Abstract:
A marine multiband antenna array includes a nearly virtual bowtie UHF antenna and a connected VHF/FM antenna that together function as an AM antenna. A diplexer separates the AM/FM radio signals from the UHF/VHF television signals.

Description:
[0001]    This application claims priority on U.S. Provisional Patent Application No. 61/081,244, filed Jul. 16, 2008, incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to antennas and more particularly to marine antennas. 
         [0004]    2. Description of the Related Art 
         [0005]    Contoured antennas for boats that improve appearance are known. See, for example, U.S. Pat. No. 6,927,743, commonly assigned. Multiband antennas that resonate well in different frequency ranges are also known. See, for example, U.S. Pat. No. 5,734,352, commonly owned. 
         [0006]    TV reception for a boat is typically optimized in a horizontal loop antenna of the type made and sold by Glomex of Ravenna, Italy. For example, the Glomex model V9130 antenna comprises horizontal loops in a semi-spherical housing with a reception angle of 60°. The Glomex model V9112 antenna has three horizontal loops in a saucer-shaped housing. Although promoted as being omni-directional, gain patterns of the Glomex antennas show nulls that effectively make them directional, requiring rotation to obtain the best reception. Moreover, both antennas further require an amplifier to boost the signal from the radiator since the amplifier is designed for a power range of only about 12V. A problem with amplifying the signal from such an antenna is that it also amplifies noise and results in less than optimal reception. 
         [0007]    There is a need for a more robust multiband marine antenna that can accommodate VHF and UHF frequency ranges without an amplifier and also resonate at other useful frequencies such as AM/FM radio, all packaged in a single antenna housing of the type disclosed in the &#39;743 patent. 
       SUMMARY OF THE INVENTION 
       [0008]    According to the invention, a marine multiband antenna assembly includes a base plate adapted to function as a ground plane and an antenna extending normally from the base plate. The antenna comprises a lower portion mounted to the base plate and configured to resonate in the UHF band and an upper portion extending from the lower portion and configured to resonate in the FM and VHF frequency ranges whereby the antenna is adapted to receive signals in the AM, FM, VHF, and UHF frequency ranges. The marine antenna is nondirectional and limited in length. The triangular radiator and whip assembly allow the antenna to accommodate the very large frequency range of AM, FM, and television signals. A diplexer for a marine multiband antenna includes an input adapted to connect to a marine multiband antenna, a signal splitter connected to the input for splitting signals from the antenna into two sides, an FM blocking circuit on one side adapted to block signals in the FM frequency range and a capacitor in series with the FM blocking circuit sized to block signals in the AM frequency range wherein the resulting signal is adapted to be received by a conventional TV receiver, and a first inductor connected in series to a second conductor and a capacitor in parallel sized to pass signals in the AM and FM frequency ranges wherein the resulting signal is adapted to be received by a conventional AM/FM receiver. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a sectional view in elevation of a marine housing incorporating a multiband antenna according to the invention. 
           [0010]      FIG. 2  is an expanded side view of the antenna according to the invention. 
           [0011]      FIG. 3  is side view of the whip portion of the antenna of  FIG. 2 . 
           [0012]      FIG. 4  is plan view of the base of the antenna of  FIG. 2 . 
           [0013]      FIG. 5  is a schematic view of the circuit in a diplexer for use with the antenna of  FIG. 2  to separate signals. 
           [0014]      FIG. 6  is a side view of the housing and antenna of  FIG. 1 . 
           [0015]      FIG. 7  is a perspective view of the antenna of  FIG. 2 . 
           [0016]      FIG. 8  is an exploded view of the antenna of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]      FIGS. 1 and 6  show a contoured antenna assembly  10  comprising a cowling  12  and an antenna assembly  14  according to the invention. The cowling  12  will preferably be of a construction such as that disclosed in U.S. Pat. No. 6,927,743, the entire disclosure of which is incorporated herein by reference. 
         [0018]    Looking now also at  FIG. 2 , the antenna assembly  14  comprises a base plate  16  on which is mounted a vertically extending stanchion  18 . An antenna  20  comprises a lower portion  22  and a whip portion  24 . The lower portion  22  comprises a printed circuit board  25  vertically mounted to the base  16  by brackets  26  and, preferably, secured to the stanchion  18 . A flat triangular radiator  28  is disposed on a printed circuit board  25  and is adapted to function as one half of a bow tie antenna for reception in the UHF TV band. The triangular radiator  28  is preferably in the form of an isosceles triangle with a base  30  at an upper edge of the printed circuit board  25  and a vertex  32  facing toward the base plate  16 . To enhance signals in the UHF band, the triangular radiator  28  is preferably disposed such that the longitudinal axis extending from the vertex  32  to the base  30  is disposed approximately at a 25° angle relative to the vertical, thereby providing a horizontal complement to the bow tie. The vertex  32  is electrically connected to a coaxial connector  34  extending through the base plate  16 . 
         [0019]    The whip portion  24  extends at a longitudinal axis  27  from the end of the stanchion  18 . The longitudinal axis  27  is preferably not normal to the base plate  16 , and the rake angle of the whip portion is mostly ornamental, offering an appearance of speed. 
         [0020]    Looking again at  FIG. 1  and also at  FIGS. 4 and 6 , it will be understood that the cowling  12  is secured to the base plate  16 . The whip portion  24  projects through the cowling  12 , generally along the longitudinal axis  27 . The base plate  16  comprises a plurality of fasteners  28  to mount the cowling  12 . Two apertures  30  are provided to secure the brackets  26 , and another aperture  32  is provided to mount the stanchion  18 . Yet a third aperture  34  is provided to secure the coaxial connector  34 . 
         [0021]    Looking now at  FIGS. 2 ,  3 , and  8 , it can be seen that the whip portion  24  comprises an elongated dielectric core  40 , preferably made of fiber glass. An insulated copper wire  42  is wrapped helically around the core from near the proximal end  44  at the stanchion  18  to the distal end  46 . A first section  48  of copper foil tape is wrapped over the insulated wire on the whip near the proximal end  44 , and a second section  50  of copper foil tape is wrapped over the insulated wire on the whip portion near the distal end  46 . The first and second sections  48 ,  50 , are spaced from each other at a gap  52 . A disc capacitor  54  is disposed in a gap  52  and electrically wired to the first and second sections  48 ,  50  across the gap. The end of the insulated copper wire  42  at the distal end  46  is electrically connected to the second section  50 , and the end of the insulated copper wire at the proximal end  44  is electrically connected to the first section  48 . Finally, an inductive coil  56  is wired between the first section  48  and the flat triangular radiator  28 . A protective fiberglass sleeve  58  can be provided for that part of the whip portion  24  that extends outwardly of the cowling  12 . 
         [0022]    With this structure it can be seen that the antenna  20  is nondirectional and limited in length. It is virtually identical in appearance to a conventional VHF marine communications antenna. Yet it can accommodate the very large frequency range of AM, FM, and television signals (0.55 to 700 MHz). The AM band (0.55-1.65 MHz) is captured by the total length of the antenna  20  from the ground plane at the base plate  16  through the flat triangular radiator  28 , the inductor  56 , the insulated copper wire  42  and the second section  50  of the copper foil. The UHF band (470-700 MHz) is captured by the triangular radiator  28  and trapped by the inductive coil  56 . The VHF band (54-88, and 174-216 MHz), and the FM band (88-108 MHz) are captured by the whip portion  24  and the triangular radiator  28 . The first and second sections of copper foil sleeves  48 ,  50  provide effective broad banding within the VHF ranges. The disc capacitor  54  aids in receiving the middle VHF band at 174-216 MHz, and avoids shorting the insulated copper wire  42 . To enhance reception in the VHF band, an additional wire can be connected at the base plate or ferrite beads can be provided on a feed line coaxial cable at approximately a one quarter wavelength in the FM band, or the ground plane can be extended by the addition of a larger horizontal plate. 
         [0023]    If only FM and TV signals were desired from the antenna, it would be conventional to incorporate a notch or bandpass filter to separate the FM frequencies from the middle of the TV frequency range. But where AM signals are also desired, a conventional bandpass filter will not work. The solution can be found in the diplexer circuit  60  according to the invention in  FIG. 5 . Signals from the antenna  20  are split and sent on one side to an FM blocking circuit  62  and on the other side to an inductor  64 . The FM blocking circuit  62  comprises first and second capacitors  66 ,  68  in parallel, and an inductor  70  in parallel with the capacitors. The remaining signal from the FM blocking circuit  62  passes through a capacitor  72  sized to block signals in the AM frequency range. The remaining signals are in the UHF and VHF TV frequency bands to be picked up by a conventional TV receiver. On the other side of the split the signal leaving the inductor  64  is sent to a capacitor  74  and another inductor  76  in parallel to work together to pass the AM and FM signals to be picked up by a conventional AM/FM receiver. 
         [0024]    While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.