Abstract:
An apparatus mounted beneath or behind a surface and being operable to transmit or receive wireless communication signals for transmitting information from one location to a remote location. The apparatus includes an antenna mounted substantially flush with a surface. The apparatus also includes a communication device and a matching network having a radial transmission line. The communication device is connected to the antenna via the matching network and includes either a transmitter, a receiver or a transceiver.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to antennas for effecting wireless communication from an electronic device, and particularly, to a flush-mounted antenna for the device. 
   There are many applications in which it is desired to obtain information from a electronic device via wireless communication. Often, the device is located beneath a surface of a supporting structure, integrated into a surface of a supporting structure and/or positioned within a housing or enclosure having an outer surface. In order to effect wireless communication, the communication signal much somehow be transmitted through the surface. In the usual case, this is done by inserting an antenna through a hole in the surface. 
   SUMMARY OF THE INVENTION 
   In some applications, however, it is desirable that the antenna not extend outward from the surface, but rather be mounted flush with the surface. Often, mounting the antenna flush with the surface limits the area the antenna can occupy. Furthermore, mounting the antenna flush with the surface may limit the ability of the device to transmit and/or receive signals through the antenna. It therefore becomes desirable, in these applications, to provide a matching network for the device that will not significantly reduce the total efficiency of the device during transmission and/or reception and that can be configured in a small, compact construction. 
   Accordingly, the invention provides an apparatus mounted beneath or behind a surface and being operable to transmit or receive wireless communication signals for transmitting information from one location to a remote location. The apparatus includes an antenna mounted substantially flush with a surface. In one embodiment, the antenna is an annular slot antenna. 
   In another embodiment, the invention provides an apparatus for transmitting and/or receiving wireless communication signals. The apparatus is positioned beneath a surface and includes an antenna positioned substantially flush with the surface. The apparatus also includes a communication device and a matching network having a radial transmission line. The communication device is connected to the antenna via the matching network and includes either a transmitter, a receiver or a transceiver. 
   In still another embodiment, the invention provides an apparatus for transmitting and/or receiving wireless communication signals. The apparatus is positioned beneath a surface and includes an annular slot antenna positioned substantially flush with the surface. The apparatus also includes a transmitter coupled to the antenna via a radial transmission line. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  is a section view of an apparatus embodying the invention. 
       FIG. 2  is an exploded view of the apparatus shown in FIG.  1 . 
       FIG. 3  is a detailed view of the encircled portion of the apparatus as shown in FIG.  1 . 
       FIG. 4  is a perspective sectional view of another apparatus embodying the invention with a portion of the apparatus broken away. 
       FIG. 5  is an exploded view of the apparatus shown in  FIG. 4  with another portion of the apparatus broken away. 
       FIG. 6  is a schematic diagram illustrating a first electrical circuit equivalent of the apparatus shown in FIG.  1 . 
       FIG. 7  is a schematic diagram illustrating a second electrical circuit equivalent of the apparatus shown in FIG.  1 . 
       FIG. 8  is a schematic diagram illustrating an electrical circuit equivalent of the apparatus shown in FIG.  4 . 
   

   Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected,” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting, and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. 
   DETAILED DESCRIPTION 
   A first embodiment of an apparatus  20  in accordance with the present invention is shown in  FIGS. 1-3  and illustrated schematically in  FIGS. 6 and 7 . The apparatus  20  is configured to be positioned substantially beneath a surface  25  as shown in FIG.  1 . In some constructions, the surface  25  is an outer surface of a housing or enclosure that defines a cavity into which a communication device, such as, for example, a transmitter, a receiver and/or a transceiver (all not shown), is positioned. In some constructions, the surface  25  is included in a support structure or is a portion of a street, sidewalk or ground. 
   The apparatus  20  includes a top portion  30  which is positioned substantially flush with the surface  25  and a bottom portion  35  which is positioned substantially beneath the surface  25 . The top portion  30  includes an antenna  40 , which will be discussed below. The bottom portion  35  includes a matching network  45  to couple the antenna  40  to the communication device. In some constructions, the matching network  45  couples the antenna  40  to a transmission line (not shown), such as coaxial cable, which in turn couples to the communication device. 
   Still referring to  FIGS. 1-3 , the apparatus  20  includes a can  50 . In the illustrated embodiment, the can  50  is substantially cylindrical and includes a base  55  and a sidewall  60 . As shown in  FIGS. 1 and 2 , the diameter of the base  55  is substantially greater than the height of the sidewall  60 . In other constructions and in other embodiments, the can  50  may have a different shape and/or size than the can  50  illustrated in  FIGS. 1-3 . In some constructions, the can  50  is formed from a conductive material or metal. In other constructions, the can  50  is a plastic mold which is plated with a conductive material or metal. 
   The sidewall  60  of the can  50  includes an inner surface  65  and an outer surface  70 . The base  55  of the can  50  includes a bottom surface  75  and a top surface  80 . The base  55  also defines an aperture  85 . The top surface  80  of the base  55  and the inner surface  65  of the sidewall  60  partially define a cavity  90 , i.e., the interior portion of the can  50 . 
   The can  50  also includes an enlarged lip  95  extending from the top of the sidewall  60 . The lip  95  extends around the entire length of the sidewall  60 . A portion of the lip  95  is cut away forming an annular shelf  100 . 
   The apparatus  20  also includes a connecting element  110  which extends through the aperture  85  in the base  55  of the can  50 . Transmission line, such as coaxial cable (not shown), connects to the connecting element  110 , as will be discussed below. The connecting element  110  is a standard RF connector, such as a threaded coaxial connector. In the illustrated embodiment, the connecting element  110  is an SMA connector configured to receive the coaxial cable transmission line. As illustrated in  FIGS. 1 and 2 , the connecting element  110  includes an inner conductor feed  115  positioned near the top of the connecting element  110  and extending through the middle of the connecting element  110 . In this embodiment, the inner conductor feed  115  couples to the center conductor of the coaxial cable when a connection between the cable and the connecting element  110  is made. 
   The connecting element  110  also includes an outer conductor feed  120  substantially surrounding the inner conductor feed  115 . The outer conductor feed  120  couples to the outer conductor or shield of the coaxial cable when a connection between the cable and the connecting element  110  is made. The outer conductor feed  120  also electrically couples to the base  55  of the can  50 . The inner conductor feed  115  is electrically isolated by the outer conductor feed  120  by an insulator  125  formed from an insulating material, such as, for example, plastic. 
   The apparatus  20  also includes a tuner element  140  positioned within the cavity  90  of the can  50 . In the illustrated embodiment, the tuner element  140  is a round plate having a top side  145 , a bottom side  150 , a sidewall  152  and an aperture  158 . In other constructions and in other embodiments, the tuner element  140  can vary in shape and/or size without deviating from the spirit of the invention. The tuner element  140  is positioned above the top surface  80  of the base  55  of the can  50  by the connecting element  110  and forms a space  152  between the top surface  80  of the base  55  and the bottom side  150  of the tuner element  140 . The inner conductor feed  115  of the connecting element  110  extends through the aperture  158  of the tuner element  140  and electrically couples to the tuner element  140 . During operation, the base  55  of the can  50  and the tuner element  140  form a radial transmission line  320  (shown schematically in FIGS.  6  and  7 ). 
   In some constructions, the tuner element  140  is a non-conductive disc, such as a plastic disc, plated with a conductive material. As illustrated in  FIG. 2 , the tuner element  140  is plated such that a portion  155  of the top side  145  is plated with the conductive material and a portion (not shown) of the bottom side  150  is plated with the conductive material. In this construction, the tuner element  140  also includes apertures  160 . The sidewalls defining the apertures  160  are also plated such that the plated portion  155  of the top side  145  is electrically coupled to the plated portion of the bottom side  150 . As shown in  FIG. 2 , the plated portion  155  of the top side  145  and the plated portion of the bottom side  150  do not extend across the entire diameter of the tuner element  140 . Stated differently, there is a non-conductive annular region  156  between the tuner element  140  and the can  50  along the entire periphery of the tuner element  140 , and on both the top side  145  and the bottom side  150 . 
   In other constructions, the tuner element  140  is a conductive disc. As shown in  FIG. 1 , the tuner element  140  includes a conductive disc  170  surrounded by a non-conductive ring or gap  175 . In this construction, the top side  145  and the bottom side  150  are electrically coupled by the conductive disc  170 . 
   The apparatus  20  also includes a conductive post  180  positioned on top of the tuner element  140 . The conductive post  180  is electrically coupled to the inner conductor feed  115  of connecting element  110  either directly or via the tuner element  140 . In some constructions, the conductive post  180  is a solid cylinder of conductive material or metal. In other constructions, the conductive post  180  is a hollow cylinder of conductive material. In the embodiment illustrated in  FIGS. 1 and 2 , the conductive post  180  includes a conductive base  185  defining an aperture  188  and coupling to a conductive sidewall  190 . As shown in  FIGS. 1 and 2 , the inner conductor feed  115  extends through the aperture  188  and electrically couples to the conductive post  180 . In other constructions, the conductive post  180  is a plastic cylinder plated with a conductive material. 
   The apparatus  20  also includes a top plate  200  positioned on top of the post  180 . As shown in  FIG. 1 , the top plate  200  is configured to be positioned on the annular shelf  100  of the can  50 . In some constructions, the top plate  200  is mounted to the post  180 . In other constructions, the top plate  200  is mounted to the annular shelf  100 , and in further constructions, the top plate  200  is mounted to both the annular shelf  100  and the post  180 . 
   The top plate  200  includes a top side  205 , a bottom side  210 , a sidewall  215  and apertures  218 . As shown in  FIGS. 1-3 , the top plate  200  is plated such that the top side  205  includes a first conductive portion  220  and a first non-conductive portion  222 , and the bottom side  210  includes a second conductive portion  225  and a second non-conductive portion  228 . As shown in  FIGS. 1 and 2 , the first conductive portion  220  is substantially circular. As shown in  FIG. 3 , the first conductive portion  220  is electrically coupled to the second conductive portion  225  by the conductive sidewalls  230  defining the apertures  218 . 
   Referring to  FIG. 1 , the first conductive portion  220  and the first non-conductive portion  222  of the top plate  200  and the lip  95  of the can  50  form an annular slot antenna  40 . In some constructions, the annular slot antenna  40  radiates and/or receives signals at a center frequency of approximately 900 MHz and is an omni-directional antenna. The annular slot antenna  40  is positioned substantially flush with the surface  25 . The remainder of the can  50 , the connecting element  110 , the tuner element  140 , the post  180  and the second conductive portion  225  of the top plate  200  form the matching network  45 . Furthermore, when the antenna  40  is radiating, the can  50  serves as a reflector. During operation, a portion of the radiation transmitted by the antenna  40  that is directed at the can  50  is reflected by the conductive base  55  and conductive sidewall  60  of the can  50 . 
     FIG. 6  is a schematic diagram illustrating a first electrical circuit equivalent for the matching network  45  and the antenna  40  included in the apparatus  20  illustrated in  FIGS. 1-3 .  FIG. 7  is a schematic diagram illustrating a second electrical circuit equivalent for the matching network  45  and the antenna  40  included in the apparatus  20  illustrated in  FIGS. 1-3 . 
   Referring to  FIGS. 6 and 7 , the matching network  45  can be equivalent to both the first electrical circuit matching network  300  and the second electrical circuit matching network  305 . Both matching networks  300  and  305  include a conductor  310 , whose structural equivalent is the connecting element  110 , and an inductor  315 , which represents the inductance of the inner conductor feed  115 . 
   The matching networks  300  and  305  also include a radial transmission line  320 , a first capacitor  325  and a second capacitor  330 . The radial transmission line  320  is the electrical circuit equivalent for the base  55  of the can  50  and the tuning element  140 . The first capacitor  325  is the electrical circuit equivalent for the capacitance produced between the tuning element  140  and the sidewall  60  of the can  50 . The second capacitor  330  is the electrical circuit equivalent for the capacitance produced between the second conductive portion  225  of the top plate  200  and the sidewall  60  of the can  50 . 
   The difference between the first matching network  300  and the second matching network  305  is the electrical circuit equivalent for the post  180 . For the first matching network  300 , the electrical circuit equivalent for the post  180  is a second inductor  335  representing the inductance of the post  180 . However, the post  180  may also be represented electrically by a low impedance transmission line, such as the transmission line  340  included in the second matching network  305 . 
   The electrical circuit matching networks  300  and  305  and the structural equivalent, matching network  45 , are used to efficiently match the impedance of the antenna  40  (shown schematically as antenna  350 ) to the impedance of the coaxial cable transmission line (not shown) coupling the apparatus  20  to the communication device (not shown). Typically, coaxial cable has an impedance of approximately 50 ohms. In most constructions, the annular slot antenna  40  has a high and/or complex impedance, such as, for example, an impedance greater than approximately 100 ohms and/or an impedance having a large capacitive reactance. In the illustrated embodiment, the annular slot antenna  40  has an impedance of approximately 200 ohms to approximately 300 ohms and has a highly capacitive reactance. 
   In the illustrated embodiment, the dimensions of the components included in the matching network  45  are configured to efficiently match the impedance of the antenna  40  to the impedance of the coaxial cable transmission line (not shown). In the illustrated embodiment, the cavity  90  defined by the can  50  has a height of approximately 1-inch (“in”) and a diameter of approximately 3.25-in. The sidewall  60  has a thickness of approximately 0.2-in. The tuner element  140  has a diameter of approximately 3.25-in and a thickness of approximately 0.2-in. The conductive portion  155  of the tuner element  140  has a diameter of approximately 3.0-in. The post  180  has a diameter of approximately 0.9-in and a height of approximately 0.6-in. The top plate  200  has a diameter of approximately 3.7-in. The sidewall  215  of the top plate  200  has a height of approximately 0.2-in, and the first conductive portion  220  of the top plate  200  has a diameter of approximately 2.7-in. 
   Another embodiment of an apparatus  420  in accordance with the present invention is shown in  FIGS. 4 and 5  and illustrated schematically in FIG.  8 . Common elements have the same reference number as shown in the drawings relating to the apparatus  20 . 
   Similar to the apparatus  20  shown in  FIGS. 1-3 , the apparatus  420  includes a top portion  430  which is positioned substantially flush with the surface  25  (shown in  FIG. 1 ) and a bottom portion  435  which is positioned substantially beneath the surface  25 . The top portion  430  includes an antenna  440 , and the bottom portion  435  includes a matching network  445  to couple the antenna  430  to the communication device. In some constructions, the matching network  445  couples the antenna  440  to a transmission line (not shown), such as coaxial cable, which in turn couples to the communication device. 
   Referring to  FIGS. 4 and 5 , the apparatus  420  includes a can  450  similar to the can  50  shown in the first embodiment. As shown in  FIGS. 4 and 5 , the can  450  is substantially cylindrical and is formed from a conductive material, such as metal. 
   Similar to the can  50  shown in  FIGS. 1 and 2 , the can  450  includes a base  455  and a sidewall  460 . The sidewall  460  of the can  450  includes an inner surface  465  and an outer surface  470 , and the base  455  of the can  450  includes a bottom side or surface  475  and a top side or surface  480 . The base also defines an aperture  485 . The top surface  480  of the base  455  and the inner surface  465  of the sidewall  460  partially define a cavity  490 , i.e., the interior portion of the can  450 . The can  450  also includes an enlarged lip  495  extending from the top of the sidewall  460 . The lip  495  extends around the entire length of the sidewall  460 . As shown in  FIGS. 4 and 5 , a portion of the lip  495  is cut away forming an annular shelf  500 . 
   In the illustrated embodiment, the connecting element  110  extends through the aperture  485  of the can  450 . Similar to the apparatus  20  in the first embodiment, the outer conductor feed  120  of the connecting element  110  electrically couples to the can  450 . 
   As illustrated in  FIGS. 4 and 5 , the apparatus  420  also includes a tuning cup  540  as the tuner element. The tuning cup or tuner element  540  includes an indented base  550  and a sidewall  555 . The sidewall  555  includes an inner surface  560 , an outer surface  565  and a top surface  566 . As shown in  FIG. 4 , the apparatus  420  includes a space  568  between the inner surface  465  of the sidewall  460  of the can  450  and the outer surface  565  of the sidewall  555  of the tuner element  540 . Also shown in  FIG. 4 , the apparatus  420  includes another space  569  between the base  550  of the tuner element  540  and the top surface  480  of the can  450 . During operation, the base  455  of the can  450  and the tuner element  540  form a radial transmission line  720  (shown schematically in FIG.  8 ). 
   In the illustrated embodiment, the base  550  of the tuner element  540  includes a top surface  570 , a bottom surface  572 , a distal perimeter  574 , a proximal perimeter  575  and an aperture  576 . As shown in  FIGS. 4 and 5 , proximal perimeter  575  of the base  550  is raised compared to the distal perimeter  574  of the base  550 . The result is that the height of the space  569  between the bottom surface  572  of the tuner element  540  and the top surface  480  of the can  450  is larger near the proximal perimeter  575  than near the distal perimeter  574 . 
   The apparatus  420  also includes a pogo pin  580  coupling a post  585  to the inner conductor feed  115  of the connecting element  110 . As shown in  FIG. 4 , the post  585  and the pogo pin  580  extend through the aperture  576  of the tuner element  540  to electrically couple to the inner conductor feed  115 . Thus, the tuner element  540  electrically couples to the inner conductor feed  115  of the connecting element  110  via the post  585  and the pogo pin  580 . 
   Similar to the apparatus  20  in the first embodiment, the apparatus  420  includes a top plate  600  positioned on top of the post  585 . As shown in  FIG. 4 , the top plate  600  is configured to be positioned on top of the post  585  and on top of the annular shelf  500  of the can  450 . In the illustrated embodiment, the top plate  600  defines an aperture  602  to receive the post  585 . 
   As shown in  FIGS. 4 and 5 , the top plate  600  includes a top side  605 , a bottom side  606  and a sidewall  608 . In the illustrated embodiment, the top plate  600  is a non-conductive plate, such as a plastic plate, and does not include a conductive portion positioned on the top side  605  of the plate  600  (such as the first conductive portion  220  as shown in FIGS.  1 - 3 ). Rather, the apparatus  420  includes a circular conductive plate  610  positioned on the bottom side  606  of the top plate  600 . In some constructions, the conductive plate  610  is adhered to the bottom side  606  of the top plate  600  with a conductive or non-conductive adhesive. In other constructions, the conductive plate  610  defines an aperture  615  to receive the post  585  and is positioned and held near the bottom side  606  by the post  585 . In further constructions, the conductive plate  610  is plated onto the bottom side  606  of the top plate  600 . When the conductive plate  610  is positioned on the bottom side  606  of the top plate  600  and the apparatus  420  is assembled, the conductive plate  610  defines a non-conductive portion  630  of the top plate  600  which extends between the lip  495  of the can  450  and the conductive plate  610 . 
   Referring to  FIG. 4 , the conductive plate  610  and the non-conductive portion  630  of the top plate  600  and the lip  495  of the can  450  form an annular slot antenna  440 . Similar to the annular slot antenna  40  illustrated in  FIGS. 1-3 , the annular slot antenna  440  is also an omni-directional antenna and radiates and/or receives signals at a center frequency of approximately 900 MHz. Also similar to the first embodiment illustrated in  FIGS. 1-3 , the remainder of the can  450 , the connecting element  110 , the tuner element  540 , the post  585  and the pogo pin  580  form the matching network  445 . Furthermore, similar to the can  50  of the first embodiment, the can  450  of the second embodiment serves as a reflector when the antenna  440  is radiating. During operation, a portion of the radiation transmitted by the antenna  440  that is directed at the can  450  is reflected by the conductive base  455  and conductive sidewall  460  of the can  450 . 
   Referring to  FIG. 8 , the matching network  445  is equivalent to the electrical circuit matching network  700 . The matching network  700  includes a conductor  710 , whose structural equivalent is the connecting element  110 , an inductor  715 , which represents the inductance of the inner conductor feed  115  and the pogo pin  585 , and a radial transmission line  720 . The radial transmission line  720  is the electrical circuit equivalent for the base  455  of the can  450  and the base  550  of the tuning element  540 . 
   The matching network  700  also includes a first capacitor  730 , a second capacitor  740  and a series shorted stub tuner  745 . The first capacitor  730  is the electrical circuit equivalent for the capacitance produced across the space  568 . The second capacitor  740  is the electrical circuit equivalent for the capacitance produced between the top surface  566  of the sidewall  555  of the tuner element  540  and the conductive plate  610 . The shorted stub tuner  745  is the electrical circuit equivalent of the coaxial transmission line formed by the sidewall  555  of the tuner element  540  and the post  585 . 
   Similar to the matching networks  300  and  305 , the electrical circuit matching network  700  and the structural equivalent, matching network  445 , is used to efficiently match the impedance of the antenna  440  (shown schematically as antenna  750 ) to the impedance of the coaxial cable transmission line (not shown) coupling the apparatus  420  to the communication device (not shown). As stated previously, coaxial cable typically has an impedance of approximately 50 ohms. In most constructions, the annular slot antennas  440  has a high and/or complex impedance, such as, for example, an impedance greater than approximately 100 ohms and/or an impedance having a large capacitive reactance. In both the first embodiment and the second embodiment, the antennas  40  and  440  each have an impedance of approximately 200 ohms to approximately 300 ohms and has a highly capacitive reactance. 
   As stated previously, the dimensions of the components included in both matching networks  45  and  445  are configured to efficiently match the impedance of the antennas  40  and  440  to the impedance of the coaxial cable transmission lines (not shown). In the embodiment shown in  FIGS. 4 and 5 , the cavity  490  defined by the can  450  has a height of approximately 0.9-in and a diameter of approximately 2.3-in. The tuner element  540  has a diameter of approximately 2.1-in, and the sidewall  555  of the tuner element  540  has a height of approximately 0.7-in. The post  585  has a diameter of approximately 0.3-in and a height of approximately 0.55-in. The top plate  600  has a diameter of approximately 2.75-in. The sidewall  608  of the top plate  600  has a height of approximately 0.125-in, and the conductive plate  610  has a diameter of approximately 1.85-in. In other constructions and in other embodiments, the dimensions of the components included in the matching networks  45  and  445  are greater than or less than the dimensions listed of the components shown in  FIGS. 1-5 . 
   Thus, the invention provides, among other things, an apparatus for transmitting and/or receiving wireless communication signals. Various features of the invention are set forth in the following claims.