These are patch antennas which are ground dependent, i.e., they must be placed on a metallic surface of dimensions of at least ten times the size of the antenna footprint area for acceptable performance in SDARS applications. These patch antennas, when placed at a proper location on a vehicle roof, have acceptable gain at the horizon (for receiving TER signals) and acceptable gain between 20 and 90-degree elevation angles (for receiving SAT signals). As a result, new single-branch receivers are now being designed resulting in a lower receiver/antenna cost.  
           [0005]    There is a need then, for single-arm mast-type (ground-independent) antennas. These types of antennas can be used in the place of dual-arm glass-mount and mast SDARS antennas.  
           [0006]    A typical mast-type ground-independent antenna used in SDARS applications, is a printed quadrifilar antenna which consists of four helices spaced equally and circumferentially on a cylinder. FIG. 1 [from reference: “Combination linearly polarized and quadrifilar antenna,” A. Petros, U.S. Pat. No. 6,483,471] shows such a quadrifilar antenna consisting of four helical elements and feed network printed on a flexible substrate. As discussed in Antenna Engineering Handbook by Richard C. Johnson and Henry Jasik, pp. 13-19 through 13-21 (1984), a quadrifilar helix (or volute) antenna is a circularly polarized antenna having four orthogonal fractional-turn helixes excited in phase quadrature. Each helix is balun-fed at the top or bottom with four helical arms of wires or metallic strips of resonant lengths (l=.lambda./4, m=1, 2, 3, . . . ) wound on a small diameter with a large pitch angle.  
           [0007]    One embodiment of the novel antenna structure is shown in FIG. 2. It is a combination of quadrifilar antenna and substantially parallel and substantially concentric metallic rings positioned along the longitudinal axis of the quadrifilar antenna. This antenna is capable of efficiently receiving both satellite and terrestrial signals. FIGS. 3 and 4 show additional embodiments of the present invention according to FIG. 2. FIGS. 5 and 6 show alternative embodiments of the novel antenna in accordance with the teachings of the present invention. The quadrifilar antenna elements and rings are arranged on cylindrical structures. These structures are in turn arranged to provide a novel antenna structure of the same radiation properties as the novel antenna structure of FIG. 2. As shown in FIGS. 7 and 8, the radiation pattern of the novel antenna shows improved performance on both SAT and TER cases over the standard quadrifilar antenna. This novel antenna then is an ideal structure for use in SDARS applications.  
           [0008]    An additional benefit of the technique presented here is that it yields lower profile antennas. The height of antennas produced using this technique, is reduced by approximately 15%.  
         SUMMARY OF INVENTION  
         [0009]    In a first aspect of the present invention, the novel quadrifilar helix antenna comprises a flexible substrate where, antenna elements are etched on a first portion of the flexible substrate, and metallic parasitic rings are etched on a second portion of the flexible substrate.  
           [0010]    In a second aspect of the present invention, the novel quadrifilar helix antenna comprises a flexible substrate where, parts of antenna elements and parts of metallic parasitic rings are etched on the same portion of the flexible substrate.  
           [0011]    In a third aspect of the present invention, the metallic rings are shaped into tubular form and inserted inside the tubular quadrifilar antenna.  
           [0012]    In a fourth aspect of the present invention, the metallic rings are arranged in a tubular form and placed over and around the total or partial length of the tubular quadrifilar antenna.  
           [0013]    In a fifth aspect of the present invention, the metallic rings and quadrifilar antenna elements are arranged on the same tubular structure.  
           [0014]    In a sixth aspect of the present invention, a novel method is presented of reducing the height of a quadrifilar antenna by adding substantially circular metallic rings positioned concentrically and longitudinally along the whole or partial length of the quadrifilar antenna helical elements.  
           [0015]    In a seventh aspect of the present invention, a novel method is presented of tuning a quadrifilar antenna by adding substantially circular metallic rings positioned concentrically and longitudinally along the whole or partial length of the quadrifilar antenna helical elements. For example, by removing one or more rings, the frequency of operation increases. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0016]    [0016]FIG. 1 is a diagram that illustrates a conventional quadrifilar helix antenna and its feed network, etched on a thin flexible substrate in accordance with the teachings of the prior art.  
         [0017]    [0017]FIG. 2 is a diagram of an embodiment of the antenna arrangement of the present invention.  
         [0018]    [0018]FIG. 3 is a diagram of an alternative embodiment of the of the antenna arrangement of FIG. 2.  
         [0019]    [0019]FIG. 4 is a diagram of an additional alternative embodiment of the antenna arrangement of FIG. 2.  
         [0020]    [0020]FIG. 5 is a diagram of an embodiment of the antenna arrangement of the present invention using two different substantially cylindrical structures.  
         [0021]    [0021]FIG. 6 is a diagram of an embodiment of the antenna arrangement of the present invention using two different substantially cylindrical structures.  
         [0022]    [0022]FIG. 7 shows a comparison of satellite radiation patterns generated by a typical conventional quadrifilar helix antenna and a quadrifilar helix antenna implemented in accordance with the teachings of the present invention.  
         [0023]    [0023]FIG. 8 shows a comparison of terrestrial radiation patterns generated by a typical conventional quadrifilar helix antenna and a quadrifilar helix antenna implemented in accordance with the teachings of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0024]    Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention.  
         [0025]    While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.  
         [0026]    Referring to FIG. 1, a front plane view of a front side  10  of a substrate  13  used for a conventional quadrifilar helix antenna  19  is shown. The antenna preferably comprises a quadrifilar antenna elements  12  and a feed network  11  etched on a first or top portion of the flexible substrate  13 . The antenna feed point  14 , along with ground  15 , comprise a 50-Ohm point that connects to the receiver&#39;s LNA. The back side  16  of substrate  13  is comprised of a ground plane  17  and a short microstrip line with two vias at its ends  18  as part of feed network  11 . Ground plane  17  is preferably directly underneath feed network  11 .  
         [0027]    [0027]FIG. 2 shows the modified quadrifilar antenna  28  in accordance with the teachings of the present invention. The front side  21  of the antenna is of similar arrangement as that of the conventional quadrifilar antenna. Bck side  22  cis omprisesdof substantially horizontal andparallel metched etallic lstrips or ines  23  spaced a t adistance d  29  with respect to each other. Lines  24  and  25  are such lines. When the quadrifilar antenna is shaped into a cylindrical form  28 , the ends of these lines are connected forming parasitic metallic rings such as in  26  and  27  along the inside wall of quadrifilar antenna  28  and spaced a t adistance d  29  with respect to each other.  
         [0028]    [0028]FIG. 3 shows an alternative embodiment of the novel quadrifilar antenna in accordance with the teachings of the present invention. The front side  31  of the antenna is of similar arrangement as that of the conventional quadrifilar antenna. The back side  32  cis omprisesdof substantially horizontal parallel lines  33  etched on a section of back side  32  and spaced a distance d  39  with respect to each other. Lines  34  and  35  are such lines. When the quadrifilar antenna is shaped into a cylindrical form  38 , the ends of these lines are connected forming parasitic rings such as in  36  and  37  along a section of the inside wall of quadrifilar antenna  38  and spaced a t adistance d  39  with respect to each other.  
         [0029]    [0029]FIG. 4 shows a different embodiment of the novel quadrifilar antenna in accordance with the teachings of the present invention. The front side  41  of the antenna is of similar arrangement as that of the conventional quadrifilar antenna. The back side  42  comprises of substantially horizontal parallel metalliclines  43  etched on a section of back side  42  and spaced at variable distances, i.e., d 1   49  and d 2   50 , with respect to each other. Lines  44  and  45  are such lines. When the quadrifilar antenna is shaped into a cylindrical form  48 , the ends of these lines are connected forming parasitic rings such as in  46  and  47  along a section of the inside wall of quadrifilar antenna  48  and spaced at variable distances with respect to each other.  
         [0030]    [0030]FIG. 5 shows two other embodiments of the novel quadrifilar antenna in accordance with the teachings of the present invention. Antenna structure  51  is comprised of two substantially cylindrical structures: the quadrifilar antenna  52  and the tube  53  with pmetallic ings  54  attached to it. Tube  53  serves as a support structure for pings  54 . The quadrifilar antenna tube  52  diameter is smaller than that of supporting tube  53 . The substantially parallel p metallic rings  54  are spaced a distance d  55  with respect to each other and wrap around and over a section of the quadrifilar antenna  52 . Antenna structure  56  is comprised of two substantially cylindrical structures: the quadrifilar antenna  57  and the tube  58  with pmetalli rings  59  attached to it. Tube  58  serves as a support structure for pings  59 . The substantially parallel pmetalli rings  59  are spaced at variable distances, i.e., d 1   60  and d 2   61 , with respect to each other and wrap around and over a section of the quadrifilar antenna  57 .  
         [0031]    [0031]FIG. 6 shows two more embodiments of the novel quadrifilar antenna in accordance with the teachings of the present invention. Antenna structure  62  is comprised of two substantially cylindrical structures: quadrifilar antenna  63  and tube  64  with pmetalli rings  65  attached to it. Tube  64  serves as a supporting structure for rings  65 . The quadrifilar antenna tube  63  diameter is larger than that of supporting tube  64 . The substantially parallel pings  65  are spaced a distance d  66  with respect to each other and are enclosed by quadrifilar antenna  63 . Antenna structure  67  is comprised of two substantially cylindrical structures: quadrifilar antenna  68  and tube  69  with pings  72  attached to it. Tube  69  serves as a supporting structure for pings  72 . The substantially parallel pings  72  are spaced at variable distances, i.e., d 1   70  and d 2   71 , with respect to each other and are enclosed by quadrifilar antenna  68 .  
         [0032]    The novel quadrifilar may be optimized to provide a desired radiation pattern. This is depicted in FIG. 7 which shows a comparison of satellite radiation patterns generated by a typical conventional quadrifilar helix antenna  76 , and that of a quadrifilar helix antenna implemented in accordance with the teachings of the present invention  77 . Two polar plots are shown in FIG. 7. Circle  75  represents elevation angles with zero degrees being zenith or directly above the antenna, + and60 degrees corresponds to the elevation angle of 30 degrees, and +/−180 degrees being directly below. As seen in FIG. 7, the satellite radiation pattern of the novel antenna iexhibits slightly better. gain  
         [0033]    The real advantage of the antenna implemented in accordance with the teachings of the present invention, is in the terrestrial performance., i.e., antenna gain along the horizon This is depicted in FIG. 8 which shows a comparison of terrestrial radiation patterns generated by a typical conventional quadrifilar helix antenna  86 , and that of a quadrifilar helix antenna implemented in accordance with the teachings of the present invention  87 . Two pazimuth olar plots are shown in FIG. 8. Circle  85  represents elevation angle of zero degrees or the horizon. As seen in FIG. 8, the terrestrial radiation pattern of the novel antenna is better by approximately 3 dB. S Thus a significant improvement in terrestrial reception is achieved without degradation on satellite performance.  
         [0034]    It should be noted that the embodiments described herein should not limit the scope of the invention. For example, ihe quadrifilar antenna in accordance with the present invention can be tuned to receive signals not only for Satellite Digital Audio Radio System (SDARS) signals, but also global positioning satellite signals, or other suitable satellite or terrestrial signals.  
         [0035]    As previously mentioned, although the present invention is described with specific embodiments, variations of these embodiments would still provide excellent performance and should be contemplated and interpreted within the scope of the present invention. For example:, prasitic lmetallic ines or rings do not have to be parallel with respect to each other. Parasitic metalliclines do not have to be etched on the same side of a substrate. Parts of quadrifilar elements and parts of rings can be etched on the same substrate side. PBoth prts of quadrifilar elements and parts of rings can be arranged on the same tubular structure. At least one metallic ring can be arranged on a different tubular structure than other metallic rings. One or more pings may form open ends resulting in open loops. One or more pings can be connected to other pings. Quadrifilar elements and rings can be realized with slots. Rings or loops can extentdbeyond the length of the quadrifilar antenna. The quadrifilar antenna can be any type of helix antenna. Rings or loops can be part of the antenna radome or housing. Rings or loops can be active rings, i.e., they can be connected to one or more antenna elements.