Patent Application
20150222242
The presently disclosed invention is generally related to connectors for vehicle antennas and, more specifically, to connectors for use in connection with laminated glass antennas such as a wire antenna that is embedded in a window laminate or a slot antenna that is located at the perimeter of a panel of window glass that is coated with an infrared reflective thin film.
Vehicle window antennas that include embedded wires or silver print antennas in the rear window and windshield have been used in the prior art as an alternative to conventional whip antennas and roof mounted mast antennas. More recently, vehicle windows that are coated with an infrared reflective, thin metal film also have been used in connection with vehicle antennas. In the case of laminated glazing, the glass is formed of outer and inner glass plies that are bonded together by an interposed layer, preferably of a standard polyvinylbutyral or similar plastic material. The antenna may be screen printed on one of the inner surfaces of the glass plies using conductive ink such as silver paste or, alternatively, the antenna may be a thin conductive wire that is embedded in one of the surfaces of the interlayer.
There have been two ways to feed an antenna that is located in a laminated glazing—galvanic feed or coupling feed. The most common method has been direct feed by a galvanic connection through a flexible, flat connector. The flat connector comprises a conductor trace that is printed on a dielectric layer and covered with a dielectric tape. One end of a flat cable or film connector is soldered to an antenna wire or conductive printed pad and remains in the glazing structure when the window is laminated. The other end of the connector wraps over the outside edge of the glazing to connect to the exterior vehicle electronics.
Another method for connecting to antennas that are located in a laminated glazing has been a coupling feed. The coupling feed eliminates the need to solder the antenna to a connector or to pass a connector beyond the perimeter edge of glass to feed the antenna. For example, U.S. Pat. No. 8,077,100B2 to Baranski discloses an antenna coupling apparatus that transfers the antenna signal from an antenna wire situated inside laminated glass to a connector on an exterior surface of the glass. However, the Baranski antenna connector is based on transmission line coupling theory so that it cannot meet wide frequency band requirements such as for TV antennas that have as many as five frequency bands.
For efficient performance, the impedance of an antenna must be matched to the impedance of the transmission line that carries signals to and from the antenna. Any mismatch in impedance between antenna and the transmission line will increase the standing wave that is present on the transmission line when transmitting or reduce the signal present on the transmission line when receiving. Such impedance matching must occur physically at the point of interconnection between the laminated glass antenna and a coaxial cable or an antenna amplifier input. Preferably, the impedance matching occurs in the FM, TV or other operating frequency bands where the input impedance is often 50Ω. WIPO Patent Application WO/2012/136411 to Bernhard discloses a flat antenna connector with a conductive shield on top of the antenna trace to increase capacitive coupling to the ground to improve signal transmission and reduce interference. The coupling capacitance acts as a high pass filter that improves the TV antenna performance at the UHF band (470 MHz-860 MHz). However, that design tends to degrade antenna performance at the lower frequency band such as the TV VHF band from 47 to 240 MHz.
With rapid growth in the demand for vehicle electronics, more and more antennas are being integrated to vehicles. Even though traditional mast or whip antennas have provided satisfactory performance in the past, often they are no longer preferred because they are considered to detract from vehicle aesthetics. With a greater number of antennas being integrated into window glazing, it was seen that there was a need in the prior art for an antenna connector that provided impedance matching to the laminated glass antenna. Such an antenna would be advantageous in comparison to a standard antenna connector.
In accordance with the presently disclosed invention, an antenna connector for use with laminated glass antennas provides wideband impedance matching to improve antenna performance. The antenna connector is compatible with embedded wiring, silver print, or IR coated antennas. The antenna connector is adapted to receive signals from an antenna and provides impedance matching to an electronic device. The antenna connector includes a flexible insulating substrate, a transmission line that is printed on the insulating substrate to conduct a signal between the antenna and the electronic device, and an insulating cover tape that isolates the transmission line from electrical ground.
The transmission line includes a solder pad that is laminated inside the glass and galvanically connected to the antenna, a thin conductive trace portion that is partially inside the laminated glazing and partially outside the glazing and taped to the exterior surface of the glass, a wide conductive trace portion that is capacitively coupled to the vehicle ground frame, and a terminal portion that is connected to an electronics device that is mounted on the metal frame of the vehicle.
In the presently preferred embodiment, the thinner portion of the transmission line is equivalent to a series inductor and the wider portion of the transmission line which is coupled to the vehicle ground frame is equivalent to a shunt capacitor. The inductor and capacitor form an LC matching network between the antenna and the coaxial cable or vehicle electronic device. The inductance and capacitance of the LC network is adjustable by changing the trace length and width of each portion of the transmission line so as to match the impedance of the electronic device to the impedance of the antenna at the selected frequency range for which the antenna is designed.
For a more complete understanding of the presently disclosed invention, reference should be had to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention. In the drawings:
Windshield 20 is a laminated vehicle windshield that is formed of outer and inner glass plies 14 and 12. Glass plies 12 and 14 are bonded together by an interposed layer 18, preferably of a standard polyvinylbutyral or similar plastic material. Outer glass ply 14 has an outer surface 140 (conventionally referred to as the number 1 surface) on the outside of the vehicle and an inner surface 142 (conventionally referred to as the number 2 surface). Inner glass ply 12 has an outer surface 122 (conventionally referred to as the number 3 surface) on the inside of windshield 20 and an inner surface 120 (conventionally referred to as the number 4 surface) that is internal to vehicle interior. The interlayer 18 is between surfaces 142 and 122.
As shown in
Windshield 20 may further include an electro-conductive element 16 that occupies the daylight opening of the transparency. Element 16 is preferably a transparent electro-conductive coating that is applied to surface 142 of the outer glass ply 14 (as shown in
The conductive coating 16 has a peripheral edge 17 that is spaced laterally inward from the vehicle body window edge 11 to define an annular slot antenna between edge 11 and coating edge 17. The slot antenna may be fed directly by an antenna connector 32 as illustrated in
Referring to
The thinner metal trace 334 of transmission line 330 limits capacitive coupling between the metal trace and the vehicle grounding structure. The antenna impedance has a real component and reactive component, but only the real component results in radiation loss. For windshield imbedded wire antennas, there are limitations as to wire placement in the glass area. The limitations include aesthetics, obtrusiveness, and visibility. Therefore, most antenna wires are located out of the daylight area of the window and near the window frame grounding structure. This generally causes the impedance of the antenna to have a capacitive reactive component in the UHF band. The same applies for the IR coated slot antenna. A thin trace has self-inductance which partly offsets the capacitive reactance of the antenna impedance in the UHF band. Preferably, the connector is designed so that the inductance of thin trace 334 cancels out the capacitive reactance of the antenna. The inductance of thin trace 334 is a function of the cross-sectional area of the metal trace, the trace length, the operating frequency and the materials surrounding the metal trace.
The wider conductive trace 333 of transmission line 330 is capacitively coupled to vehicle ground body 30 where the electronic device 50 is mounted. The wider conductive trace 333 forms a shunt capacitor to the ground and tends to contribute to matching the antenna impedance across the VHF and UHF bands. Capacitance between trace 333 and ground flange 38 is determined by their interfacing area, the space between them measured in the normal direction, and the dielectric constant of the material between the trace 333 and the ground flange 38. Accordingly, the area of the interface and the normal dimension between trace 333 and ground flange 38 can be designed to match antenna impedance to transmission line impedance. This tends to minimize the net reactive component presented to the transmission line and thereby maximize radio frequency energy transfer in the VHF and UHF frequency bands.
In the presently disclosed invention, the antenna connector described herein is not only simple in construction and easy to manufacture, but has capability for antenna tuning and impedance matching. The antenna matching LC network is tunable. Its capacitance and inductance can be adjusted to match the antenna impedance to the input impedance of an electronic device or a coaxial cable which is typically 50Ω at resonate frequencies. The inductance of the antenna connector is adjusted by changing the length and cross-sectional area of metal trace 334. The trace width can be from 0.01 mm to 1.0 mm with a 35 μm thick metal trace. For windshield TV antenna applications, a trace width between 0.1 mm and 0.3 mm was found to be a preferred range for the presently disclosed embodiment. The capacitance of the antenna connector is adjusted by changing the length, and/or the width of the wider trace 333 and/or its relative distance to the grounding flange. A preferred trace width between 4 mm to 12 mm has been found to be suitable for a windshield TV antenna application. The total length of the antenna connector can be optimized such that the LC network provides best antenna impedance matching in the operating frequency band under the selected location of the antenna connector exiting a window and the mount location of associated electronics, because the length of the antenna connector and its distance to the grounding flange affect the shunt capacitance of the LC network.
The invention described and illustrated herein represents a description of illustrative preferred embodiments thereof. It will be within the ability of one of ordinary skill in the art to make alterations or modifications to the present invention, such as through the substitution of equivalent materials or structure arrangements, or through the use of equivalent process steps, so as to be able to practice the present invention without departing from the spirit and scope of the appended claims.
