Patent Publication Number: US-11024949-B2

Title: Dipole arm assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. § 119 to Chinese Patent Application No. 201810811153.2 (Serial No. 2018072400713300), filed Jul. 23, 2018, the entire content of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present disclosure generally relates to cellular base station antennas and, more particularly, to dipole arm assemblies for low frequency band radiators of cellular base station antennas. 
     BACKGROUND 
     A cellular communication system connects a user&#39;s cellular device to a wireless network through a base station. The base station includes a baseband unit, a radio, and a base station antenna that performs bi-directional radio frequency communication with the user. The base station antenna may be mounted on a tower or other raised structure and generates an outwardly directed radiation beam to serve a corresponding geographic region. 
     Multi frequency band base station antennas are base station antennas that are designed to operate in two or more of the cellular frequency bands. For example, a dual frequency band base station antenna includes at least one or more low frequency band radiators and one or more high frequency band radiators. One known low frequency band radiator has a central feed portion and a dipole (or a pair of dipoles) arranged on the central feed portion. Each dipole includes a pair of dipole arms with a certain length. As shown in  FIGS. 1A and 1B , the dipole arm  100 ′ includes a central shaft  110 ′ and a plurality of hollow tubes  120 ′ that are spaced apart along the central shaft  110 ′. The central shaft  110 ′ includes a stem portion  111 ′ and a plurality of circular flanges  112 ′ that project radially outward from the stem portion  111 ′. The flanges  112 ′ and the stem portion  111 ′ are integrally formed. The hollow tubes  120 ′ are fixed to the central shaft  110 ′ by engaging the bottom of each hollow tube  120 ′ with a respective one of the flanges  112 ′. 
     The stem portion  111 ′ and the flanges  112 ′ of the central shaft  110 ′ are integrally formed by means of cutting using a numerically controlled lathe, which involves high production costs. The central shaft  110 ′ is easily deformed during high-speed cutting, resulting in difficult machining and a high rejection ratio. In addition, a large amount of raw materials need to be cut away during lathe machining, so that there is a low utilization ratio of the material. 
     The hollow tube  120 ′ is formed by extruding a raw material that is cut into segments, and the bottom portion of each tube then undergoes high precision machining. Consequently, manufacturing the hollow tubes  120 ′ is also time-consuming and labor-intensive, and has high production costs. 
     The bottom of each hollow tube  120 ′ is fitted to a respective flange  112 ′ of the central shaft  110 ′ by rolling. The rolling process is a low efficiency process and may sometimes produce a loose engagement between the inner surface of the hollow tube  120 ′ and the outer surface of a corresponding flange  112 ′, which may affect the subsequent performance parameters of the antenna. 
     SUMMARY 
     According to a first aspect of the present disclosure, dipole arm assemblies for a low frequency band radiator of a cellular base station antenna are provided that include a central shaft and at least one barrel having a first end, a second end, and a peripheral wall located between the first end and the second end. The first end includes an end wall provided with an engagement portion, and the barrel is engaged with the central shaft through the engagement portion and disposed about the central shaft. 
     In one embodiment, the second end is open outwardly. 
     In one embodiment, the at least one barrel is circular or elliptical in cross-section. 
     In one embodiment, the at least one barrel comprises a metallic material. 
     In one embodiment, the at least one barrel includes a plurality of barrels axially spaced apart along the central shaft. 
     The plurality of barrels may have the same structure or different structures. 
     The plurality of barrels may have the same diameter or different diameters, and may have the same axial length or different axial lengths. 
     In one embodiment, the plurality of barrels have sequentially incremental axial lengths along the central shaft. 
     In one embodiment, the second ends of the plurality of barrels are open outwardly towards the same direction. 
     In one embodiment, the at least one barrel is mechanically engaged and electrically connected with the central shaft by the engagement portion. 
     In one embodiment, the engagement portion includes a hole provided at the center of the end wall through which the central shaft passes through. 
     In one embodiment, the engagement portion includes a protrusion extending about the hole inwardly from the end wall along an axial direction. 
     The distance by which the protrusion extends inwardly along an axial direction may be, for example, less than an axial length of the peripheral wall, less than one-half of an axial length of the peripheral wall or less than one-quarter of an axial length of the peripheral wall. 
     In one embodiment, the hole and the protrusion may have cross-sections that match the size and shape of the central shaft. 
     In one embodiment, the central shaft may be fitted in the protrusion by an interference fit. 
     In one embodiment, transverse cross-sections of the central shaft may have the same shape. 
     In one embodiment, the central shaft may be circular, polygonal, or elliptical in cross-section. 
     In one embodiment, the central shaft may be made of aluminum, aluminum alloy, or other metallic materials. 
     In one embodiment, the space between the barrel and the central shaft may be completely filled or partially filled with a dielectric material. 
     In one embodiment, the dipole arm may have a length of approximately one-quarter wavelength (λ/4) or one-half wavelength (λ/2). 
     In one embodiment, the dipole arm assembly may be in combination with a second dipole arm and a central feed portion to form the low frequency band radiator, the low frequency band radiator being part of a base station antenna. 
     In one embodiment, adjacent barrels may be positioned to form a radio frequency choke that interrupt currents from a high band radiator that is included in the base station antenna. 
     According to another aspect of the present disclosure, a method for manufacturing a dipole arm is provided in which metallic raw material is extruded to form a column which is cut into segments to form a central shaft. The metallic raw material is deeply punched to form at least one barrel having a first end, a second end, and a peripheral wall between the first end and the second end, where the first end includes an end wall provided with an engagement portion. The central shaft and the at least one barrel are assembled together using the engagement portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  are a perspective view and a cross-sectional view of a conventional existing dipole arm; 
         FIG. 2  is a schematic view of a portion of a dual-frequency band cellular base station antenna; 
         FIGS. 3A and 3B  are a perspective view and a cross-sectional view of a dipole arm according to an embodiment of the present disclosure; 
         FIG. 4  is a perspective view of a central shaft of a dipole arm according to an embodiment of the present disclosure; and 
         FIGS. 5A and 5B  are a perspective view and a cross-sectional view of a barrel of a dipole arm according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will be described below with reference to the drawings, in which several embodiments of the present disclosure are shown. It should be understood, however, that the present disclosure may be presented in multiple different ways, and not limited to the embodiments described below. In fact, the embodiments described hereinafter are intended to make a more complete disclosure of the present disclosure and to adequately explain the protection scope of the present disclosure to a person skilled in the art. It should also be understood that, the embodiments disclosed herein can be combined in various ways to provide more additional embodiments. 
     It should be understood that, in all the drawings, the same reference signs refer to the same elements. In the drawings, for the sake of clarity, the sizes of certain features may be deformed. 
     It should be understood that, the wording in the specification is only used for describing particular embodiments and is not intended to define the present disclosure. All the terms used in the specification (including the technical terms and scientific terms), have the meanings as normally understood by a person skilled in the art, unless otherwise defined. For the sake of conciseness and/or clarity, the well-known functions or constructions may not be described in detail. 
     The singular forms “a/an”, “said” and “the” as used in the specification, unless clearly indicated, all contain the plural forms. The wordings “comprising”, “containing” and “including” used in the specification indicate the presence of the claimed features, but do not exclude the presence of one or more other features. The wording “and/or” as used in the specification includes any and all combinations of one or more of the relevant items listed. 
     In the specification, when one element is referred to as being “on” another element, “attached to” another element, “connected to” another element, “coupled to” another element, or “in contact with” another element, the element may be directly located on another element, attached to another element, connected to another element, coupled to another element, or in contact with another element, or one or more intermediate elements may be present. By contrast, where one element is referred to as being “directly” on another element, “directly attached to” another element, “directly connected to” another element, “directly coupled to” another element, or “in direct contact with” another element, there will not be any intermediate elements present. In the specification, where one feature is arranged to be “adjacent” to another feature, it may mean that one feature has a portion that overlaps with an adjacent feature or a portion that is located above or below an adjacent feature. 
     In the specification, the spatial relation wordings such as “up”, “down”, “left”, “right”, “forth”, “back”, “high”, “low” and the like may describe a relation of one feature with another feature in the drawings. It should be understood that, the spatial relation wordings also contain different orientations of the apparatus in use or operation, in addition to containing the orientations shown in the drawings. For example, when the apparatus in the drawings is overturned, the features previously described as “below” other features may be described to be “above” other features at this time. The apparatus may also be otherwise oriented (rotated 90 degrees or at other orientations). At this time, the relative spatial relations will be explained correspondingly. 
     A low frequency band radiator of a dual frequency band cellular base station will be disclosed hereinafter. The following description will disclose a number of specific details including the shape and material of the dipole arm, as well as the dielectric material and the like. However, it should be clear to those skilled in the art that various modified solutions and/or alternative solutions may be set forth for the aforementioned details without departing from the scope and spirit of the present disclosure, and certain details may also be omitted. 
     In some embodiments, the low frequency band may be a frequency band such as 698 to 960 MHz (or a portion thereof), while the high frequency band may be a frequency band such as 1695 MHz to 2690 MHz or a portion thereof. However, the present disclosure is not limited to these frequency bands. For example, the low frequency band may further include low frequencies (e.g., the 600 MHz band) and/or the high frequency band may further include the 1400 MHz band. A “low frequency band radiator” refers to a radiator that is configured to operate in the low frequency band, and a “high frequency band radiator” refers to a radiator that is configured to operate in the high frequency band. Throughout the present disclosure, “dual frequency band” includes at least a low frequency band and a high frequency band. It will also be appreciated that herein the term “dual frequency band antenna” refers not only to antennas that operate in the low frequency band and the high frequency band, but also to antennas that operate in one or more additional frequency bands such as, for example, the 3.5 GHz frequency band or the 5 GHz frequency band. 
     The embodiments of the present disclosure relate generally to a dual frequency band cellular base station antenna. The use of dual frequency band antennas may enable an operator of a cellular communication system to use a single type of antenna to cover multiple frequency bands using a single antenna, which may allow the operator to reduce the number of antennas in its network, thereby reducing the rental cost of a tower, and at the same time accelerating the marketing ability. The dual frequency band cellular base station antenna supports multiple frequency bands and technical standards. 
     More specifically, embodiments of the present disclosure relate to a dual frequency band antenna for a cellular base station. In some embodiments, the dual frequency band antenna may be configured to operate in a low frequency band of 698 MHz to 960 MHz or a part thereof as well as in a high frequency band of 1695 MHz to 2690 MHz or a part thereof. 
       FIG. 2  shows a schematic view of a portion of a dual frequency band cellular base station antenna. The dual frequency band cellular base station antenna  1  includes a plurality of low frequency band radiators  10  (only one of which is visible in  FIG. 2 ) and a plurality of high frequency band radiators  20 . In the illustrated example, the high frequency band radiator  20  includes four high frequency band radiators arranged in a 2×2 matrix, and one low frequency band radiator  10  is interposed between the four high frequency band radiators. 
     As shown in  FIG. 2 , the low frequency band radiator  10  includes a central feed portion  11  in a cross shape, and a −45 degree slant dipole  12  and a +45 degree slant dipole  13  that are arranged on the central feed portion  11  and perpendicular to each other. The central feed portion  11  includes two cross-interlocked printed circuit boards (“PCBs”). Feed lines for the −45 degree slant dipole  12  and the +45 degree slant dipole  13  are formed on the two cross-interlocked PCBs. The central feed portion  11  supports the −45 degree slant dipole  12  and the +45 degree slant dipole  13  at a certain height above a reflection plate of the antenna  1 , preferably at a height of one-quarter wavelength (λ/4). 
     Four high frequency band radiators  20  are arranged about the four quadrants. By repeating the pattern shown in  FIG. 2 , the entire base station antenna  1  may be constructed. 
     The −45 degree slant dipole  12  includes a pair of dipole arms  12 A and  12 B with a certain length, and the +45 degree slant dipole  13  includes a pair of dipole arms  13 A and  13 B with a certain length. The dipole arms  12 A and  12 B may have a length that is the same as or different from the dipole arms  13 A and  13 B. In some embodiments, the dipole arms  12 A,  12 B,  13 A, and  13 B may have a length of approximately one-quarter wavelength (λ/4) or one-half wavelength (λ/2), although embodiments of the present invention are not limited thereto. 
       FIGS. 3A and 3B  illustrate a dipole arm  100  for a low frequency band radiator  10  of a cellular base station antenna  1 , which may be used to implement any one of the dipole arms  12 A,  12 B,  13 A, and  13 B shown in  FIG. 2 . The dipole arm  100  includes a central shaft  110 , and a plurality of barrels  120  that are axially spaced along the central shaft  110  and arranged about the central shaft  110 . In the illustrated example, the dipole arm  100  includes three barrels  120   a ,  120   b , and  120   c , but it will be understood that the dipole arm  100  may include more than three or less than three barrels  120 . 
     The dipole arm arrangement shown in  FIGS. 3A and 3B  creates a series of coaxial RF chokes along the length of the dipole arm  100 . In particular, the gap between barrel  120   a  and barrel  120   b  acts as a first coaxial choke and the gap between barrel  120   b  and  120   c  acts as a second coaxial choke. These gaps may interrupt currents of RF signals emitted by the high frequency band radiators. Consequently, RF energy emitted by the high frequency band radiators will not tend to flow on the dipole arm  100 , and hence the low band radiators may have little or no impact on the radiation pattern of the high band radiators. In other words, the barrels  120  are used to form a series of RF chokes along the dipole arm  100  that may render the dipole arm  100  substantially invisible to RF energy in the high frequency band. 
     In some embodiments, the space between the barrel  120  and the central shaft  110  may be filled with air. As an alternative solution, the space between the barrel  120  and the central shaft  110  may be completely filled or partially filled with a solid or foamed dielectric material. 
     As shown in  FIG. 4 , the central shaft  110  is in the shape of a straight column, and may be made of aluminum, aluminum alloy, or other metallic materials. The central shaft  110  is circular in cross-section; however, it the central shaft  110  may alternatively be polygonal or elliptical in cross-section. The central shaft  110  may have a constant transverse cross-section. For example, in the depicted embodiment where the central shaft  110  has a circular transverse cross-section, the diameter of the transverse cross-section may be constant along the entire length of the central shaft  110 . In some embodiments, an end of the central shaft  110  that mounts to the central feed portion  111  may have a different cross section than the remainder of the central shaft  110  to facilitate mounting the central shaft  110  on the central feed portion  111 . The central shaft  110  may have a length of between 99 mm and 104 mm, and a diameter of 3.0 mm, in an example embodiment. 
     As shown in  FIGS. 5A and 5B , each barrel  120  includes two ends, and a peripheral wall  125  located between the two ends. One end of each barrel  120  includes an end wall  121  and the other end is open outwardly. The barrels  120  may be made of aluminum, an aluminum alloy, or other metallic materials. Each barrel  120  may have a circular transverse cross-section; however, it may be contemplated that the barrel  120  may alternatively have an elliptical, rectangular or other transverse cross-section in other embodiments. The end wall  121  is provided with an engagement portion  122  that is mechanically engaged and electrically connected with the central shaft  110 . 
     In some embodiments, the engagement portion  122  includes a hole  123  provided at the center of the end wall  121 , and a protrusion  124  extending around the hole  123  inwardly from the end wall  121  along an axial direction. The hole  123  and the protrusion  124  may have a cross-section that matches the size and shape of a corresponding portion of the central shaft  110  that the barrel  120  will be mounted on, so that the central shaft  110  can pass through the protrusion  124  and/or the hole  123 , and the outer surface of the central shaft  110  is closely attached to the inner surface of the protrusion  124  when the barrel  120  is mounted on the central shaft  110 . The distance by which the protrusion  124  extends inwardly along an axial direction is less than an axial length of the peripheral wall  125 , in some embodiments less than one-half the axial length of the peripheral wall  125 , and in further embodiments less than one-quarter the axial length of the peripheral wall  125 . 
     The plurality of barrels  120  may have the same or different structures. In some embodiments, as shown in  FIGS. 5A and 5B , the peripheral wall  125  of the barrel  120   c  is provided with an orifice  126  and a cutout  127  for connection and fixation with a PCB of the central feed portion  111 , and the peripheral walls of the barrels  120   a  and  120   b  are not provided with any orifices and cutouts. 
     The plurality of barrels  120  may have the same or different diameters, and the same or different axial lengths. In some embodiments, the plurality of barrels  120  may have the same diameter (e.g., 16.0 mm), but different axial lengths. For example, the axial length of barrel  120   c  (e.g., 31.5 mm) is greater than that of barrel  120   b  (e.g., 28.5 mm), which is greater than that of barrel  120   a  (e.g., 25.5 mm). 
     In general, the barrel  120  and the central shaft  110  may have an optimized size so that the radiation pattern of the high frequency band radiator  20  is not affected by the low frequency band radiator  10  to a great extent. 
     A method for producing the dipole arm  100  will be introduced below in combination with  FIGS. 3A-3B . First, the metallic raw material is extruded to form a column which is cut into segments to form a central shaft  110 . Then, metallic raw material is deeply punched to form a plurality of barrels  120   a ,  120   b , and  120   c . Then, the central shaft  110  is inserted into the protrusions of the barrels  120   a ,  120   b  and  120   c  in such a manner that the openings of the plurality of barrels  120  face in the same direction, and the central shaft  110  and the barrels  120   a ,  120   b , and  120   c  are assembled together, by an interference fit between the outer surface of the central shaft  110  and the inner surface of the protrusion  124 , so as to form the dipole arm  100 . 
     The dipole arm  100  of the invention is suitable for automatic mass production with a highly stable quality, and can achieve superior passive intermodulation (PIM) distortion performance. 
     Although the exemplary embodiments of the present disclosure have been described, a person skilled in the art should understand that, he or she can make multiple changes and modifications to the exemplary embodiments of the present disclosure without substantively departing from the spirit and scope of the present disclosure. Accordingly, all the changes and modifications are encompassed within the protection scope of the present disclosure as defined by the claims. The present disclosure is defined by the appended claims, and the equivalents of these claims are also contained therein.