Patent Publication Number: US-11658377-B2

Title: Substrate-mountable electromagnetic waveguide

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of co-pending U.S. application Ser. No. 17/013,504 filed on 4 Sep. 2020 titled “Substrate-Mountable Electromagnetic Waveguide” from which benefits are claimed under 35 U.S.C. § 120. 
    
    
     TECHNICAL FIELD 
     The disclosure relates generally to electromagnetic waveguides and more particularly to dielectric waveguide components that are mountable on a substrate. 
     BACKGROUND 
     Electromagnetic waveguides generally comprise a metallized conduit that defines boundaries within which the propagation of energy is constrained. Dielectric filled waveguides are often used for higher frequency applications, like microwaves. The geometry of the waveguide affects characteristics of the waveguide like impedance, cutoff frequency and propagation mode. Waveguides can be configured as couplers, polarizers, and filters among other circuit elements in small-scale radio frequency (RF) and microwave systems. These and other waveguide systems often require mounting of a waveguide component on a printed circuit board (PCB) for transitioning to coplanar, microstrip, stripline or other impedance controlled transmission lines. To facilitate such integration, micros trip transmission lines sometimes include a widening apron that forms a transition for interfacing with the waveguide. It&#39;s also known to provide a tapered spacing between conductive posts in substrate integrated waveguides (SIW) to form a narrowing transition for interfacing with a coplanar transmission line. The transition interface between waveguide components and impedance controlled transmission lines however tends to be a source of impedance mismatch or reduced bandwidth and may require increased component size. 
     The objects, features and advantages of the present disclosure will become more fully apparent to those of ordinary skill in the art upon careful consideration of the following Detailed Description and the appended claims in conjunction with the accompanying drawings described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a top perspective view of a waveguide. 
         FIG.  2    is a bottom perspective view of the waveguide in  FIG.  1   . 
         FIGS.  3 - 7    show various waveguide implementations. 
         FIG.  8    is a perspective view of a waveguide mounted on a host device. 
         FIG.  9    is a perspective view of a portion of a host device. 
         FIG.  10    illustrates electric field strength of a waveguide mounted on a host device. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates generally to electromagnetic waveguides mountable on a substrate like a printed circuit board (PCB) as described further herein. Such waveguides can be configured as a coupler, a polarizer, resonator, or filter among other electrical components for use in small-scale radio frequency (RF) systems or subassemblies. The term “radio frequency” as used herein includes microwaves. 
     The waveguide generally comprises a dielectric substrate, also referred to herein as a dielectric, having at least partially conductive portions that define boundaries within which propagating radio frequency energy is confined. The dielectric can comprise a ceramic, glass, or plastic among other materials and compositions having suitable permittivity and other characteristics. The conductive portions can be metallized surfaces of the dielectric substrate formed by selectively applying metal or other conductive material on portions of the dielectric substrate. The metal can be a base metal, precious metal, metal alloy or some other conductive material. Metals can be applied by sputtering, plating or other known or future deposition processes. The conductive material can also be conductive sheet material layered onto the dielectric. 
     Characteristics of the waveguide depend on its geometry as well as dielectric material properties. For example the cutoff frequency is a function of spacing between the side conductors, i.e., a width of the waveguide, dielectric constant of the substrate material, and impedance is a function of the spacing or height between the conductors on the upper and lower surfaces of the waveguide. 
     One such waveguide is a transverse electric (TE) mode waveguide. In  FIGS.  1 ,  2  and  8   , a rectangular waveguide  100  comprises a dielectric  110  having a cuboid shape. More generally however the dielectric substrate and hence the waveguide can have other shapes, like cubic or cylindrical shapes. One of the conductive surfaces of the waveguide can be a ground plane mountable on a printed circuit board (PCB) of a host device as described herein. 
     In  FIG.  1   , the waveguide comprises a conductor  122  adjacent a top surface of the dielectric  110 . In  FIG.  2   , the waveguide includes a conductor  124  adjacent a bottom surface of the dielectric  110 . In some implementations, the conductor  124  is a ground plane. Generally, the conductor  122  is electrically coupled to the conductor  124  by a first side conductor adjacent a first side surface portion of the dielectric and by a second side conductor adjacent a second side surface portion of the dielectric. In other implementations, the conductors  122  and  124  can have other shapes or structures, e.g., metallic screens among others, to constrain the radio frequency energy. 
     The first and second side conductors of the waveguide can be implemented in any one of many different forms. In  FIGS.  1 ,  2  and  6   , the first and second side conductors are metallized surfaces  126  and  128  disposed on and covering substantially all of the outer surfaces of corresponding side wall portions of the dielectric. The conductive surfaces  126  and  128  interconnect the conductor  122  and the ground plane  124 . In other implementations, however, the first and second side conductors do not cover the entire side wall portions of the dielectric. In  FIG.  3   , the first and second side conductors each comprise a metallized slot  131  and  132  disposed on outer surface portions of corresponding dielectric side walls. The conductive slots  131  and  132  interconnect the conductor  122  and the ground plane. In  FIG.  4   , the first and second side conductors comprise a corresponding plurality of metallized cylindrical vias  133  and  134  extending through openings in the dielectric adjacent corresponding side walls of the dielectric. The conductive vias  133  and  134  interconnect the conductors on the upper and lower surfaces of the dielectric. In  FIG.  5   , the first and second side conductors comprise a corresponding plurality of metallized semi-cylindrical castellations  135  and  136  formed on an outer surface of the dielectric side walls. The conductive castellations  135  and  136  interconnect the conductors on the upper and lower surface of the dielectric. In other implementations, the first and second side conductors can be other than sheet like conductors to constrain radio frequency energy. For example, the conductive materials can be implemented as metallic screens, or meshes or other structures. 
     The waveguide also comprises a conductive excitation member at one or both ends thereof. In some implementations, the signal is introduced at an input of the waveguide and extracted at an output of the waveguide. Generally, the excitation member is electrically coupled to the conductor and is disposed through or across a portion of the dielectric at or near an end surface of the dielectric that is devoid of conductive material, wherein portions of the end surface, on opposite sides of the conductive excitation member, are devoid of conductive material. The excitation member also includes a host interface electrically isolated from the ground plane and connectable to a transmission line on a host device. 
     In  FIGS.  1  and  2   , a conductive excitation member  140  is electrically coupled to the conductor  122  and includes a semi-cylindrical shaped castellation  142  disposed across the first end surface portion  112  of the dielectric. In other embodiments, the castellation  142  can have other shapes and need not be located on the end surface of the dielectric. For example, the castellation can have a cylindrical shape and be located in an opening through the dielectric spaced inwardly from the end surface  112 .  FIG.  2    shows dielectric portions  111  and  113  on opposite sides of the excitation member  140  devoid of conductive material. In  FIG.  2   , the excitation member  140  includes a host interface embodied as a flange  144  extending therefrom for integration with the host. The host interface flange is separated and electrically isolated from the ground plane  124  by a dielectric portion  146 . An impedance of the transition is a function of the gap exposing the dielectric portion  146  between the outermost portion of the host interface flange  144  and the ground plane  124 . In  FIG.  2   , the host interface flange  144  is coplanar with the ground plane  124 . In other implementations however the host interface can have other shapes and spatial orientations and configurations to accommodate a complementary non-planar interface on a host device. 
     In some implementations, the waveguide includes one or more lateral conductors interconnecting the conductive member and the ground plane. The one or more lateral conductors are disposed on or near the same end surface portion of the dielectric where the conductive excitation member is located, wherein at least a portion of the first end surface portion of the dielectric is devoid of conductive material between the one or more lateral conductors and the conductive excitation member. An input impedance of the waveguide is a function of the one or more lateral conductors and the size of the excitation member. In implementations including first and second lateral conductor, the conductive excitation member can be located between the first and second lateral conductors. In  FIGS.  1 - 5   , the waveguide includes lateral conductive material  150  and  152  disposed on corresponding corners of the waveguide. In  FIG.  6   , the lateral conductive material corresponds to conductive material  126  and  128  on the side surfaces of the dielectric, wherein the end surface portion  112  of the dielectric is devoid of conductive material. In  FIG.  7   , the waveguide includes only a single lateral conductive member or material  150  disposed on a corner of the waveguide. In the illustrated embodiments, the lateral conductive material is disposed on an outer surface of the dielectric. In other embodiments, however, the lateral conductive materials may be castellations formed in or on through-holes located inwardly of an outermost surface or surfaces of the dielectric. 
     In  FIG.  8   , a waveguide  100  is mounted on a substrate  200 , which may be a printed circuit board (PCB) or other component of a host device or subassembly.  FIGS.  8  and  9    show a PCB substrate comprising conductive transmission line portions  202  and  204  and ground plane  206  formed thereon. The transmission line can be a microstrip, stripline, coplanar waveguide trace or other transmission structure. The conductive excitation members of the waveguide are electrically coupled to corresponding transmission lines and the ground plane of the waveguide is electrically coupled to the ground plane of the substrate. In  FIG.  8   , the conductive excitation member  140  and particularly the host interface flange  144  thereof is electrically coupled to the transmission line  202 . The ground plane  124  on the underside of the waveguide is shown coupled to the ground plane  206  of the substrate. The waveguide is a surface-mount component that can be mounted on the substrate by reflow soldering or other known or future affixation processes. Alternatively, the ground plane  124  can have though-hole contacts that are disposed in, and soldered to, corresponding openings in the substrate. 
       FIG.  10    illustrates the magnitude of the TE mode electric field inside of a rectangular waveguide mounted on a host substrate with microstrip transmission line feeds. 
     While the present disclosure and what is presently considered to be the best mode thereof has been described in a manner establishing possession by the inventors and enabling those of ordinary skill in the art to make and use the same, it will be understood and appreciated that equivalents of the exemplary embodiments disclosed herein exist, and that myriad modifications and variations may be made thereto, within the scope and spirit of the disclosure, which is to be limited not by the exemplary embodiments described but by the appended claims.