Communications: radio wave antennas – Antennas – With vehicle
Reexamination Certificate
2000-08-03
2001-11-13
Wimer, Michael C. (Department: 2821)
Communications: radio wave antennas
Antennas
With vehicle
Reexamination Certificate
active
06317090
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a vehicle antenna and, more particularly, to a solar-ray vehicle antenna provided in the windshield of a vehicle for AM/FM radio reception, that includes a mirror wiring ground strap.
2. Discussion of the Related Art
Most modern vehicles include a vehicle radio that requires an antenna system to receive amplitude modulation (AM) and frequency modulation (FM) broadcasts from various radio stations, Present day vehicle antenna systems may include a mast antenna that extends from a vehicle fender, vehicle roof, or some applicable location on the vehicle. Although mast antennas provide acceptable AM and FM reception, it has been recognized by vehicle manufacturers that the performance of a mast antenna cannot be significantly increased, and therefore, improvements obtained in other areas of in-vehicle entertainment systems will not include reception capabilities of the mast antenna. Consequently, vehicle manufacturers have sought other types of antenna designs to keep pace with consumer demands for increased vehicle stereo and radio capabilities.
Improvements in vehicle antenna systems have included the development of backlite antenna systems, where antenna elements are formed on a rear window of the vehicle in various designs. Backlite antenna systems have provided a number of other advantages over mast antenna systems, including no wind noise, reduced drag on the vehicle, elimination of corrosion of the antenna, no performance change with time, limited risk of vandalism, and reduced cost and installation.
A new concept for antenna systems provides an antenna between the inner and outer laminated glass sheets of a vehicle windshield. U.S. Pat. No. 5,528,314, titled “Transparent Vehicle Window Antenna” issued Jun. 18, 1996 and U.S. Pat. No. 5,739,794 titled “Vehicle Window Antenna With Parasitic Slot Transmission Line,” issued Apr. 14, 1998, disclose “Solar-Ray” antennas of this type, and U.S. Pat. No. 6,020,855 transparent vehicle window antenna with capacitive connection apparatus, issued Feb. 1, 2000.
FIG. 1
is a diagrammatic view of a known Solar-Ray vehicle antenna
10
of the type disclosed in the above mentioned patents laminated in a windshield
12
of a vehicle, The windshield
12
will be mounted within an opening of a vehicle body that is made of an electrically conductive metal, such as steel or aluminum, by known window mounting techniques. The windshield
12
includes a dark tinted region
18
formed along a top border of the windshield
12
that reduces glare for the vehicle operator. The translucent nature of the tinted region
18
can be used to reduce the visibility of the antenna
10
.
The antenna
10
is provided in the windshield
12
as a conductive film applied to the inner surface of an outer glass of the windshield
12
to be contained between outer and inner glass layers of the windshield
12
. The film of the antenna
10
is essentially transparent to visible light, highly reflective of infrared radiation, electrically conducting, and preferably has a sheet resistance of 3 ohms per square or less. An example of a suitable film material is described in U.S. Pat. No. 4,898,789 to Finlay, issued Feb. 6, 1990. The film described herein can include a first anti-reflective metal oxide layer, such as oxide of zinc and tin, an infrared reflect,on metal layer, such as silver, a primer layer containing titanium, a second metal oxide layer, a second infrared reflective metal layer, such as silver, another primer layer, a third anti-reflective metal oxide layer, and an exterior protective layer of titanium metal or titanium oxide.
The antenna
10
includes two basic elements, a horizontally elongated tuning element
20
substantially parallel to and spaced from a top edge
22
of the windshield
12
, and an impedance matching element
24
. The tuning element
20
is essentially rectangular. although As horizontal edges may follow the curvature of the windshield edge
22
and its comers may be rounded for a more pleasing appearance. The tuning element
20
has an effective horizontal length of an odd integer multiple of one-quarter of the wavelength to which it is tuned, and thus exhibits a zero reactive impedance at the tuned wavelength. Different tuning element configurations can be provided in different designs.
In one embodiment, the tuning element
20
is tuned to a wavelength in the center of the FM frequency band (88 MHz-108 MHz), such as 3 meters, and thus has an effective horizontal length of about 0.75 meters. The physical length of the element
20
at resonance is actually somewhat shorter than one-quarter of the center frequency of the FM band to provide coupling to the vehicle body. The length by which the element
20
is shorter will vary with the specific vehicle application. In one particular vehicle, the tuning element
20
has been found to work well with a horizontal length of 60 cm and a vertical width of 50 mm. The element
20
is ideally spaced below the windshield edge
22
by a distance which provides maximum FM gain. However, this distance may be varied to provide other advantages for a particular vehicle design. The antenna
10
provides AM reception through capacitive coupling with the vehicle body.
The impedance element
24
includes a main body portion
28
which covers substantially all or most of the windshield
12
below the tinted region
18
to provide FM impedance matching. In the '794 patent, the impedance element can be a ribbon in various configurations to form a parasitic slot transmission line for FM impedance matching purposes. The main portion
28
has a peripheral edge
32
with a horizontal upper portion
34
spaced at least 25 mm below the lower edge of the element
20
, so as to minimize transmission coupling effects therebetween. The upper portion
34
is connected to the element
20
by a narrow vertical portion
36
to provide an electrical current flow. The upper portion
34
of the peripheral edge
32
is preferably within the tinted region
18
of the windshield
12
along its entire length from one side to the other side of the windshield
12
, so that the tinted region
18
overlaps the main portion
28
of the element
24
. The remaining portion of the peripheral edge
32
is spaced a certain distance from the edge of the vehicle body so as to provide, in combination therewith, a planar slot transmission line that is parasitically coupled to the element
20
. In one embodiment. the distance between the edge of the vehicle body and the main portion
28
is preferably within the 10-25 mm range. The length of the slot is substantially an integer multiple of one-half of the wavelength to which the tuning element
20
is tuned, so that each end of the slot transmission line, at the junctions of the upper portion
34
and the remaining portion of the peripheral edge
32
, appears as an electrical open circuit.
The impedance element
24
is used to adjust the real component. of the antenna's impedance to match the characteristic impedance, typically 125 ohms, of the coaxial cable used to feed the antenna
10
. This is accomplished by the predetermined width between the remaining portion of the peripheral edge
32
and the adjacent portion of the edge of the windshield. For appearance purposes, and to maximize the infrared reflecting efficiency of the windshield
12
, an opaque painted band
40
may be provided around the sides and bottom of the windshield
12
to substantially or completely cover the area outward from the remainder portion of the peripheral edge
32
to the outer edge of the windshield
12
. This band can be broken into dots of decreasing size towards the inner boundary for a fade-out effect, as known in the industry. If such a band is provided in combination with the tinted region
18
, substantially the entire viewing area of the windshield
12
can be uniformly provided with the infrared reflecting film of the antenna
10
.
The impedance element
24
also provides an added benefit at AM wavelengths.
Martin Douglas Courtney
Nagy Louis Leonard
DeVries Christopher
General Motors Corporation
Wimer Michael C.
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