Abstract:
An antenna disposed on glass including first and second spatially separated grid portions is disclosed. The first grid portion is electromagnetically coupled to the second grid portion to provide reception of AM and FM signals.

Description:
TECHNICAL FIELD  
       [0001]     This invention generally relates to vehicle radio antennas and more specifically relates to vehicle radio antennas which are integrated with the vehicle windows.  
       BACKGROUND OF THE INVENTION  
       [0002]     In order to enhance a vehicle&#39;s aesthetic qualities, it is common to integrate vehicle radio antennas with one or more of the vehicle&#39;s windows (commonly known as hidden antenna systems or on-glass AM/FM antenna systems). Unlike mast (i.e. rod) antennas, on-glass antenna systems do not introduce any external vehicle protrusions and they typically offer excellent mechanical stability and satisfactory reception performance. Although on-glass antennas are widely used, they do suffer from various drawbacks. Specifically, on-glass antennas are difficult to design because a small change in a vehicle&#39;s body design can radically change the reception performance of the antenna.  
         [0003]     On-glass antenna systems are usually fabricated by printing metallic conductors on an inner surface of the back-glass or the side-glass ( FIG. 1 ) of a vehicle window. A low-noise-amplifier (LNA) circuit is typically mounted in close proximity to the on-glass antenna and is electrically coupled to the on-glass antenna to amplify the weak signal received by the antenna before it is sent to the radio receiver for further conditioning. The on-glass antennas are typically fed vertically (close to the vehicle roof) so that the LNA circuit can be housed in the vicinity where the vehicle roof intersects the window.  
         [0004]     Referring to  FIG. 2 , it is also known to locate on-glass antennas on the back glass  3  (i.e. rear windshield glass) of a vehicle, V, to provide an AM/FM antenna system. As illustrated, the rear windshield glass  3  includes a plurality of horizontally-fed wires  4  that function as a defroster grid to melt or snow and ice from the glass  3 . Additional grid lines (not shown) that are on or, in close proximity to the horizontal defroster grid lines  4  may also be used as the AM/FM antenna system. However, such additional grid line are generally not adequate to provide a desired signal reception performance.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0006]      FIG. 1  is an environmental view of a conventional on-glass antenna;  
         [0007]      FIG. 2  is a conventional environmental view of a defroster grid disposed on a rear-windshield glass;  
         [0008]      FIG. 3  is a dual grid antenna according to an embodiment; and  
         [0009]      FIG. 4  is a dual grid antenna according to another embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]     Referring to  FIG. 3 , an AM/FM antenna  10  is shown located on a rear-windshield glass  11 . Although the illustrated embodiment is disclosed in conjunction with a rear-windshield glass implementation, it is to be understood that the illustrated embodiment is not limited to a rear-windshield glass implementation and that the illustrated embodiment can just as easily be implemented on the side glass or front-windshield of a vehicle, V.  
         [0011]     The AM/FM antenna consists of two separate wire-grid structures  12   a ,  12   b . The first grid structure  12   a , which is the FM antenna, utilizes the already existing defroster grid, which includes a plurality of horizontally-disposed wires  14   a - 14   d  and an added modification defined by a plurality of vertical wires  16   a - 16   d  and a defroster grid perimeter defined by side wires  20   a ,  20   b  and upper and lower wires  20   c ,  20   d . The FM antenna  12   a  also includes a main feed  18  that extends generally horizontally and connects to the defroster-grid perimeter at the side wire  20   a . As illustrated, the vertical wires  16   a - 16   d  intersect the horizontally disposed wires  14   a - 14   d  to connect the upper and lower wires  20   c ,  20   d.    
         [0012]     The second grid structure  12   b , which is the AM antenna, is located above the FM antenna  12   a . The AM antenna  12   b  includes a main feed  22  that extends generally horizontally and is connected to a bifurcated wire feed fork that includes a side wire  24   a  and upper and lower wires  24   b ,  24   c . As illustrated, the AM antenna  12   b  is electromagnetically coupled to the bifurcated wire feed fork. A plurality of vertical wires  28   a - 28   c  intersect a plurality of horizontally disposed wires  30   a - 30   c  to connect the upper and lower wires  26   b ,  26   c.    
         [0013]     The side wire  26   a , the upper and lower wires  26   b ,  26   c , the vertical wires  28   a - 28   c , and the horizontally-disposed wires  30   a - 30   c , form multiple loop structures, which is shown for example, at the arrow, L, which is formed by the wires  28   a ,  28   c ,  30   b ,  30   c . Accordingly, the loop structures, such as L, aid the directionality of the FM antenna pattern over its entire frequency range. Directionality is defined as the difference between maximum and minimum gains in a radiation pattern. For example, if the maximum gain is +3 dBd at 45° but the minimum gain is −8 dBd at 143°, then directionality is 11 dB. Typically, automotive original equipment manufacturers (OEM) specify the directionality at 15 dBd.  
         [0014]     As illustrated, the AM antenna  12   b  includes a generally defined ‘open end,’ which is designated generally at  32 , such that the horizontally-disposed wires  30   a - 30   c  are not connected by a vertical wire, which is similar to the side wire  26   a  that connects the upper and lower wires  26   b ,  26   c . As illustrated, the FM and AM grids  12   a ,  12   b , although spatially separated, are electromagnetically-coupled. The location of the AM antenna grid  12   b  also provides a uniform ground for FM antenna  12   b , which, as a result, improves overall FM antenna performance.  
         [0015]     Referring to  FIG. 4 , another embodiment of the invention is disclosed generally at reference numeral  100 , which includes a remote keyless entry (RKE)/tire pressure monitoring (TPM) antenna  12   c  located substantially above the AM antenna  12   b . The RKE/TPM antenna  12   c  includes a feed line  50  and an antenna element  75 . The horizontal length of the antenna element  75  is not relatively long enough and the inverted T-structured spacing from the vehicle roof (not shown) formed by the feed line  50  does not interfere with the operation of the AM antenna  12   b . Therefore, by being able to locate the RKE/TPM antenna  12   c  on the same glass  11  as the FM and AM antennas  12   a ,  12   b , additional design flexibility is enabled without compromising the operation of the FM or AM antennas  12   a ,  12   b.    
         [0016]     All of the embodiments disclosed herein have a preferred range of antenna conductor width of 0.25 mm to 1.50 mm. However, it will be appreciated that other conductor widths may be used if desired. As such, it is recognized that those skilled in the art may make various modifications or additions to the embodiments chosen here to illustrate the present invention, without departing from the spirit of the present invention. Accordingly, it is to be understood that the subject matter sought to be afforded protection hereby should be deemed to extend to the subject matter defined in the appended claims, including all fair equivalents thereof.