Abstract:
The antenna configuration presented is an integral component of a retrofit module designed to incorporate a data telemetry transceiver within the confines of a utility meter.

Description:
NOTICE REGARDING COPYRIGHTED MATERIAL  
       [0001]     A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure as it appears in the Patent and Trademark Office file or records, but otherwise reserves all copyright rights whatsoever.  
       FIELD OF THE INVENTION  
       [0002]     This invention relates to antennas for use with utility meters.  
       BACKGROUND OF THE INVENTION  
       [0003]     Antenna performance parameters such as efficiency, radiation/reception pattern, and resonant frequency are affected when the antenna is placed in the vicinity of metallic infrastructures. The incumbent or resident metallic infrastructures in conventional electromechanical utility meters (such as GE Watthour Meter I-70-S and ABB AB-1) greatly affect the performance parameters of conventional half-wave dipole or quarter-wave whip antennas when such antennas are incorporated within the confines of a conventional meter. The interactions between the metallic infrastructure in a conventional meter and such conventional antennas are highly sensitive in the sense that the difference in the metallic infrastructures themselves between different meter models is sufficient to cause inconsistent antenna performance. The goal of the invention is to increase the stability and efficiency of antenna performance over many meter types.  
       SUMMARY OF THE INVENTION  
       [0004]     There is provided an antenna arrangement for a conventional utility meter having a cover and metallic infrastructure plus RF communications capability, comprising a slot antenna formed to fit under the cover and cooperating with said RF communications capability.  
         [0005]     There is also provided a method of managing the varying effects of differing incumbent metallic infrastructures on the performance of a radiating/receiving element of an antenna, comprising the steps of inserting a metallic structure closer to the radiating/receiving element than the incumbent metallic infrastructure. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     A better understanding of the present invention can be obtained when the following detailed description of the preferred embodiment is considered in conjunction with the following drawings, in which:  
         [0007]      FIG. 1  shows an exploded view of a RF retrofit module with the slot antenna of the present invention.  
         [0008]      FIG. 2  shows the slot antenna of the present invention, formed to the contour of the RF retrofit module.  
         [0009]      FIG. 3  shows the actual dimensions of the slot antenna of the preferred embodiment.  
         [0010]      FIG. 4  shows a view complementary to that of  FIG. 1 .  
         [0011]      FIG. 5  shows a front perspective, partially broken away view of a meter with the RF retrofit module that includes the antenna invention installed.  
         [0012]      FIG. 6  shows a view complementary to that of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]     With reference to  FIGS. 1 and 2 , a conventional meter  100  houses electromechanical (incumbent or resident) metallic infrastructures (consisting of gears, brackets, prongs, tumblers, disks, rivets and the like, identified generally as  140 ) enclosed by a transparent (typically glass or plastic) cover  90 . Herein, the term “metallic infrastructure” is meant to describe the (resident or incumbent) infrastructure  140  whereas the term “metallic structure” is meant to describe the contribution of the present invention.  
         [0014]     As seen in  FIGS. 1 and 2 , the present invention teaches the use of a slot antenna  10  and  20  with a RF retrofit module  40  that is placed within meter  100  under the cover  90 . RF retrofit module  40  has transceiver assembly  70  and is shaped to be attached to the resident metallic infrastructure  140  of meter  100 . Details of quarter-wave slot  125  in antennas  10  and  20  are explained below. The fully assembled version of the exploded view of  FIGS. 1-2 , is shown in  FIGS. 5-6 .  
         [0015]     Those skilled in the art realize that an efficient antenna that is insensitive to meter incumbent metallic infrastructures placed in its vicinity, faces conflicting requirements. In the present invention, the quarter-wave radiating slot  125  is inherently adjacent to the metallic structure of the brass sheet  115  it is cut out of. Thus the metallic infrastructure  140  of the conventional meter  100  is relatively “far” away from the slot  125 , resulting in an antenna that is less sensitive to de-tuning when compared to the aforementioned conventional antenna types.  
         [0016]     Cover  90  is typically frusto-conical (as the result of conventional manufacturing processes). RF retrofit module  40  is pre-formed and shaped accordingly as a smaller frusto-cone to fit under cover  90 . The frusto-conical shape of the brass sheet  115  is required to form snugly over the upper surface of RF retrofit module  40  as seen in  FIGS. 1, 4 ,  5 - 6 .  
         [0017]     Mounting holes  110  and  120  in antennas  10  and  20  are elongated to allow for thermal expansion and contraction over the expected operating temperature range of the antenna  10  and  20 . Antenna  10  is attached to the RF retrofit module  40  with four plastic rivets  30  inserted through the mounting holes  110  and  120  in  FIG. 3  and through the mounting holes  80  in the RF retrofit module  40 . The plastic rivets  30  are heat-staked to complete the fastening.  
         [0018]     Antenna  10  is pre-formed to the contour of the RF retrofit module  40  as shown in  FIG. 2 . In the same fashion the complementary, pre-formed antenna  20  is attached to the RF retrofit module  40 . Antenna  10  is coupled to the transceiver assembly  70  via coaxial cable  50 . Coaxial cable  50  is soldered to the transceiver assembly  70  at a transceiver coupling point. The other end of coaxial cable  50  is soldered to antenna  10  as per the detail A in  FIG. 3  at points  130 . In the same fashion antenna  20  is coupled to the transceiver assembly  70  via coaxial cable  60 . The fully assembled RF retrofit module  40  is fastened to meter  100  (by conventional means like screws or snap/friction fit) and enclosed by the cover  90 .  
         [0019]     The radiation/reception pattern of antenna  10  is nevertheless perturbed to some degree when incorporated into the meter  100 . Accordingly, in the preferred embodiment, two slot antennas  10  and  20  are used and are placed offset from the center of the top surface of the retrofit module  40 . The resultant dominant null in the radiation/reception pattern for each of antennas  10  and  20  occurs at different azimuths such that one antenna mitigates the null of the other. The selection of antenna  10  and  20  is conventionally performed by the transceiver assembly  70  where the selection is made by assessing the quality of the received signal for each antenna in the actual operating environment. As such, a switched-diversity antenna is implemented. Alternatively, as a function of the capabilities of transceiver assembly  70 , both antennas  10  and  20  may be active to perform transceive functions.  
         [0020]     Antenna  10  and  20  are made of hard brass material of about 8 mil thickness. The brass material is selected for its oxidation and solderability properties that are favourable for the environment which the antennas are intended to operate in (e.g. hot and humid climates which would result in considerable heat and humidity under cover  90 ). In other environments, copper and stainless steel would suffice, as a matter of routine design choice.  
         [0021]      FIG. 3  shows the antenna dimensions (including those of notch  125 ) in millimeters for a resonant frequency of 915 MHz in the preferred embodiment, with details on the coupling points that gives the best return loss in a 50 ohm system. Those skilled in the art could scale the dimensions to operate at other frequencies for maximum effectiveness.  
         [0022]     RF retrofit module  40  has a housing or frame made of polycarbonate plastic or other like material with dielectric properties that may be advantageous (e.g. fibreglass). RF Retrofit module  40  has transceiver assembly  70  but it is placed as far away as possible relative to the slot antenna  10  and  20 .  
         [0023]     An alternative embodiment of the invention (not shown) uses a single slot antenna. The dimensions of this antenna would remain about the same as for antenna  10  or  20  but its location on the surface of the RF retrofit module  40  would change so that the (longitudinal) center of the notch  125  would align with the top or twelve o&#39;clock position of the RF retrofit module  40  and accordingly that of the meter  100 .  
         [0024]     An alternative embodiment of the invention (not shown) uses three slot antennas, appropriately sized, to cover the available surface area of the RF retrofit module  40 . Depending on the intended application and environment, three antennas are identical in size and shape and are equi-spaced and uniformly orientated on the surface area of RF retrofit module  40 , or they may be of differing sizes, shapes and orientations. The variations can be accomplished easily by the empirical means (e.g. experimentation for the intended application and environment with consequent design (of shape, size, orientation)).  
         [0025]     For these alternative (single or more than two slot antennas) embodiments, the transceiver assembly  70  of the preferred embodiment (for two antennas  10  and  20 ), and any upstream application, would be adapted and programmed conventionally to accommodate the single path or the switching of the multiple antenna paths, as the case may be.  
         [0026]     Although the preferred and alternative embodiments have been given in the context of a conventional utility meter, the present invention is not limited to such contexts. The present invention teaches that incumbent or resident metallic infrastructures which are problematic because they vary, can be substantially “tamed” by inserting a second, metallic structure that becomes more “dominant” than the first mentioned “adjacent” metallic infrastructure because of its closer proximity to the radiating/receiving element of the subject antenna. This second, “dominant” metallic structure is more manageable than the varying incumbent or resident metallic infrastructures because its effects are more uniform and thus predictable.  
         [0027]     All drawings are drawn for ease of explanation of the basic teachings of the present invention only; the extensions of the drawings with respect to number, position, relationship, and dimensions of the parts to form the preferred embodiment will be explained or will be within the skill of the art after the following teachings of the present invention have been read and understood. Further, the exact dimensions and dimensional proportions to conform to specific force, weight, strength, RF performance and similar requirements will likewise be within the skill of the art after the following teachings of the present invention have been read and understood.  
         [0028]     Where used in the various drawings, the same numerals designate the same or similar parts. Furthermore, when the terms “top”, “bottom”, “first”, “second”, “inside”, “outside”, “edge”, “side”, “front”, “back”, “length”, “width”, “inner”, “outer”, and similar terms are used herein, it should be understood that these terms have reference only to the structure shown in the drawings as it would appear to a person viewing the drawings and are utilized only to facilitate describing the invention.  
         [0029]     Although the method and apparatus of the present invention has been described in connection with the preferred embodiment, it is not intended to be limited to the specific form set forth herein, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents, as can be reasonably included within the spirit and scope of the invention as defined by the appended claims.