Abstract:
An antenna (and concomitant method of making and communications method) comprising a conical radiating element and a circular radiating element surrounding a base of the conical radiating element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of the filing of U.S. Provisional Patent Application Ser. No. 61/226,894, entitled “Reduced-Height Sleeve Discone Antenna with Extended Low-Frequency Operation”, filed on Jul. 20, 2009, and the specification and claims thereof are incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
       [0003]    Not Applicable. 
       COPYRIGHTED MATERIAL 
       [0004]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0005]    1. Field of the Invention (Technical Field) 
         [0006]    The present invention relates to communications antennas and corresponding methods of use and manufacture. 
         [0007]    2. Description of Related Art 
         [0008]    Certain communications applications, particularly in aeronautics applications, require vertically-polarized, omnidirectional, multiband antennas to support an upgraded data link system. However, aerodynamic constraints hamper the capabilities of such antennas. 
         [0009]    The present invention provides methods and apparatuses for accomplishing same. One antenna preferably covers portions of the L, S, and C bands, approximately 1.7 to 5.9 GHz. For good omnidirectional coverage at small elevation and depression angles, the antenna is preferably located on the bottom of the air scoop that protrudes from the underside of the pod. To avoid interference with the pod&#39;s loading apparatus and for minimal aerodynamic impact, the antenna should not protrude more than about one inch. 
       BRIEF SUMMARY OF THE INVENTION 
       [0010]    The present invention is of an antenna (and concomitant method of making and communications method) comprising: a conical radiating element; and a circular radiating element surrounding a base of the conical radiating element. In the preferred embodiment, the antenna additionally comprises a shroud attached to a rim of the conical radiating element. The antenna provides about a 4:1 frequency bandwidth or better, and operates at frequencies between about 1.7 GHz and 5.9 GHz, and/or in the UHF band. The antenna protrudes no more than about one inch from a mounting surface. 
         [0011]    Further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0012]    The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating one or more preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings: 
           [0013]      FIG. 1  is a sectional view of one embodiment of the invention; 
           [0014]      FIG. 2  is a perspective view of the invention with an optional resistive curtain; 
           [0015]      FIG. 3  is a graph of typical voltage standing wave ratio (VSWR) achievable with the invention; 
           [0016]      FIG. 4  is a graph of typical input impedance achievable with the invention; 
           [0017]      FIG. 5  is a sectional view of another embodiment of the invention; 
           [0018]      FIG. 6  is a side view of that embodiment; 
           [0019]      FIG. 7  is a front sectional view of that embodiment; 
           [0020]      FIG. 8  is a front sectional view showing possible dimensions for that embodiment; 
           [0021]      FIG. 9  is a graph of typical VSWR for that embodiment; and 
           [0022]      FIG. 10  is a graph of typical input impedance achievable for that embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The sleeve discone antenna of the invention combines two conventional antenna types to improve performance of a reduced-height design: the (upside-down) discone antenna (conical monopole) and the sleeve monopole antenna. The invention provides an omnidirectional radiation pattern over a wide frequency bandwidth. Specifically, it preferably operates at full efficiency for discone heights as small as about one-eighth wavelength with low VSWR over about a minimum 4:1 frequency bandwidth. Furthermore, low-VSWR operation at much lower frequencies, where the antenna dimensions are a small fraction of a wavelength, is preferably made possible by a resistive shroud that imparts frequency-selective loss. This greatly extends the usable bandwidth, yet reduces antenna efficiency only at these lower frequencies. 
         [0024]    The present invention provides wideband performance in a reduced-height configuration, optionally provides a frequency-selective loss technique that extends low-frequency operation, employs a mechanical design that is easily ruggedized, employs a low-cost, readily manufacturable design, and may be housed within a low-profile, aerodynamic radome. 
         [0025]    One antenna preferably covers portions of the L, S, and C bands, most preferably approximately 1.7 to 5.9 GHz. For good omnidirectional coverage at small elevation and depression angles, the antenna is preferably located on the bottom of an air scoop that protrudes from the underside of a pod. To avoid interference with the pod&#39;s loading apparatus and for minimal aerodynamic impact, the antenna should not protrude more than about one inch. 
         [0026]      FIGS. 1-2  show one embodiment of the antenna  10  of the invention, comprising conical radiating element  12 , coaxial input  14 , sleeve  16  (comprising impedance matching section and dielectric spacer), and optional resistive curtain  18  for extended low-frequency performance. In  FIG. 2 , the invention is shown disposed on a portion of an air scoop  20 . Preferred materials for the radiating element include any conventional conductive material, such as brass or aluminum, and materials conventional in fabricating printed circuit boards. Preferred configurations for the resistive curtain include continuous resistive film or resistive strips (e.g., card or printed strips). The curtain operates as a frequency selective method to add loss only at lower frequencies and to allow higher frequencies to pass through. 
         [0027]      FIG. 3  shows typical voltage standing wave ratios (VSWR) achievable with the embodiment of  FIGS. 1-2  in the relevant frequencies.  FIG. 4  shows via Smith chart typical input impedance achievable with the embodiment of  FIGS. 1-2 . 
         [0028]      FIGS. 5-8  show another embodiment of the antenna  30  of the invention, comprising conical radiating element  12 , probe  34 , sleeve  16 , and wires  36 , 38 . In  FIG. 5 , the invention is shown disposed within a radome  32  and supported by support cradle  40 . 
         [0029]      FIG. 9  shows typical VSWR achievable with the embodiment of  FIGS. 5-8  in the relevant frequencies.  FIG. 10  shows a typical Smith chart for the embodiment of  FIGS. 5-8 . 
         [0030]    The sleeve discone antenna provides at least the following benefits: (1) it provides omnidirectional radiation patterns with high operating efficiency (minimal loss) over a minimum 4:1 frequency bandwidth, thus easily satisfying requirements for the L, S, and C bands; and (2) it provides wideband performance in a reduced-height configuration. Furthermore, the optional resistive curtain implements a frequency-selective loss technique that extends low-frequency operation and provides at least the following additional benefits: (1) it extends operation to lower frequencies, but with reduced antenna gain only at these lower frequencies; (2) it absorbs low-frequency power to provide good VSWR over a very wide frequency bandwidth; (3) it allows substantial high-frequency radiation to pass through and minimally affects the VSWR at these higher frequencies; and (4) it provides very wideband performance in a reduced-height configuration. 
         [0031]    Note that in the specification and claims, “about” or “approximately” means within twenty percent (20%) of the numerical amount cited. All computer software disclosed herein may be embodied on any computer-readable medium (including combinations of mediums), including without limitation CD-ROMs, DVD-ROMs, hard drives (local or network storage device), USB keys, other removable drives, ROM, and firmware. 
         [0032]    Although the invention has been described in detail with particular reference to these preferred embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference.