Patent Publication Number: US-9899720-B2

Title: Dielectric waveguide comprised of a cladding of oblong cross-sectional shape surrounding a core of curved cross-sectional shape

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Chinese Patent Application No. 201510477529.7, filed on 6 Aug. 2015, which is incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     The subject matter herein relates generally to dielectric waveguides. 
     Dielectric waveguides are used in communications applications to convey electromagnetic waves along a path between two ends. Dielectric waveguides may provide communication transmission lines for connecting antennas to radio frequency transmitters and receivers and in other applications. For example, although electromagnetic waves in open space propagate in all directions, dielectric waveguides direct the electromagnetic waves along a defined path, which allows the waveguides to transmit high frequency signals over relatively long distances. 
     Dielectric waveguides include at least one dielectric material. A dielectric is an electrical insulating material that can be polarized by an applied electrical field. The polarizability of a dielectric material is expressed by a value called the dielectric constant or relative permittivity. The dielectric constant of a given material is its dielectric permittivity expressed as a ratio relative to the permittivity of a vacuum, which is 1 by definition. A first dielectric material with a greater dielectric constant than a second dielectric material is able to store more electrical charge by means of polarization than the second dielectric material. 
     Some known dielectric waveguides include a core dielectric material and a cladding dielectric material that surrounds the core dielectric material. The cladding may be used to isolate electromagnetic wave signals traveling through the core from external influences which may interfere with the signal transmission and degrade the signal. For example, such external influences may include a human hand that touches the dielectric waveguide and/or another conductive component that contacts or comes in close proximity to the waveguide. The cladding layer around the core is typically circular. However, a circular cladding layer may make connecting the dielectric waveguide to electrical components or other waveguides difficult. For example, some waveguides include a rectangular or other oblong-shaped core. It is important for the orientation of the core of a first waveguide to align with the orientation of the core of a second waveguide at a connecting interface in order for the electromagnetic waves to cross the interface between the two waveguides. If the cores and/or claddings of the two waveguides are not properly aligned, at least some of the electrical energy being conveyed through the waveguides will not bridge the interface between the waveguides. For example, the shapes of the core and cladding orient the electrical field orientation or polarization through the waveguide. If the cores are rotationally offset relative to one another, then the electromagnetic waves through the first waveguide may be polarized or oriented differently than the electromagnetic waves through the second waveguide. As a result, the electromagnetic waves from the first waveguide may reflect at the interface instead of being received across the interface into the second waveguide. Since the cladding is circular, there is no planar surface or angled edge along a perimeter of the cladding that can be used for aligning the two waveguides together such that both the cores and claddings have matching orientations. Thus, one of the waveguides may roll relative to the other, which misaligns the waveguides and may result in degraded signal transmission across the interface between the waveguides. 
     A need remains for a dielectric waveguide that provides better mechanical alignment for connecting the waveguide to other waveguides and electrical components in order to increase the quality and integrity of signal transmission across a connection interface. 
     SUMMARY OF THE INVENTION 
     In an embodiment, a dielectric waveguide for propagating electromagnetic signals is provided that includes a cladding member. The cladding member extends a length between two ends. The cladding member has an oblong cross sectional shape. The cladding member is formed of a first dielectric material. The cladding member defines a core region that extends through the cladding member the length of the cladding member. The core region has a circular cross sectional shape. The core region is filled with a second dielectric material having a dielectric constant value that differs from a dielectric constant value of the first dielectric material of the cladding member. 
     In another embodiment, a dielectric waveguide for propagating electromagnetic signals is provided that includes a core member and a cladding member. The core member extends a length between two ends. The core member has a circular cross sectional shape. The core member is formed of a first dielectric material. The cladding member surrounds the core member along the length of the core member. The cladding member has an oblong cross sectional shape. The cladding member is formed of a second dielectric material having a dielectric constant value that differs from a dielectric constant value of the first dielectric material of the core member. 
     In yet another embodiment, a dielectric waveguide for propagating electromagnetic signals is provided that includes a core member and a cladding member. The core member extends a length between two ends. The core member is formed of a first dielectric material having a dielectric constant value less than 3. The cladding member surrounds the core member along the length of the core member. The cladding member has an oblong cross sectional shape. The cladding member is formed of a second dielectric material having a dielectric constant value that is between 3 and 7. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of a dielectric waveguide formed in accordance with an embodiment. 
         FIG. 2  is a cross-sectional view of the dielectric waveguide according to a first embodiment. 
         FIG. 3  is a cross-sectional view of the dielectric waveguide according to a second embodiment. 
         FIG. 4  is a top perspective view of the dielectric waveguide according to an alternative embodiment. 
         FIG. 5  is a cross-sectional view of the dielectric waveguide according to another alternative embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a top perspective view of a dielectric waveguide  100  formed in accordance with an embodiment. The dielectric waveguide  100  is configured to convey electromagnetic signals along a length of the waveguide  100  for transmission of the electromagnetic signals to or from an antenna, a radio frequency transmitter and/or receiver, or another electrical component. The electromagnetic signals may be in the form of electromagnetic waves. The dielectric waveguide  100  may be used to transmit sub-terahertz radio frequency signals, such as in the range of 120-160 GHz. The signals are millimeter-wave signals since the signals in this frequency range have wavelengths less than five millimeters. The dielectric waveguide  100  may be used to transmit modulated radio frequency (RF) signals. The modulated RF signals may be modulated in orthogonal mathematical domains to increase data throughput. The dielectric waveguide  100  is oriented with respect to a vertical or elevation axis  191 , a lateral axis  192 , and a longitudinal axis  193 . The axes  191 - 193  are mutually perpendicular. Although the elevation axis  191  appears to extend in a vertical direction generally parallel to gravity, it is understood that the axes  191 - 193  are not required to have any particular orientation with respect to gravity. The dielectric waveguide  100  extends a length along the longitudinal axis  193  between two ends  104 . 
     The dielectric waveguide  100  includes a cladding member  102  that extends the length of the dielectric waveguide  100 . The cladding member  102  is formed of a dielectric material, referred to herein as a cladding material. Thus, the cladding material is an electrical insulator that may be polarized by an applied electric field. The cladding member  102  has an oblong cross sectional shape. For example, the cross sectional shape of the cladding member  102  is longer in one direction than in another direction. The oblong shape of the cladding member  102  may orient the electromagnetic waves that propagate through the dielectric waveguide  100  in a horizontal or vertical polarization. The cladding member  102  may be rectangular with right angle corners, rectangular with curved corners, trapezoidal, elliptical, oval, or the like. In the illustrated embodiment, the cladding member  102  has a top side  106 , a bottom side  108 , a left side  110 , and a right side  112 . As used herein, relative or spatial terms such as “first,” “second,” “top,” “bottom,” “left,” and “right” are only used to distinguish the referenced elements and do not necessarily require particular positions, orders, or orientations in the dielectric waveguide  100  or in the surrounding environment of the dielectric waveguide  100 . 
     The cladding member  102  defines a core region  114  that extends through the cladding member  102  for the length of the cladding member  102  between the two ends  104 . The core region  114  includes an opening  116  at both ends  104  of the cladding member  102 . In the illustrated embodiment, the core region  114  has a circular cross sectional shape. In an alternative embodiment, the core region  114  may have an oblong cross sectional shape. The core region  114  is filled with a dielectric material, referred to herein as a core material. The core material has a dielectric constant that is different from the dielectric constant of the cladding material. 
     The different dielectric constants of the core material and the cladding material affect the distribution of the electric field within the waveguide  100 . For example, the electric field through the waveguide  100  may concentrate within the material having the greater dielectric constant, at least for two dielectric materials having dielectric constants in the range of 0-15. Thus, if the cladding material has a dielectric constant that is greater than the core material, a majority of the electric field is distributed within the cladding member  102  (such that the field strength is greatest within the cladding member  102 ), although some of the electric field may be distributed within the core region  114  and/or outside of the cladding member  102 . On the other hand, if the core material has a greater dielectric constant than the core material, a majority of the electric field may be distributed within the core region  114  and a minority of the field is within the cladding member  102  and/or outside of the cladding member  102 . 
     In an embodiment, at least one of the sides  106 ,  108 ,  110 ,  112  of the dielectric waveguide  100  is planar or includes at least a planar surface. The at least one planar side may be used as a reference surface for mechanically aligning the waveguide  100  in an interconnection with a connecting waveguide (not shown), a connector, an antenna, or another electrical component. For example, the waveguide  100  may be configured to be connected to a connecting waveguide that is substantially identical to the waveguide  100  (except perhaps for length) by abutting one end  104  of the waveguide  100  against an end of the connecting waveguide at an interface to form a butt joint. The one or more reference surfaces of the waveguide  100  may be aligned with a complementary planar side of the connecting waveguide to ensure that the cladding member  102  and the core region  114  align with the respective cladding member and core region of the connecting waveguide. In the illustrated embodiment, all four sides  106 - 112  are planar, such that each of the sides  106 ,  108 ,  110 ,  112  may be a reference surface used to align the waveguide  100  in an interconnection. 
       FIG. 2  is a cross-sectional view of the dielectric waveguide  100  according to a first embodiment. In the illustrated embodiment, the core region  114  defined by the cladding member  102  is filled with air. Air defines the core dielectric material within the core region  114 . Thus, the core region  114  is not filled with a solid material. Air has a dielectric constant that is approximately 1. The cladding material of the cladding member  102  has a dielectric constant that is greater than the dielectric constant of air. For example, the cladding material may have a dielectric constant between 2 and 15. More specifically, the cladding material may have a dielectric constant between 3 and 7. As used herein, a range that is “between” two end values is meant to be inclusive of the end values. Since the dielectric constant of the cladding material is greater than the dielectric constant of air, a majority of the electric field through the waveguide  100  is distributed within the cladding member  102 . In an embodiment, the dielectric constant value of the cladding material may be between 3 and 4 such that the difference in dielectric constant values between the core material within the core region  114  and the cladding material within the cladding member  102  is between 2 and 3. Thus, due to the relatively small difference in dielectric constant values, the field strength of the electric field is distributed within both the cladding member  102  and the core region  114 , although the majority of the field strength is in the cladding member  102 . 
     The cladding material of the cladding member  102  may be a dielectric polymer, such as a plastic or another synthetic polymer. For example, the cladding material may be polypropylene, polyethylene, polytetrafluoroethylene (PTFE), polystyrene, nylon, a polyimide, or the like, including combinations thereof. Such polymers may reduce loss through the dielectric waveguide  100 , allowing signals to propagate farther than other waveguide materials. In other embodiments, the cladding dielectric material may be or include paper, mica, rubber, salt, concrete, Neoprene synthetic rubber, Pyrex® borosilicate glass, silicon dioxide, or the like. The cladding member  102  may be flexible or semi-rigid. 
     In the illustrated embodiment, the top side  106  and the bottom side  108  of the cladding member  102  are longer than the left side  110  and the right side  112  of the cladding member  102 . As such, the cladding member  102  has a width (W) that is greater than a height (H) of the cladding member  102 . The electromagnetic waves may be oriented with a horizontal polarization due to the width being greater than the height. In the illustrated embodiment, the cladding member  102  is rectangular. For example, the top side  106  is parallel to the bottom side  108 , the left side  110  is parallel to the right side  112 , and the cladding member  102  defines right angles between adjacent sides  106 ,  108 ,  110 ,  112 . Each of the sides  106 ,  108 ,  110   112  is planar. The cladding member  102  in  FIG. 2  thus includes two pairs of opposing planar sides, where the first pair is the top and bottom sides  106 ,  108  and the second pair is the left and right sides  110 ,  112 . In an alternative embodiment, however, the cladding member  102  may include only one pair of opposing planar sides, which orients the electric field within the cladding member  102 . The planar sides also serve as reference surfaces for mechanically aligning the waveguide  100  in an interconnection. 
     The cladding member  102  may have various dimensions. In an embodiment, the cladding member  102  has a height of approximately 0.8 mm and a width of approximately 1.2 mm. The aspect ratio for the width to the height is less than two in the illustrated embodiment. The aspect ratio may be at least two in alternative embodiments. As described above, the cladding member  102  may have other oblong shapes in other embodiments, such as rectangular with rounded corners, trapezoidal, elliptical, oval, or the like. 
     The cladding member  102  may be fabricated using standard manufacturing processes and/or techniques, such as by extrusion, drawing, fusing, molding, or the like. In one example, the cladding member  102  is extruded to form the cladding member  102  and define the core region  114  within the interior of the cladding member  102 . The core region  114  may have various sizes relative to the cladding member  102 . In an embodiment, the diameter of the circular core region  114  is approximately half of the height of the cladding member  102  (such as 0.4 mm), and the core region  114  is located along a center region of the cladding member  102 . 
       FIG. 3  is a cross-sectional view of the dielectric waveguide  100  according to a second embodiment. In the embodiment shown in  FIG. 3 , the dielectric waveguide  100  includes a core member  118  within the core region  114  of the cladding member  102 . The core member  118  extends the length of the dielectric waveguide  100  between the two ends  104  (shown in  FIG. 1 ). The core member  118  fills the core region  114  such that no clearances or gaps exist between an outer surface of the core member  118  and an inner surface of the cladding member  102 . The cladding member  102  engages and surrounds the core member  118  along the length of the core member  118 . 
     The core member  118  is formed of the core dielectric material mentioned in  FIG. 1 . The core dielectric material of the core member  118  in an embodiment is a solid dielectric material, and is not air as is shown in  FIG. 2 . For example, the cladding member  102  and the core member  118  of the dielectric waveguide  100  may both be formed of dielectric polymers, such as plastics or other synthetic polymers. The core member  118  may include one or more of polypropylene, polyethylene, polytetrafluoroethylene (PTFE), polystyrene, or the like. The core material of the core member  118  differs from the cladding material that forms the cladding member  102 . 
     In one embodiment, the dielectric constant of the core material is less than the dielectric constant of the cladding material. The core material may have a dielectric constant less than 3, while the cladding material has a dielectric constant between 3 and 12, or more specifically between 3 and 7. In an embodiment, the dielectric constant value of the core material differs from the dielectric constant value of the cladding material by less than 5. For example, the difference in the respective dielectric constants may be between 1.5 and 3. In an example embodiment, the core material of the core member  118  may be PTFE, having a dielectric constant of 2.1, and the cladding material of the cladding member  102  may be nylon, having a dielectric constant of approximately 4 (with the difference between the dielectric constants being 1.9). In an alternative embodiment, the dielectric constant of the core material may be greater than the dielectric constant of the cladding material. 
     Optionally, the dielectric waveguide  100  shown in  FIG. 3  may be fabricated using standard manufacturing processes and/or techniques, such as by extrusion, drawing, fusing, molding, or the like. In one example, the core dielectric material and the cladding dielectric material are co-extruded such that the core member  118  and the cladding member  102  are formed simultaneously. Alternatively, the core member  118  may be pre-formed and the cladding dielectric material may be extruded, molded, drawn, or the like, over the core member  118  to form the cladding member  102  around the core member  118 . 
     In the illustrated embodiment, the core member  118  has a circular cross sectional shape. It may be beneficial for the core member  118  to have a circular shape because it may be easier to extrude or otherwise form the core member  118  in a circular shape than in an oblong shape. Since the cladding member  102  has an oblong shape, the cladding member  102  functions to orient the electric field in the dielectric waveguide  100  instead of the core member  118 . Although core member  118  is circular in the illustrated embodiment, in an alternative embodiment the core member  118  may be oblong or have a different cross sectional shape. 
       FIG. 4  is a top perspective view of the dielectric waveguide  100  according to an alternative embodiment. The embodiment of the dielectric waveguide  100  shown in  FIG. 4  differs from the embodiment shown in  FIG. 1  because the waveguide  100  in  FIG. 4  includes an outer jacket  120  that surrounds the cladding member  102  along the length of the waveguide  100 . The outer jacket  120  may be used to better isolate the electromagnetic signals within the waveguide  100  from external influences that may interfere and degrade the signal transmission. For example, the outer jacket  120  may be formed of a dielectric material, referred to as a jacket material, which has a dielectric constant value that is less than the dielectric constant value of the cladding material. Since the cladding material has a greater dielectric constant than the jacket material, the electric field is concentrated in the cladding member  102  rather than in the outer jacket  120 . Therefore, a majority of the electric field is spaced apart from the boundary between the outer jacket  120  and the external environment, where external influences such as a human touch may disturb the field along the boundary. The jacket material may have a dielectric constant that is greater than, less than, or equal to the core material within the core region  114  of the cladding member  102 . For example, the jacket material optionally may be the same material as the core material. 
     In the illustrated embodiment, the outer jacket  120  has an oblong cross sectional shape. For example, the outer jacket  120  is rectangular with two opposing longer sides  122  and two opposing shorter sides  124 . The longer sides  122  align with the longer top and bottom sides  106 ,  108  of the cladding member  102  such that the longer sides  122  are parallel to the top and bottom sides  106 ,  108 . In addition, the shorter sides  124  align with the shorter left and right sides  110 ,  112  of the cladding member  102  such that the shorter sides  124  are parallel to the left and right sides  110 ,  112 . Although the outer jacket  120  obstructs the view of the cladding member  102  within the outer jacket  120 , when connecting the dielectric waveguide  100  to an identical or substantially similar connecting waveguide, an operator or a machine may align the two waveguides by aligning the outer jacket  120  of the waveguide  100  with the outer jacket of the connecting waveguide. For example, the jackets may be aligned by arranging the longer sides  122  of the jacket  120  with the corresponding longer sides of the outer jacket of the connecting waveguide to provide a continuous plane extending across the connection interface. Such alignment of the jackets also aligns the cladding member  102  within the waveguide  100  with the cladding of the connecting waveguide. As a result, the polarized electromagnetic waves within the dielectric waveguide  100  are readily received across the interface and into the connecting waveguide without being reflected back into the dielectric waveguide  100 . 
     In an alternative embodiment, the outer jacket  120  may have a circular or square cross sectional shape instead of having an oblong shape. In order to align the dielectric waveguide  100  with a connecting waveguide, a segment of the jacket  120  at one or both of the ends  104  of the waveguide  100  may be stripped or otherwise removed to expose the oblong cladding member  102 . The exposed cladding member  102  may be used to align the waveguide  100  with the connecting waveguide. Optionally, a dielectric tape or the like may be applied around the exposed cladding member  102  after the connection is made in order to reduce interference caused by external influences. 
       FIG. 5  is a cross-sectional view of the dielectric waveguide  100  according to another alternative embodiment. In  FIG. 5 , the core region  114  defined by the cladding member  102  has an oblong cross sectional shape. In the illustrated embodiment, the core region  114  is filled by a solid core member  118 , but the core region  114  may be filled with air in an alternative embodiment. The core member  118  may be formed of a dielectric material that has a dielectric constant value that is less than a dielectric constant value of the cladding material of the cladding member  102 . As such, the electric field within the waveguide  100  may be distributed primarily within the cladding member  102 , with less of the field being within the core member  118 . For example, the dielectric constant of the core material of the core member  118  may be less than 3, and the dielectric constant of the cladding material of the cladding member  102  may be between 3 and 7. Optionally, the embodiment of the waveguide  100  shown in  FIG. 5  may be surrounded by an outer jacket, such as the outer jacket  120  shown in  FIG. 4 . Although the core member  118  has a rectangular cross sectional shape with right angle corners in the illustrated embodiment, the core member  118  may have other oblong shapes in other embodiments, such as elliptical, oval, trapezoidal, rectangular with rounded corners, or the like. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Dimensions, types of materials, orientations of the various components, and the number and positions of the various components described herein are intended to define parameters of certain embodiments, and are by no means limiting and are merely exemplary embodiments. Many other embodiments and modifications within the spirit and scope of the claims will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C.§112(f), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.