Abstract:
An asymmetric dipole antenna assembly is provided for wireless communications devices, and includes separate upper and lower conductor traces and a low impedance feedpoint at the junction of the conductor traces. The upper conductor trace may include a matching network and may be printed on a planar printed circuit board mounted proximate the top of the a hand-held wireless transceiver. The upper conducting trace provides ¼ wave resonance over a desired frequency range and a 50 ohm input impedance for the antenna. The lower conductor trace may be provided by the ground trace of the wireless device circuitry, requiring only a minimum effective trace length of ¼ wavelength at the lowest frequency of operation. Polarization of the antenna is determined by the orientation of the longest dimension of the lower conductor.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority pursuant to 35 USC §119(e)(1) from the provisional patent application filed pursuant to 35 USC §111(b): as Ser. No. 60/121,989 on Feb. 27, 1999, which disclosure is incorporated herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to an antenna assembly for a wireless communication devices, such as a cellular telephone. Particularly, the present invention relates to a compact asymmetric dipole antenna assembly. Still further, the present invention relates to an antenna assembly effective over two or more resonance frequency bands. 
     BACKGROUND OF THE INVENTION 
     Known wireless communications devices such as hand-held cellphones and data modems (LANs) typically are equipped with an external wire antenna (whip), which may be fixed or telescoping. Such antennas are inconvenient and susceptible to damage or breakage. The overall size of the wire antenna is relatively large in order to provide optimum signal characteristics. Furthermore, a dedicated mounting means and location for the wire antenna are required to be fixed relatively early in the engineering process. Several antenna assemblies are known, and include: 
     Quarter Wave Straight Wire 
     This is a ¼ wavelength external antenna element, which operates as one side of a half-wave dipole. The other side of the dipole is provided by the ground traces of the transceiver&#39;s printed wiring board (PWB). The external ¼ wave element may be installed permanently at the top of the transceiver housing or may be threaded into place. The ¼ wave element may also be telescopically received into the transceiver housing to minimize size. The ¼ wave straight wire adds from 3-6 inches to the overall length of an operating transceiver. 
     Coiled Quarter Wave Wire 
     An external small diameter coil that exhibits ¼ wave resonance, and which is fed against the ground traces of the transceiver&#39;s PWB to form an assymetric dipole. The coil may be contained in a molded member protruding from the top of the transceiver housing. A telescoping ¼ wave straight wire may also pass through the coil, such that the wire and coil are both connected when the wire is extended, and just the coil is connected when the wire is telescoped down. The transceiver overall length is typically increased by ¾-1 inch by the coil. 
     Planar Inverted F Antenna (PIFA) 
     Consists of an external conducting plate which exhibits ¼ wave resonance, and is fed against the ground traces of the PWB of a transceiver to form an asymmetric dipole. The plate is usually installed on the back panel or side panel of a transceiver and adds to the overall volume of the device. 
     Patch 
     Typically consists of a planar dielectric material having a resonant structure on one major surface of the dielectric and a second ground plane structure disposed on the opposite major surface. A post may electrically couple (through the dielectric) the resonant structure to a coaxial feedline. 
     Additionally, there have been numerous efforts in the past to provide an antenna inside a portable radio communication device. Such efforts have sought at least to reduce the need to have an external whip antenna because of the inconvenience of handling and carrying such a unit with the external antenna extended. 
     SUMMARY OF THE INVENTION 
     The present invention replaces the external wire antenna of a wireless communication device with a planar conformal element which is installed within the housing of a wireless device and closely-spaced to the printed circuit board and antenna feedpoint of the wireless device. Electrical connection to the wireless device&#39;s main PWB may be achieved through automated production equipment, resulting in cost effective assembly and production. Electrical performance of the internal (embedded) antenna in wireless systems is nominally equal to that of a conventional wire antenna. 
     It is an object of the present invention to provide an antenna assembly which can resolve the above shortcomings of conventional antennas. Additional objects of the present invention include: the elimination of the external antenna and its attendant faults such as susceptibility to breakage and impact on overall length of the transceiver; the provision of an internal antenna that can easily fit inside the housing of a wireless transceiver such as a cellphone, with minimal impact on its length and volume; the provision of a cost effective antenna for a wireless transceiver, having electrical performance comparable to existing antenna types; and, the reduction in SAR (specific absorption rate) of the antenna assembly, as the antenna exhibits reduced transmit field strength in the direction of the user&#39;s ear for hand held transceivers such as a cellular telephone, when compared to the field strength associated with an external wire type antenna system. 
     The present invention provides an antenna assembly including a first planar element having a conductive trace, and at least one conductive member disposed near the first element to jointly form an asymmetrical dipole antenna. The resonant frequency range of the dipole is primarily determined by the dimensions of the conductive trace on the first planar element, which may be selected to exhibit ¼ wave resonance. The elongate second element has a minimum electrical length dimension of ¼ wavelength at the lowest frequency of operation, and may consist solely of the ground traces of the printed wiring board(s) of a wireless transceiver such as a cellular telephone. 
     In the preferred embodiment the first printed circuit element is rectangular having a thickness in the range 0.010-0.125 inches. Alternatively, the conductive traces may be printed on any number of conventional dielectric materials having a low to moderate dielectric loss such as plastics and fiberglass. Furthermore, the rectangular size of the first element may conform to available volume in the housing of a wireless transceiver such as a cellular telephone. The antenna assembly may be excited or fed with 50 ohm impedance, which is a known convenient impedance level found at the receiver input/transmitter output of a typical wireless transceiver. 
     In a preferred embodiment, the antenna assembly includes a matching network defined between a shorted end of the printed conducting trace (shorted to the second elongate conductor element (ground plane)) and a tap point further along the trace which results in a 50 ohm impedance referenced to a nearby point on the elongate conductor element. This feed system makes possible very close spacing between the first and second planar elements of the asymmetric dipole antenna, which minimizes the volume required when integrating the antenna into a wireless transceiver. Spacing on the order of 0.007 wavelength at the lowest frequency of operation between the elements is typically achieved in this manner. The spacing required without this matching system is typically 0.021 wavelength. The printed circuit element(s) of this invention are functional without the matching network, but may require increased spacing from the conductor element. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above set forth and other features of the invention are made more apparent in the following Detailed Description of the Preferred Embodiments when read in conjunction with the attached drawings, wherein: 
     FIG. 1 is an exploded perspective view of a wireless communication device incorporating an antenna assembly according to the present invention; 
     FIG. 2 illustrates a side elevation view of an antenna assembly of the present invention; 
     FIG. 3 illustrates a side elevational view of another embodiment of an antenna assembly of the present invention; 
     FIG. 4 illustrates a side elevational view of yet another embodiment of an antenna assembly of the present invention; 
     FIG. 5 illustrates a portion of the antenna assembly of FIGS. 1-4 and shows the matching network, resonant portion, and electrical connection feedpoints for a single-band planar printed circuit antenna element/half dipole; 
     FIG. 6 illustrates a front elevational view of a dual band antenna assembly according to the present invention; 
     FIG. 7 illustrates a front elevational view of a dual band antenna assembly according to the present invention; 
     FIG. 8 illustrates a front elevational view of another antenna assembly according to the present invention without impedance matching circuit; 
     FIG. 9 illustrates a front elevational view of a tri-band antenna assembly according to the present invention; 
     FIG. 10 illustrates an exploded perspective view of another antenna assembly according to the present invention; 
     FIG. 11 illustrates a perspective view of the antenna assembly of FIG. 10; and 
     FIG. 12 illustrates yet another embodiment of an antenna assembly according to the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like numerals depict like parts throughout, preferred embodiments of an antenna assembly  20  according to the present invention are illustrated in FIGS. 1-12. The antenna assembly  20  may implemented within single or multiple frequency wireless communication devices, for instance devices operating over the GPS (1575 MHz), cellular telephone (824-890 MHz and 860-890 MHz), PCS device (1710-1880 MHz, 1750-1870 MHz, and 1850-1990 MHz), cordless telephone (902-928 MHz), or BLUETOOTH™ specification (2.4-2.5 GHz.) frequency ranges. Those skilled in the relevant arts may appreciate that principles of the present invention are equally applicable for antenna assemblies operating at alternative frequency ranges. In alternative embodiments, the dimensions of the antenna assembly  20  may be scaled in proportion to provide operation at other frequencies, including frequencies in the 800 MHz. to 3,000 MHz. range. Such modifications are considered within the scope of the applicant&#39;s claims. 
     FIG. 1 illustrates an antenna assembly  20  disposed within a wireless communication device, such as a cellular telephone  10 . The antenna assembly  20 , disposed near the upper portion of the device  10  (away from the user&#39;s hand during operation), is received and incorporated within the housing  12  of the device  10 . Although the antenna assembly  20  can be installed in locations within or external to the housing  12 , it is presently preferred that it be disposed within the housing  12 . Wireless communication device  10  contains electrical apparatus, such as a receiver and/or transmitter, herein referred for convenience together as a transceiver component  14 . 
     Referring also to FIGS. 2-3, the antenna assembly  20  includes first and second planar elements  22 ,  24  disposed in substantially perpendicular relationship. A first conductor trace  26  is disposed upon the first planar element  22 , and a second conductor trace  28  is disposed upon the second planar element  24 . The first conductor trace  26  is operatively coupled to the transceiver signal input/output componentry  14  via connection  30 . The first conductor trace  26  is disposed upon a major surface of the first planar element  22  and directed in a direction ‘Z” away from the second conductor trace  28 . 
     The first and second conductor traces  26 ,  28  of the antenna assembly  20  are disposed upon respective first and second planar elements  22 ,  24 , which may be a printed wiring boards (PWB) or similar materials capable of supporting the conductor traces. The meandering first conductor trace  26  has a length dimension which is substantially larger than the dimensions of the first planar element  22 . Preferably, the second conductor trace  28  is the printed ground plane circuit of the transceiver  14 . Both the first and second conductor traces  26 ,  28  may be disposed upon respective PWB using known circuit fabrication techniques, such as surface printing, photolithography, and etching processes. The first planar element  22  and/or the second planar element  24  may be configured to conform to a portion of the housing  12 , for example to assume a convex or more complex form. Those skilled in the arts will appreciate that the design and selection of either the first or second planar elements  22 , 24  with reference to a particular wireless communication device may result in such complex shapes. 
     FIGS. 2 and 3 illustrate embodiments of the antenna assembly  20  wherein the first planar element  22  is substantially perpendicular to the second planar element  24 . The isolation distance ‘D’ between the ground plane ( 23 ) of the transceiver  14  and the first planar element  22  is approximately 3 millimeters (or approximately 0.007 λ at 900 MHz.). In FIG. 2, portions of the first planar element  22  are disposed relative both major surfaces of the second planar element  24  (a “T” shaped configuration), as opposed to FIG. 3, where the first planar element  22  extends from one major surface of the second planar element  24  (an “L” shaped configuration). 
     FIG. 4 illustrates another embodiment of the antenna assembly  20  wherein the first and second planar elements  22 ,  24  are disposed in parallel orientation. The isolation distance ‘D’ is approximately 1 millimeter (at 900 MHz.). The first conductive trace  26  may be operatively coupled to the transceiver  14  through known surface mount interconnections  30 . 
     FIG. 5 illustrates the first planar element  22  and first conductor trace  26  of the embodiment of FIGS. 1-4. The conductor trace  26  is disposed upon a single major surface of the first planar element  22  and is operatively coupled to the transceiver electronics  14  of the second planar element  24  via a feedpoint  32 . One end  34  of the conductive trace  26  is coupled to the second conductive trace  28  (the ground plane of the second planar element  24 ) via leads  36  or other electrical connection. A length of ends  36  should preferably be minimized. A distance ‘M’ further along the conductive trace  24 , the feedpoint connection  32  is made between the first conductive trace  26  and the transceiver electronics  14  of the second planar element  24 . The connections between the ground plane  24  and signal feed  32  may be achieved via plated through-holes in the first planar element  22 . 
     The region of the first conductor trace  26  between the ground connection  34  and the feedpoint  32  (the distance ‘M’ ) functionally operates a matching network to effect an approximate 50 ohm feedpoint. A 50 ohm feedpoint is thus defined across feedpoint  32  and ground trace  28 . The matching network length ‘M’ is approximately 0.03 λ (λ: a wavelength within the range of antenna operating frequencies). 
     Still referring to FIG. 5, the first planar element  22  may be a printed wiring board or similar dielectric material having a range of thickness between 0.01 and 0.062 inches, for example. The first conductive trace  26  is disposed at the periphery of the first planar element  22  away from a central region  38 . The first conductive trace  26  includes variable width traces  26   a, b, c  with antenna broadband operational characteristics being a function of trace widths. 
     FIG. 6 illustrates another embodiment of the present invention which functions across a pair of frequency bands for dual band transceiver devices. The first conductive trace  26  includes both a high- and low-frequency band resonant portion  26   d, e.  The first conductive trace  26  is coupled to the ground plane of the second planar element  24  at location  34  and coupled to the signal generating circuit  14  at single feed point  32 . FIG. 7, in comparison, includes a pair of feedpoints  32   a, b  between the first conductive trace  26  and the transceiver electronics  14 . The feedpoint  32   a  is for high frequency band, while the feedpoint  32   b  is for a lower frequency band. A ground connection is not required for the high frequency portion. 
     FIG. 8 illustrates another embodiment of the present invention. A simplified first conductive trace element  26  is disposed upon the first planar element  22  without a matching network as in the embodiments of FIGS. 1-7. Embodiments of FIGS. 1-7 may also employ this feed method, however the isolation distance “D” may increase. 
     FIG. 9 illustrates another embodiment of the present invention. The antenna assembly of FIG. 9 depicts a tri-band antenna assembly  20  functioning across a cellular band (880-960 MHz.), a PCS band (1710-1880 MHz.) and the BLUETOOTH™ band (2.4-2.5 GHz.). Cellular and PCS band operation is effected through first conductor trace  40 . BLUETOOTH™ band operation is effected through conductor trace  42 . Conductor trace  40  is coupled to ground of the second planar element at point  44  and to the signal generating circuitry  14  via feedpoint  46 . Conductor trace  42  is coupled to ground of the second planar element  24  at point  48  and to the appropriate signal generating circuitry via feedpoint  50 . Dimensions for preferred embodiments of the antenna assembly of FIG. 10 are included in Table  1 . Horizontal and vertical dimensions are measured with respect to origin point ‘O’. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Position 
                 Distance from Origin Point ‘O’ (Inches) 
               
               
                   
                   
               
             
             
               
                   
                 A 
                 0.000 
               
               
                   
                 B 
                 .075-1.905 
               
               
                   
                 C 
                 .305-7.747 
               
               
                   
                 D 
                 .365-9.271 
               
               
                   
                 E 
                  .415-10.541 
               
               
                   
                 F 
                  .703-17.856 
               
               
                   
                 G 
                  .820-20.828 
               
               
                   
                 H 
                  .885-22.479 
               
               
                   
                 I 
                 1.048-26.619 
               
               
                   
                 J 
                 1.080-27.432 
               
               
                   
                 K 
                 1.300-33.020 
               
               
                   
                 L 
                 1.415-35.941 
               
               
                   
                 M 
                 1.485-37.719 
               
               
                   
                 N 
                 1.500-38.100 
               
               
                   
                 O 
                 .015-.381  
               
               
                   
                 P 
                 .105-2.667 
               
               
                   
                 Q 
                 .151-3.835 
               
               
                   
                 R 
                 .216-5.486 
               
               
                   
                 S 
                  .422-10.719 
               
               
                   
                 T 
                  .484-12.294 
               
               
                   
                 U 
                  .529-13.437 
               
               
                   
                 V 
                  .544-13.818 
               
               
                   
                 W 
                  .559-14.199 
               
               
                   
                 X 
                  .574-14.580 
               
               
                   
                 Y 
                  .585-14.860 
               
               
                   
                 Z 
                  .600-15.240 
               
               
                   
                 AA 
                 1.400-35.560 
               
               
                   
                 BB 
                 1.385-35.179 
               
               
                   
                 CC 
                 1.227-31.166 
               
               
                   
                 DD 
                 1.202-30.531 
               
               
                   
                 EE 
                  .953-24.206 
               
               
                   
                 FF 
                  .928-23.571 
               
               
                   
                 GG 
                  .807-20.500 
               
               
                   
                 HH 
                  .782-19.863 
               
               
                   
                 II 
                  .532-13.513 
               
               
                   
                 JJ 
                  .507-12.878 
               
               
                   
                 KK 
                 .040-1.016 
               
               
                   
                 LL 
                 .015-.381  
               
               
                   
                 MM 
                  .560-14.224 
               
               
                   
                 NN 
                  .545-13.843 
               
               
                   
                 OO 
                  .515-13.081 
               
               
                   
                 PP 
                  .500-12.700 
               
               
                   
                 QQ 
                  .450-11.430 
               
               
                   
                 RR 
                 .360-9.144 
               
               
                   
                 SS 
                 .280-7.112 
               
               
                   
                 TT 
                 .245-6.223 
               
               
                   
                 UU 
                 .193-4.902 
               
               
                   
                 VV 
                 .075-1.905 
               
               
                   
                 WW 
                 0.000 
               
               
                   
                   
               
             
          
         
       
     
     FIGS. 10-11 illustrate another embodiment of an antenna assembly according to the present invention. FIG. 10 shows an exploded view, and FIG. 11 illustrates an assembled perspective view with the first antenna element  51  disposed upon a second planar element  24 . First antenna element  51  consists of three substantially identical dielectric sections  52 - 54  which are disposed upon each other in a laminated or superimposed fashion. Electrical connection between conductor traces  26  disposed upon the dielectric sections  52 - 54  are made through plated through holes and associated conductors  56 . The assembly  51  may be surface mounted to one side of the planar element  24  via the mounting pad  57  to the circuit ground trace  28  and via mounting pad  58  to the circuit signal input/output  14 . The isolation distance “D” between the assembly ( 51 ) and the ground plane ( 28 ) may be reduced to less than 1 mm. Overall dimensions (height×width×length) for operation over 824-894 MHz are approximately 6 mm×4.5 mm×38 mm. 
     FIG. 12 illustrates another embodiment of the first planar element of present invention which is adapted to be secured relative the second planar element via mounting tabs  60 - 62 . These tabs  60 - 62  are sized to be received into corresponding elements on the second planar element. A dimension “T” is chosen to be greater than or equal to the thickness of the printed wiring board. Connections are made to transceiver circuitry  14  at tab  60  and  61 . Tab  62  is partially metallized and provides mechanical support for the first planar element  22 . Tabs  60 ,  61 ,  62  thus provide both mechanical and electrical connection between the first planar element  22  and the second planar element  24 . Connections may be made through known fabrication techniques, including solder reflow processes and other high volume production techniques. 
     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.