Heatable vehicle window glass with antenna

Abstract

A slot antenna in a heatable vehicle glazing is located between the peripheral edge of a heating busbar, a busbar extension, and an IR-reflective coating. The antenna slot can be directly fed by a voltage source, a current source, or a coupled coplanar line at a location that excites both fundamental and higher-order modes for multi-band antenna applications. The slot antenna can be located between split busbars or split busbar extensions to limit heat losses and improve antenna efficiency. Multiple antennas can be integrated into the heatable glazing for multi-band applications and / or diversity antenna systems.

Description

[Technical Field]

[0001] The present invention relates generally to radio frequency ("RF") antennas, and more particularly to antennas for transmitting and receiving radio signals formed in association with automotive glazing having an electrically heatable coated surface. [Background technology]

[0002] Windows coated with a transparent layer of metal film to control infrared (IR) radiation are used in a wide variety of applications, such as modern buildings and vehicles. The metal coating provides good thermal insulation for buildings and vehicles by reflecting solar energy, thereby limiting interior temperature rise while remaining transparent to light in the visible spectrum. In addition, transparent metal films of the window panes may be used on vehicle windows to allow the flow of DC current across the window in response to a DC voltage applied to the metal coating. Such embodiments are typically used for defrosting (i.e., melting snow and ice) or defogging windows.

[0003] Automotive transparencies, such as windshields, side windows, and rear windows, often incorporate antennas for receiving and transmitting radio frequency waves, such as AM, FM, TV, DAB, telephone, and RKE. These antennas are formed by lines, such as silver or copper, silkscreened onto the transparency or by metal wires or strips attached to the transparency. One consequence of using metal-coated windows is that they tend to attenuate the propagation of RF signals passing through the window. As a result, wireless communication into and outside buildings, vehicles, and other structures that use metal-coated windows to reduce heat loads may be limited. One solution for applications in which the metal coating interferes with signal propagation through the window has been to remove the portion of the metal coating that interferes with the antenna. Removing the metal coating facilitates the transmission of RF signals through the removed portion of the metal coating. However, removing the metal coating can increase solar energy penetration into the interior of the vehicle, thereby increasing the vehicle's temperature. Also, in glazings where a metal coating is used to heat the glazing, removal of the metal coating can deflect or interrupt the flow of direct current or create unheated zones.

[0004] Metal coatings on window glass have also been used to incorporate antennas into metal-coated windows. Antennas have been proposed based on the theory of operation of a quarter-wave or half-wave slot antenna formed between the metal frame of the window and a conductive transparent film or coating on the transparent body. For example, Patent Documents 1 to 4 show various antenna shapes formed by thin films on vehicle windows. Patent Documents 5 to 9 also disclose other slot antenna structures.

[0005] Generally, to pass current through the transparent conductive coating of a transparency, a voltage source is connected to the conductive coating via a pair of highly conductive bus bars located on either side of the region of the transparency to be heated. Because the bus bars have a higher conductivity than the coating, the current flows uniformly throughout the region to be heated. U.S. Patent No. 5,629,999 to Lotterer and Bernhardt discloses a motor vehicle window that is partially heated by a heating device and utilizes the unheated portion of the window as an antenna for transmitting and receiving electromagnetic waves. U.S. Patent No. 5,629,999 to Lotterer and Bernhardt describes an electrically heated window with an antenna. The antenna is fed at two locations: a top feed directly connected to the heatable coating and a bottom feed capacitively coupled to a heating panel. U.S. Patent No. 5,629,999 to Kagaya also discloses an electrically heated window with an antenna. The antenna includes a transmission line attached to a conductive patch that is capacitively coupled to a heating bath extension.

[0006] Antennas disclosed in the prior art use the slot antenna concept. The slot antenna is formed between the metal frame of the window and the side edges of a conductive transparent film layer or coating bonded to the window. The slot antenna has been located on the side of the coating that does not have a heating bus bar. In these designs, the bus bars are configured substantially parallel to and on both edges of the transparency. For example, when the bus bars are located on the top and bottom of the transparency, the antenna is positioned on the side of the transparency. In the case of a side-by-side heating bus configuration, the antenna has been located on the top and bottom of the transparency. Separate electrical leads are attached to each of the bus bars on both edges of the transparency. When the window glass is installed in a vehicle, this design requires separate connections for each of the electrical leads to a positive and negative power source.

[0007] Locating both electrical leads on the same side of the transparency, and preferably closely adjacent to each other, can facilitate integration of the transparency into a vehicle and simplify electrically connecting the transparency to a power source. However, in such a design, the bus bar is essentially a conductive strip located on all four sides of the transparency, resulting in the bus bar overlapping the window frame. Configuring the bus bar in this manner would short out the antenna slot located between the window's metal frame and the side edges of the conductive transparent film layer or coating. This is particularly problematic on vehicle windshields, where there is very limited area near the edge of the glass available for bus bar layout. Thus, conventional slot antennas have not been used in heatable windows.

[0008] Furthermore, when a slot formed between the window frame and the side edges of the conductive transparent film layer or coating on the transparency is used as an antenna, the transparency is bonded to the window frame by an annular seal member located in the middle of the slot. The annular seal member must be a non-conductive material so that it does not impose a load on the slot antenna. Therefore, the thickness and location of the annular seal member, the relative location of the coating to the glass, and the location between the glass and the window frame affect the performance of the slot antenna. It is difficult to adequately control such variables to tight tolerances during a commercial production process. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 4,849,766 [Patent Document 2] U.S. Patent No. 4,768,037 [Patent Document 3] U.S. Patent No. 5,670,966 [Patent Document 4] U.S. Patent No. 4,864,316 [Patent Document 5] U.S. Patent No. 4,707,700 [Patent Document 6] U.S. Patent No. 5,355,144 [Patent Document 7] U.S. Patent No. 5,898,407 [Patent Document 8] U.S. Patent No. 7,764,239 [Patent Document 9] U.S. Patent No. 9,337,525 [Patent Document 10] European (German) Patent No. 10 2012 008 033 [Patent Document 11] U.S. Patent No. 10,347,964 [Patent Document 12] U.S. Patent No. 9,647,319 [Patent Document 13] U.S. Patent No. 10,638,548 [Patent Document 14] U.S. Patent No. 3,655,545 [Patent Document 15] U.S. Patent No. 3,962,488 [Patent Document 16] U.S. Patent No. 4,898,789 Summary of the Invention [Problem to be solved by the invention]

[0010] It would therefore be advantageous to provide an antenna that solves the above-mentioned problems, particularly an antenna that is concealed in an electrically heatable, infrared-reflective window. The slot antenna disclosed herein does not actively use the window frame as one edge of the slot. The antenna meets system performance requirements while maintaining all the solar benefits and superior aesthetics of a heat-reflective coating. [Means for solving the problem]

[0011] In the glazing disclosed herein, a slot antenna suitable for use in vehicle applications includes heating capabilities. The disclosed glazing includes various antenna feed configurations, providing improved stability and flexibility with respect to antenna performance and antenna location. The slot antenna provides improved performance in the VHF and UHF bands while maintaining the benefits of a heat-reflective coating and window heating capabilities for defrosting, thawing, and defogging, as well as superior aesthetics.

[0012] The slot antenna is formed between the heating bus bar and a conductive transparent film or coating on the transparent body. It is desirable for the window glass to have electrical terminals located along the same edge of the transparent body and closely adjacent to each other. The bus bars are located along both sides of the heated area of ​​the transparent body. A first bus bar can be close to the terminal location, and a second bus bar can be on the opposite side of the window glass, away from the terminal location. In the window glass disclosed herein, the second bus bar is connected to an electrical circuit by extending highly conductive members from both ends of the second bus bar along both ends of the transparent body. The extended conductive members are insulated from the conductive coating on the transparent body by laser erase lines near the conductive members. When a DC voltage is applied to the electrical terminals, current flows through the conductive coating on the surface of the transparent body, heating the window glass. If current does not pass through the coating, the coating continues to function as a solar control coating, limiting infrared radiation passing through the window glass. The conductive members overlap the windshield frame and are electrically connected to the vehicle body through capacitive coupling at the antenna's operating frequency. A slot antenna is created by removing the conductive coating in the peripheral area adjacent to the conductive member. The slot dimensions are designed to support the fundamental and higher order modes within the frequency band of interest. Preferably, the total length of the slot is equal to one-half wavelength for the fundamental mode and one wavelength for the first higher order excitation mode.

[0013] A slot antenna can be excited by a voltage source, such as a balanced parallel transmission line connected to both edges of the slot or a coaxial transmission line electrically connected to both edges of the slot. A slot antenna can also be fed by a coplanar line probe. In this case, the inner conductor is extended along the center of the slot to form a coplanar transmission line, effectively providing a capacitive voltage feed. A slot antenna can also be excited by a current source, such as the end of a looped coaxial cable, which excites the slot antenna through magnetic coupling. Energy applied to the slot antenna causes current to flow in the conductive coating and conductive material of the window glass. The current is not confined to the edges of the slot but spreads throughout the conductive film and conductive material. Radiation then occurs from the edges and sides of the conductive sheet and conductive material.

[0014] Traditionally, slot antennas have employed a slot located between the windshield frame and the side edges of a conductive transparent film layer or coating on the transparency. The transparency is bonded to the windshield frame by an annular seal member located in the center of the slot. However, the annular seal member is a dielectric material and can impose loads on the slot antenna. Therefore, the thickness and location of the annular seal member, the relative location of the coating on the glass, and the location between the glass and the windshield frame all affect the performance of the slot antenna. Tolerances for all of these variables are difficult to control in mass production. Furthermore, for conventional slot antennas to function, costly non-conductive adhesives must be used to bond the transparency to the windshield frame. In the window panes disclosed herein, the slot antenna is shifted from the annular seal member and positioned closer to the portion of the window pane between the conductive member and the edge of the conductive coating. This improves tolerance control in mass production and provides additional cost savings to customers by allowing the use of lower-cost adhesives for windshield bonding.

[0015] According to the disclosed invention, an electrically heatable window pane receivable in a frame cooperates with the frame to define an antenna. The window pane includes a transparent body sheet having a major surface defined inside a peripheral edge. The transparent body sheet has a conductive coating on the major surface. A first bus bar has a conductivity greater than that of the conductive coating. The first bus bar contacts the conductive coating adjacent to a first portion of the peripheral edge of the transparent body sheet. A second bus bar has a conductivity greater than that of the coating and contacts the conductive coating adjacent to a second portion of the peripheral edge of the transparent body sheet. The second portion of the peripheral edge of the transparent body sheet is located on opposite sides of the transparent body sheet from the first portion of the peripheral edge of the transparent body sheet. The window pane also includes a first conductive member electrically insulated from the DC current in the second bus bar and the DC current in the conductive coating. The first conductive member has a first portion located between the first bus bar and the second portion of the peripheral edge of the transparent body sheet. The first conductive member also has a second portion located adjacent to a second portion of the periphery of the transparency sheet. The second conductive member is electrically insulated from the DC current in the second bus bar and the DC current in the conductive coating. The second conductive member has a first portion located between the first bus bar and the second portion of the periphery of the transparency sheet. The second conductive member also has a second portion located adjacent to the second portion of the periphery of the transparency sheet. The antenna slot in the window glass has one side defined by the first or second conductive member and an opposite side. The second side of the antenna slot is located opposite the one side of the slot and is defined by a portion of the periphery of the conductive coating. The antenna slot has a length and width that cooperate with one of the first or second conductive member, the frame, and the conductive coating to define a slot antenna. Electrical leads are connected to the first and second bus bars and extend from the second portion of the periphery of the transparency sheet. The window glass also includes an antenna feed connector that is electrically connected to the slot antenna.

[0016] Preferably, the first and second bus bars and the first and second conductive members are bonded to the transparency sheet of the window glass adjacent to the periphery of the transparency sheet. The first and second bus bars and the first and second conductive members overlap the frame so that the slot antenna is capacitively coupled to the frame at RF frequencies. The conductive coating, the first and second bus bars, and the first and second conductive members cooperate with the frame to define a ground plane at RF frequencies.

[0017] Also preferably, the first slot lines in the conductive coating insulate the first and second conductive members from DC current flowing through the conductive coating and DC current flowing through the second bus bar. The first slot lines may have a width in the range of 0.05 mm to 0.2 mm, preferably in the range of 0.08 mm to 0.1 mm. The conductive coating is electrically connected to the first and second conductive members at RF frequencies via capacitive coupling across the first slot lines in the conductive coating.

[0018] In some embodiments, a portion of the conductive coating is removed or absent adjacent a first edge of at least one of the first and second conductive members to define a slot antenna, and at least one of the first and second conductive members has a first edge facing the conductive coating such that a portion of the first edge of at least one of the first and second conductive members defines one side of the slot antenna and a portion of an outer or peripheral edge of the conductive coating defines an opposing side of the slot antenna.

[0019] In a particular embodiment, the slot antenna is fed by a coaxial cable, the outer conductor of which is electrically connected to the frame and also to the capacitively coupled first or second conductive member, and the center conductor of the coaxial cable is connected to at least one antenna feed pad provided on the periphery or outer side edge of the conductive coating.

[0020] In some embodiments, the slot antenna in the window pane is fed by a coaxial cable, the outer conductor of which is electrically connected to the frame and also to a capacitively coupled first or second conductive member, and the center conductor of which is connected to a first antenna feed pad on the periphery of the conductive coating and to a second antenna feed pad also on the periphery of the conductive coating.

[0021] According to the invention disclosed herein, the second slotline electrically isolates the first antenna feed pad or the second antenna feed pad from DC current in the conductive coating, and the first antenna feed pad or the second antenna feed pad is capacitively coupled to the conductive coating at RF frequencies.

[0022] The disclosed glazing embodiments may include a second slotline in the conductive coating, the second slot defining a first end at a location where the second slot intersects a portion of the outer lateral edge of the conductive coating that defines the opposite side of the antenna slot. The second slotline further defines a second end at a second location where the second slotline intersects a portion of the outer lateral edge of the conductive coating that defines the opposite side of the antenna slot. Either the first antenna feed pad or the second antenna feed pad is located on a portion of the periphery of the conductive coating that defines the opposite side of the antenna slot and is also located between the first and second ends of the second slotline. In this manner, the second slotline mitigates cold spots on the conductive coating between the first and second antenna feed pads and mitigates hot spots on the conductive coating adjacent the first and second antenna feed pads.

[0023] In some embodiments, the first and second antenna feed pads are located at outer lateral edges of the conductive coating that define opposite sides of the antenna slot. The window glass further includes a second slotline in the conductive coating. The second slotline defines a first end at a location that intersects with a portion of the periphery of the conductive coating that defines the opposite side of the antenna slot. The first end is located outside a portion of the periphery of the conductive coating that is located between the first and second antenna feed pads. The second slotline further defines a second end that terminates within the conductive coating equidistant from the first and second antenna feed pads, such that the second slot defines an "L" pattern between the first and second ends of the second slotline. The "L-shaped" second slotline biases the DC current flowing in the conductive coating around the second slotline so that the voltage potential at the first antenna feed pad tends to be equivalent to the voltage potential at the second antenna feed pad.

[0024] In some embodiments of the glazing, the slot antenna is fed by a coupling coplanar line spaced laterally intermediate an edge of the first conductive member and a periphery of the conductive coating that defines an opposite side of the antenna slot. The coupling coplanar line can also be spaced laterally intermediate an edge of the second conductive member and a periphery of the conductive coating that defines an opposite side of the antenna slot.

[0025] In the disclosed glazing embodiments, the outer conductor of the coaxial cable is connected to either the first or second conductive member, and the center conductor of the coaxial cable is extended and coiled within the antenna slot and reconnected to either the first or second conductive member, forming a loop in the center conductor that magnetically couples to excite the slot antenna.

[0026] In some embodiments of the disclosed window glass, the antenna feed connector may preferably further include a first conductive trace portion located on the inside of the window glass laminate. One end of the first conductive trace portion is connected to at least one of the first antenna feed pads of the second antenna feed pads. The second conductive trace portion of the antenna feed connector is located at least partially on the outside of the window glass laminate. The second conductive trace portion has a cross-section that is larger than the cross-section of the first conductive trace portion. The first conductive trace portion can reduce capacitive coupling between the antenna feed connector and the first and second conductive members, improving impedance matching of the slot antenna. The second conductive trace portion can increase capacitive coupling between the antenna feed connector and the frame, improving impedance matching of the slot antenna.

[0027] Some embodiments of the disclosed window panes may include at least one of a first conductive member and a second conductive member defining two branches. In the window pane, the two branches cooperate to form a slot antenna between the two branches. The branch of the first conductive member or the branch of the second conductive member has a higher conductivity than the conductive coating. Current in the slot antenna can be concentrated in the two branches. The branches can improve the efficiency of the slot antenna by reducing resistive losses due to current. In some embodiments, at least one of the first busbar or the second busbar can be split into two sub-busses, with the sub-busses defining a split-sub-bus slot antenna between the two sub-busses. In some embodiments of the disclosed window panes, multiple split sub-busses are positioned at respective multiple locations within the window pane to form respective multiple slot antennas. Preferably, the split sub-busses are positioned at least λ / 4 wavelengths apart relative to the wavelength of the operating frequency of the window pane to provide an antenna diversity system.

[0028] In some examples of the disclosed glazings, a slot antenna on a split busbar is used for a UHF antenna, including DAB and TV frequencies. The antenna slot can be spaced from the periphery of the transparency sheet so that the adhesive bonding the transparency sheet to the frame does not affect the performance of the slot antenna. Preferred embodiments of the disclosed glazings can have a slot antenna, which allows for tolerance control during commercial production.

[0029] The advantages of the present invention are particularly important for automotive windshields where there is very limited space to hide the heating busbar and antenna structure. Such applications are typically heated automotive windshields, although the invention is not limited thereto.

[0030] For a more complete understanding of the disclosed invention, reference should now be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of example of the invention. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a plan view of an automobile windshield incorporating inventive features disclosed herein; [Figure 2] FIG. 2 is a partially exploded cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 1 is a plan view of a windshield omitting the outer glass and incorporating a preferred embodiment of the busbar arrangement of the present invention. [Figure 4] 1 is a schematic diagram of an embodiment of a glazing incorporating features of the glazing disclosed herein, with slot antennas formed on each side of the windshield; [Figure 5] FIG. 10 is a diagram of another embodiment of a glazing incorporating features of the glazing disclosed herein in which the slot antenna is fed in two locations using a first slot for DC isolation and a second slot to control extreme temperatures of the conductive coating. [Figure 6]FIG. 10 is a diagram of another embodiment of a glazing incorporating features of the glazing disclosed herein in which the slot antenna is fed in two places using an L-shaped slot for DC isolation. [Figure 7] FIG. 10 is a diagram of another embodiment of a window glass incorporating features of the window glass disclosed herein, with slot antennas formed on each side of the window glass. [Figure 8] FIG. 10 is a simulated plot of antenna return loss for one embodiment of a vehicle glazing showing return loss across a resonant frequency band of 470 MHz to 690 MHz. [Figure 9] FIG. 10 is a measured gain plot of a vehicle antenna glazing showing the antenna average gain from 470 MHz to 690 MHz in vertical polarization for two different antenna connectors. [Figure 10] FIG. 10 is a measured gain plot of a vehicle antenna glazing showing the antenna average gain from 470 MHz to 690 MHz in horizontal polarization for two different antenna connectors. [Figure 11] FIG. 10 is a diagram of another embodiment incorporating glazing features disclosed herein, in which six slot antennas are integrated into the windshield. DETAILED DESCRIPTION OF THE INVENTION

[0032] FIG. 1 is a plan view of a transparent windshield 10 incorporating inventive features disclosed herein. The windshield 10 is a laminated vehicle windshield formed from an outer glass ply 14 and an inner glass ply 12 bonded together by an intervening layer 16, which is preferably made of polyvinyl butyral, polyvinyl chloride, polyurethane, or a similar material. The outer glass ply 14 defines an exterior surface (conventionally referred to as surface 1) facing the outside of the vehicle and an interior surface (conventionally referred to as surface 2). The inner glass ply 12 defines an interior surface (conventionally referred to as surface 3) facing the interior of the vehicle and forming the interior of the windshield 10 (conventionally referred to as surface 4). The intervening layer 16 is located between surfaces 2 and 3.

[0033] 2, the windshield 10 may include a dark band 42, which is formed by screen printing an opaque ink onto the glazing and subsequently baking it around the perimeter of the windshield. The dark band 42 has a closed inner edge 36 that defines the daylight opening (DLO) of the glazing 10. The dark band 42 is wide enough to conceal bus bars, heating circuits, antenna elements, and other devices around the edge of the glass, as will be shown and described below.

[0034] The windshield 10 further includes a conductive coating or element 18 that blocks the daylight opening in the transparency. The conductive coating functions as a solar shield, reducing infrared and ultraviolet radiation transmission through the window glass. The conductive element 18 is preferably a transparency coating applied to the second surface of the outer glass ply 14 or the third surface of the inner glass ply 12 (as shown in FIG. 1) in any manner known in the art. The coating may be a single-layer or multi-layer metal-containing coating, such as those disclosed in U.S. Patent No. 6,229,999 to Gillery et al., U.S. Patent No. 6,229,999 to Gillery, and U.S. Patent No. 6,229,999 to Finley. The conductive coating has a sheet resistance of about 2.7 Ω / for about 75% light transmission.

[0035] 1 and 2, the windshield 10 further includes a top bus bar 20 and a bottom bus bar 22, each of which is attached to, overlaps, and electrically connected to the conductive coating 18. The conductive coating 18 has a coated edge 38 that is spaced from the side, top, and bottom outer edges of the windshield 10. The uncoated areas between the coated edge 38 and the outer edges of the windshield 10 may be formed by masking the areas during the coating process. Alternatively, the entire surface of the outer glass ply 14 may be coated, and the coating subsequently removed from the areas between the coated edge 38 and the side, top, and bottom outer edges of the outer glass ply 14.

[0036] As shown in FIG. 1 , the connection to the top bus bar 20 includes two conductive strips 26, 24 and a side conductive strip 28 (only one side is shown in FIG. 1 ), with the conductive strips 26, 24 each extending in opposite directions from the terminal area along the bottom edge of the windshield 10 and the side conductive strip 28 extending along both sides of the windshield 10. The side conductive strip 28 connects the two conductive strips 26, 24 to the ends of the top bus bar 20, respectively. The bus bars 20, 22 and conductive strips 24, 26, 28 are preferably made of a silver-containing ceramic material of a type known in the art. The bus bars 20, 22 and conductive strips 24, 26, 28 are silkscreened onto the glass surface and then fused together by heating. The electrical conductivity of the bus bars 20, 22 and conductive strips 24, 26, 28 is selected to be substantially greater than the electrical conductivity of the coating 18 to reduce energy losses due to heating within the bus bars and conductive strips. The electrical connection between the power supply 40 and the windshield 10 is preferably made along the bottom edge of the terminal area. However, the connection may be adjacent to any edge of the windshield 10 or any location along the edge. Locating the leads on the same side of the transparency, and preferably closely adjacent to each other, facilitates installation of the transparency in the vehicle and simplifies the connection between the windshield 10 and the power supply 40. An electrical lead 30 connects the bottom bus bar 22 to one pole of the power supply 40. The strips 26, 24 leading to the top bus bar 20 may be commonly wired to the opposite pole of the power supply 40 by a jumper wire 34 and a lead 32. In this manner, current flows across the metal layer 18 between the bus bars 22 and 20, heating the windshield.

[0037] In the prior art, vehicle windows have a metal coating that limits infrared radiation passing through the window, and a spacing is defined around the periphery of the metal coating to form a slot antenna within the window. The slot is formed between the window's metal frame and a conductive transparent film or coating bonded to the window. One or more side peripheral edges of the transparent film are spaced from the inner edge of the window frame to form the slot antenna. The total length of the slot is one wavelength for an annular slot or one-half wavelength for a non-annular slot, relative to the fundamental excitation mode.

[0038] 3, the top bus bar 20 covers the slot at the top of the window pane, and the bottom bus bar 22 and conductive strips 24, 26 cover the slot at the bottom of the window pane. In addition, a conductive strip 28 covers a slot on each of the two sides of the window pane. The top bus bar 20, bottom bus bar 22, and conductive strips 24, 26, 28 all overlap and capacitively couple to the window frame, connecting the coating 18 to the window frame at RF frequencies. Thus, heating of the bus bars 22, 20 in combination with the conductive strips 24, 26, 28 shorts the antenna slot to the window frame.

[0039] Referring now to FIG. 4 , coating 18 covers the entire inner surface of outer ply 14, but forms a band 50 that does not cover the band of coating 18 removed from the inner surface of outer ply 14 between the inner edge of conductive strip 28 and a removed edge 52 of coating 18. Coating 18 is removed from window glass 10 by either a mask removal technique or a laser removal technique. Removed edge 52 is located laterally on window glass 10 between the inner edge 36 of dark band 42 and the inner edge of conductive strip 28. Band 54 is formed in the same manner on the opposite side of window glass 10 from band 50. Conductive strips 28, 26, and 24 are insulated from coating 18 and bottom bus bar 22 by laser removal lines 44. Laser removal lines 44 are thin slots created by a laser beam to provide DC isolation between conductive strips 28, 24, and 26 and coating 18 and bottom bus bar 22. The laser ablation lines 44 have a width ranging from 0.05 mm to 0.2 mm, preferably from 0.08 mm to 0.1 mm. The narrow slots in the laser ablation lines 44 provide DC electrical isolation, but at RF frequencies, the coating 18 is electrically connected to the conductive strips 28, 26, 24 by capacitive coupling across the narrow slots. This removal of the coating 18 provides the basic structure of the antenna slot above the coating 18.

[0040] Conventional slot antennas use a slot formed between the window frame and the side edges of a conductive, transparent film layer or coating. The film layer or coating overlies a transparency, with the side edges of the film layer positioned near the periphery of the transparency. In a vehicle, the transparency is bonded to the window frame by an annular seal member located substantially in the center of the antenna slot. The annular seal member must be non-conductive, otherwise its dielectric properties would impose a load on the slot antenna. Therefore, the thickness and location of the annular seal member, the relative location of the coating on the transparency, and the separation between the transparency and the metal frame all affect the performance of the slot antenna. During commercial production, it is difficult to control the tolerances of each of these elements and the positional variations between them to the degree necessary to produce satisfactory, consistent antenna performance. Furthermore, for conventional slot antennas to function, relatively expensive, non-conductive adhesives are required to bond the transparency to the window frame. The embodiments disclosed herein relocate the slot antenna to a location in the transparency between the conductive strip 28 and the side edges 52 of the coating 18, as shown in FIG. 4 . This aids in better control of tolerances and positioning during commercial production, and also allows for cost savings by using low-cost conductive adhesives for window bonding.

[0041] The windshield 10 and associated heating element define an antenna slot 50 between a portion of the inner edge of the conductive strip 28 on one side and a coating edge 52 of the coating 18 on the opposite side. The slot width of the slot 50 must be large enough to negligible capacitive effects across the slot 50 at the operating frequency to prevent signal shorting. The slot width is preferably greater than 10 mm. The preferred length of the slot is an integer multiple of half the wavelength for the applicable resonant frequency. For a typical vehicle windshield, the slot length is designed to resonate in the VHF and UHF bands, which can be used for FM, DAB, TV, and FM applications.

[0042] The slot antenna can be excited by a voltage source, such as a balanced parallel transmission line connected to both edges of the slot, or by an unbalanced transmission line, such as a coaxial transmission line connected to both edges of the slot. Figure 4 shows that the antenna slot 50 is fed by a coaxial cable 60. The ground conductor of the coaxial cable 60 is connected to the vehicle chassis by a wire 64 and capacitively coupled to the conductive strip 28 near one edge of the slot 50. The ungrounded conductor, such as the center conductor of the coaxial cable 60, is connected to the coating 18 near both edges of the slot 50 by an antenna connector 62 and an antenna feed pad 70. The antenna connector 62 is insulated from the conductive strip 28 and the window frame by insulating layers on the top and bottom of the antenna connector 62. The antenna connector 62 and the center conductor of the coaxial cable 60 are also DC isolated from the coating 18, preferably by a series capacitor at the amplifier input. In this way, the antenna feed network is DC isolated from the conductive strip 28 and the coating 18, and heating functions do not interfere with the slot antenna feed network.

[0043] 5 and 6 show a variation for feeding the slot 50, in which two antenna feed pads 70a, 70b are located on the coating edge 52. A conductive line 70c connects the antenna feed pads 70a, 70b. An antenna connection pad 70d is located midway between the conductive line 70c and is connected to one end of the antenna connector 62. Because the antenna feed pads 70a, 70b on the coating 18 are connected by the highly conductive line 70c, when the coating 18 is used for heating, DC current flows through the line 70c and bypasses the coating 18 between the antenna feed pads 70a, 70b. This current bypass creates a cold spot in the coating 18 between the antenna feed pads 70a, 70b and a hot spot near the antenna feed pads 70a, 70b. As shown in FIG. 5, the slot line 72 provides DC isolation between the antenna feed pad 70a and the coating 18. The slot width is small, preferably in the range of 0.1 mm, so that the antenna feed pad 70a is capacitively coupled to the coating 18 at the antenna operating frequency. Figure 6 shows a variation in which an inverted "L" shaped slot 74 extends partially around the periphery of the antenna pad 70a. The slot 74 diverts DC current around the edges of the slot 74 so that the same voltage potential is achieved at the antenna feed pads 70a, 70d, resulting in minimal or no DC current in the conductive line 70c.

[0044] The antenna connector 62 connects the slot antenna 50 to an electronic device. The antenna connector 62 shown in FIGS. 5 and 6 provides better impedance matching for the slot antenna. The antenna connector 62 includes (1) a flexible insulating substrate, (2) a transmission line printed on the insulating substrate for transmitting signals from the antenna to the electronic device, and (3) an insulating cover tape for insulating the transmission line from ground. The transmission line further includes (1) a solder pad located on the inside of the laminated glass and galvanically connected to the antenna connection pad 70d, (2) a narrow conductive trace portion 62c located on the inside of the laminated glass and overlapping the heating bus side strip 28, (3) a wide conductive trace portion 62b located on the outside of the laminated glass and capacitively coupled to the vehicle's ground frame, and (4) a terminal portion 62a connected to an electronic device mounted on the vehicle's metal frame. The narrow conductive trace portion 62c reduces capacitive coupling between the antenna connector 62 and the conductive strip 28. The wide conductive trace portion 62b increases capacitive coupling between the antenna connector 62 and the window frame. In this way, the antenna connector improves the antenna impedance match to the electronic device.

[0045] FIG. 4 shows that a slot antenna can also be fed by a coupled coplanar line. The antenna slot 54 has a coplanar line 66 located midway between the inner edge of the conductive strip 28 and the side edge of the coating 18 and parallel to the conductive strip 28. The coplanar line 66 effectively provides a capacitive feed without being connected to the conductive strip 28 or the coating 18. In this case, the capacitive feed is a distributed feed, and the coplanar line 66 intersects both the fundamental and higher-order mode voltage points of the slot 54. Excitation of higher-order modes is desirable for accommodating high-frequency and multi-band antenna applications, such as TV antennas and antennas with more than one frequency band.

[0046] The slot antenna may also be excited by a current source, as shown in antenna slot 56 in Figure 7. Figure 7 shows that antenna connector 62 of coaxial cable 60 is connected to wire 68, which is wound or coiled within slot 56 and connected back to conductive strip 28. Ground wire 64 of coaxial cable 60 is also electrically connected to conductive strip 28 by capacitive coupling. The wound or coiled wires 62, 68 and ground wire 64 effectively form a loop that excites slot antenna 56 by magnetic coupling. Coaxial cable 60 is DC isolated from conductive strip 28 by a series capacitor between the coaxial cable and conductive strip 28, such as wires 62, 64.

[0047] The antenna slots 50, 54, and 56 are formed between the inner edge of the conductive strip 28 on one side and the side edge of the coating 18 on the other side. The edges and surface of the coating 18 have relatively low conductivity, and currents at the edges and surface of the coating 18 cause resistive losses that degrade antenna performance. In a slot antenna, currents concentrate near the antenna feed point and the edges of the slot. As a result, significant resistive losses can occur at the surface and edges of the conductive coating 18. To improve antenna efficiency, FIG. 7 shows highly conductive strips 281 (e.g., silver or copper) printed in the high current density areas along the edges of the slot antenna 58 and in contact with the coating 18. The highly conductive strips 281 define the slot antenna between the edge strip 28 and the edges of the strip 281. Most of the RF current is concentrated in the highly conductive material of the strips 28 and 281, reducing losses. Increasing the conductivity of the current path improves the radiation efficiency of the antenna. The strips 28, 281 also provide a more uniform current distribution, avoiding high current densities and further reducing signal resistance losses. Preferably, for best performance, the strips 28, 281 cover the entire length of the slot 58 edge. However, the most critical portion of the current path is approximately one-half to one wavelength from the antenna feed point, where the current density is highest. The conductive strips 28, 281, 26, 24 are insulated from the coating 18 and bottom bus bar 22 by laser ablation lines 46.

[0048] An embodiment similar to that shown in Figures 4 and 5 with a voltage probe feed was simulated and tested in a vehicle. Figure 8 shows simulated plots of return loss (S11) for a vehicle slot antenna with two different antenna connectors. The solid simulation S11 shows the return loss of the antenna feed using a uniform 7 mm wide transmission line antenna connector. The dashed simulation S11 shows the return loss of the antenna feed using a modified transmission line connector. The modified connector includes a narrow (1 mm wide) conductive trace section on the inside of the laminated glass and a wider (7 mm wide) conductive trace section on the outside of the laminated glass. The simulated antenna return loss with the modified antenna connector shows improved antenna matching in the 470 MHz to 690 MHz television frequency band.

[0049] Figures 9 and 10 show the average antenna gain of a vehicle window assembly using the same connector as described in connection with Figure 8. Figure 9 shows the antenna performance in vertical polarization across the television frequency band of 470 MHz to 690 MHz. Figure 10 shows the antenna performance in horizontal polarization across the television frequency band of 470 MHz to 690 MHz. The solid line shows the measured antenna gain at the antenna feed when using a connector with a uniform transmission line that is 7 mm wide. The dashed line shows the measured antenna gain at the antenna feed when using a modified connector with a transmission line that has a narrow (1 mm wide) conductive trace portion on the inside of the laminated glass and a wide (7 mm wide) conductive trace portion on the outside of the laminated glass. The measured antenna gain shows that the modified antenna connector improves the antenna gain in the television frequency band of 470 MHz to 690 MHz.

[0050] The embodiment of FIG. 11 represents a further development according to the invention disclosed herein. In the embodiment of FIG. 11, portions of the top busbar 20 and the bottom busbar 22 are separated into separate lengths or segments defining split or slot openings that create multiple slot antennas. Each length or segment corresponds to a respective slot antenna. FIG. 11 shows six separate slot antennas: two slot antennas on the top busbar 20, two slot antennas on the bottom busbar 22, and a slot antenna on each side of the window glass, all integrated into the windshield. Each antenna is independently fed by a voltage source or coupled coplanar line. The two top antennas are symmetrically positioned along the top side of the windshield. The two antenna feeds are weakly coupled because they are at least λ / 4 wavelength apart, meaning that both can be used simultaneously for VHF and UHF diversity antenna systems. The same applies to the two bottom antennas, which can be used for diversity antenna applications. The antennas can also be fed from both sides of the window transparency, thereby creating further spatial and pattern diversity.

[0051] Although the present invention has been described and illustrated with reference to certain preferred embodiments and examples, it should be understood that those skilled in the art may adopt various modifications without departing from the spirit of the invention and the scope of the claims.

Claims

1. 1. An electrically heatable glazing that is receivable in a frame, the glazing cooperating with the frame to define an antenna when the glazing is received in the frame, comprising: a transparency sheet having a major surface configured within a periphery; a conductive coating located on a major surface of the transparency sheet; a first bus bar having a conductivity greater than that of the conductive coating and contacting the conductive coating adjacent a first portion of a periphery of the transparency sheet; a second bus bar having a conductivity greater than that of the conductive coating and adjacent to a second portion of the periphery of the transparency sheet and in contact with the conductive coating, the second portion of the periphery of the transparency sheet being located on an opposite side of the transparency sheet from the first portion of the periphery of the transparency sheet; the transparent body sheet further includes two conductive members, each of which has a first portion electrically insulated from the DC current in the second bus bar and the DC current in the conductive coating and located between the first bus bar and a second portion of the periphery of the transparent body sheet, and a second portion located adjacent to the second portion of the periphery of the transparent body sheet, one of the two conductive members being the first conductive member and the other being the second conductive member; a slot in the conductive coating having oppositely disposed sides, one side of the slot being defined by one of the first conductive member and the second conductive member, and the other side of the slot being defined by a portion of an edge of the conductive coating opposite the one side of the slot, the slot having a length and width that cooperates with one of the first conductive member and the second conductive member, the frame, and the conductive coating to define a slot antenna; further comprising an antenna feed connector electrically connected to the first bus bar and the second bus bar and extending outside a second portion of the periphery of the transparent sheet; A window pane wherein a portion of the edge of the conductive coating that defines the slot is located on a side away from the top and bottom of the window pane.

2. 10. The window pane of claim 1, wherein the first bus bar, the second bus bar, the first conductive member, and the second conductive member are bonded to the transparency sheet adjacent a periphery of the transparency sheet and overlap the frame such that the slot antenna is capacitively coupled to the frame at RF frequencies, and the conductive coating, the first bus bar, the second bus bar, the first conductive member, and the second conductive member cooperate with the frame to define a ground plane at RF frequencies.

3. 3. The glazing of claim 2, wherein first slot lines in the conductive coating insulate the first conductive member and the second conductive member from DC current flowing through the conductive coating and DC current flowing through the second bus bar.

4. 4. A glazing according to claim 3, wherein the first slot line has a width in the range 0.05 mm to 0.2 mm.

5. 4. The glazing of claim 3, wherein the conductive coating is electrically connected at RF frequencies to the first conductive member and the second conductive member through capacitive coupling across first slot lines in the conductive coating.

6. 6. A window pane as claimed in claim 5, wherein a portion of the conductive coating is removed adjacent a first edge of at least one of the first conductive member and the second conductive member to define the slot antenna, and at least one of the first conductive member and the second conductive member has a first edge facing an edge of the conductive coating, whereby a portion of the first edge of at least one of the first conductive member and the second conductive member defines one side of the slot antenna and a portion of a periphery of the conductive coating defines an opposite side of the slot antenna.

7. 7. A window pane according to claim 6, wherein the slot antenna is fed by a coaxial cable, the outer conductor of the coaxial cable being electrically connected to the frame and capacitively connected to the first conductive member or the second conductive member, and the center conductor of the coaxial cable being connected to an antenna feed pad located on a periphery of the conductive coating.

8. 7. The window pane of claim 6, wherein the slot antenna is fed by a coaxial cable, the outer conductor of the coaxial cable being electrically connected to the frame and capacitively connected to the first conductive member or the second conductive member, and the center conductor of the coaxial cable being connected to a first antenna feed pad located on the periphery of the conductive coating and to a second antenna feed pad located on the periphery of the conductive coating.

9. A window glass as described in claim 8, further comprising a second slot line in the conductive coating, the second slot line electrically insulating the first antenna power pad or the second antenna power pad from the DC current of the conductive coating, and the first antenna power pad or the second antenna power pad being electrically connected to the conductive coating at RF frequencies by capacitive coupling.

10. further comprising a second slot line in the conductive coating, the second slot line having a first end at a first location where the second slot line intersects with the portion of the periphery of the conductive coating that defines the opposite side of the slot antenna, and a second end at a second location where the second slot line intersects with the portion of the periphery of the conductive coating that defines the opposite side of the slot antenna; 9. The window pane of claim 8, wherein either the first antenna feed pad or the second antenna feed pad is located on a periphery of the conductive coating that defines opposite sides of the slot antenna and between the first and second ends of the second slot line, such that the second slot line mitigates cold spots in the conductive coating between the first and second antenna feed pads and mitigates hot spots in the conductive coating adjacent the first and second antenna feed pads.

11. the first antenna feed pad and the second antenna feed pad are located on peripheries of the conductive coating that define opposite sides of the slot antenna; 10. The window pane of claim 8, further comprising a second slotline in the conductive coating, the second slotline having a first end where the second slotline intersects with the portion of a periphery of the conductive coating that defines an opposite side of the slot antenna, the first end of the second slotline being located outside a side of the slot antenna that is between the first antenna feed pad and the second antenna feed pad, the second slotline further having a second end that terminates within the conductive coating at a location equidistant from the first antenna feed pad and the second antenna feed pad, such that the second slotline defines an L-shaped pattern between the first end and the second end.

12. 12. The glazing of claim 11, wherein the L-shaped patterned second slotline biases a DC current flowing through the conductive coating around the second slotline such that a voltage potential at the first antenna feed pad is equal to a voltage potential at the second antenna feed pad.

13. the slot antenna is fed by a coupled coplanar line spaced laterally between an edge of the first conductive member and a periphery of the conductive coating that defines an opposite side of the slot antenna; or 7. The glazing of claim 6, wherein a coupled coplanar line is spaced laterally between an edge of the second conductive member and a periphery of the conductive coating that defines an opposite side of the slot antenna.

14. The slot antenna is fed by a coaxial cable, the outer conductor of the coaxial cable is electrically connected to the frame; 7. A window pane as claimed in claim 6, wherein a centre conductor of the coaxial cable is extended and coiled within the slot antenna and connected back to the first conductive member or the second conductive member to form a loop within the centre conductor that excites the slot antenna by magnetic coupling.

15. the coaxial cable further includes a first conductive trace portion located on the interior side of the glazing laminate and a second conductive trace portion located on the exterior side of the glazing laminate; the first conductive trace portion has one end connected to at least one of the first antenna feed pad and the second antenna feed pad; 9. The pane of claim 8, wherein the second conductive trace portion is electrically connected to the first conductive trace portion and has a cross-sectional area that is greater than a cross-sectional area of ​​the first conductive trace portion.

16. 16. The window pane of claim 15, wherein the first conductive trace portion reduces capacitive coupling between the antenna feed connector and the first and second conductive members to improve impedance matching of the slot antenna.

17. 16. The glazing of claim 15, wherein the second conductive trace portion increases capacitive coupling between the antenna feed connector and the frame to improve impedance matching of the slot antenna.

18. 1. An electrically heatable glazing that is receivable in a frame, the glazing cooperating with the frame to define an antenna when the glazing is received in the frame, comprising: a transparency sheet having a major surface configured within a periphery; a conductive coating located on a major surface of the transparency sheet; a first bus bar having a conductivity greater than that of the conductive coating and contacting the conductive coating adjacent a first portion of a periphery of the transparency sheet; a second bus bar having a conductivity greater than that of the conductive coating and adjacent to a second portion of the periphery of the transparency sheet and in contact with the conductive coating, the second portion of the periphery of the transparency sheet being located on an opposite side of the transparency sheet from the first portion of the periphery of the transparency sheet; the transparent body sheet further includes two conductive members, each of which has a first portion electrically insulated from the DC current in the second bus bar and the DC current in the conductive coating and located between the first bus bar and a second portion of the periphery of the transparent body sheet, and a second portion located adjacent to the second portion of the periphery of the transparent body sheet, one of the two conductive members being the first conductive member and the other being the second conductive member; a slot in the conductive coating having oppositely disposed sides, one side of the slot being defined by one of the first conductive member and the second conductive member, and the other side of the slot being defined by a portion of an edge of the conductive coating opposite the one side of the slot, the slot having a length and width that cooperates with one of the first conductive member and the second conductive member, the frame, and the conductive coating to define a slot antenna; further comprising an antenna feed connector electrically connected to the first bus bar and the second bus bar and extending outside a second portion of the periphery of the transparent sheet; At least one of the first conductive member and the second conductive member has two branches, a split is configured between the two branches, and the two branches cooperate to form a slot antenna therebetween.

19. 20. The pane of claim 18, wherein a branch of the first conductive member or a branch of the second conductive member has a higher electrical conductivity than the conductive coating.

20. 20. A glazing as claimed in claim 19, wherein the current in the slot antenna is concentrated in the two branches.

21. 21. A glazing as claimed in claim 20, wherein the prongs improve the efficiency of the slot antenna by reducing resistive losses caused by current flow.

22. 1. An electrically heatable glazing that is receivable in a frame, the glazing cooperating with the frame to define an antenna when the glazing is received in the frame, comprising: a transparency sheet having a major surface configured within a periphery; a conductive coating located on a major surface of the transparency sheet; a first bus bar having a conductivity greater than that of the conductive coating and contacting the conductive coating adjacent a first portion of a periphery of the transparency sheet; a second bus bar having a conductivity greater than that of the conductive coating and adjacent to a second portion of the periphery of the transparency sheet and in contact with the conductive coating, the second portion of the periphery of the transparency sheet being located on an opposite side of the transparency sheet from the first portion of the periphery of the transparency sheet; the transparent body sheet further includes two conductive members, each of which has a first portion electrically insulated from the DC current in the second bus bar and the DC current in the conductive coating and located between the first bus bar and a second portion of the periphery of the transparent body sheet, and a second portion located adjacent to the second portion of the periphery of the transparent body sheet, one of the two conductive members being the first conductive member and the other being the second conductive member; a slot in the conductive coating having oppositely disposed sides, one side of the slot being defined by one of the first conductive member and the second conductive member, and the other side of the slot being defined by a portion of an edge of the conductive coating opposite the one side of the slot, the slot having a length and width that cooperates with one of the first conductive member and the second conductive member, the frame, and the conductive coating to define a slot antenna; further comprising an antenna feed connector electrically connected to the first bus bar and the second bus bar and extending outside a second portion of the periphery of the transparent sheet; At least one of the first bus bar and the second bus bar is divided into two segments, and the two divided segments form a slot antenna therebetween.

23. 23. A window pane according to claim 22, wherein a number of the divided segments are located at respective locations within the window pane to form a number of slot antennas, spaced apart from one another by at least λ / 4 wavelength measured according to the wavelength of the operating frequency of the slot antennas to form an antenna diversity system.

24. 24. A glazing according to claim 23, wherein the divided segment slot antenna is used for UHF antennas including DAB and TV frequencies.

25. 25. The glazing of claim 24, wherein the slot antenna is laterally spaced from a periphery of the transparency sheet such that adhesive bonding the transparency sheet to the frame does not affect the performance of the slot antenna.

26. 26. The glazing of claim 25, wherein the slot antenna allows for tolerance control during commercial production.

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