Window antenna

A vehicle window assembly. The window assembly includes a glass ply and an electro-conductive coating located on a surface of the glass ply. The electro-conductive coating has an outer peripheral edge that is adapted to be spaced from an inner metal edge of a vehicle frame so as to define an antenna slot. The electro-conductive coating includes at least one deleted portion adjacent the outer peripheral edge, wherein the deleted portion is sized to tune the antenna slot to a desired resonant frequency.

BACKGROUND

Automotive vehicle window antennas, including embedded wire or silver print antennas in rear windows and windshields, have been used for many years. More recently, metal coated infrared ray reflective thin films have been used as antennas.

Several antennas have been proposed which use a wire antenna of a quarter or half wavelength that is formed in a vehicle window by a thin film or a conductive coating on or between the layers of the glass window. Such designs may include automotive antennas that have several electrically interconnected coating regions and a transparent coating in the shape of a “T”. Also, antennas that divide the conductive coating into two pieces and have the AM and FM antennas separated to reduce AM noise and improve system performance are known.

Another proposed solution is to form a slot antenna between the metal frame of a window and a conductive transparent film panel that is bonded to the window and has an outer peripheral edge spaced from the inner edge of the window frame to define the slot antenna. Examples utilize at least one edge with a conductive coating overlapping the window frame of the vehicle body to short the coating to ground at high frequencies by coupling so as to improve transmission and reception of radio frequency waves.

From an aesthetic point of view the slot antenna concept is a generally good solution because the antenna is invisible and can be used on any window. Another benefit is a heat load reduction because the slot antenna removes a small area of heated reflective coating compared to other antenna concepts. There are various technical challenges to implementing slot antennas, especially on the windshield of a vehicle. First, there is only a limited area around the window perimeter to put the antenna elements and it may be difficult to design an antenna to meet the performance requirements. Second, slot antennas are difficult to tune to a frequency band because the antenna characteristics depend on the slot dimensions. For example, the perimeter of the window defines the maximum slot length, which defines the lowest frequency application. The lowest frequency applications may not be in the frequency band of interest. Various windshield and back glass window slot antennas can cover the FM frequency band but not the TV band I (47 MHz-68 MHz). Thus, there is a need for an antenna, for example a windshield hidden antenna, with a tunable frequency band for different applications. There is also a need for a vehicle slot antenna with advanced antenna matching and frequency tuning methods that can be used to design an antenna with acceptable performance while retaining all solar benefits of the heat reflective coating and having good aesthetics.

SUMMARY

Various embodiments of the present invention are directed to a vehicle window assembly. The vehicle window assembly includes a frame having an inner metal edge and a window pane fixed to the frame. The window pane includes an inner glass ply, an outer glass ply, and an interlayer between the inner glass ply and the outer glass ply. The window pane also includes an electro-conductive coating located on a surface of the outer glass ply, wherein the electro-conductive coating has an outer peripheral edge spaced from the inner metal edge of the frame to define an antenna slot, and wherein the electro-conductive coating includes at least one deleted portion adjacent the antenna slot, wherein the deleted portion is sized to tune the antenna slot to a desired resonant frequency. The vehicle window assembly further includes an antenna feed structure electrically connected to the outer peripheral edge of the electro-conductive coating.

Various embodiments of the present invention are directed to a vehicle window assembly. The window assembly includes a glass ply and an electro-conductive coating located on a surface of the glass ply. The electro-conductive coating has an outer peripheral edge that is adapted to be spaced from an inner metal edge of a vehicle frame so as to define an antenna slot. The electro-conductive coating includes at least one deleted portion adjacent the outer peripheral edge, wherein the deleted portion is sized to tune the antenna slot to a desired resonant frequency.

Those and other details, objects, and advantages of the present invention will become better understood or apparent from the following description and drawings showing embodiments thereof.

DESCRIPTION

Embodiments of the present invention are directed to a slot antenna for a vehicle. The slot antenna forms between the metal frame of a window and a conductive transparent film panel that is bonded to the window and has an outer peripheral edge spaced from the inner edge of the window frame to define a slot antenna. The slot length is chosen such as to support fundamental modes, at frequency bands of interest. The annular slot formed between the vehicle frame and the conductive coating edges is the longest slot size and thus defines the fundamental mode with the lowest resonant frequency. The total slot length may be one wavelength for annual slot antenna or one-half wavelength for non annular shaped slot for the fundamental excitation mode.

The slot length can be electrically shorted by overlapping one or more edges of the window coating with the vehicle frame such that the radio frequency signal is shorted to the vehicle frame through coupling. This provides a manner of tuning the slot antenna for different applications of higher frequency bands. Slot antennas formed from different sides of a window have different field distributions and different antenna patterns and hence yield a diversity of reception.

The slot length can be increased by introducing one or more slits on its perimeter by removing the conductive coating. The radio frequency current is forced to detour around the slits and therefore increases the electrical length of the slot. As a result the resonant mode frequency is shifted towards lower frequency bands. The length, width, and number of slits are determined by the window size and the frequency band of interest.

In various embodiments, the slot antenna can either be fed directly or by capacitive coupling. The coupling feed may have the advantage of easier antenna tuning and manufacture. The antenna feeding structure in various embodiments is designed to excite multiple modes of the slot antenna to support applications of different electronic devices at different frequency bands.

FIG. 1illustrates a transparent windshield assembly10and its associated body structures according to various embodiments of the present invention. A windshield20is surrounded by a metal frame30, which has a window aperture defined by a vehicle body window edge11. As described herein, embodiments of the present invention may be used on windows and window assemblies that are not windshields but other types of windows or window assemblies. For example, embodiments of the present invention may be incorporated into any window or sunroof. In the interest of clarity, all such windows and window assemblies are referred to herein as windshield20. An outer edge21of the windshield20overlaps an annular flange38of the frame30to allow securing of the windshield20to the vehicle body of which the frame30is a part. As seen inFIG. 2, an annular sealing member35is placed between the windshield20and the flange38and a molding34bridges the outer gap between the frame30and the windshield20.

The windshield20may be a standard laminated vehicle windshield formed of outer glass ply12and inner glass ply14bonded together by an interposed layer, or interlayer,18. The interposed layer18may be constructed of, for example, a standard polyvinylbutyral or any type of plastic material. The outer glass ply14has an outer surface140(conventionally referred to as the number1surface) on the outside of the vehicle and an inner surface142(conventionally referred to as the number2surface). The inner glass ply12has an outer surface122(conventionally referred to as the number3surface) on the inside of the vehicle and an inner surface120(conventionally referred to as the number4surface) internal to the windshield20. The interlayer18is between the surfaces142and122.

As shown inFIG. 2, the windshield20may include a dark, or black, paint band22around the perimeter of the windshield20to conceal the antenna elements and other apparatus (not shown) around the edge of the windshield20.

The windshield20further includes an electro-conductive element, or conductive coating,16which occupies the daylight opening of the transparency. The coating16may be constructed of transparent electro-conductive coatings applied on the surface142of the outer glass ply14(as shown inFIG. 2) or on the surface122of the inner glass ply12, in any manner known in the art. The coating16may include in single or multiple layers, a metal containing coating such as, for example, those disclosed in U.S. Pat. No. 3,655,545 to Gillery et al., U.S. Pat. No. 3,962,488 to Gillery and U.S. Pat. No. 4,898,789 to Finley.

The conductive coating16has a peripheral edge17which is spaced from the vehicle body window edge11and defines an annular antenna slot13between the edge11and the peripheral edge17. In one embodiment, the slot width is sufficiently large enough that the capacitive effects across it at the frequency of operation are negligible such that the signal is not shorted out. In one embodiment, the slot width is greater than 10 mm. In one embodiment, the length of the slot13is an integer multiple of wavelength for an annular slot or an integer multiple of one-half of the wavelength for a non-annular slot with respect to resonant frequency of the desired application. For a windshield of a typical vehicle, the slot length is such as to resonant at the VHF band and can be used for TV VHF band and FM applications.

FIG. 2illustrates one embodiment in which the slot antenna is directly fed by an unbalanced transmission line, such as a coaxial cable50. A metal foil, such as a copper foil,32is conductively connected to the peripheral edge17and is laminated with the interlayer18between the outer glass ply14and the inner glass ply12. The copper foil32is folded back around the edges of the interlayer18and the inner glass ply12and sandwiched between the surface120of the inner glass ply12and the sealing member (e.g., a glue bead)35. The copper foil32is conductively connected to a center conductor44of the coaxial cable50. The copper foil32may be covered by, for example, plastic tape so that it is isolated from contact with the frame30and shorts out the radio frequency signals when they pass through the flange38and the sealing member35. The cable ground46is connected to the frame30near the inner metal edge11of the window flange38.

It may be difficult to conductively connect the center conductor44of the coaxial cable50to the coating16because the coating16is thin. Also, the antenna matching and tuning may be difficult because the antenna elements may be laminated inside the glass plies12and14without easy access. The higher order modes of the slot13present a significant reactive component and, in one embodiment, only the two lower modes in the VHF band can be excited with mode impedance of approximately 50Ω using the antenna feeding method described herein.

FIG. 3illustrates an embodiment of an antenna feeding arrangement that can be used to capacitavely connect the center conductor44to the coating16using a printed ceramic line on surface120of the inner glass ply12. The center conductor44is thus connected to a more robust ceramic print on the surface of the inner glass ply12. A shown inFIG. 3, the antenna feeding element40is incorporated between the glass plies12and14. The feeding element40may be, for example, a metal layer such as a copper tape, a silver ceramic, or any other metal tape that is bonded to the surface122of the inner glass ply12and is separated from the coating16by the interlayer18. A metal foil, such as a copper foil,33, soldered to the antenna feeding element40and covered with, for example, plastic tape, is connected conductively to the center conductor44of a coaxial cable50in, for example, a conventional manner, such as soldering or through a mating blade connector.

FIG. 4illustrates an embodiment in which an antenna feeding element41, such as a metal tape or a silver ceramic, is bonded to the interior surface120of the inner glass ply12. The antenna feeding element41is separated from coating16by the interlayer18and the inner glass ply12. The center conductor44of the coaxial cable50is connected to the antenna feeding element41by an insulated wire or foil in, for example, a conventional manner, such as soldering or through a mating blade connector.

The capacitive coupling may preferably, in various embodiments, be an antenna feeding arrangement because in various embodiments it provides a relatively easier manufacturing process and gives an opportunity for antenna tuning and impedance matching. The antenna feeding arrangement presents an impedance transfer into the slot antenna modes with its own impedances, which is a function of feed position, frequency and mode. Only the modes that are matched to the transmission line characteristic impedance, for example 50Ω, can be excited. Comparing to the direct feed as shown inFIG. 2, the capacitive coupling feed as shown inFIG. 4may provide easier access for tuning the capacitance for impedance matching because the antenna feeding element41is on the interior surface120of the inner glass ply12. The impedance of the slot antenna13in accordance with embodiments of the present invention has a real component and a reactive component. In various embodiments, the higher order modes of the slot antenna13were found to have a reactive component which is conductive. Only the real part represents radiation loss. Because the capacitance between the antenna feeding element41and the coating16is determined by the interfacing area, the distance between the elements, and the dielectric constant of the material, the interfacing area and the distance can be selected by design to match the antenna to the transmission line and thus minimize the net reactive component seen by the transmission line and thereby maximize radio frequency energy transfer, especially for the UHF frequency band. The antenna feed location can be selected such that certain modes can be excited for each application of different frequencies. The capacitive coupling also provides DC isolation from the coating16when the resistance of the coating16is used for, for example, defogger or deicing purposes.

Referring again toFIG. 1, in one embodiment two antennas may be symmetrically located along an A-pillar of the vehicle body in which the windshield20is mounted. In one embodiment the two antenna feeds are at least λ/4 wavelength apart and are weakly coupled and thus both can be used simultaneously for, for example, an FM and TV diversity antenna system. The antenna can be fed at the top and the bottom of the windshield20resulting in more spatial and pattern diversity. The antenna feed at the sides provides more antenna gain for horizontal polarization while the antenna feed at the top and bottom gives more gain in vertical polarization.

The resonant frequencies of the antenna fundamental modes are determined predominantly by the slot length, which can be designed such that the mode resonant frequencies are aligned with the operation frequencies of vehicle electronics systems. The slot length can be shorted by overlapping one or more side edges of the coating16with the vehicle frame30such that the radio frequency signal is shorted to the frame30through capacitive coupling. Such an arrangement allows for tuning the slot antenna13for different applications of higher frequency bands. The longest slot length is the total length of the windshield perimeter, i.e., the length of the slot13as shown inFIG. 1. The slot length can be further increased by introducing one or more slits near the edge portions of the coating16by removing a portion or portions of the coating16. The radio frequency current is forced to detour around the slits and therefore increases the electrical length of the slot13. As a result the resonant mode frequency is shifted towards a lower frequency band. Therefore, antennas incorporating features of embodiments of the present invention provide an arrangement that can tune the antenna resonant frequency higher or lower to meet the needs of the vehicle electronics system.

FIG. 5illustrates a transparent glass antenna according to various embodiments of the present invention. The total slot length is increased by introducing three slits46on the perimeter of the coating16. This is done by removing the coating16at targeted areas through, for example, mask or laser deletion. The electromagnetic current is forced to detour around the slits46and therefore the electrical length of the slot13is increased. As a result the resonant mode frequency is shifted towards a lower frequency band. The length, width, and number of slits are determined by the window size and the frequency band of interest. In one embodiment, the slits are introduced in any part of the conductive coating16in, for example, the dark paint band22such that the deletion is not visible.

An embodiment similar to that illustrated inFIG. 5was constructed and tested.FIG. 6is a plot of the return loss (S11) of the slot antenna13. Return loss S11represents how much power is reflected from the antenna. If S11=0 dB, then all the power is reflected from the antenna and nothing is radiated. If S11=−10 dB, this implies that 10% of the power delivered to the antenna is reflected. The rest was “accepted” by the antenna and the majority of the power delivered to the antenna is radiated.FIG. 6shows that the antenna radiates well in multiple bands from 45 MHz up to 860 MHZ, which covers TV band I (47-68 MHz), TV band III (174 MHz-230 MHz), DAB band III (174 MHz-240 MHz), Remote Keyless Entry (RKE) (315 MHz and 433.92 MHz), and TV bands IV and V (474 MHz-860 MHz). The slot antenna demonstrates the capability for multi-band application which can reduce the number of antennas, simplify antenna amplifier design, and reduce overall costs for the antenna system.

FIGS. 7-16are polar plots showing the amplitude of the received signal as a′ function of the direction of arrival of the signal with respect to the front of the vehicle at4frequency bands. In the plots, the radius is proportional to the signal power reference to dBi (relative to an isotropic antenna source), with each circle representing a 10 dB change. The circular axis represents the 360° divisions of direction with respect to the vehicle front. Each plot illustrates the antenna gain pattern at one frequency of each frequency band at vertical and horizontal polarizations.FIGS. 7 and 8illustrate antenna gain patterns at 59 MHz in TV band I for vertical and horizontal polarizations, respectively. The patterns exhibit noticeable nulls in the two sides for vertical polarization and in the top and bottom for horizontal polarization.FIGS. 9 and 10show antenna patterns of the same antenna for both polarizations at 230 MHz in TV band III. There are nulls in the pattern but not in the same directions for passenger side and driver side antennas, the combination of both antennas for diversity antenna systems provide a more uniform pattern over 360° of azimuth angles.FIGS. 11 and 12illustrate the antenna pattern at the Remote Keyless Entry frequency of 433.92 MHz. For either vertical or horizontal polarizations, both antennas exhibit an azimuthally omnidirectional behavior with little signal variation as the orientation of the vehicle to a transmitter is changed. Antenna gain patterns of vertical and horizontal polarization at 474 MHz for TV band IV are illustrated inFIGS. 13and14. There are nulls in the patterns that do not occur in the same directions for passenger side and driver side antennas which provide more azimuthally uniform coverage for TV diversity antenna systems.FIGS. 15 and 16show antenna patterns of the same antenna for both polarizations at 858 MHz in TV band V. There are noticeable nulls in the pattern but not present in the same locations for passenger side and driver side antennas, the combination of both antennas for diversity antenna system provide a more uniform pattern over 360° of azimuth angles.

Embodiments of the present invention are directed to a transparent slot antenna for, by way of example, a vehicle such as an automobile. The slot antenna includes an electro-conductive coating on the surface of an outer glass ply applied to an area of the window. The conductive coating peripheral edge is spaced from the window edge to define an annular slot antenna. The resonant frequencies of the first two modes are adjustable by introducing a number of slits around the peripheral edges of the conductive coating by removing the coating in, for example, a dark, or black, paint band. A capacitive coupling feed structure is used to excite at least, for example, six modes of the slot antenna to cover the frequency range from, for example, 45 MHz to 860 MHz, which includes the TV VHF/UHF, the Remote Keyless Entry (RKE), and the DAB III frequency bands.

While several embodiments of the invention have been described, it should be apparent that various modifications, alterations and adaptations to those embodiments may occur to persons skilled in the art with the attainment of some or all of the advantages of the present invention. It is therefore intended to cover all such modifications, alterations and adaptations without departing from the scope and spirit of the present invention.