Abstract:
A vehicle window/antenna system with enhanced heating and AM/FM reception. The system includes a window and a heating/antenna grid supported thereon. The grid is separated into upper and lower portions, and functions as an FM antenna. A flat AM antenna is supported on the window between the upper and lower grid portions. The positioning of the AM antenna within the heating grid enables ice and snow to be cleared from the AM antenna. Antenna leads extend from both the upper and lower grid portions as well as the AM antenna. The two FM leads are connected to a Balun transformer to balance the FM signals.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to active antenna systems incorporated into vehicle windows, and more particularly to such systems including two or more antennas for different frequency ranges (such as AM and FM). 
     Active antenna systems are widely used in automotive applications. Such systems include mast antennas and window antennas, which may be integrated into the front, side, or rear windows of a vehicle. Increasingly, the rear window has become a candidate for antenna placement in view of recent aerodynamic design trends. Specifically, the window surface area has increased, particularly on the rear window where the glass is often mounted at a very low angle. Heating the entire rear window for visibility is not necessary, and accordingly, heating grids are typically located over only a portion, for example half, of the glass area. The non-heating grid portion of the window provides adequate space for antennas. 
     It is known to use the heating grid on one of the vehicle windows (usually the rear window) as an antenna for either AM or FM. In such cases, it is necessary to include a second antenna for the other of AM or FM. Fortunately, with the increased surface area on rear windows, there is adequate room for both a heating grid and a second antenna. 
     In a first approach, the heating grid is used as the FM antenna; and a flat AM antenna is incorporated on or in the glass above the heating grid. The system is optimized by both the configuration of the AM antenna and its spacing from the heating grid and the surrounding sheet metal. An example of such a system is illustrated in U.S. Pat. No. 4,791,426 issued Dec. 13, 1988 to Lindenmeier et al and entitled “Active Antenna in the Rear Window of a Motor Vehicle.” 
     In a second approach, the heating grid is used as the AM antenna, which is isolated to ground through an inductor or coil. A separate FM antenna is incorporated on or in the glass above the heating grid, and the FM antenna is capacitively coupled to the heating grid. 
     A disadvantage of both approaches is the reduced sensitivity of the unheated antenna during snow and ice build-up. The heating grid melts snow and ice only in the area of the grid, and consequently snow and ice can accumulate on top of the unheated antenna. Such build-up reduces the sensitivity and performance of the unheated antenna by as much as 3 to 7 dB (decibels). 
     Further, use of the Lindenmeier design on increasingly larger rear windows results in an AM antenna with extremely high gain and sensitivity. This can be undesirable because additional countermeasures must be taken to reduce vehicle noise, overload, FM intrusion, power line noise, and radio settings (e.g. stereo/mono threshold, noise blanker, and frequency high cut). Such counter measures are costly and may also raise the noise floor of the system. 
     SUMMARY OF THE INVENTION 
     The aforementioned problems are overcome in the present invention wherein both AM and FM antennas are provided and configured on a vehicle window so that snow and ice can be removed from both antennas. Specifically, the window heating grid serves as the FM antenna. The heating grid is separated into upper and lower portions spaced from one another. A flat AM antenna is positioned between the upper and lower portions of the heating grid so as to be substantially surrounded by the heating grid. 
     The new design has several advantages. First, snow and ice can be removed from the entire antenna area because the heating grid surrounds the AM antenna. Consequently, activation of the heating grid produces enough heat in the AM antenna area to melt at least the undersurface of snow and ice so that they slide off the entire antenna area, if not melt completely. Second, because the AM antenna is surrounded by the heating grid, the sensitivity of the AM antenna is reduced to a desired level, eliminating the need for countermeasures. 
     These and other objects, advantages, and features of the invention will be more readily understood and appreciated by reference to the detailed description of the preferred embodiments and the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of a first embodiment of the invention; 
     FIG. 2 is a schematic diagram of a second embodiment of the invention; 
     FIG. 3 is a schematic diagram of a third embodiment of the invention; and 
     FIG. 4 is a view similar to FIG.  3  and additionally showing desired spacing relationships between the antenna elements. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     I. First Embodiment 
     A vehicle window and antenna system constructed in accordance with a first embodiment of the invention is illustrated in FIG.  1  and generally designated  10 . The system includes a window  12 , a heating/FM antenna grid  14 , an AM antenna  16 , and an active amplifier system  18 . The grid  14  is arranged, or separated, into an upper portion  14   a  and a lower portion  14   b . The AM antenna  16  is positioned between the upper and lower grid portions  14   a  and b so as to be substantially surrounded by the grid  14 . The amplifier system  18  provides an active output to the radio. 
     The present invention results in enhanced snow and ice removal, particularly from the AM antenna  16 . The heat from the upper and lower portions  14   a  and b of the heating grid  14  cooperates to remove snow and ice from the AM antenna  16 . At a minimum, the heating grid  14  surrounding the AM antenna  16  “cuts” a block of snow or ice that may be over the AM antenna so that the block can slide down onto the lower portion  14   b  for melting. Consequently, the sensitivity of the AM antenna is not impacted by accumulations of snow and ice as in prior art antennas. 
     The window, glass, or window substrate  12  is generally well known to those skilled in the art and will not be described in detail. Appropriate glass is manufactured, for example, by PPG Industries of Pittsburgh, Pennsylvania and Libby-Owens-Ford of Toledo, Ohio. The present invention is not dependent on the window or glass. The window  12  includes a pair of lateral or side edges  13   a  and  13   b  defining the width of the window. 
     Also, the techniques (but not the configuration) for forming the heating grid  14  and the antenna  16  are generally well known. For example, the grid and antenna can be silk-screened onto the interior of the glass or sandwiched between layers of the glass. The particular technique for creating the antennas  14  and  16  is not important to the present invention. 
     The heating antenna grid  14  is used both to heat the window  12  and to serve as the FM (frequency modulation) antenna. As noted above, the FM antenna  14  is arranged or divided into two portions—an upper portion  14   a  and a lower portion  14   b.    
     The lower portion  14   b  includes a pair of opposite bus bars  20   a  and  20   b  located proximate the side edges of the window  12 . A plurality of horizontal grid lines  22  extend between the bus bars  20  to provide an electrically conductive path therebetween. The number of lines will depend on the desired heating and antenna characteristics. Vertical improvement lines  24  interconnect the horizontal lines  22  to improve FM reception as generally know in the art. Additionally, one or more lines (not shown) of varying configuration can be added at the bottom of the grid to fine-tune antenna characteristics, again as generally known in the art. 
     The upper portion  14   a  of the heating grid/FM antenna  14  includes lines  28  which are electrically connected to the bus bars  20 . The lines  28  of the upper portion  14   a  are spaced from the horizontal lines  22  of the lower portion  14   b . As illustrated, the upper portion  14   a  includes two lines  28 . Greater or fewer lines  28  can be included depending on the window configuration and antenna application. It is believed that a single line will perform adequately. 
     Circuitry is included for supplying electrical power to the heating grid  14 . Specifically, power is supplied to the bus bar  20   b  through a coil  32 . The high voltage is grounded  36  through an RF filter  34 , which serves as an FM isolation coil. The bus bar  20   a  is grounded  36  through coil  38 . The described system of powering the heating grid is generally known to those skilled in the art. Other power supply circuitry could be used depending on the application. 
     The second or AM antenna  16  is a flat antenna located between the upper portion  14   a  and the lower portion  14   b  of the FM antenna. The AM antenna  16  includes a side bar  40  and a plurality of linear elements or horizontal lines  42 . Other configurations for implementing a flat antenna are generally known to those skilled in the art. For example, the antenna could include one or more discrete areas of conductive film of the type used in metallized heat-reflecting windows. The flat antenna is completely surrounded by the grid  14 . 
     The amplifier system  18  is also generally known in the art. The system includes an AM amplifier  50  coupled to the AM antenna  16  and an FM amplifier  52  coupled to the FM antenna  14 . The output of the amplifiers  50  and  52  both feed to a common coaxial connection  54  which may be connected to a radio. 
     Second Embodiment 
     A second embodiment of the invention is illustrated in FIG.  2  and generally designated  110 . The window  12  and grids  14  and  16  of the second embodiment are identical to their counterparts in the first embodiment  10  with one exception. Specifically, the bus bar  20   b  has two portions—a lower portion  20   b ′ and an upper portion  20   b ″ separated from one another on the window by a relatively short distance. Consequently, the antenna  16  is substantially surrounded by the grid  14 . However, the two portions  20   b ′ and  20   b ″ are electrically interconnected through a coil  50  in the amplifier system  118 . 
     The amplifier system  118  is different from the amplifier system  18  of the previous embodiment. Specifically, the amplifier system  118  provides diversity of antenna in the FM frequency range. The amplifier system  118  includes an AM amplifier  150  and a pair of FM amplifiers  152 ′ and  152 ″. The AM amplifier receives its input from the AM antenna  16 . The first FM amplifier  152 ′ receives its input from the upper bus portion  20   b ; and the second FM amplifier  152 ″ receives its input from the lower bus portion  20   b ′. The output of the AM amplifier  150  and the first FM amplifier  152 ′ are connected to an AM/FMI lead  154 ′. And the output of the second FM amplifier  152 ″is connected to the FM 2  lead  154 ″. 
     The remaining components of the second embodiment  110  are the same as the first embodiment  10 . 
     Third Embodiment 
     A third embodiment of the present invention is illustrated in FIG.  3  and is generally designated  210 . The window  12 , the antenna heating grid  14 , and the AM antenna  16  are all identical to those of the second embodiment  110 . Only the amplifier system  218  is different from the second embodiment. 
     The amplifier system  218  includes an AM amplifier  250  that receives its input from the AM antenna  16 . The system  218  further includes an FM amplifier  252  and a Balun transformer  256 . The transformer  256  is connected to both of the bus bar portions  20   b ′ and  20   b ″, and has a single output connected to the input of the FM amplifier  252 . As is known in the art, the Balun transformer forces balancing between the two antenna inputs. Accordingly, the directionality of the FM antenna is improved; and currents within the antenna lead  254  are eliminated. 
     Spacing and Relationships 
     FIG. 4 is the same as FIG.  1  and additionally includes identifiers related to the spacing and relationships of the AM antenna elements—both to one another and to the grid  14 . The spacings indicated on FIG. 4 are as follows: 
     L 1  The vertical distance between the upper grid portion  14   a  and the lower grid portion  14   b  (preferably in the range of 140 mm to 160 mm) 
     L 2  The height of the AM antenna 
     L 3  The vertical distance between the AM antenna and both of the upper grid portion  14   a  and the lower grid portion  14   b    
     s The horizontal distance between the AM antenna and the grid  14  (preferably a minimum of 2 mm) 
     s The spacing between the AM antenna elements 
     n The number of antenna elements (preferably 3 or 4 lines) 
     The currently preferred approximate relationships between the spacings are as follows:          L   2     =       2        L   1       3               L   3     =         L   1     -     L   2       2             p   =       L   2       n   -   1                              
     The defined spacings and relationships are believed to optimize AM gain and to provide a signal-to-noise ratio closely approximating that of a conventional passive mast antenna mounted externally on a rear fender of a vehicle. The dimensions L 1 , L 2 , and L 3  will vary with the sensitivity of the amplifier connected to the grid. 
     All of the embodiments have been described in conjunction with AM and FM frequencies. The present invention is readily extendable to other frequencies (e.g. long wave (LW) and short wave (SW) frequencies) by appropriate modification of the antennas. Also, more than two frequency ranges are possible through the inclusion of additional antennas on the window. 
     The above descriptions are those of preferred embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the claims, which are to be interpreted in accordance with the principles of patent law, including the doctrine of equivalents.