Abstract:
An omni-directional antenna assembly is provided for wireless communications devices requiring multiple polarization characteristics. An antenna assembly for a communications device operating at a predetermined wavelength and having a transceiver circuit including a signal output and a ground plane, the antenna assembly including a conductive planar element disposed away from the ground plane and a conductive leg member coupled to the planar element proximate a perimeter, the planar element being disposed a distance away from the ground plane of the communications device to define a region capable of receiving one or more components associated with the wireless communications device.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims the benefit of priority, pursuant to 35 U.S.C. §120, from copending application Ser. No. 09/675,774 filed Sep. 27, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to antenna structures for wireless communications devices, and more particularly to compact, high efficiency, electrically small loop antennas for use in conjunction with portable wireless communication devices.  
         BACKGROUND OF THE INVENTION  
         [0003]    The physical size of modem compact communication devices often is dictated by the size of the antenna needed to make them function effectively. To avoid devices that are too large, pagers and other devices have made use of electrically small rectangular loop ({fraction (1/10)} wavelength). However, these small antennae tend to be inefficient as a result of their very low radiation resistance and comparatively high resistive loss. Likewise, as a result of their high Q they tend to be sensitive to their physical environment.  
           [0004]    Yet another consideration and challenge of designing modem wireless communications devices is the efficiency of packaging the necessary components within an increasing smaller physical package. As the overall size of wireless devices has continued to decrease, a particularly difficult challenge to those skilled in the relevant arts has been the efficient placement of components, such as batteries, antenna structures, RF signal reception and transmission circuits, and other digital and/or analog devices or module, within the overall device package. Especially important has been the placement of antenna structures and assemblies relative to the RF signal generating components or modules. Those skilled in the relevant arts recognize the difficulties in preventing electromagnetic coupling between these componenents.  
           [0005]    To overcome the disadvantages of electrically small loop antennas, there is a continuing need for antennas small in physical dimension; having relatively high efficiency; capable of being placed in close proximity to associated electronic circuits without adversely effecting performance; easy to manufacture using standard, low-cost components; and capable of having radiation patterns altered to support different applications.  
           [0006]    For some wireless communications devices, an antenna assembly may be located remotely from the electronic device or devices it is serving. Remote location of the antenna assembly relative the associated wireless device may minimize coupling of RF energy into digital or other circuitry from the strong fields around the antenna or for the antenna to have access to signals. GPS receivers, and BLUETOOTH® or other types of UHF and microwave digital transceivers, particularly those having the antenna integrated on or within the device, often benefit by having the antenna assembly remotely disposed relative to the RF signal generating/receiving components.  
           [0007]    One limitation associated with a remote antenna is that power is lost through the transmission line connecting the antenna assembly to the electronics. Obviously, this is undesirable as it degrades the performance of the system by increasing the noise and reducing the transmit power. A decrease in important antenna parameters, such as gain, results from power loss in the transmission line. Signal reception is also negatively impacted by transmission line losses.  
           [0008]    Also known are circular polarization antenna structures or systems for reception of left hand and right hand polarized signals. Circular polarization is typical of satellite systems, such as the Global Positioning System (GPS). This field is in rapid expansion due to the vast range of possible applications and the relative low cost of implementing these systems.  
           [0009]    The fixed and mobile land devices associated with such systems have required more specialized antennas designed to perform specific functions effectively. Two types of antennas have to date been used in circular polarization communication and navigation systems on mobile devices: the first is the “helix” or helicoidal antenna, while the second is known as the “patch” antenna.  
           [0010]    In helicoidal antennas, circular polarization is obtained by exciting a progressive wave on a helicoidal wire; the direction of the circular polarization (left or right) is determined by the sense of helicoidal wire winding.  
           [0011]    The helicoidal antennas have the advantage of being very simple to design and produce and have a considerable band width which ensures high sensitivity; this characteristic of the helicoidal antenna makes the tolerance range wider, making it possible to use inexpensive materials which are easy to obtain on the market. This type of antenna has the added advantage of having a good gain value in an axial direction with an equally good axial ratio that, as the experts in the field know, is the most important reference parameter for the quality of circular polarization.  
           [0012]    The disadvantage of helicoidal antennas is their by no means negligible height which makes them inconvenient for certain applications, such as installation on vehicles or hand-held devices where low profile antennas are required, obviously because they must be streamlined.  
           [0013]    The low profile is the main characteristic of the second type of antenna mentioned above, known as the patch antenna, where circular polarization is obtained by exciting a resonant current distribution on a planar conducting surface. The direction of circular polarization is determined by a precise calculation of the position of the “point of excitation” of the surface.  
           [0014]    This type of antenna, however, requires the use of relatively expensive materials, and, above all great precision during setting up and production due to the small tolerances to respect.  
           [0015]    Considering the above state-of-the-art, another type of circular polarization two-way antenna was designed with the aim of offering all the advantages of both of the above antennas, without the disadvantages or application limitations of either.  
         SUMMARY OF THE INVENTION  
         [0016]    An omni-directional antenna which includes a conductive loop element supported above a conductive ground plane of a wireless communication device by a conductive leg member. The conductive leg member further defines a feedpoint at which the antenna is operatively coupled to the device&#39;s signal generating circuitry. A dielectric element may optionally be disposed between the loop and ground plane.  
           [0017]    The improved antenna displays gain in both the vertical and horizontal orientations. The horizontal gain is due to currents in the loop. The vertical gain (perpendicular to the loop and the ground plane) is due to displacement current fields within the conductive leg member disposed between the loop and the ground plane.  
           [0018]    Circular polarization is obtained by exciting a wave along a loop wire. The loop defines a closed path, which need not necessarily be a circular path. An antenna including a rectangularly defined loop is also disclosed herein. Different approaches may be utilized to effect wave polarization (left-hand or right-hand); the first consists in exciting the loop wire at two separate points staggered at an angle of 90 degrees with respect to the center of the loop wire and providing a source in phase quadrature. Alternatively, the loop wire may be excited at only one point by discriminating one of the two polarizations by means of a passive probe, a directional probe or other suitable means.  
           [0019]    The operational frequency band of the antenna is largely determined by the outside circumference dimension of the conductive loop. The outer circumference dimension is substantially equivalent to ½ of the wavelength of the frequency of response. Thus the system performs similarly to a ½ wave slot antenna. Tuning of the antenna can be accomplished by adjusting the feed network. Adjusting the width and location of the conductive leg member will transition the frequency and impedance.  
           [0020]    Another aspect of the present invention addresses the problem of power loss in the transmission line connecting the antenna to the RF electronics. In embodiments of the present invention, this concern is addressed by proving a low noise amplifier (LNA) proximate the antenna structure. In one preferred embodiment, the LNA may be disposed within the antenna structure, such as within a cavity defined in a portion of the antenna.  
           [0021]    Another aspect of the present invention is the provision of an antenna wherein various components of the transceiver and/or handset, such as a LNA, are placed within or under the antenna, importantly without negatively impacting antenna performance. A LNA with or without pre/post filter may be disposed within a cavity of a portion of the antenna assembly. In one preferred embodiment, the electronic or other components, may be disposed within a cavity defined within a disk-shaped dielectric element.  
           [0022]    Yet another aspect of the present invention is the provision of an antenna structure having a conductive loop resonator element disposed in operative relationship to a conductive ground plane element. In one embodiment, the conductive ground plane may be the ground plane of a wireless communications device. In another embodiment, the conductive ground plane may be a separate conductive panel or element which is coupled to the ground plane of the wireless device. For example, the antenna may be remotely disposed relative to the wireless device and coupled thereto by a transmission line, such as a coax signal line, etc.  
           [0023]    Yet another feature of embodiments of the present invention is a notch element in the conductive leg member. Changes in the notch height can be used to adjust the antenna match. Further tuning can be accomplished by adjusting the width of the ring. As the ring is made wider, the operational frequency range becomes higher.  
           [0024]    One advantage of the invention is that the antenna performance is largely independent of the dimensions of the ground plane. Thus the antenna can be readily adapted to different devices having various ground plane dimensions.  
           [0025]    The above and other objects and advantageous features of the present invention will be made apparent from the following description with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 shows a perspective view of a wireless communications device utilizing an antenna according to the present invention;  
         [0027]    [0027]FIG. 2 is a perspective view of a portion of the wireless communications device of FIG. 1, illustrating the ground plane element and the loop element of the antenna assembly;  
         [0028]    [0028]FIG. 3 is another perspective view of a portion of the wireless communications device of FIG. 1, illustrating the ground plane element and the loop element of the antenna assembly;  
         [0029]    [0029]FIG. 4 is a perspective view of the loop element of the antenna assembly of FIG. 3;  
         [0030]    [0030]FIG. 5 is another perspective view of the loop element of the antenna assembly of FIG. 3;  
         [0031]    [0031]FIG. 6 is a top plan view of one preferred embodiment of the loop antenna assembly according to the present invention;  
         [0032]    [0032]FIG. 7 is a side elevational view of the preferred embodiment of FIG. 6;  
         [0033]    [0033]FIG. 8 is a polar chart of gain characteristics of an antenna assembly of FIG. 6;  
         [0034]    [0034]FIG. 9 is a VWSR vs. frequency plot of the antenna of FIG. 6;  
         [0035]    [0035]FIG. 10 is another embodiment of the loop element of the antenna assembly according to the present invention;  
         [0036]    [0036]FIG. 11 is a top plan view of the antenna assembly of FIG. 10;  
         [0037]    [0037]FIG. 12 is a side elevational view of the antenna assembly of FIG. 10;  
         [0038]    [0038]FIG. 13 is another embodiment of the loop element of the antenna assembly according to the present invention;  
         [0039]    [0039]FIG. 14 is a top plan view of the embodiment of FIG. 13;  
         [0040]    FIGS.  15 - 18  are side elevational views of the embodiment of FIG. 13;  
         [0041]    [0041]FIG. 19 is a perspective view of another embodiment of an antenna assembly according to the present invention;  
         [0042]    [0042]FIG. 20 is a perspective view of another embodiment of an antenna assembly according to the present invention;  
         [0043]    [0043]FIG. 21 is a perspective view of the antenna assembly of FIG. 20;  
         [0044]    [0044]FIG. 22 is a perspective view of another embodiment of an antenna assembly according to the present invention illustrating an alternative feed approach; and  
         [0045]    [0045]FIG. 23 is a perspective view of another embodiment of an antenna assembly according to the present invention illustrating an alternative feed approach. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0046]    [0046]FIG. 1 illustrates an antenna assembly  10  disposed within a wireless communications device  12 , such as a cellular telephone or PDA device. The antenna assembly  10  includes a circular loop resonator element  14  defining a loop surface  16  disposed away from a ground plane element  20 . The ground plane element  20  may be ground plane of a printed wiring board of the device  12  or may be a separate conductive element which is coupled to the ground plane of the device  12 .  
         [0047]    In preferred embodiments, the antenna assembly  12  can be implemented to transmit and receive on desired frequencies, including analog or digital U.S. or European cell phone bands, PCS cell phone bands, 2.4 GHz BLUETOOTH® bands, or other frequency bands as would be obvious to one skilled in the art.  
         [0048]    The antenna assembly  10  is disposed near the upper portion of the device  12  (away from the user&#39;s hand during operation), and is received and incorporated within the housing  22  of the device  12 . Although the antenna assembly  10  can be installed in locations within or external to the housing  22 , it is presently preferred that it be disposed within the housing  22 . Wireless communication device  12  contains an electronic device, such as a receiver and/or transmitter herein referred for convenience together as a transceiver component  24 .  
         [0049]    Referring now to FIGS.  2 - 7 , the loop surface  16  of the circular loop resonator element  14  is disposed in substantially parallel relationship to the ground plane element  20 . Ground plane  20  is illustrated herein as a substantially rectangular form. It should be recognized that ground plane  20  may assume alternative shapes or forms, provided that at least one major dimension is approximately ¼ wavelength long at the lowest frequency of operation. A conductive leg element  26  is contiguous with and extends from an edge of the loop surface  16  toward the ground plane element and defines a feed tab  28  for the antenna assembly  12 . The feed tab  28  is operatively coupled to the transceiver signal input/output component  24 , such as via a coax line  25  of FIG. 5. The conductive leg element  26  further defines a ground tab  30  for coupling the leg element  26  to a circuit ground. Loop resonator  14  is thus electrically connected to the ground plane  20  via the ground tab  30 . A slot-like removed portion  32  is defined between the feed tab  28  and the ground tab  30  of the conductive leg element  26 . In one preferred embodiment, the slot-like removed portion  32  is illustrated as a slot having generally parallel edges. Alternative embodiments of the slot-like removed portion  32  may be practicable, including but not limited to notch structures, or other removed portions. The dimensions of the loop resonator element  14  may be varied to conform to a portion of the housing  22 . Those skilled in the arts will appreciate that the design and selection of the loop resonator element  14  with reference to a particular wireless communication device may result in such complex shapes.  
         [0050]    In the embodiment of FIGS.  2 - 7 , a disk-shaped dielectric element  40  is disposed between the conductive loop resonator element  14  and the ground plane  20 . The dielectric element  40  may include a glass filled polymer such as ULTEM 1000 (available from Boedeker Plastics, Inc. of Shiner, Tex.) for the dielectric disk. This material is a glass filled polymer which has a dielectric constant of approximately 3.15. This dielectric material is suitable for the antenna  10  to be surface mounted through a thermal reflow solder process. Other dielectric materials can be used as well. Those skilled in the relevant art will appreciate that selection of a dielectric material having a higher dielectric constant can result in a smaller, more compact, antenna  10 . Dielectric constant values are preferably in the range from 1 to 35. The selection of dielectric materials should include considerations including high temperature resistance, and low loss factor for antenna performance. Other dielectric materials which may be suitable include ceramic materials, and aerogels. Ceramic filled plastics can also be used, such as TMM material manufactured by Rogers Corporation, of Chandler, Ariz., which is available in dielectric constant values from 3 to 10, and which is resistant to solder reflow temperatures. TMM material consists of a hydrocarbon thermoset plastic (ceramic-filled) that provides a tight control of dielectric constant, low loss, and excellent temperature stability. The dielectric element  40  may include a cavity into which one or more components of the WCD  12  may be disposed. FIGS.  20 - 21  illustrate such an embodiment as further described herein.  
         [0051]    The conductive loop resonator element  14  and leg element  26  can be integrally manufactured from a single conductive metal or other suitable conductive material. In one embodiment, as illustrated in FIGS. 6 and 7, the conductive metal would be 0.25 mm thick brass for operation about the 2.4-2.5 GHz frequency range. The conductive members  14 ,  26  can be shaped by stamping, milling, plating or other suitable method as would be obvious to one skilled in the relevant arts. The conductive members  14 ,  26  may also be overmolded with a polymeric dielectric  40 , or mechanically secured onto the dielectric member  40 . In another embodiment (not shown), the conductive members  14 ,  26  may be selectively plated onto the dielectric member  40  using electrolytic or electroless or other suitable methods. One particular method would employ the MID technology of two shot molding followed by electroless plating. In another embodiment the manufacturing method may employ insert molding over the existing conductive portion.  
         [0052]    The loop resonator element  14  can be soldered onto the wiring board of the communication device  12  for electrical and mechanical coupling of the feed tab  28  to the signal transceiver component  24 , and the ground tab  30  to the ground portion of the transceiver component  24 . Alternatively, a microstrip feedline (not shown) from the communication device  12  to the antenna  10  can also be employed.  
         [0053]    A primary advantage of this invention is that multiple polarizations can be obtained from a very compact design. As illustrated in FIG. 8, the unit produces right hand and left hand circular polarizations as well as vertical and horizontal responses. With reference to FIG. 3, the right hand side of the antenna  10  transmits and receives right hand circular polarized radiation, while the left side of the antenna  10  transmits and receives left hand circular polarized radiation. The antenna  10  also transmits and receives vertical polarization in the azimuthal direction which is nearly perfectly omni-directional, and horizontal polarization at zenith.  
         [0054]    As a result, the antenna  10  is particularly well suited for GPS usage at 1.575 GHz due to the right hand circular polarization response. The antenna  10  can also be built scaled in size to perform in the BLUETOOTH® frequency band, at 2.4 GHz. This antenna  10  is also well suited for BLUETOOTH® and ISM applications since the multiple dimensions of polarization performance allow the unit to be oriented in many angles of configuration and still have good response. Thus the antenna  10  can be used in a handheld device  12  which can be carried in any orientation and still provide acceptable signal transmission and reception quality.  
         [0055]    Referring again to FIG. 8, it has been determined that the antenna has both a right hand and left hand CP component at Ø=90° and −90° respectively. The antenna  10  can be considered as a ½ wave loop antenna with an electrical distance around the ring of ½ wavelength at 2.45 GHz. Describing the antenna  10  in this manner leads to the definition of points about the ring corresponding to distances along the wavelength. In FIG. 3 the 0, ¼ and ½ wave points are indicated by A, B and C respectively.  
         [0056]    At resonance, a current standing wave (CSW) is set up around the ring  16 . In addition, a voltage standing wave (VSW), phase shifted 90°, is established between the ring  16  and the groundplane  20 . The conduction current of the CSW produces a horizontally polarized E-field and the displacement current from the VSW produces a vertically polarized E-field. Circular polarization requires a 90° phase shift between polarizations, which is inherent in this design. As a second requirement for circular polarization, the E-fields from the two polarizations must be equal in magnitude. This second requirement does not occur at any of the locations on the ring having either a current or a voltage null (0, ¼ and ½ wave points). However, between these locations, including possibly the ⅛ or ⅜ wave points, it may occur that the magnitude of the E-field components are approximately equal. In addition, the antenna assembly  10  may display right- and left-hand circular polarization responses at Ø=90° and −90° respectively, near the ⅛ and ⅜ wavelength points. FIG. 9 illustrates the voltage standing wave ratio (VWSR) vs. frequency plot for the antenna of FIGS.  6 - 7 . The radiation pattern of this particular antenna is nearly omnidirectional for vertical polarization, in the plane which is parallel to the ground plane. In comparison, this radiation pattern is substantially different from a typical PIFA antenna pattern.  
         [0057]    Minor tuning adjustments may be necessary upon integration of the antenna assembly  19  into the wireless device  12 . Two dimensions on the antenna  10  can be adjusted to tune the antenna  10  into the desired operational band. To tune the antenna  10  to a lower frequency, material can be removed from the left side of the conductive leg element  26  and ground tab  30  as shown in FIG. 4 as phantom lines  60 . Changes should be of the order of 0.25 mm to change the resonance frequency by 25 MHz. These numbers are not exact but do give an order of magnitude. This removal of the material makes the slot longer and thereby lowers the frequency. To adjust the match to a higher impedance the slot between the leg element  26  and ground tab  30  and the feed tab  26  should be lengthened (as indicated by phantom line  70  in FIG. 4). Relatively minor changes of the order of 0.25 mm should be necessary.  
         [0058]    FIGS.  10 - 12  illustrate another embodiment of an antenna assembly  10  for a wireless communications device  10 . In this embodiment, a conductive leg member  50  includes a feed point  52  defined a distance away from both the ground plane  20  of the device  12  and the ground tab  54  of the conductive leg member  50 . Coupling to the device transceiver component  24  may be via a coax or other signal line.  
         [0059]    FIGS.  13 - 18  illustrate yet another embodiment of an antenna assembly  10  for a wireless communications device  10 . The loop resonator  14  and dielectric substrate element  40  of this embodiment are preferably rectangular in form, and yet more preferably substantially square in shape. FIGS.  14 - 18  are additional views of the antenna of FIG. 13. The antenna of FIGS.  13 - 18 . include a plurality of side conductor panels  70 ,  72 ,  74  electrically coupled to the loop resonator element  14  proximate its perimeter. In this embodiment, a conductive leg member  60  includes a feed point  62  defined a distance away from both the ground plane  20  of the device  12  and the ground tab  64  of the conductive leg member  60 . As a result, a 50 ohm unbalanced electrical feed point is provided between feed point  62  and ground tab  64 . Coupling to the device transceiver component  24  may be via a coax or other signal line.  
         [0060]    Referring now to FIG. 19, another embodiment of an antenna assembly  10  according to the present invention is illustrated. In this embodiment, the antenna  10  may be disposed away from the associated wireless communications device  12 . The loop surface  16  of the circular loop resonator element  14  is disposed in substantially parallel relationship to the ground plane element  20  which may be a conductive element separate from the ground plane of the wireless device  12 . It should be recognized that ground plane  20  may assume alternative shapes or forms, provided that at least one major dimension is approximately ¼ wavelength long at the lowest frequency of operation. A conductive leg element  26  is contiguous with and extends from an edge of the loop surface  16  toward the ground plane element and defines a feed tab  28  for the antenna assembly  12 . The feed tab  28  is operatively coupled via a conductor  78  to the output  80  of a low noise amplifier  82  which is coupled to a transmission line, such as coax line  25 . The shield conductor  84  of the coax line  25  is coupled to the ground plane  20  of the antenna assembly. In this embodiment of the present invention, a component, such as a low noise amplifier  82 , is disposed between in a region  81  between the conductive loop resonator element  14  and the ground plane  20 . One or more components, such as circuits or other electronic devices or systems, may be disposed in such relationship, i.e., between the conductive loop resonator element  14  and the ground plane  20 . It has been determined that for preferred operability of the antenna assembly  10  the height of the component(s) or circuit(s) disposed between the loop resonator element  14  and the ground plane  20  should be less than approximately 50% of the distance between the loop resonator  14  and the ground plane  20 .  
         [0061]    Similar to the embodiment of FIGS.  3 - 7 , the conductive leg element  26  further defines a ground tab  30  for coupling the leg element  26  to the ground plane  20 . Loop resonator  14  is thus electrically connected to the ground plane  20  via the ground tab  30 . A slot  32  is defined between the feed tab  28  and the ground tab  30  of the conductive leg element  26 . The dimensions of the loop resonator element  14  may be varied to conform to a portion of the housing  22 . Those skilled in the arts will appreciate that the design and selection of the loop resonator element  14  with reference to a particular wireless communication device  12  may result in such complex shapes.  
         [0062]    In the embodiment of FIGS. 20 and 21, a disk-shaped dielectric element  40  is disposed in the region  81  between the conductive loop resonator element  14  and the ground plane  20 . The dielectric element  40  may include a glass filled polymer such as ULTEM 1000 (available from Boedeker Plastics, Inc. of Shiner, Tex.) for the dielectric disk. This material is a glass filled polymer which has a dielectric constant of approximately 3.15. This dielectric material is suitable for the antenna  10  to be surface mounted through a thermal reflow solder process. Other dielectric materials can be used as well. Those skilled in the relevant art will appreciate that selection of a dielectric material having a higher dielectric constant can result in a smaller, more compact, antenna  10 . Dielectric constant values are preferably in the range from 1 to 35. The selection of dielectric materials should include considerations including high temperature resistance, and low loss factor for antenna performance. Other dielectric materials which may be suitable include ceramic materials, and aerogels. Ceramic filled plastics can also be used, such as TMM material manufactured by Rogers Corporation, of Chandler, Ariz., which is available in dielectric constant values from 3 to 10, and which is resistant to solder reflow temperatures. TMM material consists of a hydrocarbon thermoset plastic (ceramic-filled) that provides a tight control of dielectric constant, low loss, and excellent temperature stability. As particularly illustrated in FIG. 21, the dielectric element  40  may include a cavity  86  into which one or more components of the WCD  12 , such as the low noise amplifier  82 , may be disposed. One or more components of the wireless device  12  may be placed within the cavity or cavities  86  of a dielectric element  40 .  
         [0063]    Referring now to FIGS. 22 and 23, alternative feed approaches are illustrated for use with a loop resonator element  14 . The feed structure  90  of FIG. 22 includes a pair of conductive wires  92 ,  94  coupled to the center conductor  83  and shield conductor  84  of coax line  25 , respectively. Shield conductor  84  and conductive wire  94  are connected to the ground plane  20 . The conductive wires  92 ,  94  may have circular cross sections with a diameter, D 2 . The conductive wires  92 ,  94  are disposed away from each other a distance, D 1 . Tuning of the feed structure  90  may be accomplished by varying the distances D 1  and D 2 .  
         [0064]    The feed structure  98  of FIG. 23 is a high impedance (voltage feed) structure which includes an inductor  100  and capacitor  102  coupled in parallel. The inductor  100  and capacitor  102  may be separate, discrete components, or may be incorporated within a LC tuning network. The center conductor  83  of a coax feed line  25  is coupled proximate to the inductor  100 , and the shield conductor  84  is coupled to the ground plane  20 . The feed structures  90 ,  98  of FIGS. 22 and 23 are illustrated to include a coax signal line  25 . Alternative signal lines may also be practicable in alternative embodiments of the antenna, e.g., a micro-strip transmission line.  
         [0065]    Although the invention has been described in connection with particular embodiments thereof other embodiments, applications, and modifications thereof which will be obvious to those skilled in the relevant arts are included within the spirit and scope of the invention.