Patent Publication Number: US-2019198987-A1

Title: Method and Apparatus for Reducing Surface Waves in Printed Antennas

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims benefit under 35 USC 119(e) of Application Ser. No. 62/537,349, filed Jul. 26, 2017, the content of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to antennas, and more particularly to printed antennas. 
     BACKGROUND OF THE INVENTION 
     Printed antennas, such as patch antennas, have been widely used where low profile, flat, or conformal footprint is required. The ease of production of such antennas makes them attractive for mass production and consumer products. In order to reduce the energy loss in the metal structures of such antennas, relatively thick substrates may be used. However, as the substrates becomes thicker, the energy loss in the substrate due to surface waves increases. 
       FIG. 1A  is a cross-sectional schematic view of a patch antenna  10  formed on a printed circuit board (PCB)  15 . Antenna  10  is configured to radiate electromagnetic waves in response to the electric signal it receives via metallic antenna feed  30 . Positioned below PCB  15  is ground plane  20 . Also shown in  FIG. 1  are surface waves  25 .  FIG. 1B  is a top view of PCB  15  showing patch antenna  10  and antenna feed  30 . The surface waves pose challenges in, for example, phased arrays by increasing the coupling between adjacent elements. Such coupling results in undesirable phase pulling. 
     BRIEF SUMMARY OF THE INVENTION 
     An antenna, in accordance with one embodiment of the present invention, includes in part, a metal piece formed on a surface of a substrate and configure to radiate electromagnetic waves, a metal feed formed in the substrate and configure to supply electrical signal to the metal piece, and a multitude of metallic walls formed in the substrate and enclosing the metal piece. 
     In one embodiment, the antenna is a patch antenna. In one embodiment, the antenna is a monopole antenna. In one embodiment, the antenna is a dipole antenna. In one embodiment, each metallic wall includes a via that is fully or partially filled by a metal. In one embodiment, each metallic wall is an electroplated tub formed in the substrate. 
     In one embodiment the antenna further includes, in part, a metallic trace formed on the surface of the substrate and enclosing the antenna patch. In one embodiment, the substrate is a printed circuit board. 
     A method of radiating an electromagnetic waves from an antenna formed on a substrate includes, in part, supplying an electrical signal through a metallic feed formed in the substrate, and applying a ground potential to a multitude of metallic walls formed in the substrate and enclosing the antenna. 
     In one embodiment, the antenna is a patch antenna. In one embodiment, the antenna is a monopole antenna. In one embodiment, the antenna is a dipole antenna. In one embodiment, each metallic wall includes a via that is fully or partially filled by a metal. In one embodiment, each metallic wall is an electroplated tub formed in the substrate. 
     In one embodiment, the method further includes, in part, applying a ground potential to a metallic trace formed on the surface of the substrate and enclosing the antenna patch. In one embodiment, the substrate is a printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-sectional schematic view of a patch antenna, as known in the prior at. 
         FIG. 1B  is a top view of the patch antenna shown in  FIG. 1A . 
         FIG. 2A  is a cross-sectional schematic view of a patch antenna, in accordance with one embodiment of the present invention. 
         FIG. 2B  is a top view of the patch antenna shown in  FIG. 2A , in accordance with one embodiment of the present invention. 
         FIG. 2C  is a top view of the patch antenna shown in  FIG. 2A , in accordance with another embodiment of the present invention 
         FIG. 3A  is a cross-sectional schematic view of a patch antenna, in accordance with one embodiment of the present invention. 
         FIG. 3B  is a top view of the patch antenna shown in  FIG. 2A , in accordance with one embodiment of the present invention. 
         FIG. 4A  is a cross-sectional schematic view of a patch antenna, in accordance with one embodiment of the present invention. 
         FIG. 4B  is a top view of the patch antenna shown in  FIG. 2A , in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with embodiments of the present invention, a printed antenna, such as a patch antenna, formed above a substrate, such as a printed circuit board (PCB), is enclosed with electrically conductive walls that are connected to the ground potential, thereby to prevent or substantially reduce propagation of the surface waves in the substrate. In one embodiment, the conductive walls may be formed in closely spaced vias formed around the antenna. 
       FIG. 2A  is a cross-sectional schematic view of a patch antenna  10  formed on a PCB  15 , in accordance with one embodiment of the present invention. Patch antenna  10  is configured to radiate electromagnetic waves in response to the electric signal it receives via metallic antenna feed  30 . Positioned below PCB  15  is ground plane  20 . To eliminate or substantially reduce surface waves, patch antenna  10  is enclosed with conductive walls  40  that are formed in substrate  15  and connected to ground plane  20 . Metal traces  50  are configured to shield any routing and circuitry that may be present around antenna  10 . 
       FIG. 2B  is a top view of patch antenna  10  and antenna feed  30  of  FIG. 2A . Metal trace  50  is shown as enclosing patch antenna  10 . Conductive walls  40  formed in substrate  15  are also shown as enclosing patch antenna  10 . 
     In one embodiment, conductive walls may be formed by creating vias in PCB  15  and filling the vias, either partially or fully, along the depth of the vias, with a metal such as copper, as is shown for example, in  FIGS. 2A, 2B and 2C . The distance between each pair of adjacent vias is less than the wavelength of the electromagnetic wave being radiated by patch antenna  10 . 
     In accordance with another embodiment, the conductive walls may be formed by creating a number of moats in the PCB around the patch antenna and then electroplating the interior sides of the moats with conductive material such as copper.  FIG. 2C  shows a PCB  15  that includes a multitude of moats  60  enclosing patch antenna  10 . The interior sides of the moats are electroplated to form conductive walls around patch antenna  10 . The conductive walls, such as the ones shown in  FIGS. 2A and 2B , reflect the surface waves back in the region (also referred to herein as a tub) formed between the walls  40  in the PCB, thereby preventing the energy loss otherwise caused by the surface waves. As a result of such reflections, the surface waves cancel out each other as long as the dimensions of the tub is not resonant at the radiation frequency. If the surface waves are resonant, the reflected surface waves amplify each other and radiate out of the tub through the antenna and thus contribute to the radiated waves. 
       FIG. 3A  is a cross-sectional schematic view of a monopole antenna  100  formed on a PCB  15 , in accordance with one embodiment of the present invention. Monopole antenna  10  is configured to radiate electromagnetic waves in response to the electric signal it receives via metallic antenna feed  30 . Positioned below PCB  15  is ground plane  20 . To eliminate or substantially reduce surface waves, monopole antenna  100  is enclosed with conductive walls  40  that are formed in substrate  15  and connected to ground plane  20 . Metal traces  50  are configured to shield any routing and circuitry that may be present around antenna  10 . 
       FIG. 3B  is a top view of monopole antenna  100  and antenna feed  30  of  FIG. 3A . Metal trace  50  is shown as enclosing monopole antenna  100 . Conductive walls  40  formed in substrate  15  are also shown as enclosing monopole antenna  100 . 
     In one embodiment, conductive walls may be formed by creating vias in PCB  15  and filling the vias, either partially or fully, along the depth of the vias, with a metal such as copper, as is shown for example, in  FIGS. 3A and 3B . The distance between each pair of adjacent vias is less than the wavelength of the electromagnetic wave being radiated by monopole antenna  100 . In one embodiment, the PCB substrate has a thickness (depth) of nearly one quarter of the wavelength of the signal being transmitted by monopole antenna  100 . 
     In accordance with another embodiment, the conductive walls may be formed by creating a number of moats in the PCB around the monopole antenna and then electroplating the interior sides of the moats with conductive material such as copper, similar to that shown in  FIG. 2C . 
       FIG. 4A  is a cross-sectional schematic view of a dipole antenna  200  formed on a PCB  15 , in accordance with one embodiment of the present invention. Dipole antenna  200  is configured to radiate electromagnetic waves in response to the electric signal it receives via metallic antenna feeds  30 . Positioned below PCB  15  is ground plane  20 . To eliminate or substantially reduce surface waves, dipole antenna  200  is enclosed with conductive walls  40  that are formed in substrate  15  and connected to ground plane  20 . Metal traces  50  are configured to shield any routing and circuitry that may be present around antenna  200 . 
       FIG. 4B  is a top view of dipole antenna  200  and antenna feeds  30  of  FIG. 4A . Metal trace  50  is shown as enclosing dipole antenna  200 . Conductive walls  40  formed in substrate  15  are also shown as enclosing dipole antenna  200 . 
     In one embodiment, conductive walls may be formed by creating vias in PCB  15  and filling the vias, either partially or fully, along the depth of the vias, with a metal such as copper, as is shown for example, in  FIGS. 4A and 4B . The distance between each pair of adjacent vias is less than the wavelength of the electromagnetic wave being radiated by dipole antenna  100 . In one embodiment, the PCB substrate has a thickness of nearly one quarter of the wavelength of the signal being transmitted by the dipole antenna  100 . 
     In accordance with another embodiment, the conductive walls may be formed by creating a number of moats in the PCB around the dipole antenna and then electroplating the interior sides of the moats with conductive material such as copper, similar to that shown in  FIG. 2C . 
     The above embodiments of the present invention are illustrative and not limitative. The embodiments of the present invention are not limited by the type or dimensions of the antenna. The above embodiments of the present invention are not limited by the wavelength or frequency of the signal being transmitted. Other modifications and variations will be apparent to those skilled in the art and are intended to fall within the scope of the appended claims.