Abstract:
An antenna assembly achieving improved directionality and signal strength using a configured conductive radiator disposed in relationship with the ground plane element of a wireless communication device. The configured conductive radiator includes an elongate slot aperture and surfaces directed toward the ground plane element. The antenna assembly further includes a dielectric element for communicatively coupling the conductive radiator and the ground plane member. Preferably, the dielectric element may be disposed between a portion of the radiator element and the ground plane member, thus forming a compact, directional antenna system.

Description:
This is a continuation-in-part application pursuant to 37 C.F.R. 1.53(b) of application Ser. No. 09/008,618 filed on Jan. 16, 1998, now U.S. Pat. No. 5,945,954. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to antenna assemblies for hand held radio frequency transmitters or receivers, and more particularly to antenna assemblies for communication devices such as cellular telephones, PCS devices, and the like. 
     2. Description of the Related Art 
     Various antennas have been proposed and implemented for radio frequency communication devices such as cellular phones, PCS telephones and the like. Antennas have also been proposed and developed for other applications, for example, U.S. Pat. No. 5,677,698 shows a slot antenna arrangement for portable personal computers. Prior antennas for radio frequency transceivers for telecommunication devices such as cellular telephones and PCS devices have had significant limitations including limited signal range, limited directionality, significant radio frequency radiation output to the user, significant multipath interference, and other related performance limitations. 
     Accordingly, it is the primary object of this invention to provide an improved antenna for communication devices including hand-held radio frequency transceivers such as cellular phones and PCS devices with improved directionality, broadband input impedance, increased signal strength, and increased battery life. The present invention reduces radio frequency radiation incident to the user&#39;s body and reduces the physical size requirements for a directional antenna used on communication devices. Other benefits include a reduction in multipath interference, an increased front-to-back ratio, and improved peak gain. The antenna assembly of the present invention may be integrated into the housing of a cellular transceiver, for example, at the rear portion of a cellular telephone, and is accordingly less susceptible to damage during normal operation. 
     In general, wireless communication devices, and hand held cellular telephones in particular, use external whip antennas which radiate nominally omnidirectionally. Minimal reduction in transmitted RF energy toward the user&#39;s head is provided. As a consequence, typical specific absorption rates (SAR) values of 2.7 mw/g at 0.5 watts input are realized. The external whip antenna is also susceptible to damage and misalignment. Gain of the whip antenna is typically in the range of −5 to +1.5 dBi. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     SUMMARY OF THE INVENTION 
     To achieve the foregoing objects, and in accordance with the purpose of the invention as embodied and broadly described herein, a multiple element directive antenna assembly for a hand-held radio frequency communication device, such as a cellular telephone or PCS device, is provided. The antenna assembly has a configured active radiating conductor element disposed relative to a conductive ground plane element. A dielectric spacing member may be provided to communicatively couple the active radiating conductor element to the ground plane. The conductive ground plane member may be provided by a printed circuit board or other conductive surface of the hand-held radio frequency transceiver. The multiple-element directive antenna allows for improved directionality and reduced user exposure to radio frequency radiation. 
     The antenna assembly according to the present invention may be used in wireless communication device such as a cellular telephone or PCS devices where a low physical profile antenna is desired. The antennas of the present invention are particularly suited to receive and radiate electromagnetic energy in the 1850-1990 MHz band. The disclosed antenna offers a rugged, low cost antenna assembly having improved physical parameters while providing superior conformal capability for a handset chassis. Importantly, the overall volume occupied by the present antenna assembly can be held to a minimum. Due to their relative size and conformability, such antenna is preferably housed within an interior portion of the communication device, or on a back chassis surface of the device. 
     The antenna assembly according to the present invention may operate proximate a ground plane element of a communication device and provide 0-6 dBi gain and 3-18 dB front-to-back directivity, over 2:1 VSWR bandwidths of 8% with linear polarization. Significant improvements include: a reduced overall size relative to known antenna assemblies having similar performance characteristics; the ability to incorporate the antenna within a communication device housing without external appendages; a provision of an interior region within the conductor element and the printed wiring board in which componentry of the communication device may be disposed; and a reduction in the RF energy directed toward a user&#39;s head during operation of a hand-held communication device. The present invention provides a substantially smaller and more compact antenna assembly relative to known antenna assemblies having similar gain and directivity characteristics. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention, and together with a general description given above and the detailed description of the preferred embodiment given below, serve to explain the principles of the invention, wherein: 
     FIG. 1 is a perspective view of a telephone hand-set with the directional antenna of the present invention positioned in a lower hinged panel, according to the invention; 
     FIG. 2 is a perspective view of a telephone hand-set with the directional antenna of the present invention positioned in an upper hinged panel, according to the invention; 
     FIG. 3 illustrates a cellular handset with such antenna positioned on the rear top thereof, according to the invention; 
     FIGS. 4 a  and  4   b  show plan and elevation views of such antenna, according to the invention; 
     FIG. 4 c  is a table showing preferred dimensions of such antenna and is designated Table 1, according to the invention; 
     FIG. 5, shows the location of the antenna assembly with respect to the handset ground plane, according to the invention; 
     FIG. 6, shows the antenna of the present invention positioned on a rear portion of a cellular handset, according to the invention; 
     FIGS. 7A and 7B show front and elevational views of the antenna of the present invention positioned on a rear portion of a cellular handset, according to the invention; 
     FIGS. 8 a  and  8   b  show preferred routings of a coax feed line from the radiating conductor element, according to the invention; 
     FIG. 9 illustrates a top plan view of another embodiment of an antenna assembly according to the present invention; 
     FIG. 10 illustrates a right side elevational view of FIG. 9; 
     FIG. 11 illustrates a bottom side elevational view of FIG. 9; 
     FIG. 12 illustrates a perspective view of the antenna assembly of FIGS. 9-11; 
     FIG. 13 illustrates a detailed view of another embodiment of an antenna assembly according to the present invention; 
     FIG. 14 is a bottom plan view of another embodiment of an antenna assembly according to the present invention and illustrates one preferred feed configuration; 
     FIG. 15 is a right side elevational view of FIG. 14; 
     FIG. 16 is a bottom plan view of another embodiment of an antenna assembly according to the present invention and illustrates another preferred feed configuration; and 
     FIG. 17 is a right side elevational view of FIG.  16 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to preferred embodiments of the invention as illustrated in the accompanying drawings. 
     In accordance with the present invention, an antenna assembly is provided for a radio frequency communication device such as a cellular or PCS telecommunication device. The antenna assembly includes a configured radiating conductor element disposed relative a ground plane member. The ground plane member may be disposed upon a major surface of a dielectric substrate opposite the radiating conductor element, and may consist of the ground plane of the printed circuit board of the communication device or portion thereof, conductive portions of the device chassis or housing, the battery pack of the device, or a separate conductive surface. 
     The radiating conductor element of the present invention may includes an elongate slot aperture disposed upon substantially planar surfaces, as in FIGS. 4-5, or a concave surface, as in FIGS. 6-7. The slot aperture may be substantially rectangular in form and extend in a direction which is substantially parallel to the radiating conductor element&#39;s axis of concavity. A coaxial feed line may extend generally perpendicularly to the axis of the slot or away from and parallel to the slot. Feed points of the antenna assembly are made at points proximate the slot aperture&#39;s periphery. 
     The radiating conductor element is constructed of a conducting material and is disposed upon a top surface of a dielectric substrate member. The radiating conductor element, dielectric substrate member, and a ground plane member are positioned in generally overlapping or “laminated” relationship to each other. The spacing or relative position between the radiating conductor and the ground plane is an important parameter to the antenna assembly&#39;s electrical performance. The ground plane may be capacitively or directly coupled to a conductive ground plane of the radio frequency transceiver device to obtain the desired performance benefits. Coupling to the inherent transceiver ground plane in this fashion allows the improvements in electrical performance to be achieved more independently of transceiver design. 
     FIGS. 1 and 2 illustrate the antenna assembly  10  for a communication device according to a preferred embodiment of the invention on a hand held cellular telephone handset  12 . In FIG. 1 the antenna assembly is disposed within a lower hinged “flip” or, panel portion. In FIG. 2, the antenna assembly is disposed on the outside portion of upper hinged “flip” or panel portion. The handset includes a main body portion  13  and a hinged “flip” or panel portion  14 , which in FIGS. 1 and 2 is shown in its opened, operational position. Telephone handset  12  preferably includes a front side  15  having a speaker and microphone (not shown) and a rear side  16 . The existing conducting ground plane  17  in handset  12  is electrically connected to a conducting ground plane  18  located within the flip portion  14 . This may be accomplished by a hinge  19  or the like. The antenna assembly  10  and the ground plane extension  18  are preferably concealed or encased in the handset  12 . Antenna assembly  10  is preferably formed by a planar or concave radiating conductor element generally separated from a larger ground plane by a dielectric material. The dielectric material may be, for example, the case of a cellphone. The ground plane may be the inherent ground plane in a cellphone. 
     With reference now to FIG. 3, cellular telephone handset  12  and antenna assembly  10  are shown with antenna assembly  10  concealed or encased in the housing of the transceiver. The antenna location shown is preferred so as to minimize the potential for contact by the user&#39;s hand. Antenna assembly  10  may also be used with other types of communication devices such as PCS devices, LAN apparatuses, and the like. 
     Referring now to FIGS. 4 a  and  4   b,  antenna assembly  10  is shown in plan and elevation view with antenna assembly  10  having transmission side (a) and opposite side (b). Placement of the antenna assembly  10  on the transceiver device  12  is such that during operation the transmission side (a) is generally directed away from the user. Antenna assembly  10  preferably includes a radiating conductor element  20  with slot  21 , preferably rectangularly configured, a dielectric substrate  22 , and a conducting ground plane member  23 . A low impedance coax feed line may be connected along the edges of slot  21  at points x and y. The shape and size of the radiating conductor  20 , slot  21 , location of feed line connection points x and y, and the spacing  24  to the ground plane  23  are critical to operation of antenna assembly  10 . In FIG. 4 c,  Table 1 lists dimensions and typical values for 1850-1190 MHz range. The dielectric  22  and ground plane  23  may extend beyond the edges of radiating conductor  20 . The dielectric material may have a dielectric constant of one or greater. Antenna assembly elements  20 ,  22 , and  23  may be positioned in a laminar fashion and glued or otherwise secured together. 
     As seen in FIG. 5, antenna assembly  10  may be positioned on or above the ground plane  17  that exists within the communication device  12  or the extension thereof  18  in flip portion  14 . This is illustrated without the handset present. The separation of ground planes  17  and  23  is generally not critical, however, it provides sufficient capacitive or direct (dc) coupling over the frequency band(s) of interest, and may be filled with a dielectric material of relative dielectric constant one or greater. The polarization of the antenna assembly  10  is linear, and in a direction at 90 degrees to slot  21  and parallel to the plane containing slot  21 . 
     Antenna assembly  10  may be formed as a C-shaped radiating conductor element critically spaced from a ground plane of a similar projected area by a dielectric spacer. Radiating conductor element  20  preferably has a slot fed through low impedance coax. The ground plane  23  is coupled directly or capacitively to a larger ground plane, for example, the inherent ground plane of a cellphone. 
     In FIG. 6, cellular telephone handset  12  and an antenna are shown with antenna  25  mounted directly to the dielectric material on the rear  16  of handset  12 , which may be a battery pack. The general location shown is preferred, so as to minimize potential contact with the user&#39;s hand during operation. Antenna  25  may be incorporated into the plastic of the battery pack or that of the handset. In one embodiment of the invention, as seen in FIGS. 7 a  and  7   b , antenna  25  comprises a radiating conductive element only. Previously discussed dimensions and design considerations discussed with reference to antenna assembly  10  apply to this embodiment of the antenna as well. 
     Referring now to FIGS. 8 a  and  8   b,  a preferred routing or location of coax feed line  27  from antenna assembly  10  or antenna  25  is shown. Preferably coax leads x and y are connected to periphery  31  of slot  21  by soldering. The inclusion of the cellphone&#39;s inherent ground plane, which is generally rectangular in shape, into the antenna assembly  10  results in increased gain over that expected from a conventional slot antenna. 
     FIGS. 9-17 disclose other preferred embodiments of the present invention. Referring particularly to FIGS. 9-13, an antenna assembly  40  includes a conductor element  42  disposed relative to a ground plane  44  element of a wireless communication device. Ground plane element  44  may be defined as a portion of the printed wiring board (PWB) of the communication device. The conductor element  42  includes first, second, and third conductive surfaces  46 ,  48 ,  50 , and may be a single formed metallic element. The conductor element  42  is approximately “C” shaped when viewed from its side, as illustrated in FIG. 10, and defines an interior region  52  disposed between the conductor  42  and the ground plane element  44 . Components of the communication device  80  may be disposed within the interior region  52  to effect a reduction in overall volume of the device. 
     The first conduction surface  46  is disposed a predetermined distance above the ground plane element  44 , and is electrically coupled to a downwardly-directed, perpendicular second conduction surface  48 , which is shorted to the ground plane  44  at end mounting tab  54 . One or more mounting tabs  54  may be practicable to provide for stability of conductor  42  or routing requirements of the printed wiring board of the communication device. 
     First conduction surface  46  is also coupled to a downwardly-directed perpendicular third conduction surface  50 . Third conduction surface  50  includes a perpendicular plate section  56  for capacitively coupling conductor  42  to the ground plane member  44 . One or more perpendicular plate sections  56  may be practicable to provide for conductor stability or wire routing requirements of the printed circuit board of the communication device. Ground plane element  44  has a minimum length in a direction of polarization ‘DP’ of approximately one-quarter wavelength (for a wavelength within the range of operation). Second and third conduction surfaces  48 ,  50  extend from opposed edges of conduction surface  46 . Conductor element  42  may be a single metallic formed element having a thickness within the range of 0.005 to 0.09 inch. 
     Still referring to FIGS. 9-13, first conduction surface  46  includes removed angled corner portions  58  for minimizing the overall volume occupied by the antenna assembly  40 . Other shapes or configurations (or entire deletion) of the removed portions  58  may be practicable. The antenna assembly  40  may be disposed within the communication device at the rear panel and proximate the upper portion of the handset (away from a user&#39;s hand), as illustrated in the embodiment of FIGS. 3 and 5. 
     Conductor element  42  defines one side or plate of a two plate capacitor  60 . Plate element  56  is spaced away from the ground plane element  44  by a dielectric element  62  so as to form a capacitor. Dielectric element  62  may have a dielectric constant of 0-10. FIG. 13 illustrates another embodiment of the capacitor  60  wherein a second plate element  64  is disposed upon the surface of the printed wiring board substrate and operatively coupled to the ground plane element  44 . 
     Conductor element  42  further includes an elongate slot element  66  defined within the conduction surface  46 . When viewed as in FIG. 9, slot  66  laterally extends within the boundary of the conduction surface  46  and is approximately aligned with the conduction surfaces  48  and  50 . Slot element  66  defines two feed points  68 ,  70  for electrically coupling the conductor element  42  to the communication device via coax feed line  76 . Feed points  68 ,  70  are disposed along the lateral centerline of the slot element  66 . FIGS. 14-17 illustrate alternative feed line orientations relative to the conductor section  42 . In FIGS. 14-15, the feed line  76  is disposed within the interior region  52  of the conductor element  42  and approximately aligned with a longitudinal direction of the slot  66 . In FIGS. 16-17, the feed line  76  is disposed within the interior region  52  of the conductor element  42  and obliquely aligned relative to the slot  66 . The coax feed line  76  may be a 50 ohm coaxial line having an outer shield conductor  78  coupled to the slot element  66  at feed point  68 , and an inner conductor  82  coupled at opposite feed point  70 . 
     Particular dimensions of one preferred embodiment according to the present invention are included as Table 2. 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Dimension 
                 Inch 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 j 
                 1.10 
               
               
                   
                 k 
                 .75 
               
               
                   
                 l 
                 .3 
               
               
                   
                 m 
                 1.25 
               
               
                   
                 n 
                 .47 
               
               
                   
                 o 
                 .91 
               
               
                   
                 p 
                 .80 
               
               
                   
                 q 
                 .57 
               
               
                   
                 r 
                 .20 
               
               
                   
                 s 
                 .18 
               
               
                   
                 t 
                 .015 
               
               
                   
                   
               
             
          
         
       
     
     In operation and use the antenna assembly is extremely efficient and effective. The antenna assembly of the present invention provides improved directivity, broadband input impedance, increased signal strength, and increased battery life. The antenna of the present invention reduces radio frequency radiation incident to the user&#39;s body, and reduces the physical size requirements of directional antenna used in cell phone handsets, PCS devices and the like. The disclosed antenna also increases front-to-back ratios, reduces multipath interference, and is easily integrated into the “flip” or rear panel portion of a cellular transceiver device, which minimizes the risk of damage or interference. 
     Additional advantages and modification will readily occur to those skilled in the art. The invention in its broader aspects is, therefore, not limited to the specific details, representative apparatus and illustrative examples shown and described. Accordingly, departures from such details may be made without departing from the spirit or scope of the applicant&#39;s general inventive concept.