Abstract:
A radio frequency (RF) antenna of the present invention generally comprises an electrical conductor and a unitary metallic surface mounting structure. The electrical conductor, which performs the radiator function, is secured to the surface mounting structure so that the electrical conductor may use the surface mounting structure not only as a surface mount but additionally as a ground plane. The surface mounting structure is presented in a cross-configuration having outward extending arms. The arms perform the ground plane function and are bent to a desired angle to produce a desired radiation pattern and/or impedance. A plastic radome with a metallic insert is preferably used to cover the electrical conductor and to secure the electrical conductor to the surface mounting structure.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to radio frequency (RF) antennas and, more particularly, to an RF antenna that employs a unitary, metallic, surface mounting structure that additionally serves as the ground plane for the antenna.  
         BACKGROUND OF THE INVENTION  
         [0002]    In RF communication systems and, specifically, utility meter fixed network systems, the RF antenna that transmits the utility consumption data is most often integral to the utility meter transceiver. The utility meter transceiver is, in turn, most often integral to the utility meter box. Thus, when mounting the utility meter box, or when mounting other system RF devices that transmit data via an integral antenna, it is possible for the integral antenna to be shielded by terrain features or structures, e.g., buildings, subway tunnels, etc., such that propagation from the RF antenna is not acceptable and the utility meter data is not obtainable.  
           [0003]    One solution to this problem is to provide a different technology mix of meters and transceivers suitable to the shielded location. However, the use of such a technology mix usually results in added installation cost and added complexity to the overall RF system.  
         SUMMARY OF THE INVENTION  
         [0004]    A radio frequency (RF) antenna of the present invention generally comprises an electrical conductor and a unitary, metallic, surface mounting structure. The electrical conductor, the antenna&#39;s radiating element, is secured to the metallic surface mounting structure so that the electrical conductor may use the metallic surface mounting structure not only as a surface mount but additionally as a ground plane. The metallic surface mounting structure is presented in a cross-configuration having outward extending arms (radials). The arms perform the ground plane function and are bent to a desired angle to produce a desired radiation pattern and/or impedance. A plastic radome with a metallic insert is preferably used to cover the electrical conductor and to secure the electrical conductor to the surface mounting structure.  
           [0005]    A method of assembling the radio frequency antenna of the present invention generally comprises the steps of forming a unitary, surface mounting structure from a metallic material, the formed surface mounting structure having a number of extending arms that are bent to a desired angle, and securing an electrical conductor to the surface mounting structure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 provides a perspective view of an assembled antenna with unitary ground plane and surface mounting structure of the present invention.  
         [0007]    [0007]FIG. 2 provides a side view of a conductive element of the antenna of the present invention.  
         [0008]    [0008]FIG. 3 provides a side view of a radome of the antenna of the present invention.  
         [0009]    [0009]FIG. 4 provides a cross-sectional view of the radome taken along line  4 - 4  in FIG. 3.  
         [0010]    [0010]FIG. 5 provides a plan view of an unbent unitary ground plane and surface mounting structure of the antenna of the present invention.  
         [0011]    [0011]FIG. 6 provides a bending diagram of the unitary ground plane and surface mounting structure of FIG. 6.  
         [0012]    [0012]FIG. 7 provides an antenna radiation pattern of an embodiment of the antenna of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    The radio frequency (RF) antenna with unitary ground plane and surface mounting structure of the present invention finds utility in a wide variety of antenna applications, and is especially useful in fixed utility metering systems. Specifically, the RF antenna with unitary ground plane and surface mounting structure of the present invention provides a low-cost, minimal component option in addressing the problem of transmission-shielded transceivers by using off-the-shelf components and inexpensive, easily accessible materials. Rather than reverting to a technology mix of meters and transceivers to overcome antenna propagation that is shielded by terrain or structures, the present invention enables a consumer of an RF meter system to utilize a single technology scheme that ultimately results in reduced installation and maintenance costs.  
         [0014]    I. Antenna Elements  
         [0015]    Referring to FIG. 1, the RF antenna  10  with unitary ground plane and surface mounting structure of the present invention is depicted. The antenna  10  generally comprises a conductive element assembly  12 , a radome assembly  14 , and the unitary ground plane/surface mounting structure  16 .  
         [0016]    The conductive element assembly  12 , see FIG. 2, preferably includes an off-the-shelf (OTS) RF bulkhead connector  20  and a piece of wire conductor  22 . In the instance of a quarterwave antenna, the wire conductor  20  is preferably trimmed to ˜{fraction (1/4)} wave length. The length of the wire conductor  22  will vary depending on the desired frequency. As shown, the RF bulkhead connector  20  preferably includes a first threaded end  24  that enables the connector  20  to be connected, via cable  21 , to a remotely positioned transceiver  23  (cable and transceiver shown in FIG. 1). The RF bulkhead connector further includes a stop plate  26  that contacts the underside of the unitary ground plane/surface mounting structure  16  (described below). A second threaded end  28  of the connector  20  provides a threaded surface to secure the radome assembly  14 . A lockwasher  30  is provided to ensure contact between the unitary ground plane/surface mounting structure  16  and the connector  20 . The RF bulkhead connector  20  also includes a mounting tip  32  to which the wire conductor  22  is preferably soldered. In a preferred embodiment, the RF bulkhead connector  20  comprises a Pasternack Enterprises PE4063 TNC Female Bulkhead (mat&#39;ls: body—brass nickel plated; contact—gold plated; and insulator—PIFE).  
         [0017]    The radome assembly  14 , see FIGS. 3 and 4, generally comprises the radome  40  itself and a brass insert  42 . The radome  40  is preferably made of a plastic material that is suited for protecting the wire conductor  22  in both interior and exterior environments. In a preferred embodiment, the radome  40  is made from DELRIN® acetal resin, which is a DuPont product. The radome  40  is preferably molded into a configuration such that the distal end  44  is accepting of the brass insert  42  via a press fit, and such that a central cavity  46  is provided to accommodate the RF bulkhead connector  20  and the wire conductor  22  soldered thereto. The brass insert  42  is preferably provided with a threaded inner surface  48  enabling it to be threaded onto the second threaded end  28  of the RF bulkhead connector  20  so as to secure the radome assembly  14  to the connector  20  and the connector  20 , via lockwasher  30 , to the unitary ground plane/surface mounting structure  16 .  
         [0018]    The unitary ground plane/surface mounting structure  16  is shown in an unfolded state in FIG. 5, wherein the cross-shaped configuration of the structure  16  is exemplified, and in a folded state in FIG. 6. The unitary ground plane/surface mounting structure  16  incorporates the unitary components of a central connector mounting plate  50 , three radial arms  52 , and a mounting arm  54 . The central connector mounting plate  50  includes an aperture  56  therethrough for the positioning and mounting of the RF bulkhead connector  20 . The three radial arms  52 , and as well, the mounting arm  54 , are of a slightly diminished width from that of the central connector mounting plate  50  (e.g., 1.6 inch width—plate  50  and 1.4 inch width arms  52 ,  54 ) to enable easier bending of the arms  52  and  54  relative to the central connector mounting plate  50 . Note that the outer corners  57  of each of the radial arms  52  have been chamfered for safety. The mounting arm  54  preferably includes a plurality of mounting apertures  58  through which appropriate fasteners may be inserted to secure the unitary ground plane/surface mounting structure  16  to a surface, e.g., wood, metal, plastic, etc., surface of a structure. In a preferred embodiment, the unitary ground plane/surface mounting structure  16  is stamped, cut, or otherwise formed from a sheet of stainless steel having a thickness of 0.047 inches then bent per antenna design specifications. It should be noted that the bending, or angular adjustment, of the arms  52  and  54  of the unitary ground plane/surface mounting structure  16  is preferably performed during manufacture in accordance with design specifications that have been developed to optimize operation of the RF antenna  10 . As such, in the preferred embodiment, the RF antenna  10  is not designed to be field tunable/retunable through further angular adjustment of the arms  52  and  54 .  
         [0019]    II. Antenna Assembly and Operation  
         [0020]    As indicated above, during manufacture of the unitary ground plane/surface mounting structure  16  the three radial arms  52  and the mounting arm  54  are bent downward from the plane defined by the mounting plate  50 . Each of the arms  52  and  54  is preferably positioned at the same angle relative to the mounting plate  50 , e.g., see FIG. 6, wherein each of the arms  52  and  54  is at an angle of 135 degrees relative to the mounting plate  50 . Additionally, the mounting arm  54  is bent yet again along line  59 , so as to present the plurality of mounting apertures  58  in an orientation that is substantially perpendicular to the central connector mounting plate  50 , allowing the mounting plate  50  to reside in a substantially horizontal orientation when the unitary ground plane/surface mounting structure is secured to a surface.  
         [0021]    With the unitary ground plane/surface mounting structure appropriately configured, the RF antenna  10  of the present invention may be assembled by soldering the wire conductor  22  to the mounting tip  32  of the RF bulkhead connector  20  and trimming the wire conductor  22  to the appropriate length to achieve the desired frequency. The second threaded end  28  of the RF bulkhead connector  20  is then inserted through the aperture  56  of the central connector mounting plate  50  of the unitary ground plane/surface mounting structure  16  until the stop plate  26  of the RF bulkhead connector  20  is in contact and flush against the underside of the mounting plate  50 . With the conductive element assembly  12  appropriately positioned relative to the unitary ground plane/surface mounting structure  16 , the radome assembly  14  is threaded, via the threaded inner surface  48  of the brass insert  42 , onto the second threaded end  28  of the RF bulkhead connector  20  until the lockwasher  30  is secured between, and in contact with both, the brass insert  42  and the upperside of the central connector mounting plate  50 . With the conductive element assembly  12  secured to the mounting plate  50  via the radome assembly  14  (i.e., continuous metal contact between the conductive element assembly  12 , the radome assembly  14 , and the structure  16 ), the mounting plate  50  and surrounding arms  52  and  54  operate as the ground plane for the wire conductor  22 .  
         [0022]    It should be noted that the impedance and the radiation pattern of the RF antenna  10  can be tuned by changing the bend angle and dimensions of the three radial arms  52  and the mounting arm  54  of the unitary ground plane/surface mounting structure  16 . It should further be noted that not only does the unitary ground plane/surface mounting structure  16  enable tuning of the RF antenna  10 , it also supplies a platform for physically mounting the RF antenna  10  to a surface whereby the RF antenna  10  is positioned at an appropriate and consistent distance from any mounting surface so as to minimize distortion to the radiation pattern of the RF antenna  10 . The ability to position the RF antenna  10  at a consistent distance from a mounting surface also aids in minimizing the affect of different mounting surface materials, e.g., wood, metal, masonry, etc., on the radiation pattern of the RF antenna  10 .  
         [0023]    [0023]FIG. 7 depicts the omni-directional radiation pattern of one embodiment of the RF antenna  10 . In this embodiment, each of the radial arms  52  and the mounting arm  54  are bent at an angle of 135 degrees relative to the central connector mounting plate  50  (or 45 degrees as measured from a vertical reference). Further, each of the radial arms  52  and that portion of the mounting arm  54  that comprises the radial are 1.4 inches in width and 2.6 inches in length, and are stamped from 0.047 inch stainless steel. The RF bulkhead connector  20  is a PE4063 connector, and the radome assembly  14  described above was provided and covered the antenna element, i.e., wire conductor  22 .  
         [0024]    The RF antenna  10  may now be mounted in a desired unshielded location and connected, via cable threadably secured to the first threaded end  24  of the RF bulkhead connector  20 , to a remote transceiver (e.g., meter box, hub, relay, etc.). The ability to remotely mount the inexpensive, yet high performance, RF antenna  10  of the present invention enables access to hard-to-read meters while maintaining the integrity of the overall metering system.  
         [0025]    The present invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof, therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.