Abstract:
A universal antenna housing suited for deployment under the glass dome of a utility meter. The housing is fitted with an integrated antenna for wireless radio communications. Applications include the transmission and receiving of radio communication for wireless automatic meter reading (AMR) systems, as well as commercial, industrial or residential utility meters that operate at a plurality of unlicensed or licensed radio frequencies. A configuration and method for economical assembly of an antenna is also disclosed.

Description:
RELATED APPLICATION  
       [0001]     This application claims benefit of U.S. Provisional Application Ser. No. 60/691,789, filed Jun. 17, 2005, which is hereby fully incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The field of the invention relates generally to antennas. Specifically, the invention relates to a low profile housing for containment of antennas.  
       BACKGROUND OF THE INVENTION  
       [0003]     Over the years, utility providers have evolved toward so-called automated meter reading (AMR) systems for the collection of utility data. See, e.g., U.S. Pat. No. 5,298,894 (discussing a remote meter reading arrangement wherein data is collected by a hand held or mobile data collection units) and U.S. Pat. No. 6,653,945 (discussing a radio communications network that transmits data to a central station via fixed point relay stations).  
         [0004]     A vital component in AMR systems is the antenna that receives and transmits the local meter information. Newer utility meters feature electronic signal generation that is readily digitized for AMR transmission. Retrofit kits have also been developed that generate electronic data within existing conventional meters. Some AMR-compatible meters require antennas that are externally mounted.  
         [0005]     Other AMR devices, such as that disclosed in U.S. Pat. No. 6,181,294, feature small antennas that mount within the meter itself, transmitting and receiving radio signals through a dielectric portion of the meter housing. The configuration of these antennas is such that they must occupy a certain footprint within the meter, and are thus precluded from deployment in many retrofits. Also, these antennas cannot typically be oriented to optimize the signal received by remote collection devices.  
         [0006]     The need exists for a low profile antenna assembly that can be incorporated into new and existing utility meters and can be physically oriented for optimum transmission and reception.  
       SUMMARY OF THE INVENTION  
       [0007]     Various embodiments of the invention disclosed herein provide a universal housing for a wide variety of low profile antenna assemblies. The housing and assembly occupy a minimal footprint within the dielectric housing of a utility meter, and is particularly suited for mounting under glass domes common to electric utility meters. The assembly can be oriented to optimize signal transmission and reception to and from a remote location, and is compatible with a variety of antenna arrangements. Antennas and balanced-to-unbalanced transformers (BALUN) that are compatible with the universal housing are also disclosed.  
         [0008]     In one configuration of the invention, a lunate housing receives a flexible dipole antenna within a recess on the lunate housing. The lunate housing may be disposed in the annular region between a metering device and a dielectric dome that surrounds the metering device. The recess in the antenna housing enables the antenna to be located in close proximity to the internal components of the meter without significant degradation of performance.  
         [0009]     The housing may be mounted to a surface within the meter with posts or set screws that pass through the antenna housing and onto or through the mounting surface. Alternatively, the housing may be configured to resiliently clamp itself to internal meter structures, thereby securing the antenna in a fixed orientation.  
         [0010]     The antenna embodiments disclosed have printed circuit patterns with feed points in close proximity to each other near the center of the pattern. The close proximity enables coaxial cables or printed circuit strips to be attached to the feed points in a straight alignment, without need for bending or otherwise routing the leads to contact the feed points. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is an isometric view of an embodiment of the invention.  
         [0012]      FIG. 2  presents a layout and a connection scheme for a printed circuit antenna in an embodiment of the invention.  
         [0013]      FIG. 3  depicts a layout and a connection scheme for a printed circuit antenna in an embodiment of the invention.  
         [0014]      FIG. 4  shows an exploded view of an application in a utility meter according to an embodiment of the invention.  
         [0015]      FIG. 5  depicts an assembly of the  FIG. 4  embodiment of the invention.  
         [0016]      FIG. 6  illustrates lateral axes of symmetry for a variety of cross-sections. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0017]     Referring to  FIG. 1 , an embodiment of the universal antenna housing  10  is shown in isometric projection. The antenna housing  10  may be formed from an injection molded single piece resilient strip  12  of lunate shape having an inner radius  13  about a central axis  11 , an inner face  14 , end portions  16  and  18 , and a mid portion  17 . A gap  19  separates the free ends of the end portions  16 ,  18 . The housing  10  may be manufactured from ABS plastic or a similarly resilient material.  
         [0018]     The universal antenna housing  10  may utilize a mounting scheme that is similar in concept to a plastic head-band or bicycle clip. Here, the concept is adapted for this novel application and used here for housing and mounting of an antenna for a so-called “under glass mounted” electric utility meter in an Automated Meter Reading (AMR) communications network. The invention may also be applied in other fixed, drive by, mobile or mesh network applications, other than the electricity utility meters, such as for water and gas utility reading. While much of the discussion herein is directed to the housing of flexible antennas, it is noted that the invention is equally applicable to many non-flexible antennas.  
         [0019]     A first alignment post  20  may depend from the end portion  16 , and a second alignment post  30  may depend from the other end portion  18 . In one embodiment, the first alignment post  20  has a smaller diameter than the second alignment post  30 . The alignment posts  20 ,  30  may be oriented to protrude radially inward, and may be of a constant cross-section (e.g. a cylinder) or of varying cross-section (e.g. a frustum). In one embodiment, the alignment posts  20 ,  30  are formed integrally with the single strip resilient strip  12 , but are frangibly connected to the strip  12  to allow the posts  20 ,  30  to be easily removed. In another embodiment, a mark (not depicted) such as an “X” or a center punch is formed on the back end of the posts  20 ,  30  so that a user can readily drill out the posts  20 ,  30 . Either way, a hole (not depicted) results which can be used as a guide for forming a hole on the surface of the object to which the housing is to be mounted.  
         [0020]     In one embodiment, an elongated recess  40  having an interior face  42  is formed on the inner face  14 . A plurality of tab portions  60  extending over at least a portion of the recess  40  and are flush with the inner face  14 . The tab portions  60  may be located proximate to each corner of the elongated recess  40 . Tabs may also extend from the perimeter of the recess  40  away from the corners.  
         [0021]     The embodiment of  FIG. 1  portrays a housing  10  having a truly lunate profile, i.e. having a thickness  15  that is greater along the mid portion  17  than on the end portions  16  and  18  to accommodate the depth of the recess  40 . However, one may utilize a c-shaped profile of substantially uniform thickness, or even of reduced thickness in the mid portion  17  relative to the end portions  16  and  18  for selective flexibility of the housing  10 . Other profiles are also possible without departing from the spirit of the invention, such as continuous ring, rectangular, partial rectangular or U-shaped profile.  
         [0022]     Referring to  FIG. 2 , a printed circuit antenna  50  according to an embodiment of the invention is shown. The antenna  50  fits within the recess  40  of  FIG. 1  and is captured at the corners by the tab portions  60 . The antenna  50  may be constructed of a woven fiberglass such as FR4, or of a similar flexible circuit board material suitable for use at the operating frequencies. Other flexible antennas, such as a stamped metal antenna, are candidate antennas for mounting in the housing  10 . Also, antenna configurations other than dipole (e.g. monopoles and planar inverted F antennas) may be accommodated by the housing  10 . The printed circuit antenna  50  may be sufficiently flexible to enable bending by hand between the forefinger and thumb and inserted into the recess  40  and underneath the tab portions  60 . After mounting, the printed circuit antenna  50  registers flush against the interior face  42  of the recess  40 . In this way, the housing  10  provides a standoff or otherwise suspends the antenna  50 , thereby preventing unwanted contact with external devices that can hinder antenna performance.  
         [0023]     The antenna  50  in the  FIG. 2  embodiment has a printed dipole pattern  52  and is connected to a radio modem (not shown) via a length of cable  80 . The cable  80  is a coaxial cable comprising a center conductor  82  and a ground shielding  84 . The coaxial cable  80  is attached to an antenna feed point  90  at one end and may be terminated with a coaxial connector such as a SMA, MMCX or other commercially available connector. Cables and connector types other than coaxial may also be utilized 0002E  
         [0024]     For the efficient electrical operation of the antenna  50 , a balanced to unbalanced transformer (BALUN)  100  comprising a quarter wavelength solid core wire  105  may be connected between the antenna feed point  90  and the ground shielding  84  of the coaxial cable  80  at a distal location  110  displaced by the feed point  90  by roughly a quarter wavelength. The BALUN  100  converts the balanced dipole impedance to the unbalanced line impedance of the coaxial cable  80 , thereby significantly reducing ground currents that may degrade antenna efficiency and radiation performance.  
         [0025]     The layout of the printed circuit antenna  50  shown in  FIG. 2  includes a pair of pads  130  and  132  at the feed point  90  that that lie along an axis  136 . The pads  130  and  132  facilitate a pre-trimmed and cut coaxial cable  80  for easy application of solder points  138  without bending the coaxial cable  80  to bridge between the two feed points of the printed dipole pattern  52 . This method of attachment has proven cost effective in mass production, avoiding the need for adhesive or other mechanical means of anchoring the coaxial cable  80  to the antenna  50 . The pads  130  and  132  can be used in a variety of printed antenna frequency designs including unbalanced and planar inverted F antennas, and is especially useful for dipole type configurations.  
         [0026]     Referring to  FIG. 3 , a different embodiment of a dipole antenna printed on flexible substrate is depicted. Like the  FIG. 2  embodiment, the center conductor  82  and the ground shield  84  of the coaxial line  80  are in electrical contact with the pads  130  and  132 , respectively. However, the printed dipole pattern  52  includes a printed quarter-wavelength structure  55  between pads  130  and  132 . The quarter-wavelength structure  55  thus serves as integrated BALUN and, akin to the BALUN of  FIG. 2 , reduces cable currents that may degrade the antenna performance. Because there is no need to connect an external BALUN, the number of solder points  138  in the assembly process as well as the number of components to be handled in the assembly process is reduced, further increasing assembly line productivity.  
         [0027]     Referring to  FIGS. 4 and 5 , the housing  10  and antenna assembly is depicted “under glass mounted” in an electric utility meter assembly  140  in exploded and assembled view, respectively. The exploded view of  FIG. 4  shows alignment posts  20  and  30  as being removed from the single piece resilient strip  12  to reveal openings  22  and  32 . The utility meter assembly  140  may include a panel mounted metering device  150 . A dielectric dome  160  is typically made of glass or polycarbonate, but may be made of any other suitably rugged dielectric material.  
         [0028]     Traditionally, the dome  160  is made from a transparent material, or has a transparent component that allows viewing of the face of the metering device  150 . The utility meter assembly  140  also includes a mounting surface  170  that surrounds the perimeter of the metering device  150 . It is noted that a mounting surface that completely surrounds the metering device  150  is not necessary; many meters have mounting surfaces that occupy only a portion of the perimeter of the metering device  150 , and can still utilize embodiments of the invention.  
         [0029]     In one embodiment of the invention, it is desirable to mount the antenna housing  10  so that the gap  19  is on the right or left side as one faces the metering device  150 . The resulting antenna radiation pattern is vertically polarized so that maximum antenna gain is achieved in a horizontal direction, thereby optimizing the signals transmitted to a remote receiver. Likewise, the antenna housing  10  could be oriented for polarization in the horizontal plane for maximum antenna gain in the vertical direction, or oriented for maximum gain in an arbitrary plane between horizontal and vertical.  
         [0030]     The use of alignment posts  20 ,  30  of different diameter helps avoid improper orientation of the antenna housing  10 . In one embodiment of the invention, the objective device  170  is formed or pre-drilled with mounting holes  172 ,  174  that correspond to the differing diameters of the alignment posts  20  and  30 , respectively. The differing diameters of the posts  20  and  30  effectively keys the installation of the housing  10  and prevents misalignment of the antenna polarization pattern to ensure repeatable and consistent antenna electrical radiation patterns and fields of electrical polarization for between installations.  
         [0031]     Alternatively, a single alignment post having a cross-section with at most one lateral axis of symmetry and cooperating with an appropriately formed mating receptacle may serve to key the antenna housing  10  in a particular orientation upon mounting. (Herein, a “lateral axis” refers to an axis that is on the plane of the cross-section of the post.) Referring to  FIG. 6 , a post having an L-shaped cross-section  176  (i.e. a first leg longer than a second leg) has no lateral axis of symmetry. Accordingly, a mating hole that conforms to the L-shaped cross-section  176  enables mounting of the antenna in only one orientation. Likewise, a post having a semi-circular cross-section  178  has only one lateral axis of symmetry  180 , and can also be mounted in only one orientation. In contrast, single mounting posts that have more than one lateral axis of symmetry are not keyed for a single orientation. For example, a single post having a circular cross-section  182  has an infinite number of lateral axes of symmetry, and the post may be mounted in any rotational orientation. A square cross section  184  has four lateral axes of symmetry  186 ,  188 ,  190  and  192 , thus enabling mounting in four different orientations. A rectangular cross section  194  has two lateral axes of symmetry  196  and  198  and enables two different orientations. Hence, when using a single post, cross sections that are asymmetrical or symmetrical with respect to only one lateral axis enable a mounting orientation thereby providing a specific polarization field.  
         [0032]     In another embodiment, there are no pre-formed mounting holes; instead, the openings  22  and  32  in the single piece resilient strip  12  serve as a guide for drilling mounting holes  172  and  174  into the objective device  170  in a field installation. This means of securing the housing  10  allows optimization of the field radiation pattern by allowing the installer to rotate the housing  10  about the perimeter of the metering device  150  until the transmitter gain performance or reception of the carrier signal from the base station is maximized.  
         [0033]     In still another embodiment of the invention, the housing  10  does not require mounting posts  20  or  30 , or the attendant openings  22  or  32  or the mounting holes  172  or  174 . Instead, the c-shaped or lunate configuration of the housing  10  in combination with the resiliency of the strip  12  acts to clamp the housing  10  to the objective device  170 . In this embodiment, the housing  10  may be formed with an effective inner radius  13  that is smaller than the effective radius of the objective device  170 . A housing  10  that having a radius that is approximately 70-80% of the mounting radius of the objective device  170  is typical.  
         [0034]     The reduced inner diameter of the housing  10  provides a restoring force  120  (denoted by arrows in  FIG. 1 ) when the housing  10  is radially expanded to fit over the objective device  170 , applying a substantially uniform clamping pressure over portions of the objective device  170 . In some cases, this embodiment negates the need for a substantial mounting surface altogether; the housing  10  may instead register directly on the support structure that suspends the metering device  150  from the mounting panel (not depicted).  
         [0035]     The above descriptions disclose a lunate or c-shaped housing. A continuous ring geometry may also be utilized. A ring geometry could be fixed in place by set screws that extend radially through the ring to seat on the mounting surface.  
         [0036]     The antenna  50  may be designed for operation in any part of the licensed or unlicensed FCC or international radio spectrum (licensed or unlicensed) typically used in AMR Radio Communication Networks. For AMR fixed wireless networks and mesh wireless networks that are presently available and planned, the anticipated operational frequency is in the 902-928 MHz ISM band, the 2.4 GHz ISM band, the GSM 800 MHz band, the CDMA 850 MHz band, the GSM 900 MHz band, the DCS 1800 MHz band, the PCS 1900 MHz band and the UMTS 2.1 GHz, or other privately held license frequency bands such as the 1.409 GHz band. These operating frequency bands are offered as exemplary, and embodiments of the invention are not limited to any specific licensed or unlicensed operational frequency. Certain embodiments of the invention may be configured to operate at one or more FCC approved radio frequencies by exchanging the antenna  50  with one designed for the desired frequencies of operation.  
         [0037]     While the above descriptions are directed to electric utility meters, the invention is considered to be universal in nature. The application to water and gas utility meters is readily apparent. Also, because the operating frequency band of the antenna  50  may be tailored to any situation, and the radiation field can be optimized in any direction about the central axis of the housing, the invention has utility outside the AMR applications. Moreover, the low profile design and self-clamping aspects of the housing  10  permits application in a number of circumstances.  
         [0038]     All aspects of the embodiments presented and discussed in detail above are exemplary of the invention, and are non-limiting. For example, many of the embodiments described and depicted herein are directed to printed circuit dipole antennas. Such depictions and descriptions are exemplary in nature, and would not preclude the use of antennas that are neither printed circuit nor dipole antennas. Various other modifications and changes with which the invention can be practiced and which are within the scope of the description provided herein will be readily apparent to those of ordinary skill in the art.