Patent Publication Number: US-9837721-B2

Title: Low profile dipole antenna assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/752,026, which was filed on Jan. 14, 2013, by Son Huy Huynh for a LOW PROFILE DIPOLE ANTENNA ASSEMBLY and is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates generally to dipole antennas and, in particular, to dipole antenna assemblies. 
     Background Information 
     A dipole antenna is a well known type of antenna that consists of two radiating elements that are center fed. The two radiating elements operate as positive and negative sides, or halves, of the dipole antenna. Due to the configuration of the antenna (that is, where the ends of the antenna correspond to anti-nodes and the center to nodes), the antenna resonates well. 
     Dipole antennas are considered balance devices because they are symmetrical and work best when they are fed with a balanced current. In other words, the current is of equal size on both halves (e.g., and phase shifted 180 degrees). When the antenna is fed with an unbalanced feed, such as a coaxial cable, the antenna assembly typically includes a type of circuit or transformer called a balun (from BALanced and UNbalanced). 
     Generally, a dipole antenna assembly has a “T” shaped configuration, in which the two radiating elements extend outwardly in different directions from one another and are arranged perpendicular to the balun. To increase the bandwidth and/or improve the performance of the dipole antenna, the respective antenna radiating elements may also have various shapes, which increases the width of dipole antenna assembly. The configuration of the antenna assembly and the various shapes of the antenna elements result in dipole antenna assemblies that overall are large and ungainly. While the relatively large overall size and configuration of the assemblies may be suitable for use with many types of devices, the size and configuration are not well suited for use with handheld devices and, in particular, handheld communication devices, which are being designed smaller, thinner and sleeker. Further, the configurations with or without shaped antenna elements are not aesthetically pleasing for such handheld communication devices. 
     SUMMARY OF THE INVENTION 
     A compact, low profile dipole antenna assembly includes first and second linear radiating elements that form the positive and negative sides of the dipole antenna, and a balun that extends in parallel with the second radiating element, i.e., the negative side of the dipole antenna. The second radiating element is connected to ground at one end and is an open circuit at an opposite end. A main feed line, which is part of the balun, also connects to a common ground with the second radiating element. The balun and the connection to ground act as an impedance transformer, and the second radiating element acts as the negative side of the dipole antenna as well as a ground plane for the balun. The balun and the second radiating element share a volume, with the second radiating element electrically shielding the balun and the main feed probe connecting to ground within the shared volume. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention description below refers to the accompanying drawings, of which: 
         FIGS. 1A and 1B  depict a dipole antenna assembly constructed in accordance with the invention; 
         FIGS. 2A-C  depict various components of the dipole antenna assembly of  FIGS. 1A and 1B  in more detail; 
         FIG. 3  depicts the dipole antenna assembly of  FIGS. 1A and 1B  with an optional tuning circuit; 
         FIGS. 4A and 4B  depict an alternative dipole antenna assembly constructed in accordance with the invention; 
         FIG. 5  depicts a section of the dipole antenna assembly of  FIGS. 4A and 4B  in more detail; and 
         FIGS. 6A and 6B  depict an alternative dipole antenna assembly constructed in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT 
     Referring to  FIGS. 1A and 1B  and  FIGS. 2A-C , a compact, low profile dipole antenna assembly  100  includes first and second radiating elements  102 ,  103  that form the positive and negative sides, or halves, of a dipole antenna  104 . The radiating elements are printed on opposite sides of a dielectric substrate  101 .  FIG. 1  depicts the second radiating element  103 , which is on the back side of the dielectric substrate  101 , as a dotted line. 
     A balun  106  is printed on the same side of the dielectric substrate  101  as the first radiating element  102 . The balun connects between the radiating element  102  and an antenna feed circuit  150 , that connects, in turn, through an edge launch connector (not shown) to an external connector  1004  ( FIG. 2C ). The balun  106  includes a main feed probe  110  and a balun feed circuit  112  that operate to provide signal and return paths between the dipole antenna  104  and the antenna feed circuit  150 . The balun is arranged in parallel with the second radiating element  103 . 
     The second radiating element  103  connects to the main ground of the antenna feed circuitry through one or more signal ground vias  114  that are positioned at a bottom end  132  of the second radiating element  103 . A second, opposite end  130  of the second radiating element is an open circuit, and thus, the end  132  connected to ground is an RF short circuit. 
     The first and second radiating elements  102 ,  103  and the balun  106 , that is, the main feed probe  110  and the balun feed circuit  112  are all respectively approximately 0.25λ/√{square root over (∈)} in length, where λ is the wavelength of interest. The radiating elements may be approximately 0.08λ/√{square root over (∈)} in width, and the ends of the respective radiating elements may be tapered, as illustrated in  FIG. 2A , to provided increased bandwidth. 
     The main feed probe  110  and the balun feed circuit  112  operate as an impedance transformer at the frequency of interest. Accordingly, the open end  130  of the second radiating element  103 , which is in a region proximate to the connection of the main feed probe  110  to the first radiating element, has low impedance and the end  132  connected to ground has high impedance. The first and second radiating elements thus operate together as the positive and negative sides, respectively, of the dipole antenna  104 . 
     The second radiating element  103  also provides a path to ground for the main feed probe  110 , and acts as a ground plane for the balun  106 . The balun and the second radiating element thus share a common volume and the second radiating element electrically shields the balun. Notably, the main feed probe connects to ground on the inside of the shared volume, and thus, the various components can operate in close proximity. 
     The configuration of the linear radiating elements with the balun in parallel with the second radiating element and also sharing a common volume with the second radiating element allows the balun and the second radiating element to operate together in close proximity as a ground plane, radiator, main feed network and balun. The result is a compact and low profile dipole antenna assembly that is particularly suited for use with a handheld communication device. 
     To ensure an equal potential is maintained with the main ground of the antenna feed circuitry  150 , one or more feed circuit mode suppressors  500   a  and  500   b  may be included on the same side of the dielectric substrate  101  as the balun  106 . A plurality of plated ground vias  502  provide connections between the mode suppressors and the main ground, that is, the ground of the antenna feed circuitry. The suppressors  500   a  and  500   b  connect to one another through the ground of the edge connector  1006  ( FIG. 1B ) in the antenna feed circuitry  150 , and operate to minimize surface waves from higher order modes. 
       FIG. 1B  depicts a side view of the compact, low profile dipole antenna assembly  100 . 
     Referring now also to  FIG. 3 , a tuning circuit  200  may be included to improve input impedance matching and radiator bandwidth performance. The tuning circuit  200  includes a capacitor  204  which may be tunable and may also further include an inductor (not shown) in series or in parallel with the capacitor  204 . The drawing depicts the tuning circuit  200  as an in-line capacitor. 
     As shown in  FIG. 2C , a radome  1000  fits over the antenna assembly  100  and connects to a base plate  1002  that supports the dielectric substrate  101  and the external connector  1004 , to form an enclosure for the dipole antenna assembly  100 . 
       FIGS. 4A-B  illustrate a compact dipole antenna assembly  300  constructed using tubes  302  and  303  as the first and second radiating elements. A balun  306  extends within the tube  303 , which operates as the negative side of the dipole antenna. The length of the tubes is approximately 0.25λ/√{square root over (∈)}, and the tubes are approximately 0.08λ/√{square root over (∈)} in width. 
     As shown in  FIGS. 4A, 4B and 5 , a main feed probe  310  is a center conductor of a ground connector  305 . The main feed probe is part of the antenna feed circuitry  350 , which also includes an external connector ground  355  that connects to an external signal line (not shown). The main feed probe  310  also connects to the first radiating element  302  and to a balun feed circuit  312  through connections to copper conductive lines  409  on a first conductive section  411  of a circuit board support  511 . The balun feed circuit  312  connects on an opposite end to the ground connector  305  by a connection  307 . The main feed probe  310 , the balun feed circuit  312  and interconnections  307  and  409  form the balun  306 . Conductive lines  309  on a second conductive section  311  of the circuit board support  511  provide a ground connection between the ground connector  305  and an end  330  of the second radiating element  303 . 
     An opposite end  331  of the second radiating element is an open circuit, and the end  330  connected to ground acts as an RF short circuit. The main feed probe  310 , the balun feed circuit  312  and the ground connector  305  operate as an impedance transformer, and the end  330  of the second radiating element that is in proximity to the main feed probe has low impedance. The second radiating element  303  acts as a negative radiator, a ground enclosure for the main feed probe  310  and a ground plane for the balun  306 . 
     The balun  306  and the second radiating element  303  are configured in parallel, with the balun inside the second radiating element. Accordingly, the balun and the second radiating element, which acts also as the ground plane for the balun, share a common volume. Notably, the ground connection for the main feed probe is inside the shared volume, and the balun and the ground connection are electrically shielded by the second radiating element  303 . The configuration results in the various components being capable of operating in close proximity and produces a compact and a low profile dipole antenna assembly  300  that is well suited for handheld communication devices and so forth. As shown in  FIG. 4B , a radome  1000  with end caps  1001  may enclose the antenna assembly  300 . 
       FIG. 5  depicts an optional tuning circuit  400  that connects between the first radiating element  302  and the main feed probe  310 . The tuning circuit, which operates in a known manner, may be included to improve input impedance matching and radiator bandwidth performance. The tuning circuit  400  depicted as a capacitor  414  may also further include an inductor (not shown) in series or in parallel with the capacitor  414 . The capacitor  414  may also be tunable. With the tuning circuit  400  in place, the main feed probe  310  connects to the second radiating element  302  through the tuning circuit, here the capacitor  414 , and a main feed line extension  310   a  that connects to the copper conductive lines  409 . 
     For ease of understanding, the drawings depict the circuit board support  511  exaggerated in size relative to the first and second radiating elements, and the respective connections to the conducting lines  309  and  409  are not explicitly shown. 
     The tubular arrangement of  FIGS. 4A, 4B and 5  may be used with lower frequencies to provide higher power. For ease of manufacture, the printed circuit arrangement of  FIGS. 1A-3  may be used with higher frequencies. 
     Referring now to  FIGS. 6A and 6B , a large volume compact dipole antenna assembly  600  includes a balun  606 , with a main feed probe  610  and a balun feed circuit  612 , formed as a printed circuit on a first side of a dielectric substrate  601 . An associated ground plane  623  is printed on an opposite side of the dielectric. The balun  606  connects also to an antenna feed circuit  650 . The radiating elements of the antenna assembly  600  include tubes  602  and  603  that are selectively connected to respective antenna components that are printed on the substrate  601 . The use of both printed circuit components and tubular components provides a compact low profile dipole antenna with a large volume, which can be efficiently and cost effectively manufactured. 
     The balun  606  connects electrically to the positive radiating element of the antenna assembly  600 . For ease of manufacture, the balun  606  may connect to a printed element  622  that is, in turn, connected to the tube  602 . The tube  602 , which is similar to the tube  302  of  FIG. 4 , electrically connects to the element  622  along the length of the element  622 , by, for example, soldering, to form the positive radiating element of the antenna assembly. The tube  603 , which is similar to the tube  303  of  FIG. 4 , electrically connects, for example by soldering, to a top end  630  of the ground plane  623 , to form the negative radiating element of the antenna assembly. The ground plane  623  connects also to the ground of the antenna feed circuit  650  through vias  614  at a bottom end  632  of the ground plane. Further, a plurality of feed circuit mode suppressors  500   a  and  500   b  and associated vias (not shown) may be included in the antenna assembly  600  in the manner discussed above with reference to  FIG. 1 . In addition, a tuning circuit (not shown) may be included in the antenna assembly  600  in the manner discussed above with reference to  FIG. 3 . 
     The dipole antenna assembly  600  provides a large volume that is useful with lower frequencies to provide more band width, and includes printed circuit components that are very efficiently manufactured.