Patent Publication Number: US-10320053-B2

Title: Wideband coplanar waveguide fed monopole applique antennas

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the priority date of U.S. Provisional Patent Application Ser. No. 62/295,822, titled, Wideband Coplanar Waveguide Fed Monopole Applique Antennas, filed Feb. 16, 2016. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates generally to a thin, flexible, wideband antenna configured on a dielectric substrate and, more particularly, to a thin, flexible, wideband co-planar waveguide (CPW) antenna that may include transparent conductors so as to allow the antenna to be adhered to a visible part of vehicle windows. 
     Discussion of the Related Art 
     Modern vehicles employ various and many types of antennas to receive and transmit signals for different communications systems, such as terrestrial radio (AM/FM), cellular telephone, satellite radio, dedicated short range communications (DSRC), GPS, etc. Further, cellular telephone is expanding into 4G long term evolution (LTE) that requires two antennas to provide multiple-input multiple-output (MIMO) operation. The antennas used for these systems are often mounted to a roof of the vehicle so as to provide maximum reception capability. Further, many of these antennas are often integrated into a common structure and housing mounted to the roof of the vehicle, such as a “shark-fin” roof mounted antenna module. As the number of antennas on a vehicle increases, the size of the structures required to house all of the antennas in an efficient manner and providing maximum reception capability also increases, which interferes with the design and styling of the vehicle. Because of this, automotive engineers and designers are looking for other suitable areas on the vehicle to place antennas that may not interfere with vehicle design and structure. 
     One of those areas is the vehicle glass, such as the vehicle windshield, which has benefits because glass makes a good dielectric substrate for an antenna. For example, it is known in the art to print AM and FM antennas on the glass of a vehicle where the printed antennas are fabricated within the glass as a single piece. However, those known systems are generally limited in that they could only be placed in a vehicle windshield or other glass surface in areas where viewing through the glass is not necessary. 
     SUMMARY OF THE INVENTION 
     The present invention discloses and describes a thin, flexible antenna that has particular application to be mounted to a dielectric substrate on a vehicle, such as vehicle glass, where the antenna has a wideband antenna geometry for various communications systems, and where the conductive portion of the antenna can employ transparent conductors. 
     Additional features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a vehicle showing a vehicle windshield; 
         FIG. 2  is a rear view of the vehicle showing a vehicle rear window; 
         FIG. 3  is a profile view of a vehicle window including a thin, flexible antenna formed thereon; 
         FIG. 4  is an illustration of a CPW antenna feed structure including opposing and coupled ground planes with a signal line therebetween; 
         FIG. 5  is an illustration showing the CPW antenna feed structure and including an RF connector; 
         FIG. 6  is an illustration of the CPW antenna feed structure and including a coaxial cable feed line; 
         FIG. 7  is a top view of a wideband co-planar antenna including a radiator fed by a CPW feed structure; and 
         FIG. 8  is a top view of another wideband co-planar antenna including a radiator and a CPW feed structure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following discussion of the embodiments of the invention directed to a thin, flexible wideband antenna suitable to be adhered to a curved dielectric structure is merely exemplary in nature, and is in no way intended to limit the invention or its applications or uses. For example, the discussion herein talks about the antenna being applicable to be adhered to automotive glass. However, as will be appreciated by those skilled in the art, the antenna will have application for other dielectric structures other than automotive structures and other than transparent or translucent surfaces. 
       FIG. 1  is a front view of a vehicle  10  including a vehicle body  12 , roof  14  and windshield  16 , and  FIG. 2  is a rear view of the vehicle  10  showing a rear window  18 . 
     As will be discussed in detail below, the present invention proposes providing a wideband antenna on the windshield  16 , the rear window  18 , or any other window or dielectric structure on the vehicle  10 , where the antenna is flexible to conform to the shape of the particular dielectric structure, and where the antenna can be mounted at any suitable location on the dielectric structure, including locations on the windshield  16  that the vehicle driver needs to see through. As will become apparent, the antenna provided on the dielectric structure may be operable for various communications systems, such as AM/FM radio antennas, DSRC antennas, satellite radio antennas, GPS antennas, cellular antennas, including MIMO antennas, etc. In one embodiment, the antenna is a wideband monopole appliqué antenna that is installed directly on the surface of the dielectric structure by a suitable adhesive. The disclosed antenna can be designed to operate on automotive glass of various physical thicknesses and dielectric properties, where the antenna only operates as intended when installed on the glass since the antenna geometry pattern on the carrier substrate will not have good impedance matching. 
       FIG. 3  is a profile view of an antenna structure  20  including a windshield  22  having an outer glass layer  24 , an inner glass layer  26  and a polyvinyl butyral (PVB) layer  28  therebetween. The structure  20  includes an antenna  30  formed on a thin, flexible film substrate  32 , such as a mylar layer, and adhered to a surface of the layer  26  by an adhesive layer  34 . The adhesive layer  34  can be any suitable adhesive or transfer tape that effectively allows the substrate  32  to be secured to the glass layer  26 , and further, if the antenna  30  is located in a visible area of the glass layer  26 , the adhesive or transfer tape can be transparent or near transparent so as to have a minimal impact on the appearance and light transmission therethrough. The antenna  30  can be protected by a low RF loss passivation layer  36 , such as parylene. An antenna connector  38  is shown connected to the antenna  30  and can be any suitable RF or microwave connector such as a direct pig-tail or coaxial cable connection. Although the antenna  30  is shown being coupled to an inside surface of the inner glass layer  26 , the conductor  30  can be adhered to the outer surface of the outer glass layer  24  or the surface of the layers  24  or  26  adjacent to the PVB layer  28  or the surfaces of the PVB layer  28 . 
     The antenna  30  can be formed by any suitable non-lossy conductor, such as copper, gold, silver, silver ceramic, etc. If the antenna  30  is at a location on the vehicle glass that requires the driver or other vehicle occupant to see through the glass, then the antenna conductor can be any suitable transparent conductor, such as indium tin oxide (ITO), silver nano-wire, zinc oxide (ZnO), etc. Performance of the antenna  30  when it is made of a transparent conductor could be enhanced by adding a conductive frame along the edges of the antenna  30  as is known in the art. 
     The thickness of automotive glass may vary over 2.8 mm-5 mm and have a relative dielectric constant ε r  in the range of 4.5-7.0. The antenna  30  includes a single layer conductor and a co-planar waveguide (CPW) feed structure to excite the antenna radiator. The CPW feed structure can be configured for mounting the connector  38  in a manner appropriate for the CPW feed line or for a pigtail or a coaxial cable. When the connector  38  or the pigtail connection to the CPW line is completed, the antenna  30  can be protected with the passivation layer  36 . In one embodiment, when the antenna  30  is installed on the glass, a backing layer of the transfer tape can be removed. By providing the antenna conductor on the inside surface of the vehicle windshield  22 , degradation of the antenna  30  can be reduced from environmental and weather conditions. 
       FIG. 4  is a top, cut-away view of a CPW feed structure  40  including a signal line  42  that is coupled to the antenna radiator (not shown in  FIG. 4 ) and that is spaced apart from opposing ground planes  44  and  46  defining a gap  48  therebetween. The ground planes  44  and  46  are electrically coupled by a conductor  50  at a connector region  52  to provide installation of a surface mount connector or direct mount pigtail or coaxial cable that connects the antenna to a suitable circuit, such as a transceiver (not shown), where the antenna, feed structure and connector are all in the same plane. The dimensions of the conductor  50  can be less than a quarter-wavelength at the center of the frequency band of interest. 
       FIG. 5  is a top, cut-away view of a CPW antenna feed structure  60  similar to the antenna structure  40 , where like elements are identified by the same reference number. In this embodiment, a surface mount connector  62  feeds the structure  60  and is electrically coupled to the ground planes  44  and  46  and the conductor  50  through tabs  64 , which are electrically isolated from a tab  66  coupled to the signal line  42 . 
       FIG. 6  is a top, cut-away view of a CPW antenna feed structure  70  similar to the antenna structure  40 , where like elements are identified by the same reference number. In this embodiment, a coaxial cable  72  feeds the structure  70  and includes an inner conductor  74  electrically coupled to the signal line  42  and an outer ground conductor  76  electrically coupled to the conductor  50 , where the conductors  74  and  76  are separated by an insulator  78 . 
       FIG. 7  is a top view of a CPW antenna structure  80  including a feed structure  82  having opposing ground planes  84  and  86  and a signal line  88  extending therebetween that is electrically isolated from the planes  84  and  86  by a gap  90 , where a conductor  92  is coupled to the ground planes  84  and  86 . The feed line to the feed structure  82  is not shown. A specially configured radiator  94 , here pentagon-shaped, fed by the feed structure  82  is electrically coupled to the signal line  88  at a tip of the radiator  94 , as shown, where the radiator  94  flairs to a dimension that provides signal reception and transmission in the frequency band of interest, such as the 700 MHz-2.2 GHz frequency range suitable for LTE communications. For this embodiment, the overall length of the structure  80  is 13.5 cm and the width of the structure  80  is 12 cm. 
       FIG. 8  is a top view of a CPW antenna structure  100  similar to the antenna structure  80 , but having different dimensions for DSRC communications operating at 5.9 GHz. The antenna structure  100  includes a feed structure  102  having opposing ground planes  104  and  106  and a signal line  108  extending therebetween that is electrically isolated from the planes  104  and  106  by a gap  110 , where a conductor  112  is coupled to the ground planes  104  and  106 . The feed line to the feed structure  102  is not shown. A specially configured radiator  114 , here pentagon-shaped, fed by the feed structure  102  is electrically coupled to the signal line  108  at a tip of the radiator  114 , as shown, where the radiator  114  flairs to a dimension that provides signal reception and transmission in the frequency band of interest. 
     The foregoing discussion discloses and describes merely exemplary embodiments of the present invention. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the invention as defined in the following claims.