Multilayer glass patch antenna

Abstract

An antenna suitable for use in the 5 GHz WLAN / Wi-Fi and DSRC frequency bands is integrated into a vehicle window. The vehicle window includes an outer transparent ply and an inner transparent ply, which are bonded to each other by an intermediate layer. The inner transparent ply and the intermediate layer function as an antenna substrate. A first conductive layer is formed on the inner surface of the outer transparent ply, and a second conductive layer having a coupling slot is formed on the outer surface of the inner transparent ply. The antenna is excited by a coaxial cable or microstrip line that traverses the coupling slot.

Description

[Technical Field]

[0001] This application claims priority to U.S. Provisional Patent Application No. 62 / 944,669, entitled "Multilayer Glass Patch Antenna," filed December 6, 2019, which is incorporated herein by reference in its entirety. [Background technology]

[0002] The invention disclosed herein relates to patch antennas, and more particularly to multi-layer patch antennas embedded in laminated glazing for receiving and / or transmitting electromagnetic signals for connected vehicle communications.

[0003] In automotive glazing, such as windshields and rear windows, antennas are often supported by or integrated into the glazing for receiving and / or transmitting radio frequency waves, such as AM, FM, TV, DAB (digital audio signal), RKE (remote keyless entry), etc. Such antennas are formed by printing conductive lines, such as silver or copper, onto the glazing transparency or by laminating metal wires or strips between transparent layers of the vehicle glazing. Such antennas provide benefits to the aerodynamic performance of the vehicle and also contribute to an aesthetically pleasing, streamlined appearance for the vehicle.

[0004] In recent years, the automotive industry has developed vehicles capable of communicating via radio frequency signals and other communication channels. Such vehicles are often referred to as "connected cars." New vehicle models offer an increasing variety of optional features, such as improved safety features and features that enable dedicated short-range communication (DSRC) radios for vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications. Currently, the automotive industry is moving from assisted driving to autonomous driving. Each new vehicle connection, whether via cellular, wireless local area network (WLAN), or DSRC, requires an antenna to support each communication channel. In some cases, as many as six antennas are required for cellular service and six DSRC antennas for V2V and V2I communications. Designing antennas that can be accommodated within the available space in a vehicle poses significant challenges. Integrating the antenna into the vehicle glass provides the advantages of improved aesthetics, simplified antenna packaging, reduced weight, theft and vandalism deterrence, and elimination of holes in the vehicle body that are prone to water intrusion and other problems. Thus, there is a need for an antenna that is capable of operating at high frequencies (e.g., greater than 2 GHz) and that can be mounted on a vehicle without protruding from the exterior of the vehicle or into the interior of the vehicle. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2018 / 0037007 [Patent Document 2] U.S. Patent No. 7,126,549 Summary of the Invention [Problem to be solved by the invention]

[0006] U.S. Patent No. 6,269,949 shows a patch antenna attached to the inner surface of laminated glass for Global Navigation Satellite System (GNSS) applications. U.S. Patent No. 6,269,949 describes a patch antenna attached to the inner surface of the inner frame of laminated glass for Satellite Digital Audio Radio Services (SDARS). Both of these patch antennas are mounted on the inner surface of a transparency and provide the narrow bandwidth characteristic of patch antennas. In addition, these designs require relatively expensive, low-loss substrate materials, and due to the curvature of vehicle glass, the substrate may not be properly bonded to the glass. Furthermore, the antenna patch is printed on one of the inner surfaces of the transparency, which is covered with black paint for aesthetic reasons. Such designs make alignment of the antenna substrate and patch even more problematic for commercial volume production.

[0007] The rapid growth of connected vehicle communications has created a need to integrate more and more antennas into vehicles. Therefore, there is a need for surface-mounted antennas for DSRC, Wi-Fi, WLAN, and Bluetooth® that do not extend from the exterior of the vehicle or protrude into the interior passenger compartment. Additionally, there is a practical need for such antennas to be accommodated at minimal cost by existing vehicle components, such as standard equipment. It is also important that such antennas maintain the aesthetics or appearance of the vehicle and require only limited modifications to existing glass structures and manufacturing processes. Furthermore, there is a need for a single antenna with wideband characteristics that can receive and transmit across the entire Wi-Fi and DSRC frequency bands. [Means for solving the problem]

[0008] The invention disclosed herein discloses a slot-coupled glass patch antenna suitable for 5 GHz WLAN / Wi-Fi, DSRC, V2V, and V2I communications. The disclosed patch antenna is embedded in laminated vehicle window glass and has multiple antenna feed methods. The antenna has wideband impedance matching and frequency tuning capabilities.

[0009] The laminated glass material includes an inner ply and an outer ply. The inner and outer plies are bonded together by an interlayer, preferably made of standard polyvinyl butyral (PVB) or a similar plastic material. The outer ply has an outer surface defining the exterior of the glass material and an inner surface. The inner ply has an outer surface facing the interior of the glass material and an inner surface defining the interior of the glass material and facing the interior of the vehicle. The patch antenna includes a first conductive element and a second conductive element. The second conductive element is spaced apart from, substantially parallel to, and overlaps the first conductive element. The first conductive element of the antenna is disposed on the inner surface of the outer ply, and the second conductive element of the antenna is disposed on the inner surface of the inner ply.

[0010] The first conductive element is the radiating element of the patch antenna, and the second conductive element is the ground plane of the patch antenna. The ground plane further includes an antenna coupling slot aligned with and spaced apart from the radiating element, the antenna coupling slot constituting the antenna feed region. When the antenna coupling slot is excited by an electromagnetic wave, the field distribution within the slot is composed of a set of orthogonal modes. For a long, thin slot, the electric field amplitudes of such modes have sinusoidal periods that are integer multiples of the length of the slot, causing these mode sets to be excited preferentially over other mode sets.

[0011] The patch antenna is excited by a microstrip feed line. This antenna feed method requires a thin antenna feed substrate under the inner ply, with the feed substrate having a microstrip feed line etched on its bottom. The patch antenna may be fed by a coaxial cable, with the ground end of the coaxial cable connected to a ground plane near one side of the slot and the center conductor of the coaxial cable extending across the slot and connected to the other side of the slot. When fed directly by a coaxial cable, the entire antenna is part of the glass and does not require an additional antenna feed network. In addition, the patch antenna may be embedded around the window glass, providing more flexibility in packaging vehicle antennas for reliable high-speed data communications.

[0012] For a more complete understanding of the disclosed invention, reference should now be made to the embodiments illustrated in more detail in the accompanying drawings and described below by way of example of the invention. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a plan view of a vehicle embodying the invention disclosed herein and having antennas included in the front, rear and side windows; FIG. [Figure 2] 2 is a cross-sectional view of a portion of a first embodiment of one of the antennas shown in FIG. 1, taken along line 2-2 in FIG. [Figure 3] FIG. 3 is an exploded view of the embodiment of the patch antenna shown in FIGS. [Figure 4] FIG. 2 is an exploded view of a second embodiment of a patch antenna according to the invention disclosed herein. [Figure 5] 1 is a plan view of a patch antenna disclosed herein showing a first conductive layer and a second conductive layer including a rectangular slot. [Figure 6] FIG. 10 shows the electric field distribution in the slots of the second conductive layer. [Figure 7]FIG. 1 is a plan view identifying selected dimensions of a preferred embodiment of the invention disclosed herein. [Figure 8] 8 is a table listing dimensions of the preferred embodiment of the present invention identified in FIG. 7. [Figure 9] 1 is a plan view of a vehicle incorporating the invention disclosed herein and having an antenna formed in the windshield; [Figure 10] 10 is a graph showing simulated and measured frequency responses of the antennas shown in FIGS. 7-9 embodying the disclosed invention. [Figure 11] 1 is a graph showing the vertical gain pattern of the disclosed patch antenna obtained at 5 GHz Wi-Fi and DSRC frequencies and an elevation angle of 5 degrees. [Figure 12] 1 is a graph showing the vertical gain pattern of the disclosed patch antenna at 5 GHz Wi-Fi and DSRC frequencies and 0 degrees elevation angle. DETAILED DESCRIPTION OF THE INVENTION

[0014] FIG. 1 shows a vehicle 10 having a windshield 12, a rear window 14, and two side window glazings 16. The windshield 12 and rear window 14 may include a concealment band 32, which is applied by screen printing an opaque ink onto the glass and subsequently firing it around the perimeter of the window glass. The purpose of the concealment band 32 is to conceal antenna elements and other devices located near the edges of the glass. To minimize the visibility of the antenna 20, the antenna 20 is formed within the windshield 12, preferably within the silhouetted or painted area of ​​the concealment band 32. While the presently preferred embodiment of FIG. 1 shows the antenna 20 formed within the windshield 12, the antenna 20 may also be located within the rear window 14, the side window glazings 16, or any other glazing or sunroof of the vehicle 10. The antenna 20 may also be formed within a non-vehicle window, such as a building.

[0015] FIG. 2 is a partial cross-sectional view of the antenna 20 within the windshield 12 taken along line 2-2 of FIG. 1. The windshield 12 is a laminated glass or window pane that includes an inner transparent ply 34 and an outer transparent ply 30. The transparent plies are preferably composed of glass. The inner ply 34 and the outer ply 30 are bonded together by an interlayer 36. Preferably, the interlayer 36 is made of polyvinyl butyral or a similar material. The outer ply 30 has an outer surface 130 (conventionally referred to as surface 1) that constitutes the outer, or outward-facing, surface of the windshield 12. The outer ply 30 also has an inner surface 132 (conventionally referred to as surface 2) disposed opposite the outer surface 130. The inner ply 34 has an outer surface 134 (conventionally referred to as surface 3) that faces away from the vehicle passenger compartment and toward the interior of the glass 12, opposite the inner surface 132 of the outer transparent ply 30. The inner transparent ply 34 also has an inner surface 136 (commonly referred to as surface 4) that defines the interior or inward-facing surface of the glazing material that faces the passenger compartment of the vehicle. The interlayer 36 is located between the inner surface 132 and the outer surface 134.

[0016] 1 and 2, the glazing material 12 may include a concealment band 32, such as a paint band, that is applied to the outer ply 30 by screen printing an opaque ink around the periphery of the inner surface 132 of the outer ply 30 and then firing the periphery of the outer ply 30. The concealment band 32 has a closed inner edge 38 that defines the daylight opening (DLO) of the glazing material 12. The concealment band 32 is wide enough to cover the disclosed windshield antenna elements and other devices that may be included near the periphery of the glazing material 12, as will be described below.

[0017] The glass material 12 further includes a first conductive layer 22 and a second conductive layer 24. The first conductive layer 22 is disposed on the hidden band 32 on the inner surface 132 of the outer ply 30, and the second conductive layer 24 is disposed on the inner surface 136 of the inner ply 34. The second conductive layer 24 is substantially parallel to and spaced apart from the first conductive layer 22. The intermediate layer 36 and the inner ply 34 act as a dielectric substrate for the first conductive layer 22 and the second conductive layer 24.

[0018] The first and second conductive layers 22, 24 may be implemented in other ways, as further illustrated herein by way of example. The first and second conductive layers 22, 24 may be composed of conductive paint, a metal film deposited by sputtering or vapor deposition, or a silver paste screen meshed onto a non-conductive panel. Furthermore, the first and second conductive layers 22, 24 may be formed on the surface of a single-layer non-conductive panel, such as a tempered glass window, or on any layer of a multi-layer laminate transparency of glass or plastic layers. The first and second conductive layers 22, 24 may also be bonded to the surface of a non-conductive panel, such as an interior or exterior fiberglass panel.

[0019] The first conductive layer 22 is often referred to as a "patch." In the disclosed embodiment, the patch (first conductive layer 22) is the main radiating element of the antenna. The first conductive layer 22 can have any predetermined contour shape, such as a rectangle, a circle, a triangle, or an ellipse. In the disclosed example embodiment, a rectangular contour shape is preferred. The second conductive layer 24 acts as an electrical ground plane. The first conductive layer 22 cooperates with the second conductive layer 24, the middle layer 36, and the inner ply 34 to form a patch antenna. The second conductive layer 24 further includes a slot 42. The slot 42 can have various contour shapes, such as a straight, L-shaped, or U-shaped slot. Energy is electromagnetically coupled through the slot 42 in the second conductive layer 24. The slot 42 is preferably oriented relative to the center of the first conductive layer 22 because this is the location of the patch antenna's maximum magnetic field. To achieve maximum coupling, the slot 42 is preferably parallel to the two radiating edges 46, 48 of the first conductive layer 22, as shown in FIG. 5 . The disclosed patch antenna with electromagnetic coupling slot 42 advantageously avoids the need for a hole in the windshield 12 to pass the antenna through. Manufacturing vehicle glazing and other glass windows with holes presents challenges related to cost, yield, and reliability.

[0020] When the slot 42 is excited by an electromagnetic wave, the electric field distribution within the slot 42 can be described according to a set of orthogonal modes. When the slot 42 is relatively long and narrow, the amplitudes of the electric fields of the set of orthogonal modes have a sinusoidal period that corresponds to an integer multiple of the slot length, as shown in FIG. 6. A relatively long and thin (i.e., narrow) slot can excite one set of these modes preferentially over the other modes. The frequency of actuation is also important. FIG. 6 shows that the amplitudes of the electric field distributions of the odd modes (i.e., the TE10 and TE30 modes) reach their maximum values ​​at the center of the slot 42. Conversely, the even modes (i.e., the TE20 and TE40 modes) reach their minimum values ​​at the center of the slot 42. When the slot 42 is excited at its middle, the TE10 and TE30 modes are at their maximum values, thus enabling strong coupling to these modes. At the same time, the TE20 and TE40 modes are at their minimum values, resulting in near-zero coupling to these modes.

[0021] Referring to FIG. 3 , the disclosed patch antenna is fed by a microstrip line 44 etched into the bottom surface of a thin substrate 40. The patch antenna is excited by two very similar coupling mechanisms: one between the microstrip line 44 and the slot 42, and the other between the slot 42 and the first conductive layer 22. The characteristic impedance of the microstrip line 44 and the width of the microstrip line 44 affect the electromagnetic coupling to the slot 42. For maximum coupling, the microstrip line 44 is oriented relative to the slot 42, i.e., with its longitudinal dimension perpendicular to the longitudinal centerline of the slot 42, which is defined as the midpoint between the long edges of the slot 42. When the microstrip line 44 is tilted away from a perpendicular orientation relative to the longitudinal centerline of the slot 42 (i.e., when the microstrip line 44 forms a tilt angle), or when the microstrip line 44 is positioned near one end of the slot 42 (i.e., the end of the width of the slot 42 formed between the long sides), that is, far from the opposite end, the coupling to the fundamental TE10 mode of the patch antenna is reduced.

[0022] The patch antenna disclosed herein includes an additional antenna feed substrate 40. Due to the curvature of the windshield 12's outer ply 30 and inner ply 34, the windshield 12 cannot easily accommodate the antenna feed substrate 40. Additionally, the first conductive layer 22 is embedded inside the windshield 12 and is often covered by a hidden band 32 for aesthetic reasons, which makes proper alignment between the microstrip line 44 and the first conductive layer 22 more difficult. Therefore, other designs are sometimes preferred due to commercial manufacturing costs and equipment.

[0023] A preferred alternative embodiment is shown in FIG. 4. In the embodiment of FIG. 4, the patch antenna is powered directly from the coupling slot 42 using a coaxial cable 50 having a center conductor 54 and an outer shield 52. The center conductor 54 extends over the slot 42 and is galvanically connected to the farthest side of the slot 42 at a solder pad 56 on the second conductive layer 24. The outer shield 52 is galvanically connected to the near side of the slot 42 at a solder pad 58 on the second conductive layer 24. The coaxial cable 50 and slot 42 transmit electromagnetic energy to and receive electromagnetic energy from the first conductive layer 22. An advantage of the invention disclosed herein is that it combines the advantageous electrical properties of an antenna with physical components, allowing the antenna to be more easily incorporated into current windshield or other transparency designs using existing manufacturing processes. Another advantage of the antenna disclosed herein is that it can be more easily and conveniently connected via a conductive connection to electronic circuitry external to the antenna.

[0024] FIG. 7 shows another preferred patch antenna and includes dimensions for illustrating this embodiment. The first conductive layer 22, the second conductive layer 24, and the slot 42 are all relatively sized according to the dimensions listed in FIG. 8. The length Lp of the first conductive layer 22 determines the resonant frequency of the patch antenna. The width Wp of the first conductive layer 22 affects the resonant resistance of the patch antenna, with wider patches producing lower resistance. The coupling level of the patch antenna is primarily determined by the total length Ls = Ls1 + Ls2 + Ls3 of the U-shaped coupling slot 42 and the back radiation level. Therefore, the slot 42 should not be longer than necessary for impedance matching. Also, the width Ws of the slot 42 affects the coupling level, but to a much smaller extent than the slot length Ls. A preferred ratio of the slot width (Ws) to the slot length (Ls) is typically 1 / 10.

[0025] An embodiment of a patch antenna shown in FIGS. 4-7 and having the dimensions specified in FIG. 8 was fabricated on the windshield of a convertible vehicle, as shown in FIG. 9. The patch antenna was placed at the bottom of the third visor area of ​​the windshield. FIG. 10 is a plot of a return loss (S11) comparison between actual measurements and simulation results obtained using the FEKO simulation tool. Of the power delivered to the antenna, return loss S11 is a measure of how much power is reflected from the antenna and how much power is "received" by the antenna and radiated. FIG. 10 shows that the return loss is less than -10 dB in the 5.1-6.1 GHz frequency range. This means the antenna can be used in UNII, ISM, IEEE 802.11a and 802.11ac, wireless local area networks (RLANs), fixed wireless access systems (FWAs), WiMAX and MESH wireless networks from 5.18-5.85 GHz, and DSRC bands from 5.85-5.925 GHz.

[0026] Vehicle antenna gain patterns were measured at an outdoor antenna range. Figure 11 shows the vehicle antenna radiation patterns for vertical polarization at frequencies of 5.3 GHz, 5.6 GHz, and 5.85 GHz. The elevation angle is 5 degrees. The patch antenna's maximum gain is approximately 0 dBi and is pointed toward the front of the vehicle. The half-power beamwidth in the azimuth plane is approximately 70 degrees.

[0027] Figure 12 shows the vertically polarized vehicle antenna radiation pattern at an elevation angle of 0 degrees. The patch antenna's maximum gain is approximately 3 dBi and is pointed toward the front of the vehicle. For a patch antenna embedded in the windshield, the higher the elevation angle, the broader the patch antenna with maximum gain; therefore, only measurement data at elevation angles of 0 and 5 degrees is shown. The antenna's gain and beamwidth also depend on the angle of the vehicle's windshield. The antenna performs better with a vertically oriented windshield than with a windshield tilted away from the vertical plane. Windshield antennas provide better coverage in the forward vehicle direction than in the rearward or sideward directions. Antennas may be embedded in the windshield, rear window, and side windows for a diversity system with an omnidirectional far-field radiation pattern in the ground wave direction.

[0028] While several preferred embodiments of the invention disclosed herein have been shown and described, those skilled in the art will recognize various modifications that may be employed without departing from the spirit of the invention as claimed and disclosed herein.

Claims

1. A glass material including a patch antenna, an inner transparent ply including oppositely disposed first and second surfaces; an outer transparent ply including oppositely disposed first and second surfaces; an intermediate layer positioned between the first surface of the inner transparent ply and the second surface of the outer transparent ply; a first conductive layer having a peripheral edge and positioned between the second surface of the outer transparent ply and the intermediate layer; a second conductive layer having a peripheral edge and located on a second surface of the inner transparent ply; the second conductive layer has an L-shaped or U-shaped slot located inside the outer periphery of the second conductive layer, the slot being aligned transversely with the first conductive layer such that the center of the slot is aligned with the center of the first conductive layer, and the slot has a length equal to half the wavelength of the fundamental TE10 frequency mode; the second conductive layer is aligned laterally with respect to the first conductive layer such that an outer periphery of the first conductive layer is aligned inside the outer periphery of the second conductive layer and such that the slot is aligned inside the outer periphery of the first conductive layer; the slot is spaced from the first conductive layer such that an electrical signal applied to an edge of the slot is electromagnetically coupled to the first conductive layer; a total length of the slot greater than a width of the first conductive layer;

2. 10. The glass material of claim 1, wherein the first conductive layer is a primary radiating element of the patch antenna.

3. 3. The glass material of claim 2, wherein the second conductive layer is an electrical ground element for the patch antenna.

4. 3. The glazing of claim 2, wherein the intermediate layer and the inner transparent ply comprise a dielectric substrate for the patch antenna.

5. 3. The glass material according to claim 2, wherein the bandwidth of the patch antenna covers the Wi-Fi band based on the IEEE 802.11a / ac standard from 5.18 to 5.85 GHz and the DSRC band from 5.85 to 5.925 GHz.

6. 3. The glazing of claim 2, wherein the patch antenna is fed by a microstrip line etched into a substrate disposed on the second surface of the inner transparent ply.

7. 7. The glass material of claim 6, wherein the patch antenna is excited by two coupling stages, one coupling stage between the microstrip line and the slot, and one coupling stage between the slot and the first conductive layer.

8. 8. The glass material of claim 7, wherein the characteristic impedance of the microstrip line and the width of the microstrip line affect the coupling with the slot.

9. The glass material of claim 7 , wherein the microstrip lines are oriented perpendicular to the centerlines of the slots.

10. 3. The glazing material of claim 2, wherein the patch antennas are embedded in a front window, a rear window, or a side window to form a diversity antenna system having an omnidirectional far-field radiation pattern in the terrestrial direction.

11. 10. The glass material of claim 1, wherein a maximum electromagnetic field within the slot occurs at a center of the slot and a maximum magnetic field in the first conductive layer occurs at a center of the first conductive layer.

12. 10. The glass material of claim 1, wherein energy is electromagnetically coupled between the slot and the first conductive layer.

13. 10. The glass material of claim 1, wherein the slots support pairs of even and odd modes oriented orthogonally to each other.

14. 14. The glass material of claim 13, wherein the odd mode has a maximum electromagnetic field strength occurring at the center of the slot.

15. 10. The glass material of claim 1, wherein the patch antenna comprises a coaxial cable having a center conductor surrounded by an outer shield, the outer shield of the coaxial cable being coupled to one side of the slot and the center conductor of the coaxial cable being coupled to an opposite side of the slot.

16. 16. The glass material of claim 15, wherein the coaxial cable and the slot transmit electromagnetic energy to the first conductive layer and receive electromagnetic energy from the first conductive layer.

17. 2. The glass material of claim 1, wherein the length of the first conductive layer determines the resonant frequency of the patch antenna, and the width of the first conductive layer affects the resonant resistance of the patch antenna.

18. 10. The glass material of claim 1, wherein the length of the slot determines the coupling level and back radiation level of the patch antenna.

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