Abstract:
A dual frequency wideband antenna assembly for use in a wireless communication device. The antenna assembly having a first resonator element disposed away from the ground plane element, said first resonator element being operatively coupled at a first location to the ground plane and being operatively coupled at a second location to the RF signal port; a second resonator element disposed away from the ground plane. The first and second resonator elements are coupled via a bridge conductor and a capacitive tuning network. The capacitive tuning network may include a discrete capacitor or an adjustable capacitor which varies in response to a signal.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an antenna assembly suitable for wireless transmission of analog and/or digital data, and more particularly to a dual frequency, wideband resonator element providing at least one adjustably tuned component. 
     BACKGROUND OF THE INVENTION 
     Recent advances in wireless communications devices have renewed interest in antennas suitable for such systems. Several factors are usually considered in selecting an antenna for a wireless telecommunications device. Significant among these factors are the size, VSWR, gain, bandwidth, and the radiation pattern of the antenna. 
     Currently, monopole antennas, patch antennas and helical antennas are among the various types of antennas being used in wireless communications devices. These antennas, however, have several disadvantages, such as limited bandwidth and large size. Also, these antennas exhibit significant reduction in gain at lower elevation angles (for example, 10 degrees), which makes them undesirable in some applications. 
     As mentioned above, one type of antenna is an external half wave single or multi-band dipole. This antenna typically extends or is extensible from the body of a wireless communication device in a linear fashion. Because of the physical configuration of this type of antenna, electromagnetic waves radiate equally toward and away from a user. Thus, there is essentially no front-to-back ratio and little or no specific absorption rate (SAR) reduction. Specific absorption rates for this type of antenna are typically 2.7 mw/g at a 0.5 watt transmission power level. With multi-band versions of this type of antenna, resonances are achieved through the use of inductor-capacitor (LC) traps. With this antenna, gains of +2 dBi arc common. While this type of antenna is acceptable in some wireless communication devices, it has drawbacks. One significant drawback is that the antenna is external to the body of the communication device. This places the antenna in an exposed position where it may be easily damaged. 
     A related antenna is an external quarter wave single or multi-band asymmetric wire dipole. This antenna operates much like the aforementioned antenna, but requires an additional quarter wave conductor to produce additional resonances. This type of antenna has drawbacks similar to the aforementioned antenna. 
     SUMMARY OF THE INVENTION 
     A dual band antenna assembly for use in a wireless communications device (WCD) is disclosed. The antenna assembly provides simultaneous wideband resonances over two or more different frequency bands when disposed relative to a ground plane of the wireless communications device. One or more of the operational frequency bands of the antenna assembly may be selectively adjusted via a capacitive tuning network. The selective adjustment of the capacitive tuning network may be achieved during the manufacture or subsequent use of the wireless communications device. In this manner, a tuning process over a much wider range of frequencies in each band may be achieved without an alteration of the physical size or structure of the antenna element. The selectively tunable antenna according to the present invention permits a single mechanical embodiment to accommodate a variety of different frequency bands, thus providing a manufacturing and assembly economy over prior art antennas (where timing has typically required an alteration of the physical structure of the antenna, or selection from among a plurality of differently sized antenna elements). The selective tuning of the antenna assembly of the present invention may be achieved via a variety of automatic or manual approaches. In one embodiment, the capacitive tuning network, such as a varactor, may be electrically tuned via the WCD microprocessor in response to an internal program or one or more external signals. In another embodiment, the capactive tuning network may be controlled via a manual operated switch, such as through a PIN diode switching device. 
     The antenna assembly includes first and second conductive surfaces disposed relative the ground plane of the WCD, preferably at the upper rear portion of the WCD. The first and second conductive surfaces are in substantial collateral relation and include a conductive bridge element disposed therebetween. The first and second conductive surfaces are also operatively coupled together via a capacitive tuning network, as further described herein. A conducting feed element operatively connects the first conductive surface to a signal line of the WCD. The feed element includes a feed arm defining a 50 ohm feed point. The first conductive surface is further coupled to the ground plane of the WCD via a grounding element. 
     In another embodiment, the antenna assembly is spaced a predetermined distance from the ground plane of a printed wiring board, and is operatively connected thereto at several predetermined locations by several components. One component, a capacitor or tuning network, capacitively couples the second conductive surface to the ground plane. Another component, the feed point of the antenna, operatively couples the first conductive surface to the RF input/output port or terminal of the WCD. Additionally, a third component, a grounding element, operatively connects the second radiating element to the ground plane. Since the distance between the antenna assembly and the ground plane is a function of the particular frequencies or wavelengths in use, the space between the antenna assembly and the ground plane may vary depending on the frequency band desired. However, it will be appreciated that various componentry may be positioned within the open space(s) between the antenna assembly and the ground plane to facilitate compact construction. 
     It is an object of the present invention to provide an antenna assembly which may be incorporated within the interior of a wireless communication device. 
     It is an object of the present invention to enhance operation of an antenna assembly by increasing its operational bandwidths and performance thereof. 
     It is another object of the present invention to provide an antenna assembly exhibiting at least one major polarization and one minor polarization. 
     Yet another object of the present invention is to provide a multiple band antenna for wireless communications devices that exhibits lower specific absorption rate (SAR) as compared to typical external antennas. 
     It is another object of the present invention to provide a multiple band antenna assembly wherein at least one of the frequency bands is selectively tunable by manual control or electrically tunable variable capacitor element. 
     It is yet another object of the present invention to provide a control assembly for adjusting the capacitance of the electrically tunable variable capacitor element, such as a digital control structure. 
     It is another object of the present invention to provide a variable capacitor element control assembly which is responsive to external signals received from the wireless communications system. 
     It is yet another object of the present invention to provide a variable capacitor element control assembly which is response to internal signals of the wireless communications device. 
     A feature of the present invention includes the provision that one or more portions of the resonator elements of the antenna assembly are tunable over a broad range of frequencies. 
     Another feature of the present invention includes the provision of a single feed point for a multi-band antenna system. The multiple band antenna assembly according to the present invention may exhibit a VSWR of approximately 2:1 over two different frequency bands, such as 880-960 MHz and 1710-1880 MHz or 824-894 MHz and 1850-1990 MHz. These and other objects, features and advantages will become apparent in light of the following detailed description of the preferred embodiments in connection with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an antenna assembly according to the present invention disposed within a wireless communications device; 
     FIG. 2 is a perspective view of the antenna assembly according to the present invention disposed upon a printed circuit board assembly; 
     FIG. 3 is views of a resonator portion of the antenna assembly of FIG. 1; 
     FIG. 4 is a perspective view of another embodiment of an antenna assembly according to the present invention disposed on a printed circuit board assembly; 
     FIG. 5 is a schematic diagram of a capacitive tuning network for use with the antenna assembly according to the present invention; and 
     FIG. 6 includes back plan, side, and top elevational views of an antenna assembly according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein like numerals depict like parts throughout, FIG. 1 illustrates an antenna assembly  20  according to the present invention disposed near the upper rear portion of a hand-held wireless communications device  22 . The antenna is disposed within the housing  24  of the wireless communications device  22 . The antenna assembly  20  according to the present invention includes a resonator structure  26  disposed relative to a ground plane  28  of the wireless communications device  22 . As depicted, the resonator structure  26  of the antenna assembly  20  is disposed at an upper end portion of a printed wiring board (PWB)  30  and is operatively coupled to the PWB  30  by a pair of conducting elements  40 ,  42 , including a grounding conductor  40  and a feed conductor  42 . Feed conductor  42  element includes a first end which is operatively connected at a predetermined position along an edge  64  of the resonator structure  26 . The other end of the feed element  42  is operatively connected to the PWB  30  at the RF  50  ohm input/output terminal or port. The feed element  42  is illustrated as an integrated planar portion of the resonator structure  26 , though an alternative feed element  42  may include a coaxial cable, a microstrip line, or other suitable conductors. The grounding element  40  has two ends, one end of which is operatively coupled to a portion of the resonator structure  26  of the antenna assembly  20 . The other end of the grounding element  40  is operatively connected near the top of the PWB  30  to the ground plane  28  in a conventional manner. 
     The resonator element  26  of the antenna assembly  20  includes a substantially planar top surface  50  defining two separated conductive regions  52 ,  54 . The two conductive regions  52 ,  54  are coupled together via a conductive bridge element  56  and a capacitive tuning network  71 . Resonator element  26  can include first and second front surfaces  60 ,  62  and a side surface  64 . Resonator structure  26  further defines a pair of removed portions  66 ,  68 , the physical size of which may be varied depending on the particular application. The two conductive regions  52 ,  54  are disposed in a side-by-side relationship and are operatively coupled by the conductive bridge element  56  and by a capacitor for fixed tuned operation or a capacitive tuning network  71  for electrically tuned function. Conductive bridge element  56  is illustrated as an integrated planar portion of resonator structure  26 . Alternative embodiments may include a bridge element  56  being a separate conductor, such as a wire, having different dimensions as compared to the bridge element  56  of FIGS. 1-4. 
     The first conductive region  52  is sized to resonate at the lower frequency band. The second conductive region  54  is sized to resonate at the higher frequency band and is functionally dependent on the capacitive tuning network  71  coupled between the first and second conductive regions  52 ,  54 . In one embodiment, a variable capacitive tuning network  71  has range of approximately 0.7-1.4 picofarads for operation over the 1710-1800 MHz frequency band. Importantly, the capacitance value of the capacitive tuning network  71  is capable of being selectively varied to tune the resonator over a range of frequencies without changing the physical characteristics of the resonator  26 . In preferred embodiments, the capacitive tuning network  71  may be controlled via a user-manipulated switch, or even via an internal digital controller  70 . In one embodiment, a digital controller  70  may receive control input from the user, an internal program, or from an external signal such as from a cell phone system or wireless datalink base station. The external signal may be extracted from a separate transmitted signal which is received by the antenna  20  or even defined as a portion of or contained within the communication protocol. 
     FIG. 5 illustrates one possible capacitive tuning network  71  for use with the antenna assembly  20 . The two conductive regions  52 ,  54  of FIG. 4 are capacitively coupled together by the capacitive tuning element  158 , and a DC blocking capacitor  159  which are components of the tuning network  71 . Capacitive tuning element  158  may be a varactor element. Analog tuning network  17  of antenna assembly  120  further includes an inductor or RF choke  75  which allows a control voltage to vary the capacitance of the varactor capacitive tuning element  158 . The value of the control voltage may be controlled via a digital controller, D/A and/or CPU or manual switching, as appreciated by those skilled in the relevant arts. 
     In another embodiment, the capacitive tuning network  71  and associated control device  70  may be automatically responsive to a continuously or semi-continuously transmitted signal to aid in maintaining the signal quality, change of protocol of the communications link or to enable encryption. In this regard, a single resonator element  26  may be used to achieve relatively seamless transitions or “hand-offs” as the wireless communication device  22  is used between differing RF spectra, encryption, and/or communications protocols. 
     The antenna assemblies  20 ,  120  of FIGS. 1-4 are sized to exhibit a VSWR of approximately 2:1 over two different frequency bands, such as 880-960 MHz and 1710-1880 MHz or 824-894 MHz and 1850-1990 MHz. FIG. 3 illustrates views of the resonator element  26  of the antenna assembly  20  of the present invention. Dimensions of the features of the components indicated in FIG. 3 are as follows: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 Item 
                 Dimension (in.) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 a 
                 .075 
               
               
                   
                 b 
                 .57 
               
               
                   
                 c 
                 .36 
               
               
                   
                 d 
                 .248 
               
               
                   
                 e 
                 .010 
               
               
                   
                 f 
                 .068 
               
               
                   
                 g 
                 .05 
               
               
                   
                 h 
                 1.00 
               
               
                   
                 i 
                 1.1 
               
               
                   
                 j 
                 1.42 
               
               
                   
                 k 
                 .602 
               
               
                   
                 l 
                 .64 
               
               
                   
                 m 
                 .76 
               
               
                   
                 n 
                 .315 
               
               
                   
                 o 
                 .449 
               
               
                   
                 p 
                 .137 
               
               
                   
                 q 
                 1.33 
               
               
                   
                 r 
                 0.7 pF 
               
               
                   
                   
               
             
          
         
       
     
     FIG. 4 illustrates another embodiment of the antenna assembly  120  according to the present invention. As depicted in FIG. 4, the antenna assembly  120  includes a resonator structure  126  disposed relative to a ground plane  128  of the wireless communications device  122 . As depicted, the resonator structure  126  of the antenna assembly  120  is disposed at an upper end portion of a printed wiring board (PWB)  130  and is operatively coupled to the PWB  130  by a feed conductor  142 . Feed conductor element  142  includes a first end which is operatively connected at a predetermined position along an edge of the resonator stricture  126 . The other end of the feed element  142  is operatively connected to the PWB  130  at the RF input/output terminal or port. The feed element  142  is illustrated as an integrated planar portion of the resonator structure  126 , though alternative feed elements may include a coaxial cable, a microstrip line or other suitable conductors. 
     The resonator element  126  of FIG. 4 includes a substantially planar top surface  150  defining two separated conductive regions  152 ,  154  coupled together via a bridge element  156  and a tuning network  171 , which includes a capacitive tuning element  158  (See, FIG.  5 ). Bridge element  156  of FIG. 4 is illustrated as an integrated planar portion of resonator structure  156 . Alternative embodiments may include a bridge structure  156  being a separate conductor, such as a wire, having different dimensions as compared to the bridge element  156  of FIG.  4 . 
     As illustrated in FIG. 5, the two conductive regions  152 ,  154  of FIG. 4 may be capacitively coupled together by the capacitive tuning element  158 , and DC blocking capacitor  159  which are components of the tuning network  171 . Capacitive tuning element  158  may be a varactor element. Analog tuning network  171  antenna assembly  120  further includes an inductor or RF choke  175  which allows a control voltage to vary the capacitance of the varactor capacitive tuning element  158 . The value of the control voltage may be controlled via a digital controller, CPU, or manual switching, as appreciated by those skilled in the relevant arts. 
     The antenna assembly  120  further includes a second tuning network  172  which is coupled between the second conductive region  154  of the resonator  126  and the ground plane  128  of the wireless communications device  122 . The second varactor  159  on tuning network  172  may be controlled in similar manner to the first varactor element  158 , i.e., via RF choke  176 , a controllable voltage via digital controller, D/A, and CPU. 
     FIG. 6 includes back plan, side, and top elevational views of an antenna assembly according to the present invention. The view of FIG. 6 are not necessarily to view, but illustrate possible orientations and components of a wireless communications device including an antenna assembly according to the present invention. 
     It should be noted that the drawings may indicate proportions and dimensions of components of the antenna device. However, e.g., thickness of conductive layers have been exaggerated for clarity. Although, in many embodiments conductive plates have been mentioned, it is understood that it includes the use of conductive layers, possibly attached to dielectric substrate(s). Although the invention is described by the above examples, naturally, a skilled person would appreciate that many other variations than those explicitly disclosed are possible within the scope of the invention. 
     Additional advantages and modifications 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.